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ORNL-3 3 73
Contract No. W- 7 4 0 5-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
OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION
s
c
6 L.
I
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iii
CONTENTS
...................... Introduction ..................... Methods . . . . . . . . . . . . . . . . . . . . . . . . D i r e c t Thermal A n a l y s i s . . . . . . . . . . . . . . . N o r m a l Procedure . . . . . . . . . . . . . . . . . . S p e c i a l Procedure . . . . . . . . . . . . . . . . . Quenching Techniques . . . . . . . . . . . . . . . . . P r e p a r a t i o n of Samples . . . . . . . . . . . . . . . P r e p a r a t i o n of Quench Tubes . . . . . . . . . . . . Tubes for N o n - v o l a t i l e S a l t s . . . . . . . . . . . Tubes for V o l a t i l e S a l t s . . . . . . . . . . . . . Quench F u r n a c e s . . . . . . . . . . . . . . . . . . F u r n a c e s w i t h S t a t i o n a r y Thermocouples . . . . . . F u r n a c e s w i t h T r a v e l i n g Thermocouples . . . . . . Abstract..
E
l
I. 2: 4:
4: 4: 9 13
13 14. 14:
18 21.
21. 23
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26
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28,
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29
Accuracy and P r e c i s i o n of Measurement Acknowledgment R e f e re n c e s
Page --
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THERMAL ANALYSIS AND GRADIENT QUENCHING APPARATUS AND TECHNIQUES FOR THE INVESTIGATION OF FUSED SALT PHASE EQUILIBRIA
H. A. Friedman, G. M. H e b e r t , and R. E. Thoma ABSTRACT A d e t a i l e d d e s c r i p t i o n is p r e s e n t e d of appara-
t u s and methods u s e d a t ORNL f o r d e t e r m i n a t i o n of h i g h t e m p e r a t u r e e q u i l i b r i u m phase r e l a t i o n s h i p s i n condensed s y s t e m s of molten s a l t s .
P r i n c i p a l empha-
sis is g i v e n t o e x p e r i m e n t a l t e c h n i q u e s r e q u i r e d f o r i n v e s t i g a t i o n of n o n - v o l a t i l e h y g r o s c o p i c f l u o r ides.
E q u i l i b r i u m phase b e h a v i o r is e l u c i d a t e d by
t h e combined r e s u l t s of e x p e r i m e n t s i n which measurements are made of t h e t h e r m a l e f f e c t s o c c u r r i n g on m e l t i n g and f r e e z i n g polycomponent m i x t u r e s , and o t h e r s i n which u n e q u i v o c a l i d e n t i f i c a t i o n of s o l i d p h a s e s formed d u r i n g c r y s t a l l i z a t i o n is o b t a i n e d . Apparatus d e v i s e d a t ORNL f o r u s e i n p r e p a r a t i o n , p u r i f i c a t i o n , e q u i l i b r a t i o n , and h a n d l i n g of m a t e r -
i a l s f o r a p p l i c a t i o n i n f l u o r i d e phase s t u d i e s is described i n detail.
The methods and t e c h n i q u e s
d e s c r i b e d are unique i n p r o v i d i n g s u c h l a r g e quan-
t i t i e s of phase d a t a t h a t phase diagrams of complex s y s t e m s may be c o n s t r u c t e d i n a r e l a t i v e l y s h o r t t i m e .
-2-
INTRODUCTION The a d v e n t of molten s a l t s i n n u c l e a r reactor t e c h n o l o g y a s f u e l s , converter-breeder
blankets, heat transfer f l u i d s ,
and r e p r o c e s s i n g media f o r s p e n t f u e l e l e m e n t s h a s n e c e s s i t a t e d a l a r g e number of phase e q u i l i b r i u m i n v e s t i g a t i o n s . Although many e x p e r i m e n t a l methods have been a p p l i e d i n s t u d -
ies of phase e q u i l i b r i a a t e l e v a t e d t e m p e r a t u r e s ,
1
e. g.,
t h r o u g h measurements of t h e r m a l e x p a n s i o n , magnetic p r o p e r -
t i e s , v i s c o s i t y , thermodynamic p r o p e r t i e s and c r y s t a l l i z a t i o n e q u i l i b r i a , o n l y t h e l a t t e r two of t h e s e methods are s u i t e d for r a p i d l y a c q u i r i n g t h e l a r g e number of d a t a needed i n
c o n s t r u c t i n g complex phase diagrams.
These t w o g e n e r a l
methods have t h e r e f o r e been a p p l i e d f o r s e v e r a l years t o i n v e s t i g a t i o n s of molten s a l t phase e q u i l i b r i a a t ORNL.
Adapt-
a t i o n s of e x p e r i m e n t a l metnods t o s p e c i f i c problems o b v i o u s l y r e q u i r e c o n s i d e r a t i o n of t h e m o s t annoying p r o p e r t i e s of t h e
materials t o be s t u d i e d and m o d i f i c a t i o n of t h e methods t o p e r m i t i n v e s t i g a t i o n of t h e m a t e r i a l s d e s p i t e t h e i r i n t r a n s i g e n c e . Molten h a l i d e s a t e l e v a t e d t e m p e r a t u r e s p o s s e s s an i m p r e s s i v e
l i s t of t h e s e c h a r a c t e r i s t i c s .
