PU BLICATIONS llllifimiS a,.c.

NIST SPECIAL PUBLICATION 260-107

U.S. DEPARTMENT OF COMMERCE/National Institute of Standards and Technology

Standard Reference Materials:

Description of the SRM 1965 Microsphere Slide

-QC

100 . W. Hartman and R. L. McKenzie

.U57

#260-107

1988

C.2

Standard Reference Materials:

Description of the SRM 1965 Microsphere Slide

A. W. Hartman

Precision Engineering Division

National Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, IVID 20899

R. L. McKenzie

Office of Standard Reference IVIaterials

National IVIeasurement Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

^OP Co NOTE: As of 23 August 1988, the National Bureau of

U.S. DEPARTMENT OF GOiVliVlERCE, C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Ernest Ambler, Director

(formerly National Bureau of Standards)

and

Standards (NBS) became the National Institute of

Standards and Technology (NIST) when President

Reagan signed into law the Omnibus Trade and

Competitiveness Act

\

Issued November 1988
Library of Congress Catalog Card Number: 88-600598

National Institute of Standards and Technology

Special Publication 260-107, 67 pages (Nov. 1988)

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1988

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Preface

Standard Reference Materials (SRM's) as defined by the National Institute

of Standards and Technology (NIST) are well-characterized materials,

produced in quantity and certified for one or more physical or chemical

properties. They are used to assure the accuracy and compatibility of

measurements throughout the Nation. SRM's are widely used as primary

standards in many diverse fields in science, industry, and technology,

both within the United States and throughout the world. They are also

used extensively in the fields of environmental and clinical analysis.

In many applications, traceability of quality control and measurement

processes to the national measurement system is carried out through the

mechanism and use of SRM's. For many of the Nation's scientists and

technologists, it is therefore of more than passing interest to know the

details of the measurements made at NIST in arriving at the certified

values of the SRM's produced. An NIST series of papers, of which this

publication is a member, called the NIST Special Publication - 260

Series . is reserved for this purpose.

The 260 Series is dedicated to the dissemination of information on different phases of the preparation, measurement, certification, and use of NIST SRM's. In general, much more detail will be found in these

papers than is generally allowed, or desirable, in scientific journal

articles. This enables the user to assess the validity and accuracy of

the measurement processes employed, to judge the statistical analysis,

and to learn details of techniques and methods utilized for work

entailing greatest care and accuracy. These papers also should provide

sufficient additional information not found on the certificate so that

new applications in diverse fields not foreseen at the time the SRM was originally issued will be sought and found.

Inquiries concerning the technical content of this paper should be

directed to the author(s). Other questions concerned with the

availability, delivery, price, and so forth, will receive prompt

attention from:

Office of Standard Reference Materials

National Institute of Standards and Technology

Gaithersburg, MD 20899

Stanley D. Rasberry, Chief

Office of Standard Reference Materials

iii
OTHER NIST PUBLICATIONS IN THIS SERIES

Seward, R. W., ed., NBS Standard Reference Materials

Catalog 1988-89, NBS Spec. Publ. 260 (January 1988)

Michaelis, R. E., and Wyman, L. L., Standard Reference

Materials: Preparation of White Cast Iron

Spectrochemical Standards, NBS Misc. Publ. 260-1

(June 1964). COM74-11061**

Michaelis, R. E., Wyman, L. L., and Flitsch, R., Standard Reference Materials: Preparation of NBS CopperBase Spectrochemical Standards, NBS Misc. Publ. 260-2 (October 1964). COM74-11063**

Michaelis, R. E., Yakowitz, H., and Moore, G. A., Standard Reference Materials: Metallographic Characterization of an NBS Spectromeuic Low-Alloy Steel Standard, NBS Misc. Publ. 260-3 (October 1964).

COM74-11060**

Alvarez, R., and Flitsch, R., Standard Reference

Materials: Accuracy of Solution X-Ray

Spectrometric Analysis of Copper-Base Alloys, NBS

Misc. Publ. 260-5 (March 1965). PB168068**

Shultz, J. I., Standard Reference Materials: Methods for the Chemical Analysis of White Cast Iron Standards,

NBS Misc. Publ. 260-6 (July 1965). COM74-

11068**

Bell, R. K., Standard Reference Materials: Methods for the Chemical Analysis of NBS Copper-Base

Spectrochemical Standards, NBS Misc. Publ. 260-7

(October 1965). COM74-11067**

Richmond, M. S., Standard Reference Materials:

Analysis of Uranium Concentrates at the National

Bureau of Standards,NBS Misc. Publ. 260-8 (December 1965). COM74-11066**

Anspach, S . C. , Cavallo, L. M. , Garfinkel, S . B. , Hutchinson, J. M. R., and Smith, C. N., Standard Reference

Materials: Half Lives of Materials Used in the Preparation of Standard Reference Materials of

Nineteen Radioactive Nuclides Issued by the National Bureau of Standards, NBS Misc. Publ. 260-9

(November 1965). COM74-11065**

Yakowitz, H., Vieth, D. L., Heinrich, K. F. J., and

Michaelis, R. E., Standard Reference Materials:

Homogeneity Characterization ofNBS Spectrometric

Standards II: Cartridge Brass and Low-Alloy Steel,

NBS Misc. Publ. 260-10 (December 1965). COM74-

11064**

Napolitano, A., and Hawkins, E. G., Standard Reference

Materials: Viscosity of Standard Lead-Silica Glass,

NBS Misc. Publ. 260-11 (November 1966).

Yakowitz, H., Vieth, D. L., and Michaelis, R. E., Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards IE: White Cast

Iron and Stainless Steel Powder Compact, NBS Misc.

Publ. 260-12 (September 1966).

Menis, O., and Sterling, J. T., Standard Reference

Materials: Determination of Oxygen in Ferrous Materials—SRM 1090, 1091, and 1092, NBS Misc.

Publ. 260-14 (September 1966).

Yakowitz, H., Michaelis, R. E., and Vieth, D. L., Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards IV: Preparation

and Microprobe Characterization of W-20% Mo

Alloy Fabricated by Powder Metallurgical Methods,

NBS Spec. Publ. 260-16 (January 1969). COM74-

11062**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements

on the Vapor Pressure ofGold (Certification of Standard Reference Material 745). NBS Spec. Publ. 260-19

(January 1970).PB190071**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements

on the Vapor Pressures of Cadmium and Silver, NBS

Spec. Publ. 260-21 (January 1971).COM74-11359**

Yakowitz, H., Fiori, C. E., and Michaelis, R. E., Standard Reference Materials: Homogeneity Characterization of Fe-3 Si Alloy, NBS Spec. Publ. 260-22

(February 1971). COM74-11357**

Napolitano, A., and Hawkins, E. G., Standard Reference

Materials: Viscosity of a Standard Borosilicate Glass,

NBS Spec. Publ. 260-23 (December 1970). C0M71-

00157**

Sappenfield, K. M., Marinenko, G., and Hague, J. L., Standard Reference Materials: Comparison of Redox

Standards, NBS Spec. Publ. 260-24 (January 1972).

COM72-50058**

Hicho, G. E., Yakowitz, H., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials: A

Standard Reference Material Containing Nominally

Four Percent Austenite, NBS Spec. Publ. 260-25

(February 1971). COM74-11356**

Martin, J. F., Standard Reference Materials: National

Bureau of Standards-US Steel Corporation Joint Program for Determining Oxygen and Nitrogen in Steel, NBS Spec. Publ. 260-26 (February 1971). PB

81176620**

iv
Gamer, E. L., Machlan, L. A., and Shields, W. R., Standard Reference Materials: Uranium Isotopic Standard

Reference Materials, NBS Spec. Publ. 260-27 (April

1971). COM74-11358**

Heinrich, K. F. J., Myklebust, R. L., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials:

Preparation and Evaluation of SRM's 481 and 482

Gold-Silver and Gold-Copper Alloys for

Microanalysis, NBS Spec. Publ. 260-28 (August

1971). COM71-50365**

Geller, S. B., Standard Reference Materials: Calibration

of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference

Tape Amplitude Measurement "Process A-Model

2," NBS Spec. Publ. 260-29 (June 1971). C0M71-

50282**

Gorozhanina, R. S., Freedman, A. Y., and Shaievitch, A.

B. (translated by M. C. Selby), Standard Reference

Materials: Standard Samples Issued in the USSR (A

Translation from the Russian), NBS Spec. Publ. 260-

30 (June 1971). COM71-50283**

Hust, J. G., and Sparks, L. L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31

(November 1971). COM71-50563**

Mavrodineanu, R., and Lazar, J. W., Standard Reference

Materials: Standard Quartz Cuvettes for High Accuracy Spectrophotometry, NBS Spec. Publ. 260-32

(December 1973). COM74-50018**

Wagner, H. L., Standard Reference Materials: Comparison of Original and Supplemental SRM 705, Nar- row Molecular Weight Distribution Polystyrene,

NBS Spec. Publ. 260-33 (May 1972). COM72-

50526**

Sparks, L. L., and Hust, J. G., Standard Reference

Materials: Thermal Conductivity of Austenitic Stainless Steel, SRM 735 from 5 to 280 K, NBS Spec. Publ. 260-35 (April 1972.) COM72-50368**

Call, J. P., Mandel, J., Moore, L. J., and Young, D. S., Standard Reference Materials: A Referee Method for the Determination of Calcium in Serum NBS SRM

915, NBS Spec. Publ. 260-36 (May 1972). COM72-

50527**

Shultz, J. I., BeU, R. K., Rains, T. C, and Menis, O.,

Standard Reference Materials: Methods of Analysis

of NBS Clay Standards, NBS Spec. Publ. 260-37

(June 1972). COM72-50692**

Clark, A. F., Denson, V. A., Hust, J. G., and Powell, R.

L., Standard Reference Materials: The Eddy Current Decay Method for Resistivity Characterization of

High-Purity Metals, NBS Spec. Publ. 260-39 (May

1972). COM72-50529**

McAdie, H. G., Gam, P. D., and Menis, O., Standard

Reference Materials: Selection of Thermal Analysis

Temperature Standards Through a Cooperative Study

(SRM 758, 759, 760), NBS Spec. Publ. 260-40

(August 1972) COM72-50776**

Wagner, H. L., and Verdier, P. H., eds.. Standard

Reference Materials: The Characterization of Linear

Polyethylene, SRM 1475, NBS Spec. Publ. 260-42

(September 1972). COM72-50944**

Yakowitz, H., Ruff, A. W., and Michaelis, R. E., Standard Reference Materials: Preparation and

Homogeneity Characterization of an Austenitic Iron- Chromium-Nickel Alloy, NBS Spec. Publ. 260-43

(November 1972). COM73-50760**

Schooley, J. F., Soulen, R. J., Jr., and Evans, G. A., Jr., Standard Referenc^^aterials: Preparation and Use of

Superconductive Fixed Point Devices, SRM 767,

NBS Spec. Publ. 260-44 (December 1972). COM73-

50037**

Greifer, B., Maienthal, E. J., Rains, T. C, and Rasberry,

S. D., Standard Reference Materials: Powdered LeadBased Paint, SRM 1579, NBS Spec. Publ. 260-45

(March 1973). COM73-50226**

Hust, J. G., and Giarratano, P. J., Standard Reference

Materials: Thermal Conductivity and Electrical

Resistivity Standard Reference Materials: Austenitic

Stainless Steel, SRM's 735 and 798, from 4 to 1200

K, NBS Spec. Publ. 260-46 (March 1975). COM75-

10339**

Hust, J. G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and Austenitic Stainless Steel, SRM 798, from 5 to 280 K,

NBS Spec. Publ. 260-47 (February 1974). COM74-

50176**

Mangum, B. W., and Wise, J. A., Standard Reference

Materials: Description and Use of Precision Thermometers for the Clinical Laboratory, SRM 933 and

SRM 934, NBS Spec. Publ. 260-48 (May 1974).

COM74-50533**

Carpenter, B. S., and Reimer, G. M., Standard Reference

Materials: Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260-49 (November

1974). COM74-51 185**

Hust, J. G., and Giarratano, P. J., Standard Reference

Materials: Thermal Conductivity and Electrical

Resistivity Standard Reference Materials: Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS

Spec. Publ. 260-50 (June 1975). COM75-10698**

V
Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Glass Filters As a Standard

Reference Material for Spectrophotometry-Selection, Preparation, Certification, Use-SRM 930 NBS

Spec. Publ. 260-51 (November 1975). COM75-

10339**

Hust, J. G., and Giarratano, P. J., Standard Reference

Materials: Thermal Conductivity and Electrical

Resistivity Standard Reference Materials 730 and

799, from 4 to 3000 K, NBS Spec. Publ. 260-52 (September 1975). COM75-11193**

Durst, R. A., Standard Reference Materials: Standardization of pH Measurements, NBS Spec. Publ. 260-53 (February 1988, Revision of December 1975

version).

Burke, R. W., and Mavrodineanu, R., Standard

Reference Materials: Certification and Use of Acidic

Potassium Dichromate Solutions as an Ultraviolet Absorbance Standard, NBS Spec. Publ. 260-54

(August 1977). PB272168**

Ditmars, D. A., Cezairliyan, A., Ishihara, S., and

Douglas, T. B., Standard Reference Materials: Enthalpy and Heat Capacity; Molybdenum SRM 781,

from 273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). PB272127**

Powell, R. L., Sparks, L. L., and Hust, J. G., Standard

Reference Materials: Standard Thermocouple

Material, Pt-67: SRM 1967, NBS Spec. Publ. 260-56

(February 1978). PB277 172**

Barnes, J. D., and Martin, G. M., Standard Reference

Materials: Polyester Film for Oxygen Gas Transmission Measurements SRM 1470, NBS Spec. Publ. 260-

58 (June 1979). PB297098**

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Reference Materials: A

Reference Method for the Determination of Sodium

in Serum, NBS Spec. Publ. 260-60 (August 1978).

PB286944**

Verdier, P H., and Wagner, H. L., Standard Reference

Materials: The Characterization of Linear

Polyethylene (SRM 1482, 1483, 1484), NBS Spec.

Publ. 260-61 (December 1978). PB289899**

Soulen, R. J., and Dove, R. B., Standard Reference

Materials: Temperature Reference Standard for Use

Below 0.5 K (SRM 768), NBS Spec. Publ. 260-62

(April 1979). PB294245**

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., and Gramlich, J. W., Standard

Reference Materials: A Reference Method for the Determination of Potassium in Serum, NBS Spec.

Publ. 260-63 (May 1979). PB297207**

Velapoldi, R. A., and Mielenz, K. D., Standard

Reference Materials: A Fluorescence Standard

Reference Material Quinine Sulfate Dihydrate (SRM

936), NBS Spec. Publ. 260-64 (January 1980). PB80-

132046**

Marinenko, R. B., Heinrich, K. F. J., and Ruegg, F. C,

Standard Reference Materials: Micro-Homogeneity

Studies of NBS Standard Reference Materials, NBS

Research Materials, and Other Related Samples, NBS

Spec. Publ. 260-65 (September 1979). PB300461**

Venable, W. H., Jr., and Eckerle, K. L., Standard

Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of

Spectrophotometers-SRM 2009, 2010, 2013, and

2014, NBS Spec. Publ. 260-66 (October 1979). PB80-

104961**

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Murphy, T. J., and Gramlich, J. W., Standard

Reference Materials: A Reference Method for the Determination of Chloride in Serum, NBS Spec. Publ. 260-67 (November 1979). PB80-1 10117**

Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Metal-On-Quartz Filters as a Standard Reference Material for Spectrophotometry

SRM 2031, NBS Spec. Publ. 260-68 (April 1980).

PB80-197486**

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., Gamer, E. L., and Rains, T. C, Standard Reference Materials: A Reference Method for the Determination of Lithium in Serum, NBS Spec. Publ. 260-69 (July 1980). PB80-209117**

Marinenko, R. B., Biancaniello, F., Boyer, P. A., Ruff, A. W., and DeRobertis, L., Standard Reference

Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis,

NBS Spec. Publ. 260-70 (May 1981). PB84-

165349**

Seward, R. W., and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical

Laboratory Standards Issued by the National Bureau

of Standards, NBS Spec. Publ. 260-71 (November

1981).PB82-135161**

Reeder, D. J., Coxon, B., Enagonio, D., Christensen, R.

G., Schaffer, R., Howell, B. F., Paule, R. C, and Mandel, J., Standard Reference Materials: SRM 900, Antiepilepsy Drug Level Assay Standard, NBS Spec.

Publ. 260-72 (June 1981). PB81-220758

Interrante, C. G., and Hicho, G. E., Standard Reference

Materials: A Standard Reference Material Containing

Nominally Fifteen Percent Austenite (SRM 486),

NBS Spec. Publ. 260-73 (January 1982). PB82-

215559**

vi
Marinenko, R. B., Standard Reference Materials:

Preparation and Characterization of K-4 1 1 and K-4 14 Mineral Glasses for Microanalysis: SRM 470, NBS

Spec. Publ. 260-74 (April 1982). PB82-221300**

Weidner, V. R., and Hsia, J. J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance Standards (SRM 2003a), NBS Spec. Publ. 260-75 (May

1982).PB82-221367**

Hicho, G. E., and Eaton, E. E., Standard Reference

Materials: A Standard Reference Material Containing

Nominally Five Percent Austenite (SRM 485a), NBS

Spec. Publ. 260-76 (August 1982). PB83-1 15568**

Furukawa, G. T., Riddle, J. L., Bigge, W. G., and Pfieffer, E. R., Standard Reference Materials: Application

of Some Metal SRM's as Thermometric Fixed Points,

NBS Spec. Publ. 260-77 (August 1982). PB83-

117325**

Hicho, G. E., and Eaton, E. E., Standard Reference

Materials: Standard Reference Material Containing

Nominally Thirty Percent Austenite (SRM487), NBS

Spec. Publ. 260-78 (September 1982). PB83-

115576**

Richmond, J. C, Hsia, J. J., Weidner, V. R., and Wilmering, D. B., Standard Reference Materials: Second Sur- face Mirror Standards of Specular Spectral

Reflectance (SRM's 2023, 2024, 2025), NBS Spec.

Publ. 260-79 (October 1982). PB84-203447**

Schaffer, R., Mandel, J., Sun, T., Cohen, A., and Hertz, H. S., Standard Reference Materials: Evaluation by

an ID/MS Method of the AACC Reference Method

for Serum Glucose, NBS Spec. Publ. 260-80 (October

1982).PB84-216894**

Burke, R. W., and Mavrodineanu, R., Standard

Reference Materials: Accuracy in Analytical

Spectrophotometry, NBS Spec. Publ. 260-81 (April

1983). PB83-2 14536**

Weidner, V. R., Standard Reference Materials: White

Opal Glass Diffuse Spectral Reflectance Standards

for the Visible Spectrum (SRM's 2015 and 2016),

NBS Spec. Publ. 260-82 (April 1983). PB83-

220723**

Bowers, G. N., Jr., Alvarez, R., Call, J. P., Eberhardt, K.

R., Reeder, D. J., Schaffer, R., and Uriano, G. A., Standard Reference Materials: The Measurement of

the Catalytic (Activity) Concentration of Seven En- zymes in NBS Human Serum SRM 909, NBS Spec.

