ORNL-3373.txt

\ 1 1969

AN

ORNL=3373
UC=-80 — Reactor Technology
TI1D-4500 (18th ed.)

MAGTER

THERMAL ANALYSIS AND GRADIENT
QUENCHING APPARATUS AND TECHNIQUES
FOR THE INVESTIGATION OF FUSED
SALT PHASE EQUILIBRIA
H. A. Friedman

G. M. Hebert
R. E. Thoma

OAK RIDGE NATIONAL LABORATORY
operated by

UNION CARBIDE CORPORATION
for the

U.S. ATOMIC ENERGY COMMISSION

DISCLAIMER

This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor any agency Thereof, nor any of their employees,
makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any
agency thereof. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States
Government or any agency thereof.
DISCLAIMER

Portions of this document may be illegible In
electronic image products. Images are produced
from the best available original document.
Printed in USA. Price: $0.75 Available from the
Office of Technical Services
U. S. Department of Commerce
Washington 25, D, C.

LEGAL NOTICE

This report was prepared as an account of Government sponsored work. Neither the United States,

nor the Commission, nor any person acting on behalf of the Commission:

A. Makes any warranty or representation, expressed or implied, with respect to the accuracy,
completeness, or usefulness of the information contained in this report, or that the use of
any information, apparatus, method, or process disclosed in this report may not infringe
privately owned rights; or

B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of
any information, apparatus, method, or process disclosed in this report.

As used in the above, '‘person acting on behalf of the Commission’’ includes any employee or

contractor of the Commission, or employee of such contracter, to the extent that such employee

or contractor of the Commission, or employee of such contractor prepares, disseminates, or
provides access to, any information pursuant to his employment or contract with the Commission,
or his employment with such contractor.

ORNL-3373

Contract No. W-7405-eng-26

REACTOR CHEMISTRY DIVISION

THERMAL ANALYSIS AND GRADIENT QUENCHING APPARATUS AND
TECHNIQUES FOR THE INVESTIGATION OF FUSED SALT
PHASE EQUILIBRIA
H. A. Friedman, G. M. Hebert,

and
R. E. Thoma

DATE ISSUED

JBH & - 1963

OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee
operated by
UNION CARBIDE CORPORATION
for the
U.S. ATOMIC ENERGY COMMISSION
~ THIS PAGE
WAS INTENTIONALLY
LEFT BLANK
lf“ i
-~

o)

iii
CONTENTS
Abstract . . . . . . . o . 0 . .
Introduction e e e e e e e e e
Methods . . . . .+ « ¢« ¢ « « .+ o .
Direct Thermal Analysis « v e e
. Normal Procedure . . . . . . .
Special Procedure . . . . .
Quenching Techniques . . . . . .
Preparation of Samples . . .

Preparation of Quench Tubes
Tubes for Non-volatile Salts
Tubes for Volatile Salts . .

Quench Furnaces . . « .« + .« .

Furnaces with Stationary Thermocouples

Furnaces with Traveling Thermocouples

Accuracy and Precision of Measurement

Acknowledgment . . . . . . . . .

References . « ¢« o« o o o o+ o o o &

Page

28

29
THERMAL ANALYSIS AND GRADIENT QUENCHING APPARATUS AND
TECHNIQUES FOR THE INVESTIGATION OF FUSED SALT PHASE EQUILIBRIA

H. A. Friedman, G. M. Hebert,
and
R. E. Thoma

ABSTRACT

A detailed description is presented of appara-
tus and methods used at ORNL for determination of
high temperature equilibrium phase relationships in
condensed systems of molten salts. Principal empha-
sis is given to experimental techniques required
for investigation of non-volatile hygroscopic fluor-
ides. Equilibrium phase behavior is elucidated by
thec combined results of experiments in which measure-
ments are made of the thermal effects occurring on
melting and freezing polycomponent mixtures, and
others in which unequivocal identification of solid
phases formed during crystallization is obtained.
Apparatus devised at ORNL for use in preparation,
purification, equilibration, and handling of mater -
ials for application in fluoride'phase studies is
described in detail. The methods and techniques
described are unique in providing such large quan-
tities of phase data that phase diagrams of complex

