NASA-CP-306019910010894 NASA Conference Publication 3060

National Educators"

Workshop: Update 88

Standard Experiments in

Engineering Materials

Science and Technology

. . . _ ..... •

• _ ,::: :

Proceedings of a workshop held in

Gaithersburg, Maryland

May 10-12, 1988

I

NASA Conference Publication 3060

National Educators"

Workshop: Update 88

Standard Experiments in

Engineering Materials

Science and Technology

Compiled by

James E. Gardner

NASA Langley Research Center

Hampton, Virginia

James A. Jacobs

Norfolk State University

Norfolk, Virginia

Proceedings of a workshop sponsored by the

National Aeronautics and Space Administration,

Washington, D.C., and the National Institute of Standards

and Technology, Gaithersburg, Maryland, and held in

Gaithersburg, Maryland

May 10-12, 1988

N/_A

NationalAeronauticsand

SpaceAdministration

Officeof Management

Scientific and Technical

Information Division

1990

PREFACE

Many new and modified materials continue to emerge on the engineering

and technology scene. Those responsible for educating the technical

personnel who will be charged with keeping the United States world

competitive must ensure that materials science, engineering, and technology

courses develop competencies in the emerging materials without forsaking

traditional engineering materials.

NEW Update 86 brought together leaders from industry and education

to learn new materials and to develop strategies for integrating them into

engineering materials technology instruction. These leaders concluded that

educators need new laboratory experiments and class demonstrations to

expose students to the nature and properties of the new engineering

materials.

NEW Updates 86, 87, and 88 made progress in improving teaching in

engineering materials, science and technology by presenting information to

educators on

Materials in Manufacturing

Recent Developments in Metallurgy

Metallic Coatings and Surface Modification

Advances in Polymeric Materials

Adhesives Bonding and Interface Technology

Service Life Prediction of Organic Materials

Developments in Optical Fibers

Electronic Materials Development

Advances in Composite Materials

Ceramic Materials

Long-Range Macro-Materials Cost-Estimating

Microcomputers for Design and Analysis

Modular Units for Teaching

The goal of NEW Update 88 was to obtain and to share with the

educational community a large number of experiments relating to the

nature and properties of engineering materials that cover the field.

Further, we sought single experiments that encompassed a variety of

iiJ.
concepts while not requiring elaborate or expensive setups as they focus on

newer materials.

Hopefully, the experiments and ideas presented in this publication provide

useful information to assist in teaching about materials in a manner that

will excite students and motivate them to probe for the facts and wonders

related to all materials.

NEW Update 88 and this printing resulted from considerable

cooperative efforts by individuals in government, private industry, and

education. While the goal of putting together a comprehensive manual of

experiments for the ever emerging field of materials science has yet to be

fulfilled, this collection represents a good effort in that direction. The

workshop organizers express their appreciation to all those who assisted

and hope this material is useful to you.

Workshop Co-Directors,

Jonice S. Harris

Institute for Materials Science and Engineering

National Institute of Standards and Technology (NIST)

James A.Jacobs

School of Technology

Norfolk State University

iv
CONTENTS

PREFACE ............................................................................................................ iii

HIGH TC SUPERCONDUCTORS: ARE THEY MAGNETIC? ............................................. 1

Dr. Robert D. Shull - Institute for Materials Science and Engineering

National Institute of Standards and Technology

FLUORESCENT PENETRANT INSPECTION ............................................................... 7

Dr. Sankar Sastri - New York City Technical College

MAGNETIC PARTICLE INSPECTION ........................................................................ 9

Dr.SankarSastri- NewYorkCityTechnicalCollege

RADIOGRAPHIC INSPECTION ................................................................................ 11

Dr. Sankar Sastri - New York City Technical College

CONTACT ANGLE DETERMINATION PROCEDURE AND DETECTION OF AN

INVISIBLE SURFACE FILM ............................................................................... 13

G. Meyer and R. Grat - ram6-hart, inc.

SENSITIZATION OF STAINLESS STEEL ................................................................... 27

James P. Nagy - Erie Community College

THE USE OF COMPUTERS IN A MATERIALS SCIENCE LABORATORY ........................... 31

J. P. Neville - Wentworth Institute of Technology

CRYSTAL GROWING ........................................................................................... 35

J. P. Neville - Wentworth Institute of Technology

A DEMONSTRATION OF CHILL BLOCK MELT SPINNING OF METAL ............................ 37

Robert B. Pond - John Hopkins University

FRACTURE OF BRITTLE SOLIDS ............................................................................ 41

R. D. Doherty and S. K. Nash - Drexel University

LOW CARBON STEEL: METALLURGICAL STRUCTURE VS. MECHANICAL PROPERTIES .. 47

Dr. Robert D. Shull - Institute for Materials Science and Engineering NIST

THE KELVIN WATER-DROP EXPERIMENT ............................................................... 51

Dr. Robert D. Shull - Institute for Materials Science and Engineering NIST

REVEALING THE MICROSTRUCTURE OF MATERIALS ...... ,........................................ 55

James A. Nelson - Buehler Ltd.

COMPOSITES: FIBERGLASS HAND LAMINATING PROCESS ....................................... 59

Battelle Northwest

GLASSES AND CERAMICS: MAKING AND TESTING SUPERCONDUCTORS ................... 63

Battelle Northwest

HIGH TEMPERATURE SUPERCONDUCTORS: A TECHNOLOGICAL REVOLUTION .......... 71

Colorado Superconductor Inc.

ATTENDEES LIST ................................................................................................ 85

HIGH Tc SUPERCONDUCTORS: ARETHEYMAGNETIC?

Dr. Robert D. Shull

Institute for Materials Science and Engineering

National Institute of Standards and Technology

OBJECTIVE: To demonstrate the magnetic characteristics of the new superconducting

oxides with transition temperatures above liquid nitrogen temperature

(77 K).

EQUIPMENT: Liquid nitrogen, a disc (plus a partial disc) and a rod of the superconducting oxide YBa2Cu307_x (O<x<O.5), a strong cylindrical tube

magnet, a small (Oolg) samarium cobalt magnet, a Styrofoam cup, a ring

stand, and plastic tweezers. (Another good project to precede this one

would be to make your ownYBa2Cu307_x superconductors from powders of

barium carbonate, yttrium oxide, and copper oxide.)

PROCEDURE: (1) First find out whether YBa2Cu307_× is magnetic at liquid nitrogen

temperature and if so, what the sign of its magnetic susceptibility is.

Tie a string around the middle of the rod of YBa2Cu307_x and suspend it

from a ring stand; partially fill a Styrofoam cup with liquid nitrogen

and immerse the rod in the liquid by slipping the cup around it from

underneath.

SAFETYWARNING: LIQUID NITROGENIS EXTREMELYCOLDANDCANEASILY FREEZE

THE WATERIN YOURBODY. THEREFORE,WEARGLOVESWHEN

****************************************************

Lower the cup and quickly bring the tubular magnet (because its field

lines are convex with respect to the center) close to the cold rod

(the magnet's axis pointing toward the rod) and observe the rotation of

the sample. If the long axis of the rod is parallel to the axis of the

magnet, the rod has a negative susceptibility (i.e., diamagnetic); and

if it lines up perpendicular to the magnet's axis, the rod has a

positive magnetic susceptibility (i.e., it is paramagnetic or ferromagnetic). You may need to perform this test several times so that

you can be sure that your observation is being made while the

YB2Cu307_x is still colder than 90 K (this material's superconducting

transition temperature, Tc, above which the material is NOTsuperconducting).

(2) Whena material becomes a superconductor it will exclude all

magnetic flux that exists in it before the transition. This is called

the Meissner effect and is shown schematically in Figure I. In this

figure the magnetic field (H) lines are shown by arrows. Note that no

lines penetrate the superconducting sphere at temperatures below Tc

when the field intensity is less than the critical field value, Hc.

_ctually, He, the field value above which the material also loses its

superconductivity, is temperature dependent: equal to zero at Tc and

increasing in value very quickly with decreasing temperature.) Such a

phenomenon results from the creation of circulating electrical currents

inside the superconductor to completely oppose the external field,

thereby also creating a repulsive force. If the external field is

created by a permanent magnet, the repulsive force may be strong enough
to actually move the magnet. Figure 2A shows just such an experiment to test this

possibility for YBa2Cu307_y. Turn the Styrofoam cup upside down and on top of it

place the superconduct6r dTsc. On top of the superconductor place the small samarium

cobalt magnet and then pour liquid nitrogen around the superconductor (the small rim

on the cup's bottom will contain the liquid) until it reaches 77 K (you can tell when

this occurs by the large decrease in bubbling of the liquid). What does the magnet

do? Can you push it around with the tweezers?

Normal; Superconducting;

T > Tc T < Tc

orH >He orH< Hc

FIGURE I

(3) Actually, the high Tc superconducting oxides, like YBa2Cu307.x, are Type II

superconductors: that is, they allow some magnetic flux lines into the material when

the field exceeds a critical field value slightly lower than Hc, and the material

remains partially superconducting to field values much larger than Hc. If these flux

lines get trapped, i.e., pinned in the material, the magnitude of the supercurrents

will decrease as less field is being opposed. Consequently, for materials like this,

it might be expected that the levitation experiment just performed would be dependent

upon whether or not there was a magnetic field present when the material was cooled

to below Tc. The experiment depicted in Figure 2B tests this possibility; perform it

by cooling the YBa_Cu_O_.. disc to 77 K and then place the magnet on top. This is

a test of the'_agn_ti_ _elding" of the superconductor. Does the magnet levitate

now? Is there any difference between the two experiments shown in Figure 2? Look at

the magnetic hysteresis loops for this material measured at two different temperatur_

sho_ in Figure 3 to explain these differences (or lack of differences) observed.

From these hysteresis loops, note that they enclose more area the lower the temperature of measurement; recall that Hc increases from zero with decreasing temperature

below Tc. (An interesting question arises from Figure 3B: after applying a field of

3000 Oe and reducing it to zero, there is a net positive magnetization from the

trapped flux remaining. If the small magnet were now brought close to this superconductor, would there actually be an attraction rather than a repulsion?)

(4) During either experiment depicted in Figure 2, could the magnet be pushed to the

side of the disc and still remain in the air? Repeat the experiments shown in Figure

2, but this time use the incomplete disc of YBa2Cu307_x. Does anything different

occur? Why? What is the difference between pushing the magnet near the edge of the

complete disc and putting the magnet in the center of the partial disc?

2
"HIGH" TEMPERATURE

SUPERCONDUCTINGOXIDES

(A) (B)

Superconducting Disc

_net _

300 K

3OOK

77 K 77 K

I

MAGNETICLEVITATIONEXPERIMENTS

Figure 2

3
Magnetic Hysteresis Loops

0.3

,_ 0.2 ,,._.,,"i"_ \ Ba-Y-Cu-O

"_" _ ' 77 K

o 0

-

o

._N

"" -0.1 til

(A)

-0.2

-0.3 , , , _ , ,

-4 -2 0 2 4

Field (kOe)

i

4,

3 _'_ Ba-Y-Cu-O

g

-3

_4 i i i | ! i

-4 -2 0 2 4

Field (kOe)

Figure 3

4
INSTRUCTOR'SNOTES

The YBa2Cu307_xis diamagnetic when T<Tc (this is the definition of a superconductor)°

There is not much difference between the two experiments in Figure 2 performed on this

material at 77 K. The difference in the levitating ability of the superconductor

between field-cooling and zer_field-cooling the material is a reflection of the flux

pinning of the material. At 77 K, Figure 3A also shows the lack of any significant

flux trapping: the width of the loop is small, enclosing a small area, and the

magnetization value on reducing the field to zero after applying 3 kOe is very small.

In fact, for this material (density, p, of 6 g/cm3) the trapped flux, which is equal

to 4_Mrp , is just 70e. Since the samarium cobalt magnet possesses a field of over

2 kOe, the difference in levitation force would hardly be noticeable. However, at

40 K the trapped flux would be about 140 Oe and the difference between the Meissner

effect and the magnetic shielding effect should be detectable.

The interesting possibility about an attractive force existing at 40 K in this

material is true. For small fields (_140 Oe), the net susceptibility is positive,

and therefore would act to pull the superconductor toward the magnetic field (i.e.,

the magnet). Of course, as the magnetappro_hes the superconductor, the field at the

superconductor increases to the point where the YBa2Cu307_x susceptibility becomes

negative and the force on the magnet becomes repulsive again.

When the magnet is pushed to the edge of the superconductor, the forces on it are no

longer symmetrical; and since there is a repulsive force between the two objects, the

magnet will be pushed outside the edge of the superconductor. Whenthe magnet is

placed on top of the partial disc, the edges are much closer and the region in which

there is stable levitation becomes much smaller. In addition, due to the irregular

topography, a smaller region of stability results from an increased localization of

the induced currents in the partial superconductor.

5

FLUORESCENT PENETRANTINSPECTION

Dr. SankarSastri

New York City Technical College

OBJECTIVE: The purpose of this experiment is to familiarize the student with

fluQrescent penetrant inspection and to relate it to classification of various

defects.

The penetrant method of nondestructive testing is a method for finding discontinuiti_

open to surface in solids and essentially nonporous bodies. The method employs a

penetrating liquid which is applied over the surface and enters the discontinuity

or crack. After the excess of penetrant has been cleaned from the surface, the

penetrant which exudes or is drawn back out of the crack indicates the presence and

location of a discontinuity.

EQUIPMENT: Zyglo inspection equipment: ZL-15 fluorescent penetrant; ZP4 powder;

black light: samples with defects.

PROCEDURE:

I. Inspect samples and parts to be free of any rust, scale, burrs, grease, oil, dir_

and other contaminants which would tend to give irrelevant indications.

2. Apply the penetrant by immersion of parts in the bath. Allow sufficient time

for penetration into all discontinuities. Minimum penetrating time is as follow_

Nonferrous castings, forgings, weldments -I0 min.

Ferrous castings, forgings, weldments -20 min.

Carbide tipped parts -30 min.

Ceramics - I min.

Plastics - 5 min.

Glass - 5 min.

3. Parts shall be washed in water immediately after time for full penetration has

been allowed. The water temperature shall be maintained between 90 and 120° F.

4. Dry parts as thoroughly as possible by exposure to clean air. The drying temperature shall not exceed 165o F.

5. Dip the dried parts in the developing powder. Developing time is as follows:

15 minutes - Aluminum; 30 minutes - other parts.

6. Enter the black light booth. Allow 30 seconds for darkroom adaptation time.

Examine the parts under black light. The intensity of black light shall be I00

foot candles minimum at a distance of 15' measured perpendicularly from the

front of the light filter.

7. Separate the parts into categories of defects such as forging laps, grinding

cracks, hot tear, shrinkage, porosity, and cold shuts.

REFERENCE:Nondestructive Inspection and Quality Control, ASMMetals Handbook,

Vol. 11, 8th Edition.

SOURCEOFSUPPLIES: Magnaflux Corporation, Chicago, lllinois.

7

MAGNETICPARTICLEINSPECTION

Dr. Sankar Sastri

New York City Technical College

OJBECTIVE: The purpose of this experiment is to familiarize the student with

magnetic particle inspection and relate it to classification of various defects.

Magnetic particle inspection is a method of detecting the presence of cracks, laps,

tears, inclusions and similar discontinuities in ferromagnetic materials such as

iron and steel. This method will most clearly show defects that are perpendicular to

the magnetic field (Fig. 1).

The Magnaglo method uses a liquid containing fluorescent magnetic particles. The

liquid is sprayed on the workpiece to be inspected and the part is magnetized at the

same time. The workpiece is then viewed under black light and the presence of

discontinuity is shown by the formation of a bright indication formed by the magnetic

particles over the discontinuity.

EQUIPMENT: Y5 magnagflux yoke it, fluorescent magnetic penetrant, black light,

samples with defects.

PROCEDURE:

I. Inspect samples and parts to be free of any rust, scale, burrs, grease, oil,

dirt, and other contaminants which would tend to give irrelevant indications.

2. Place the Y5 yoke on the workpiece perpendicular to the direction of suspected cracks.

3. Trigger the switch and apply the inspection medium.

4. Inspect the part for any crack or defects. The yoke is capable of finding

defects in a 25 square inch area across the magnetic field.

5. Locate the defect by circling with a red pencil and separate the parts into

types of defects such as shrinkage porosity, gas porosity, cold shuts,

and cracks.

6. Demagnetize the piece.

REFERENCE:Nondestructive Inspection and Quality Control, ASMHandbook, Vol. II,

8th Edition.

SOURCEOFSUPPLIES: Magnaflux Corporation, Chicago, lllinois

o..dp............-._Iron powder

•

Magnetic _f " _ _ "

Fleld . _ _- .

1 _ D D

D _ IL _---

Principle of Operation

FIGURE1

9

RADIOGRAPHIC INSPECTION

Dr. Sankar Sastri

New York City Technical College

OBJECTIVE: This experiment has several objectives which will familiarize the studen_

with

I. Use of radiographic inspection system

2. The method of taking a radiograph

3. Dark room procedures in developing

4. Inspection of a radiograph

EQUIPMENT: Faxitron model 8075 radiographic inspection system

PROCEDURE:

I. Since X-rays are potentially dangerous, students should follow all safety

procedures posted on the X-ray machine.