I t is t h e purpose of t h i s
r e p o r t t o f u r n i s h d e t a i l e d d e s c r i p t i o n s of t h e p r a c t i c a l proc e d u r e s which have found s p e c i a l a p p l i c a t i o n a t ORNL f o r i n v e s t i g a t i o n s of molten s a l t phase e q u i l i b r i a . Phase e q u i l i b r i u m diagrams are g e n e r a l l y d e r i v e d from two k i n d s of e x p e r i m e n t s , t h o s e from which d e d u c t i o n s are made from measurements of t h e r m a l e f f e c t s o c c u r r i n g
in
h e a t i n g and c o o l i n g c u r v e s , and t h o s e which p e r m i t a d i r e c t
-3-
or i n d i r e c t i d e n t i f i c a t i o n of t h e numbers and c o m p o s i t i o n s of p h a s e s o c c u r r i n g a t a l l temperature-composition
points.
Commonly, f u s e d s a l t diagrams are based on i n f o r m a t i o n from c o o l i n g c u r v e s .
Changes i n s l o p e of t h e t e m p e r a t u r e
of t h e sample, when p l o t t e d as a f u n c t i o n of t i m e , r e f l e c t phase changes which occur on c o o l i n g .
T h i s t e c h n i q u e is
g e n e r a l l y adequate f o r determining a l l except t h e s t e e p -
e s t l i q u i d u s c u r v e s ; s t e e p c u r v e s r e p r e s e n t s m a l l changes i n s a t u r a t i o n c o n c e n t r a t i o n s w i t h t e m p e r a t u r e and hence s m a l l heat e f f e c t s .
Cooling c u r v e s a l s o p r o v i d e i n f o r m a t i o n on
t h e s o l i d u s and s u b s o l i d u s phase c h a n g e s , b u t are prone t o g i v e m i s l e a d i n g i n d i c a t i o n s because of t h e i m p o s s i b i l i t y i
of m a i n t a i n i n g e q u i l i b r i u m d u r i n g c o o l i n g .
Phase t r a n s i t i o n s
i n f e r r e d from c o o l i n g c u r v e s are v e r i f i e d by quenching of e q u i l i b r i u m samples and a n i d e n t i f i c a t i o n of t h e p h a s e s by c r y s t a l l o g r a p h i c e x a m i n a t i o n w i t h m i c r o s c o p i c and X-ray diffraction techniques.
Chief i n t e r e s t i n s a l t phase
e q u i l i b r i a has f o c u s e d on t h e f l u o r i d e s and c h l o r i d e s of the a c t i n i d e e l e m e n t s and on l o w m e l t i n g s o l v e n t s f o r these f i s s i l e and f e r t i l e m a t e r i a l s .
Such s a l t s v a r y w i d e l y w i t h
r e s p e c t t o t h e i r hygroscopic c h a r a c t e r .
I t is n e c e s s a r y t o
employ e x p e r i m e n t a l t e c h n i q u e s which m a i n t a i n a g e n u i n e l y nvironment f o r t h e
salts.
Though t h e t r i - and
t e t r a f l u o r i d e s of t h e a c t i n i d e s , r a r e e a r t h s and z i r c o n i u m a r e n o t h y g r o s c o p i c , t h e y are e a s i l y h y d r o l y z e d a t e l e v a t e d temperatures.
I t is n e c e s s a r y , t h e r e f o r e , i f t h e sample
L
-4under e x a m i n a t i o n is t o be f r e e from e x t r a n e o u s p h a s e s due t o t h e p r e s e n c e of o x i d e s or o x y f l u o r i d e s , t o remove a l l
water and t o p r o t e c t t h e h e a t e d sample from c o n t a c t w i t h a i r . METHODS D i r e c t Thermal A n a l y s i s
Two t e c h n i q u e s have been developed f o r o b t a i n i n g thermalanalysis data.
These have e v o l v e d as a "normal" p r o c e d u r e ,
employed f o r m i x t u r e s which are known t o be non-hygroscopic, and a " s p e c i a l " p r o c e d u r e , employed f o r h y g r o s c o p i c m i x t u r e s . Normal Procedure A c o n v e n i e n t means of accommodating f o u r s a m p l e s i n graph-
i
i t e or n i c k e l c r u c i b l e s is shown i n F i g u r e ( 1 ) . c r u c i b l e s , 5' 1 / 2 " I
1/8",
h i g h , 1 5/8"
The g r a p h i t e
o.d., w i t h a w a l l t h i c k n e s s of
are f a b r i c a t e d from h i g h d e n s i t y g r a p h i t e ; t h e n i c k e l
c r u c i b l e s , 5 1/2"
h i g h , are c o n s t r u c t e d from 1 l / Z ? ? t u b i n g
with a 1/16" w a l l thickness.
A g r a p h i t e d i s c , approximately
t h e s i z e of t h e i n t e r n a l d i a m e t e r of t h e c r u c i b l e and w i t h two h o l e s t o a d m i t t h e s t i r r e r and thermocouple w e l l , may be i n s e r t e d i n t o t h e c r u c i b l e on t o p of t h e sample i f t h e major i n g r e d i e n t h a s an a p p r e c i a b l e vapor p r e s s u r e .
The d i s c re-
duces t h e v o l a t i l i z a t i o n of t h e sample by f l o a t i n g on t h e
melt
t h u s d e c r e a s i n g t h e l i q u i d s u r f a c e area.
An a n n e a l e d
copper g a s k e t between t h e f l a n g e of t h e reactor v e s s e l and t h e l i d acts as a s e a l when t h e assembly is f a s t e n e d t o g e t h e r w i t h t h r e e clamps. N i c k e l stirrers of 1/8" d i a m e t e r s h a n k s and 14" i n l e n g t h
are i n s e r t e d i n t o t h e m e l t s through c l o s e l y f i t t i n g s l e e v e s
-5-
UNCLASSIFIED ORNL-LR-OWG 62213R
STIRRING ROD ALIGNER
DRIVE BELT (COILED SPRING)
\
/ BUSHING (GRAPHITE)
ALIGNER SUPPORT ROD(AI)
~
---'-.Ti c
f
GAS INLET
GAS OUT -THERMOCOUPLE
7 SWAGELOK FITTINGS ,,-BUSHING (GRAPHITE)
CRUCIBLE (GRAPHITE/
STIRRING ROD ( NI)
THERMOCOUPLE WELL
Fig.