Publ. 260-83 (June 1983). PB83-239509**

Gills, T. E., Seward, R. W., Collins, R. J., and Webster,

W. C, Standard Reference Materials: Sampling,

Materials Handling, Processing, and Packaging of

NBS Sulfur in Coal Standard Reference Materials

2682, 2683, 2684, and 2685, NBS Spec. Publ. 260-84

(August 1983). PB84-109552**

Swyt, D. A., Standard Reference Materials: A Look at Techniques for the Dimensional Calibration of Standard Microscopic Particles, NBS Spec. Publ. 260-85

(September 1983). PB84-1 12648**

Hicho, G. E., and Eaton, E. E., Standard Reference

Materials: A Standard Reference Material Containing

Two and One-HalfPercent Austenite, SRM 488, NBS

Spec. Publ. 260-86 (December 1983). PB84-

143296**

Mangum, B. W., Standard Reference Materials: SRM

1969: Rubidium Triple-Point - A Temperature

Reference Standard Near 39.30 °C, NBS Spec. Publ. 260-87 (December 1983). PB84- 149996**

Gladney, E. S., Bums, C. E., Perrin, D. R., Roelandts, I., and Gills, T. E., Standard Reference Materials: 1982

Compilation of Elemental Concentration Data for NBS Biological, Geological, and Environmental

Standard Reference Materials, NBS Spec. Publ. 260-

88 (March 1984). PB84-2 18338**

Hust, J. G., Standard Reference Materials: A FineGrained, Isotropic Graphite for Use as NBS Thermophysical Property RM's from 5 to 2500 K, NBS

Spec. Publ. 260-89 (September 1984). PB85-

112886**

Hust, J. G., and Lankford, A. B., Standard Reference

Materials: Update of Thermal Conductivity and

Electrical Resistivity of Electrolytic Iron, Tungsten,

and Stainless Steel, NBS Spec. Publ. 260-90 (September 1984). PB85-1 15814**

Goodrich, L. F., Vecchia, D. F., Pittman, E. S., Ekin, J. W., and Clark, A. F., Standard Reference Materials:

Critical Current Measurements on an NbTi Superconducting Wire Standard Reference Material, NBS

Spec. Publ. 260-91 (September 1984). PB85-

118594**

Carpenter, B. S., Standard Reference Materials:

Calibrated Glass Standards for Fission Track Use

(Supplement to NBS Spec. Publ. 260-49), NBS Spec.

Publ. 260-92 (September 1984). PB85-1 13025**

Ehrstein, J.R., Standard Reference Materials: Preparation and Certification of Standard Reference

Materials for Calibration of Spreading Resistance

Probes, NBS Spec. Publ. 260-93 (January 1985).

PB85-177921**

vii
Gills, T. E., Koch, W. F., Stolz, J. W., Kelly, W. R., Paulsen, P. J., Colbert, J. C, Kirklin, D. R., Pei, P.T.S., Weeks, S., Lindstrom, R. M., Reming, R. F., Greenberg, R. R., and Paule, R. C., Standard Reference

Materials: Methods and Procedures Used at the National Bureau of Standards to Certify Sulfur in Coal

SRM's for Sulfur Content, Calorific Value, Ash Content, NBS Spec. Publ. 260-94 (December 1984).

PB85-165900**

Mulholland, G. W., Hartman, A. W., Hembree, G. G.,

Marx, E., and Lettieri, T. R., Standard Reference

Materials: Development of a 1 |im Diameter Particle Size Standard, SRM 1690, NBS Spec. Publ. 260-95

(May 1985). SN003-003-02665-4*

Carpenter, B. S., Gramlich, J. W., Greenberg, R. R., Machlan, L. A., DeBievre, P., Eschbach, H. L., Meyer, H., Van Audenhove, J., Connolly, V. E., Trahey, N. M., and Zook, A. C, Standard Reference

Materials: Uranium-235 Isotopic Abundance Standard Reference Materials for Gamma Spectrometry

Measurements, NBS Spec. Publ. 260-96 (September

1986).PB87-108544**

Mavrodineanu, R., and Gills, T. E., Standard Reference

Materials: Summary of the Coal, Ore, Mineral, Rock,

and Refactory Standards Issued by the National

Bureau of Standards, NBS Spec. Publ. 260-97 (September 1985). SN003-003-02688-3*

Hust, J. G., Standard Reference Materials: Glass Fiberboard SRM for Thermal Resistance, NBS Spec. Publ. 260-98 (August 1985). SN003-003-02674-3*

Callanan, J. E., SulUvan, S . A., and Vecchia, D. F., Standard Reference Materials: Feasibility Study for the Development of Standards Using Differential Scanning Calorimetry, NBS Spec. Publ. 260-99 (August

1985). SN003-003-02675-1*

Taylor, J. K., Standard Reference Materials: Handbook

for SRM Users, NBS Spec. Publ. 260-100 (September 1985). PB86-1 10897**

Mangum, B. W., Standard Reference Materials: SRM

1970, Succinonitrile Triple-Point Standard: A

Temperature Reference Standard Near 58.08 °C, NBS

Spec. Publ. 260-101 (March 1986). SN003-003-

02722-7*

Weidner, V. R., Mavrodineanu, R., Mielenz, K. D., Velapoldi, R. A., Eckerle, K. L., and Adams, B., Standard Reference Materials: Holmium Oxide Solution Wavelength Standard from 240 to 640 nm - SRM

2034, NBS Spec. Publ. 260-102 (July 1986). PB86-

245727**

Hust, J. G., Standard Reference Materials: Glass

Fiberblanket SRM for Thermal Resistance, NBS

Spec. Publ. 260-103 (September 1985). SN003-0O3-

02687-5*

Mavrodineanu, R., and Alvarez, R., Standard Reference

Materials: Summary of the Biological and Botanical

Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-104 (November 1985).

SN003-003-02704-9*

Mavrodineanu, R., and Rasberry, S. D., Standard

Reference Materials: Summary of the Environmental

Research, Analysis, and Control Standards Issued by

the National Bureau of Standards, NBS Spec. Publ. 260-105 (March 1986). SN003-003-02725-1*

Koch, W. F., ed., Standard Reference Materials:

Methods and Procedures Used at the National Bureau

of Standards to Prepare, Analyze, and Certify SRM

2694, Simulated Rainwater, and Recommendations

for Use, NBS Spec. Publ. 260-106 (July 1986).PB86-

247483**

Hartman, A. W., and McKenzie, R. L., Standard

Reference Materials: SRM 1965, Microsphere Slide (10 |im Polystyrene Spheres), NBS Spec. Publ. 260-

107 (In Preparation).

Mavrodineanu, R., and Gills, T. E., Standard Reference

Materials: Summary of Gas CyUnder and Permeation

Tube Standard Reference Materials Issued by the National Bureau of Standards, NBS Spec. Publ. 260-108

(May 1987).

Candela, G. A., Chandler-Horowitz, D., Novotny, D. B., Marchiando, J. F., and Belzer, B. J., Standard

Reference Materials: Preparation and Certification of

an EUipsometrically Derived Thickness and Refractive Index Standard of a Silicon Dioxide Film (SRM

2530), NIST Spec. Publ. 260-109 (October 1988).

Kirby, R. K., and Kanare, H. M., Standard Reference

Materials: Portland Cement Chemical Composition

Standards (Blending, Packaging, and Testing), NBS

Spec. Publ. 260-110 (February 1988).

Gladney, E. S., O'Malley, B. T., Roelandts, I., and Gills, T. E., Standard Reference Materials: Compilation of

Elemental Concentration Data for NBS Clinical,

Biological, Geological, and Environmental Standard

Reference Materials, NBS Spec. Publ. 260-111

(November 1987).

*Send order with remittance to Superintendent of

Documents, U.S. Government Printing Office,

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viii
DESCRIPTION OF THE SRM 1965 MICROSPHERE SLIDE

A. W. Hartman

Precision Engineering Division

and R. L. McKenzie

Office of Standard Reference Materials

Table of Contents

Preface iii

1 . Introduction and Overview 1 2. Description of the SRM 1965 Microsphere Slide 1 3. The Microsphere Slide as a measurement tool 2

3.1 A microlength scale 2

3.1.1 Microsphere scales involving 1 to 100 spheres 5

3.1.2 Comparison with a stage micrometer 7

3.1.3 Readout of the photomicrographs 7

3.2 Image distortion and magnification in a microscope 8

3.2.1 Principle 9

3.2.2 An example 10

3.3 Spurious changes in microscope image magnification 12

3 .4 Use as a standard for particle sizing instruments 13

4. Uses of the Microsphere Slide in education and training 13

4.1 Array Sizing 13

4.2 The Kubitschek Effect 14

4.3 Measuring the microsphere diameter distribution 15

4.4 Do "contacting" microspheres actually touch? 16

4.5 Measuring sphere roundness 18

4.6 Presence of dried solute matter between spheres 20

4.7 Simulation of Bragg diffraction 20

4.8 Lattice faults 22

4.9 Aspects of sphere position readout 23

5. Making the Microsphere Slide 24

5 . 1 Growing monosize polystyrene microspheres 24

5.2 Making preparations of contacting microspheres 26

References 28

Appendix A SRM Certificates 29

A. 1 SRM 1965, Microsphere Slide (10-|im Polystyrene Spheres) 29

A.2 SRM 1960, Nominal lO-jim Diameter Polystyrene Spheres 31

A. 3 SRM 1961, Nominal 30-|im Diameter Polystyrene Spheres 33

A.4 SRM 1691, Nominal 0.3-|im Diameter Polystyrene Spheres 35

A. 5 SRM 1690, Nominal One-|im Polystyrene Spheres 37

Appendix B Related Papers 39

B. l Processing Materials in Space: The History and the Future 39

B .2 The First Products Made in Space: Monodisperse Latex Particles 50

ix
List of Figures

1 . Close-packed microsphere structures 1 2. Diagram of the Microsphere Slide 2

3 . Parallel illumination producing focal spots 3

4. Focal spots of microspheres of 3- and 30-|im diameter 4

5 . An object micrometer and a 10-|im microsphere scale 4

6 . Calculating radial and tangential magnification (see text) 9

a) radial magnification b) tangential magnification

7 . Finding image magnification and distortion 11

8. Scatter in length measurements vs. measured length 12

9. Microsphere settings in array sizing 14

10. Microsphere structures without air gaps 15

1 1 . Diameter distribution of the Microsphere Slide material 16

12. Detecting air gaps by measuring selected microsphere structures (see text). . . 17

13. Air gaps in hexagonal arrays distorting center distance measurements 18

14. Focal spot shape affected by microsphere deformation: 19

a) deformed 30-|im spheres; b) deformed focal spots.

15. Normal and elongated 0.7-|im focal spots of 10-|im spheres 19

16. lO-^m spheres with focal spots in two different planes 20

17. Microsphere illumination used to produce Bragg-like patterns 21

18. Bragg-like patterns caused by a) hexagonal and b) rhombic ordering 21

19. Microsphere arrays with various "lattice faults" 22

20. Crystal damage caused by a single outsize sphere 23

2 1 . Microsphere formation by emulsion polymerization 25

(courtesy L. B. Bangs, Ref. 8).

22. Swollen Microspheres 27

X
1 . INTRODUCTION AND OVERVIEW

This report describes the construction, preparation, and recommended uses of the

microsphere shde. The preparation material consists of monosize polystyrene microspheres with a Gaussian diameter distribution characterized by a mean diameter, D, of 9.89 ± 0.04 |im and a standard deviation, a^, of 0.09 ± 0.01 |im. This material was made under conditions of

microgravity during several NASA space shuttle flights, and is available from NIST (formerly

NBS) as a Standard Reference Material for particle size (SRM 1960). The size distribution is narrow, and the sphericity is very good. Its dimensional calibration was at the time (1985) the

most accurate microsphere particle calibration done at NBS.

The microsphere material has been deposited as fixed, two-dimensional, close-packed

structures, permanently sealed on a microscope slide. The dimensional information that these

slides contain is offered to microscopists as a measurement tool, and to teachers and students for

purposes of teaching and studying aspects of micrometrology and crystallography.

In Section 2 the Microsphere Slide is briefly described. Its use as a measurement tool is discussed in Section 3, several educational uses for the slide are given in Section 4 and a description of how the slide was made is given in Section 5. The Appendix contains reprints of

two papers describing various experiments of materials processing under conditions of

microgravity and the details of the production of the monodisperse polystyrene microspheres

aboard the space shuttle.

2. DESCRIPTION OF THE SRM 1965 MICROSPHERE SLIDE

The slide contains two separate groupings of microspheres. In one area the sphere

grouping is ordered in two-dimensional hexagonal arrays, in the other area the sphere grouping is unordered and resembles strings of beads in contact. Examples of each type of grouping are shown in Figure 1.

Figure 1. Close-packed microsphere structures.

The spheres are permanently sealed in an air chamber, formed by the microscope slide as a

flat substrate, a cover glass with central hole defining the sphere deposition area and forming the

chamber cavity, and a second cover glass sealing the chamber and protecting the microsphere

structures (Fig. 2).

1
'A v. 7. '/. 7. 7./7. 7. 7.' 7 7.

The microsphere material is the same as that

used in NIST Standard Reference Material

SRM 1960 - polystyrene spheres with a Gaussian diameter distribution,

characterized by mean diameter, D, of

9.84 ± 0.04 |im and a standard deviation,

ao, of 0.09 ±0.01 ^m.

Figure 2. Diagram of the Microsphere Slide.

3 . THE MICROSPHERE SLIDE AS A MEASUREMENT TOOL

The slide carries microscopic spheres of nominally equal and statistically known size; it can

therefore serve as a ruler or length standard of microscopic dimensions. It can be used in the

calibration of microlength measuring instruments or procedures that utilize optical microscopes,

including the determination of image magnification and image distortion of the microscope itself. In this section a number of uses will be described of the Microsphere Slide as a measurement tool.

3.1 A microlength scale

The ordered microsphere grouping on the slide contains many hexagonal arrays

which consist of rows of almost equal-size spheres. A microsphere row can be considered

a microlength scale, each scale division being one sphere diameter in length.

The length of a row can be read by sighting the sphere centers or the contact areas between spheres, using an eyepiece micrometer scale or crosshairs. The resolution of this

readout process is typically 5% - 10% of a sphere diameter (0.5 - 1 ^.m ). The scale

divisions can be made to look sharper by stopping the microscope condensor way down

(or taking it out), allowing almost parallel light to illuminate the microsphere area. Because

each sphere is transparent, it acts as a spherical lens, refracting the parallel incoming light

into a small focal spot just above each sphere. If the microscope is refocused onto the

common back-focal plane of the spheres, rows of small and equispaced focal spots will

appear in the field of view as bright points of light (see Fig. 3).

2
Microscope slide

Figure 3. Parallel illumination producing foc^ spots.

These focal spots, which mark the sphere centers in the field or on a photomicrograph, are circular, uniform, and much smaller that the spheres themselves. A

ray trace for a polystyrene sphere, illuminated by parallel blue-green light and viewed by a 0.50 NA microscope objective, predicts that the focal spots have a diameter of 0.03 D

where D is the sphere diameter. For spheres smaller than about 20 ^im the focal spot

diameter becomes equal to that of an Airy diffraction disk (1.2A./NA, or 1 [im for lO-^im

spheres). Examples are shown in Figure 4. It is thus possible to realize a microscopic

scale or ruler, consisting of a row of equispaced focal spots as in Figure 5, in which each

scale division can be read out with very high resolution.

The diameter of each sphere in the microsphere scale is known only statistically,

therefore the scale accuracy goes up in relative terms as the number of spheres in the scale

increases. The minimum scale length is 10 \im , the maximum is 100 - 200 |im depending on the available array row lengths on the microsphere slide and on the field of view.

It is possible to increase the relative accuracy of the scale beyond that of the longest

available microsphere row by including several neighboring rows. In this way ordered

assemblies containing 100 and more spheres can be used. For instance, a 10 x 10 array can define the image magnification at the array image area in the film plane with an accuracy

close to 0.5%, as will be shown below.

3
Figure 4. Focal spots of microspheres of 3- and 30-|im diameter.

Figure 5. An object micrometer and a

10-(xm microsphere scale.

4
3.1.1 Microsphere scales involving 1 to 100 spheres

In the following paragraphs the accuracy of a microsphere scale will be

estimated for cases involving 1 to 100 spheres. The selected confidence level is 95% (2 Sigma).

a) A single sphere

A single sphere selected at random will have a diameter D given by:

D = D ± = (9.89 ± 0.04) ± 2 x 0.09 ^im

= 9.89 ± 0.21 nm.

Of the 0.04 |im uncertainty, 0.01 |im is a random part and 0.03 [im is a systematic

part [5]. The random part adds in quadrature to the lo^ contribution which is random also, giving 0.21 jim total. Due to edge diffraction this distance will be

read out with considerably larger uncertainty: about 0.5 - 1 \im.

b) A contacting sphere pair

When the spheres are illuminated with parallel light a focal spot forms above

each sphere: the separation distance of the spots is equal to the sum of the radii of

the two contacting spheres. When the sphere diameters have a normal diameter

distribution, the sum of two radii will be normally distributed also, with a mean

diameter of D and a standard deviation equal to g^J^.

At the contact area the spheres will be slightly flattened due to mutual van

der Waals attraction resisted by elastic deformation forces [5]. This causes a calculated 0.02 ixm decrease in sphere center distance (see Sect. 3.4). The expected

sphere center distance, C, as represented by the focal spot spacing, is:

C = C ± 2aD/V2, = (9.89 - 0.02 ± 0.04) ± 0.13 ^im

= 9.87 ± 0.16 ^im.

Sphere pairs can be found in the unordered microsphere grouping on the

microsphere slide. It would not be possible to read a single lO-p-m division of a calibrated stage micrometer from photomicrographs at accuracies aproaching 0.16

|j,m.

c) An eleven- sphere row

When spheres are arranged in a hexagonal array, each sphere cannot

simultaneously touch all six of its neighbors (see Sect. 4.2). There is a distribution

of small gaps between spheres, scattered throughout the array. The average gap

width is (0.46 ± 0.03)00 [1].

This phenomenon causes the distribution of sphere centers to deviate from

Gaussian; it can be approximated by a normal distribution with a standard deviation

<Sq = Lloj) instead of csq = g^J^, giving <Sq= 0.10 |im.

5
In an array row, the average value C for a sphere center distance will be

equal to D + 0.460^ - 0.02 (due to two-sided sphere flattening at the contact area) +

0.03 (due to sphere swelling occurring during the array deposition process) = (9.89

± 0.04) + 0.05 = 9.94 ± 0.04 ^im.

An eleven-sphere row will have 10 center distances, and a total length Cio

given (at the 95% (2-sigma) confidence level) by:

Cio = IOC ± IgdVIO = 99.4 ± 0.4 ± 0.6 = 99.4 ± 0.9 urn.

The microscope slide contains array rows with lengths typically 10-20 spheres.

The calibration of an ocular micrometer (an eyepiece containing a reticle scale) can be done with an accuracy of about 0.7% when using the microsphere slide.

However, if the purpose is to calibrate magnification in the film plane of a photographic microscope, then improved accuracies are possible, as shown below.

d) A microsphere row combination containing 100 center distances

Improved accuracy can be obtained by measuring several neighboring

(parallel) rows to give a longer total length. If the microscope has been calibrated

for radial image distortion, the measured row lengths can be corrected, and the film

scale for zero distortion can then be obtained with considerable accuracy.

Assuming one has measured 10 parallel rows of 10 center distances each, one finds

the following:

Cioo = lOOC ± 2aD%/T00 = 100(99.4 ± 0.04) ± 2.0 = 994 ± 6 jim.

It is therefore possible to determine the magnification in the film plane of a photographic microscope with an accuracy approaching 0.5%, provided all other

variables are under control. The major variables are:

1) Image distortion

If no correction is to be made for image distortion only the central 20

- 25 % of the field of view diameter should be used. The FOV diameter will

then be some 50 spheres or 0.50 mm. The corresponding image

magnification will be fairly low, about 200x if 4 x 5 inch sheet film is used.

For higher magnification, for instance 800x to lOOOx, the separately

measured row lengths should be corrected for image distortion; a procedure

is given in Section 3.2.

2) For maximum accuracy, a number of repeated film exposures

should be used, in order to reduce the effect of fluctuations in magnification

caused when inserting fresh films (see Sect. 3.3). A useful number is five

repeated exposures.

3) As with all microsphere row length measurements, the rows should

be visually flawless, without cracks or curved rows. Such flaws would

6
indicate the presence of slack in the array and therefore loss of contact

between spheres which would introduce measurement errors.

3.1.2 Comparison with a stage micrometer

A microsphere scale consists of a row of small and equispaced circular

spots. Their spacings can be read with high resolution, about 0.03 )im when using

photomicrography and lO-pim spheres. However, because the sphere diameters are only statistically known and not all spheres actually touch each other, the accuracy

of such a microsphere scale is limited, to about 1.0% for a single 100-jj.m length,

and 0.6% when using 10 such lengths.