2. Turn the automanual selector switch to manual.

3. Adjust the KVP control to zero. Open the exposure compartment door and place

the film on the shelf and the specimen in such a manner as to afford the best

radiographic view. Place the identifying lead numbers in suitable places.

Close the door completely.

4. Adjust the KVP control for the desired voltage on KVP meter.

5. Turn the timer knob to the desired exposure duration (for the stainless

steel bracket casting) KVP 130, MA 3, time 30 sec.

6. Press the expose button.

7. After set time, the expose light will extinguish. Adjust KVP control to zero.

Remove the film.

8. Process the film by developing it for five minutes with agitation in

developer. Rinse it in water before putting the film in fixer. After five

minutes in fixer, wash the film in water for thirty minutes and dry it in

the dryer for 30 minutes.

9. Inspect the radiograph in light carefully to see any defects such as porosity

crack, shrinkage, hot tear, impurities, etc. Compare the defects with A_SoT,M.

standards and locate the area in the actual piece.

REFERENCE: Nondestructive Inspection and Quality Control, ASM Handbook, 8th Edition.

SOURCE OF SUPPLIES: Picker International, Trevose, PA 19047

II
SAFETY FACTORS

RADIOGRAPHY

1. The radiation safety features of X-ray systems are designed, built, and tested

to conform to the Exempt Protective Installation classification as defined in

Section 3.1 of the National Bureau of Standards Handbook 93.

2. Use a radiation meter of the type and quality Victoreen 440 to check X-ray

systems upon installation. Perform maintenance periodically.

3. Use a film badge service for cumulative individual monitoring°

ZYGLO

i. Flammability of penetrant materials

2. Volatility of penetrant materials

3. Annoyance created by dust of dry powder developers if not properly ventilated

4. Decomposition of chlorinated solvents at high temperature

5. Skin reaction - long or frequent exposures to penetrant materials

MAGNAFLUX

In addition to safety procedures of Zyglo, do not wear any watches that are not

antimagnetic.

Demagnetize after inspection.

12
CONTACT ANGLE DETERMINATION PROCEDURE AND DETECTION OF AN INVISIBLE SURFACE FILM

G. Meyer and R. Grat

rame-hart, inc.

INTRODUCTION, OBJECTIVES AND KEY WORDS

INTRODUCTION

The contact angle value, i.e., the tangent angle of a drop of liquid resting on a

planar solid surface is a basic parameter which can be applied in a wide range of

applications. One example of the successful application of this type of study

was to create a cleaning process which permitted the salvage of much of the

equipment which had been installed on an aircraft carrier which caught fire

during construction, and which was damaged by smoke, oil and sea water

contamination [i]. The work of developing suitable cleaning techniques was

carried out at the Naval Research Laboratory under Dr. William A. Zisman who

devoted a great deal of effort to the establishment of contact angle measurement

as a practical tool for solving many problems concerning wetting interactions of

liquids on surfaces.

The book Contact Angle_ Wettability and Adhesion [i] did much to promote this

science. Many other researchers, publications and short courses have greatly

contributed to the understanding and utilization of this basically simple

measurement technique, while providing a readily available source of information

for others interested in applying it.

The purpose of this tutorial is not to provide highly technical information

concerning contact angle theory, associated calculations and potential

applications. (Such information is readily available from other sources.) The

goal is rather to provide a basic understanding of the measurement technique,and

to present a simple illustration that can be applied as a quality control method;

namely, detection of a surface contaminant which exists on a surface that appears

clean to the unaided eye.

References provided with this presentation should prove helpful to those wishing

to explore other applications of contact angle data, or to gain knowledge of

associated theory.

OBJECTIVES:

i. To acquaint the experimenter with the technique of measuring contact

angles.

2. To conduct an experiment to illustrate how an invisible film on the

surface of a substrate can be quickly detected using a relatively

inexpensive instrument.

3. To create an awareness of contact angle measurement and provide

references to assist those wishing to learn more about the topic.

13
KEY WORDS:

CONTACT ANGLE:

The tangent angle value of a sessile drop at its interface with a horizontal

substrate. (Refer to CONTACT ANGLE, WETTABILITY AND ADHESION[l], Relation of the

Equilibrium Contact Angle to Liquid and Solid Constitution,. W.A. Zisman, for a

discussion of this topic.)

This value is dependent upon the surface tension of the solid phase, the surface

tension of the liquid phase and the surface tension of the vapor phase (normally

air), surrounding the liquid/solid system.

SESSILE DROP:

A drop of liquid resting upon a horizontal substrate, known also as the "Liquid

or Drop Phase".

SUBSTRATE:

A solid, planar surface,upon which the sessiledrop is placed, known also as the

"SolidPhase".

LIQUID/SOLID INTERFACE:

The common boundary shared by the liquid (sessile drop), and solid (Substrate

Surface), phases of the experiment.

WETTING/SPREADING:

A liquid/solid system in which the liquid wets the surface of the solid has a

resultant contact angle of zero. Contact angles having relatively low values

indicate that the liquid is capable of spreading readily across the surface of

the solid, without spontaneously wetting it. Contact angles of high values

indicate that the liquid resists spreading.

PENDANT DROP:

A small drop extending from and still attached to the tip of a vertically

oriented, drop-phase dispensing needle.

MICRO-SYRINGEATTA6"dMENT:

An accessory to the contact angle goniometer,used to form the pendant drop of

liquidand place it, in the form of a sessiledrop, onto the substratesurface.

CONTACTANGLE GONIOMETER:

An optical instrument employing a low-power, horizontallyoriented microscope

having a graduated reticule assembly,used to determine the contact angle of a

liquid solid system.

14
PRERF_UISITEKNOWLFJ)GERF_UIRED

A general background in laboratory experimental procedures, including a basic

understanding of microscopy.

EQUIPMENT AND SUPPLIES

Two standard glass microscope slides [a]

Butcher's Bowling Alley Paste Wax [b]

Distilled water, used to form the sessile drop [c]

l

Contact Angle Goniometer, rame-hart, inc. Model 100-00(115), with Micro-Syringe

Attachment Model i00-i0 and 22 gage Drop-Forming Needle. [d]

EXPERIMENTAL PROCEDURE

Specimen Preparation:

Uncoated Specimen:

I. The slide was carefully removed from a freshly opened box of precleaned

slides and five contact angle readings immediately taken at different

locations on one of its surfaces, as described below.

2. The slide was handled only by its edges and extreme care was exercised at

all times to prevent contamination of the test surface.

Coated Specimen:

i. This slide also was very carefully handled to prevent contamination.

2. A small amount of the wax was applied as evenly as possible to one

surface of the slide, using a lens tissue and applying the wax with a

circular motion.

3. The wax film was allowed to dry under ambient conditions for

approximately 20 minutes.

4. The coated surface was gently buffed employing a clean, dry lens tissue

and using a straight-line motion, parallel to the long axis of the glass

slide.

15
Instrumentation:

NRL Contant Angle Goniometer, Model i00-00, [Fig. i], is comprised of four major

components:

Optical Bench approximately 500 mm long.

Horizontally mounted Goniometer/Microscope assembly containing a reticule

assembly having two independently rotatable crosshairs, (known as the "baseline" and "measuring" crosshairs), and a graduated scale having one-degree

divisions.

A stage assembly, equipped with screw-driven elevation and left-to-right

motions, and a rack-and-pinion focusing motion. This stage is used to

support and position the substrate during the experiment.

An illuminator assembly, equipped with a green filter, variable-intensity

controller, and lamp-positioning/focusing controls.

Micro-Syringe Attachment, Model i00-i0:

This drop-dispensing attachment is mounted to the stage of the goniometer and

employs a micrometer-operated glass syringe assembly equipped with a Teflon

piston. A 22-gage stainless steel, "square-ended" needle is affixed to the

discharge end of the glass barrel and functions as the drop-forming tip.

The micro-syringe itself is mounted on a moveable head assembly which permits the

needle-tip to be accurately pre-positioned above the substrate, readily raised

from the area when not needed, and accurately repositioned to its original

location when again needed.

Instrument Setup:

I. The contact angle goniometer is set up in accordance with its instruction

manual. The micro-syringe is filled with distilled water and the microsyringe installed in its mount.

2. Adjustments are made as required to position the needle tip on the

optical axis of the instrument with the drop-forming needle tip

approximately 3 mm above the substrate. The micro-syringe attachment's

head assembly is then lifted and rotated to a raised standby position.

3. The illuminator's control is turned on and the variable intensity control

set to produce a low level of light. The light level is gradually

increased to a comfortable working level, while viewing through the

microscope.

CAUTION: To prevent eye injury, =are must be taken to prevent setting

of the brightness to an excessivelyhigh level.

16
Goniometer Hicroscope - Alignment and Focusing:

NOTE: An inverted image is observed through the microscope due to the optical

characteristics of the lens systems employed.

I. The microscope slide substrate is placed centrally on the goniometer's

specimen stage top plate.

2. The elevation of the stage assembly is adjusted to position the top

surface of the substrate approximately on the optical axis of the

microscope.

3. The microscope is focused on the edge of the substrate located nearest

the microscope, using the focusing knob located on the left side of the

microscope base.

4. The stage elevation knob and baseline crosshair rotation adjustment are

employed to align the top surface of the substrate with the baseline

crosshair, defining what will become the liquid/solid interface area.

[Fig. 2A]

5. The micro-syringe attachment's head assembly is now returned to its

working position and the drop-forming needle tip enters the field of

view.

Drop Formation and Placement:

i. The stage is now realigned as necessary and the microscope readjusted,

bringing the drop-forming needle-tip sharply into focus.

2. A small pendant drop, approximately 1.5 mm diameter, is formed at the

needle tip.

3. The micro-syringe is lowered using the screw adjustment provided,

allowing the bottom of the pendant drop to contact the surface of the

substrate.

4. The micro-syringe is again raised to the standby position, causing

release of the pendant drop from the needle tip, forming the sessile drop

upon the substrate surface.

5. The microscope is readjusted to produce a sharply focused image of the

drop boundary. [Fig. 2C]

6. The illuminator's lamp position and focusing adjustments are set to

produce a sharply defined silhouette image of the sessile drop.

17
Contact Angle Determination:

i. The measuring crosshair is adjusted to an angle which is somewhat less

than the apparent contact angle, and the stage is readjusted to cause the

measuring crosshair to become tangent to a point on the drop boundary

which is located between the drop's base and crest. [Fig. 2D]

This technique creates a visual aid which greatly lessens operator

subjectivity in adjusting the measuring crosshair to its final position

by providing a small wedge of light which can be used to accurately set

the crosshair.

The light wedge is bounded on one side by the measuring crosshair, on its

second side by the drop boundary, and by the substrate surface on its

third side.

2. The measuring crosshair is now rotated toward the base of the drop, and

the stage moved left to right (or right to left), to maintain a tangent

condition between the drop boundary and the measuring crosshair. As

these adjustments are continued, the light wedge diminishes and finally

ceases to exist. When this occurs, the measuring crosshair is tangent

to the drop boundary at the liquid/solid interface, and the measuring

crosshair is set to the contact angle value. [Fig. 2E]

3. The contact angle value is now read from the reticule assembly at the

short vertical line located at the "Six O'Clock Position" of the reticule.

DATA ACQUIRED AND RESULTS:

Data

Uncoated Specimen Coated Specimen

#i #2 #3 #4 #5 #i #2 #3 #4 #5

Contact Angle, Degrees: 8.0 7.5 7.0 7.0 6.0 70.0 71.0 71.0 72.0 73.0

Mean Contact Angle: 7.1 71.4

Results

The different surface tensions at the liquid/solid interfaces (clean glass on the

uncoated substrate, a wax film on the other) have caused contact angles of

distinctly different values to form.

The use of the contact angle goniometer has enabled the user to quickly ascertain

the presence of a surface contaminant and to quantify the resultant contact angle

value. Such information can be applied in a number of ways to improve formulations, optimize processes and function as a quality control method.

18
COMMENTS:

i. The same basic test could be employed to determine if a hand lotion

intended to protect the skin resists wetting(and soiling), or conversely,

if a formulation or process designed to remove soils from a surface

actually accomplishes the task.

2. As localized surface effects may influence the contact angle value,

several drops should be placed upon the substrate surface and their

contact values determined. These values should be averaged to ascertain

the mean contact angle value which should be employed in any subsequent

calculations.

CAUTION:

Mid-Range contact angle values (20 to 70 degrees) can be readily measured

with good precision: it is possible to estimate their value to 0.25

degrees. Contact angle values beyond these limits ! become more

subjective. In general, the manufacturer of the rame-hart, inc. Model

I00 Goniometer has indicated reliable repeatability of +/- 2 degrees_

however, many users of this instrument have indicated their feeling that

following their initial acclimation to the instrument, repeatability is

in the area of +/- 0.5 degrees for mid-range contact angle values.

3. It should be noted that contact angle studies have been successfully

employed in a tremendously wide range of applications. A few of these

are

Adhesion Studies: Adhesive and coatings formulation optimization.

Surface treatment evaluation: research, development and quality control.

Biomedical implant materials surface characterization.

Printing ink formulation and printing roller surface studies.

Oil reclam_ation: tar sands and tertiary oil recovery technique

studies.

Evaluation of the spreading effects of lubricants.

Studies involving biological surfaces, e.g., stomach lining and human

skin.

4. Although a wide variety of applications can be accommodated with the

basic instrumentation demonstrated in this experiment, other applications

require the use of temperature or atmospheric control, or the use of

photographic attachments or other special accessories. A well-designed

contact angle apparatus should be of modular construction, which permits

the addition of such accessories. [Fig. 3].

19
CONCLUSION

The simple experimentpresentedhas demonstratedthat contact angle values can be

readily determined and the resultantinformationapplied in a useful manner. It

has also demonstrated that the equipment is relatively simple and easily used.

Our experience as a supplier of surface science instrumentationover a period of

some twentyyears indicatesthat

Contact angle studies are readily carried out with relativelyinexpensive

equipmentand produce meaningfuldata.

Applicationof contact angle data frequentlyproduces dramaticresults in

problem solving, formulationor process optimizationand cost reduction.

The existing reference base and educationalprograms available greatly

assist in implementing contact angle-based research and development

programs.

Even in situations where textbook results are not experienced, the

studies produce meaningful,problem-solvingresults.

SOURCES OF EQUIPMENTAND SUPPLIESEMPLOYEDIN THE EXPERIMENT:

a. Glass microscopeslides: Local ScientificEquipmentSupply

House

b. Butcher'sBowlingAlley Paste The Butcher Polish Company

Wax: Marlborough,MA 01752

c. Distilled water Local Scientific Equipment

SupplyHouse

d. ContactAngle Goniometer rame-hart,inc.

and accessories: 43 BloomfieldAvenue

MountainLakes, NJ 07046

2O
REFERENCES:

i. "Contact Angle, Wetability and Adhesion:

Advances in Chemistry Series, Volume 43.

Special Issue Sales

American Chemical Society

1155 16th Street, Northwest

Washington, D.C.

2. "A Bibliography of Contact Angle Use in Surface Science"

f

rame-hart, inc.

43 Bloomfield Avenue

Mountain Lakes, NJ 07046

Although the following publications are not referred to in the text of this

presentation, they contain a great deal of information related to contact angle

studies and related topics.

3. "Adsorption at Interfaces"

K.L. Mittal

A.C.S. Symposium Series No. 8, 1961

A.C.S., Washington, DC

4. "Adsorption from Aqueous Solution"

Advances in Chemistry Series, Volume 79, 1968

A.C.S., Washington, DC

5. "Chemistry and Physics of Interfaces", 1965

A.C.S., Washington, DC

6. "Chemistry of BioSurfaces", Volume 2, 1972

M.L. Hair, Editor

Marcel Dekker, New York, NY

7. "Dictionary of the Physical Sciences", 1987

Cesare Emilliani, XXVl

Oxford University Press

8. "Guidelines for Physicochemical Characterization of Biomaterials"

U.S. Department of Health and Human Services

National Institutes of Health Publications No. 80-2186, September, 1980

9. "Interaction of Liquids at Solid Substrates"

Advances in Chemistry Series, Volume 87, 1968

A.C.S., Washington, DC

i0. "Physical Chemistry of Adhesion", 1971

D.H. Kaelble

John Wiley and Sons, Inc., New York, NY

21
ii. "Physical Chemistry of Surfaces", Third Edition

Arthur W. Anderson

Wiley Interscience, New York, NY

12. "Solid Surfaces and the Gas-Solid Interface:

Advances in Chemistry Series, Volume 33, 1961

A.C.S., Washington, DC

13. "Surface and Colloid Science", Volume 2, 1979

R.J. Good and R.R. Stromberg, Editors

Plenum Press, New York, NY

14. "Surface Chemistry: Theory and Industrial Applications", 1962

Lloyd I. Osipow

Reinhold Publishing Co., New York, NY

15. "Treatise on Adhesion and Adhesives", Volume I, 1967

R.L. Patrick, Editor

Marcel Dekker, New York, NY

22
_- "BASE-LINE" DIAL ILLUMINATOR

/-'MEASURING" DIAL GREEN FILTER Xw_ /

OBJECTIVE LENS

SPECIMEN STAGE " "

VERTICAL

FINE

I- ADJUSTMENT

EYEPIECE VE KNOB

COARSE

POSITIONING

THUMB

SCREW

IMAGE FOCUS

KNOB

CROSS-TRAVEL

DIAL

ILLUMINATOR CONTROL

L BENCH

LEVELING SCREWS (4)

NRLCONTACTANGLE GONIOMETER

MODEL100-00

FIGUREI

23
1. Focus on the top surface of the

Specimen Stage _ _ substrate at the edge nearest the

Microscope_Adjust _e substrateand

Sub s t r a t e | ._" II _e "base-line'"to achie_ cOin(:ider_€_

Baseline Crosshajr . /_ J ,/ NOTE: DO not disturb this setting

11/

during the course of acquinng the

Measuring Crosshai r reading.

