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Temperature Gradient Compatibility Tests of Some Refractory Metals and Alloys in Bismuth and Bismuth-Lithiun Solutions J. R. DiStefano 0. B. Cavin

National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road, Springfield, Virginia 22161 Price: Printed Copy $4.00;Microfiche $2.25 This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the Energy Research and Development Admininrationlunited States Nuclear Regulatory Commission, nor any of their employees, nor any of their contractors, subcontractors, or 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 i t s use would not infringe privately owned rights.

ORNL/TM-5503 Distribution Category UC-76

Contract No. W-7405-eng-26 METALS AND CERAMICS DIVISION

TEMPERATURE GRADIENT COMPATIBILITY TESTS OF SOME REFRACTORY METALS AND ALLOYS IN BISMUTH AND BISMUTH-LITHIUM SOLUTIONS :

J. R. DiStefano and 0. B. Cavin

I: ite Published: November 1976

OAK RIDGE NATIONAL LABORATORY

Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION for the ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

CONTENTS c

.............................. Introduction ........................... Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quartz Tests .Group 1 . . . . . . . . . . . . . . . . . . . . Quartz Tests .Group 2 . . . . . . . . . . . . . . . . . . . . Metal Loop Tests i n Bi-2.5% L i .Group 3 . . . . . . . . . . . Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abstract

. .

iii

1 1 11 11

30 32 33 33

TEMPERATURE GRADIENT COMPATIBILITY TESTS OF SOME REFRACTORY MGTALS AND ALLOYS I N BISMUTH AND BISMUTH-LITHIUM SOLUTIONS J. R. DiStefano and 0. B. Cavin

ABSTRACT

Quartz, T-111 and Mo thermal-convection loop tests w e r e conducted a t temperatures up t o 7OOOC (100OC A!l') t o determine t h e compatibility of several r e f r a c t o r y metals/alloys with bismuth and bismuth-lithium s o l u t i o n s f o r molten s a l t breeder r e a c t o r applications. Methods of evaluation included weight change measurements, metallographic examination, chemical and e l e c t r o n microprobe a n a l y s i s , and mechanical p r o p e r t i e s tests. Molybdenum, T-111, and Ta-10% W appear t o be t h e most promising containment materials, while niobium and iron-based a l l o y s are unacceptable.

INTRODUCTION A key f e a t u r e i n t h e conceptual design of the single-fluid molten s a l t breeder r e a c t o r (MSBR) i s t h e connecting chemical processing p l a n t t o continuously remove protactinium and f i s s i o n products from t h e f u e l s a l t (Fig. 1 ) . Protactinium, t h e intermediate element i n t h e breeding chain between thorium and 233U, has a s i g n i f i c a n t neutron capture cross s e c t i o n and must be kept out of t h e core t o obtain a good breeding r a t i o . Rare-earth-element f i s s i o n products are a l s o neutron poisons and so m u s t be s t r i p p e d from t h e f u e l . A promising approach f o r MSBR f u e l processing uses l i q u i d bismuth containing dissolved l i t h i u m and thorium as reductants t o e x t r a c t protactinium and rare e a r t h elements from f u e l s a l t containing both uranium and thorium (Fig. 2). I n 1968 t h e chemical f e a s i b i l i t y of t h i s process w a s demonstrated. One of t h e requirements f o r t h e development of t h e reductive e x t r a c t i o n process is i d e n t i f y i n g materials t h a t are compatible w i t h both molten f l o u r i d e salts and bismuth-containing reductants. Hastelloy N (Ni-7% Cr-16% M d % Fe) has e x c e l l e n t Compatibility with molten s a l t s a t 50O-7oO0C; however, i t does not have good compatibility with bismuth. Of t e n elements t e s t e d , graphite, tungsten, and molybdenum appear most promising (Table 1 ) and they are also compatible with molten f l o u r i d e mixtures. Extensive i n v e s t i g a t i o n s of bismuth as a r e a c t o r coolant have shown t h a t i n h i b i t o r s such as magnesium, titanium, and zirconium are o f t e n required t o reduce t h e high corrosion rates of conventional materials i n bismuth. 2-1 However, these types of i n h i b i t o r s would not be r e a d i l y acceptable f o r use i n t h e molten s a l t system because they would be eliminated from t h e bismuth stream by several of the proposed s t e p s i n processing.

1 n

ORNL-DWG '68-1185ER

PRIMARY SALT PUMP

CHEMICAL PROCESSING PLANT

Fig. 1.

'LiF -BeF2-ThF,

SECONDARY SALT PUMP

- UF,

Single-Fluid, Two-Region Molten-Salt Breeder Reactor. .;

ORNL-DWG 74-9004R

FUEL SALT RECONSTITUTION AEXCESS U FOR SALE

URANIUM REACTOR

REMOVAL \

PROTACTINIUM ' \

REMOVAL

RARE EARTH ELEMENTS REMOVAL

FISSION ~RODUCTS TO WASTE

Fig. 2. Simplified Flowsheet for Processing the Fuel in a MoltenSalt Breeder Reactor.