With a stage micrometer the situation is the reverse: its scale divisions can be calibrated with great accuracy (about 0.04 [im for a micrometer of lithographic

quality using cornplex photo-electric instrumentation and an interferometric object

stage). However, the resolution of the scale readout by means of

photomicrography is considerably less: about 0.2 |im because of the relatively large

widths of the lines that mark the scale divisions (2.5 - 3 ^.m, compared to 0.7 |im

for focal spot diameters produced by 10-|im spheres and photographed at 500x) as indicated in Figure 5. As a result, the photographic accuracy of a calibrated stage

micrometer is about 0.2 - 0.3% for a 100-|im length and about 0.5 - 1% for an

uncalibrated one. If the length of a selected microsphere row is compared with a corresponding length segment of a calibrated stage micrometer, the possibility

exists to obtain a microsphere "ruler" or scale with almost the same accuracy. This

is because the losses in accuracy from image distortion corrections and from

pinpointing the focal spots are relatively small.

Hexagonal microsphere arrays can be deposited on a microscope slide with

ease; using a mean sphere size in the range from 1 - 30 [im the rows are typically 70

-15 spheres long, respectively. A microsphere array can thus serve as a twodimensional microsphere scale, with a selectable length of its divisions.

3.1.3 Readout of the photomicrographs

In many cases the image magnification in the photomicrograph will lie in the

lOOx - 10(X)x range. The focal spots that mark sphere centers and make up a microsphere ruler will then show up in the film as circular "dots", with diameters

about 0.2 - 0.8 |im. The positions of their centers can be located with a precision of

0.01 - 0.03 |im, using a low-power microscope with crosshairs.

Adjacent dots representing touching microspheres will then be spaced 1-10

mm apart and the microsphere rows will have lengths ranging from about 10 mm to a full film frame (124 mm for 4x5 Polaroid^positive film).

The choice of which equipment to use to measure the films will depend on

several factors such as cost, skills of the operator, availability of components or

setups that can be converted to use for film readout, etc. Several possibilities are

listed below.

Hn order to adequately describe materials and experimental procedures, it was occasionally necessary to identify

commercial products by manufacturer's name or label. In no instance does such identification imply endoresement

by the National Institute of Standards and Technology not does it imply that the particular products or equipment is necessarily the best available for that purpose.

7
a) A coordinate measuring machine (CMM)

The mechanical probe of the CMM is replaced by a low-power microscope

with crosshairs, the film is placed on the CMM table and held flat by placing a weighted sheet of glass or acrylic on it, and is illuminated obliquely from above the

film with a microscope light (such as the Nicholas Illuminator from Bausch and

Lomb).

The microscope is centered manually over each dot to be measured, the

corresponding CMM coordinates are recorded, and the positions are then corrected

for image distortion in the film (Sect. 3.2). This readout process may be

automated, using a TV image sensor with centroid-seeking circuitry and a CMM

with X-Y travel under computer control.

The positions of the dot centers in the film can be found visually with 0.015 - 0.02 mm precision using a low-power microscope with crosshairs. A TVmicroscope can achieve better than 0.01-mm precision. The X-Y scales of a CMM

have accuracies considerably better than 0.01 mm.

b) A toolmaker's microscope

These microscopes with crosshairs have a specimen stage with X-Y

micrometer drives, typically 25 x 25 to 1(X) x 100 mm. The stage travel can be read

with a precision of 1 - 2 ^im, the scale accuracy being typically 1-5 [im.

c) A standard microscope with graduated specimen stage

These stages typically have a travel of 50 x 75 mm with millimeter scales

that can be read to 0.05 - 0.1 mm. Their accuracy is typically 0.05 - 0.10 mm

also.

d) A reticle magnifier

This is a low-power (7x to lOx) magnifier with a wide, flat field. It contains a reticle scale which is typically 20 mm long, with 0.1 -mm divisions. The

scale can be read out to 0.02 - 0.03 mm. Scale accuracy is typically 0.05 mm.

It is apparent that microsphere row lengths can be measured with equipment as simple as d). If individual microsphere center spacings are to be measured in order to determine diameter distributions, then a technique at least as precise and accurate as d) is required. A useful all-round approach is b). However, the CMM technique, a), is by

comparison the best.

3.2 Image distortion and magnification in a microscope

The magnification of a microscope can be found by measuring the image length of a stage micrometer placed such that it crosses the center of the field of view. When this is used to determine the length of a microscopic object or feature, the object must be

positioned such that the end points of the feature dimension coincide with the stage

micrometer marks photographed earlier, in order to avoid errors due to image distortion.

If the object is considerably smaller than a field of view diameter, if it can occur anywhere in the field of view, and if an accurate measurement is sought, the "local" (off8
axis) value of the magnification can be used rather than its field- averaged value. This value can differ by several percent from the magnification found above, due to image distortion.

This distortion can also cause the local magnification to be dependent on object orientation.

In the following paragraphs a method is described to find the image distortion and

the image magnification as a function of off-axis distance. Accuracies of 0.5% are possible, permitting the photographic microscope to be used for high-precision twodimensional micrometrology using low-cost standard equipment. In Section 3.2.1 the

principle of this method is outlined, followed by a worked-out example in Section 3.2.2.

3.2.1 Principle

Image distortion causes imaged points of an object to be displaced from their

expected positions in the image plane. For high-quality well-centered optics, these image

point shifts are radial ones: an image point located at an expected off-axis distance r will

have shifted radially to r+f(r), with f(r)«r.

A radially oriented line image AB with length L will have its end points shifted by

different amounts as indicated in Figure 6a, point A will move from Tj to rj -t- f(ri) and B

shifts from Tj to rj -t- f(r2). Consequentiy, the length AB = L = rj - rj will change to: d f AB = r2 + f(r2) - rj - f(ri) =T2-h+ (^2 - ri)^^

df

The local radial magnification Mr differs by a small fraction ^

Mo. -;

- from its on-axis value

Field of view

Figure 6. Calculating radial and tangential magnification

a) radial magnification b) tangential magnification

One can measure Mr as a function of r by making a series of photographs of a given

length segment oriented radially in a series of positions spanning a field-of-view diameter,

and measuring the changes in the imaged length. Expressed in terms of its on-axis value,

df

these length changes are equal to ^ from which f(r) can be found by graphic integration.

A faster way requiring only one additional photograph is to utilize a whole row of equalsize length segments, shifting it in-line by one (or a few) segment lengths, and measuring

9
how much each segment changed in length as a function of: initial off-axis distance, length

of the shift, and length of the line segment. The row of equal-size line segments is conveniently represented by a row of equispaced focal spots as part of a hexagonal

microsphere array. The changes in length of each segment in the row are found as follows:

the line segment, with its end points initially located at rj + f(rj) and + f(r2), is shifted by an amount Ar causing the end points to move to new positions rj + Ar +

f(ri -I- Ar) and r2+ Ar -i- f(r2 + Ar). The new segment length is : r2+ f(r2 +Ar) - r, - f(ri-i- Ar) = r2-ri + f(r2) + Ar^ X df

f(ri)-Ar3p

1 - -1- Ar

df

dr

A df

T2 dr

d^f

The radial shift Ar of each length L has caused length changes proportional to ^

and a graphic integration will yield the radial magnification Mr =

Different results are obtained if the Une segment AB is oriented tangentially, as in Figure 6b. Image distortion f(r) causes the associated arc length ar to change

to or -f- af(r) = ai(l + ^^~r-]- The chord length AB changes in proportion, and the

If the image f df ^ tangential magnification Mj changes to Mt = Mo 1 + ^

distortion happens to be proportional to r, f(r) = ar , then Mr and Mt will be equal:

Mr = Mt = Mo(l +a).

Mo itself can be found by imaging a known object length and correcting the

measured image length for the effects of image distortion. The ratio, reflecting the

absence of image distortion, is the on-axis magnification value Mq.

3.2.2 An example

A row of 10-|im microspheres was shifted in-line by 30 |j,m, and the changes in

focal spot center distances along the row were measured (see Fig. 7a). The magnification

could be obtained from that Figure by fitting a curve plus a graphic integration. Instead,

the curve fitting and integration (with its errors) was replaced by a cumulative summation

process described below, using the data points of Figure 7a. This resulted in Figure 7b in

which the data scatter now showed up as well. A curve was fitted showing M vs. r, and a

graphic integration yielded f(r) (see Fig. 7c).

10
MAGNIFICATION

OFF-AXIS DISTANCE (mm)

b)

IMAGE DISTORTION (^m)

150 -

100 -

1 \ 50 -

1 -40 -20 C) 20 40

OFF-AXIS DISTANCE (mm)

Figure 7. Finding image magnification and distortion.

The row was shifted by an amount 3D rather than D in order to improve data

resolution in Figure 7b. It did not result in an averaging of the obtained radial function over 3D but only over D, as will be apparent from the following description of this

cumulative summation process to obtain Figure 7b from Figure 7a.

Starting at the first (left) position, the accumulated length changes are found when a

focal spot center distance of length D is shifted in-hne by 3D; the data points obtained are marked as small circles in Figure 7b. The process is repeated starting at the second

position, then again at the third. The result is three data sets which are arranged such that

they fall on a common curve, Mr vs. r. From this the image distortion f(r) vs. r is found

(Fig. 7c). Also marked in that Figure is the calculated tangential image magnification Mt.

The microscope optics consisted of a 20x/0.50NA objective, a 2x relay lens, and a 12.5x photo eyepiece, giving a photographic magnification of nominally 500x and a 200-

|jm field of view.

The accuracy of the magnification data shown in Figure 7b can be estimated as follows. A lOO-pim section of a stage micrometer was used; its calibration, done at NIST,

had an accuracy of 0.04 |im. The photomicrographs were read out with a precision of 0.

1

nm. The image distortion increased the apparent length of the 95-^mi object by 0.7 |im,

with 0.07-pin uncertainty. This value was arrived at in an interative process, because the

data in Figure 7c are derived straight from Figure 7b while the data in Figure 7b depend -

albeit weakly - on those in Figure 7c. In addition, errors are introduced by spurious

changes in magnification caused when placing new sheet film in the cassette (see Sect.

3.3). These changes can amount to 0.2% when using a single photograph, or 0.1% when

five repeated photographs are used. The above considerations, and similar ones for the

off-axis variations in magnification lead to estimates for the accuracy of the magnifications

Mo, Mr and Mt amounting to 0.3 - 0.4%.

1 1
When a photomicrograph containing dimensional information is measured under

computer control, the image distortion curve and the value for are used to construct an X-Y reference frame in the object plane in which the object is then mapped. If, however,

the object is relatively small and manual readout is used, a measuring microscope or a

reticle magnifier may be used and the data are then evaluated based on local magnification

values. If the object contains very sharply defined surface features allowing highresolution micrometrology, then the question of tangential vs. radial magnification may also

come in.

3 . 3 Spurious changes in microscope image magnification

When a microscope is refocused its object distance changes. Its image distance

measured from the last imaging lens (which can be the photo ocular or equivalent) changes

and the image magnification changes in proportion. If the film plane is held stationary the

image scale in that plane stays almost constant, although the image at the film plane will

lose sharpness. If on the other hand a film sheet is replaced and the new film is now at a

slightly different position on the optical axis, the film scale will vary. The film-to-eyepiece

distance is typically 150 - 200 mm and the position tolerance of typical Polaroid sheet film

in its cassette is about 0. 1 - 0.2 mm, therefore spurious magnification changes can be

expected at the 0. 1 percent level.

This effect can be measured as follows. A row of microspheres is placed so as to cross the center of the field of view, the sphere preparation is illuminated with parallel light

and the resultant row of focal spots is photographed several times (for instance five times).

Center distances between focal spots (ranging from D, 3D, 5D,... to a full field diameter)

are measured in each photograph, and the scatter in each measured distance is calculated. A

graph is made of this scatter as a function of the measured distance, resulting in a plot as in

Figure 8. For large distances the plot approaches a straight line going through the origin.

The slope of this line represents that part of the scatter which is proportional to length, and

thus is caused by fluctuations in magnification (0.2% in the Fig.).

0.15

Such an uncertainty in

<

o

CO

LUIE

E

0.10

magnification applies to every

photograph taken with the

microscope. It is caused by

the use of flexible film sheets

and a film cassette without a vacuum platen.

Because the film is <

O

0.05 held by its edges, these

magnification fluctuations will

be maximum near the center

and essentially constant only over a relatively small central area (one-half of the field of

view or less), therefore the

sphere rows used should not

be too long.

CO

<N 0 ^ 1 I 1—

0 25 50 75

MEASURED LENGTH (mm)

Figure 8. Scatter in length measurements vs. measured length.

12
3.4 Use as a standard for particle sizing instruments

Single spheres, with statistically known diameters, can be used as test objects for

particle sizing instruments that analyze particle images. If an odd number of particles (for

instance three) touch each other to form a closed loop, measurements of all center distances

will then yield all diameters (after correction for sphere flattening, see below), thus

providing accurately known test objects.

When two spheres touch, van der Waals attraction forces [4] at the initial contact

area will also pull adjacent areas into contact, much like two optical flats exhibit progressive

contacting when initially pressed together at one area. This phenomenon is resisted by

elastic sphere deformation, resulting in a flattening of the spheres at contact and in a decrease of the center distance between touching spheres. As already mentioned in section

3.1.1, this decrease amounts to a calculated 0.02 ^im.

The calculation is based on a paper by Muller et. al. [6], who have analyzed the

balance between sphere-to-sphere attraction and sphere deformation. They give

expressions for the flattening of spheres in contact with a flat substrate. These estimate the

sphere deformation at and around the contact area, and indicate that the active noncontacting zone is relatively small (when no external forces are present). In that case the

flattening of a sphere contacting an equal-size sphere will be essentially equal to that of a sphere contacting a plane. One can then double the Muller expression to find the decrease

in sphere center distance C due to van der Waals attraction. This decrease AC is equal to:

r\ = Poisson constant (= 0.3 for polystyrene)

R = sphere radius (= 5x10'"* cm)

A = Hamaker constant (= 1x10'^^ erg for polystyrene)

E = Young's modulus (= 3x10^^ dn/cm^ for polystyrene)

e = distance of closest approach (= 3x10"^ cm).

This gives AC = 2x10"^ cm = 0.02 ^im.

4 . THE MICROSPHERE SLIDE USED IN EDUCATION AND TRAINING

In the following paragraphs a number of subjects are discussed that can form a basis for a

test or measurement in the Physics Laboratory, or a classroom demonstration. The student will

gain experience in - and an appreciation for - aspects of micrometrology. A close inspection of the

microsphere slide will also reveal items that are out of order, and which can make the life of a

particle analyst miserable: spheres that are "clearly" larger or smaller than the main population and

thus must be considered outliers, dust and dirt which was impossible to filter out or to otherwise

remove prior to sealing the slide, polystyrene particles of strange shapes (twin spheres, or elongated spheres), sealed-in "crystals" that defy identification, and so on.

This chapter is primarily addressed to you, the student, and we hope that you will get

inspiration and fun out of your measurements done on the slide.

4.1 Array Sizing

This is a technique to measure the mean size of a collection of microspheres which

have essentially the same diameter (the spheres are "monosize"). The spheres are deposited

13
in hexagonal arrays containing many straight rows, and measurements of row lengths

containing a known number of microspheres yield a surprisingly accurate value for the

average diameter of the spheres [2,3].

The row lengths can be measured in several ways. You can use the aerial image

itself, in which case the measurements are made by an eyepiece micrometer, or you can use photomicrographs. The settings can be made on the apparent center of the spheres, or on

the contact areas (see Fig. 9). In both cases, use is made of the sensitivity of the human

eye for symmetry: the eyepiece crosshairs can be set with a resolution of less than onetenth of the sphere diameter, or better than 1 micrometer.

For these measurements the microscope magnification and image distortion should

be well-known; a calibration procedure is given in Section 3.2. Error sources will be the

Kubitschek Effect (Sect. 4.2), sphere flattening (Sect. 3.4), and possibly sphere swelling

(Sect. 5.2).

4.2 The Kubitschek Effect

Kubitschek [1,5] has pointed out that a two-dimensional hexagonal array structure of microspheres having a distribution of sizes will contain a distribution of air gaps

throughout the array; the average air gap width between spheres is 0.460^. As a result, the

mean diameter (D) is found oversize by that amount. Consider for instances a smaller

sphere surrounded by six equal-size larger ones. The smaller sphere can touch only two of

the six, leaving four air gaps in that part of the array.

The existence and magnitude of the Kubitschek effect can be found by making

mean diameter measurements using two types of close-packed microsphere structures made

from the same microsphere material: one which has the air gaps (hexagonal arrays) and the

other which does not. Examples of the latter structure are square and rhombic arrays, and

strings of spheres in contact (Figs. 1 and 10). In square and rhombic array structures each

sphere can in principle touch all of its four neighbors. In string structures the attention will

be focused on those spheres that have no more than two neighbors: air gaps need not form

during formation of such string structures.

Figure 9. Microsphere settings in

array sizing.

A different way is to not use

microsphere images at all. Instead, one

illuminates the spheres with parallel Ught,

approximated by stopping the condensor

way down or by taking it out altogether.

The spheres refract this light into very

small focal spots (see Sect. 3.1), the

microscope is refocused on the common

back focal plane containing these spots

(which mark the sphere centers in the

field of view), and the row lengths are measured as the distance from the center

of the first spot to the center of the last spot. In this way the length measurement

can be done with improved resolution:

less than 0.05 micrometers when using

photomicrographs (see Fig. lb).

14
h

o

Figure 10. Microsphere structures without air gaps,

a) Rhombic arrays b) String structures

Square or rhombic arrays form rarely; your slide may not have any. However, the

microsphere slide contains beside an area of hexagonal arrays also an area of unordered

string-like close-packed microsphere structures. By determining a large number of sphereto-sphere distances from measurement of center distances of these structures viewed in

parallel light) you will obtain a mean value of the sum of sphere-pair radii. This value is equal to the mean diameter of the microspheres themselves (Why?).

A comparison between the mean diameter values found from arrays (D) and from

strings (Do) will show them to be significantly different, with the array value being larger.

The predicted value of that difference is D - Do = 0A6cd [1]; this can be confirmed

experimentally by measuring also the size distribution of the microspheres on the slide (see

Sect. 4.3). The material on the Microsphere Slide has a normal size distribution with CTd =

0.09 ± 0.01 pm. If the comparison between D and Do is to be done at a level of 0.01 iim

with 2-sigma (95%) confidence, how large should the number of measured spheres be?

4. 3 Measuring the microsphere diameter distribution

For this measurement the unordered sphere structures are used. The structures are illuminated with parallel light, and photomicrographs of the focal spot pattems are made. A

large number (300 - 1000) of center distances between adjacent spots in the film are measured carefully, then converted into distances (^im) in the object plane. For this

conversion the microscope magnification as a function of off-axis distances should be

known (see Sect. 3.2).

To avoid possible errors introduced by "invisible" (<0.2 |im) air gaps, the

measurement path is selected such that the measured sphere grouping is not

overconstrained. During the drying process each sphere would then have been able to freely come into contact with its neighbors. This implies in general a measurement path in

which each measured sphere has no more that two neighbors. Also, each sphere must be

measured only once (Why?).

15
The center distance (C) distribution is plotted and examined. If it is found to be a normal one (How?) then the diameter (D) distribution is normal also, with a mean D equal

to C and a standard deviation = Oq^TI (Why?). The mean diameter and the diameter

distribution of the microsphere material on the microsphere slide was measured in this way

at NIST; the result is shown in Figure 11. This microsphere sizing technique by optical

microscopy is called "Center Distance Finding" (CDF); it is described in detail in Reference

5.

9.6 9.8 10.0 10.2 9.7 9.6 9.9 10.0 10.1 DIAMETER (pm) DIAMETER (Mm)

Figure 1 1 . Diameter distribution of Microsphere Slide material.