A

2. DeposJt a smallvolume of hqutd

onto the substrate to form a sessile

drop ha_ngadame_erof appro_ma_e_y

Sessile Drop 2.5 mm. The drop size may van/

tO suit certain studies.

8

3 Refocusthe M_croscop_andadjust

-_ extreme left or r,ght side of the

sessde drop. Verify accuracy of

focus by shsftmgthe hneof stght

If the drop profile appears to move

relatrveto the "measunng"cross-hne,

C proper focus _snot attained

4 Adlust the"measurmg" cross-line

tO tangency above the base of the

drop to create a wedge of hght

bounded by the two cross-linesand

the drop profile.

O

5. Slowly rotate the 'measunng"

-__ ,., cross-linewh,le adjust,ng the cross-

,_ travelof theSpecimenStageAssembly

////,,X /////.,1 SOthatthe wedge of light isgradually

._/ extinguishedand the cross-lineattains

tangency with the drop profile at

the base of the drop.

E

Microscope Slide for Platform Leveling

F_TCURE2 .

24
TABLE 2

ALTERNATE OTPICALCOMBINATIONS

The following are examples of Microscope

Objective Lenses which may be substituted

for the Objective lens supplied with the

Goniometer. The user may acquire alternate

lenses from the manufacturers noted or from

others not listed. This table is intended

as a guide to assist the user in determining

the working distance which may be expected if

the overall system magnification is changed.

The overall system magnification is obtained

by multiplying the Objective Lens magnification

by I0 X (Eyepiece magnification). For users

who may desire to determine other optical

characteristics through calculations, the

optical tube length is 160 mm.

Objective Lenses available from Gaertner

Scientific Corporation, 1201Wrightwood Ave.,

Chicago, IL 60614

mag. Working dist. cat#

1.0 x 155m M-226

1.4 x 109mm M-225-C

1.7 x 89mm M-225

3.2 x 45mm M-222

4.0 x 35mm M-220

Objective Lenses available from

The Ealing Corporation

22 Pleasant Street

South Natick, MA 01760

mag. Working dist. cat#

1.0 x 150m 11-8216

1.5 x 100mm 11-8224

2.0 x 75mm 11-8232

4.0 x 35mm 11-8240

6.0 × 20mm 11-8257

I0.0 x 15mm 11-8265

25
A,R Z _AS 1.3.,<ApO_... 1"5_AS I16VA_OR'I

I SOLID

L __.__HEAVY - _"--I

__,o__ ,.-o

I L_ (_OR(_ I(_i'<_=LI ORQUID-'']

•" I® .1

X • REQUIRED _ ATEMBIENT MPERATURE ATMOSPTO30 HER0E°C. a TEMP ONLYERATURE

0 = OPTIONAL <_= TO 300°C.,VACUUM,8 TO I0 PSIG

O: REQUIRED FOR ENVIRONMENT NOTED ®=1"0 230°C. & TO I000 PSIG

"GAS"= INERT GAS _>= HOT MELT PENDANTDROP-T0230°C.

INSTRUMENT OR ACCESSORY CATALOG N° 112 3 4 5 6 7 8 9 10"11 12 13 1411516;17

NRLCONTACTANGLEGONIOMETER IO0-OO A X iX X X X X X X X X X X X X X X X

ENVIRONMENTAL CHAMBER 100"07 C X X X X X X _l_ X X X X :_<_>

CHAMBERCOVERW,STTAGE H ,oo-os-loc o o o o _>x xx

HIGH PRESSURE CHAMBER 100"08/30 C _>(_(_ (_)

.... -INVERTED NEEDLE 100"08"17 - _>

M,CRO-SYR,N ATTAGECHMENT ,00-,0 - x x x x x xx _x _ ®_

" " -INVERTED NEEDLE 100-10-13 - _ X _>

ELEVATED TEMRSYRINGE 100-11 E 0 0 0 O! _ X X X <_> t

FILM CLAMPS 100-15 A 0 i I

IMMERSIBLE FILM STAGE 100-16 C O 0 0 0 i

i J

i

ROTATING IMMERSlBLE STAGE 100-18 8 0 0 0 0 t

TILTING BASE 100-06 FOR ADVANCING & RECEDING CONTACT ANGLES

35ram CAMERA 100-13 FOR RECORD/MEASUREMENT PHOTOGRAPHS

POLAROID CAMERA 100-14 " " " "

FINGER SUPPORT 100-19 FOR CONTACT ANGLES ON SKIN

NRLCONTACTANGLEGONIOMETER

SYSIEMGUIDE

FIGURE 3

26
SENSITIZATIONOF STAINLESSSTEEL

Professor James P. Nagy

Erie Community College

Main and Youngs Road

Buffalo, NY

PREREQUISITE The completion of the study of stainless steels in a basic course in

materials science.

OBJECTIVE I. The objective of this experiment is to determine the corrosion

rates of 18-8 stainless steels that have been sensitized at

various temperatures.

2. Show the application of phase diagrams.

EQUIPMENT Heat treat furnace

Analytical scale

I000 ML Polyethylene beaker

Polyethylene graduated cylinder

Metallurgical polishing equipment

Metallurgical microscope

Safety goggles, rubber gloves, and apron

SUPPLIES 304 stainless steel samples I" X 1⁄2" X .032"

Cold mounting compound

Nitric acid

Hydrofluoric acid

PROCEDURE The laboratory instructor will assign each student one of the

following temperatures to which the sample will be heated.

Identify the samples as follows:

TEMPERATURE IDENTIFICATION

As received grind off one corner

550 C grind off two corners

600 C grind off three corners

650 C grind off four corners

700 C grind off no corners

750 C bend one corner

800 C bend two corners

850 C bend three corners

900 C bend four corners

950 C cut one notch in sample

1000 C cut two notches in sample

1050 C cut three notches in sample

1. Bend the sample so that it is "U" shaped.

2. Heat the sample to the assigned temperature for one half hour and

then water quench the sample.

3. Weigh the sample and record the weight.

27
4. The laboratory instructor will prepare the following test solution in a 1000 ML

polyethylene beaker:

Hydrofluoric acid 15 ML

Nitric acid 50 ML

Water 435 ML

SAFETYNOTE: Whenmaking this test solution always add the acids to the water.

Hydrofluoric acid will attack glass; polyethylene beakers and graduated cylinders must be used. This test solution will work at room

temperature. When handling acids or test solution, always wear safety

goggles, rubber 91oves, and rubber apron.

5. After all the students in the laboratory class have heat treated and weighed

samples, place all the samples in the test solution at the same time. It will take

approximately 24--48 hours for the samples to corrode. If in that time the test

solution turns a dark blue-green color, the solution is depleted. If more corrosion

is desired, discard the solution and prepare a fresh one, and continue corroding the

samples.

6. Weigh the sample; record the weight.

7. Mount the "U" shaped sample on its edge in a cold mounting material so the cross

section of the sample can be observed and then polish the sample. Observe the edge

of the sample under a microscope using low magnification.

REQUIRED

I. Determine the percent weight loss for all the samples.

2. Plot a graph of percent weight loss versus temperature.

3. Draw the sample showing the most intergranular corrosion.

4. Draw the sample showing the least intergranular corrosion.

QUESTIONS

1. Which of the samples corroded the most?

2. What was the reason the as-received and low temperature samples had little, if

any intergranular corrosion?

3. Using a phase diagram, explain why the high temperature samples had little, if

any intergranular corrosion.

4. What alloy addition could be added to this steel to retard intergranular

corrosion? Explain why.

28
NOTESFORTHE LABORATORYINSTRUCTOR

This experiment has worked out very well for us. If your furnace will not go up to

1050 C, no problem. We can only get up to 900 C and that is good enough. If you

can reach 1050 C, that would be better.

The samples are marked by cutting off corners or bending corners because the test

solution will remove any markings put on the samples.

It will take about 24m48 hours to corrode the samples; you can tell when you have

gone far enough. The samples heated to about 650m700 C will feel very granular on

the surface. There are times when we have let the samples stay too long and the

samples have completely dissolved!

ANSWERSTO THE QUESTIONS

I. The samples heated to 650 C_700 C will corrode the most because the stainless

steel is sensitized the most in this temperature range.

2. The as-received sample and the ones heated to a low temperature were not

sensitized because chromium carbides were not formed at the grain boundaries.

3. The samples heated to high temperatures were in the all gammaregion of the

phase diagram, and upon quenching, the carbon was held in solution.

4. In stainless steels, the alloys of Ti, Nb, and Ta will tie up the carbon so that

no chromium carbides will form at the grain boundaries.

REFERENCE

Brick, Pense and Gordon, Structure and Properties of Engineering Materials. Fourth

Edition, NewYork: McGrawHill, P. 340.

29
SE_ITTZATION OF STAINLESS STEEL

DATA SHEET

J

. I

I

_P[_,A'FdRE WEIG{T I WETG_IT PERC{_NT WETG{T { (3U{_N'I_ ON THE MIC_Qb_RUCI_RE

(3e SAMPLE _ TEST ! AFTI_ TEST [X_3_ J OF TIIE SAMPLE

i

Received i

55oOc ! I

I ! ...... 6QO°C t

6_o°c {

700°C ! .....

750°c { i

8oooc l

{

8r4_°C !

i I

.q_t_°C !

1600i_ Liquid

j-.

p !2c_°

_J

r',

E_ 800 [ 7+Carbide

I--.-

40O

, , I

0 0.5 1.0

Fe.ISCr. 8Ni wt. % C

3O
THE USE OF COMPUTERSIN A MATERIALSSCIENCE

LABORATORY

by J. P. Neville,Prof. MaterialScience,

Wentworth Instituteof Technology, Boston.

PREREQUISITEKNOWLEDGEREQUIREDFOREXPERIMENT:None

OBJECTIVE: To make available a method of easily recording the microstructure of a

sample by means of a computer. This method requires a minimum investment and little or

no instruction on the operation of a computer.

EQUIPMENT AND SUPPLIES: The following is one set of commercially available

equipment which will easily capture microstructures at a low cost and also be useful as a

regular computer.

An RCA model TC 2511 camera with a 16 mm lens was used to record the structures

shown in this experiment. This camera was positioned in direct contact with a Bausch &

Lomb metallurgical microscope, equipped with a 40X objective lens and a 5X eye piece.

The image was fed into a MacVision unit, made by Koala Technologies Corp. The signal

was then fed into a 512K Macintosh computer and the results printed out on the standard

Apple Imagewriter dot matrix printer. The entire system costs less than $3000.

The choice of Apple equipment was influenced by both the low price and ease of

operation. Macintosh has the added feature of allowing the microstructures to be saved as a

"MacPaint" document. In this program the structure is easily modified, text can be added, or

features can beenhanced. The larger capacity 512K machine was chosen because of its

speed when programmed with an internal "Ram Disc". The operation is almost instantaneous

in this mode and the added cost over the 128K model is minor. An SE model could also

be used.

PROCEDURE: The setup needed to view microstructures is as simple as placing the

lens of the TV camera in direct contact with the eye piece of the microscope. For ease of

focus, a metallurgical microscope which has two viewing lenses is ideal. This permits

adjusting the field of view without removing the camera and directly comparing the original

with the structure projected on the computer screen. The student has control over the

brightness and contrast of the pictures. The pictures obtained can be lightened to only show

outlines, with the idea of havingthe student fill in the details; or the pictures can be

reproduced with various shades, capturing most of the phases present. Programs and

equipment have been available for some time to analyze metallurgical microstructures but

all have been expensive and tend to give more information than is needed by a student at

the introductory level. The setup described here can be used to make good reproductions

of microstructures in the lab or pictures of actual test equipment.

The pictures obtained do not contain all the fine details that are seen in the microscope

or with a camera. For example, the fine grain boundaries present in some

microstructures are not reproduced by inexpensive systems. However, this is both an

advantage and a disadvantage to the student who is exposed to microstructures for the first

time. While the expert may well be frustrated by the missing details, the beginning student

will easily be able to see gross differences in structure and learn how these changes affect

31
the behavior of the material. By only seeing the major contrasts of the sample, the student is

not confused or overwhelmed by too much detail. Note that the differences in structure of

white, malleable and nodular cast irons are easily identified. Distortion of grains due to cold

working is also well defined.

Detail is best seen when the grains are different colors. This may be brought out more

by using a contrasting or "tint" etch which will color one phase more than another. Metal

Progress Magazine, published by ASM, ran an article on tint etches in the Mar 85 issue,

Dages.,:_1-41.

When the student advances in experience, it will be easy for him to add any missing

features he saw in the microscope to his finished print. The structure can be worked on or

improved by hand or by using computer graphics or drawing programs. Grain boundaries

can be brought out and phases can be labeled using this technique, and the results can be

included in a report.

Even without improving them, the pictures obtained are better than most students are

capable of reproducing by hand, as seen below.

Original figure not available

REFERENCE: Neville, "The Computer and the Microscope," Journal of Engineering

Technology, Vol 2, No. 2, p. 18-19.

32
DIAGRAm OF EQUIPmEnT J

BRIGHTNESS

CONTRAST Black & White

TV Camera

Digitizer

control box

17

Metallurgical

microscope

v

To the Printer

Irregularcarbon White Cementite

Flakes of Carbon Round spheres of carbon

TYPICAL MICROSTRUCTURES CAPTURED BY

THE SET-UP DESCRIBED HERE

33

CRYSTALGROWING

J. P. Neville

PREREQUISITEKNOWLEDGEREQUIREDFOREXPERIMENT: NONE

OBJECT: To demonstrate the way crystals grow and how they affect the behavior of

material.

To compare the growth of crystals in metals and nonmetals.

EQUIPMENT:

Hot plates, glass plates, beakers, and glass rods; balance to weigh out the salt and

water; furnace crucibles, sand, safety glasses gloves, firebricks, metal tray, and

tongs. Materials in the form of Epsomsalts, water, 50%Aluminum - Copper alloy

(previously formulated).

SAFETY:

Whenever you are dealing with hot liquids, there is the potential for burns and spills.

Protect yourself from the "possible", especially around the hot metal. Make sure

you know where any potential spillage will go and place something in the way to

protect yourself. In part B be careful of the hot metal. Remember, it will still be

very hot, even when it is a solid.

PROCEDURE:

PARTA: A supersaturated solution of salt will separate into crystals on cooling.

The size of the crystals is a function of the rate of cooling, the amount of

impurities present and the degree of supersaturation (concentration of salt present).

I. Dissolve 25 grams of Epson salts in 25 ml of water. Heat the water

until all the salt dissolves, but keep below the boiling point. If all

• the salt will not dissolve, add water in small quantities until it does.

Pour some of the solution onto a clean glass plate so as to form a thin

film and watch it solidify. If it solidifies too rapidly, return it to

your beaker, add some more water, and try again. If no crystals form,

return the liquid to the beaker and add more salt. Whenyou achieve

the proper mixture, you should be able to observe the crystals start

to form at the edge and slowly "grow" toward the center.

2. Record the ratio of salt/water you used and sketch the crystals you saw,

giving particular attention to the area where two crystals meet or join.

PARTB: If an alloy of two metals forms a eutectic and a solid solution ( or

intermetallic compound) on cooling, the eutectic can be poured off and crystals

formed by the solid solution will be exposed.

This part of the experiment lends itself best to a demonstration. (Let the

instructor burn himself instead of you.) An alloy has been prepared by

melting equal weights of pure copper and aluminum together overnight in the

furnace. An intermetallic compound, CuAI2, and a eutectic are formed. The

compound takes the form of large needles if slow-cooled.

I. Heat the copper-aluminum alloy up to approximately 700°C and pour it

into a hollowed out firebrick resting on a metal tray full of sand or a

hollow made in dry s_nd contained in a metal tray. USECAREDURINGTHIS

TIME!

2. As the liquid cools you will first observe small bubbles on the surface

as the solubility of the dissolved gases decreases. Next, you may be

35
able to see a hint of motion just under the surface as the

crystals of metal are forming. Tilt the pan slightly to see this

structure. When there seems to be some rigidity or structure inside

the liquid, tip the pan to let liquid (or eutectic) flow out.

Depending on when you decide to tip the pan, you will see large

crystals that have formed throughout the system. Note the size of

the crystals in the liquid that was poured out as compared to those

left behind.

3. Repeat the procedure again by remelting the mixture. Note how

brittle this mixture is - most unlike copper or aluminum - Why?