systems may be constructed in a relatively short time.
—2-

INTRODUCTION

The advent of molten salts in nuclear reactor technology
as fuels, converter-breeder blankets, heat transfer fluids,
and reprocessing media for spent fuel elements has necessi-
tated a large number of phase equilibrium investigations.
Although many experimental methods have been applied in stud-
ies of phase equilibria at elevated temperatures,1 e.g.,
through measurements of thermal expansion, magnetic proper-
ties, viscosity, thermodynamic properties and crystallization
equilibria, only the latter two of these methods are suited
for rapidly acquiring the large number of data needed in
constructing complex phase diagrams. These two general
methods have therefore bheen applied for several years to in-
vestigations of molten salt phase equilibria at ORNL. Adapt-
ations of experimental methods to specific problems obviously
require consideration of the most annoying properties‘of the‘.
" materials to be studied and moditfication of the methods to per-
mit investigation of the materials despite their intransigence.
Molten halidés at elevated temperatures possess an impressive
list of these characteristics. It is the purpose of this
report to furnish detailed descriptions of the practical pro-
cedures which have found spepial application at ORNL.for in-
vestigations of molten salt phase equilibria.

Phase equilibrium diagrams are generally derived from
two kinds of experiments, those from which deductions are
made from measurements of thermal effects.occurring in

heating and cooling curves, and those which permit a direct
o,

-3

or indirect identification of the numbers and compositions
of phases occurring at all temperature-composition points.
Commonly, fused salt diagrams are based on information

from cooling curves. Changes in slope of the temperature

of the sample, when plotted as a function of time, reflect
phase changes which occur on cooling. This technique is
generally adequate for determining all except the steep-

est liquidus curves; steep curves represent small changes in
saturation concentrations with temperature and hence small
heat effects. Cooling curves also provide information on
the solidus and subsolidus phase changes, but are prone to
give misleading indications because of the impossibility

of maintaining equilibrium during cooling. Phase transitions
inferred from cooling curves are Qerified by quenching of
equilibrium samples and an identification of the phases by
crystallographic examination with microscopic and X-ray
diffraction techniques. Chief interest.in salt phase
equilibria has focused on the fluorides and chlorides of the
actinide elements and on low melting solvents for these
fissile and fertile materials. Such salts vary'widely with
respect to their hygroscopic character. It is necessary to
employ experimental techniques which maintain a genuinely
anhydrous environment for these salts. Though the tri- and
tetrafluorides of the actinides, rare earths and zirconium
are not hygroscopic, they are easily hydrolyzed at elevated

temperatures. It is necessary, therefore, if the sample
e
under examination is to be free from extraneous phases due
to the presence of oxides or oxyfluorides, to remove all
water and to protect the heated sample from contact with air.
METHODS
Direct Thermal Analysis
Two techniques have been developed for obtaining thermal-
analysis data. These have evolved as a '"'mormal" procedure,
employed for mixtures whiéh are known to be non-hygroscopic,
and a "special' procedure, employed for hygroscopic mixtures.

- Normal Procedure

A convenient means of accommodating four samples in graph-
ite or nickel crucibles is shown in Figure (1). The graphite
crucibles, 5 1/2" high, 1 5/8" o.d., with a wall thickness of
1/8", are Tabricated from high density graphite; the nickel
crucibles, 5 1/2" high, are constructed from 1 1/2" tubing
with a 1/16" wall thickness. A graphite disc, approximatoly
the size of the internal diameter of the crucible and with
two holes to admit the stirrer and thermocouple well, may be
inserted into the crucible on top of the sample if thc major
ingredient has an appreciable vapor pressure. The disc re-
duces the volatilization of the sample by floating on the
melt thus decreasing the liquid surface area. An annealed
copper gasket between the flange of the reactor vessel and
the 1id acts as a seal when the assembly is fastened together
with three clamps.