1.
Reactor V e s s e l .
3
-6-
e
of g r a p h i t e i n t h e l i d of t h e assembly ( F i g u r e 2 ) .
A holder
c a p a b l e of f i n e a d j u s t m e n t s a l i g n s t h e t o p of t h e s t i r r e r s (Figure 3 ) .
The m e l t s are p r o t e c t e d from t h e atmosphere by
m a i n t a i n i n g a s m a l l p o s i t i v e p r e s s u r e of h e l i u m , p u r i f i e d by p a s s a g e through a l i q u i d n i t r o g e n - c h a r c o a l sembly.
t r a p , i n t h e as-
Leakage of helium t h r o u g h t h e g r a p h i t e b u s h i n g s on
t h e l i d p r e v e n t s d i f f u s i o n of a i r t o t h e molten m i x t u r e .
Pow-
e r is s u p p l i e d t o t h e s t i r r e r t h r o u g h t h e b e l t of c o i l e d s p r i n g ( F i g u r e 1 ) ; s l i p p a g e of t h e b e l t p r e v e n t s p o s s i b l e damage t o t h e d r i v e motors.
Temperatures a r e measured w i t h
Chromel-Alumel thermocouples i n a t h i n w a l l e d (10 m i l ) n i c k e l thermocouple w e l l immersed i n t h e m e l t .
The e . m . f . ' s
are
measured u s i n g Minneapolis Honeywe 11 " E l e c t r o n i k " Recorders t h a t are f r e q u e n t l y c a l i b r a t e d w i t h a p o t e n t i o m e t e r . To remove o x i d e and water v a p o r , 1 0 grams of ammonium b i f l u o r i d e * are added t o each c r u c i b l e f o l l o w e d by t h e sample. The c r u c i b l e s are t h e n l o a d e d i n t o t h e r e a c t o r v e s s e l and t h e
reactor is assembled and p l a c e d i n t o a 5" p o t f u r n a c e .
The
stirrers are a l i g n e d and t h e f u r n a c e h e a t e d u n t i l t h e ammonium b i f l u o r i d e becomes m o l t e n , 120-225OC. These low t e m p e r a t u r e s are m a i n t a i n e d f o r a t l e a s t one hour b e f o r e h e a t i n g t o e l e v a t e d temperatures.
Fuming of ammonium b i f l u o r i d e o c c u r s u n t i l ap-
p r o x i m a t e l y 55OoC.
When e v o l u t i o n of t h e fumes is no l o n g e r
*Ammonium b i f l u o r i d e w i l l r e a c t w i t h a number of o x i d e s , i n c l u d i n g t h o s e of uranium, z i r c o n i u m , y t t r i u m , aluminum, b e r y l l i u m , c o b a l t , i r o n , vanadium, c e r i u m , and chromium ( v a l e n c e 6 ) t o form f l u o r i d e s . N i c k e l and chromium ( v a l e n c e 3 ) o x i d e s w i l l n o t be f l u o r i n a t e d w i t h ammonium b i f l u o r i d e . (Private communication from B . J . Sturm, Reactor Chemistry D i v i s i o n , ORNL )
.
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I t
UNCLASSIFIED ORNL-LR-DWG 62215
HOLE FOR THERMOCOUPLE (4) 7
GAS INLET (GRAPHITE 1
-LID ( N i l
GAS OUTLET
-8-
UNCLASSIFIED
ORNL-LR- DWG 622t4
i Fig. 3 .
S t i r r e r Rod A l i g n e r .
-9o b s e r v e d , t h e e s c a p e v e n t ( F i g u r e s 1 and 2 ) is c l o s e d w i t h a g r a p h i t e p l u g , F i b e r f r a x i n s u l a t i o n is packed on t h e t o p of t h e r e a c t o r and t h e s t i r r e r motors are s t a r t e d .
One of s e v -
e r a l e l e c t r i c timers can s t a r t or s t o p any p a r t of t h e e q u i p ment m e c h a n i c a l l y .
A m i n e r a l o i l bubbler l o c a t e d i n t h e gas
e x i t l i n e is u s e d t o check f o r a p o s i t i v e p r e s s u r e . The f u r n a c e is c o o l e d a f t e r t h e t e m p e r a t u r e h a s r e a c h e d a p p r o x i m a t e l y 1 0 0 째 C above t h e h i g h e s t e s t i m a t e d l i q u i d u s of any sample and t h e i n g r e d i e n t s of e a c h sample have m e l t e d and mixed.
The r a t e of c o o l i n g is r e g u l a t e d by c o n t r o l l i n g
t h e v o l t a g e t o t h e f u r n a c e w i t h an a u t o - t r a n s f o r m e r .
The
h e a t i n g and c o o l i n g cycles are u s u a l l y r e p e a t e d w i t h t h e c o o l i n g r a t e v a r i e d t o v e r i f y the thermal d a t a .
I t is p o s s i b l e
t o magnify t h e t h e r m a l e f f e c t by i n c r e a s i n g t h e sample s i z e and by d e c r e a s i n g t h e c o o l i n g r a t e .
An a p p r o x i m a t e l y o p t i m a l
c h o i c e of sample s i z e a p p e a r s t o be 5 0 g.
This size choice
is a compromise of d e s i r a b l y l a r g e r sample s i z e s w i t h t h e convenience of employing l a b o r a t o r y s c a l e equipment. a b l e c o o l i n g r a t e s for s u c h sample s i z e s are 3-4OC/
Suitmin.