Sketch the shape of the crystals both in the hollow structure and

those in the material that was poured off.

CONCLUSIONS:

Can you give some general conclusions as to why crystals grow the way they do? What

can you conclude by comparing the growth of the metallic crystals as compared to the

Epsom salts? What would you recommend doing if you wanted small crystals or if you

wanted large crystals present in a sample?

REFERENCE:Neville, "Demonstration of Crystal Structure," Engineering Education, Vol.

75, No. 5 pp. 299-300.

36
A DEMONSTRATIONOF CHILL BLOCKMELT

SPINNINGOF METAL

Robert B. Pond

Department of Materials Science and Engineering

Johns Hopkins University

Prerequisite knowledge

One of the most exciting adventures in materials in recent times has been the

discovery of amorphous metals and the pursuit of methods of manufacturing various

alloys into various shapes which are amorphous. Someof these alloys possess

electrical properties which are extremely beneficial, whereas others offer different

benefits such as corrosion resistance and no solidification shrinkage anomalies.

There are a number of techniques for producing such amorphous shapes, but one of the

earliest systems used is now referred to as CHILL BLOCKMELTSPINNING.

Objective, Equipment, and Supplies

A chill block melt spinning demonstration is a spectacular and intriguing

exercise. The object of this demonstration is to show the simplicity of the

process. The apparatus used in the demonstration can be quite simple, easy to

construct, and extremely inexpensive.

The basic components of the apparatus consist of A) an ejection tube, B) a

pressure bulb and hose to generate an ejecting force on the metal in the ejecting

tube, C) a rotating chill block, and D) a drive motor for the chill block.

A and B) Since it is advantageous (for safety reasons) to use low melting

temperature metals for this demonstration, a Pyrex glass tube works well as an

ejection tube. Any tube size can be used, but a I0m12 mmsize is convenient. One

end of this tube should be sealed by heating and drawing the glass and the heated

mass, then redrawn to produce a conical cavity with a small apex angle as illustrated

in Fig. I. The glass wall is then ground away to produce an orifice approximately

300--500 microns in diameter. See Fig. 2. The tube is cut to a length of about

25 cm and provided with a rubber hose which connects it directly to a hand operated

pressure bulb.

A tin rod (having a diameter slightly less than the I.D. of the tube) when

inserted and melted in the tube can now be ejected in a continuous stream by

applying pressure on the squeeze bulb. If the free fall of the stream is sufficiently

great to allow solidification before impingement on a solid surface, and if the

stream velocity is sufficiently great to cause the Rayleigh break-up to be beyond

the point of solidification, then a round tin wire will be produced.

C and D) A simple, but most effective chill block can be constructed from a

new aluminum 9-inch cake pan. The exterior rim of this pan should be buffed to a

high sheen. A new pan is generally delivered in this condition. The center of the

pan can be located by balancing it on the point of a pencil. A small (6 to 8 mm

diameter) hole is drilled in the center of the pan. A small bolt inserted into the

hole provides an axle for the pan and allows it to be mounted on a hand drill. See

Fig. 3.

37
Procedure

If the stream of molten tin previously described is directed at the rotating

outer flat portion of the cake pan rim, then the circular cross section molten

stream will be converted into a flat solid ribbon, the thickness and continuity of

which will be dependent on the drill speed.

A standard hand drill will run at about I000 revolutions per minute, and the

rim surface of the cake pan will be traveling at approximately 1200 cm per second.

The ribbon is therefore cast at a speed of 1200 cm per second. This is by no means

the casting speed limit! Substitution of a higher speed motor will result in thinner

fibers, higher quench rates, and greater casting speeds.

Although the dwell time (or distance) of the tin on the wheel is very small, it

will tend to lengthen if the wheel becomes warm by extended operation.

It will be noticed that by controlling the point of impingement of the molten

stream, one also controls the emanating trajectory of the solid fiber. Best results

are obtained by using small attack angles (approximately 30 degrees) and molten

stream flight distances of about 20 to 50 mm.

38
FIGURE1 FIGURE2

G'-----_+#\__° -s.

°o

o.

FIGURE3

39

FRACTUREOF BRITTLESOLIDS

R.D.DohertyandS.K.Nash

Departmentof MaterialsEngineering

DrexelUniversity

Philadelphia,Pennsylvania

PREREQUISITE

KNOWLEDGE

This experiment is one of four devoted to the mechanical properties of metals,

polymers, and ceramics, as part of a one quarter laboratory course taken by

sophomore materials engineering students. In addition to freshman calculus,

chemistry, and physics, an intensive course in fundamentals of materials must precede

or accompany the laboratory exercises.

OBJECTIVES

Upon completion of this experiment, the student should be able to 1) give an

elementary account, orally or in writing, of brittle versus ductile failure, both from a

theoretical and applications point of view, 2) conduct a three-point bend test on a

tensile testing machine, and 3) statistically analyze experimental data that exhibit

inherently wide scatter.

PROCEDURE

Attach a low capacity load cell (say 50 Ibs.)to the tensile testing machine; calibrate the

machine with known weights; attach a three-point bending jig (Figure 1), and adjust

the machine to produce full-scale deflection on the chart recorder for a load of 10 Ibs.

While wearing latex gloves, open a fresh package of clear, 1 X 3 in. glass microscope

slides. Stress five slides to fracture and record data. Repeatthis procedure on slides

that have been scored lengthwise and widthwise, respectively, on 400 grit silicon

carbide abrasive paper. Figure 2 shows a simple holding fixture that helps produce

uniform scratches. Next, repeat each of the aforementioned test conditions, but in

addition, immerse each specimen in 5% HF solution for three to five minutes. (Tensile

testing and immersion can be coordinated to save time.) When the tests have been

completed, calculate the maximum (tensile) bending stress for each specimen in

accordance with the beam formula shown under Figure 1. For each group of five

fracture stress values, compute an arithmatic mean, standard deviation, and standard

error of the mean. The report on this experiment includes a summary of relevant

brittle fracture theory and all pertinent observations of specimen behavior in relation to

the numerical data and the applicable theory.

41
CAUTION: a) wear safetygogglesthroughoutthis experiment, b)

Placea transparent(Plexiglas) screenaroundthetest apparatus.

c) Whenhandlingslides,wearlatexglovesandholda slideat its edges.

Usea polypropylenebeakerandTeflon-coatedstainlesstongswhen

immersingslidesin HFsolution;rinseslidesindistilledwateranddryin

blastof warmair beforetesting, d) Alwayswearlatexgloveswhen

handlingHFacid or its solutions.

BIBLIOGRAPHY

1. M.F.Ashbyand D.R.H.Jones,EngineeringMaterials2, An Introductionto Microstructures

ProcessingandDesign. PergamonPress,New York:1986,pp.165-166.

2. A.G.Guy, Introductionto MaterialScience. McGraw-Hill, New York:1972, pp.462-473.

3. Z.D.Jastrzebski,The NatureandPropertiesof EngineeringMaterials.JohnWiley'

and Sons.New York:1976,pp.266-267.

4. L.H.VanVlack, Elementsof MaterialScienceandEngineering.Addison-Wesley,Reading,

MA; 4thEdition,1980, pp.219-223;312-313.

5. J.E. Gordon,Structures.PenquinBooks,NewYork: 1978,pp.242,379, 382.

SOURCES OF SUPPLIES

Precleaned plain glass microslides, hydrofluoric acid (52%), Teflon-coated stainless

steel tongs, and a polypropylene beaker are generally available in the chemistry

stockroom; if not, enough of these expendable and reusable items for a large number

of experiments may be purchased from a chemical supply house, e.g., Fisher or

Thomas, for about $50.

42
TYPICALEXPERIMENTALRESULTS:

BRITTLEFRACTUREOFGLASS

CONDITION 1 - AS-RECEIVED GLASS SLIDES:

10 specimens

Breakingloads: 2.9,5.7,5.1,5.5,3.8,5.1,3.3,5.9,4.7,3.5kgs

Deflections:(last5 readings) 0.9,0.8,1.1,0.8,0.8 mm

Meanfracture stress: 130MPa

Standarddeviation: -30MPa

Standarderrorof mean: (S.D.A/n) -10 MPa

CONDITION2 - AS-RECEIVEDGLASSSLIDES

AFTERETCHING:

5 Specimens

Breakingloads: 20.1,35.7,30.7,20.1,17.7kgs

Deflections: 1.8,2.5,2.6,1.3, 1.6mm

Meanfracturestress: 244MPa

Standarddeviation: -69MPa

Standarderrorof mean:(S.D./_/n) -31 MPa

CONDITION3 - AS-RECEIVEDGLASSSLIDES

AFTERABRADING

5 Specimens

Breakingloads: 4.4,5.0,4.4,4.3,3.1kgs

Deflections: 0.4,0.4,0.4,0.4,0.4mm

Meanfracturestress: 42MPa

Standarddeviation: -6MPa

Standarderrorof mean:(S.D./_!n) -3 MPa

CONDITION 4 - AS-RECEIVED GLASS SLIDES

AFTER ABRADING AND ETCHING

5 Specimens

Breakingloads: 10.0,8.9,27.2,29.0,9.9kgs

Deflections: 0.8,0.8,2.0,2.2,0.8mm

Meanfracturestress: 165MPa

Standarddeviation: -90MPa

Standarderrorofmean: (S.D./_/n) -40 MPa

43
VISUAL OBSERVATIONS

1. Etching did not significantly affect the appearance of the slides. The abraded

slidesshowed no detectable change, with the abrasionmarks still visible. The

as-received slides showed, after etching, some surface flaws. The etching has

blunted the sharp cracks, but in so doing,has apparentlymade the flaws

sufficiently wide at the surface to scatter light so that they could then be seen.

2. The strongest slides, those which after etching had fracture loads exceeding

20 kgs, were very highly bent just before fracture. These heavily elastically

bent samples almost exploded on fracture, producing numerous very small

pieces of flying glass.

3. Abraded samples showing the smallestfracture loads often only broke into two

pieces. These could be fitted together exactly. Samples with higher fracture

loads were increasingly fragmented as the fracture stress rose; that is, as the

stored elastic energy at fracture was higher.

Section bd t_ F

@ - __ @

FI2 = _r at tractu re FI2

FIGURE1. Schematicofthree-pointbendingfixture,whereF istheappliedload,Iisthe

distance between loading points, d is the thickness, and b the width of the

sample (slide). The equation for calculating the maximum tensile stress in the

surface, i.e., the modulus of rupture is

2

Tr = 3F_/2bd

44
l

II

|1

II

II

II

II

I!

tl

FIGURE 2. A simple holder for scoring a slide surface on 400-grit SiC abrasive

paper.

45

LOW CARBON STEEL: METALLURGICAL STRUCTURE VS. MECHANICAL PROPERTIES

Dr. Robert D. Shull

Institute for Materials Science and Engineering

National Bureau of Standards

PREREQUISITE: A knowledge of phase diagrams and basic metallurgical

polishing techniques.

OBJECTIVE: To provide a low-cost, simple experiment for either

demonstration purposes or as a laboratory experiment that will

teach the student the importance of the thermal-mechanical

history of a metallic alloy in determining that material's

mechanical behavior.

EQUIPMENT: Several metal hairpins, a candle, a propane torch, matches, a

bucket of water, a nonflammable surface, pliers, and

(optional) access to a metallurgical laboratory w_th polishing

wheels and cameras.

PROCEDURE: (a) Bend one of the hairpins in the middle to show how ductle

it is in the as-received condition.

(b) While holding one of the hairpins with a pair of pliers,

heat up a portion of it (the middle is most convenient) with

the propane torch as shown in Figure la until it is "red hot"

and then quench the hairpin quickly by dropping it into the

bucket of water.

SAFETY WARNING: THE METAL IS VERY HOT EVEN WHEN NOT RED IN COLOR.

THEREFORE, HANDLE IT ONLY WITH THE PLIERS!!

Test the ductility of the hairpin by bending it after this

high temperature heat treatment. What has happened? If you

have a high temperature thermocouple (e.g., Type K: ChromelAlumel or Type S: Platinum-10% Rhodium) measure the

temperature of the torch flame.

(c) Take a second hairpin and heat treat it with the propane

torch as performed in (b), followed by a fast quench.

Before testing its ductility, place the heat treated region

over a burning candle as shown in Figure ib for a couple of

minutes and then quench in water. If you are able, measure

the temperature of the candle flame. Test the ductility of

the hairpin as before. Has anything changed? Why or why not?

Hint: Compare the above two experiments with respect to the

iron-carbon phase diagram shown in Figure 2..(The hairpin is a

low carbon steel containing approximately 0.I0 wt.% carbon,

originally in a rolled condition).

47
(d) If you have access to a metallurgical polishing laboratory, make

cuts of the heat treated regions of the hairpins used in steps (b)

and (c) and observe their micros_ructures after mounting,

polishing, and etching them. Compare these with the "asreceived" microstructure. A good etchant to use is a 1-2 vol._

solution of nitric acid in ethanol.

SAFETY WARNING: MIXING AN ACID WITH A SOLVENT (LIKE ETHANOL) IS

VERY EXOTHERMIC!!! THEREFORE, ALWAYS ADD THE ACID TO THE SOLVENT!

*******************************************************************

Can you see a relationship between the microstructure and the

ductility of the hairpin?

+

Figure la Figure Ib

]'he metastohle System .on-iron ccrb._e

J800

16oo

(S-r,!1400. l._

1200 .....

Au$lllnlle

1000 F-,, i¢

A_$temte _ FeiC

800

60(

Fe,,de _errlle _ Fe I C

40(

Z30" "_1

200 . .

I_err,te _ _e z 1C I FII zC

0

F'e I 3 4 5 G 7 8 9 I0 II J2

;,!eighl= Percentage Carbon

Figure 2

48
INSTRUCTOR'S NOTES

In the "as received" condition, Figure 3 shows that the hairpin was initially

prepared from a rolled sheet of low carbon steel that received a substantial

reduction in cross sectional area (probably close to 90 % as judged by the

small thickness of the highly elongated grains). The absence of non-elongated

regions indicates that this material either received no subsequent heat

treatment or only a short low temperature stress relief anneal.

While heating the hairpin to a bright red glow in the propane torch (the

temperature will reach approximately i000 degrees Centigrade), the steel will

transform to the high temperature face centered cubic (austenite) phase:

refer to the metastable phase diagram in Figure 2. On quenching, this steel

will change to a body centered cubic structure, but will do so via a

martensitic transformation (hence, the sharp needles observed in Figure 4,

which show the microstructure for this condition). It's interesting to note

that since the habit plane of this martensite is the (iii) plane of the

original austenite, sometimes one may observe the appearance of hexagonal

networks of martensite plates. The internal structure of these martensite

plates (needles) is highly dislocated (and therefore highly stressed). The

brittleness of the material in this condition is a result of these high

residual stresses caused by the phase transformation.

Figure 5 shows the microstructure of the hairpin after aging the martensitic

structure in the candle (temperature of approximately 600 degrees

Centigrade). During this treatment the substructure of dislocations is

slowly eliminated (thereby relieving the stress associated with them) and the

material undergoes recovery. The material is now referred to as being in the

"tempered" condition. As this tempering process continues, the relatively

high carbon content of the martensite is reduced and both metastable

cementite, Fe3C, (dark regions in Figure 5) and ferrite (light colored

regions) form, initially at the plate boundaries.

MICROSTRUCTURE OF HAIRPIN "AS RECEIVED"

Figure 3

Original figure not available.

49

l-
MICROSTRUCTURE OF HAIRPIN "HEAT TREATED"

Figure 4

MICROSTRUCTURE OF HAIRPIN "TEMPERED"

Figure 5

Original figures not available°

50

I
THE KELVIN WATER-DROPEXPERIMENT

Dr. Robert D. Shull

Institute for Materials Science and Engineering

National Bureau of Standards

PREREQUISITE: This is an experiment originally designed and performed by Lord

Kelvin (William Thomson) in the late 1800's to demonstrate the

creation of an electric potential simply by means of dividing up a

body of flowing water. A basic understanding of electricity is a

prerequisite together with a curiosity and desire to find an

explanation for the unexpected.

OBJECTIVE: To demonstrate the power of electrical forces in a material as

commonas water and to help teach the student that even simple,

well understood phenomena sometimes present unexpected results that,

at first thought, defeat explanation.

EQUIPMENT: Two (or three) large coffee cans, two meters length of copper tubing,

two (or three) small tuna fish cans with their tops and bottoms

removed, two (or three) glass jars with lids; one bucket, one copper

T-joint, one shut-off valve, scrap wood, water, paper towels, and

(optional) a voltmeter.

PROCEDURE: (a) Construct a wooden frame to support the apparatus shown in

Figure i: Bucket (PI) should be suspended by strings above pails

(P2 and P3) as shown, with tuna fish cans (C2 and C3) connected by

means of copper tubing lengths (W2 and W3) to these pails. Good

electrical connections should be made at each end of these tubes,

and the tubes should be located near each other but not touching. A

water cut-off valve under PI is helpful, and pails P2 and P3 should

be electrically isolated from each other by sitting on top of glass

jars.

