NATIONAL BUREAU OF STANDARDS REPORT

7467

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PROGRESS REPORT No, 14

October 1 - December 3l, 1961

Contract No. DO (33-616) 61-02

Task No. 73603

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

and various consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1009-11-10491 7467

STANDARDIZATION OF THERMAL EMITTANGE MEASUREMENTS

PROGRESS REPORT No, 14

October 1 - December 31, 1961

Contract No. DO 33(616) 61-02

Task No. 73603

The two phases of this project are conducted under the supervision

of the following persons, who have approved this project.

Horace M„ Joseph

Electronic Engineer, Data Processing Systems Division

William N„ Harrison - Coordinator

Chief, Enameled Metals Section, Mineral Products Division

to

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

IMPORTANT NOTICE

NATIONAL BUREAU OF

intended for use within tt to additional evaluation an

listing of this Report, eithi the Office of the Director, however, by the Governme

to reproduce additional cc

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

• progress accounting documents

formally published it is subjected

g, reproduction, or open-literature

lission is obtained in writing from

. Such permission is not needed,

ly prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NOTICES

When Government drawings, specifications, or other data are used for

any purpose other than in connection with a definitely related Government

procurement operation, the United States Government thereby incurs no responsibility nor any obligation whatsoever; and the fact that the

Government may have formulated, furnished, or in any way supplied the

said drawings, specifications, or other data, is not to be regarded by

implication or otherwise as in any manner licensing the holder or any

other person or corporation, or conveying any rights or permission to

manufacture, use, or sell any patented invention that may in any way be

related thereto.

This document may not be reproduced or published in any form in

whole or in part without prior approval of the Government. Since this

is a progress report, the information herein is tentative and subject to

changes, corrections, and modifications.

I. SUMMARY

Calibration of the platinum working standards of normal spectral

emittance was completed , A statistical analysis of the data obtained in

approximately 5400 measurements indicates that the error of measurement,

expressed as a standard deviation, was approximately 0,4 in units of

emittance x 100 (or 0,004 without the multiplier). This analysis also

showed that the error of measurement was nearly constant over the temperature range of 800° to 1400°K, and over the wavelength range from 1 to 15

microns

.

It was found that there were real differences in emittance between

the different specimens measured, even though they had been prepared

from the same batch of platinum and were subjected to the same treatment

throughout. These differences, expressed as a standard deviation, were

on the order of 1,2 in units of emittance x 100 (or ,012 without the

multiplier). The differences in emittance between specimens did not vary

appreciably with temperature over the range 800° to 1400 K, but did vary

significantly with wavelength.

Construction of the data-processing equipment was nearly completed,

and installation during the next report period was promised,

II, IN STRUMENTATI ON

A,

Some maintenance work on this equipment was required during the re- port period, A vibrator in the amplifier used in the differential temperature control developed a malfunction and was replaced. Also the 80

nickel- 20-chromium alloy cores of the two blaekbody furnaces were detached

for removal of accumulated oxide, and replaced,

B , Reflectance Equipment

The design and construction of equipment for the measurement of re- flectance under conditions approximating normal illumination and hemispherical viewing was described in WADC Technical Report 59-510 Part III,

Construction of this equipment was financed in part by the Marshall Space

Flight Center of NASA,
- 2 -

The vibration-dampening supports referred to in WADC Report 59-510

Part III were reasonably effective in isolating the Golay detector from

building vibration . It was found on further investigation that part of

the interfering vibration was caused by gears on the wavelength drive of

the monochromator. This latter vibration was not eliminated by the supports since the monochromator is mounted on a table that is rigidly

fastened to the framework supporting the detector. Such rigid connection

is required in order to maintain optical alignment of the several mirrors

in the system. A new air-spring mount for the detector was designed and

built, and is functioning well. Oscilliscope tests of the equipment

indicate, however, that the actual resonant frequency is slightly greater

than the design frequency, probably due to an effect of the diaphragm

material o Use of the new support system has indicated that vibration is no longer a serious problem, but further smoothing of the signal is to be

undertaken by addition of an appropriate electronic filter.

It is desirable that the detector be placed alternately at the two

foci of the ellipsoidal mirror, for checking the spectral reflectance

curve of the standard. The sensitivity adjustment on the Golay detector

is quite critical, and in order to control and stabilize this adjustment,

a mechanical system for positioning the detector was designed, built and

installed. Also, the specimen mount was modified to facilitate installation of the specimen-heating device. The ellipsoidal mirror was re- surfaced, and handles were cemented to the outside, to facilitate lifting it. A new drum for the string drive was purchased and installed,

which gives a considerably flatter H 1GQ% curve” over the wavelength

range of 3 to 15 microns than the previous drive did.