A complete h e a t i n g a n d c o o l i n g cycle r e q u i r e s a b o u t 6 h o u r s .
S p e c i a l Procedure To o b t a i n e q u i l i b r i u m c o o l i n g c u r v e s and quench d a t a i n
s y s t e m s of h y g r o s c o p i c s a l t s a l l m a n i p u l a t i o n s e x c e p t weigh-. i n g t h e s t a r t i n g m a t e r i a l s are performed i n a vacuum dry-box.
a
-10-
e
Samples are p u r i f i e d i n t h e same manner as d e s c r i b e d i n t h e o t h e r p r o c e d u r e and m e l t e d i n a 5" p o t f u r n a c e s e t i n t o t h e f l o o r of t h e dry-box.
Ammonium b i f l u o r i d e fumes are e x h a u s t e d
through a n i c k e l funnel (Figure 4 ) .
I n u s e , t h e f u n n e l is
p l a c e d over t h e f u r n a c e w e l l and sealed t o t h e w e l l w i t h t h e t e f l o n gasket.
Fumes e v o l v e d d u r i n g t h e ammonium b i f l u o r i d e
p u r i f i c a t i o n s t e p are p u l l e d by a vacuum pump i n t u r n t h r o u g h t h e f u n n e l , a r u b b e r hose, and 3/4"
d i a m e t e r copper t u b i n g i n -
t o a s o d a l i m e t r a p and i n t o a s u l f u r i c a c i d t r a p .
The fun-
n e l is p l a c e d i n its rack a t t h e back of t h e dry-box when fuming is c o m p l e t e , as i n d i c a t e d by t h e t e m p e r a t u r e of a thermocouple f i t t i n g i n t o a w e l l i n t h e n i c k e l f u n n e l ; t h e s t i r r i n g mechanism, which a l s o c o n t a i n s t h e thermocouple w e l l s ,
is t h e n p o s i t i o n e d o v e r t h e h e a t i n g w e l l a f t e r i t h a s been removed from its h o l d e r ( F i g u r e 5 ) .
One thermocouple w e l l
and one s t i r r i n g r o d a r e i n s e r t e d i n t o e a c h c r u c i b l e .
A single
motor r o t a t e s t h e f o u r stirrers which have s l i p c l u t c h e s t o p e r m i t t h e motor t o r e v o l v e w i t h o u t damage when t h e m e l t s freeze
.
Temperatures are measured and r e c o r d e d u s i n g Chromel-
Alumel thermocouples i n s e r t e d i n t o t h e dry-box t h r o u g h Conax fittings*. An atmosphere of a r g o n g a s , d r i e d by p a s s i n g t h r o u g h magnesium p e r c h l o r a t e and d r y i c e - t r i c h l o r o e t h y l e n e t r a p s , is m a i n t a i n e d i n t h e dry-box.
*
Made by Conax Corp.,
The dry-box e n t r a n c e chamber is
2 3 0 0 Walden Avenue, B u f f a l o 2 5 , N e w York.
-11-
-12-
Fig. 5.
S t i r r e r Mechanism.
-13e v a c u a t e d and r e f i l l e d w i t h d r i e d argon after each -transit througrh
t h e c h a m ber.
Metal p l a t e s c o v e r t h e glove p o r t s when t h e
dry-box is e v a c u a t e d and when t h e p o r t s are n o t i n u s e .
The
atmosphere is c i r c u l a t e d i n s i d e t h e box over s e v e r a l t r a y s of P,05 t o a b s o r b any m o i s t u r e .
An oxygen-free
must be m a i n t a i n e d i n t h e box.
d r y atmosphere
In u s u a l o p e r a t i o n with c l o s e d
g l o v e p o r t s , t h e w a t e r c o n t e n t of t h e dry-box atmosphere can. be m a i n t a i n e d a t a b o u t 2 0 ppm. Quenching Techniques P u r i f i e d m e l t s from t h e t h e r m a l a n a l y s i s p r o c e d u r e may be f u r t h e r used by b e i n g e q u i l i b r a t e d a t and quenched from e l e v a t e d temperatures t o v e r i f y t h e t r a n s i t i o n temperatures and t o o b s e r v e t h e p h a s e s p r e s e n t a t t h e t r a n s i t i o n s .
Quench
t u b e s c o n t a i n i n g 25-28 sample segments are e q u i l i b r a t e d i n g r a d i e n t quench f u r n a c e s o v e r pre-determined
temperature
Methods u s e d t o i n t e r p r e t
r a n g e s and t h e n r a p i d l y c o o l e d .
t h e r m a l g r a d i e n t quenching d a t a have been d i s c u s s e d i n r e p o r t s of f l u o r i d e phase i n v e s t i g a t i o n s
2-4
and will n o t be t r e a t e d
here. P r e p a r a t i o n of Samples t o be e q u i l i b r a t e d are o b t a i n e d from e i t h e r clf e d by a s p e c i a l p r e p a r r e d from p u r e components.
Thie
d i n t h e normal t h e r m a l a n a l y s i s
a dry-box,
ground w i t h an elec-
t r i c mortar and p e s t l e t o < l o 0 mesh, b o t t l e d , removed from t h e A
-14dry-box and homogenized on a c o n v e r t e d b a l l m i l l ( F i g u r e 6 ) f o r approximately 1 6 hours.
These b o t t l e s , s e a l e d w i t h a
c o a t i n g of p a r a f f i n and beeswax, are clamped i n t o p l a c e on t h e face p l a t e .
A f t e r mixing, t h e samples are r e t u r n e d t o
t h e dry-box and loaded i n t o quench t u b e s .