Table 1. S o l u b i l i t i e s of Some Elements i n Bismuth a t 6OOOC ,

Element

S o l u b i l i t y , ppm ~

Reference ~

~~~

Not detectable

5;6 6

45 ;110

7;11

50 1 45 100-200

5 5 8

590

65,750

W C Mo Be V Fe Cr

The low s o l u b i l i t y of graphite, tungsten, and molybdenum i n bismuth has been confirmed i n compatibility tests by o t h e r i n v e s t i g a t o r s , and, i n addition, rhenium, tantalum, tantalum a l l o y s , and c e r t a i n ceramic oxides and carbides a l s o appeared t o be promising f o r bismuth containment. 12-â&#x20AC;? I n a high temperature isothermal system thermodynamic equilibrium among components is generally reached r e l a t i v e l y quickly; t h e compatibility of t h e system can o f t e n be predicted i f phase diagrams of t h e components are known. When t h e r e are thermal f l u c t u a t i o n s and/or gradients w i t h i n a system and t h e equilibrium constant f o r a corrosion r e a c t i o n i s temperature dependent, continuing corrosion can occur. For example, i f i r o n dissolves i n bismuth, and t h e s o l u b i l i t y increases with temperature, simultaneous d i s s o l u t i o n and deposition of i r o n w i l l occur i n t h e system. Under steady state conditions the s o l u t i o n o r deposition rate equation f o r a given l o c a t i o n can be expressed:

where J i s t h e f l u x of material e n t e r i n g o r leaving t h e l i q u i d metal, K i s a rate constant, C is t h e equilibrium s o l u b i l i t y â&#x20AC;&#x2122; o f t h e s o l u t e , and C is t h e a c t u a l concgkbation of the solute. The d r i v i n g f o r c e f o r e i t h e r d i s s o l u t i o n o r deposition i s d i r e c t l y proportional t o t h e concentration d i f f e r e n t i a l t h a t exists i n t h e system a t a p a r t i c u l a r l o c a t i o n and t h e appropriate rate constant f o r t h e rocess. Our d a t a (Table 1) agree with I s very l o w previous eompatibility experimentsp2-17 t h a t suggest t h a t Cs f o r g r a p h i t e and t h e r e f r a c t o r y metals tungsten, rhenium, mofybdenum, and tantalum. Niobium and i r o n are somewhat less promising, b u t s t i l l show r e l a t i v e l y low s o l u b i l i t y i n bismuth.

4 The reductive e x t r a c t i o n process f o r protactinium removal uses bismuth containing small concentrations of lithium, and t h e metal t r a n s f e r process f o r removing rare e a r t h element f i s s i o n products from t h e f u e l s a l t uses bismuth containing 2-3 w t % L i . Since t h e s o l u b i l i t y of materials i n bismuth-lithium s o l u t i o n s could be appreciably d i f f e r e n t from t h e i r s o l u b i l i t y i n pure bismuth (Table l ) , tests had t o be conducted i n t h e appropriate chemical processing solutions. Thermal convection loops used i n t h e s e tests were f a b r i c a t e d from quartz, T-111 (Ta-8% W-2% Hf), and molybdenum. The quartz loops w e r e s a t i s f a c t o r y f o r t e s t i n g i n pure bismuth and i n bismuth containing up t o 0 . 0 1 w t % lithium. No quartz loops with higher l i t h i u m concentrations w e r e operated because of t h e r e a c t i o n between S i 0 2 and lithium. Loops f a b r i c a t e d from q u a r t z were r e l a t i v e l y inexpensive and could be operated i n an a i r environment. Samples of t h e materials being t e s t e d w e r e suspended i n t h e vertical hot- and cold-leg s e c t i o n s (Fig. 3). To prevent t h e samples from f l o a t i n g , they were attached t o a quartz rod t h a t was held a t the top of each leg. Several types of sample geometries were used, including f l a t t a b s , c y l i n d r i c a l tubes, and c y l i n d r i c a l and s h e e t t e n s i l e specimens. External h e a t e r s were placed on each l e g t o preheat t h e loop above the melting p o i n t of bismuth o r t h e Bi-Li s o l u t i o n . A pot containing t h e m e l t t o be c i r c u l a t e d was attached by a mechanical connector t o t h e bottom of t h e cold l e g (Fig. 3.). Before f i l l i n g , the loop w a s evacuated so a pressure d i f f e r e n t i a l would f o r c e t h e l i q u i d i n t o t h e loop. During operation, t h e m e t a l l i n e below t h e quartz w a s unheated t o allow formation of a s o l i d plug t o serve as a f r e e z e valve. When t h e t e s t w a s completed, t h i s s e c t i o n of t h e l i n e w a s heated t o allow t h e f l u i d t o d r a i n back i n t o t h e attached pot. The design of t h e m e t a l thermal convection loops w a s similar t o t h a t of the q u a r t z loops (Fig. 4). Two s e c t i o n s of 7/8-in. OD X 0.050 i n . tubing w e r e bent t o form one vertical-horizontal segment (Fig. 4). The segments were joined by making gas-tungsten-arc saddle welds a t t h e top and bottom of t h e vertical legs. Tubular s h e e t and t e n s i l e specimens w e r e suspended i n each of t h e vertical legs. Wires linked t h e specimens together t o r i d i g l y a t t a c h t h e specimen chain t o t h e vertical l e g s a t t h e top and bottom. The metal loops were used t o test a bismuth-lithium a l l o y containing 2.5 w t % L i . This a l l o y w a s prepared and p u r i f i e d i n a molybdenum-lined s t a i n l e s s s t e e l container (labeled " t