Nickel stirrers of 1/8" diameter shanks and 14" in length

are inserted into the melts through closely fitting sleeves
"x

W

UNCLASSIFIED
ORNL-LR-DWG 622!13R

CRIVE BELT (COILED SPRING})

BUSHING (GRAPHITE)

/ALIGNER SUPPORT ROD (Al

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GAS OUTLET ~ GAS INLET

| — THERMOCOUPLE
VENT PLUG (GRAPHITE ) —a 1

7— SWAGELOK FITTINGS

VENT
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INCHES
I T T T T N I L
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Fig. 1. Reactor Vessel.
—b—

of graphite in the 1id of the assembly (Figure 2). A holder
capable of fine adjustments aligns the top of the stirrers
(Figure 3). The melts are protected from the atmosphere by
maintaining a small positive pressure of helium,'purified by
passage through a liquid nitrogen-charcoal trap, in the as-
sembly. Leakage of helium through the graphite bushings on
the 1lid prevents diffusion of air to the molten mixture. Pow-
er %S supplied to the stirrer through the bclt of coilcd
spring (Figure 1); slippage of the belt prevents possible dam-
age to the drive motors. Temperatures are measured with
Chromel-Alumel thermocouples in a thin walled (10 mil) nickel
thermocouple well immersed in the melt. The e.m.f.'s are
measured using Minneapolis Honeywell "Electronik" Recorders
that are frequently calibrated with a potentiometer.

To remove oxide and water vapor, 10 grams of ammonium .
bifluoride* are added to each crucible followed by the sample. .
The crucibles are then loaded into the reactor vessel and the
reactor is assembled and placed into a 5" pot furnace. The
stirrers are aligned and the furnace heated until the ammonium
bifluoride becomes molten, 120-225°C. These low temperatures are
maintained for at least one hour before heating to elevated
temperatures. Fuming of ammonium bifluoride occurs until ap-

proximately 550°C. When evolution of the fumes is no longer

*Ammonium pifluoride will react with a number of oxides, in-
cluding those of uranium, zirconium, yttrium, aluminum, beryl-
lium, cobalt, iron, vanadium, cerium, and chromium (valence
6) to form fluorides. Nickel and chromium (valence 3) oxides
will not be fluorinated with ammonium bifluoride. (Private
communication from B.J. Sturm, Reactor Chemistry Division,
ORNL. )
UNCLASSIFIED
ORNL-LR-DWG 62215

VENT HOLE FOR THERMOCOUPLE (4}

T
e GAS INLE

LID (Ni)

~
T~ GAS QUTLET

[

Fig. 2. Reactor Vessel Top.
UNCLASSIFIED
ORNL-LR-DWG 62214

ALIGNER .SUPPORT ROD (Al)
- ADJUSTMENT SCREW

Fig. 3. Stirrer Rod Aligner.
-9-

observed, the escape vent (Figures 1 and 2) is closed with a
graphite plug, Fiberfrax insulation is packed on the top of
the reactor and the stirrer motors are started. One of sev-
eral electric timers can start or stop any part of the equip-
ment mechanically. A mineral oil bubbler located in the gas
exit line is used to check for a positive pressure.

The furnace is cooled after the temperature has reached
approximately 100°C above the highest estimated liquidus of
any sample and the ingredients of each sample have melted
and mixed. The rate of cooling is regulated by controlling
the voltage to the furnace with an auto-transformer. The
heating and cooling cyclcs are usually repeated with the cool-
ing rate varied to verify Llhe thermal data. It is possible
to magnify the thermal effect by increasing the sample size
and by decreasing the cooling rate. An approximately optimal
choice of sample size appearé to be 50 g. This sizé choice
is a compromise of desirably larger sample sizes with the
convenience of employing laboratory scale equipment. Suit-
able cooling rates for such sample sizes are 3-49C/ min.

A complete heating and cooling cycle requires about 6 hours.