Hygroscopic s a m p l e s ,
p u r i f i e d i n t h e s p e c i a l t h e r m a l a n a l y s i s p r o c e d u r e , are homcge n i z e d b y hand mixing w i t h i n t h e dry-box r a t h e r t h a n e x t e r n a l -
1 Y* P r e p a r a t i o n of quench t u b e s Tubes f o r n o n - v o l a t i l e
s a l t s . - A r o l l i n g and c r i m p i n g
machine ( F i g u r e 7 > 5 h a s been c o n s t r u c t e d t o i n s u r e e q u a l s a m p l e s p a c i n g i n t h e quenching t u b e and t o l e s s e n t h e t i m e required f o r loading.
A n i c k e l t u b e 6-1/2"
l o n g , 0.10''
i n out-
i n w a l l t h i c k n e s s which h a s been
s i d e d i a m e t e r , and 0.010''
a n n e a l e d f o r 1 hour i n a H2 atmosphere a t 8 O O 0 C or a d r i e d p l a t i n u m t u b e of s i m i l a r s i z e is r o l l e d w i t h t h e k n u r l e d wheel t o f l a t t e n a l l b u t 3/8" tube has a void space 0.015"
a t one end. thick.
The f l a t t e n e d
The bottom of t h e t u b e
is t h e n s e a l e d by w e l d i n g , A sample is l o a d e d by i n s e r t i n g t h e end of t h e sample t u b e i n t o t h e s h a f t of a s p e c i a l l y c o n s t r u c t e d f u n n e l (Figu r e s 7 and 8 ) .
A s m a l l l i p on t h e i n s i d e of t h e f u n n e l s h a f t
prevents over-insertion
of t h e t u b e .
The t u b e is t a p p e d
a g a i n s t a s o l i d s u r f a c e t o i n s u r e complete f i l l i n g , and t h e n crimped w i t h p l i e r s 3/8"
from t h e t o p .
The upper 3/8"
is
c l e a r e d of powder, c l e a n e d w i t h a p i p e c l e a n e r and f l a t t e n e d
3
ii
-15-
k a,
x
-16-
c
i c
c
Fig. 7 .
R o l l e r and Crimping Machine.
i
r d
6
-17-
-18with p l i e r s .
Care must be t a k e n t o see t h a t t h i s s p a c e is
w e l l c l e a n e d , f o r a s m a l l amount of t h e sample lodged i n t h e The t u b e is removed
weld c a n p r e v e n t s e a l i n g of t h e t u b e .
from t h e box, f l a t t e n e d i n a v i s e , crimped w i t h t h e crimpi n g wheel, and t h e end c l o s e d w i t h a gas-oxygen
A
torch.
p i e c e of w e t c l e a n s i n g t i s s u e h e l d around t h e upper p o r t i o n
of t h e t u b e w h i l e w e l d i n g p r e v e n t s v a p o r i z a t i o n of t h e sample. Tubes f o r v o l a t i l e s a l t s . - N i c k e l
o r p l a t i n u m quench t u b e s
p r e p a r e d as d i s c u s s e d above are of l i t t l e u s e f o r i n v e s t i g a t i n g s y s t e m s c o n t a i n i n g one o r more components which e x e r t 4
s i g n i f i c a n t vapor p r e s s u r e a t e l e v a t e d t e m p e r a t u r e s .
An i n -
n o v a t i o n i n t h e t u b e d e s i g n w a s made t o minimize e x p a n s i o n of crimped j o i n t s by v o l a t i l e m a t e r i a l s and m i g r a t i o n of
s a l t s within the tubes.
The sample is loaded i n t o a n u n f l a t t e n -
e d s t a n d a r d quench t u b e by means of a 1 6 gauge 6 1 / 2 ? ' I r v i n g
caudal needle with plunger (Figure l o ) ,
The n e e d l e is i n -
s e r t e d , a f t e r w i p i n g , i n t o t h e bottom of t h e quench t u b e and t h e sample d e p o s i t e d by p u s h i n g t h e p l u n g e r ; t h e n t h e p l u n g e r
is r e t r a c t e d and t h e n e e d l e removed. where t h e sample is l o c a t e d (1/8"
A p o r t i o n of t h e t u b e
i n l e n g t h ) is f l a t t e n e d
a l o n g w i t h a 1/8" p o r t i o n above t h e sample by r o t a t i n g t h e wheel of t h e s p a c e c r i m p i n g machine. u n t i l an a u t o m a t i c s t o p
is r e a c h e d ( F i g u r e 9 ) .
The n e x t segment is l o a d e d w i t h t h e
n e e d l e , a s t o p r e l e a s e d and t h e wheel r o t a t e d .
The p r o c e s s
is c o n t i n u e d u n t i l t h e t u b e is f i l l e d t o w i t h i n 3/8" of t h e top.
Another t u b e is l o a d e d i n t h e same manner, b u t 1/8"
-19-
-20-
PI I
a,
d
a)
a
a,
R
d
cd
u
-21-
more s p a c e is l e f t a t t h e t o p .
When t h e t u b e s are i n v e r t e d
t h i s e x t r a s p a c e a l l o w s t h e u n f i l l e d s p a c e i n one t u b e t o be o p p o s i t e a f i l l e d segment i n t h e o t h e r .
Two t u b e s a r e re-
q u i r e d t o f u r n i s h an u n i n t e r r u p t e d series of segments (Figure 10).
The loaded t u b e s are removed from t h e dry-box,
f l a t t e n e d i n a v i s e , and t h e e n d s welded w i t h an oxygen-gas torch.
A p i e c e of w e t c l e a n s i n g t i s s u e used as mentioned
above p r e v e n t s
v a p o r i z a t i o n of t h e sample.