r a n s f e r pot" i n Fig. 4). The l i n e s extending from t h e top of t h e loop surge tank were made of tantalum f o r ease of f a b r i c a t i o n and corrosion r e s i s t a n c e . A commercially-produced Nb--l% Zr-type 316 s t a i n l e s s steel d i s s i m i l a r metal j o i n t connected t h e t r a n s f e r pot t o t h e loop. The N b 4 % Z r end w a s welded t o t h e tantalum tube; a mechanical f i t t i n g connected t h e stainless steel end t o t h e t r a n s f e r p o t l i n e s . Two types of h e a t e r s w e r e used: The main hot-leg h e a t e r contained a r a d i a t i n g tantalum element while standard Calrod h e a t e r s were strapped t o o t h e r portions of t h e loop (Fig. 4). The molybdenum loop i s shown (Fig. 5) p r i o r t o being i n s t a l l e d i n a vacuum chamber where t h e test was run.

1 I I

i I

I i i

I I

I ~

Fig. 3. Quartz Thermal Convection Loop with Metal Samples i n Hot and Cold Legs.

ORNL-DWG 74-t2762 PRESSURE TO VACUUM/ 7

rTHERMOCOUPLE WELL

THERMOCOUPLE WELL--. CLOSED FILL LINE TRANSFERPOT

MOUNTING FRAME\ l

--k I

i !

I I i

TEST SPECIMENSTYPICAL 2 VERTICAL LEGS ---,

DUMP TANK

F i g . 4.

I I t

‘-CALROD

HEATERS

( 3 LEGS)

POST TEST DRAIN LINE-

I I

Design of Metal Thermal Convection Loop Apparatus.

Fig. 5. Molybdenum Thermal Convection Loop Prior to Test in Vacuum Chamber.

After evacuation and baking o u t of t h e vacuum chamber, t h e e n t i r e loop w a s heated t o 5OO0C, s i n c e t h e melting p o i n t of Bi-2.5 w t % L i i s s l i g h t l y less than 5OO0C (Fig. 6). As t h e t r a n s f e r pot was heated t o 6OO0C (900OC i n t h e case of t h e molybdenum loop), t h e loop was evacuated, and d i f f e r e n t i a l pressure w a s used t o t r a n s f e r t h e bismuth-lithium s o l u t i o n i n t o t h e loop. During operation t h e tantalum h e a t e r heated t h e hot l e g , but t h e required temperature d i f f e r e n t i a l w a s maintained with l i t t l e o r no h e a t t o t h e rest of t h e loop from t h e Calrod h e a t e r s . To s t o p t h e test, t h e h e a t e r s were turned o f f and t h e bismuthlithium s o l u t i o n w a s allowed t o s o l i d i f y . When t h e system had cooled, t h e vacuum chamber was opened and t h e bottom of t h e cold l e g c u t o f f . A d r a i n tank was placed immediately under this p o r t i o n of t h e cold l e g , t h e chamber re-evacuated, and t h e loop heated t o approximately 6OO0C t o allow it t o drain. Samples generally required cleaning before meaningful weight and dimensional measurements could b e obtained. Several d i f f e r e n t techniques removed t h e bismuth o r Bi-Li t h a t adhered t o t h e samples. If t h e amount w e r e small, mechanically cleaning t h e samples w a s s u f f i c i e n t . A more s a t i s f a c t o r y technique w a s t o amalgamate t h e bismuth by dipping t h e sample i n t o h o t mercury (approximately 100-l5O0C) and then removing t h e amalgam mechanically. Bismuth used i n t h e s e s t u d i e s w a s Grade 69 obtained from Cominco American Corporation. Except f o r Quartz loops 1 and 2, t h e as-received material w a s f i r s t p u r i f i e d by bubbling hydrogen through t h e molten metal f o r two hours a t 350째C, i n a molybdenum-lined container. I n i t i a l l y t h e e x i t gas burned i n t e r m i t t e n t l y and had a reddish hue. Subsequently t h e gas burned continuously and w a s almost c o l o r l e s s i n d i c a t i n g t h a t r e a c t i o n with hydrogen had ceased. I f an a l l o y w e r e required, s o l i d lithium w a s added t o s o l i d , p u r i f i e d bismuth, and t h e mixture w a s heated above t h e melting temperature of t h e a l l o y . The phase diagram shows t h a t t h e melting temperature of the a l l o y varies with lithium concentration (Fig. 6). Additionally, i n t h e Group 1 series (see r e s u l t s s e c t i o n ) t h e bismuth o r bismuth-lithium s o l u t i o n w a s f i l t e r e d p r i o r t o introduction i n t o t h e loop through a type 316 s t a i n l e s s steel f i l t e r having openings of 10 pm. Determinations of various i m p u r i t i e s before and a f t e r t h e various treatments (Table 2) showed no s i g n i f i c a n t improvement i n t h e p u r i t y of t h e bismuth; however, v i s u a l observations of t h e e x i t gas flame and t h e appearance of t h e bismuth indicated t h a t some p u r i f i c a t i o n had occurred during hydrogen f i r i n g . The addition of more lithium t o bismuth as required f o r t h e two metal thermal convection loop tests w a s much more d i f f i c u l t because (1) t h e melting temperature of t h e a l l o y is much higher, (2) t h e bismuth-lithium r e a c t i o n is strongly exothermic, and (3) during a l l o y i n g t h e r e i s a tendency t o form L i 3 B i (Si+% L i ) , which m e l t s a t 1150OC. A s p e c i a l apparatus w a s used t o prepare Bi-2.5% L i f o r these tests (Fig. 7). Lithium w a s f i r s t p u r i f i e d by hot g e t t e r i n g with zirconium f o i l a t 8OO0C, and the required amount t r a n s f e r r e d i n t o a type 304 s t a i n l e s s steel Sequential s t e p s were then as follows: container. 1. S o l i d bismuth w a s loaded i n t o a molybdenunr-lined s t a i n l e s s steel container and t h e container was sealed under argon.