A light-tight enclosure for the ref lactometer to isolate the detector from the room light was constructed and installed. The rear panels

of this enclosure were hinged to afford easy access for inserting speci- mens or adjusting the detector.

The work of calibrating the ref lactometer is proceeding.

III. CALIBRATION OF WORKING STANDARDS

A, Platinmti Specimens

Normal spectral emittance curves for the platinum working standards

were established over the wavelength range of approximately 1 to 15 mi- crons and at temperatures of 800 , 1100 and 1400 K.
- 3

-

The platinum specimens were received from the fabricator as 0.035

inch sheet, three each in the following shapes and sizes; discs 7/8,

1, 1 1/8 and 1 1/4 inches in diameter, 2x2 inch squares, and strips

1 x 10, and 3/4 x 10 inches in size, and six l/4-x-8-inch strips. It

had been specified that the specimens were to be supplied with highly

polished surfaces. The finish actually supplied was not as smooth as had been desired, but it vjas decided to use the finish supplied,

rather than send the specimens back for reworking. A 1/8-inch hole

was drilled in one end of each strip specimen, to facilitate hanging

during annealing.

Each specimen was washed in hot tap water to which a commercial

detergent had been added, rinsed in running hot tap water, then in

distilled water, and finally in ethyl alcohol. Rubber surgical gloves

were worn at all times while handling the specimens, and the central

portion, observed for emittance determinations, was not touched after

cleaning. The specimens were dried in air and placed in a closed con- tainer, supported by the ends or edges only, for storage prior to

annealing

.

All specimens were annealed in an electrically-heated, siliconcarbide-element furnace. The strip specimens were hung by means of

platinum hooks suspended from aluminum oxide rods in the furnace; the

square and disc specimens were supported by the edges only on ceramic

forms resting on a flat ceramic slab. All of the specimens were then

enclosed in a ceramic muffle. Starting with a cold furnace, the

temperature of the furnace was raised to 1523°K (1250°G) over a period

of six hours, and held at that temperature for one hour The power was

then turned off, and the specimens were allowed to cool in the furnace,

which required two days

.

The specimens were removed from the furnace by means of cleaned

platinum- tipped tongs and were placed in individual plastic holders,

in which they were supported only by the ends or edges. Each plastic

holder, containing a specimen, was then placed in an individual cardboard box, to protect it from contamination.

All of the specimens thus prepared, except the l/4-x-8=inch strips

were delivered to the Aeronautical Systems Division by hand on October

31, 1961.

6/ X

The 1/4-x-S-inch strips were prepared for measurement by welding

a platinum-platinum, 10% rhodium thermocouple to each specimen. A

shallow groove was scratched in each specimen, normal to its axis and

located at the mid-length. The 10-mil thermocouple wires were separate

ly welded to the specimen by means of a condenser-discharge type of

electronic spot welder. Each wire was laid in the shallow groove to

position it for welding, and the welding operation was observed through

a low-power microscope.
- 4 -

Precautions were taken at all times to avoid contamination of the

specimens. They were handled as little as possible, and when handling

was unavoidable the use of rubber gloves was continued, and even then

the center portion of the specimen was not touched.

Three sets of curves were made for each strip specimen at each of

three temperatures, 800°K, 1100°K, and 1400°K„ Each set of curves con- sisted of (1) a ”100% curve", obtained when the two blackbody furnaces

at the test temperature were the sources for the respective beams, (2)

a "zero curve", obtained when the specimen beam was blocked near the

specimen furnace, and (3) a specimen curve, obtained with the comparison blackbody at the test temperature as one source and the specimen

at the same temperature, as the other „ Each curve was recorded over

the range of wavelength drum settings of 16.7 to 1.2 turns (16.5 to 1„2

at 800°K), corresponding to a wavelength range of approximately 1.0 to

15.0 microns.

The normal spectral emittance was computed at each 0.1 turn of the

wavelength drum from 16.7 to 12.0, and at each 0.2 turn from 12.0 to

1.2 turns, a total of 100 points. The wavelengths corresponding to

these settings are given in column 1 of table 1. The normal spectral

emittance was computed as the height of the specimen curve above the zero curve divided by the height of the 100% curve above the zero curve

.