Special Procedure

To obtain equilibrium cooling curves and quench data in
systems of hygroscopic salts all manipulations except weigh-

ing the starting materials are performed in a vacuum dry-box.
-10-

Samples are purified in the same manner as described in the
other procedure and melted 1in a 5" pot furnace set into the
floor of the dry-box. Ammonium bifluoride fumes are exhausted
through alnickel funnel (Figure 4). 1In use, the funnel is
placed over the furnace well and sealed to the well with the
teflon gasket. Fumes evolved during the ammonium bifluoride
purification step are pulled by a vacuum pump in turn through
the funnel, a rubber hose, and 3/4" diameter copper tubing in-
to a soda lime trap and into a - sulfuric acid trap. The fun-
nel is placed in its rack at the back of the dry-box when
fuming is complete, as indicated b& the temperature of a
thermocouple fitting into a well in the nickel funnel; the
stirring mechanism, which also contains the thermocouple wells,
is then positiqned over the heating'well after it has been
removed from its holder (Figure 5). One thermocouple well

and one stirring rod areinserted into each crucible. A single
motor rotates the four stirrers which have slip clutches to
permit the motor to revolve without damage when the melts
freeze, Temperatures are measured and recorded using Chromel-
Alumel thermocouples inserted into the dry-box through Conax
fittings*.

An atmosphere of érgon gas, dried by passing through mag-

nesium perchlorate and dry ice-trichloroethylene traps, is

maintained in the dry-box. The dry-box entrance chamber is

* Made by Conax Corp., 2300 Walden Avenue, Buffalo 25, New York,
UNCLASSIFIED
PHOTO 562814

CONAX FITTINGS
FOR THERMOCOUPLE

9/, 3/1-i~. Cu LINE TO

D e sooyLive Rap if
i | vfi. ; b

GASKET
o "

NICKEL FJNNEL

!

STIRRER
MECHANISM |

=P

FURNACE

Fig. 4. Vacaum Dry-Box.
-12-

PHOTO 36217

(o)
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————— T A

Mechanism.

Stirrer

Ds

Fig.
-=]3=

evacuated and refilled with dried argon after each transit through
the cham ber. Metal plates cover the glove ports when the
dry-box is evacuated and when the ports are not in use. The
atmosphere is circulated inside the box over several trays of
P,0; to absorb any moisture. An oxygen-free dry atmosphere
must be maintained in the box. In usual operation with closed
glove ports, the water content of the dry-box atmosphere can
be maintained at about 20 ppm.
Quenching Techniques

Purified melts from the thermal analysis procedure may
be further used by being equilibrated at and quenched from
elevated temperatures to verify the transition temperatures
and to observe the phases present at the transitions. Quench
tubes containing 25-28 sample segments are equilibrated in
gradient quench furnaces over pre-determined temperature
ranges and then rapidly cooled. Methods used to interpret
thermal gradient quenching data have been discussed in reports
of fluoride phase investigationsz_4 and will not be treated
here.

Preparation of Samples

Specimens to be equilibrated are obtained from either of
the thermal analysis procedures, purified by a special prepar-
ation described below, or prepared from pure components. The
samples which have been purified in the normal thermal analysis
procedure are transferred into a dry-box, ground with an elec-

tric mortar and pestle to <100 mesh, bottled, removed from the
~14-

dry-box and homogenized on a converted ball mill (Figure 6)

for approximately 16 hours. These bottles, sealed with a
coating of paraffin and beeswax, are clamped into place on

the face plate. After mixing, the samples are returned to

the dry-box and loaded into quench tubes. Hygroscopic samples,
purified in the special thermal analysis procedure, are homocg-
enized by hand mixing within the dry-box rather than external-
1¥a

Preparation of quench tubes

Tubes for non-volatile salts.- A rolling and crimping

machine (Figure 7)5 has been constructed to insure equal sam-
ple spacing in the quenching tube and to lessen the time re-
quired for loading. A nickel tube 6-1/2" long, 0.10" in out-
side diameter, and 0.010" in wall thickness which has been
annealed for 1 hour in a H, atmosphere at 800°C or a dried
platinum tube of similar size is rolled with the knurled
wheel to flatten all but 3/8" at one end. The flattened

tube has a void space 0.015" thick. The bottom of the tube
is then sealed by welding.