(b) Fill P1 with water, open the cut-off valve to let water flow

down the tubes and observe what happens. Measure the voltage between

the pails as a function of time. Is there any change? Is the water

flow diverted at any time? What about its width? Adjust the height

of the water flow above the cans C2 and C3 to change the relative

position where the flow breaks up into drops. Is there any relationship to the creation of sparks observed? Hang two copper plates

loosely from tubes W2andW3 so that they are parallel and free to

move and form a capacitor with a large surface area. What happens?

Why?

(c) If you are indeed adventurous, modify the apparatus to include

three pails as shown in Figure 2. How does this modify the effect

observed in the first apparatus? If you have three voltmeters,

simultaneously monitor the electrical potential between each pair

of pails P2, P3, and P4. Plot these voltages versus time on the

same graph paper. Are they related?

51
THE KELVIN EXPERIMENT

Figure 1

A THREE-PAILKELVIN EXPERIMENT

PI

Figure 2

52
INSTRUCTOR'SNOTES

The experiment in (b) will result in the generation of electrical sparks between

W2and W3, the frequency and strength depending on the distance separating them.

However, it is critical that the water flows be adjusted so that the water forms

droplets near (or inside) the cans C2and C3 (don't let the drops hit these cans).

The water initially separates into two flows of equal potential underneath PI.

Sometime shortly after starting the flow, one of the water drops formed from flows

A or B will possess an extra electron. Let's say it occurs under flow B. This drop

will fall into P3 giving it a negative charge. Since C3 is connected to P3, it will

develop a negative charge which will exert an electical (repulsive) force on the

electrons in the water in flow A. This force will result in the formation of drops

under flow A with a deficiency in electrons and therefore will be positively

charged. P2 (and therefore C3) will become positively charged and exert an attractive

force on the electrons at the end of water flow B as it breaks up into drops: thereby

creating more drops on this side that are negatively charged. Consequently, P3

develops a larger negative potential, which causes an increased repulsive force on

the electrons at the end of flow A and results in more drops forming under flow A

with a positive charge. The potential difference between P2 and P3 continues to

build up with time until it exceeds the capacitive breakdown potential between them,

and a spark will be created (usually between W2and W3--the closest points) to allow

charge to flow between them. As charge builds up in cans C2 and C3, the attractive

force between them and the drops falling through them will result in a greater

deflection of the water streams.

By hanging copper plates from W2and W3, a greater charge will build up between

them, and the electrical force between them will cause them to move toward each

other. On touching (if close enough) the plates will swing away from each other

(by gravity) and one will begin to observe the coupled oscillator phenomena (with the

transfer of kinetic energy back and forth between the plates).

The configuration shown in Figure 2 will create a three phase alternating potential,

but it is more difficult to get working.

53

REVEALINGTHE MICROSTRUCTUREOF MATERIALS

JamesA. Nelson

PREREQUISITEKNOWLEDGE:

GeneralHighSchoolEducation;AverageManualDexterity

OBJECTIVES:

Demonstratehowthemicrostructureof materialsmaybe revealedbyabrasivepolishingand

chemicaletching.

Illustratehowmicrostructuralinformationis usedto monitormanufacturingprocesses,provideindepth inspectionandperformfailureanalysis.

EQUIPMENTREQUIRED:

LowSpeedSaw BUEHLER11-1180-160

SpecimenPolisher BUEHLER69-1000-160

DrillFixture BUEHLER69-1550

HandDrill,1/4"

Microscope,Metallurgicaltype

TV CameraandMonitor(Optional)

SUPPLIES:

• TestMaterial:

Bareplatedthrough-holeprintedwiringboardsamples,doublesided,

I"X 3-3/8"(standardIPCTestCouponConfiguration)

• CuttingFluid

• Coldmountingresinsand molds

• Abrasivepapers,2-7/8"dia.assortment

• Polishingcloths,2-7/8"dia.TEXMET_ and MICROCLOTH®

• Abrasive,diamondpaste,6 micron

• Abrasivepolishingalumina,0.05micron

• Abrasiveextender

• Distilledordeionizedwater

• Ammoniumhydroxide

• Hydrogenperoxide,3%

• Alcohol,methyl(methanol)

SOURCES:

Specimenpreparationequipment Author'scompany

Suppliesforabove Author'scompany

Microscope,TV cameraandmonitor Author'scompany

Ammoniumhydroxide,3% Chemicalsupplier

Alcohol,reagentgrade Chemicalsupplier

Hydrogenperoxide,3% Drugstore

55
PROCEDURE:

Introduction: MicrostructuraAlnalysisistheprocedureusedtorevealtheinternalmicrostructural

detailsofa materialor partby sectioningandpolishingthecutsurfacesothatitmaybeexamined

undera suitablemicroscopeW. henthissurfaceiscorrectlyprepared,theobserverisabletoobserve,evaluateandmeasurevariousmicrostructurafelatures.The informatioonbtainedhelpsthe

investigatotor assessthesoundnessofthemateriaorl determineifcertainprocessesuchas

platinghavebeencorrectlyperformed.MicrostructurAnal alysismaybea solemeansofinvestigationbutitismoreoftenperformedinconcertwithothertestprocedures.

TestMaterial:A printedwiringboardhasbeenselectedas atestmaterialbecauseitcontains

bothmetalsandnonmetalths athavea distinctmicrostructure,andbecausethistechniqueisused

throughouttheelectronicindustryasa keyqualitycontrotool. l Thethreeprincipalcomponent

materialsinprintedwiringboardsare

Glass/epoxylaminatefacedwithcopperfoil

Copper,depositedbybothelectrolesand s electrolyticplating

Tin/leadsolder,eutectic

Printedwiringboardsaremanufacturedbya placinga photographicmageofthecircuitrinclud- y

ingholesandthepadsthatsurroundthemontolaminatethatiscoveredwithcopperfoil.Thecircuitryisproducedby aseriesofplatingandstrippingoperationthat s mustbecarefullycontrolled.

Becausethe processhasmanystepsandmanyparameterstocontrolth, erearenumerouspotentialsourcesofdefects.Microstructural Analysis(metallographyprovide ) sanin-depthvisual

analysisofthewiringboardcross-sectionthathelpsmonitotrhemanufacturingprocessesand

preventseconomiclossduetorejectabledefectsorfailuretomeetdesignspecifications.

SamplePreparation:

(1.)Sectionin(cutting): g Theprintedwiringboardcouponisattachedtothe,armofthelow

speedsaw byinsertingitintoa chuckandaligningthecouponwiththeabrasivebladesothatthe

cutwilljustmissthetestholesthataretobeexamined.Asecondcutismade,ifrequired,to

producea samplethatisnotmorethat1/2"high.Refertothesupplemental literatureforadditional details.

(2.)Thecutsampleisthoroughlycleanedtoremovecuttingfluidandmoisturethatcould

preventhemountingresinfromadheringtothesamplesurface.

Mounting:Usingplasticclipsas a support,the sampleis placedintothe cavityof a 1-1/4"dia.

mold. Themountingresinis measuredandmixedaccordingto the manufacturer'sinstructions

andcast intothe moldcavitytakingcarethatthe resindoesnottopplethe sampleor pushitto

oneside ofthe mold.Whencured,the mountedsampleis removedfromthe mold.

Grinding:Thecuredmountis placedintothe alignmentfixtureand a holeisdrilledintothe back

face(oppositethe sample)to allowattachmento the polisher.A240-gritsiliconcarbideabrasive

discis nextattachedto a glassplatenand placedintothe polishingbowl.A modestamountof tap

wateris appliedto the discandthe sampleis placedintothe bowl.Thetip ofthe polisherarmis

insertedintothe holethatwasdrilledintothe backof the samplemount.Settingsforspeed,time

andpressurefor thegrinder/polisheraredetailedinthe MINIMETMETALDIGESTrMunder

PreparationProcedures,sequenceA, page 8.(3)Theprocedureis repeatedfor eachof the

successivelyfiner steps(320,400and600grit).Thepolishedsamplemustbe rinsedbetween

eachgrindingstepandthoroughlywashedatthe conclusionofthis sequence.

Polishing:

A. Usinga similarset-upprocedure,the specimenis nextpolishedusing6-microndiamond

abrasivepasteappliedto an unnapped(TEXMEi"_'e)clothfor about2 minuteswiththe additionof a

56
modest amount of liquidextender.Thesample is washed thoroughly and dried atthe conclusion

ofthis step.

B. The sample is final polishedfor about30 secondson a nappedcloth (MICROCLOTH®)that

has been charged with 0.05 micron aluminapolishing suspension.At the conclusion of this step,

the sample is again washed, rinsed with alcohol and air dried.

Examination"

A. As-polished: The polished specimen isexamined under the microscopeby scanningthe entire area at 50-100 X magnification. This cursory examination will reveal very little detail in the

metallic layers because the sample has not been etched. Gross defects, if present, will beseen,

but finer defects will be masked by the normal smearing of the softer metals. The woven glass

pattern may befaintly visible.

B. Etched Examination: The polishedsample is etched with a solution consisting of equal parts

of concentrated ammonium hydroxide and hydrogen peroxide (3%). Using a cotton swab, a

copious amount of etchant is appliedto the polished samplefor approximately 3-5 seconds. The

sample is then immediately rinsed with tap water to stop the etching action,followed by a rinse in

alcohol and warm air dry. Examination will reveala lightly etchedcondition with microstructural

details not too clearly visible due to residualdeformation. To remove remaining residualdeformation, repolishthe sample on the final polishing cloth for about 30seconds, followed by a rinse and

dry as before. The sample shouldthen be re-etchedfor a longer duration(about 6-8 seconds),

washed and dried as before. Examination will reveal clearer details than were visible after the initial etching, revealing distinct interfaces betweenthe various plated layers and the actual

microstructure ofthe copper and tin/lead layers.

C. Analysis: The polishedand etchedsample should beexamined thoroughly at lower magnifications (50X-100X) first and in selected areasat higher magnificationsto more clearly identify possible problem areas. Ifthe microscope hasa camera, photomicrographs may be taken to record

the results. A typical photomicrographis shown as anexample.

D.Interpretation: The two photomicrographs that are shown were madefrom the same polished

sample but at two different magnificationsto illustratethe nature ofthe information that may be

obtained. (Seefigures.)

• 50X: Illustrates the value of low magnifications to obtain view of the entirethrough-hole

cross-section.

• 200X: Illustrates the use of higher magnifications to obtain closer look at areas that appeared suspicious at the lower magnification

Bibliography

1. James A. Nelson, "Basic Steps for Cross Sectioning PCB's", INSULATION/CIRCUITS, May,

1977, Reprint No. 26,

2."ISOMET @Low Speed Saw Sectioning of Materials," BUEHLER METAL DIGEST@,Vol. 22,

No. 1, 1983

3. "MINIMET ® Polisher/Grinder," BUEHLER METAL DIGES']°, Vol.20, No. 1, 1981

57
Entirethrough-hole

at 50x mag.

(As polished)

Laminate

Delamination

Kneeof the

though-hole

at 200 x mago

Interlayer

withEtchback

Solder

Etched

AmmoniumHydroxideHydrogenPeroxide3%

58

F
COMPOSITES

Fiberglass Hand Laminating Process

BattelleNorthwest - 1987

Richland Schools, Richland Washington

Key Words: Composite,glassfibers,epoxyresin,catalyst,exothermicreaction.

PrerequisiteKnowledge:

Inthestudyofpolymersitis importanttoknowaboutthermosetandthermoplastic

polymers.Forthestudentstobetterunderstandthis experiment,theywillneedto

knowthatepoxyresinswhenreactedwitha catalyst,formathermosetpolymer.The

chemicarleactionthattakesplaceasthestudentsmixthesecompoundstogether

causesa specialpolymerbondknownascrosslinkingIt. isbecauseof this

crosslinkingthatthetough,rigidpropertiesofathermosetpolymeroccurandare

usefulinthisexperiment.

LearningObjective:

The studentwillbe abletocomplywiththe procedureformakingthiscomposite

material.

The studentwill beabletomakea fiberglasscompositetoapplyandtesttheconcept

of combiningtwodifferentmaterialstoobtaina newmaterial.

The newmaterialwillexhibitnewandbetterpropertiesthanthe originalmaterials.

The studentwillunderstandthe reasonforcombiningmaterialsto makea composite.

Materials/Equipment:

1. Fiberglass

2. epoxy resin and catalyst (hardener)

3. 4-6 oz. paper measuringcup

4. brush (1inch)

5. polyethylenefilm 8-10 in. sq. (clear plastic bag)

6. acetone

7. tongue depressorfor a stir stick

8. plasticgloves

Procedure:

1. Cut five tosix 4 X 4 in. fiberglass squares with scissors.

2. Measure two ounces of epoxy resin into paper cup and proceed to follow directions

provided by the manufacturer. (See Instructor Notes.) Thoroughly mix contents

with tongue depressor for 3 -5 minutes.

59
3. Place polyethylene film on tabletop.

4. Pour a small amount of resin onto the polyethylene surface. (Note: resin does not

stick to polyethylene.) Spread to 4 X 4 in. area with brush.

5. Place one fiberglass 4 X 4 in. mat onto resin.

6. Dip brush into resin and begin to brush the resin on the fiberglass mat from the

middle outward. The fiberglass will absorb the previously poured resin as you

brush. Apply only enough resin with the brush to saturate the fiberglass.

7. Place second fiberglass mat (dull side up) onto the first layer. Apply resin with

brush, working from the center out to prevent air bubbles. Add only enough

resin (with the brush)to saturate fiberglass.

8. Repeat process with each additional fiberglass laminate until desired

thickness is achieved.

9. Cover the fiberglass laminate with a polyethylene sheet. Apply a heavy, flat object

to the top of the composite to compress the fibers and drive off excess resin.

10. Observe the contents of the cup and brush to verify that the resin is curing. The

cup will feel warm from an exothermic reaction that is taking place. An increasing

odor will be noticed as the reaction evolves.

11. Cleanthe epoxybrushwith acetone. Discardthe cup andcleanthe tabletopif

necessary.

12. Allow the resin in the composite to cure. Then the composite will be ready to

remove easily from the polyethylene sheets to be examined and/or tested.

Overnight should be ample time for curing the material.

INSTRUCTOR NOTES:

It is significant to know that on the market there are many different epoxy resins and

hardeners available. When mixing these compounds, it is very important to follow the

ratios suggested by the manufacturer of the resin. A data sheet to instruct the user

normally accompanies the resin. Carefully follow these instructions to obtain a desired

reaction and thermoset polymer.

60
**CAUTION**

Two ounces of epoxyresinis recommendedinthis experimentto keep

the quantityof materialsat a minimum butalsoto limitthe reactionif

the compoundsare mixedincorrectlyor a mistakeis made. The

reaction hasbeenknownto getvery hot. If thisoccurs,puton leather

glovesandmove ittoa heatresistantsurfaceandto anareawherethe

air is ventedto the outside.

This simple experiment can be enhanced in many ways. Other materials can be used

in place of the fiberglass to form the composite (i.e., Kevlar or graphite fibers). Fillers

can also be used to make lighter and/or thicker materials. Types of epoxy resins and

hardeners can be varied or even completely changed to use other types of polymers

as bonding agents in the composites. These suggested enhancements can also be

considered as completely different experiments because of the changes that are

made. To ensure success, the instructor would need to understand the variations

and complications that are involved when working with the vast arrays of polymeric

materials.

Testing materials is also another area that can be studied and can be considered an

entirely different field of study. Tests can be designed for strength, impact, chemical,

and environmental resistance, and reactions to temperature-- to name a few.

Sourcesof Supplies:

All of the above supplies can be purchased locally. Sometimes the materials can be

found in complete kits at your local hardware store. In some cases, it may take some

phone calls to locate all the items needed. A good place to check would also be local

auto body shops and auto supply stores.

61

GLASSESAND CERAMICS

Making and Testing Superconductors

Battelle Northwest- 1987

Richland Schools, Richland Washington

Key Words: Superconductor, superconductivity, resistance, degrees Kelvin (°K), ceramic,

metal oxides, sinter, ohm, Meissner effect, mole, molar ratio, molecular

formula, critical temperature (Tc).

PrerequisiteKnowledge:

Superconductors are conductive materials which have an extremely low resistanceto the flow

of an electriccurrent;that is,they havea theoreticalresistance(R) equalto zero ohms. Most

materialswhichexhibitsuperconductivitypossessthispropertyonlyat very lowtemperatures.

Until 1986, these temperatureswere close to absolutezero (0°K) (see instructornote2). In

a recentbreakthrough,superconductivitywas observedat temperaturesslightlyabovethat of

liquidnitrogen(77°K). Nowthe raceis oninthe scientificcommunitytocreatea superconductor

whichisabletoconductelectricitywithoutresistanceat evenhighertemperatures.Althoughthe

new superconductorsare inthe developmentalstage,somedaytheymay be used insuperfast

computers,magneticallylevitatedtrains, high-poweredelectriccars and energytransmission

lines which transmit electricity with virtually no power loss.

Follow this procedure to make a ceramic superconductor from three metal oxides: yttrium oxide

(Y203), barium peroxide (BaO2), and copper (11)oxide (CuO). BaCO3can be used in place of

BaO2. The molar ratio of the three metals in the complex is 1:2:3, yttrium to barium to copper.