The data for the 18 determinations at each temperature and wave- length drum setting were tabulated, and the following values were com- puted: (1) E, the arithmetic average of the 18 measured values; (2) at , the total standard deviation^ of the 18 values about the average of the

18 values; (3) e, the 957= confidence error of E; (4) cm, the average of

six standard deviations, each computed from the three measured values

on one of the six specimens, and (5) as > the standard deviation of the

six average values, one for each of the six specimens, about the grand

average for all six. All of these computed values are given in table I.

The average normal spectral emittance of the six platinum speci- mens E, is plotted as a function of wavelength for readings at 800°K in

figure 1, at 1100°K in figure 2, and at 1400°K in figure 3.

1/ All standard deviations computed in this study are precisely defined

as "estimates of the standard deviation of the parent population from

which the measurements were drawn." This quantity is assigned the symbol

a, to distinguish it from the root -mean- square standard deviation S.D.

of individual values from the mean of a given sample.
- 5

-

It is apparent that the normal spectral emittance at each wavelength

increases with an increase in temperature. This effect would be predicted

from electrical conductivity, according to the Hagen-Rubens equation.

The maximum that occurs at a wavelength of about 1.8 microns at 800°C

shifted to shorter wavelengths with increase in temperature. The maximum

at about 9.5 microns did not shift in wavelength with increase in temperature, but diminished in magnitude. A third maximum in

Q

the vicinity of

15 microns is not visible at 800°K, but appears at 1100 K and increases

in magnitude with temperature. Spectral data at wavelengths longer than

15 microns will be required to establish with certainty whether or not

this maximum shifts with temperature.

The lower curves in figures 1, 2 and 3 are plots of the 957, confi~

dence errors—^ of the average emittance values plotted in the upper curves

The value Cm is a measure of the reproducibility of the test procedure, or the precision measurement. The average value of Cm , for all of

the 100 wavelengths, is 0.35 at 800°K, 0.45 at 1100°K and 0.36 at 1400°K.

Thus the overall precision of measurement for the equipment and test procedure is on the order of ± £L,4,. in units of emittance x 100 (or 0.004

without the multiplier). In order to show any trend of cm with wavelength

the moving average for five values at adjacent wavelengths was computed,

and plotted as a function of wavelength to obtain the lower curves in

figures 4, 6 and 6, respectively. This curve is identified in each figure

as the standard deviation due to error of measurement. The scatter due

to errors of measurement, am , does not vary appreciably with either wavelength or temperature.

The value as indicates actual differences in emittance of the speci- mens that were measured. The average value of 0's for all 100 wavelengths

is 1.22 at 800°K, 1.29 at 1100°K and 1.18 at 1400°K; the grand average

for scatter due to real differences between specimens is ± 1.23, in units

of emittance. x 100 (or 0.012 without the multiplier) and does not vary

appreciably with temperature.

2/ The 957, confidence error has the following statistical significance.

If the measurements were repeated a large number of times, say 1000 times,

and the average and 957, confidence error was computed for each group of

18 measurements, then the limits of the group average ± the 957, confidence

error would bracket the overall average of the 1000 groups of measurements

about 19 times out of 20.
- 6 »

In order to show any trend of crs with wavelength, the moving average

of five values at adjacent wavelengths was computed, and plotted as a function of wavelength to produce the upper curve in figures 4, 5 and 6,

respectively. The curve is identified in each figure as the standard

deviation due to differences in specimens. These curves show a definite

relation of scatter to wavelength, and are similar in shape.

The values of as are larger than the corresponding values of at

each wavelength at each temperature, by an amount sufficient to demonstrate statistically that the observed differences between specimens

are real, and could not occur due to chance fluctuations of the error

of measurement

.

B . Use of Emittance Data

The data given in table I and plotted in figures 1, 2 and 3 apply

only to measurements made with the NBS equipment and procedures, on the

six specimens that were measured. If other equipment and procedures are used on these specimens, the values for E and a3 still apply. However,

the values for will then depend upon the precision of the equipment

and procedure used for the measurements, and the values of at and e will

depend in part on such measurements.

Platinum working standards of other sizes and shapes, which were

prepared at the same time and from the same Material as the l/4~by-8~inch

specimens from which the data in table I were obtained, were not measured

at the National Bureau of Standards. They can, however, be used as working standards of normal spectral emittance, with the assigned values of E

4nd cts given in table I, The true E value for any one of these specimens

may vary from the corresponding E value given in table I by an amount

that can be statistically predicted on the basis of the reported 0’s value,

but the actual magnitude and sign of this difference for any individual

specimen cannot be computed.