The u n f i l l e d
s p a c e s between t h e samples are welded w i t h an Ampower p o r t -
r I
a b l e s p o t welder w i t h e l e c t r o d e s m o d i f i e d t o weld a 1/16" spot. Quench Furnaces Furnaces w i t h s t a t i o n a r y thermocouples .-Two t y p e s of gradi e n t t e m p e r a t u r e f u r n a c e s have been developed as modif i c a t i o i i s of t h e Tucker and Joy
6
furnace, a furnace with s t a t i o n a r y ther-
mocouples u s e d f o r t e m p e r a t u r e s t o 9OO0C and a f u r n a c e w i t h
a t r a v e l i n g thermocouple f o r h i g h e r t e m p e r a t u r e s .
The f u r -
n a c e s u s e d f o r t e m p e r a t u r e s up t o 9 O O 0 C , have v e r t i c a l l y k
mounted nichrome wound ceramic c o r e s * w i t h s e v e r a l c o n n e c t i o n s 3
t o v a r y t h e l e n g t h of t h e h e a t e d s e c t i o n and t h e t e m p e r a t u r e g r a d i e n t (Figure 11).
Within t h e ceramic c o r e a n i c k e l s a m -
p l e b l o c k 1 0 " l o n g , 2" d i a m e t e r w i t h a c e n t e r h o l e 9 1 / 2 "
*
lo:ng,
The Alundum t u b e cores, 2 1 / 2 ? ? I.D. x 16" long, u s e d f o r Mars h a l l Tubular T e s t Furnaces , are purchased from M a r s h a l l P r o d u c t s Company, 2 0 7 West Lane Avenue, Columbus 2 , Ohio.
-22-
GAS I N L E T \
0
t-
c
-
/BLOCK SUPPORT TO TEMPERATURE CONTROLLER
v)
z
UNCLASSIFIED ORN L- L R D W G 5 2 17 8R2
POWER SOURCE
MM
o W
z z
0
o
CONTROLLING THERMOCOUPLE
W
I-
a z E W
5 a
3LE
SAMPLE TUBE SUPPORT
Gradient Quenching Apparatus
Fig. 11.
Type I.
-23and 21/64''
i n diameter, bored lengthwise, is suspended.
t e e n Chromel-Alumel
Eigh-
thermocouples, s p a c e d one h a l f i n c h a p a r t
a l o n g t h e l e n g t h of t h e b l o c k , p e n e t r a t e t o w i t h i n 1/32" of i
t h e c e n t r a l sample h o l e .
A s many as f o u r sample t u b e s are
i n s e r t e d i n t o t h e c e n t r a l h o l e s i m u l t a n e o u s l y on a p e d e s t a l of known h e i g h t .
T h i s p e d e s t a l rests on a p i v o t l a t c h which
can be r o t a t e d t o d r o p t h e t u b e s i n t o t h e o i l b a t h f o r quenching.
The t e m p e r a t u r e of e a c h segment of a t u b e is d e t e r m i n e d
by p l o t t i n g t h e t e m p e r a t u r e s i n d i c a t e d from t h e thermocauplc? v o l t a g e s r e a d w i t h a p o t e n t i o m e t e r as a f u n c t i o n of t h e pos i t i o n of e a c h segment i n r e l a t i o n s h i p t o t h e thermocouples <, I f t h e samples are t o be h e l d a t t e m p e r a t u r e s above 500째C
i t is d e s i r a b l e t o p r o t e c t t h e c o n t a i n e r t u b e s from o x i d a t i o n by a f l o w of helium a d m i t t e d t h r o u g h t h e b l o c k s u p p o r t v i a
a s m a l l tube.
The f u r n a c e s are c o n t r o l l e d t o *1/4OC by a u t o -
t r a n s f o r m e r s and by c o n t r o l l e r s c o n t a i n i n g p r o p o r t i o n a l u n i t s . Furnaces w i t h t r a v e l i n g thermocouples.-Other
t y p e s of
f u r n a c e s ( F i g u r e 1 2 ) have been developed t o a n n e a l s a m p l e s -to 12OO0C.
s i n c e t h e Chromel-Alumel
thermocouples have r e l a -
t i v e l y s h o r t l i f e a t t e m p e r a t u r e s above 900'C. t h i s f u r n a c e is wound t o 1/2"
The core* of
of t h e t p p and t o 5 1 / 2 "
bottom w i t h 2 0 gauge p l a t i n u m w i r e .
of t h e
The quench b l o c k , a 2"
n i c k e l r o d 10'' l o n g , is bored l e n g t h w i s e w i t h t w o h o l e s 9 1/2"
1
I
*Same core t h a t is u s e d i n t h e o t h e r t y p e f u r n a c e s .
i
-24UNCUSSIFIED ORNL-LR-DWG 25153
r TO CONTROLLER ,-GAS
BLOCK SUPPORT
INLET
7
c
v
TO RECORDER
GRADIENT QUENCHING APPARATUS
Fig. 1 2 .
Type 11.
-25-
d e e p t o c o n t a i n t h e samples and t h e thermocouple. i
p l e h o l e (21/64" a t e d 1/32''
The s a m -
i n d i a m e t e r ) is c e n t r a l l y l o c a t e d and s e p a r -
from t h e thermocouple h o l e (3/16"
i n diameter).
Helium g a s is u s e d i n t h i s f u r n a c e as i n 0ther.s t o p r e v e n t t h e o x i d a t i o n of t h e n i c k e l sample t u b e s .
A t e m p e r a t u r e r e c o r d of t h e t h e r m a l g r a d i e n t is prov i d e d by a t r a v e l i n g thermocouple.