A sample is loaded by inserting the end of the sample
tube into the shaft of a specially constructed funnel (Fig-
ures 7 and 8). A small lip on the inside of the funnel shaft
prevents over-insertion of the tube. The tube is tapped
against a solid surface to insure complete filling, and then
crimped with pliers 3/8" from the top. The upper 3/8" is

cleared of powder, cleaned with a pipe cleaner and flattened
Fig.

6.

Mixer.

UNC_ASSIFIED
PHCTO 36190

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—
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Fig. 7.

Roller and Crimping Machine.

UNCLASSIFIED
PHOTO 30159
UNCLASSIFIED
ORNL-LR—DWG 70688

L

8. Loading Funnel.

Fig.
T B

with pliers. Care must be taken to see that this space is
well cleaned, for a small amount of the sample lodged in the
weld can prevent sealing of the tube. The tube is removed
from the box, flattened in a vise, crimped with the crimp-
ing wheel, and the end closed with a gas-oxygen torch. A
piece of wet cleansing tissue held around the upper portion
of the tube while welding prevents vaporization of the sample.

Tubes for volatile salts.=Nickel or platlinum queunclh tubes

prepared as discussed above are of little use for investi-
gating systems containing one or more components which exert
significant vapor pressure at elevated temperatures. An in-
novation in the tube design was made to minimize expansion

of crimped joints by volatile materials and migration of
salts within the tubes. The sample is loaded into an unflatten-
<d standard quench tube by means of a 16 gauge 6 1/2" Irving
caudal needle with plunger (Figure 10). The needle is in-
serted, after wiping, into the bottom of the quench tube and
the sample deposited by pushing the plunger; then the plunger
is retracted and the needle removed. A portion of the tube
where the sample is located (1/8'" in length) is flattened
along with a 1/8" portion above the sample by rotating the
wheel of the space crimping machine until an automatic stop
is reached (Figure 9). The next segment is loaded with the
needle, a stop released and the wheel rotated. The process
is continued until the tube is filled to within 3/8" of the

top. Another tube is loaded in the same manner, but 1/8"
UNCLASESIFIED

SAMPLE TUBE SAMPLE TUBE PHOTO 3€934A

ENTRANCE 5 ENTRANCE

Fig. 9. Space Crimping Machine.

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PHOTO 58356

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OAK RIDGE NATIONAL LABORATORY

Irving Caudal Needle - Plunger and Pair oI Quench Tubes.
~21-

more space is left at the top. When the tubes are inverted
this extra space allows the unfilled space in one tube to be
opposite a filled segment in the other. Two tubes are re-
quired to furnish an uninterrupted series of segments (Fig-
ure 10). The loaded tubes are removed from the dry-box,
flattened in a vise, and the ends welded with an oxygen-gas
torch. A piece of wet cleansing tissue used as mentioned
above prevents vaporizatibn of the sample. The unfilled
spaces between the samples are welded with an Ampower port-
able spot welder with electrodes modified to weld a 1/16"
spot.

Quench Furnaces

Furnaces with stationary thermocouples.-Two types of grad-
ient temperature furnaces have been developed as modifications
of the Tucker and Joy6 furnace, a furnace with stationary ther-
mocouples used for temperatures to 900°C and a furnace with
a traveling thermocouple for higher temperatures. The fur-
naces uscd for tcmperatures up to 900°C, have vertically
mounted nichrome wound ceramic cores* with several connections
to vary the length of the heated section and the temperature
gradient (Figure 11). Within the ceramic core a nickel sam-

ple block 10" long, 2" diameter with a center hole 9 1/2" long,

* The Alundum tube cores, 2 1/2" I1.D. x 16" long, used for Mar-
shall Tubular Test Furnaces, are purchased from Marshall
Products Company, 207 West Lane Avenue, Columbus 2, Ohio.
_22-