For equipment and procedure other than those here reported, new replicate measurements on different specimens, at different wavelengths,

similar to those made to obtain the values reported in table I, are re- quired to ascertain separately, by statistical methods, the scatter due

to variation in specimens and that due to random error of measurement.

Systematic error of measurement, unlike random error, will produce

average values consistently too low or too high. If newly determined

emittance values are systematically higher or lower than the corresponding values in table I, an analysis will reveal whether or not the observed difference is statistically significant, or may be attributed to

random errors of measurement

.
- 7

-

IV. MATHEMATICAL EQUATIONS

The attempt to establish a suitable "program1 * for use with electronic

computers in solving the equations relating the absorption- index and index

of refraction of a metal to the contributions of bound and unbound electrons to the reflectance (emittance) characteristics of metals has continued. These equations are given as equations [2], T 3 1 and !~4] in WADC

Technical Report 59-510 Part III.

Numerical experiments aimed at approximately locating acceptable

values of the parameters were continued. It was established that the use

of five parameters - corresponding to the assumption of the existence of

essentially one ''family" of free electrons and one "family" of bound electrons = is insufficient for a good fit of the experimental data throughout

the 0.300 to 10.000 micron range of wavelengths. New programs were written, and experiments aimed at the utilization of a larger number of parameters, corresponding to additional "families" of electrons, are planned.

V. DATA PROCESSING EQUIPMENT

During the report period, the manufacturer has been completing the

data-logging equipment for supplying recordings of spectral data runs on punched paper tape. Although delivery was originally expected in the

middle of November 1961, a number of difficulties appeared which delayed

completion of the equipment. At the request of the manufacturer, Mr.

Horace M. Joseph of the National Bureau of Standards during December

visited the laboratory where the equipment was being assembled. During

his visit, the equipment was demonstrated, and essential portions operated successfully. It appeared that the equipment should be finished

and delivered during the next report period.

The functions of these portions were the digitization of the drum

dial rotation, the display of the resulting numbers, the adding of the

numbers in an "accumulator", the punching of numbers on the paper tape,

and the control of equipment -punching by use of an external reader of

punched-paper tape. In addition, the punching and accumulation could be

controlled by choosing to punch or accumulate at every 1st, 2nd, 5th,

10th or pre-selected (taped) drum dial position. The choice was independent and could be different for output punching and accumulation.

(The output digitizer between the electronic counter display and the

punch was not yet finished.)
- 8 -

There are two shaft encoders; one on the wavelength drum and one

on the drum of the potentiometer controlling the pen position and the

recorder. These shaft encoders utilize duplicate, coaxially mounted,

transparent discs, each printed with curved black stripes from center

to periphery. Two photocells at different positions are used to sense

light passing between the stripes of both discs. One disc is stationary; the other rotates with its shaft. The assembly produces varying

light intensity upon the photocells, depending upon the interference

of the stripes. The photocells are carefully placed so that the signal

appears first in one cell for clockwise rotation, and first on the other

cell for counterclockwise rotation. These light signals are counted,

and the counter output appears as pulses on appropriate channels according to the weight of the particular binary digit.

The digits are recorded on a paper tape in a code (as decided

earlier) called the Friden Programmatic Single Case Code. This is a fairly common code. It would be fairly easy to adapt the equipment for use of any one of quite a number of other codes.

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Figure

6.

Spectral

distribution

of

two

categories

of

standard

deviations

each^computed

from

18

measured

emittance

values

obtained

at

1400

K,

three

each

on

six

platinum

working

standards.

The

upper

curve

represents

standard

deviations

due

to

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MICRONS

II. s. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL RURKAU OK STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work,

in general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

WASHINGTON, D.C.

Electricity. Resistance and Reactance. Flectrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology,

Mass and Scale. Volumetry and Densimetry.

Meat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather- Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics. Electrolysis and Metal Deposition.

Mineral Products. Engineering Ceramics. Class. Refractories. Enameled Metals. Crystal Growth. Physical

Properties. Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat. Transfer. Inorganic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Processing Systems. Components and Techniques, Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy, Infrared Spectroscopy. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetjcs. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical .Services. Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research.

Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time Interval Standards. Electronic Calibration Center. Millimeter-Wave Research.

Microwave Circuit Standards. Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Modulation

Kesearch. Antenna Research. Navigation Systems.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.