The entire width of the diameter distribution of the Microsphere Slide material is only one-half of a micrometer. To map out such a size distribution, diameter measurements

are needed with a resolution of better than 0. 1 p-m. This is quite feasible with electron

microscopy but not when optical microscope images are used. Yet the same optical

microscope can make diameter measurements by CDF with a resolution better than 0.05

|im. Why does that technique work so well? The reason is that we do not use the image

resolution capabilities of the microscope, instead we use its position resolution for point

images. The former represents the radius of an Airy diffraction disk (0.5 ^m), while the

latter indicates the resolution with which the center position of such a disk can be found

(0.01 - 0.02 nm).

4.4 Do "contacting" spheres actually touch?

When microspheres are sized by Center Distance Finding it is necessary that the

measured spheres be in contact with each other. How can we be confident that they are actually in contact? Inspection of the optical images in string structures will not tell us; air

gaps smaller than about 0.2 nm go unnoticed. There is an indirect test however, which

goes as follows. Look for a microsphere structure that contains two or more triangular

arrangements, as in Figure 12. Starting with one triangle, a measurement of its three center

distances leads to the three diameter values. The diameter of spheres farther away are found from center distance measurements between a sphere of known diameter and the

adjacent unknown sphere. If this is done for a string of spheres starting from two different

triangular structures, one obtains two sets of diameters. If these are equal within

experimental limits, then this can be considered an indication that air gaps are absent. If unequal data sets are caused by one air gap, one can tell where that gap is and how wide it is (How?).

16
Figure 12. Detecting air gaps by measuring

selected microsphere structures (see text).

An argument that air gaps should exist in close-packed hexagonal microsphere

structures was discussed in Section 4.2 (the Kubitschek Effect). A confirmation of this can be found when center distance distributions are measured in hexagonal and in unordered

structures; distributions as in Figure 13 are then found. The random structures produce a Gaussian distribution, as expected. Measurements on the array structure appear to indicate

greater numbers of larger spheres; this is consistent with the notion that spheres and gaps

are measured together. The distorted distribution cannot be caused by sphere deformation,

because such spheres would have to be out of round by several percent (Why?) and their

focal spots would then be elliptical by some 20 - 40 percent, which would be easily

detected (see Sect. 4.5). Such deformed spheres are not present in any large amounts on

your slide. It can thus be concluded that the skewed distribution in Figure 1 3 is due to a

distribution of air gaps in the array. These gaps are on the average only some 0.05 - 0.10

\im wide.

17
I I I

I

I

I I 10.0 D 10.5|im

I

I

I I I I

I

I I M I

I

9.5 10.0 10.5 (im

Figure 13. Air gaps in hexagonal arrays distorting center

distance measurements.

4.5 Measuring sphere roundness

Figure 14 shows that microspheres with distorted shapes cause focal spot

distortion. When the sphere is Slightly oval-shaped, the centers of the two osculating

spheres will be separated by a small amount and the focal spot will be elongated by the

same amount (Why?). This is illustrated in Figure 15 for lO-jim spheres. The distorted

spot with size 0.7 \im is elongated some 10%, corresponding to a calculated non-sphericity

of 0.07 |im, or 0.7% of the sphere diameter. Such information could not be found from

the microsphere images themselves. Your microsphere slide likely will have some

distorted spheres.

1 8
Figure 14. Focal spot shape affected by microsphere deformation:

a) deformed 30-)j.m spheres b) deformed focal spots

Figure 15. Normal and elongated 0.7-^mi focal spots of 10-^im spheres.

19
4.6 Presence of dried solute matter between spheres

It is possible that your microsphere slide contains spheres that appear to be of two

types, denoted as I and II, shown in Figure 16. Their focal spots form in two different

planes that are some 5 fim apart, the grayish-looking type-II spheres in Figure 16 having

the larger focal length. This can be explained by assuming that dried and transparent solute

material was present around the contact area with the substrate surface; it makes such a sphere effectively a plano-convex lens instead of a spherical one. The solute material may,

for example, be a surfactant used in making the arrays, (see Sect. 5). It causes the dark

edge around the type-II sphere to be thinner than normal (Why?). You could argue that if much solute material dried up around the type-II spheres, there would likely be also solute

material between them. The distances between sphere centers will then be larger than

usual. What do you find for the average center distance in that case? What does that tell you about contacting spheres with dried solute material at their surface?

ft

Figure 16. 10-|im spheres with focal spots in two different planes.

4.7 Simulation of Bragg diffraction

The ordered part of the Microsphere Slide contains many smaller areas that exhibit a

single hexagonal ordering, like atomic particles in a microcrystal. The ordered areas have rows typically 5-10 spheres long. When such an area is illuminated with monochromatic

parallel light from a laser, for instance with normal incidence as shown in Figure 17, light

will emerge from the microsphere plane in discrete directions. This effect is caused by

interference between cones of light emerging from each focal spot after refraction by the

spheres. There is constructive interference in certain directions which are related to the

microsphere diameter and the laser wave length (What is this relation?). This gives us an independent method for finding the microsphere diameter, by measuring the light patterns

in two planes perpendicular to the optical axis. Examples are shown in Figure 18 b and c, using plane I for the microsphere images and plane II for viewing the interference patterns

through the microscope. The refracted light can also be recorded without using a microscope, simply by placing a film at plane HI.

20
^ \ \ f f

V / X ^ ^ / /^}rfr

h\

\\

/ 1 / 1 —1

/

LASER

Figure 17. Microsphere illumination

used to produce Bragg-like patterns.

Figure 18. Bragg-like patterns caused by

a) hexagonal and b) rhombic ordering

21
Although the Ught patterns resemble Bragg x-ray diffraction patterns from microcrystals

they are actually different, because we do not have three-dimensional structures of

radiation-scattering point sources.

4.8 Lattice faults

The hexagonally ordered microsphere area shows features that are the twodimensional analogs of three-dimensional lattice faults. Examples are shown in Figure 19.

Their presence can be seen from microsphere imagery, and can be inferred from the Bragglike patterns. Look for vacancies, slide planes, inclusions, microcrystallite boundaries,

curved "lattice planes", and various types of ordering (hexagonal, square, rhombic). Even

a single outsize particle can do considerable damage to a crystal structure, as illustrated in

the Figure 20.

Figure 19. Microsphere arrays with various "lattice faults".

22
Figure 20. Crystal damage caused by a single outsize sphere.

4.9 Aspects of sphere position readout

Most high-power microscope objectives are corrected for one of two working

conditions: 1) the space between the front lens and the object is filled with air only ("dry

objective") or 2) the space is filled with material that has the same refractive index as glass

(immersion oil, cover slip, any cement that the object is embedded in). The present

situation is between these two extremes: two air spaces plus one layer of cover glass are

present. For low-power objectives (20x, NA 0.5 or less) this hardly makes any difference,

but objectives with larger NA may show some loss in contrast resulting in somewhat larger - but unshifted - focal spots. This loss in sharpness can be offset in part by the use of

higher-contrast photographic film.

EstabUshing the center position of a photographed spot is facilitated considerably by

a slight defocusing of the microscope away from the film plane. This causes the visual

graininess of the film to be reduced, but does not introduce systematic errors (Why?).

23
5. MAKING THE MICROSPHERE SLIDE

5. 1 Growing monosize polystyrene microspheres.

The microspheres were grown by a chemical process known as emulsion

polymerization. This process is described in detail in References [7] and [8]; a brief sketch

is given below.

A concentrated solution in water is prepared of a "surfactant", a material consisting

of a compact, negatively charged, hydrophilic group of atoms (the "head") and a long

hydrocarbon chain (the "tail") with a positive charge. Above a certain concentration value

of surfactant in water, the surfactant molecules will arrange themselves into spherical

assemblies with the "tails" inside and the "heads" outside, with each assembly containing

essentially the same number of surfactant molecules. These fluid assemblies, called

micelles, are much Uke small and monosize spheres (Fig. 21a).

To the micelle solution are then added measured amounts of two other chemicals:

"initiator" and "styrene monomer". The initiator molecule looks like this:

RN = NR

with R being a hydrocarbon group.

The styrene molecule is shown below:

H H

I I c = c II

H 0

with 0 being a C6H5 group.

The two compounds diffuse into the micelles and cause them to swell, see Figure

21b. Then a polymerization takes place, which goes as follows. The initiator molecule

splits in two parts, and each part (shaded in Fig. 21c) links up one after another with a number of styrene molecules, thus forming a chain. When two such chains combine the

polymerization will stop. Using careful control of temperature, pressure, and time, the

swollen micelles (which are no longer fluid) will contain a ball-shaped conglomeration of

polymer molecules, each micelle containing equal amounts of material. When the

surfactant is removed, we now have a collection of solid, monosize polystyrene

microspheres (Fig. 2 Id).
c d

Figure 21. Microsphere formation by emulsion

polymerization (courtesy L.B. Bangs, Ref. 8).

The chemical reactions describing the polymerization are as follows:

RN = NR N2 + 2R»

H H H H II II

R. + C = C -R-C = C. II II

u gf H 0

where • denotes a free bond. After m

more steps we have:

H H

m

1 C1

1 1 H 0

H H

I I + R-C = C

I I H 0

H H

I I R— C = C

I I H 0

H H

I I

• C = C

I I H 0 m

This m-chain can combine with another chain to form a final product:

25
H H

1 1 R- C

1 H1 n

a polystyrene molecule. There are many such molecules in each micelle.

It is possible to repeat this process and make the monosize polystyrene

microspheres larger [7,8].

5.2 Making preparations of contacting microspheres

A cover glass with a central hole is cemented to a microscope slide, the spheres are then deposited inside the circular area and a regular cover slide is cemented on top to seal

off and protect the microsphere structures.

The microsphere structures feature contacting arrangements of two different types.

Close-packing is obtained by letting a drop of microsphere suspension evaporate on the

microscope slide. The surface tension forces of the evaporating liquid cause the drop to shrink until it dries, meanwhile pulling the spheres together, "raking them in" as it were.

In order to make the two types of close-packed structures: hexagonally ordered

arrays and string-like unordered formations, two different suspensions in water of the same

microsphere material are used, and deposited separately. One is the original Standard

Reference Material (SRM 1960), with a sphere concentration of about 0.5% by mass, and

containing about 0.005% sodium azide which inhibits the growth of organisms in the SRM

vial; this is used to make the unordered strings. The other is a suspension containing 3%

SRM spheres and 0.2% of a surfactant. This is used to make the arrays.

The purpose of the surfactant is to act as a lubricant between spheres as they are being pulled inwards when the liquid dries. The spheres which move as swarms, begin to order themselves when the thickness of the liquid is down to a sphere diameter or less. This ordering is "frozen-in" when the drying is complete, resulting in hexagonal arrays. In the other suspension, the absence of surfactant plus the much smaller sphere concentration causes the evaporating drop of suspension to break up during drying. This results in many

small and unordered string-like structures of touching microspheres.

The surfactant was selected from the Triton-X series by Rohm and Haas. The

compounds X-200 and up did not lubricate very well, causing shorter and less uniform

arrays. X-100 worked well, but its smaller molecule is known to diffuse into polystyrene,

causing it to swell slightly. The swelling of the lO-jim polystyrene spheres due to use of

X-100 was measured and found to be only 0.03 |im; it was therefore used to make the

microsphere suspension from which the hexagonal arrays were made.

The optical cement used for the three-piece glass assembly should not release any

styrene monomer during curing, since this could diffuse into the polystyrene spheres and

cause them to swell considerably. An example of this is shown in Figure 22. Note that the

swelling did not cause the spheres to break loose from the substrate.

26
Swollen microspheres.
List of References

[1] Kubitschek, H. E., Nature, 192 (1961) 48.

[2] Robillard, F., and Patitsas, A. J., Can. J. Phys. 51 (1973) 2395.

[3] Hartman, A. W., Powder Technol. 39 (1984) 49.

[4] Bowling, R. A., Solid State Science and Technology, Sep. (1985) 2208.

[5] Hartman, A. W., Powder Technol. 46 (1986) 109.

[6] Muller, V. M., et. al., J. Coll. Interf. Sci. 11 (1980) 91.

[7] Kornfeld, D. M., NASA TM-86487, January 1985.

[8] Bangs, L. B., Uniform Latex Particles, Seragen Diagnostics Inc.,

Indianapolis, IN.

28
Appendix A

Rational ^ur^au of Standards

Certificate

Standard Reference Material 1965

Microsphere Slide (10-jjm Polystyrene Spheres)

This Standard Reference Material (SRM) is intended for use as an optical microscopy measurement standard and teaching

tool. The SRM is a microscope slide with two different groupings of lO-fim "space beads" permanendy deposited on the surface and sealed in an air chamber (Figure 1). Each slide contains a few thousand microspheres. The microspheres are from SRM 1960, Nominal 10-^m Diameter Polystyrene Spheres, the first commercially available made-in-space product.

The microspheres in SRM 1965 are deposited in two different groupings: hexagonally ordered arrays and unordered clusters. The number average diameter of the particles in both groupings were measured by Center Distance Finding (CDF), an optical

technique related to array sizing [1]. The certified values are:

The uncertainty consists of both random and systematic errors, and includes sample-to-sample variability.

The number average diameter of the particles in the unordered clusters is the same as that of the microspheres in SRM 1960,

from which the slides were prepared. The number average diameter of the spheres as measured in the hexagonal arrays is slightly greater due to a combination of three effects: (1) the measured mean diameter of spheres in hexagonal arrays is larger than the actual mean diameter by 0.04 /zm due to the Kubitschek Effect (See SP 260-107 for detailed discussion); (2) the spheres are slightly swollen, by 0.03 fim, due to the processing required to produce the hexagonally-ordered arrays; and (3) the spheres are flattened at the contact areas by 0.02 ^m.

The size distribution of the polystyrene spheres from which SRM 1965 was prepared, as determined by CDF [1], is a narrow

Gaussian with a standard deviation of 0.9% (excluding particles with diameters not on the main peak). The number of undersized particles is negligible and the number of oversized particles is less than 1%.

The microsphere slide is expected to have an indefinite shelf life as long as the sealed cavity is not disturbed and the slide

is handled with normal precautions and care. Recommended Use: SRM 1965 can be used for a number of calibrations and exercises in micrometrology. The hexagonal

arrays can be used as a two-dimensional microlength standard to replace calibrated "stage" micrometers. The hexagonal

array can also be used for array sizing, diffraction experiments in crystallography, and for calibrating microscope image

distortion and magnification. These applications, and a number of other exercises and techniques for optical micrometrology

are described in detail in NBS Special Publication SP 260-107, which is supplied with the SRM.

January 15, 1987 Stanley D. Rasberry, Chief

Gailhersburg, MD 20899 Office of Standard Reference Materials

Number Average Diameter, ^m Uncertainty, fim Hexagonal array Unordered clusters

9.94

9.89

±0.04 + 0.04

29
The technology necessary to produce these latex particles was developed by the Lehigh University and the National

Aeronautics and Space Administration (NASA) during five shuttle missions in 1982 and 1983. The lO-fim particles in this SRM were manufactured in space aboard the Space Shuttle CHALLENGER during the NASA STS-6 mission, 4-9 April

1983. The particles were provided by NASA for certification by NBS as a Standard Reference Material to be made available

to the scientific and technical communities.

The technical direction, production and physical measurements leading to the preparation and certification were provided

by A.W. Hartman of the Precision Engineering Division.

Manufacture of the particles was carried out under the direction of J.W. Vanderhoff of the Lehigh University and

D M. Kornfeld of the National Aeronautics and Space Administration.

The technical and support aspects involved in the preparation, certification and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials by R.L. McKenzie.

[1] Hartman. A.W., Powder Technol, 42 (1985) 269.

SRM 1965, Microsphere slide

^0 fim Polystyrene Spheres

Hexagonally Unordered

Ordered Array Clusters

30
U. S. Ikp.iilriiciU III CiiiniiitKc

Mjlcoliii B-ildriyc Sccrctiirv Rational ^ureau of ^lanrfarrfs

Ol^rttftcat^

Nj|ion;il IlurcHU ^•'( St.mJ.iKjs

I rncNl Aiul»li t I hrcuoi

Standard Reference Material 1 960

Nominal 10jum Diameter Polystyrene Spheres

(In Cooperation with the American Society for Testing and Materials)

This Standard Reference Material (SRM) is intended for use as a primary particle size reference standard for the calibration of particle size measuring instruments including optical and electron microscopes. TTie SRM is a suspension of

polystyrene spheres in water at a weight concentration of about 0.4%.

The number average particle diameter was measured in air by Center EHstancc Finding (CDF), an optical technique

related to array sizing [I]. The certified value is:

The uncertainty consists of both random and systematic errors, and includes sample-to-samplc variability.

The size distribution of the polystyrene spheres, as determined by CDF [1], is a narrow Gaussian with a standard

deviation of 0.9% (excluding particles with diameters not on the main peak). The number of undersized particles is negligible and the number of oversized particles is less than 1%.

The material is expected to have at least a four-year shelf life when stored at room temperature, provided the cap on the

vial is not removed. Care should be exercised to prevent contamination once the cap has been removed. Fifty uglg of

sodium cizide was added as a biocide before the material was packaged.

Before sampling, manually shake and /or expose the SRM vial to ultrasonics until the spheres are uniformly distributed,

then take a sample by squeezing a drop from the vial. Use filtered (0.4-/im pore size filter) distilled water for dilution. When electrolytes are used for electrical sensing zone counter measurements, first dilute the sample with water to prevent

agglomeration.

T^e technology necessary to produce these latex particles was developed by the Lehigh University and the National

Aeronautics and Space Administration (NASA) during five shuttle missions in 1982 and 1983. The lO-Aim particles in SRM i960 were manufactured in space aboard the Space Shuttle CHALLENGER during the NASA STS-6 mission, 4 - 9 April 1983. The particles were provided by NASA for certification by NBS as a Standard Reference Material to be

made available to the scientific and technical communities.

The technical direction and physical measurements leading to certification were provided by T.R. Lettieri and

G O. Hcmbree of the Mechanical Production Metrology Division and A.W. Hartman of the Automated Production

Technology Division. Manufacture of the particles was carried out under the direction of J.W. Vanderhoff of the Lehigh University and

D M. Kornfeld of the National Aeronautics and Space Administration.

The overall coordination of the measurements by the cooperating laboratories was performed under the direction of R.C. Obbink. Research Associate, ASTM-NBS Research Associate Program.

The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference

Material were coordinated through the Office of Standard Reference Materials by L.J. Kieffer.

[1] Hartman, A. W.. Powder Technology (1985) (In Press).

April 4, 1985 Stanley D. Rasberry, Chief

Gaithersburg, MD 20899 Office of Standard Reference Materials

Number Average Diameter, fim Uncertainty, /xm

9.89 ±0.04

31
Cooperative determinations were performed in the following laboratories:

Climet Corporation, Rcdiands, California, L.D. Carver

Duke Scientific Corp., Palo Alto, California, S.D. Duke

Eastman Kodak Co.. Rochester, New York, B.C. Wood

Food & Drug Administration. Minneapolis, Minnesota, G.S. Oxborrow

General Electric Co., Worthington, Ohio, E.J. Connors

Lehigh University, Bethlehem, Pennsylvania, J.W. Vanderhoff

National Aeronautics & Space Administration, Huntsville, Alabama, D.M Kornfeid

Pacific Scientific, Menlo Park, California, L.D. Carver

Particle Data Laboratories, Ltd., Elmhurst, Illinois, R. Karuhn

The following results are given for information only:

Standard Deviation

Number Average of

Method Laboratory Diameter (urn) Distribution

Optical Microscopy Duke 9.90 0.05

FDA 10.215 0.176

Kodak 9.93

Electron Microscopy Lehigh 9.% 0.115

Kodak 9.90 0.05

Sensing Zone Duke 9.89 0.08

G.E. 10.02 Climet 10.08 NASA 9.93 0.12

Pacific 10.1 Scientific Particle 9.94

Data

32
U. S. Department of Commerce

Malcolm;_Baldrige

Secretary^

National PureauroTStandards

Ernest 'AmbJer. Director

Standard Reference Material 1961

Nominal 30-jjm Diameter Polystyrene Spheres

(In Cooperation with the American Society for Testing and Materials)

This Standard Reference Material (SRM) is intended for use as a primary particle size reference standard for the calibration of particle measuring instruments including flow-through counters and optical and electron microscopes. SRM 1961 is a suspension of polystyrene spheres in water at a weight concentration of about 0.5%.