ORNL-DWG 75-9963

0 Li

90 92

WEIGHT PERCENT BISMUTH 94 96 97 98

40 50 60 ATOMIC PERCENT BISMUTH

W<tOO Bi

Fig. 6. Lithium-Bismuth Phase Diagram.

Table 2.

Concentration of Impurities in Bismuth Used in Quartz Loop Tests, ppm

Bismuth Condition As-received After hydrogen treatment Filtered through stainless steel screen

% I

Uot determined.

0.2

<20

ma ma

ORNL-DWG

74-12579

TO OIL BUBBLER-VENT

304SS LITHIUM FILL LINE AND BLOW BACK LINE

304SS

304ss

THERMOCOUPLE

WELL v4

TO VACUUM

:’ =r=+ TO ARGON MOLYBDENUM MOLYBDENUM

TUBES -304ss THERMOCOUPLE WELL

LINER

L4in.d

Fig.

System Used to Prepare and Purify

2’12 in.

Bi-Li

Alloy.

304ss

I 1

The bismuth container w a s evacuated and heated a t 650OC. Hydrogen was bubbled through the molten bismuth f o r approximately 24 hr. 4. The temperature of the bismuth w a s r a i s e d t o 700OC; t h e l i t h i u m w a s heated t o 25OoC i n a s e p a r a t e container. 5 . Lithium w a s t r a n s f e r r e d i n t o t h e bismuth container by pressure d i f f e r e n t i a l . Molten l i t h i u m w a s i n j e c t e d below t h e l i q u i d bismuth s u r f a c e (Fig. 7). After a l l o y i n g a sample w a s taken and a t y p i c a l a n a l y s i s w a s lithium-2.4%, hydrogen-14 ppm, and oxygen-90 ppm. Nominal operating conditions f o r a l l of t h e loop tests w a s 7OOOC maximum h o t l e g temperature and a minimum cold l e g temperature of 59U625OC. For t h e quartz loop tests Cr-Al thermocouples were used; they were located i n w e l l s protruding through t h e quartz i n t o t h e l i q u i d stream. Thermocouples made of P t , Pt-10% Rh were s i m i l a r l y i n s e r t e d i n t o w e l l s through the T-111 tubing w a l l t o measure temperature i n test CPML-1. I n test CPML-2 P t , Pt-10% Rh thermocouples w e r e again used, b u t they w e r e strapped t o t h e o u t s i d e s u r f a c e of t h e molybdenum tubing. A l l q u a r t z loops were operated i n an e x t e r n a l air environment. Refractory m e t a l l o o s were operated i n a vacuum chamber a t pressures of 10-4 t o 10-5 Pa (lo-' t o 10-7 t o r r ) . 2. 3.

RESULTS

Compatibility results from these experiments can be grouped according t o t h e materials t e s t e d and the l i t h i u m concentration of t h e bismuth. Bismuth and Bi-O.Ol% L i s o l u t i o n s (Groups 1 and 2) were c i r c u l a t e d i n q u a r t z loops containing samples of various metals (Table 3). A s o l u t i o n of Bi-2,5% L i (Group 3) was c i r c u l a t e d i n a molybdenum loop (CPML-1) f o r 3000 h r and i n a T-111 loop (CPML-2) f o r 8700 hr. I n each case t h e loops contained samples of t h e same material as t h e loop i t s e l f . Alloys i n v e s t i g a t e d were based on molybdenum, tantalum, niobium, and iron. When Nb or Fe-based a l l o y s w e r e included, t h e tests operated f o r r e l a t i v e l y s h o r t times before the flow stopped (Quartz tests - Group 1). A l l tests using only molybdenum a l l o y o r tantalum a l l o y samples completed t h e i r scheduled operating period (up t o 10,000 h r ) (Quartz tests - Group 2).

Quartz Tests

- Group 1

Quartz loops 1 and 2 contained samples of TZM, tantalum, Nb-1 Z r and niobium and operated f o r 18 and 23 h r r e s p e c t i v e l y before flow stopped. I n loop 1 flow was stopped by a plug which formed a t t h e top of t h e cold leg. The q u a r t z f r a c t u r e d a t t h i s p o i n t , exposing t h e bismuth t o air. The samples remianed immersed i n bismuth, but t h e weight changes (Table 4) may reflect exposure t o a i r as w e l l as mass-transfer e f f e c t s . Loop 2 stopped flowing a f t e r 23 hr. Although a s o l i d plug had a g a i n formed, i t did not f r a c t u r e t h e quartz. Samples of t h e plug w e r e analyzed spectrog r a p h i c a l l y and niobium w a s found t o be the major c o n s t i t u e n t of t h e plug.

12 Table 3.

Summary of Quartz Loop Tests (700OC max, -1OOOC AT)

Loop

Samples

Fluid

Time

(hr)

Grow 1 TZMa/Ta/Nb/Nb-1% Z r TZM/Ta/Nb/Nb-1% Z r Nb/Nb-l%

Bi Bi Bi Bi

Fe-5% Mo

423

Group 2 3 6 10

M~/TZM~ Ta/T-111

Bi Bi Bi

Mo brazed with Fe-based alloys Ta-10% W

17 7 11 12 13

Bi Bi4.Ol% Bi-O.Ol% Bi-O.Ol% Bi..Ol% Bi-O.Ol%

Li Li Li Li Li Bi-fJ.Ol%L i

MO/TZM

T-111 Ta Ta-10% W

3, OOOe 3,000: 2,100, 3,O0Oe 3,000, 3,000, 3,000, 3,000, 3,000, 3,000, 10,000

a TZM i s M d . 5 % T i 4 . 1 % Z r .

bFlow stopped. C

Terminated, samples dissolved.

dT-lll

i s Ta-8% W-2% Hf.

Completed

Table 4. Materia 1

Weight Changes i n Samples From Quartz Loop la Location

Weight change (mg/cm2)

Corrosion rate (mg/cm2 yr) ~~

Tantalum

Hot leg

TZM

Hot leg

-15.9

-1% Z r

Hot leg

-54.3

Niobium

Hot leg

-31.0

Tantalum

Cold leg

TZM

Cold leg

-11.0

Nb-1% Z r

Cold leg

-4.9

4.4

+O. 3

-195 -7,738

UX46 -2 ;38%

Niobium Cold leg -1.3 -633 a After 18 hr i n bismuth a t 700째C maximum temperature and 100째C temperature d i f f e r e n t i a l .