UNCLASSIFIED
ORNL-LR-DWG 52178R2

o
A

GAS INLET ~ BLOCK SUPPORT
TO TEMPERATURE
» CONTROLLER
Z POWER
= SOURCE
5 CONTROLLING
Y 1 THERMOCOUPLE
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SAMPLE TUBE SUPPORT ~~ o = SUPPORTING PLATFORM

Grodient Quenching Apparatus

Fig. 11. Type 1.
_23—

and 21/64" in diameter, bored lengthwise, is suspended. Eigh-
teen Chromel-Alumel thermocouples, spaced one half inch apart
along the length of the block, penetrate to within 1/32" of
| the central sample hole. As many as four sample tubes are
inserted into the central hole simultaneously on a pedestal
of known height. This pedestal rests on a pivot latch which
can be rotated to drop the tubes into the o0il bath for quench-
ing. The temperature of each segment of a tube is determined
by plotting the temperatures indicated from the thermocouple
voltages read with a potentiometer as a function of the po-
sition of each segment in relationship to the thermocouples.
I1f the samples are to be held at temperatures above 500°C
it is desirable to protect the container tubes from oxidation
by a flow of helium admitted through the block support via
a small tube. The furnaces are controlled to +1/4°C by auto-
transformers and by controllers containing proportional units,

Furnaces with traveling thermocouples.-0Other types of

furnaces (Figure 12) have been developed to anneal samples to
1200°C. since the Chromel-Alumel thermocouples have rela-
tively short life at temperatures above 900°C. The core* of
this furnace is woumnd to 1/2" of the top and to 5 1/2" of the
bottom with 20 gauge platinum wire. The quench block, a 2"

nickel rod 10" long, is bored lengthwise with two holes 9 1/2"

*Same core that is used in the other type furnaces.
¢

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CONTRCLLING THERMOCOUP

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GRADIENT QUENCHING APPARATUS

Fig. 12. Type 1I.

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HEATING COILS

(5G] HANDLE TO.

UNCLASSIFIED
ORNL=LR-DWG 25153R2

/‘fi’ FURNAGE INSULATION

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-25~-

deep to contain the samples and the thermocouple. The sam-
ple hole (21/64" in diameter) is centrally located and separ-
ated 1/32" from the thermocouple hole (3/16" in diameter).
Helium gas is used in this furnace as in others to prevent
the oxidation of the nickel sample tubes.

A temperature record of the thermal gradient is pro-
vided by a traveling thermocouple. A gear train and thread-
ed rod arrangement is operated to raise and lower the monitor-
ing thermocouple at a rate of from 2-8 in./hr. Temperatures
are recorded on a Honeywcll "Electronik" instrument adjusted
so that its chart speed is identical with that of the traveling
thermocouple. Two micro switches which activate relays are
arranged so as to reverse the direction of the‘thermocouple
when contact is made. The thermocouple travels a distance
of 6 1/2", equal to the length of the sample tube, before
reversing its direction. The thermocouple wire is enclosed
in one strip of ceramic insulator 12" long. To insure that
the thermocouple measures the tempefature over the length of
the specimen, it is clamped in the thermocouple holder (Fig-
ure 1l1) so that the tip of the thermocouple coincides with
the top and bottom of the specimen tube at the extremes of
travel. Since the output of the thermocouple is recorded on
a multi-span recorder whose rate of travel is synchronized
with the motion of the thermocouple, the temperature of each
section of the specimen tube is accurately determined. The

temperature of the furnace is controlled by a 28 ampere
-2 6—

Powerstat and a 1600°C controller with a proportional unit.

Because the temperature gradient is small at the top of
the furnace and increases downward, the position of the sam-
ple in the furnace, determined by the length of the nickel
sample supporting rod, partly determines the temperature
gradient along the specimen tube during annealing.

The quenching tube and the sample support are held in
the furnace by the supporting platform, which is attached
to the furnace by a spring mechanism; the tube is dropped
into an oil bath by fiulling the handle of the supporting
platform.