The nimiber average particle diameter was measured in air using Center Distance Finding (CDF), an optical technique related

to array sizing [1]. Over 2000 particle diameters were measured with this technique. The certified value is:

The uncertainty consists of both random and systematic errors, and includes sample-to-sample variability.

The value certified for the number average diameter was confirmed by one odier measurement technique. Metrology

Electron Microscopy (MEM). In this technique, which measures the particles in an ultra-high vacuum, the particles are

individually scanned through a stationary electron beam while the position of the scanning stage is monitored by a stabilized helium-neon laser interferometer. A plot of secondary-electron intensity vs. stage position gives the particle diameter [2]. The result ft-om MEM is 29.68 ±0.05 ^^m. The size distribution of the polystyrene spheres, as determined by CDF, is Gaussian with a coefficient of variation of 0.8%

(excluding particles with diameters not on the main peak). The material was precision sieved with a 33-/im diameter-opening

electroformed sieve to remove oversized particles. As a result, the number of oversized outliers from the main peak is less than 1%; the same is true for die undersized oudiers. A sphere is defined as an oudier if it's diameter is more than 4o^ from

the number average diameter of the main peak. The material is expected to have at least a four-year shelf life when stored

at room temperature, provided the cap on the vial is not removed. Care should be exercised to prevent contamination once

the cap has been removed. Fifty ng/g of sodium azide was added as a biocide before the material was packaged.

Before sampling, manually shcike and/or expose the SRM vial to ultrasonics until the spheres are uniformly distributed, then

take a sample by squeezing a drop from the vial. Use filtered (0.4-/im pore size filter) distilled water for dilution. When

electrolytes are used for electrical sensing-zone measurements, first dilute the sample with water to prevent agglomeration.

The technology necessary to produce these latex particles was developed by Lehigh University and the National Aeronautics

and Space Administration (NASA) during five space shuttle missions in 1982 and 1983. The 30-nm particles in SRM 1961 were manufactured in space aboard the space shuttle Challenger during the NASA STS-11 mission. The particles were

provided by NASA for certification by NBS as a Standard Reference Material to be made available to the scientific and

technical commimity.

The technical direction and physical measurements leading to certification were provided by A.W. Hartman, T. Doiron.

G.G. Hembree, and T.R. Lettieri of the Precision Engineering Division of the National Bureau of Standards.

Manufacture of the particles was carried out under the direction of J.W. Vanderhoff of Lehigh University and D.M. Komfeid

of the National Aeronautics and Space Administration. The overall coordination of the measurements by the cooperating laboratories was performed under the direction of R.C. Obbink, ASTM-NBS Research Associate. The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference Material were coordinated through the NBS Office of Standard Reference Materials by R.L. McKenzie.

January 20, 1987 Stanley D. Rasberry, Chief

Gaithersburg, MD 20899 Office of Standard Reference Materials

Number Average Diameter, iim Uncertainty, iim

29.64 ±0.06

33
[1] A.W. Hanman, Powder Technology 46, 109 (1986).

[2] S. Jensen, G. Hembree, J. Marchiando, and D. Swyt in Semiconductor Microlithography VI, SPIE Vol. 275 (SPIE.

Bellingham, Wash., 1981).

Cooperative determinations were determined in the following laboratories: Duke Scientific Corp., Palo Alto, California, S.D. Duke (also performed precision sieving).

Lehigh University, Bethlehem, Pennsylvania, J.W. Vanderhoff.

National Aeronautic^ and Space Administration, Huntsville, Alabama, D. Komfeld.

Particle Data Systems, Elmhurst, Illinois, R. Karuhn.

The following results are given for information only:

Method Laboratory

Number Average

Diameter {fim)

Standard Deviation

of

Distribution (jim)

TEM Lehigh 31.31 0.39

Electrical- sensing zone DukeParticle Data

29.61

30.16

0.26

0.78

NASA 29.09 0.37

Optical

microscope

Duke 29.57

34
«. Departrinrirk^f Commerce Malcolnr^ldriBe

Naiioiul BunBliol Sundards

Emesi Anbfer. Qitectoi Rational ^ur^au of ^tandartts

d^rttftcat^

Standard Reference Material 1691

Nominal 0.3 Aim Diameter Polystyrene Spheres

(In Cooperation with the American Society for Testing and Materials)

This Standard Reference Material (SRM) is intended for use as a primary particle size reference standard for the calibra- tion of particle size measuring instruments including electron microscopes. The SRM is a suspension of polystyrene

spheres in water at a weight concentration of about 0.5%.

The number average particle diameter was determined by transmission electron microscopy (TEM) using SRM 1690

(nominal one-Min polystyrene spheres) to set the dimensional scale. The value reported is the mean of five independent

data sets each consisting of over 100 measurements of l-ntn standard spheres and over 30 measurements of nominal

0.3-Aim spheres.

The uncertainty consists of both random and systematic errors, and includes sample-to-sample variability.

The value certified for the number average diameter was confirmed by one additional technique, quasielastic light

scattering (QELS). In this technique, the average lifetime of the Brownian motion of the particles suspended in water is measured as a function of scattering angle. This gives a diffusion coefficient which can be used with the Stokes-Einstein

relationship to yield the hydrodynamic particle diameter. The result from QELS was: 0.276 ±0.007 fan. The size distribution of the polystyrene spheres, as determined by TEM, is narrow with a standard deviation less than 2%

excluding outliers (particles with diameters not on the main peak). The number of small outliers is less than 1% and the number of large outliers is less than 0.5%.

The material is expected to have at least a four-year shelf life when stored at room temperature provided the cap on the

vial is not removed. Care should be exercised once the cap has been removed to prevent contamination. Fifty ppm of sodium azide was added as a biodde before the material was packaged.

Before sampling, manually shake and/or expose SRM to ultrasonics until the spheres are uniformly distributed. Then

take a sample by squeezing a drop from the viaL. Use filtered (0. l-fim pore size filter) distilled water for dilution. When

elertrolytes arc used for electrical sensing zone counter measurements, first dilute the sample with water to prevent

agglomeration.

The technical dircrtion and physical measurements leading to certification were provided by T. Lettieri, G. Hembrce,

D. Gilsinn, and E. Marx of the Mechanical Production Metrology Division. The overall coordination of the measurements by the cooperating laboratories was performed under the direction of

R. Obbink, Research Associate, ASTM-NBS Research Associate Program.

The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference

Material were coordinated through the Office of Standard Reference Materials by L.J. Kieffer.

May 1, 1984 Sunley D. Rasberry, Chief

Washington, DC 20234 Office of Standard Reference Materials

Number Average Diameter, fim Uncertainty, /nn

0.269 ±0.007

35
Cooperative determinations were performed in the following laboratories:

Brookhaven Instruments Corp., Ronkonkoma, New York, B. Wciner

Eastman Kodak Co., Rochester, New York, D. E. DeCann

Malvern Instruments, Malvern, England, F. McNeil-Watson

G. D. Searle and Co., Skokie, Illinois, M. Groves

The following results are given for information only:

Standard Deviation

Number Average of

Method Laboratory Diameter (Mm) Distribution (/xm)

Electron Microscopy Kodak 0.248 0.0026

Light Scattering

Polarization Ratio Kodak 0.273 0.003

Quasielastic Kodak 0.272

Quasielastic Kodak 0.293

Quasielastic Brookhaven 0.273

Quasielastic Searle 0.282 0.0032

Quasielastic Malvern 0.273

Disc Centrifuge Kodak 0.25 0.0027

Ultracentrifuge Kodak 0.28 0.0029

36
Ij. S. Deparimcm of Commerce Ma Icolttt-Baldr ige

National JuriiW of Standards ErnesiUmbfcr. Director Rational '^mmn of ^tmdnxd^

Standard Reference Material 1690

Nominal One-jum Polystyrene Spheres

(In cooperation with the American Society for Testing and Materials)

This Standard Reference Material (SRM) is intended for use as a primary particle size reference standard for the calibra- tion of particle size measuring instruments including microscopes. The SRM is a suspension of polystyrene spheres in water at a weight concentration of about 0.5%. The number average particle diameter was determined by measuring the light scattered by the polystyrene spheres

suspended in water. The value used for the refractive index of polystyrene was n(Xvac = 632.99) = 1.588. The diameter was determined from the best fit of Mie light scattering theory to the measured intensity versus angle.

The uncertainty includes both random and systematic errors. The sample-to-sample variability (standard deviation) of the number average diameter, as determined on single drops

taken from 20 vials (light scattering measurements of water suspensions and electrical sensing zone counter measurements), was found to be 0.0008 /^m. The value certified for the number average diameter was confirmed by two other measurement techniques. The first of

these was by measuring the light scattered by individual spheres (8 were measured) levitated in air. In this technique both

the diameter and refractive index are determined by the best fit to light scattering theory. In the second technique the average diameter was determined by optically measuring the row length of particles in two dimensional arrays formed by

air drying. Scattering by individual particles: (0.900 ± 0.01 1 /nm). Optical array sizing: (0.900 ± 0.015 /^m). The particle size distribution of the polystyrene spheres (as determined by measurements with a transmission electron microscope) is narrow with a standard deviation of about 0.009 fim, excluding small particles with diameters less than

0.6 nm (about 0.5%) and large single particles with diameters in the range of 2-6 Mm (about 0. 1%). A discordancy test based on the sample kurtosis was used at the 5% level for rejecting these particles [V. Barnett and T. Lewis, Outliers in Statistical Data, (Wiley, 1978) p. 101]. The particles are spherical with an average deviation from sphericity,

(Dmax -Dm.n)/Dave,of about 0.006. Measurements with an electrical sensing zone counter and by optical microscopy

indicated that about 1.5% of the particles are agglomerated doublets. The material is expected to have a four year shelf life when stored at room temperature provided the cap on the vial is not removed. Care should be exercised once the cap has been removed to prevent contamination.

Before taking a sample by squeezing a drop from the vial, manually shake and / or expose to ultrasonics until the spheres

are uniformly distributed. Use filtered (0.2-/um pore size filter) distilled water for dilution. When electrolytes are used for

electrical sensing zone counter measurements, first dilute the sample with water to prevent agglomeration.

The technical direction and physical measurements leading to certification were provided by G. Mulholland, T. Lettieri. G. Hembree, A. Hartman, and E. Marx of the Mechanical Production Metrology Division, with guidance on statistical analysis provided by K. Eberhardt of the Statistical Engineering Division. The overall coordination of the measurments by the cooperating laboratories was performed under the direction of

R. Obbink, Research Associate, ASTM-NBS Research Associate Program.

The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference

Material were coordinated through the Office of Standard Reference Materials by R.K. Kirby.

Washington, D.C. 20234 George A. Uriano, Chief

December 22, 1982 Office of Standard Reference Materials

Number Average Diameter,/im Uncertainty, /i m

0.895 ± 0.008

37
Cooperative determinations were performed in the following laboratories:

Air Products and Chemicals, Allentown, Pennsylvania, D.J. Nagy

Coulter Electronics Corp., Hialeah, Florida, R.T. Rodewald

Dow Chemical Co., Midland, Michigan, M.A. Langhorst

Duke Scientific Corp., Palo Alto, California, S.D. Duke

Eastman Kodak Co., Rochester, New York, B.C. Wood

General Electric Co., Worthington, Ohio, E.J. Connors

Pacific Scientific, Menlo Park, California, L.D. Carver

The following results are given for information only.

Method Laboratory

Number Average

Diameter (p.m)

Standard Deviation

of

Distribution (/im)

Transmission Electron Microscope

Opitcal Microscope Array Sizing

Light Scattering

Polarization Ratio

Quasielastic

Quasielastic

Light Absorption

Electrical Sensing Zone

Electrical Sensing Zone

Electrical Sensing Zone

Electrical Sensing Zone

Disc Centrifuge

Disc Centrifuge

Hydrodynamic Chromatography

Type of average not specilied. "^Number median diameter.

' Volume median diameter.

Kodak

Kodak

Kodak

Kodak

Coulter

Pacific Scientific Kodak

Duke

Coulter G.E. Kodak

Air Products

Dow

0.875

0.895

0.900

0.93' 0.896'

0.87

0.89*'

0.90' 0.87'

0.89^

0.91 0.88

0.88'

0.018

0.067

0.030

0.023 0.058

0.017 0.046

0.26

38
Appendix B

PROCESSING MATEPIALS IN SPACE:

THE HISTORI AND THE FUTURE

Roger Chassay Bill Carswell

Application Payload Projects Office Get Away Special Experimenter

NASA Marshall Space Flight Center, AL San Jose State University, CA

Abstract

During the NASA Apollo missions to the

Moon, several elementary experiments were performed to look at what happens when

liquid materials are solidified without

the effects of Earth's gravity. The

results of these early experiments were

very interesting, prompting NASA to

conduct more sophisticated materials

experiments at every opportunity. From

the results obtained to date, many

possibilities exist for new alloys,

improved semiconductors, radiation

detectors of Impressive characteristics,

sophisticated high technology glasses,

new pharmaceutical products, and other

novel materials. Can these possibilities

be transformed into practical, costeffective products for the benefit of

mankind? The world's technologically

leading countries are trying to find out.

Introduction

Long before materials science was developed in a sophisticated manner,

surprising results were achieved by

processing materials on Earth, despite

the burden of gravity. Remarkably

sophisticated swords were made by

medieval blacksmiths; relatively mature

3000-year~old blast furnaces have been

discovered in Africa; [1] and

archeologists have unearthed iron

implements in Egypt that appear to be

about 5,000 years old. [2] Modern times

have provided a rapid advance in

materials technology, despite continued

gravity effects. However, we are now preparing to slip the bonds of gravity

and begin developing a true mastery over materials and the processes that bind

them

.

HISTORY

Although no one can say for sure who

first suggested low-g materials

processing, we know that in the 1780s

William Watts of the United Kingdom

obtained much better quality lead shot by

using a freefall technique which he

patented. [3] We also know that in the

l840s Joseph Plateau of Belgium suspended

oil in a liquid of the same density,

showing, among other Important things,

that the oil formed a perfect sphere when

gravitational effects were removed. [M]

The writings of the French novelist Jules

Verne in the 1860s triggered more serious

thought by Tsiolkovskiy of Russia in the

Deputy Manager

Associate Fellow AIAA

Student Member AIAA

Tbb paper U dcdand » work of the U.S. Govemmcnl and is not subject to copyright protection in the United States.

I880s. [5] Acknowledging that

experiments by others had already shown

that gravity has no effect on diffusion

of fluids, Tsiolkovskiy • s writings

addressed important phenomena regarding

liquids and gases in microgravity

:

1) surface tension creates spherical

shapes, 2) density driven segregation is

absent, and 3) diffusion and surface

tension become more prominent

Influences. He also suggested the use of

asteroids as a source of raw materials

for space bases and foresaw the creation

of Industrial activities in space.

Active interest in space processing

began in the 1960s with a very few

individuals taking the lead, principally

Hans Wuenscher of NASA's Marshall Space

Flight Center (MSEC). [6,7,8,9,10,11]

These pioneers were convinced of the

possibility of using low-g to overcome bouyancy driven convection and density

gradient driven sedimentation. [12]

Drop Towers

Early microgravity materials research

was done with the MSFC drop tower. [13]

The drop tower allowed low-g experiments

of a few seconds duration to investigate

liquid spheres, hollow spheres, thin

membranes, foaming, foams, liquid

spreading, and liquid management.

Soyuz 6 The first Soviet orbital materials

experiments were performed aboard the

Soyuz 6 spacecraft. This work Involved

the use of an electron beam to melt and

weld metals. [1^]

Apollo

American scientists got their first

chance to process materials in space when

Apollo astronauts performed elementary

experiments during their return trips

from the Moon. Apollo 1^1 carried a composite casting apparatus which

processed immiscible materials. These

samples did not exhibit immiscible

separation, the classic phenomena which occurs on Earth. Apollo 1^ and Apollo 17 Included fluid experiments which provided

data on surface tension driven flow in

low-g and indications of convection

Induced by the spacecraft and flight

crew. Electrophoresis demonstrations

performed on Apollo 1^ and on Apollo 16 showed separations, although somewhat

distorted, due to electro-osmosis. [1]

39
Early Suborbital and Aircraft Flights SALYUT-J<

Two suborbital low-g flights were conducted In October 1971 and In January

1972 by MASA-MSFC to experiment with

metallic foams and composite materials .[ 1 1

]

Short term, low-g sphere melting and

sphere forming experiments by NASA-MSFC

during KC-135 aircraft parabolic flight maneuvers began in 197?-

Skylab

The first sophisticated low-g

materials experiments were conducted

aboard the Skylab space station. Using

experiments provided by scientists from

the USA, Japan, and Belgium, astronauts

completed fourteen materials experiments

and also performed a group of nine

enlightening materials science

demonstrations. The results from the

experiments and demonstrations were

impressive: Crystals grew larger and were more pure; solid mixtures were more homogeneous; convection and sedimentation

effects seemed negligible; amorphous

materials were obtained in lieu of some crystals; and insights into low-g float

zone mechanics were obtained. [15] A complete list of materials experiments

and demonstrations carried out aboard

Skylab is provided in figure 1.

Soviet scientists initiated a series

of Salyut flight experiments in 1975 with

two experiments: metal surface coating

and the stability of rotating liquids.

Apollo-Soyuz

Also in 1975 a joint USA-Soviet

mission, the Apollo-Soyuz Test Project

(ASTP), was conducted with ten new experiments from American, Soviet, and

West German scientists. This opportunity

allowed continuation of some experiment

areas Investigated earlier on Skylab, as well as the initiation of investigations

into entirely separate areas such as low-g electrophoresis. [16] A complete

list of ASTP experiments is provided in

figure 2.

Widespread Interest

By the mid-1970s there were enough

reproducible and irrefutable low-g

experiment results to spark the interest

of most of the world's technologically

leading countries. The USA Intensified

its efforts by adding a series of

suborbital flights, called SPAR (Space

Processing Applications Rocket).

Figure 1: SKYLAB MATFRIALS EXPERIMENTS AND SCIENCE DEMONSTRATIONS

EXPERIMENTS SKYLAB MISSION

. II III IV

MATERIAL PROCESSING FACILITY

M551: Metals-Melting, P.M. Poorman, MSEC Astronautics Lab X M552: Exothermic Brazing, J. P. Williams, MSEC Product Eng. Lab X M553: Sphere-Forming, E.A. Hasemeyer, MSEC Product Eng. Lab X MULTIPURPOSE FURNACE SYSTEM

M556: Vapor Growth of II-VI Compounds, F. Wledemeier,

Rensselaer Polytechnic Institute X X M557: Immiscible Alloy Compositions, J.L. Reger, TRW Systems X X M558: Radioactive-Tracer Diffusion, A.O. Ukanwa, MSFC Space Science Lab X M559: Mlcrosegregat ion in Germanium, F.A. Padovanl, Texas Instruments X M560: Growth of Spherical Crystals, H.U. Walter, Univ. of Alabama X X M561: Whisker-Reinforced Composites, T. Kawada,

National Institute for Metals Research, Japan X X M562: Indium Antlmonlde Crystals, H.C. Gatos, MIT X X M563: Mixed III-V Crystal Growth, W.P. Wilcox, USC X X M5614: Alkali Hallde Eutectlcs, A.S. Yue, UCLA X M565: Silver Grids Melted in Space, A. Deruytherre,

Katholleke Univ., Leuven, Belgium X M566: Copper-Aluminum Eutectlc, E.A. Hasemeyer, MSFC Product Eng. Lab X X

SCIENCE DEMONSTRATIONS

Diffusion In Liquids X Ice Melting X TV 101 Liquid Floating Zone X TV 102 Immiscible Liquids X TV 103 Liquid Films X TV 105 Rochelle Salt Growth X TV 106 Deposition of Silver Crystals X TV 107 Fluid Mechanics Series X TV 117 Charged-Particle Mobility X

40
The DSSR began similar flights called

MIP-2, [111] West Germany initiated a series of suborbital flights called

TEXUS, and Japan conducted suborbital

flights designated TT-500A.