13 X-ray d i f f r a c t i o n a l s o indicated t h e presence of small amounts of To eliminate t h e p o s s i b i l i t y t h a t oxygen contamination of Bi203-Nb205. bismuth might be responsible f o r these results, bismuth used i n subsequent group 1 tests was p u r i f i e d by bubbling hydrogen through t h e molten metal f o r 2 h r a t 35OoC and then f i l t e r i n g as described previously. Loop 4 contained niobium. and -1% Z r samples and w a s operated a t a maximum temperature of 705'C with a temperature d i f f e r e n t i a l of 75OC f o r a period of 115 h r before f l o w stopped. X-ray d i f f r a c t i o n analysis of a sample taken from t h e plug t h a t had formed i n t h e cold l e g showed t h e presence of several phases: bismuth, alpha zirconium, and several unidentified phases. Niobiym was not detected by x-ray d i f f r a c t i o n analysis, but t h e atomic radius of niobium is t h e same as bismuth and i t could occupy s u b s t i t u t i o n a l l a t t i c e sites i n t h e bismuth u n i t c e l l without a f f e c t i n g t h e l a t t i c e parameter of t h e bismuth. Spectrographic analysis of a sample of t h e plug materials indicated t h a t i t contained 0.5% Nb, 100 ppm Z r , 300 ppm N i , 500 ppm Fe, with the remainder bismuth. The i r o n , nickel, and chromium probably dissolved i n t h e bismuth during t r a n s f e r through stainless steel l i n e s and f i l t e r during loadingjof t h e loop. The samples from t h i s test are shown (Fig. 8). The -1% Z r sample from t h e hot l e g w a s almost completely dissolved. Bismuth remained on t h e samples a f t e r draining and w a s not successfully removed; therefore, weight change data w e r e not recorded.

Fig. 8. Loop 4.

Niobium and -1% Z r Samples From Quartz Thermal Convection

Photomicrographs of s e l e c t e d samples are shown (Fig. 9 ) . The niobium sample from the h o t l e g i s t h i c k e r than i t was o r i g i n a l l y ; however, t h e unattacked c e n t e r s e c t i o n is less than 0.020 i n . compared t o an o r i g i n a l sample thickness of 0.027 i n . I n e l e c t r o n probe scanning images of t h i s sample (Fig. 10) t h e l a y e r adhering t o the niobium appears t o be primarily bismuth, but t h e p a r t i c l e s w i t h i n t h e bismuth are niobfum. I n niobium-1% zirconium samples from hot- and cold-leg regions of loop 4 (Fig. 9) t h e cold-leg sample has a g r e a t e r unaffected c e n t e r s e c t i o n (about 0.027 in.) than t h e hot-leg sample, and h a s g r e a t e r t o t a l thickness This suggests t h a t t h e r e has (about 0.040 i n . compared with 0.030 in.). been considerable mass t r a n s f e r of material from hot- t o cold-leg s e c t i o n s . Loop 9, which contained Fe-5% Mo samples, operated f o r 423 h r before a power f a i l u r e stopped the test. A f t e r 216 h r one of t h e samples from the h o t l e g came loose from i t s wire holder and f l o a t e d t o t h e top of t h e bismuth. When t h e loop operation w a s stopped a f t e r 423 h r t h i s w a s t h e only sample recovered; a l l o t h e r samples apparently had dissolved. Analysis of a sample of t h e bismuth from t h e top of t h e cold l e g determined t h a t i t contained 13%i r o n and 0.018% molybdenum. The unheated area of the cold l e g above t h e samples w a s t h e c o l d e s t p o r t i o n of t h e loop and is probably where deposition occurred. I f so, bismuth flowing p a s t t h e cold-

Fig. 9. Loop 4.

Niobium and -1% Z r Samples From Quartz Thermal Convection

Y-100290

Bib

Fig. 10. Electron Probe Scanning Images of Niobium Hot Leg Sample From Quartz Thermal Convection Loop 4.

l e g samples could continue t o have a strong d i s s o l u t i o n e f f e c t . S t a t i c capsule tests of t h i s a l l o y f o r 600 h r a t 65OOC i n bismuth d i d not show d e t e c t a b l e d i s s o l u t i o n , thus i n d i c a t i n g a strong influence 'of t h e rate constant K (Eq. 1) on mass t r a n s f e r of i r o n i n temperature gradient systems involving bismuth.

Quartz T e s t s

- Group 2

Ten quartz loops were t e s t e d with samples of tantalum ( a l l o y s ) and/or molybdenum (alloys).. Loops 3, 6, 10, and 16 c i r c u l a t e d bismuth while t h e remaining s i x loops c i r c u l a t e d Bi-O.Ol% L i . A l l of these loops w e r e operated f o r 3000 hr except f o r loop 10, which was operated 2100 h r , and loop 15, which w a s operated 10,000 hr. Loop 1 0 contained molybdenum samples t h a t had been brazed together with iron-based a l l o y s . Four d i f f e r e n t compositions were used: Braze Alloy Designation 16 35 36 42

M M M M

Nominal Composition (wt %) F d % M d % -1% B Fe-15% Mo-4% C 1 X B Fe-25% M d % C1% B Fe-15% M d % C1% B S % Ge

16 The loop operation w a s stopped after 2100 h r and weight changes of t h e samples were measured (Table 5). They were very small weight changes, and a n a l y s i s of t h e bismuth gave l i t t l e evidence t h a t d i s s o l u t i o n had occurred. Iron and molybdenum concentrations were less than 3 ppm, and carbon w a s 8-13 ppm. However, metallographic examination showed t h a t each of t h e braze a l l o y s contained an o u t e r s u r f a c e l a y e r (Fig. 11). A more d e t a i l e d examination was made of t h e samples brazed with a l l o y s 16 M and 35 M. For t h e a l l o y s before test no o u t e r s u r f a c e l a y e r w a s v i s i b l e (Fig. 12). An e l e c t r o n beam microprobe a n a l y s i s determined t h e d i s t r i b u t i o n of i r o n , molybdenum, and bismuth