The following is one way of expressing the molecular formula for this particular superconductor:

YBa2Cu307-x (ideally YBa2Cu307)

LearningObjective:

1. The student will make a superconductor by employing the following techniques: chemical

batching, mixing and grinding(pulverizing),heating,pressing,and tempering.

2. The studentwillbe ableto verifythe superconductivityof a materialthroughtestingby using

two methodsoutlinedin the procedure.

3. The studentwillbe able to reasonhowapplicablemethodssuperconductorscan be used in

oursociety.

Materials/Equipment:

1. balance

2. furnace capableof achieving950°C

3. furnacecontrollerto ramptemperatureat controlledrates

4. hydraulicpress

5. grindingchamber(see instructornote#5), disc mill,rocktumbler,or automatedmortarand

pestle (standard, hand-operated mortar and pestle may be used).

63
6. crucible - Alumina or ceramic crucible

7. yttrium oxide, Y203

8. barium peroxide, BaO2,(or barium carbonate)

9. copper (11)oxide, CuO

10. die to form superconductor

11. solvent: alcohol, trifluorotrichloro ethane or toluene (a solvent that evaporates quickly is

preferable)

12. disposable protective gloves (such as PVC gloves)

13. safety glasses

14. zinc stearate

15. alcohol (EtOH)

16. liquid nitrogen

17. Samarium cobalt magnet (see instructor note #6)

18. micro-ohmmeter for testing purposes (four-point type)

19. tweezers

20. annealing oven capable of achieving 475°C

21. oxygen gas (optional)

22. fume hood

23. particulate mask (recommended)

Procedure: Making Superconductors

1. Make calculations for the batch using the 1:2:3 ratio. The following is an example for a .1

mole batch, which is enough to make several superconductors. To achieve a ratio of 1:2:3

(Y, Ba, Cu), use a molar ratio of 1:4:6 for (Y2,Ba, Cu).

Molecular Multiplier Mass

Ratio Compound Weight (g/m) (for .1 mole) (g)

1 Y203 225.81 .1 22.58

4 BaO2 169.33 .4 67.73

6 CuO 79.54 .6 47.72

**CAUTION**

Someof thechemicalsusedinthe makingof superconductorasre toxic.Pleasecheckthe

contentof thesematerialsin a chemicalsafetybook.Whenchemicalsare exposed,such

as inweighingor opencontainergrinding,theworkshouldbedonein a ventilating(fume)

hood.Disposableplasticglovesshouldbeworn,anditis advisabletoweara goodquality

particulatemaskfor addedsafety.

2. Weighthechemicalsandplacethemina containertogo intoa grindingchamberor disc

mill. If a grindingchamberor disc millis not available,use a) a rocktumblerwitha very

hardobjectsuchasa chunkofstainlessteelora pieceofquartzaddedtohelpthegrinding

process;or b) a mortarandpestle.

3. Add30 gramsofalcohol,trifluorotrichloroethane(freon)ortoluenetoaid inmixing.

64
4. Grind for one hour. The smaller the resulting particles, the better. Grinding the material to

the smallest possible size is very important in producing superconductor material.

5. Let the solvent evaporate in a hood.

6. Place powdered mixture in furnace at 900-925°C for 18 hours.

7. Remove from furnace, cool, and repeat steps 3 through 7.

8. After removing from oven the second time, examine the mixture to see if any greenishcolored material is evident (see instructor note #._33). If so repeat steps 3 through 7. Morethan

25% greenish material indicates an incorrect mixture of chemicals, poor chemical quality, or

improper oxidation; a new chemical batch is necessary.

9. Grind again to a fine powder--once again, the smaller the particles, the better.

10. Weigh out quantities of the material to make pellets. The quantities are determined by

the size of the mold to be used. (We used 12g and 15g quantities to form pellets about

9 x 17 x42 mm.)

11. Clean the die with alcohol. Lubricate with a very light dusting of zinc stearate.

12. Place the material in the die and distribute it evenly.

13. Put the top on the die and prepare it for pressing on the hydraulic press.

a. Gradually increase the pressure to 5000 Ibs. (area = 1.0 in2 for a pressure of 5000-6000

Ib/in2.)

b. Hold the pressure for a couple of minutes.

c. Let the press gradually releasethe pressure itself. (The press seems to release in "jerks"

when done.)

14. Remove the top part of the die and extract the pellet.

15. Place the pellet in the furnace for sintering.

a. Heat the furnace at 300°C/hour until it reaches 950°C.

b. Allow the pellet to sinter at least 8 hours at 950°C.

c. Cool at 50°C/hour to bring the furnace back to room temperature.

16. Place in an annealing oven at 450°C for 18 hours. If oxygen gas is available, bubble 02

over the pellets while they are being annealed. After the allotted time, let the oven cool to

room temperature with the pellets inside.

17. Remove the pellets from the anealing oven. They are now ready to be tested for

superconductivity.

65
Testing the Superconductors

18. Attach the micro-ohmmeter (four-point type) to the pellet and take a resistance reading

at room temperature. Now place the pellet in liquid nitrogen so it is submerged and

take a second reading. In its cooled state the resistance measurement should read zero

ohms. (Readings from this measurement can be erratic due to poor contact or high-contact resistance.

19. Test for the Meissner effect (see instructor note #4) using a Samarium Cobalt magnet and

liquid nitrogen.

a. Place the superconductor in a pool of liquid nitrogen (a Styrofoam cup cut down to an

inch high works well in containing the liquid N2when working with the superconductor;

the pellet can be placed on a small brass block acting as a pedestal while in the liquid N2).

b. Allow the superconductor to cool for a few minutes. Continue replenishing the liquid

nitrogen supply around the pellet as the N2 dissipates.

c. With the tweezers, carefully place the magnet so that it is just above the superconductor.

The height at which the magnet will remain suspended in air varies depending on the

strength and size of the magnet--the smaller and stronger the magnet, the better. Once

the magnet is balanced above the pellet, it can be set into a spinning motion with the flick

of a finger or tweezers.

Instructor Notes:

1. This experiment is lengthy. It would be best to divide a classroom into groups of two,

three or four students each, or to let a special interest group do the experiment initially. It

may take several tries before a superconductive material is made, so allow plenty of time

for experimentation. A highly motivated group of students could go through the process

first and identify the critical areas of the process to the class before the class attempts the

experiment. The grinding process (see instructor note #5) is of crucial importance. Even

though the students may be eager to make this material, emphasize that they must perform

each step carefully. This will better ensure that they successfully produce a superconducting

material the first time through the procedure.

2. Superconductivity, in which the resistance (R) is virtually equal to zero, was first discovered

in 1911 by Heike Kamerlingh Onnes while observing mercury at liquid helium temperatures

(4°K,.-452°F). The critical temperature (Tc) at which a material is superconductive has

remained very low since that first discovery, rising only about 4°K per decade with research.

By 1973, the best of the superconductors possessed a Tc of 23°K (-418°F). The discovery in 1986 of a superconductor with a Tc greater than the temperature of liquid nitrogen (77 K,

-321 °F) was a giant step toward bringing the whole process closerto the realm of practicality.

Cooling with liquid helium is expensive, whereas the cost of a gallon of liquid nitrogen is

comparable to the cost of a gallon of milk.

3. The greenish material mentioned in step 8 of this experiment has been seen in several studies done on this particular superconductor. The greenish material is a non-superconductive

phase which has the composition of Y2BaCuOs. The black phase is the desirable superconducting material, approaching the ideal composition of YBa2CU3OT.

66
4. The Meissnereffect is a phenomenonwhichall true superconductorsexhibitwhile in their

superconductivestate. When cooledto its propertemperature(thecriticaltemperature,Tc),

the superconductorrepelsall magnetismregardlessof polarity. The classic pictureof a

magnetsuspendedin midair abovea superconductoris a resultof the Meissnereffect.

5. The mixingand grindingof these chemicalsisvery important.Thesmallerthe particlesize,

the betterthe chance superconductivitywill occur. Any numberof grindingmethodscan

be used, preferablyautomated. If hand grindingis necessary,be certain to grind as long

as possible. Oneway to do this would be for a groupof studentsto sharethe work, each

taking a ten to twentyminuteturn at grinding. If a rocktumbleris used,operateovernight

and check the consistencyof the materialthe nextday.to see if it is finallypowdered.The

other automatedsystemsshouldbe operatedfor a minimumof one hour.

6. Samariumcobalt magnets have an extremelystrong magneticfield for their size. This

is important because common magnets are generally bulky and have weak magnetic

fields. The weight of the magnet can overcomethe force of the electric field and the

levitating[Meissner]effect will not be seen. SamariumCobaltmagnetscan be purchased

commercially;thesesamemagnetsarecommonlyusedin light-weightheadphones,in case

you have an old pairto disassemble.

Resources:

Heppenheimer, T.A. "Superconducting: The New Billion Dollar Business." High Technology,

July 1987: pp. 12-18.

Maranto, Gina. "Superconductivity: Hype vs. Reality." Discover,August 1987: pp. 22-32.

"Ceramic Superconductors." Advanced Ceramics Materials Special Supplementary Issue, July

1987.

For those with low budgets, contact a local college chemistry department or industrial laboratory

for the materials and other help. The materials can be ordered from the following vendors:

GeneralVendors:

Allied Fisher Scientific, 50 Fadem Road, Springfield, NJ, 07081. Phone # (201) 379-1400.

Mortar and Restal ($75-$200), Alumina crucibles ($20-$30 ea.)

VWRScientific,P.O.Box7900,SanFrancisco,CA94120.Phone# (415)468-7150.

American Scientific Products, 1430 Waukegan Rd., McGraw Park, IL 60085. Phone # 1 (800) 325-4520.

ChemicalVendors:

AlfaProducts,MortonThiokol,Inc.; 152AndoverSt., Danvers,MA01928. Phone# (617)777-1970and

1 (800)343-0660.

Yttriumoxide(99.99%),250g,at $80;Zincstearate,1 Kg at $15;Bariumperoxide,500g at $18; CopperII

oxide, 1 Kg at $56; Ethanol,anhydrous,500 mlat $13.

6?
Aesar, Johnson Matthey, Inc., P.O. Box 1087, Seabrook, NH 03874. Phone # (603) 474-5511 and

1 (800) 343-1990.

Aldrich Chemical Co., Inc., 940 W. Saint Paul Ave., Milwaukee, Wl 53233. Phone # 1 (800) 231-8327.

Itis assumedthat the largepiecesof equipmentare availablein your schoolor froma sourcein

i_OeUr community;otherwisetheywill needto bepurchased.Someequipmentcanbeimprovised.

s can be madeby the studentsor machinedin the schoolmachineshop.

Ifthe schoolis withoutapress, an appropriatesmalldie can be madeto compressthe pellets

by strikingthe die with a five poundsledgehammer.Itwouldbe best if the die weretempered

after machining,but even untemperedsteelwill be able to makea numberof pelletsbefore it

mushroomsout and becomesunusable.The reasonfor pressingthe pelletsisto compactthe

chemicalsas close togetheras possibleand to have a solid pieceto place into the furnace.

This improvisioncan createpelletssimilarto that of a hydraulicpress.

Many institutions(i.e.,hospitals,laboratories,doctors,colleges,industries)use liquidnitrogen.

Contactthem for their sourceor to requesta donationfromthem.

See instructornote#_66for rare earthoxide magnets.

Prepared by teachers as part of a Residence in Science and Technology (REST) program at the Pacific

Northwest Laboratory operated by Battelle Memorial Institute for the U.S. Department of Energy; Summer 1987.

68
RESOURCES: "u,"°.o,..,ov.,.,,.

Associates Inc., 170

(D_scrip_ion o/ U.S. Route One. Falmouth. Maine 0410S: telephone (207)

a serviceor pvodltctiJ no_ in_ended _ an endorsemenL 781-3632: telefax (207) 781-4383; telex 294139.

Art " indicales the ert_r_ in art ezlaansiort of art earlier

ti,,,,9.) *Chemistry of High-Tc Supercon-

_5C1 announces production of two high-Tc powders, ductor5 is a new book published by the American

Chemical Society. This multidisciplinary collection (I) Y - Ba - C= - 0 CP (tm) superconductive powder

of articles presents the most current information in

produced by ¢o-pfecipitation process. All powder is 95% or

better primary orthorhombic phase, average particle size ! developing technologies for commercial usesof high-Tc

micron. Tc approximately 90 K or better with 6 K transition superconductivity. Editors are David L. Nelson, M. Stanley

width, without oxygen anneal. (2) Y - Ba -- Cu -- O Whittingham, and Thomas F. George. Cost in U.S. and

SS (tm) superconductive powder produced by "solid Canada. $64.95: overseas, $7795. For more information on

ACS Symposium Series No. 351, contact ACS, Distribution

state" process, Tc approximately 82 - 83 K. Other powder

Office Dept. _246, P.O. Box 57136, West End Station,

compositions, pressed pills and other shapes available upon

request. Contact Superconductive Components, Inc., 1145 Washington, DC 20037.

Chesapeake Ave., Columbus. OH 43212; telephone (614) Superconductivity: The Complete

486-026_ Resource Guide is published by The Bureau of

Edmund Scientific_,m.,k_,i.g_up_,_ond_,i,_N,_io°,l Afr,i,,.I.¢.BNA . _,c,ib_,i,,,"'_h_,,, _ ,ndo._y

ceramic discs for educational laboratory demonstrations, comprehensive, current sourcebook of names, addresses.

Manufactured by Tektronix Co,. the disc is composed of projects, issues, and specialized guidance focusing on the

|" - Ba - Cu - O; Tc is 83 K. Kit. including disk. holder, superconductivity industry." The C_ompleteResource Guide

instructions, and bibliography, is $20; two or more kits. $18 is made up of several services: a reference book. including

each. Contact Edmund Scientific Co.. ].0] E. Gloucester lists, directories, and calendars, overviews, texts, and how-to

Pike. Barrlngton. NJ 08007: telephone (609) 573-6250 or guides, and a hotline for updates. Charter subscription rat<:

€;47-3488. is $445: after October 30, $595. For more information.

write The Bureau of National Affairs. Inc., Circulation

Proceedings of the Beijing International Department, P.O. Box 40947. Washington, DC 20077-4925:

Workshop on High Temperature Superconductivity and or call the BNA Response Center at (800) 372-i033.

Proceedings of the Adriatico Research Conference on

High-T c Superconductors. iCTP. Trieste. Italy. 6 - 8 July Oemo kits toh_lostudents di,cover ,uperconductivity

1987, are now available from Wodd Scientific Publishing have been developed by KnutSoft Knowledg_ Systems.

Corp. World Scientific is also publishing the Proceedings of Intended for ninth-grade level and above, each kit contains

the Orexel International Conference on High-Tc . Contact: a superconducting wafer, a small magnet, and 20 booklets

World Publishing Co., P.O. Box 128, Fatter'Road. Singapore explaining the history of superconductivity, superconductor

9128: telex RS2856! WSPC: telefax 2737298: telephone applications, recent breakthroughs, and current problems.

2786188: or, in the U.S., World Scientific Publishing Co., A bibliography is included. For further information, contact

687 Hartwell Street. Teaneck. NJ 07666; telephone (800) KnutSoft Knowledge Systems. 219 Los Cerritos Or., Vallejo,

227-7562. CA 94589; telephone (707) 648-0779. _tL/.c_

Los Alamos Nat'/ Labh,,b_...med., Lake Shore Cryotronicsh,,i=,t.o.,.

part of the national superconductivity initiative. Its special I-R 100 award for its DT-470 Series Temperature Sensor.

charter is to explo(e and devdop ways for DOE labs to form "Each DT-470 series sensor incorporates a proprietary

constructive partnerships with industry. Contact Fred Morse silicon diode chip with temperature characteristics that are

(SOS) 667-1600. so stable and uniform from chip to chip that they are the

_rst mass-produced interchangeable sensorsavailable for use

Falmouth Associates h., b_... _.thecritical cryogenictemperaturerangfrom e 1.4Kto

comprehensive study of the starting materials used in 475 K .... Used in conjunction with control instrumentation,

the synthesis and fabrication of high-T c superconductors, the sensors are ideal for a variety of field applications

The study surveys the current worldwide reserve and where temperatures from 1.4 K mu_t be achieved and

production capacity of relevant raw materials, details precisely maintained." For more information, contact Jeff

how they are refined and prepared, desctibes and assesses Bergen, VP. Marketing; Lake Shore Cryotronics. Inc.; 64

lubrication routes, and forecasts demand. Subscriber$ will East Walnut St.; Westerville. OH 43081; telephone (614)

obtain • complete business analysis of the materials as 891-2243.

well as information on suppliers, fabricators, new business

opportunities. _.tc. For more information, contact Or. H;gh-T c Update. Vol l. No. 12

69
MARKET GROWING FOR HIGH SCHOOL KITS

There are now at least four companies marketing superconducting levitation demonstration kitsin the

United States. The least expensive costs $25 and will be available from American Chemet. A kit costing$49

is available fromKnutsoft Knowledge Systems. A third kit is available for $65 from a Denver firm. A fourth

company, also based in Denver, intends to offer several kits by the end of this year.