The USSR continued its orbital

materials experiment program by adding

experiments on the Salyut 5, 6, and 7 missions. Salyut-5 experiments included

metals melting and solidification,

crystal growth, diffusion studies, and

soldering demonstrations. Salyut-6

featured an electric furnace, a Czechoslovak ian smelting experiment, and

semiconductor manufacturing. [17]

A timeline showing the development of

all these international programs is shown

in figure 3.

Space Transportation System Experiments

When the USA introduced its Space

Transportation System (STS) flights,

materials scientists Jumped at the

opportunity to use this new research

facility. The world's first space

product, 10-micron latex spheres, was

FIGURE 2: ASTP EXPERIMENTS

ELECTROPHORESIS EXPERIMENTS

MA-011: Electrophoresis Technology

R.S. Snyder, MSEC Astronautics Lab

P.E. Bigazzi, State Dniv. of New York

G.A. Barlow, Abbott Laboratories

M. Bier, Veterans Administration

KA-OIH: Electrophoresis (EPE)

K. Hannig, Max Planck Institute

MULTIPDRPOSE FURNACE SYSTEM (MA-010)

MA-041: Surface Tension Induced

Convection

R.F. Reed, Oak Ridge National Lab

MA-ClU: Monotectic and Syntectlc Alloys

C. Y. Ang, Northrop Corp.

MA-060: Interface Marking In Crystals

H.C. Gatos, MIT

MA-070: Zero-G Processing of Magnets

D. J. Larson, Grumman Corp.

MA-085: Crystal Growth from the

Vapor Phase

H. Wiedemeier, Rensselaer Polytechnic

Inst itute

MA-131: Sodium Chloride-Lithium Fluoride

Eutect ic

A.S. Yue, UCLA

MA-150: Multiple Material Melting

USSR

COOPERATIVE EXPERIMENT

MA-028: Crystal Growth

M.D. Lind, Rockwell International

initially processed on STS-3 and later

completed on STS-6. In the first four

years of STS missions, USA scientists

alone conducted over 35 low-g

experiments. Figure h shows a list of

the apparatus used for these mlcrogravity

science experiments. Many other low-g

materials experiments were provided by

other countries, including Austria,

Belgium, Denmark, France, Great Britain,

Italy, The Netherlands, Spain, Sweden,

and VJest Germany.

Accomplishments

The many accomplishments achieved to date can only be summarized in this brief

paper, and, of course, a number of

accomplishments have been omitted because

we do not have access to the

information. We have grouped the

accomplishments by experiment types, by

apparatus developments, and by unique

ground facilities provided.

Bioprocessing

Protein Crystal Growth flight

activities include one experiment in

Spacelab 1 and four experiments in the

Shuttle Middeck using a very simple,

hand-held device. Since the purpose of

these early experiments was to develop

techniques for growing protein crystals

in mlcrogravity, no temperature control

was provided. Nevertheless, some excellent crystals were grown, expecially

on STS-61C when the experiment was performed by Payload Specialist, U.S.

Congressman Bill Nelson. Several crystals

yielded very high resolution x-ray

diffraction patterns, indicating a well-ordered crystalline structure.

Analysis of these crystals is still in

progress to see how they compare with the

best crystals grown on Earth.

In addition to these flight

experiments, the synergism between the

various disciplines involved in the

project has produced new insights into

the growth of protein crystals and

improved Earth-bound growth techniques.

Laboratory activities include the

investigation of lysozyme crystal growth

kinetics and development of a growth

process model which provided data used to determine the relative role of transport

and interfacial kinetics in lysozyme

crystal growth. New techniques have been

developed and used to determine the phase

diagrams for various protein crystal

growth conditions. We have also

crystallized tryptophan synthase from

E . coli . a protein that had not been

previously crystallized.

Relative growth rate measurements of

human serum albumin and sucrose clearly

show that the crystal growth rate is

greatest in the direction perpendicular

41
to the density-driven convective flow,

due to the replenishment of source material at the growth interface.

Flectrophoresis activities have

determined parameters affecting sample

stream distortion in ground- and spacebased continuous flow electrophoresis

devices. They have also established the

parameters controlling buoyancy-driven

flows in wide gap, ground-based

continuous flow electrophoresis devices.

A ribbon-like flow distortion phenomenon

has been observed in ground-based

electrophoresis-type flow chambers which

is not fully understood. A series of

ground and flight experiments is planned

to find out if the distortions are related to buoyancy effects.

A moving wall continuous

electrophoret ic separator has been built

which is uniquely adapted to space -based

separations. This technique increases

throughput and resolution for a mult icomponent sample and represents a substantial improvement over conventional

free-flow electrophoresis.

HlbTORY OP

MICROGRAVITY EXPERIMENTS OCTOBER 1986

STS 3 & SUBSEQUENT (USA) Li U nnnonnnnnonno uuuuuu uuu uuuu SALYUT 7 (USSR) d

SALYUT 6 (USSR) 1 1

^Al VI IT ^ (1 l<i<IR 1

JAPAN (SUBORBITAL) D TEXUS (GERMAN SUBORB) D D D D ra m m D3 MIR-2 (USSR SUBORBITAL)

SPAR (USA SUBORBITAL) DD DDDDQ DDDD D

APOLLO-SOYUZ (USA/USSR)

NASA AIRCRAFT ^ SALYUT 4 (USSR) 1 1 SKYLAB (USA) 1

1 NASA DROP TUBE i APOLLO 16. 17 (USA) CZI APOLLO 14 (USA)

S0YU2 6 (USSR)

NASA DROP TOWERS

1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1

70

I 1 1 1 I 1 1 1 1 1 1 1 75 80

1 1 1 1 1 85 NOTE: DATES ARE NOT PRECISE

FIGURE 3 JA-10.968-85

McDonnell Douglas used its chamber on STS-6 and -7 to determine the effects of

sample concentration and conductivity on separation performance. Large

distortions in the sample stream were

found when there was a mismatch between

sample and buffer conductivity. This

distortion had not been revealed in

previous ground-based work because the

space experiment allowed the first use of

sample concentrations high enough to have

mismatched conductivities.

Various zeta potential coatings have

been developed to control electroosmotic

flow in electrophoresis devices.

Low-G Isoelectric Focusing

experiments (separation into pH bands)

have been conducted, revealing unexpected

flow distortions. An improved electroosmotic coating has been developed which

should allow this promising method to be

developed into a usable process for

separating cells and macromolecules

.

42
Phase Partitioning experiments have

been conducted to find alternate methods

of controlling the partitioning of the

two polymer aqueous phases used in the

separation of biological cells. When

gravity drives the separation of the

mixed phases, shear forces from the rapid

fluid movement detach the biologicals

being separated from their respective

phases. This degrades the efficiency of

the technique and requires many

repetitive cycles to obtain reasonable

purity. These shear forces are greatly

reduced In low-g

.

Immunoaf f Inity phase partitioning was demonstrated at NASA-MSFC, indicating the

potential of this technique for highly

specific cell separations.

A Monodlsperse Latex Reactor (MLR)

has been flown on five shuttle missions,

beginning with STS-3, and has

successfully manufactured monodlsperse

polystyrene latex during these flights by means of seeded emulsion polymerization.

The MLR produced the world's first

space product to be sold on Earth:

10-mlcron latex particles. These tiny

spheres were certified and placed on sale

by the D.S. National Bureau of Standards

(NBS) on July 17, 1985, as Standard

Reference Material (SRM #1960). The sale

price was $384 per vial of 30 million

microspheres, and, within one year of

being released for sale, almost half of

all the vials had been sold.

The world's second space product, the

30-micron latex spheres manufactured on STS-11, has also completed certification

by NBS and will go on sale as SRM )1H961.

Electronic Materials

Semiconductor Crystal Growth

activities have resulted in improved

sample containers which reduce

undesirable grains at the container wall

through the use of a thin non-wetting

graphite coating on the inner surface of

the quartz ampoule.

Thermal models of crystal growth

furnaces have been greatly enhanced by

including radiation heat transfer. This

USA MICROGRAVITY SCIENCE AND APPLICATIONS STS EXPERIMENTS OCTOBER 1986

CY82 CY83 CY84 CY85 CY86 CY87 CY88 CY89

MIDDECK EXPERIMENTS

MONODISPERSE LATEX REACTOR (MLR) T T T

ISOELECTRIC FOCUSING (lEF) AUTOMATED DIRECTIONAL SOLIDIFICATION

FURNACE 1 (ADSF 1) T

3M ORGANIC CRYSTAL GROWTH EXPERIMENTS

AGGREGATION OF RED BLOOD CELLS (ARC)

MDAC CONTINUOUS FLOW ELECTROPHORESIS

SYSTEM (CFES)

TT T

PROTEIN CRYSTAL GROWTH (PCG)

PHASE PARTITIONING EXPERIMENT (PPE) T

FLUID EXPERIMENT ASSEMBLY (FEA) T

PAYLOAD BAY EXPERIMENTS

MATERIALS SCIENCE LAB (MSL)

THREE AXIS ACOUSTIC LEVITATOR (SAAL) W ELECTROMAGNETIC LEVITATOR (EML) w AUTOMATED DIRECTIONAL SOLIDIFICATION

FURNACE II (ADSF II) r

MATERIALS EXPERIMENT ASSEMBLY (MEA)

GENERAL PURPOSE FURNACE ISOTHERMAL (GPF-I) T

GENERAL PURPOSE FURNACE GRADIENT (GPF-G) T

SINGLE AXIS ACOUSTIC LEVITATOR 1 (SAAL 1) MODULE EXPERIMENTS

FLUIDS EXPERIMENT SYSTEM (FES)

VAPOR CRYSTAL GROWTH SYSTEM (VCGS)

FIGURE 4 JA-U4M-W

43
is required for accurate prediction of

the growth interface shapes when the

liquid is transformed to solid crystal.

New insight has been obtained into

the influence of convection in crystal

growth and on the difficulty of

suppressing convective flows, even in

microgravity . It now appears necessary

to combine strong magnetic fields with

microgravity in order to grow large

crystals in a diffusion-controlled

environment. The lines of force of a sufficiently strong magnetic field create

an induction drag across a conductive

melt. This drag dampens motion across

the magnetic lines of force, cancelling

out surface tension driven convective

flows. [18] This technique for

suppressing convection has gained

widespread use in terrestrial

semiconductor growth processes,

especially by the Japanese. [19]

Solution Crystal Growth activities

have included the development of an optical technique, using laser

interf erograms and shadowgraphs, to

directly observe the growth or dissolution of a crystal with high

precision measurement of solubility at

various concentrations. This technique

successfully supported the Triglycine

Sulfate experiment on Spacelab-3 and is now being applied to solution growth of

non-linear optical materials, which

appear to exhibit improved

characteristics when produced in low-g.

The Triglycine Sulfate Experiment on Spacelab-3 successfully produced two

detector crystals grown for the first

time in microgravity. This marks a major

milestone in growth of crystals from a solution. The experiment also provided

hundreds of holograms for use in

analyzing the distribution of solute in

the solution. Preliminary analysis of

the holograms reveal that

diffusion-controlled growth conditions

prevailed throughout most of the mission

because of the very low steady^

accelerations of less than 1Q~ g,

despite the fairly large 10~ g frequency accelerations (g-jitter) caused

by internal motions.

Vapor Crystal Growth Experiments in

the Materials Experiment Assembly (MEA)

flown on the Space Shuttle produced some surprising and unexpected results. The

vapor-growth flight samples had loose,

web-like structures of large platelets.

These experiments also produced thin

crystals that grew in the gas atmosphere

instead of on the ampoule wall. Some of

the crystals were significantly larger

than those produced on Earth. For

example, one of the space-grown crystals

was about 20mm x 10mm. Also, the

experiment samples make it very clear

that the more uniform microgravity growth

conditions have a beneficial effect on surface and bulk morphology.

The flight experiments have provided

excellent agreement with theory for four

different flux vs. pressure points.

The Mercuric Iodide Experiment , performed using a nuclear detector

material aboard Spacelab-3 (SL-3) in

1985, was developed to grow single

crystals in a microgravity environment.

Much new and useful information was obtained even prior to flight during

ground-based research. The flight

results provided a benchmark against

which comparison to Earth crystals can be

made. The following data, while

preliminary and to be regarded with some degree of caution, is very encouraging:

Electron mobilities, important for

detector performance, were measured in a sample from the space crystal and found

to be twice as high as any ever reported

for a terrestrially grown crystal.

Furthermore, hole mobilities appeared to

be as much as seven times higher than in

Earth-grown crystals.

Electronic and Electro-Optical

Materials . The first direct experimental

evidence has been obtained at MSEC for

the transitions from semiconductor to

metallic behavior in Mercuric Telluride

and in Mercuric Selenide, i.e. that the

melt has almost an order of magnitude

more conductivity than the solid.

Additionally, the importance of

gravity-driven convection has been

empirically established in the

compositional redistribution which occurs during casting of HgCdTe alloys -- the

material of choice for long wavelength

infrared detector applications, A thermal model of Brldgman growth of

Mercury Cadmium Telluride has been

developed which predicts interface shapes

for various furnace temperature profiles.

This is necessary for the optimization of

science return from low-g experiments.

Organic Thin Films and Crystalline

Solids were grown via the physical vapor

transport (PVT) method by 3M on STS-51I.

This was the first known attempt to grow

organic crystals and thin films by vapor

transport in microgravity. Each of the

solid samples was vaporized, then allowed

to recondense onto a cooler substrate.

Initial analysis of the samples has shown

very well defined substrate deposits,

both thick and thin film, in all nine of

the flight ampoules. This demonstrates a clear dependence of film formation on the

molecular weight of the buffer gas. [20]

Metals and Alloys

Deep Dndercooling

;

A 105-meter drop

tube facility is being used at NASA MSEC

to provide very deep undercooling of more

than 500 degrees C during containerless

freefall processing of Niobium-Germanium,

Niobium-Platinum, and Niobium-Silicon

alloys. Analyses have revealed a non-equilibrium eutectic phase as well as

44
an amorphous area in the Nb-Ge samples.

Drops of ten different samples of pure

metals also have been significantly

undercooled and will be used to test

current nucleation theories.

MapinetlG Materials have undergone

suborbital and orbital experiments which

indicate that convection has been

effectively damped in low-g and

diffusion-controlled growth has been

achieved. Increases in permanent

magnetic properties have been observed

which approach the theoretical maximum.

Immiscible Materials have been

studied in depth in view of the

possibility of overcoming the separation

tendencies inherent in the gravity

environment. Several low-g phenomena

have been identified which must be overcome to achieve completely

homogeneous mixtures of immiscible

alloys. Interfacial tensions induce a strong tendency toward massive phase

separation in microgravity . Thermal

gradients induce liquid droplets of one phase to migrate toward the center of the

melt as the alloy cools, resulting in the

surrounding of one material by the

other. Interfaces between vapors and

liquid surfaces contribute to surface

tension-driven convective flows, causing

phase separation. The interaction of the

droplet phase with the crucible walls

causes droplets to adhere to and spread

on the container wall, thereby inhibiting

thermocapillary droplet migration. This

may be avoided by proper selection of

crucible material. [ 21]

Metal Solidification Research

experiments conducted in space and in

low-g aircraft parabolic flights have

developed new knowledge of solidification

mechanisms and the basic structure of

metals and alloys. Iron-graphite alloy

studies have revealed the effects of

gravity on the uniformity of the

crystalline structure in cast iron.

Unexpected effects, such as changes in

dendrite arm spacing, have been

discovered in microgravity. Studies of

superalloys and monotectic alloys have

contributed to an understanding of the

basic structure of these materials and

have given important clues as to how this

information may be used in ground

processing of these materials.

Glasses

Reluctant Glass-Forming Materials

studies have shown that the possibility

of producing important new amorphous

materials can be enhanced through the use

of acoustic containerless processing.

However, in the absence of a container

the surface "skin" (or oxides) of some materials has been a source of

heterogeneous nucleation. Time,

temperature, and transformation data (TTT

curves) have been otained for a number of

glass-forming systems to determine the

cooling rates required to form a glass.

Several different nucleation mechanisms

have been identified, including

heterogeneous nucleation, caused by small

particles in the melt, on container

walls, or on the melt spinning substrate,

and dynamic nucleation, caused by

mechanical shear. In order to determine

the precise impact of homogeneous

nucleation on glass formation, it will be

necessary to determine the values and

temperature dependence of the crystal

melt interfacial tension, the driving

free energy, and the atomic mobility.

Containerless Glass Formation

experiments have been conducted in

microgravity using the single axis

acoustic levitator/furnace (SAAL). For

the first time, liquid specimens were successfully levitated in space at high

temperatures: 1250 to 1500 degrees C. Two glass forming samples, soda-limesilica and calcia-gallia-silica , were melted and cooled to glass while

levitated in space. The result was clear evidence of a two- to three-fold

increase in the glass formation tendency

(via a comparable decrease in minimum

cooling rate for glass formation) in

calcia-gallia-silica solutions.

New Space Processing Apparatus

Although many new apparatus have been

developed, we will briefly cover only the

U.S. apparatus. [3]

NASA-MSFC Apparatus

The Fluid Physics System (also called

the Fluids Experiment System) is a highly

sophisticated apparatus capable of

conducting low-g experiments in fluid

dynamics, bubble behavior, solution

crystal growth, and nucleation and

ripening phenomena. The system includes

a laser holographic capability and 22

temperature controls with accuracies to 0.01 degrees C. It was utilized on the

Spacelab-3 mission in 1985 to produce the

two Triglycine Sulfate crystals for

detector devices. The system also

includes a schlieren and shadowgraph

capability to provide multiple optical

modes for fluid dynamics analyses.

Holographic Imaging of Crystal Growth

techniques have been developed and

applied to the study of solution crystal

growth. The holograms produce high

resolution images of the growth process

and the interaction of the crystal with

its surrounding solution. These frames

can then be analyzed by interf erometric

methods at a later time. This has been

very useful for both ground-based studies

and flight experiments. Development is

underway of a two-color holographic

system, which can distinguish between the

effects of concentration gradients and

temperature gradients.

45
A Vapor Crystal Growth System was demonstrated on Spacelab-3. The system

provides precision temperature

repeatability and stability to within

0.05 degrees C. It also provides

continuous viewing of crystal growth,

which allows critical adjustments to be

made in real-time to optimize growth

conditions. The system has a capability

to interrupt the growth process, allowing

anomalous growth to be eliminated in real

time by vaporization prior to proceeding

with the crystal growth.

Laser Scattering Microscope methods

measure, in a non-destructive manner, the

distribution of defects in transparent

solution-grown crystals. Laser light is

focused and scanned throughout the

crystal. The light scattered, due to

defects, is detected and recorded by a microscope/computer system. This system

is helping determine the quality of

space-grown crystals.

General Purpose Microgravity Furnaces

have been developed to study the basic

nature of low-gravity metal

solidification. The understanding of

these processes, in turn, helps improve

manufacturing techniques on Earth.

A Multiple Experiment Processing

Furnace is being planned to process a large number of metal and semiconductor

samples during each flight. The primary

feature separating this new generation

furnace from previous models is the

ability to manually or automatically

change samples during a mission.

Pirectional Solidification Furnaces

have been developed to study the

formation of crystal structures and the

solidification process in metals and

alloys in low-g.

The Advanced Automated Directional

Solidification Furnace engineering

prototype has been developed and tested.

This highly modular prototype furnace

features a controlled gradient region

consisting of a series of microprocessorcontrolled, thin trim heaters in the

vicinity of the solidification interface.

These trim heaters can reduce radial

temperature gradients near the

solid-liquid interface, resulting from

changes in thermophysical properties as the melt crystallizes, e.g. changes in

thermal conductivity or emissivity. Such

control is required for microgravity

crystal growth of electronic and

electro-optical materials, such as lead-tin-telluride , mercurycadmium-telluride , gallium-arsenide, etc.