A g e a r t r a i n and t h r e a d -
e d r o d arrangement is o p e r a t e d t o r a i s e and lower t h e monitori n g thermocouple a t a r a t e of from 2-8 i n . / h r .
are r e c o r d e d on a Honeywell " E l e c t r o n i k "
Temperatures
instrument a d j u s t e d
s o t h a t i t s c h a r t s p e e d is i d e n t i c a l with that of t h e t r a v e l i n g thermocouple.
Two m i c r o s w i t c h e s which a c t i v a t e r e l a y s are
a r r a n g e d s o as t o r e v e r s e t h e d i r e c t i o n of t h e thermocouple when c o n t a c t is made. of 6 1 / 2 " ,
The thermocouple t r a v e l s a d i s t a n c e
e q u a l t o t h e l e n g t h of t h e sample t u b e , b e f o r e
r e v e r s i n g its d i r e c t i o n .
The thermocouple w i r e is e n c l o s e d
i n one s t r i p of ceramic i n s u l a t o r 1 2 " long.
To i n s u r e t h a t
t h e thermocouple measures t h e t e m p e r a t u r e o v e r t h e l e n g t h of
t h e specimen, i t is clamped i n t h e thermocouple h o l d e r (Fig'3
u r e 1 1 ) s o t h a t t h e t i p of t h e thermocouple c o i n c i d e s w i t h t h e t o p and bottom of t h e specimen t u b e a t t h e extremes of travel.
S i n c e t h e o u t p u t of t h e thermocouple is r e c o r d e d on
a m u l t i - s p a n r e c o r d e r whose r a t e of t r a v e l is s y n c h r o n i z e d w i t h t h e motion of t h e thermocouple, t h e t e m p e r a t u r e of each s e c t i o n of t h e specimen t u b e is a c c u r a t e l y d e t e r m i n e d , t e m p e r a t u r e of t h e f u r n a c e is c o n t r o l l e d by a 28 ampere
The
-26P o w e r s t a t and a 16OO0C c o n t r o l l e r w i t h a p r o p o r t i o n a l u n i t . Because t h e t e m p e r a t u r e g r a d i e n t is s m a l l a t t h e t o p of t h e f u r n a c e and i n c r e a s e s downward, t h e p o s i t i o n of t h e s a m p l e i n t h e furnace, d e t e r m i n e d by t h e l e n g t h of t h e n i c k e l sample s u p p o r t i n g r o d , p a r t l y d e t e r m i n e s t h e t e m p e r a t u r e g r a d i e n t a l o n g t h e specimen t u b e d u r i n g a n n e a l i n g . The quenching t u b e and t h e sample s u p p o r t are h e l d i n t h e f u r n a c e by t h e s u p p o r t i n g p l a t f o r m , which is a t t a c h e d
t o t h e f u r n a c e by a s p r i n g mechanism; t h e t u b e is dropped i n t o an o i l b a t h by p u l l i n g t h e h a n d l e of t h e s u p p o r t i n g platform. Accuracy and P r e c i s i o n of Measurement I n o r d e r t o e s t a b l i s h estimates of a c c u r a c y as w e l l as of p r e c i s i o n , e x p e r i m e n t s are conducted o c c a s i o n a l l y i n which m e l t i n g p o i n t s of s a l t s are d e t e r m i n e d which have been a c c u r a t e l y e s t a b l i s h e d elsewhere.
T y p i c a l s t a t i s t i c a l d a t a from
a v e r a g e s of t e n c o o l i n g c u r v e d e t e r m i n a t i o n s e a c h w i t h N a C l and K C 1 i n d i c a t e m e l t i n g p o i n t s of 771rt2 and 801&3OC, r e s p e c t i v e l y as compared w i t h s t a n d a r d v a l u e s f o r t h e s e s a l t s of 770.3 and 800.4'C.
I n r o u t i n e d e t e r m i n a t i o n s of t h e m e l t i n g
p o i n t s of m g r u e n t l y m e l t i n g complex f l u o r i d e compounds, e . g . , 7NaF. 6UF,,
t h e m e l t i n g t e m p e r a t u r e is g e n e r a l l y r e p r o d u c e d i n
b o t h c o o l i n g c u r v e and quenching e x p e r i m e n t s t o w i t h i n k 2 O C . The d e g r e e of p r e c i s i o n and a c c u r a c y f o r t h e o b s e r v e d t r a n s i t i o n s i n a s y s t e m depend upon s e v e r a l f a c t o r s i n c l u d i n g t h e p r o p e r t i e s of t h e s y s t e m i n v e s t i g a t e d , r e l i a b i l i t y of t h e
k
- 2 7-
thermocouples, and t h e g r a d i e n t i n t h e quench f u r n a c e s f o r t h e quenching t e c h n i q u e .
The l a r g e r t h e g r a d i e n t i n t h e quench
f u r n a c e s , t h e g r e a t e r t h e t e m p e r a t u r e increment for e a c h s e g ment.
The s p e c i f i c a t i o n s f o r Chromel-Alumel thermocouple w i r e s
a t ORNL p e r m i t a maximum a l l o w a b l e e r r o r of 0 . 7 5 % of r e a d i n g . * The t e m p e r a t u r e of t h e sample b l o c k thermocouple and t h e t e m -
p e r a t u r e of a thermocouple i n t h e sample h o l e o p p o s i t e t h e o t h e r thermocouple a g r e e d w i t h i n t h e l i m i t s of e r r o r of t h e thermocouples f o r a l l thermocouples i n e v e r y quench f u r n a c e .