i n t h e braze a f t e r test. I n a l l o y 16 M t h e o u t e r s u r f a c e l a y e r w a s r i c h i n i r o n ; t h e w h i t e - p a r t i c l e s contained 88% bismuth, 5%molybdenum, and less than 0.5% i r o n (Fig. 13). An area adjacent t o the white p a r t i c l e s contained 41% bismuth, 23% molybdenum, and 4% i r o n , while t h e dark s p o t s w e r e predominantly i r o n (about 70%). I n a l l o y 35 M t h e s u r f a c e l a y e r appears t o b e subdivided i n t o two segments (Fig. 14) with t h e outermost segment r i c h i n molybdenumand t h e i n n e r segment predominantly i r o n . Bismuth has completely penetrated t h e braze (Fig. 15). Thus, although there w a s l i t t l e evidence of mass t r a n s f e r , bismuth d i d react with t h e iron-based braze a l l o y s . The e f f e c t of lithium i n bismuth on t h e corrosion rates of Mo/TZM, Ta/T-111, and Ta-10% W i s shown i n Tables 6, 7, and 8 . Maximum corrosion rate (weight l o s s ) of molybdenum i n B i - O . O l % L i w a s 16.9 mg/cm2-yr compared with 1.64 mg/cm2*yr i n pure bismuth. Tantalum and T-111 a l s o showed higher rates of mass t r a n s f e r i n Bi-O.Ol% L i , b u t Ta-10% W showed t h e opposite e f f e c t - a higher corrosion rate i n bismuth compared with Bi-O.Ol% L i , where a l l the samples exhibited small weight gains.

Table 5.

Weight Ccanges i n Molybdenum-Braze Samples Exposed t o Bismuth i n Quartz Thermal Convection Loop T e s t s

Conditions:

7OOOC Max Hot Leg Temperature; 95OC Temperature D i f f e r e n t i a l ~

Weight Change (mg) Braze Alloy Hot Leg

Cold Leg

B) 16 M ( F A % C1%

-1.6

Sample not included

35 M ( F A % C1% B-15% Mo)

-4.2

+12.2

B-25% Mo) 36 M ( F e 4 % el% 42 M (Fe-4% C-1%

B-15% M a S X Ge)

-16.6 -0.2

+5.0 +2.2

Y-132372

%IS

Ma Brazed with AIlw 16h4

h b Brazed with Alloy 35M

F i g . 12.

Brazed Molybdenum Samples Before Test in Quartz Loop 10.

Y-106Wo

Backscattered Electrons

Fek

BiLa

Fig. 13. Electron Beam Scanning Images of Molybdenum Sample Brazed ' With Alloy 16M After Exposure t o Bismuth i n Quartz Loop 10. Lighter regions indicate higher concentration of l i s t e d element.

Backscattered Electrons

Bib

MoLa

FeKa

F i g . 14. Electron Beam Scanning Images of Molybdenum Sample Brazed With Alloy 35M After Exposure to Bismuth i n Quartz Loop 10. Lighter regions indicate higher concentration of l i s t e d element.

-Y-1 0600 1

Molybdenum Base Metal Backscattered Electrons

Bismuth Lo X-Rays

Fig. 15. Electron BeamFcymning Image of Molybdenum Sample Brazed With Alloy 35M After ExposurqRo Bismuth i n Quartz Loop 10. Bismuth has completely penetrated the bifaze a l l o y .

Table 6. Comparison of Corrosion Rates of Molybdenum and TZM Samples Exposed to Bismuth or Bi-O.Ol% Li in Quartz Thermal Convection Loop Tests for 3000 hr Corrosion Rate (mg/cm*-yr) Temperature

Location

Cold Leg

Loop 7

Loop 11

Bi-O.Ol% L i

Bi-O.Ol%

630

+O. 53

+8.65

+3.10

640

+l.72a

-0. 36a

-1.14

660

-1.64

690

+I. 58

-1.74

-9.70

680 660

+3.80

+3.56

-0.03

640

-1.02 +0.90a

-0.58 +o. 5ga

+0.26 w.44

615

+l.43

Hot Leg

Loop 3 Bismuth

("C)

-3.80

-16.9

+I. 34

TZM sample.

Table 7. Comparison of Corrosion Rates of Tantalum and T-13.1 Exposed to Bismuth and Bi-O.Ol% Li for 3000 hr in Quartz Thermal Convection Loops

Location

Corrosion Rate (mg/cm2*yr) -

Temperature ('C)

Loop 6a (Ta/T-111, Bismuth)

Loop 13b (Ta, Bi4.01X L i )

(T-111, ~~

Hot Leg

Cold Leg

6 30

+13. 73d

-16.8

+0.82

640

rH). 75d'

-41.8

-2.28

660

-47.16

690

-79.79

680

-17.50

-68.9

660

-24.40

-47.7

+0.70

-46.1

-1.46

+1.08

-6.5 -137

640

+O. 15d

615

+O. 29

-13.6 -0.85

-112.4

+0.44 ~

20 ppm tantalum i n bismuth a f t e r test; less than 2 ppm before test.

b30-150 pprn tantalum in bismuth a f t e r test; less than 1 ppm before test. C

Loop 12= BI4.01X; Li)

2HOO ppm tantalum i n bismuth a f t e r test; 3 ppm before test.

d T - l l l samples, others w e r e tantalum samples.

Table 8. Comparison of Corrosion Rates of Ta-lO% W Samples Exposed t o Bismuth o r B i - O . O l % L i i n Quartz Loop T e s t s f o r 3000 H r ~~

Corrosion Rate (mg/cm2*yr) Location

Hot Leg

Cold Leg

. w

Temperature ("C)

Loop 1 7 (Bismuth)

Loop 18 (Bi-0.OlX Li)

6 30

-1.40

+o. 22

640

-3.65

660

+0.26

690

-0.37

680

-2.86

+O .46

660

-1.43

640

-2.48

+o. 13 +o. 35

615

-1.23

+O .13

Sample damaged during bismuth removal.

The metallographic appearance of Mo and TZM samples from loops 3 and 7 is shown (Figs. 16 and 17). Hot-leg samples of molybdenum from both of these tests show g r a i n boundary corrosion t o about 0.0005 i n . L i t t l e o r no a t t a c k on TZM w a s noted. There w a s a l a y e r of extremely f i n e grains a t t h e s u r f a c e of t h e molybdenum which were attacked intergranularly. These grains w e r e probably caused by r e s i d u a l cold work from machining and subsequent r e c r y s t a l l i z a t i o n a t t h e test temperature. I f these g r a i n boundaries picked up i r o n during machining, p r e f e r e n t i a l a t t a c k might be expected. Room temperature mechanical property tests of the molybdenum samples showed t h e i r p r o p e r t i e s t o be changed only s l i g h t l y from those of t h e as-received samples (Table 9 ) . Metallographic examination of t h e t e n s i l e samples showed t h e r e was no e f f e c t of t h e i n t e r g r a n u l a r a t t a c k of t h e f i n e s u r f a c e grains. Chemical a n a l y s i s of t h e melts (Table 10) showed s l i g h t l y higher molybdenum i n Bi+I.Ol% L i a f t e r t e s t i n g . I n general, t h e results i n d i c a t e that t h e a d d i t i o n of 0.01% L i t o bismuth had l i t t l e e f f e c t on i t s compatibility with molybdenum. The a l l o y Ta-10% W showed similar r e s i t a n c e t o both bismuth and Bi-O.Ol% L i (Fig. 18). A hot-leg sample (from loop 17) exposed t o bismuth w a s s l i g h t l y corroded t o a depth of approximately 0.0005 i n . , b u t t h e r e w a s no v i s i b l e corrosion of any of t h e specimens errposed t o Bi-O.Ol% L i . Chemical analyses of t h e m e l t s a f t e r test were similar t o those before test, i n d i c a t i n g t h a t T e l O % W has good corrosion r e s i s t a n c e to both f l u i d s .

Y-99457 Cold lag

Fig. 16.

Molybdenum and TZM Samples From Quartz Loop 3.

Fig. 17.

Molybdenum and TZM Samples From Quartz Loop 7.

Table 9. Effect of Exposure t o Bi-O.Ol% L i i n Quartz Thermal Convection Loops on the Room Temperature Tensile Properties of Refractory Metals Material Molybdenum

Sample location

Tantalum

UTSa (10' psi)

Elong (X)

As-received Hot l e g 69OoC

110 ll1

a. 7 11.3

Hot l e g 660.C Cold l e g 66OoC

111 112 112

8.0 11.3 11.3

Cold l e g 64OoC %timate

T-111

UTSa

Elong

(10' PSI)

(I)

44 47 47 50

UTSa

Ta-10% W Elong.

UTSa (10' psi)

Elong

(io3 Psi)

(x)

24 23 26

94 52 61

10 0 0

a4 a7

26 25

7 7

(%)

tensile stress.

Table 10. Composition of Bismuth and Bi-O.Ol% L i Melts Before and After Exposure to Molybdenum and TZM i n Quartz Loops 3, 7 , and 11 ~~~~

Concentration (ppm) Loop

Time Sampled

Before test After test

5 <1

Before test

After t e s t

Before t e s t M ter test

22 24

0 <1 1

1 1 <1 <1

0.1 0.1

C0.5

<0.5

0.5 4

70 70

100

7 8

96 100

2 <30

30 40

8 8

3 3

0.3 0.3

0.3

<30 <30

<SO

<200

<50

Before Test

'90 , MICRONS , 390 3!p M O Y

Hot Leg:

M.26 mg/cm2/yr

Cold Leg: 40.13 mg/cm*/yr

Fig 18. Ta-10% W Samples Before and After Exposure t o Bismuth (Quartz Loop 1 7 -Upper Pictures) and B i - O . O l % L i (Quartz Loop 18 -Lower Pictures). Maximum hot leg temperature was 7OO0C and minimum cold l e g temperature w a s 60OoC. Weight changes i n tantalum and T-111 specimens were g r e a t e r when they w e r e exposed t o Bi-O.Ol% L i than when exposed t o bismuth and p o s t t e s t chemical analyses (Table 11) indicated there was a greater concentration of tantalum in the melts containing 0.01% lithium. However, metallographic examination of the samples did not show any s i g n i f i c a n t differences (Fig. 19). Weight changes i n T-111 were small and there was l i t t l e evidence of corrosion, although surface and grain boundary corrosion from 0.001-0.002 in. occurred i n tantalum. The e f f e c t of time on the mass-transfer r a t e i n t h e molybdenumB i - O . O l % L i system is indicated by comparison of the results from loops 11 and 15. Weight change data are presented i n Table 12. Corrosion rates as indicated by maximum weight l o s s i n mg/cm2=yr generally decreased with time. Tripling t h e time decreased the maximum corrosion rate by a f a c t o r of about 1.5. However, t h e n e t weight l o s s obtained by summing t h e weight changes of a l l t h e specimens increased from 549 mg t o 1754 mg, a 3.2-fold increase. After 10,000 h r , corrosion of t h e molybdenum was s t i l l less than 0.0005 in. deep (Fig. 20).

27 Table 11, Composition of Bismuth and Bi-O.Ol% Li Melts Before and After Exposure to Tantalum/T-111 in Quartz Loops 6, 13, and 12 Concentration,ppm Time

Loop 6

Before test

After test

<20

Before test

15 23

After test

200

<15

127

100

150

100 60

3 250

30 40

150

<3 <3

0 /

Y-103346

k Annealed

Hot leg

Cold leg

F i g . 19. Tantalum and T-1U. Specimens Before and After Exposure to Bismuth in Quartz Thermal Convection Loop 6. L

28 Table 12. Comparison of Weight Change and Corrosion Rate i n Molybdenum Samples Exposed t o B i - O . O l % L i i n Quartz Thermal Convection Loops f o r 3,000 and 10,000 h r ~~

Weight Change, mg/cm2 Sample

Corrosion rate, mg/cm2*yr

La ca t i o n

Temperature ("C)

Hot l e g

630

-0.39

+O. 1 7

-1.14

+0.15

640

+ l . 06

-0.23

+3.10

-0.20

660

-1.30

-4.10

-3.80

-3.59

690

-3.32

-7.08

4-70

-6.20

Cold l e g

a2-5

Loop lla (3,000 h r )

b Loop 1 5 (10,000 h r )

Loop 11 (3,000 h r )

Loop 1 5 (10,000 h r )

680

-0.01

-1.47

-0.03

-1'. 2 8

660

+o. 09

-0.55

+O. 26

-0.48

640

+o.15

-0.39

4.0.44

-0.34

615

M.46

4.0.07

+l.34

+0.06

ppm molybdenum i n bismuth after test; 2 ppm b e f o r e test.

b<lOO ppm molybdenum i n bismuth a f t e r test; < l o 0 ppm b e f o r e test.

Befae Test

Hot Lag: -3.6 ma/Un*/yr

Cold Leg: 4.6 ma/cnf/Vr c

Fig. 20. Molybdenum Samples Before and After Exposure t o B i - O . O l % L i f o r 3000 h r (loop 11-upper) and 10,000 h r (loop 16-lower). Lower samples were etched by anodizing.