Contalnerless Processing Apparatus

have been developed for microgravity

processing of experiment samples which

are adversely affected by contact with a container. These apparatus, the

1 300-degree-C NASA Electromagnetic

Levitator, the I6OO degree C Single Axis

Acoustic Levitator, and the Three Axis

Acoustic Levitator (3AAL), have all been

demonstrated in flight. These apparatus

are setting the stage for development of

advanced contalnerless processing systems

to meet our Space Station requirements.

NASA Goddard Space Flight Center Apparatus

Get Away Specials : NASA-GSFC's Get

Away Special (GAS) program was first

introduced at an AIAA meeting in 1976, at which time the first reservation was made. Since then, 53 experiments have

flown on 13 Space Shuttle missions, and

458 reservations remain unflown. The

program has acheived a high level of

respectability because of its

effectiveness in involving persons and

organizations in space research that

otherwise would never have had such an opportunity. Many GAS experimenters are now employed by NASA, its contractors,

and associated universities. The GAS

program is clearly the least expensive,

most straightforward means available of

performing small-scale materials science

investigations aboard the Space Shuttle.

Unique Ground Facilities

NASA has developed ground facilities

to aid in preparing highly productive

space experiments, since access to space

is still quite limited and space

experiment opportunities are not readily

available

.

NASA-MSFC Facilities

A Ground Control Experiments

Laboratory has been set up and used

extensively for developing the flight

protocol for many crystal growth and

metallurgical experiments. This

laboratory produces control specimens for

comparison with low-g experiment samples.

A Holographic Ground Facility has

been completed to reconstruct the

holographic images recorded in space,

primarily from the Fluids Experiment

System. Various optical techniques are being applied to the reconstructed Images

to extract the fluid and crystal growth

information so that the flight

environment can be related to the

resultant crystal growth.

105-Meter Drop Facilities , as mentioned earlier, have been developed to

allow quick-reaction, low-cost, short

duration (approx. 4 seconds) periods of

processing in low-g for investigators who

need precursory experiments prior to

Shuttle experiments.

KC-135 and F-10t> Aircraft have been

modified for conducting tests using

low-gravity parabolic flights to assess experiment apparatus which cannot be

46
calibrated or evaluated in one-g. These

flights are also used for conducting

experiments requiring only short periods

of low gravity (approx. ^5-^0 seconds).

A Semiconductor Characterization

Fac il Ity has been established for crystal

growth and characterization of electronic

and electrooptical materials to support

space-based crystal growth of these

technologically important materials. The

laboratory Includes extensive facilities

for the purification of starting

materials, casting of the desired alloys,

and crystal production by melt, solution,

and vapor growth methods. Facilities for

the slicing, polishing, and etching of

samples for characterization are also

provided. The laboratory includes

facilities for the compositional,

metallurgical, electrical, and optical

characterization of the materials,

including elevated and cryogenic

temperatures. Activities in the

laboratory include theoretical and

numerical modeling of the heat and mass transport phenomena Involved in the

various growth processes to optimize

processing parameters for flight crystal

growth experiments.

NASA Lewis Research Center

Microgravity Materials Science Laboratory

The Microgravity Materials Science

Laboratory (MMSL) contains functional

duplicates of some experiment equipment

flown on the Space Shuttle. It is

designed to give visiting scientists a chance to familiarize themselves with

flight hardware. The current focus of

the laboratory is on metal and alloy

solidification and crystal growth

research, but capabilities are being

expanded to provide equipment for

research in polymers, ceramics, and

glasses. The following is a list of

apparatus available or soon to be

available for use at the MMSL.

-General Purpose Furnace

-Electromagnetic Levitator

-Instrumented Drop Tube

-Undercooling Furnace

-Bulk Undercooling Furnace

-Transparent Directional

Solidification Furnace

-High Temperature Directional

Solidification Furnace

-Isothermal Dendrite Growth

Apparatus

-Crystal Growth Furnace

-Single Axis Acoustic Levitatlon

Furnace

Space Station by the U.S., Canada, Japan,

and the European Space Agency (ESA).

When these and other new space platforms

become available, we will see a dramatic

increase In low-g research time. The

ensuing contributions to the field of

microgravity materials science should be enormous . The Industrial Space Facility (ISF)

is being developed by Space Industries,

Inc. and West Inghouse . It will be

launched by the Space Shuttle into low

Earth orbit for commercial activities.

The ISF is expected to provide up to 12 Kw of power to its users, along with

appropriate systems for power storage,

heat dissipation, attitude control, and

data management. Man-tended processing

will be accomodated in a shirtsleeve

environment and resupply operations are planned from the Space Shuttle.

The U.S. International Space Station

will support a wide variety of

experiments near the station's center of

gravity, where there will be the lowest

practical residual accelerations.

Electrical power of 12 to 59 Kw is

expected to be available for experimental

use. Limited on-orbit sample

characterization will be provided. Some

of the several new research facilities

that may be developed for the Space

Station include:

-Small Bridgman Growth Facility

-Large Bridgman Growth Facility

-Bulk Crystal Growth Facility

-Metals and Alloys Solidification

Facility

-Float Zone Crystal Growth Facility

-Electroepitaxial Crystal Growth

Facility

-Vapor Crystal Growth Facility

-Solution Crystal Growth Facility

-Protein Crystal Growth Facility

-Organic and Polymer Crystal Growth

Facility

-Containerless Processing Facility

-Optical Fiber Pulling Facility

-Fundamental Science Facility

-Combustion Science Facility

-Cloud Microphysics Facility

-Electroklnetic Separation Facility

-Geophysical Fluid Flow Facility

-Ultra-Vacuum Facility

Each of these new apparatus will

provide a significant advancement in

capability beyond presently used low-g

apparatus. Other apparatus could be

added to the above list of development

candidates as the Space Station

availability date gets closer.

THE FUTURE To provide inputs to the design of

the Space Station, studies have been

Planned for launch by the end of performed to indicate requirements for

1992, the U.S. Industrial Space Facility Space Station resources. This was

(ISF) will support commercial research, accomplished by grouping about 25 typical

development, and manufacturing in space. low-g apparatus, both new and existing.

We will also see the development of the which would time-share these resources,

47
e.g. biotechnology, crystal growth,

solidification, fluids, combustion,

containerless processing, etc. Similar

assessments have determined typical types

of laboratory equipment which would be

required, assuming on-orbit sample

characterization is performed. [22]

The DSSR Mir Space Station , along

with its accompanying microgravity

science facilities, has been offered for

use by European scientists. Mir provides

7-10 Kw (and may eventually provide as much as 15 Kw) of power for experiments.

It also provides materials science

furnaces with operating temperatures of

from 1000 to 1500 degrees C. [233

The European Retrievable Carrier

EUREC

A

is a free-flying space platform

being developed by the European Space

Agency. This platform will support

sophisticated materials processing with

modest power levels, i.e. 1000 watts.

Several low-g apparatus have already been

developed specifically for use on EURECA.

Technology Advancements are needed in

several key areas. NASA and other

organizations are assessing particular

advanced technology needs that will allow

full utilization of the new apparatus and new space facilities such as the Space

Station and the ISF. For example,

certain low-g processes are expected to require lower residual accelerations than

the Space Station can provide.

Therefore, isolation systems may be

utilized on the Space Station which use,

for example, an electromagnetic field to

protect these highly sensitive

experiments or processes from g-jitter

andgOther harmful accelerations above

10~ g. Other items of new technology

which may be necessary are ultra-high

temperature furnace modules, high

temperatlon calibration systems,

two-color holographic interferometry

,

superconducting magnets for on-orbit

suppression of fluid motion, inflight

x-ray analysis equipment, and measurement

systems for non-invasive analysis of the

physical and chemical properties of high

temperature molten materials.

Conclusions

Twenty years ago, only a very few

individuals had even vague notions of

what could be accomplished with low-g

processing. Today, low-g processing is

widely known in every technologically

advanced country and is a rapidly

emerging new technology, well-supported

by hundreds of government and private

organizations. Obviously the future

cannot accurately be predicted, but it is

safe to say that exciting prospects exist

for marvelous new materials to be

developed in space or, perhaps more

importantly, for low-g research to point

the way for improved Earth-based

processing of materials.

REFERENCES

[1] Naumann , Herring, "Materials

Processing in Space: Early

Experiments" NASA SP-HU3, 198O.

[2] Huntsville Times, October 6, 1986.

[3] Feuerbacher, Hamacher, and Naumann,

"Material Sciences in Space," March

1986 .

[H] Dictionary of Scientific Biography,

Volume XI, 1975.

[5] "Selected Works of K.E.

Tsiolkovskiy ," NASA TT F-237, Volume

II, September 1965.

[6] Wuenscher, H.F., "Low and Zero-G

Manufacturing in Orbit," AIAA Paper

67-8^42, October 1967 .

[7] Wuenscher, H.F. "Unique Manufacturing

Processes in Space Environment,"

Seventh Space Congress, April 1970.

[8] Siegret, Petrash, and Otto, "Time

Response of Liquid-Vapor Interface

After Entering Weightlessness," NASA

TN D-2U58, 1964

[9] Aviation Week & Space Technology,

pp. 63-69, April 7, 1969.

[10] Wuenscher, H.F., "Space

Manufacturing Unique to Zero Gravity

Environment," NASA TM Report *53851,

July 1969.

[11] Yates, Yost, "Investigations of

Stability of Bubbles in Plain and

Fiber-Reinforced Metal, Melted and

Solififled in a Near-Zero-G

Environment," NASA TM X-6U665,

October 1972.

[12] McKannan, "The Growth of Materials

Processing in Space - A History of

Government Support for New

Technology," NASA-MSFC Space Science

Laboratory Preprint Series No.

83-130, August 1983.

[13] Steurer, "Revised Free-Fail

Experiment Program for 80- and

300-Foot Towers," FFX Report #3,

February 1970.

Avduyevsky, Grishin, Leskov,

Polezhayev, and Savitchev,

"Scientific Foundations of Space

Manufacturing," 198M.

[15] Stuhlinger, "Materials Processing in

Space: A Look Toward the Future,"

Astronautics and Aeronautics, May

1975.

[16] Naumann, "Materials Processing in

Space: A Program Overview," June

1978.

48
L17] Doollng, "The Space Factory" from

Space Technology, Gatland ed . , Harmony Books, I98I.

[18] Langlols, W.E., "Buoyancy-Driven

Flows In Crystal-Growth Melts," Ann

.

Rev. Fluid Mech. . 1985, pp. 191-215.

[19] Carruthers, personal communications.

[20] Debe, Cook, Poirier, Follett, Miller

and Spiering, "Vacuum Outgassing and

Gas Phase Thermal Conduction of a Microgravity Physical Vapor

Transport Experiment," 10th Annual

International Vacuum Congress,

October 27-31, 1986.

[21] Gelles, Markworth, and Mobley, "Low

Gravity Experiments on Liquid Phase

Miscibility GAP (LPMG) Alloys - Materials Experiments Assembly

(MEA)," Fourth European Symposium on Materials Science Under

Microgravity, ESA-SP191, June 1983.

[22] "Microgravity and Materials

Processing Facility Study," Teledyne

Brown Engineering Report, September

1985 .

[23] Space Business News, October 20,

1986 .
THE FIRST PRODUCTS MADE IN SPACE: MONODISPERSE LATEX PARTICLES

J. W. Vanderhoff*, M. S. El-Aasser, F. J. Micale,

E. D. Sudol, C.-M. Tseng, and H.-R. Sheu

Emulsion Polymers Institute and Departments

of Chemistry and Chemical Engineering

Lehigh University

Bethlehem, Pennsylvania 18015

and

D. M. Kornfeld

George C. Marshall Space Flight Center

Huntsville, Alabama 35812

Abs t r^ct

Twenty monodisperse polystyrene latexes

were made oy seeded emulsion polymerization

in the MLR-SEP flight hardware on the STS-3

and STS-4 flights of the Columbia and the

STS-6, STS-7, STS-11 flights of the Challenger. Two polymerizations were small-particle-size controls; eighteen were of large

particle size. Of these, six failed: four

on STS-4 owing to malfunction of the flight

hardware; one on STS-6 owing to a broken

wire; one on STS-11 owing to a broken stirrer shearpin. Nine monodisperse latexes of

4-30 pm size had narrower partiicle size

distributions than the ground-based controls. The 10 pm STS-6 latex and the 30 ^m

STS-11 latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in

space for sale on earth. The polymerization

rates in space were the same as on earth

within experimental error. The flight polymerizations produced only negligible coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, so that these con- trols were discontinued after the STS-7 ex- periments. These results confirmed the original rationale of the experiments that polymerization in space would give more uniform large-particle-size monodisperse latexes with less coagulum by: 1. the better

uniformity of all 5 \im or larger flight latexes; 2. the more perfect sphericity of

the 10 and 30 pm flight particles; 3. the

smaller number of offsize larger particles;

3. the negligible amounts of coagulum; 4. the broadening of the particle size distribution and the formation of larger offsize

particles during the completion on earth of

the polymerization of the partially converted STS-4 flight latexes.

Since 1947 monodisperse polystyrene latexes have found wide application as calibration standards and other scientific u- ses.l Series of monodisperse latexes were prepared by seeded emulsion polymerization,

i.e., by polymerizing monomer in a previously prepared monodisperse latex;2f3 the

particle size distribution is self -sharpening at small particle sizes.^"^ The emul- *Professor, Department of Chemistry

Member AIAA

Copyrighl American Inslitute of Aeronautics ano

Astronautics. Inc.. 1987. All rights reserved.

sifier concentration is critical: too little results in flocculation of the latex;

too much results ^in nucleation of a new crop of particles.

0

The first series of monodisperse latexes ranged in average diameter from 38 nm (standard deviation cr 8.0 nm) to 340 nm [a

5.2 nm) to 1171 nm ( o- 13.3 nm).3 The

standard deviations included not only the

width of the particle size distributions,

but also the errors involved in measuring

the individual particle images of the e- lectron micrographs and the difference in

magnification from one exposure to another.-^ A later series showed improved mo- nodispersity : the average particle diameters ranged from 91 nm (cr5.8 nm) to 176 nm

(o''2.3 nm) to 1100 nm (cr3.5 nm) to 2020 nm

(cr 13.5 nm)

Even larger sizes were prepared in the

laboratory, i.e., as large as 5.6 pm, in

100-gm quantities and 10-12 pm in much

smaller quantities. ^ The quantities were

small because the polymerizations produced

increasing amounts of coagulum, giving com- plete coagulation of the 10-12 ^m sizes.

The range of emulsifier concentrations that

gave neither coagulum nor a new crop of

particles was relatively broad at submicroscopic particle sizes," but narrowed with

increasing size, so that duplicate polymerizations yielding 2 pm particles gave either stable latexes contaminated with a new crop of smaller particles or relatively un- stable monodisperse latexes.

Particles larger than 2 ^m show little

or no Brownian motion; polystyrene (1.050

gm/cc) seed latex particles swollen with

styrene monomer (0.905 gm/cc) cream and the

polymerized particles settle. Of course,

creaming or settling of the particles can

be offset by stirring, which is always used

in emulsion polymerizations; however, the

large, soft, sticky monomer-swollen particles are sensitive to mechanical shear and

thus are easily coagulated by too-vigorous

stirring. The result is that the larger the

particle size, the faster must be the stirring to avoid creaming and settling; however, too-fast stirring gives mechanical coa- gulation, so that it is difficult to prepare large-particle-size latexes without

excessive coagulum.

In space, the particles would show no

50
tendency to cream or settle; therefore, the

polymerization would be stirred only well

enough to ensure good heat transfer and

mixing (for the latex to be monodisperse

,

each particle must have the same temperature-time history, as the rate of polymerization increases with increasing temperature) . Thus seeded emulsion polymerization

in space would allow growth of the particles to larger sizes without excessive co- agulum; moreover, such a system would com- prise an ideal model for a heterogeneous

chemical reaction in space. This paper describes the results of such polymerizations

carried out on the STS-3 and STS-4 flights

of the Columbia, and the STS- 6, STS-7, and

STS-11 flights of the Challenger.

Expe rimental Details and Procedures

The flight hardware comprised the Monodisperse Latex Reactor (MLR; General Electric Space Sciences Laboratory) and the

Support Electronics Package (SEP; Rockwell

International). The MLR comprised four

stirred 100-cc stainless-steel cylindrical

dilatometers in a sealed cylindrical container of 18-in diameter and 24-in height;

the polymerization conversion-time curves

were m.easured from the decrease in volume

using linear variable differential transformers (LVDT's); the temperatures in each

dilatometer were measured by four threepellet diodes in: a probe extending into

the center of the dilatometer; the top interior surface; the wall midway between top

and bottom; the bottom next to the stirrer

shaft. The SEP comprised the requisite DC

voltage converters, electronic equipment,

and data tape cassette in a sealed rectangular container. Both containers, connected

with cables, were mounted on the forward

bulkhead of the Shuttle mid-flight deck,

replacing three locker-drawers. The dilatometers were loaded with the monomer-swollen

seed latexes and mounted on the circular

base. Both containers were sealed, flushed

with helium to detect leaks, and then with

nitrogen to give an inert atmosphere. The

sealed containers were mounted in the Shuttle about 48 hours before launch.

The dilatometers were operated in the

preprocessing and processing modes; preprocessing mode comprised intermittent stirring for 90 sec every 30 min (STS-3, STS-4,

STS-6) or continuous stirring (STS-7, STS11). The processing mode comprised continuous stirring while the contents were heated

to 70° for 10.5 or 17.0 hrs, according to

the flight, and then to 90° for 0.75 hrs,

to complete the polymerization. The intermittent preprocessing stirring was used

from the time of loading until the astronauts switched to processing at the predetermined time in orbit, and between the end

of the processing and the recovery of the

flight hardware on earth; the continuous

preprocessing stirring was used from the

time of loading until the Shuttle was in

orbit, after which it was discontinued. After recovery from the Shuttle, the MLR was either stirred in the preprocessing mode

until it was unloaded, or it was left un- stirred and inverted periodically to re- disperse the settled particles.

The polymerization recipes comprised

seed latex, styrene monomer, azo initiators, inhibitors, and emulsifiers (recipes

to be published later) . The small-particlesize control polymerizations comprised 0.19

urn seed latex, styrene monomer, potassium

persulfate initiator, and sodium bicarbonate buffer. The styrene monomer was distilled twice just before use to remove inhibitors; the desired amount containing initiator and inhibitor was added to the seed

latex, and the mixture was agitated gently

for 20 hrs; the monomer not absorbed by the

latex was separated, and the monomer-swollen latexes were degassed and loaded into

the dilatometers.

After the flight, the dilatometers were unloaded and cleaned, and ground-based control polymerizations were carried out using

the same seed latex, monomer, and temperature-time schedule, except for STS-3 in

which another seed latex of the same size was used for the control polymerizations

and for STS-11 in which the control polymerizations were not run because the coagulum would have been excessive. The data

tape cassettes were processed by computer,

to give the conversion-time curve and the

four temperature-time variations for each

dilatometer. The latexes were examined by

optical microscopy immediately after un- loading to gain an impression of their mo- nodi spe rs i ty , and later by transmission

electron microscopy (Philips Model 400) or scanning electron microscopy (ETEC Autoscan) to determine the particle size distributions. The distributions were measured

using the Zeiss MOP-3 Modular System for

Quantitative Digital Analysis, and the offsize larger particles were counted.

Experimental Results and Discussion

Four polymerization experiments were

carried out on the STS-3 flight of the Columbia; three used a 2.52 monodisperse

seed latex with nominal 2:1, 4:1, and 10:1 monomer -polymer ratios; the fourth (control) used a 0.19 pm monodisperse seed latex with a 2:1 monomer-polymer ratio. The

polymerization time at 70° was 10.5 hrs.

For 24-48 hrs before opening, the MLR was inverted periodically to redisperse the

settled latex particles before the stirrers

were turned on. The rotation of the stirrer

of flight latex 2 dilatometer was restricted, so it was turned off.