Because demand isso highfor his "1-2-3Levitation" kits (whichcost $"25),Arthur Ellis of the University

of wi_.consm said he willsoon be handing the production over to American Chemet, based in Deerfield,

Illinois. About 1000high schools have been reached with the kit, and some are going over,seas. Included in

the kit is a superconducting ceramic disc (and a recipe for it), magnets, background history of superconductivity, an instruction booklet that includes an overhead projector demonstration, a list of periodicals

for research, a.tadsafety warnings. (Arthur Ellis,Chemiztry Department, University of Wisconsin, Madison,

W[ 53706.)

Knutsoft Knowledge Systems of Vallejo, Calif.,is marketing a $49 kitthat includes a disc and magnets,

an introduction to the topic, a periodical list, a lab guide and a demonstration instruction booklet. (Knutsoft

Knowledge Systems, 219Los Cerritos Dr., Vallejo, CA 94589.)

Laboratory Specialists Inc., of Denver, Colo., markets two kits: a $100deluxe kit wiai,'hcontaLasa disc,

two magnets, experimental samples, a resistivitymeasurement device, and a manual including experiments,

history and safety warnings. Its 565 basic kit contains two magnets, a disc and the manual. (Laboratory

Specialists, Inc., 2235 Hudson St., Denver, CO 80207.)

SuperconTech (formerly Oxitec Inc.), also located in Denver, has developed three kits,including an

introduction kit for the junior high level costing $65; a senior high level kit costing 51.20;and a high

school/introductory college kit costing 5250. The company is developing a fourth kit, priced at 51000,which

will contain a SQUID and Josephson junctions. The kits will be on the market by mid-December.

(SuperconTeeh, 821 Aroma St., Suite 200, Denver, CO 80204.)

SUPERCONDUCTORWEEK.November 16. 1g87

SUPERCONDUCTiVlTY KITSAVAILABLE

A "levitation kit" is now being offered for sale to highschool ducting discx. Interested highschoolteachers should contacz

science teachers for the purpose of demonstrating the Meiss- Art Ellis, Uni_rsity OfW'_ ('Phone 608-252-0421)or

her Effect. The Institute of Chemical Education (ICE) • send • $25.120check orMoney Order (payableto ICE) to Innonprofitscientifi organi c zatihoeadn quartered inMadison, stitufor tcChemicaElducatioPrn,ojec1t-2-3D,epartmentof

W'tsconsinismakingthekitavailableattheitcost,$25.00.Th¢ Chemistry, University of Wisconsin, Madison, W'tsconsin

kit concept was £u-xtintroduced to highschoolsdenc¢ teachers 53706.

at an ICEworkshop heldatthe University ofW'tsconsinduring For anyone who is not • high school science teacher and

the summer. The reception to this new educational aid has wouldliknto obtain materials to perform theMeissner Effect,

been good. According to Art EJlix,Uuiversity of Wisconsin Edmund S_c Company in Barrington. New Jersey is

Chemistry Department,"Ten percent of the flyea-sentbyICE offeringa superconducting ceramic disc for laboratory demto more than three hun&ed high schooleducators nattonwide onstndon. Manufaa_'ed by dm Tektronix Company, the

have alzeadybeen returned with• check." _ demonstration superconducting disc kit contains a one inch diameter, one

kitindudesaoneinchdiameterdisc,on_quarterofaninch eighthinch thick123di.r_com, pletewithfoamholdr-inr,structhick, coated with wax. The wax coati_ rr.duc_ the disc's tioas, andb_liography. Bymagn_ Imitation of • small saexposure to water vapor thereby incre_ its _ and mariumcobalt magnet atliquidnitrogentcm_'ature (-77 K')

extending its life.Also indtu:lcd inthe kit are twosmallsamar- the discwill demonstr_e the McL_'.r Effe_. The Edmuad

iumcobalt magn_._o,neironn_/mium boron_ and catalog_ thatmostlocal hospital andlabsupplfirmy s.

three stride reprints. The magnets zre being providedfree of have liquidn_ a_railablr_

charge by Ca'ucibleMagneti_ of Elizabethtown, I_'m_-kT. Thciniccofthesupcrcoaductingdiscis_'20Iftw. oor more

Instructionsforperformingthe_ent u.singanaverhead are ordeaedthe priceis $18each.A samariumcobalt magnet,

projcaorasweJ1Lsim_ backszound hsf_-m,elon for 5/16" diamet,_rxl/15"tlaick, maybeputchascdsepatatetyfor

teadaers _ coat_ _hthi_t _ t_ I1_ r_ $:35.00. Order th_ _ _ _ fl_m Edmtmd Scientific

Ameri:unChem_Co_'sEastHdetm, Momanaplant .Company.101EastGlouc_r Prim,Barringto_, NewJ_

willbeproviding the superconduaor to ICE undercontract. 08007.The catalognumbersfor the disc and magnet are

b,--, AmericanChemet complet= tl_ scaleupstep,theUni- A_TT,44and 6 A3"7,447,rest.

versity of Wisconsin labs will be producing the superconSUPERCONDUCTIVITYNEWS

7O
High Temperature Superconductors:

A Technological Revolution

Demonstration of the Meissner magnetic levitation and a low friction magnetic

bearing.

AUTHOR

Colorado Superconductor, Inc.

555 Spindrift Ct., P.O. Box 8223, Fort Collins, CO

PREREQUISITEKNOWLEDGREEQUIREDFORTHE EXPERIMENT

None. All experimental procedures, safety and handling precautions, and background

information is contained in the instruction manual which is provided with each set of

materials in the kit. The table of contents of the manual is reproduced below.

Introduction 3

The Demonstration Kits 4

Lecture plane 5

Overhead projector use 5

A brief history 6

The language of superconductor physics 7

The chemistry of the new superconductors 8

How do we make these superconductors? 9

Getting started: I0

- Liquid nitrogen: Sources & Handling 10

- The Kelvin scale of temperature 11

Experiments, a self-paced guide

- The Meissner Effect 12

- Determining the critical temperature 15

The four point electrical probe 18

- Electrical characterization 19

- Measuring resistance versus temperature 20

- Determining Tc, critical temperature 20

- Determining Hc, critical magnetic field 23

- Determining Ic, critical current and density 24

- The reverse ac Josephson Effect 25

Taking care of your superconductor 26

A list of superconductor reference articles 27

Safety, warnings, and handling instructions 28

Emergency Medical Information 29

Where do we go from here? 30

Note that there is especial emphasis placed on safety. While liquid nitrogen is not

and cannot be provided with the kit, both sources and safe handling procedures have

been detailed. A prior knowledge of handling liquid nitrogen is encouraged.

71
OBJECTIVES

Demonstrationof the Meissnereffect throughmagnetic levitation.

Demonstrationof one applicationof the Meissner effect: The low friction

magnetic rotationbearing.

Demonstrationof magnetic flux penetrationand the Type II nature of ceramic

superconductorsvia the stackingof the superconductordisks.

EQUIPMENTAND SUPPLIES

The CompleteDemonstrationKit, which consistsof a I inch diameterYBCO superconductordisk, neodymiumor Samariumcobaltmagnets,nonmagnetic tweezers,and

an extensiveinstructionmanual.

Liquid nitrogen. About a pint should be sufficientfor one experiment.

A small Dewar flask to hold and transportthe liquid nitrogen.

THE MEISSNER EFFECT

One of the propertiesof superconductorsmost easy to demonstrate,and also the most

dazzling,is the Meissner effect. Superconductorsare stronglydiamagnetic. That is

to say that they will repel a magnet.

A superconductoris fundamentallydifferentfrom our imaginary'perfect'conductor.

Contrary to popular belief, Faraday'slaw of inductiondoes not explainmagnetic

repulsionin a superconductor. When it is in a superconductingstate (that is, at a

temperaturebelow its criticaltemperatureTc), a superconductorwill not allow any

magnetic field to enter it. This is becausemicroscopicmagneticdipoles are induced

in the superconductorthat oppose the applied field. This induced field then repels

the source of the applied field and will consequentlyrepel the magnet associated

with that field. This impliesthat if a magneticwas placed on top of the superconductor when the superconductorwas above its criticaltemperature,and then it was

cooleddown to below Tc, the superconductorwould then exclude the magnetic field of

the magnet. This can be seen quite clearly since magnet itself is repelled,and thus

is levitatedabove the superconductor(FigureI).

This magnetic repulsionphenomenais called the Meissner effect and is named after

the person who first discoveredit in 1933. It remains today as the most unique

demonstrationof the phenomenaof superconductivity.

PROCEDURE

The shallow dish-likedepressionin the kit, or a third of an inch high portion of

the bottom of a Styrofoamcoffee cup can be used for holding liquid nitrogen for the

experiment.

I. ACTION: Carefullypour a small amountof liquid nitrogen into the dish or

Styrofoamcup until the liquid is about a quarter of an inch deep.

RESULT: The liquid boils furiouslyfor a short while. Wait until it stops.

72
2. ACTION: Using the provided tweezers, carefully place the black superconductor

disk flat in the liquid until its top is just flush with the surface of

the liquid nitrogen.

RESULT: Again the nitrogen boils around the disk. Wait until this stops too.

3. ACTION: Again using the tweezers, pick up the provided magnet, and attempt to

balance it on top of the superconductor disk.

RESULT: Instead of settling down onto the surface of the superconductor, the

magnet will simply 'float' a few millimeters above the superconductor.

This is a demonstration of the Meissner effect.

The new YBCOceramic materials are Type II superconductors; thus, the Meissner effect

appears to be a bulk phenomena. This can be demonstrated by stacking two or more

superconductor disks. With the addition of each disk, the magnet will be levitated

higher.

If one carefully sets the magnet rotating, one will observe that the magnet continues

to rotate for a long time. This is a crude demonstration of a frictionless magnetic

bearing using the Meissner effect. The rotation speed of a cube-shaped magnet can

be improved by using a plastic drinking straw to blow a stream of air at one of the

edges or corners of the cube. Another way to increase the rotational speed is to cut

out a small rectangular hole in a piece of paper and place the hole over the levitated magnet such that half of it projects above the plane of the paper; and then if

one blows at the part of the magnet above the paper, it can be made to rotate quite

rapidly.

The cubical magnet naturally is slowed by the resistance of air. Consequently, it

can be expected to stop soon. A cylindrical magnet will rotate for much longer since

it is more rotationally streamlined. However, the cubical magnet makes this

demonstration much more graphic. A research group at Cornell University has

demonstrated a frictionless superconducting bearing that rotates at the rate of i

million rotations per minute. A bearing such as this operating on the Meissner

effect is much more convenient and safe than a conventional magnetic bearing because

of The 'self-centering' nature of the Meissner effect.

SAMPLEDATA

Figure I A neodymiummagnet levitated over a YBCOdisk in nitrogen.

Original figure not available.

73

I
INSTRUCTOR'SNOTES

Precautions

I. When pouring liquid nitrogen,be careful to prevent

any splashing. Read the section in the manual on

safety and handling (pages 10, 11, 28, & 29) before

beginningthe experiment.

2. Conduct the experimentsin a well-ventilatedroom.

3. Do not touch any items immersedin the liquidnitrogen with your hand until they have warmed to room

temperature.

SomeQuestions

I. Why doesthe liquidnitrogenboilwhenyou pourit intothedish?

2. Why does it boilwhenyou put the superconductordisk intoit?

3. When the nitrogenhas evaporated,themagnetstayslevitatedfor manymore

minutes. Why is thisso? Canyou thinkof any otherexperimentsusingthis

fact?

4. Ifyou push the levitatedmagnetwiththe tweezersso as to move it acrossthe

superconductor,it willresistmovement.Why doesthishappen?

5. How canyou improvethe operationof themodelfrictionlessbearinginyour kit?

Thiswas a demonstrationof the Meissnereffect. Therearemany potentialapplicationsof thiseffect,for example:magneticallylevitatedtrains,frictionlessbearings,low vibrationmounts,etc. Canyou thinkof otherapplications?

The CriticalTemperatureof a superconductor(Tc)can be measuredby usingthe

Meissnereffect. For thispurposethe AdvancedDemonstrationKit alsocontainsa

specialdevicewith embeddedandcharacterizedthermocouplethermometer.

74
TITLE

HighTemperatureSuperconductors:Demonstrationof zeroresistanceand the

measurementof CriticalTemperatureTc.

AUTHOR

ColoradoSuperconductor,Inc.

555 SpindriftCt., P.O.Box8223,ForthCollins,CO 80526

PREREQUISITEKNOWLEDGEREQUIREDFORTHE EXPERIMENT

Previousexperiencewithelectricalpowersuppliesand voltmetersis desirable

but not essential.All experimentalprocedures,safetyand handlingprecautions,

and backgroundinformationis containedin the instructionmanualwhichis

providedwitheach setof materialsin the kit.

OBJECTIVES

Demonstrationof zeroelectricalresistancein the new ceramicsuperconductors

belowtheirCriticalTemperatureTc.

Accuratemeasurementof the CriticalTemperatureusingthe fourpointprobeand

the attachedthermometer.

Formore sophisticatedstudents,measurementof theCriticalCurrent,Critical

MagneticField,and the reverseac Josephsoneffect.

EQUIPMENTAND SUPPLIES

The UniversityDemonstrationKit, which consistsof an electricalfour point probe

device with attachedthermometer,a I inch diameterYBCO superconductordisk,

neodymiumand samariumcobalt magnets,nonmagnetic tweezers,and an extensive

instructionmanual.

Liquidnitrogen.Abouta pintshouldbe sufficientfor one experiment.

A smallDewarflaskto holdand transportthe liquidnitrogen.

A constantcurrentsource,or a powersupplyoperatingin the currentlimitedmode.

The outputshouldbe 0.5Amp.

An ammeteror secondvoltmeter(witha currentshunt)to measurecurrentflow.

A digital voltmeterwith a 10 microvoltresolutionto measurethe voltage dropacross

the voltageprobes.

Forthe measurementof the CriticalMagneticField,a I Teslamagneticfieldsource.

Forthe reverseac Josephsoneffect,an ac signalsourcewith a tunablefrequencyof

up to about20 MHz and a peak-to-peaksignalof 10 Volts.

75
THE FOURPOINT ELECTRICALPROBE

When a simple measurement of the resistance of an electrical test sample is performed

by attaching two wires to it, one inadvertently also measures the resistance of the

contact point of the wires to the sample. Typically the resistance of the point of

contact (called contact resistance) is far smaller than the resistance of the sample,

and can thus be ignored. However, when one is measuring a very small sample

resistance, especially under variable temperature conditions, the contact resistance

can dominate and completely obscure changes in the resistance of the sample itself.

The way out of this problem is to use the four point probe technique, which eliminates the effects of contact resistance. A schematic of a four point probe is shown

in figure 2. In this diagram, four wires (or probes) have been attached to the test

sample. A constant current is made to flow the length of the sample through probes

labeled 1 and 4 in the figure. This can be done using a current source or a power

supply as shown. Many power supplies have a current output readout built into them.

If not, a digital ammeter, or even another voltmeter can be used to obtain the value

of the current. A power supply capable of producing between 0.5 Ampto 1.0 Amp is

required for the superconductor four point probe device in the kit.

If the sample has any resistance to the flow of electrical current, then there will

be a drop of potential (or voltage) as the current flows along the sample between the

two wires (or probes) labeled 2 and 3 in the figure. The voltage drop between probes

2 and 3 can be measured by a digital voltmeter. The resistance of the sample between

probes 2 and 3 is the ratio of the voltage registering on the digital voltmeter to

the value of the output current of the power supply. The high impedance of the

digital voltmeter minimizes the current flow through the portion of the circuit

comprising the voltmeter. Thus, since there is no potential drop across the contact

resistance associated with probes 2 and 3, only the resistance associated with the

sample between probes 2 and 3 is measured.

PROCEDURE

The four point probe device is encapsulated in a brass jacket to protect the superconductor from mechanical and thermal stresses. The device has 6 wires. Four of

these wires form the probes and are described in the next section. The red and blue

pair of wires is connected to a low temperature thermocouple embedded in the superconductor incorporated in the four point device. This thermocouple can be used to

determine the temperature of the superconductor. A characterization table for this

thermometer is included in the instruction manual.

dc _wer S Ammeter

I Oigital

voltmeter

Test

sample

Current

probe 1 2

Current

Voltage probe

probes

Figure 2 Schematic of a four point probe.

76
Measuring Tc and the effects of temperature on device resistance

This experiment and the measurement of Hc and Ic use the superconducting four point

probe device described in this section. This experiment measures the change in

resistance of the superconductor with a change in its temperature. As a part of this

experiment, the critical temperature, Tc, of the superconductor is also obtained.

Voltage probes

Seal / 2 & 3

J _///Curfent

_'- lPr_ebs4

Thermocouple

leads

_/_lack current

Superconductordisk //_ probes1&4

Brassshield / '_eHowvoltage

I'l I " o,, ooeo,eve,

Figure3 The superconductingfourpointprobeconfiguration.