Accuracy and Precision of Measurement

In order to establish estimates of accuracy as well as
of precision, experiments are conducted occasionally in which
melting points of salfs are determined which have been accur-
ately established elsewhere. Typical statistical data from
averages of ten cooling curve determinations each with NaCl
and KC1 indicate melting points of 771+2 and 801+3°C, respec-
tively as compared with standard values fur Llhiese saltas of
770.3 and 800.4°C. In routine determinations of the melting
points of congruently melting complex fluoride compounds, e.g.,
7NaF.6UF,, the melting temperature is generally reproduced in
both cooling curve and quenching experiments to within +2°C.
The degree of precision apd accuracy for the observed tran-
sitions in a system depend upon several factors including the

properties of the system investigated, reliability of the
27—

thermocouples, and the gradient in the quench furnaces for

the quenching technique. The larger the gradient in the quench
fur naces, the greater the temperature increment for each seg-
ment. The specifications for Chromel-Alumel thermocouple wires
at ORNL permit a maximum allowable error of 0.75 % of reading.*
The temperature of the sample block thermocouple and the tem-
perature of a thermocouple in the sample hole opposite the
other thermocouple agreed within the limits of error of the
thermocouples for all thermocouples in every qQuench furnace.
Estimates of the precision obtained in measuring phase tran-
sition temperatures are derived by correlation of (a) tran-
sition temperature measurements as a function of composition
within a specific system, (b) extrapolation of transition tem-
perature data in an n-component system to one of its n-1 com-
ponent limiting systems, and (c) repetition of annealing and
quenching experiments using several of- the furnaces employed
in the phase studies. The precision limits of these inter-
nal calibrations appear to be within x2°C.

Equilibrium thermal effects are not available from mix-
tures which tehd to supercool or from salt mixtures which tend
to form glasses on cooling. Whcre these phenomena occur,
quenching procedures provide the only source of equilibrium

data. 1In other cases, crystallization rcactions at high tem-

*Private communication from W. W. Johnston,'Jr. of the Ins-
trument Department, Standards Laboratory, ORNL.
28—

peratures occur S0 rapidly that quenching experiments do not
disclose the occurrence of phase transitions. By use of the
techniques and equipment described in this report phase equi-
libria in a large number of systems have been defined in detail

with good precision and accuracy.

Acknowledgment

The authors are grateful for the benefit of profitable
discussions and counsel with their. associates on .the staff
of the Reactor Chemistry Division. .They were privileged to
be able to extend the excellent experimental methods intro-
duced by C. J. Barton and R. E. Moore. The aid of J. E.
Hammond in instrument design. and construction-is gratefully
acknowlédgedg. They are also grateful lur Lhe many:- uscful .

suggestions made by H. Insley and C. F. Weaver.

as
~29-

References

1W. D. Kingery, Property Measurement at High Temper-

atures, John Wiley and Sons, Inc., N. Y., (1959), p. 280.

2C. J. Barton, H. A, Friedman, W. R. Grimes, H. Insley,
R. E. Moore, and R. E. Thoma, '"Phase Equilibria in the Alkali
Fluoride-Uranium Tetrafluoride Fused Salt Systems: 1, The
Systems LiF-UF, and NaF-UF4 " J. Am. Ceram. Soc., 4& [6] PpP.
63 (1958).

3R. E. Thoma, et.al., '"Phase Equilibria in the Fused
Salt Systems LiF-ThF, and NaF-ThF,," J. Phys. Chem. 63
1266 (1959).

C F. Weaver, et.al,, '""Phase Equilibria in the Systems
UF,-ThF, and LiF-UF,-ThF,," J. Am. Ceram. Soc, 43 [4] 213
(1960).

5H. A. Friedman, '"Modifications of Quenching Techniques
for Phase Equilibrium Studies," J. Am. Ceram. Soc., 42 [6]
284 (1959).

6P. A. Tucker and E. F. Joy, "Thermal-Gradient Quench-.
ing Furnace for Preparation of Fused Salt Samples for Phase
Analysis," Am. Ceram. Soc. Bull,, 36 [2] 52 (1957).

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