Figure 1 shows electron micrographs of

the seed latexes and the large-particlesize flight latexes prepared on the STS-3,

STS-6, STS-7, and STS-11 flights, and Table

I gives the nominal monomer-polymer (M-P)

ratio, preprocessing/processing agitation

rates, initiator concentration [I], numberaverage diameter D^, standard deviation o, number of particles measured n, coefficient

of variation C/D^ in percent, and the num51
TABLE I

P article Size Distr ibutions

Nomina 1 Of f size

M-P [I] Dn a Larger

Lat£x Flight Ratio mM -um pro n Part*

seed STS-3 2.52 0.046 1024 1.84

flight 1 STS-3 2:1 13/13 3.9 3,44 0.064 2777 1.87 1/264

ground i o i bJz : 1 i j/ X -3

"3 "7 0 0 . / Z U . U D / i i 0 -5 1.54 1/339

flight 2 STS-3 4:1 13/13 6.6 4.08 0.069 2256 1.69 1/207

ground 2 STS-3 4:1 13/13 6.6 3.93 0.077 913 1.96 1/172

flight 3 STS-3 10 :

1

13/13 12.6 4.98 0.082 2095 1,64 1/99

ground 3 STS-3 10:1 13/13 12.6 4.74 0.167 1232 3 ,51 1/65

seed b i b 0 J . D J U . U / -3 TOO J Z 0 1.30 1/168

flight 9 STS-6 2:1 13/13 2.5 7.94 0.122 829 1,53 1/267

ground 9 STS-6 2:1 13/13 2.5 7.86 0.137 675 1,74 1/220

flight 11 STS-6 6:1 13/13 5.3 9.96 0.115 1102 1,15 1/106

ground 1 1 b i b o D : 1 1 -5/ 1 J J.J in f\ A U . zol i u b y

T on 2 , oU 1/93

seed** STS-7 7.94 0.046 1024 1 .53 1/267

flight 13 STS-7 6:1 13/13 5.3 13.12 0 .149 327 1,13 1/360

ground 13 STS-7 6:1 13/13 5.3 13.89 0.371 308 2,67 1/120

seed STS-7 10.30 0.135 300 1,31 1/130

flight 14 STS-7 4:1 13/13 4.1 16.64 0.201 322 1,21 1/90

g round bib/ 1 1 / ^ 'i 1 J/ 1

J

A ^ L I , L 1 n T Q /I u • ^ y 4

"5 T J ZD z . zy 1/ J U flight 15 STS-7 6:1 13/6 5.3 17.81 0.210 321 1.18 1/70

ground 15 STS-7 6:1 13/6 5,3 17 .68 0.949 275 5.37 >l/50

flight 16 STS-7 6:1 6/3 5.3 18.18 0 .200 321 1.10 1/110

ground 16 bib/ D : 1 0/ J

c: 0 J . J 1 D . y / U . / / 0 361 4 . J 0 seed** * STS-11 17.81 0.210 321 1,18 1/70

flight 17 STS-11 5:1 13/6 5.5 30.42 0,41 310 1.35 1/30

flight 18 STS-11 5:1 6/3 5.5 30.92 0 . 44 320 1.42 1/25

seed STS-11 10 .30 0.135 300 1.31 1/130

flight 19 STS-11 6:1 13/6 5.5 18.4

flight 20 STS-11 6:1 6/3 5.5 19 . 44 0.24 256 1.22 1/66

* relative to the main distribution

** flight latex 9 from STS-6

*** flight latex 15 from STS-7

ber of offsize larger particles relative to

the number in the main distribution. Except

where noted, all latexes were completely

polymerized when removed from the dilatometers, as determined by the lack of styrene

odor. The flight latex 2 dilatometer con- tained a small lump of hard coagulum adhering to the wall that restricted the motion

of the stirrer; the other flight latexes

contained negligible amounts of coagulum.

Figure 1 shows that all three flight

latexes were monodispe r se . Table I shows

that there were subtle differences in particle size distribution between the three

flight latexes and the ground-based control

latexes. The coefficients of variation were

about the same for all latexes except for

ground-based control latex 3, which was broader in particle size distribution. The

standard deviations increased only slightly

with increasing particle size. These standard deviations, however, express not only

the breadth of the particle size distribution, but also the errors in measuring the

particle images of the electron micrographs

and the variation in magnification from one exposure to another. For the 2.52 pm seed

latex, measurement of the same particle image twenty times gave a standard deviation

of 0.015-0,018 pm (coefficient of variation 0.6-0,7%). Earlier, it was shown that

the standard deviation of the averages of

24 exposures of 1.17 pm-size particles was

0 . 0092pm (coefficient of variation 0.8%).

3

The contributions of these two sources of error to the standard deviations are significant.

All latexes contained a small number of

particles which were 30-80% larger than

those of the main distribution. Table I shows that the relative numbers of the larger off-size particles increased with increasing monomer-polymer ratio. Moreover,

the number was slightly smaller for groundbased latex 1, slightly larger for groundbased latexes 2 and 3, as compared with

those of the flight latexes. Polymerization

of latexes of these sizes on earth gave

relative numbers of 1/60 at best, greater

than those of flight latexes 1 and 2 and

slightly greater than that of the flight

latex 3. These larger offsize particles were attributed to the coalescence of two or more monomer-swollen seed particles or the

52
a STS-3

7.9 9.96 pm

STS-7

; ///I 7.9 jjm ^^^^

.»^ovr*-v. ' *' 10.3 pm

Seed

6/1 4/1 6/1^

1 \6/l

\

13.1 16.6 pm 17.8 yim 18.2

Figure 1. Electron micrographs of

the seed and flight latexes.

presence of a few larger offsize particles

in the seed latex which grew proportionately during the polymerization. The coalescence of two particles of the main distribution would give a particle of 26% larger

diameter, three a 44% larger diameter, four

a 59% larger diameter, five a 71% larger

diameter, and six an 82% larger diameter.

d

STS-11

I V. '1^ .<'. 10.3 pm

!^'*% Seed

; 17.8

• Seed

6/1

19.4 pm 30.4 pm 30.9 pm

Figure 1. Electron micrographs of the

seed and flight latexes (contd.).

These larger offsize particles are difficult to remove by sedimentation or other

methods because they are only slightly larger than the particles of the main distribution . The smaller offsize particles can be

removed completely by repeated sedimentation-decantation or serum replacement . ^ The

number of these smaller particles was not

determined accurately; however, their relative number was small and increased with

increasing monomer-polymer ratio. Some were about the same size as the original seed

latex particles, which suggests that the

latexes became contaminated by unpolymerized seed latex particles which were lodged

in the entry ports of the dilatometers

.

Figure 2 shows the convers ion- time

curves of the large-particle-size latexes.

The data points were 1-min averages of the

tape data, which formed a continuous line

on this scale. For all three monomer-polymer ratios, the conversion-time curves of

the flight and ground-based control polymerizations were parallel; however, these curves virtually coincided when shifted

slightly along the ordinate. The initial

dips in these curves were attributed to the errors in the calibration of the dilatometers. The lab prototype dilatometer, which

has been calibrated more rigorously, showed

no such dips in the conversion-time curves. The leveling-off of the conversion-time

curves was attributed to the formation of a gas bubble or sticking of the dilatometer;

the nitrogen formed by decomposition of the azo initiator may have exceeded its solubility in the latex and thus formed a bubble;

since gas bubbles are compressible, the dilatometer reading would remain the same beyond this point . The sticking of the dilatometer would also give a leveling-off.

Despite these discrepancies, the con- version-time curves of the flight polymerizations were essentially the same as the

corresponding curves of the ground-based

control polymerizations: the 2:1 ratio gave

53
a c STS-3 STS-7

Figure 2. Variation of conversion

with time for the flight and

ground-based control latexes.

a significant upward deviation from linearity, indicative of autoacceleration, the

4:1 ratio only a slight upward deviation

from linearity, and the 10:1 ratio a nearlinear variation. Since the critical particle size for the transition from emulsion

polymerization kinetics to bulk polymerization kinetics is ca. 1.3 pm for the styrene-polystyrene system at 70°, the polymerization rate should be proportional to

the monomer concentration and the square

root of the initiator concentration in the

absence of autoaccelerat ion . The upward

deviation from linearity began earlier, the

lower the monomer-polymer ratio, as expected from the higher viscosity of the particles .Four polymerizations were carried out

on the STS-4 flight of the Columbia in June

1982; all four used a 5.5 pm ground-based

monodisperse polystyrene seed latex with

nominal 2:1, 4:1, 6:1, and 8:1 monomer-polymer ratios in flight polymerizations 5,

6, 7, and 3, respectively, and preprocessing/processing stirring rates of 13/13 rpra. All four latexes were incompletely polymerized as evidenced by the odor of styrene;

moreover, the data tape cassette yielded

only meaningless numbers for the dilatometer volume and temperature readings. A DC

voltage converter in the SEP had failed,

with the consequent failure of other electronic components, so that the temperaturetime variation of the monomer-swollen latexes was not known and the voltage signals

to the data tape cassette were inconsistent

and nonrepresentative . The conversions were 48-67% by gravimetric measurements and 54-

73% by ultraviolet absorbance of isooctane

extracts. Optical microscopy showed that

the latex particles were monodisperse with

only a few offsize larger particles; moreover, their size was that expected from the

stoichiometry of the seeded polymerizations, i.e., 7.2, 8.6, 9.5, and 10.4 pm,

respectively, for the 2:1, 4:1, 6:1, and

8:1 monomer-polymer ratios. The residual

monomer in these latex particles made them

useless as calibration standards. Moreover,

completion of the polymerizations on earth

gave a broader particle size distribution

and an increased number of larger offsize

particles, the result of further coalescence of the monomer-swollen particles during polymerization.

Four polymerizations were carried out

on the STS-6 flight of the Challenger in

April 1983. Three polymerizations used a 5.63 pm ground-based monodisperse polystyrene seed latex with nominal 2:1, 4:1, and

6:1 monomer-polymer ratios, and the fourth

control polymerization used the 0.19 pm

seed latex with a 2:1 monomer-polymer ratio. Flight latex 10 displayed a strong odor

of styrene; this sample had not polymerized

owing to a broken wire in the heating circuit. It is not known whether the wire

broke before or during the launch; however,

the reactor functioned satisfactorily in

the ground-based test polymerizations carried out two weeks before the flight.

Table I shows that the coefficients of

variation for the flight latexes were

slightly smaller than for the ground-based

control latexes. The values of the standard

deviations were similar for the two flight

latexes and slightly greater than that of

the seed latex; these values were slightly

smaller than those of the ground-based latexes, especially for flight latex 11.

All of the STS-6 latexes contained a small number of offsize larger particles.

Their numbers were slightly smaller for

flight and ground-based latexes 9, and

slightly greater for flight and groundbased latexes 11, as compared with the number for the seed latex; moreover, the num- bers for the flight latexes were slightly

smaller than for the ground-based latexes.

In summary, both flight latexes 9 and

11 were clearly superior in uniformity to

the ground-based control latexes. Flight

latex 11 (9.96 pm diameter) was accepted by

the National Bureau of Standards as a Standard Reference Material and went on sale in

July 1985, the first product made in space

for sale on earth. These particles were

54
also found to be more perfect spheres than

the ground-based particles. 1^

Figure 2 shows that the conversiontime curves were similar for the flight and

ground-based latexes. The leveling-off of

the conversion-time curves of the flight

latexes was attributed to the formation of

a nitrogen bubble or sticking of the dilatometer. The curves for the flight and

ground-based latexes 9 showed a significant

upward deviation from linearity, indicative

of autoacceleration; those for latexes 11

showed near-linear variations. The conversiontime curves of the flight polymerizations leveled-off at a relatively early

stage, which was more likely due to sticking of the dilatometer than to the formation of a nitrogen bubble. The curves for

the flight and ground-based polymerizations

were similar up to this point, with the

flight polymerizations showing slightly

faster polymerization rates. The disparity

was attributed to the poorer mixing of the

ground-based latexes, which would give a greater temperature gradient and thus a greater variation in polym.er ization rates.

The upward deviation from linearity began

earlier, the lower the monomer-polymer ratio, as expected from the higher viscosity

of the monomer-swollen particles. The failure of the curves for latexes 11 to show an upward deviation from linearity was attributed to the sticking of the dilatometers

or formation of nitrogen bubbles before the

polymerizations reached the autoacceleration stage.

Four polymerizations were carried out

on the STS-7 flight of the Challenger in

June 1983; three polymerizations used a 10.30 pm ground-based monodisperse polystyrene seed latex with nominal 4:1, and 6:1

monomer-polymer ratios; the fourth used the

7.94 pm flight latex 9 as seed with a 6:1

monomer-polymer ratio. Table I shows that

the coefficients of variation of the flight

latexes were slightly smaller than those of

the seed latexes, 1.13% for flight latex 13 as compared to 1.53% for the flight latex 9 seed, and 1.21, 1.18, and 1.10% for flight

latexes 14, 15, and 16, respectively, as compared to 1.31% for the 10.30 pm seed latex; the values for the ground-based control latexes were 2.67%, and 2.29, 5.37,

and 4.58%, respectively, significantly

greater than for the flight latexes. All

latexes contained a small number of larger

and smaller offsize particles. The numbers

of offsize larger particles were slightly

smaller for the flight latexes than for the

ground-based control latexes and increased

with increasing particle size and monomerpolymer ratio.

Figure 2 shows that the conversion-time

curves of flight latexes 13 and 16 virtually coincided with those for the ground-based control polymerizations; the curves for

the flight latexes 14 and 15 fell slightly

above those for the control latexes. The

leveling-off of the conversion-time curves

was attributed to the formation of a nitrogen bubble or sticking of the dilatometer.

The temperature gradients between the wall

and center of the dilatometer increased

with increasing latex particle size and mo- nomer-polymer ratio. The differences in

temperature gradient between the flight and

ground-based control polymerizations ranged

from 0.46° for latexes 13 to 2.850 for latexes 15.

Four polymerizations were carried out

on the STS-11 flight of the Challenger in

February 1984. Two polymerizations used the

10.30 urn ground-based seed latex used on

the STS-7 flight; two used the 17.81 pm

flight seed latex 15 prepared on the STS-7

flight with a nominal 5:1 monomer-polymer

ratio. For several hours before unloading,

the MLR was inverted periodically to redisperse the settled latex particles. When the

stirrers were turned on, the movem.ent of

the flight latex 19 stirrer was restricted;

therefore, it was turned off immediately;

the dilatometer had a broken stir rer-shaf

t

shear-pin and it contained a mass of coagulum between one side of the stirrer blade

and the wall. It is not known whether the

formation of coagulum stalled the stirrer

and broke the shear pin or the failure of

the shear pin caused the formation of coagulum: flight latex 20, which was identical

except for the stirring rates, contained no coagulum, yet failure analysis of the broken shear pin showed no evidence of fatigue

failure. Ground-based control polymerizations were not carried out for this series

because the STS-6 and STS-7 control polymerizations showed that the coagulum increased with increasing particle size so strongly that the valuable seed latex would

have been wasted.

Figure 1 shows electron micrographs of

the two seed latexes and the three flight

latexes, and Table I shows that the coefficients of variation of the flight latexes were about the same or slightly greater

than those of the seed latexes. The standard deviations were slightly greater than

those of the seed latexes.

All of the latexes contained smaller

and larger offsize particles. The smaller

offsize particles were removed by repeated

sedimentation-decantation. The numbers of

offsize larger particles determined by particle counts in the optical microscope were twice those of the seed latexes. Flight latexes 17 and 18 (30 pm) were accepted by

the National Bureau of Standards as a Standard Reference Material, the second product

made in space for sale on earth. These particles were also found to be more perfect

spheres than the ground-based particles.

H

Figure 2 shows that initially the con- version-time curves of the flight latexes

virtually coincided, but that flight latexes 17 and 18 showed a slightly greater upward deviation from linearity than flight

latexes 19 and 20, which was attributed to

the higher monomer-polymer ratio and hence

lower viscosity delaying the onset of autoacceleration.

55
Conc lusions Standards, private communication, 1986.

The preparation of large-particle- size

3-30 pm monodisperse latexes in space

confirmed the original rationale of the ex- periments: 1. the flight polymerizations

gave negligible amounts of coagulum as com- pared to increasing am.ounts for the groundbased polymerizations; 2. the flight latexes had narrower particle size distributions

than the ground-based latexes; 3. the particles of the flight latexes were more perfect spheres than those of the ground-based

latexes; 4. the number of offsize larger

particles in the flight latexes was smaller

than in the ground-based latexes; 5. the

completion on earth of the polymerizations

of the partially converted STS-4 flight latexes broadened the particle size distribution and formed more larger offsize particles. The superior uniformity of the flight

latexes was confirmed by the acceptance by

the National Bureau of Standards of the 10 um STS-6 latex and the 30 pm STS-11 latexes

as Standard Reference Materials, the first

products made in space for sale on earth.

The polymerization rates in space were the

same as those on earth within experimental

error

.

The authors acknowledge gratefully the

support of the National Aeronautics and

Space Administration under Contract NAS8-

32951, as well as the technical support and

assistance of the George C. Marshall Space

Flight Center, the ground support of the

Kennedy Space Center, and the performance

of the experiments in space by the astronauts and mission specialists of the Johnson Space Center.

1. J. W. Vanderhoff, Org. Coatings Plastics Chem. 21(2), 223 (1964).

2. T. Alfrey, Jr., E. B. Bradford, J. W. Vanderhoff, and G. Oster, J. Opt. Soc.

Am. 603 (1954) . 3. E. B. Bradford and J. W. Vanderhoff, J. Appl. Phys. ISl, 864 (1955).

4. E. A. Willson, J. R. Miller, and E. H. Rowe, J. Phys. Colloid Chem. 51, 357

(1949) . 5. J. W. Vanderhoff, J. F. Vitkuske, E. B. Bradford, and T. Alfrey, Jr., J. Polym.

Sci. 20, 225 (1956) . 6. E. B. Bradford, J. W. Vanderhoff, and

T. Alfrey, Jr., J. Colloid Sci. 11, 135

(1956) . 7. J. W. Vanderhoff, M. S. El-Aasser, and

F. J. Micale, Abstracts, 175th Meeting,

ACS, Anaheim, March 13-17, 1978, 1978

COLL-110.

8. J. W. Vanderhoff, Dow Chemical Company,

unpublished research, 1959-63.

9. V. Lowry, Lehigh University, unpublished research, 1981-2.

10. J. W. Vanderhoff and E. B. Bradford,

Tappi 12, 650 (1956) . 11. T. E. Lettieri, National Bureau of

56
U.S. DEPT. OF COMM.

DIRI DlDLIUurxMrmU inPPAPUir DATA UH 1 M

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NIST SP 260-107

2. Performing Organ. Report No. 3. Publication Date November 1988

4. TITLE AND SUBTITLE

Standard Reference Materials:

Description of the SRM 1965 Microsphere Slide

5. AUTHOR(S)

A. W. Hartman and R. L. McKenzie

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

(formerly NATIONAL BUREAU OF STANDARDS)

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Same as item #6

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Number: 88-600598

I I Document describes a computer program; SF-i85, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This manual describes a new Standard Reference Material (SRM 1965). The SRM

consists of two single-layer groupings of contacting monosize 10-ym polystyrene

spheres, that have been permanently sealed in an air chamber on a microscope

slide. One sphere grouping consists of hexagonally ordered arrays, while the

other grouping is unordered. The diameter distribution of the sphere material

(SRM 1960), which was made under microgravity conditions on a Space Shuttle,

is accurately known.

SRM 1965 has a dual function: supporting measurements involving microscopy

and supporting teachings and experiments in micrometrology . The manual

describes how to measure microscope magnification and image distortion at

levels below 0.5 percent and describes micrometrology experiments at the

0.05 ym level.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) array sizing; image distortion; Kubitschek effect; magnification; microscopy;

microsphere

13. AVAILABILITY

rXl Unlimited

I I For Official Distribution. Do Not Release to NTIS

fXI Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

67

15. Price

it U. S. GOVERNMENT PRINTING OFFICE: 1 98 8-- 2 4 2- 3 1

1 -- 9 2 58

USCOMM-DC 6043-P80


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Official Business

Penalty for Private Use $300

Stimulating America s Progress 1913-1988