E s t i m a t e s of t h e p r e c i s i o n o b t a i n e d i n measuring phase t r a n s i t i o n t e m p e r a t u r e s are d e r i v e d by c o r r e l a t i o n of ( a ) t r a n s i t i o n t e m p e r a t u r e measurements as a f u n c t i o n of c o m p o s i t i o n w i t h i n a s p e c i f i c s y s t e m , ( b ) e x t r a p o l a t i o n of t r a n s i t i o n t e m p e r a t u r e d a t a i n an n-component system t o one of i t s n-1 component l i m i t i n g s y s t e m s , and ( c ) r e p e t i t i o n of a n n e a l i n g and quenching e x p e r i m e n t s u s i n g s e v e r a l o f - t h e f u r n a c e s employed in
t h e phase s t u d i e s .
The p r e c i s i o n l i m i t s of t h e s e i n t e r -
n a l c a l i b r a t i o n s appear t o be w i t h i n & 2 " C . E q u i l i b r i u m t h e r m a l e f f e c t s are n o t a v a i l a b l e from mix-
t u r e s which t e n d t o s u p e r c o o l or from s a l t mixtures which t e n d t o form g l a s s e s on c o o l i n g .
Where these phenomena o c c u r ,
quenching p r o c e d u r e s p r o v i d e t h e o n l y s o u r c e of e q u i l i b r i u m
data.
I n o t h e r cases, c r y s t a l l i z a t i o n r e a c t i o n s a t h i g h t e m -
* P r i v a t e communication f r o m W. W. J o h n s t o n , Jr. of t h e I n s trument Department, S t a n d a r d s L a b o r a t o r y , ORNL.
-28-
p e r a t u r e s occur so r a p i d l y t h a t quenching e x p e r i m e n t s do n o t d i s c l o s e t h e o c c u r r e n c e of phase t r a n s i t i o n s .
By u s e of t h e
t e c h n i q u e s and equipment d e s c r i b e d i n t h i s r e p o r t phase e q u i l i b r i a i n a l a r g e number of s y s t e m s have been d e f i n e d i n d e t a i l w i t h good p r e c i s i o n and a c c u r a c y .
Acknowledgment
k
The a u t h o r s are g r a t e f u l f o r t h e b e n e f i t of p r o f i t a b l e
d i s c u s s i o n s and c o u n s e l w i t h t h e i r a s s o c i a t e s on t h e s t a f f of t h e Reactor Chemistry D i v i s i o n .
They were p r i v i l e g e d t o
be a b l e t o e x t e n d t h e e x c e l l e n t e x p e r i m e n t a l methods i n t r o duced by C . J. Barton and R. E . Moore.
The a i d of J . E .
Hammond i n i n s t r u m e n t d e s i g n and c o n s t r u c t i o n is g r a t e f u l l y acknowledged,
They a r e a l s o g r a t e f u l f o r t h e many u s e f u l
s u g g e s t i o n s made by H.
I n s l e y and C . F. Weaver.
-29-
References
'W. D. Kingery, P r o p e r t y Measurement a t High Tempera t u r e s , John Wiley and Sons, I n c . , N. Y . , ( 1 9 5 9 ) , p. 280. 'C. J. B a r t o n , H. A. Friedman, W. R. G r i m e s , H. I n s l e y , R. E. Moore, and R. E. Thoma, "Phase E q u i l i b r i a i n t h e A l k a l i Fluoride-Uranium T e t r a f l u o r i d e Fused S a l t Systems: 1 The J. Am. C e r a m . SOC., 42 [ 61 pp. Systems LiF-UF, and NaF-UF, ," 63 (1958).
3R. E. Thoma, e t . a l , , "Phase E q u i l i b r i a i n t h e Fused S a l t Systems L i F - T h q a n d NaF-ThF,," J. Phys. 63, - - Chem. 1 2 6 6 (1959). 4C. UF4-ThF, (1960)
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F. Weaver, e t . a l . , and LiF-UF,-ThC,"
"Phase E q u i l i b r i a i n t h e Systemis SOC,43 [ 4 ] 213 -J. -Am. C e r a m . -
5H. A. Friedman, " M o d i f i c a t i o n s of Quenching Techniqueis for Phase E q u i l i b r i u m S t u d i e s , " J. Am. C e r a m . SOC., 42 [ 6 ] 284 (1959). 6P. A. Tucker and E. F. J o y , "Thermal-Gradient Quenchi n g Furnace for P r e p a r a t i o n of Fused S a l t Samples f o r Phase A n a l y s i s , " Am. C e r a m . SOC. B u l l . , 36 [ 2 ] 52 (1957).
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1. 2-3 4. 5-6 7-41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54-73. 74. 75. 76. 77. 78. 79. 80. 81. 82.
83. 84. 85.
86. 87. 88. 89-98 99. 100. 101. 102. 103. 104. 105.
Biology Library Central Research Library Reactor D i v i s i o n L i b r a r y ORNL - Y-12 T e c h n i c a l L i b r a r y Document R e f e r e n c e S e c t i o n L a b o r a t o r y Records D e p a r t m e n t L a b o r a t o r y Records, ORNL R . C . C. J. B a r t o n A . L. Boch G. E. Boyd M. A . B r e d i g R . E. B i g g e r s W. E. B r o w n i n g G. W. C l a r k W . E. C l a r k T. F . C o n n o l l y D. M. D a v i s F. F . Dyer H. A. F r i e d m a n R . A. G i l b e r t W. R . G r i m e s C. E. G u t h r i e H. R . Gwin G . M. Hebert C. A. Horton R . W. H o r t o n P. R. K a s t e n E. E. K e t c h e n C . E. L a r s o n A . L. L o t t s W. D. Manly H. F. M c D u f f i e M. J. S k i n n e r J . A. S w a r t o u t R. E. Thoma C . F. Weaver A . M. W e i n b e r g J . C. W h i t e J. P. Young F. D a n i e l s ( c o n s u l t a n t ) F. T. Gucker ( c o n s u l t a n t ) F. T. Miles ( c o n s u l t a n t )
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