The fourpointprobedevicewith itsthermocoupleis shownin figure3. The pairof

blackwiresare the currentsourceprobes,and are labeledI and 4 in figure2. The

pairof yellowwiresare the voltagemeasurementprobes,and are labeled2 and 3 in

figure2. The pairedblueand redwiresareattachedto the thermocouplejunctionin

thedevice. Duringthe experiment,the fourpointdeviceis laidflat in the shallow

dish in the kit so thatthe blackdisk superconductoris on the top,and the red

plasticseal is at the bottom. The 6 wiresarecarefullybentso thattheyextend

abovethe deviceand out of the liquidnitrogenas shownin figure3. Whenliquid

nitrogenis pouredoverthe device,it shouldcoverthe superconductordisk,but the

endsof thewiresshouldprojectabovethe surfaceof the liquid. All electrical

connectionshouldbe madeabovethe surfaceof the liquid.

77
The voltmeterslistedin the sectionentitled,"EquipmentandSupplies",shouldbe

connectedas shownin figure2. Alternatively,a stripchartrecorderwith a 10

millivoltfull-scalerangeand a resolutionof 10 microvoltsmay be connectedbetween

probes2 and3. Thiswill providea continuousrecordof the voltagedrop. If a

two-channelrecorderor xoy plotteris used,thenthe thermocouplereadingcan also

be measuredsimultaneously.The currentsourceor powersupplyshouldbe set to

producea currentof about0.5 amp throughprobesI to 4,

The followingis a stepby stepguideformeasuringthe deviceresistanceversusits

temperature:

I. Set up equipmentas describedin the last paragraph,but

do not yet pour any liquidnitrogenover the device. The

voltage drop between probes 2 and 3 should be between 2 to

5 mV.

2. Carefullypour liquidnitrogenover the device until it is

just submerged.

3. Whenthe devicehascompletelycooled(asdeterminedby

the thermocouplereading),use the tweezersto removethe

devicefromnitrogenand set it on the benchtop. The

devicewill startto warmup. The thermocouplereading

will indicatethis.

Alternatively,the device can be allowed to warm as the

liquid nitrogenevaporates.

4. As the devicewarmsto aboveitscriticaltemperature,the

voltagedropacrossprobes2 and 3 w_llabruptlyincrease.

The temperatureat whichthisabruptincreaseoccursis

the criticaltemperatureof the superconductor.

The ratioof the voltagebetweenprobes2 and3 to currentflowingbetweenprobesI

and4 is the instantaneousresistanceof the superconductorbetweenprobes2 and

3. If thisresistanceis plottedversusthe thermocouplereading,a resultsimilar

to that in figure4 willbe obtained.A stripchartrecorderwillmuchmore

convenientlyrecordthisresult.

78
SAMPLEDATA

>__.-

II

v_

-0

Temperature from thermocouple

I 1 -

77K 90K

Figure4 Graphof resistancevariationwith temperature.

Some questions

I. Whateffectwouldone expectif the criticaltemperatureis

measuredwiththe deviceplacedinsidea functioning

electromagnet?

2. Why is the transitionin resistancegradualat thecritical

temperature?

3. A simpletwo probemeasurementof deviceresistancebelowits

criticaltemperaturexhibitsa non-zerovalue. Why?

79
Measuringthe Critical Magnetic Field, Hc

This experimentmeasures the criticalmagnetic field Hc, of a i-2-3 YBCO superconductor using the four point probe device in the UniversityDemonstrationKit.

For this experimentyou will need a magneticcoil and associatedpower supply. The

value of the field can be obtained using the geometryof the coil and a knowledgeof

the current flowing through it. The cavity in the middle of the coil needs to be

large enough to accommodatethe four point device and the liquid nitrogencontainer

in which it is immersed. To ensure accuracyduring this experiment,the four point

probe device has been designedwith no magnetic parts.

Assemble the experimentas for the measurementof the critical temperatureTc. Place

the four point device and its containerof liquidnitrogen inside the cavity of the

electromagnetcoil. Increasethe current flowingthrough the electromagnetcoil thus

increasingthe magnetic field strengthat the superconductor. The signal between the

voltage probes 2 and 3 will show an abrupt increaseat some value of applied magnetic

field strength. This value of magneticfield is the criticalmagnetic field Hc, for

the YBCO superconductorsample at the temperatureof liquid nitrogen,77 Kelvin.

The value of the criticalfield Hc, can be obtainedat other temperaturesby either

placing the device in a cryostatwhile performingthis experiment,or by removingthe

device from the liquid nitrogencontainerand monitoringthe output of the

thermocouplethermometerwhile measuringHc.

Another interestingexperimentis to measure the criticaltemperatureat different

applied magneticvalues. The result of such an experimentis shown schematicallyin

figure 5. The value of Hc has been extrapolatedto absolutezero temperature.

SAMPLE DATA

Q

0

hv

Applied magnetic field

Figure5 Variationof CriticalFieldwith operatingtemperature.

80
Measuring the Critical Current, Xc, and the Current Density

The four point device can be used to measure the criticalcurrent Ic, and also the

maximum current density of the I-2-3 YBCO superconductor. However,since the value

of current needed for this experimentis so large, great care must be exercised

during its execution. In fact, if the instructionsare not followedexactly,or the

high current is left flowing throughthe device for an extendedperiod of time, it

could be severelydamaged.

For this experiment,a power supplycapable of putting out a current of about 15 amp

across a resistanceof about I ohm is needed. Connect the device to the digital

voltmetersand power supply as explainedin the section for measuringthe critical

temperatureTc. Here however,conductthe entire experimentwhile the device is

submergedunder liquid nitrogen. The liquidnitrogenserves the additionalfunction

of keeping the device and the connectingwires cool. The wires themselvesare only

marginallyable to carry the large electricalcurrent values needed. So, they too

must be kept submergedin the liquid nitrogen.

When the two voltmetersare set,graduallyincreasethe currentthroughprobesI and

4 whilemonitoringthe voltagedropbetweenprobes2 and 3. When the currentvalue

throughprobesI and 4 exceedsthe criticalcurrentvaluefor the superconductor,the

voltagedropbetweenprobes2 and 3 will abruptlyincrease.We havefoundthatthe

criticalcurrentis about10 amp for thedeviceconfigurationused. This is the

valueof Ic at the 77 Kelvintemperatureof liquidnitrogen.

Alternatively,one can measure the change in Tc at differentvalues of current

through the current probes I and 4. This, however,necessitatesthe removal of the

device from liquid nitrogenwhich in turn has potentialfor damagingthe device.

The criticalcurrentdensitycan be obtainedby a geometricanalysisof the current

flowthroughthe devicefor the valueof thecriticalcurrent. Forthis analysisthe

followinginformationis of use. The samplediameteris 24 mm. The distancebetween

probes2 and 3 is 11 mm, and probesI and 4 is 17.5mm. The sampleis 4 mm thick.

81
TheReverse ac JosephsonEffect

In 1962 Brian Josephsonshowedthat if there is a very thin electricallyinsulati_q

film between two pieces of superconductor,then contraryto expectations,there will

continueto be a flow of electricalcurrent right through the insulator. This

superconductingcurrent is called a supercurrent. This phenomenoncan only be

explainedby the esoteric field of quantum mechanics.

The new superconductingmaterials,likethe one in thiskit,are verygranular.The

individualgrainsare believedto be superconductors.But,eachgrainis separated

fromthe next by what scientiststhinkis a verythinfilmof insulator.One would

thenexpectthe sameJosephsoneffectthroughthesethininsultingfilmstoo. In the

terminologyof the new ceramicsuperconductors,thesemultipleJosephsonjunctions

are called"weaklinks'.

One way to actuallyobserve the Josephsonsupercurrentis to perform the following

experiment. In this experiment,a high frequencyac current is imposed on the

superconductor. One will then observe adc voltage across the superconductoralong

the same directionas the applied ac signal. This is called the reverse ac Josephson

effect.

For this experimentone will need an ac signal sourcewith a variablefrequency

capable of up to about 20 MHz and a peak to peak output of about 10 Volts,appropriate

connectingwires, and a good voltage measurementsystem.

Connect the ac signal sourceto the current probes I and 4 of the four point probe

device. Attach a digital voltmeterset for measuringdc voltage in the millivolt

range between probes 2 and 3 of the device. The measureddc potentialbetween probes

2 and 3 varies between I to 2 millivoltswith a peak responseat an applied signal of

frequencyI to 3 MHz. This result is shown schematicallyin figure 6.

Another interestingresult is that if one approachesthe surface of the superconductor disk with a magnet (for example the rare earth magnets in the kit), a decrease

in the dc signal level is seen.

The experimenthas the followingverysignificantfeatures:

i. It is a macroscopicdemonstrationof a quantummechanical

approach.

2. It exhibitsthe fundamentalbasis of the Josephsoneffect.

This effect is expectedto be of great importancein

buildingthe superfastcomputersof the future.

3. It is a very sensitiveway to show that a material is

superconducting. Scientistsfrom Wayne State University

used it to show that some of these materialsmay have

a superconductingphase at temperaturesat high as

240 Kelvin.

82
S/_PLE DATA

2

IL

1 2 3 10

Al::)Ohed IIC signal fr<l_j_y 0k4HZ_

Figure 6 Plot shows the dc voltage as functionof ac frequency.

INSTRUCTOR'SNOTE

Precautions

I. When pouring liquid nitrogen,be careful to prevent

any splashing. Read the section in the manual on

safety and handling (pages10, 11, 28, & 29) before

beginningthe experiment.

2. Conduct the experimentsin a well-ventilatedroom.

3. Do not touch any items immersedin the liquid nitrogen with your hand until they have warmed to room

temperature.

83

ATTENDEES

ANDREJASIK, HENRY ASPER, NORMAN L.

L_IVERSITY OF PITTSBURGH TRENTON STATE COLLEGE

837 BENEDUM HALL DEPT MECH/IND. ENG.

PITTSBURGH, PA 15261 TRENTON, NJ 08650

412-624-9723 609-771-2774

BEASLEY, GEORGE A. COLEMAN, CLARENCE

CENTRAL VIRGINIA COMMUNITY COLLEGE NORFOLK STATE UNIV

3506 WARDS ROAD DEPT OF PHY & ENG

LYNCHBURG, VA 24502 NORFOLK, VA 23504

804-386-4651

COWAN, RICHARD DIETER, GEORGE

OHIO NORTHERN UNIV. UNIV OF MARYLAND

MEC_A_NICAL ENG. COLLEGE PARK, MD 20742

ADA, OH 45810 301-454-6347

419-772-2383

DUI_, JEROME EFIMBA, ROBERT E.

PARKERSBURG COMMUNITY COLLEGE HOWARD UNIVERSITY

ROUTE 5, BOX 167A 2300 SIXTH ST., NW

PARKERSBL_G, WV 26101-9577 WASHINGTON, DC 20059

304-424-8258 202-636-6574

FRAKER, L\'NA GILMORE, CHARLES

NATIONAL Bb_EAU OF STANDARDS GEORGE WASHINGTON UNIV

MATLS B261 SCHOOL OF ENG

GAITHERSBL_G, MD 20899 WASHINGTON, DC 20052

301-975-6009

GULBR_XSEN, L. B. R_dRRIS, JONiCE

WASHINGTON L_IVERSITY NATIONAL BUREAU OF STANDARDS

MECHANICAL ENG. B261, MATERIALS

ST. LOUIS, MO 63130 GAITHERSBURG, MD 20899

314-889-6073 301-975-6007

HARRIS, GARY HEGENBERGER, WILLIAM

HOWARD UNIV US COAST GUARD ACADEMY

ELECTRICAL ENG DEPT DEPT OF ENG

WASHINGTON, DC 20059 NEW LONDON, CT 06320

HOUSLEY, RHONDA

SPARTANBURG TECH COLLEGE HUNT, CHARLES

DRAWER 4386 NORFOLK STATE UNIV

SPARTANBD_G, SC 29305 NORFOLK, VA 23504

803-591-3659

85
JACOBS, JAMES A. JOHNSON, RONALD

NORFOLK STATE UNIV NATIONAL BUREAU OF STANDARDS

SCHOOL OF TECHNOLOGY B309, MATERIALS BLDG

NORFOLK, VA 23504 GAITHERSBURG, MD 20899

301-975-5658

KNABACK, WAYNE

KILDUFF, THOMAS SOUTH DAKOTA STATE UNIV

NORFOLK STATE UNIV ELECTRICAL ENG. DEPT

NORFOLK, VA 23504 BROOKINGS, SD 57007

605-688-4526

KRALL, DAVID MC KENNEY, ALFRED

NORFOLK STATE UNIV NORFOLK STATE UNIV

NORFOLK, VA 23504 NORFOLK, VA 23504

METZLOFF, CARLTON NAGY, JAMES P.

ERIE COMMUNITY COLLEGE ERIE COMMUNITY COLLEGE

MAIN & YOUNGS ROADS MAIN & YOUNGS ROAD

BUFFALO, NY 14221 BUFFALO, NY 14221

717-634-0800 X458 716-634-0800

NASH, SAMUEL K.

NASH, RALPH P. DREXEL UNIVERSITY

ADVENTURE IH SCIENCE 32ND AND CHESTNUT STREETS

PHILADELPHIA, PA 19104

215-895-1540

NEVILLE, JOSEPH PALUMBO, ROBERT

WENTdORTH INSTITUTE VALPARAISO UNIVERSITY

550 HUNTINGTON AVE. GELLERSEN HALL

BOSTON, MA 02115 VALPARAISO, IN 46383

617-846-2626 219-464-5135

PARSONS, ROBERT B. PIERCE, DONALD N.

BAKERSFIELD COLLEGE UNIVERSITY OF NEBRASKA

1801 PANORAMA DRIVE DEPT OF ENG. MECHANICS

BAKERSFIELD, CA 93305 LINCOLN, NE 68588-0347

805-395-4220 402-472-2385

POND, ROBERT F. RAUT, PRAVIN

JOHNS HOPKINS UNIV SAVANNAH STATE COLLEGE

MTLS SCI & ENG P.O. BOX 20489

BALTIMORE, MD 21218 SAVANNAH, GA 31404

301-338-7125 912-356-2282

REIS, HEIDI ROBERTS, THOMAS E.

NORFOLK STATE UNIV MILWAUKEE AREA TECHNICAL COLLEGE

NIMAS 700 WEST STATE ST.

NORFOLK, VA 23504 MILWAUKEE, WI 53233

414-278-6891

86
SASTRI, SANKAR

NEW YORK CITY TECHNICAL COLLEGE SHULL, ROBERT

300 JAY AVE. NATIONAL BUREAU OF STANDARDS

BROOKLYN, NY 11201 GAITHERSBURG, MD 20899

708-643-5015

SMITH, ROBERT E. SMITH, CARL

JEFFERSON TECHNICAL COLLEGE PAR!iERSBURG COMMUNITY COLLEGE

4000 SUNSET BLVD. ROUTE 5, BOX 167A

BLOOMINGDALE, OH 43952 PARKERSBURG, WV 26101-9577

614-264-5591 X272 304-424-8202

SRINIVASAN, MALUR N. TAVEL, JUDITH

TEXAS A&M UNIVERSITY DUTCHESS COMMUNITY COLLEGE

DEPT OF MECH ENG PENDELL ROAD

COLLEGE STATION, TX 77843-3123 POUGHKEEPSIE, NY 12601

409-845-1417 914-471-4500

THOMPSON, A. LANCE UZ, MEHMET

MODESTO JR. COLLEGE LAFAYETTE COLLEGE

3309 CHALFANT COURT 341 DANA HALL

MODESTO, CA 95350-9977 EASTON, PA 18042

209-575-6245 215-250-5408

87


.at,o. Space Administration Aoro. ., . t, .an. ReportDocumentationPage

1. Report No. I 2. Government Accession No. 3. Recipient°sCatalog No.

NASA CP-3060 I

4. Title and Subtitle 5. Report Date

National Educators' Workshop: Update 88 January 1990

Standard Experiments in Engineering Materials Science and 6. PerformingOrganization Code Technology

7. Author(s) Compilers; 8. Performing Organization Report No.

James E. Gardner - NASA Langley Research Center, Hampton, L-16732

Virginia and 10. WorkUnitNo.

James A. Jacobs - Norfolk State University, Norfolk, Virginia 505-63-01-15

9. Performing Organization Name and Address

NASA Langley Research Center 11. Contractor Grant No.

Hampton, Virginia 23665-5225 NAG1-976

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration Conference Publication

Washington,D.C.. 20546-0001 and 14.Sponsoring AgencyCode

National Institute of Standards and Technology

Gaithersburg, Maryland 20899

15. Supplementary Notes

James E. Gardner, Compiler- NASA Langley Research Center, Hampton, Virginia;

Jonice Harris, Workshop Co-Director - National Institute of Standards and Technology,

Gaithersburg, Maryland; and

James A. Jacobs, Compiler and Co-Director - Norfolk State University, Norfolk, Virginia

16. Abstract

This document contains a collection of experiments presented and demonstrated at the National

E _ ducators Workshop: Update 88, held May 10--12, 1988 at the National Institute of Standards and

Technology (NIST), Gaithersburg, Maryland. The experiments related to the nature and properties of

engineering materials and provided information to assist in teaching about materials in the education

community.

17. Key Words (Suggested by Author(s)) 18. Distribution Statement

Materials Unclassified - Unlimited

Experiments

Education Subject Category - 23

Unclassified Unclassified 1291

,.+.oA05,+122

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