When t h e corrosion rates of tantalum a l l o y s and molybdenum were compared (Table 13) a f t e r 3000 h r exposure t o B i - O . O l % L i , T e l O % W showed t h e g r e a t e s t r e s i s t a n c e t o corrosion, w h i l e tantalum showed t h e least r e s i s t a n c e . Metallographically Ta-10% W, T-111, and molybdenum w e r e a l l corroded t o <0.0005 i n . deep compared with 0.001 t o 0.002 i n . i n tantalum. When t h e mechanical p r o p e r t i e s of t h e materials before and a f t e r test w e r e compared (Table 9), t h r e e of t h e materials, Ta-10% W, tantalum, and molybdenum, showed l i t t l e change, b u t t h e s t r e n g t h and d u c t i l i t y of T-111 were s i g n i f i c a n t l y reduced. Loss of d u c t i l i t y i n T-111 w a s a l s o observed when t h e a l l o y w a s exposed t o unalloyed bismuth. No s i g n i f i c a n t changes i n t h e mechanical p r o p e r t i e s of T-111 were found when t h e a l l o y w a s heated i n argon f o r 3000 h r a t 700OC. In studying t h e behavior of T-111, Inouye and Liu18 found t h a t r e l a t i v e l y small a d d i t i o n s of oxygen can cause embrittlement, i f oxygen is added a t 1000째C o r lower. For example, t h e a d d i t i o n of 620 ppm oxygen t o T-111 a t 1000째C w i l l cause severe embrittlement (5% elongation), b u t as small as 370 ppm w i l l cause embrittlement i f i t i s added a t 825OC. Samples of T-111 from t h e s e q u a r t z loop tests picked up from 1 0 0 5 0 0 ppm during exposure a t 600-7OO0C, and t h i s may have caused embrittlement of the a l l o y . The source of oxygen i n t h e s e tests i s presumed t o be t h e q u a r t z loop material. The m e l t s were s l i g h t l y higher i n oxygen following t h e tests (Table 1 2 ) , i n d i c a t i n g t h a t oxygen w a s being f e d t o t h e bismuth o r Bi-O.01X L i from t h e quartz o r some o u t s i d e source. Table 13. Comparison of Corrosion Rates of Materials Exposed t o Bi-O.Ol% L i f o r 3000 h r i n Quartz

Corrosion Rate, mg/cm2 *yr Location

Hat leg

Cold leg

Temperature

("0

Loop 13 (Tal

Loop 18 (TB~OX .W)

+o. 22 M.20

630 640 660 690

-16.8 -61.8 -6.5 -137

M.26 -0.37

680 660 640 615

-68.9 -47.7 -112 -46.1

M.46 M.13 M.35 M.13

Loop 12 (T-111)

Loop 11

M.82

-1.14 +3.10 -3.80 -9.70

-2.28 +l. 08 -13.6

-0.85 +0.70 -1.46

4.0.44

(Mol

-0.03 M.26 M.44 +l. 34

Metal Loop Tests i n Bi-2.5% L i

- Group 3

Two all-metal loop tests w e r e operated with Bi-2.5% L i . One loop (of T-111) operated f o r 3000 hr while t h e second (of molybdenum) operated f o r 8700 hr. Both loops had specimens located i n t h e two vertical legs. Maximum temperature was 7OOOC and t h e AT during operation w a s approximately 100째C. The tests were conducted w i t h i n an ion-pumped high-vacuum enclosure. Maximum weight l o s s i n t h e T-111 loop w a s 2.73 mg/cm2 (7.97 mg/cm2*yr). There w a s very s l i g h t (less than 0.0005 in. deep) metallographic evidence o r corrosion, and room-temperature t e n s i l e tests showed no changes i n mechanical p r o p e r t i e s of p o s t t e s t samples compared with t h e s t a r t i n g material. The oxygen content of t h e T-111 samples averaged 240 pprn a f t e r test compared with 60 ppm before test. However, i n a d d i t i o n t o bismuth exposure, t h e T-111 samples and loop were both annealed i n vacuum f o r -2 h r a t 140OOC p r i o r t o test. That t h e samples were not b r i t t l e a f t e r test suggests t h a t much of t h e oxygen i n c r e a s e occurred during t h e vacuum anneal. I n c o n t r a s t t o t h e e f f e c t on T-111 a t lower temperatures, t h e a d d i t i o n of 100-200 ppm a t 140OoC d i d not e m b r i t t l e t h e samples. l 9 A t lower temperatures oxygen i n T-111 p r e f e r e n t i a l l y a s s o c i a t e s with hafnium as extremely f i n e hafnium-oxygen zones that are coherent w i t h the matrix. A t temperatures below 8OO0C coarsening of t h e hafnium-oxygen zones i s sluggish, b u t a t high temperatures coarsening r e a d i l y occurs and t h e a l l o y i s more d u c t i l e i n t h i s condition. Samples of b r i t t l e T-111 from t h e quartz loop tests were heat-treated f o r 1 h r a t 140OoC and d u c t i l i t y w a s r e s t o r e d as determined by room temperature bend tests, Specimens from t h e quartz loops w e r e 0.020-in.-thick f l a t samples compared with '0.125-in.-diam t e n s i l e b a r s i n t h i s test. I f oxygen were homogeneously d i s t r i b u t e d i n t h e samples, specimen geometry probably did not c o n t r i b u t e t o t h e d i f f e r e n c e i n d u c t i l i t y that w a s noted. The molybdenum loop operated f o r 8700 h r . Weight changes f o r specimens from h o t and cold l e g s e c t i o n s of t h e loop were recorded (Fig. 21). The maximum weight l o s s w a s 3.62 mg/cm2 (approximately 3.6 mg/cm2*yr o r 0.15 mil/year assuming uniform s u r f a c e removal), and occurred i n t h e specimen located i n t h e maximum temperature s e c t i o n a t t h e top of t h e h o t l e g . Deposition occurred i n sll cold l e g samples and i n the f i r s t t h r e e samples i n the heated section. The maximum corrosion rate of 3.62 mg/cm2*yr i s about t h a t found i n previous quartz loop tests t h a t c i r c u l a t e d Bi-100 ppm l i t h i u m f o r 3000 h r (Table 7) and i n d i c a t e s that mass t r a n s p o r t of molybdenum i s r e l a t i v e l y i n s e n s i t i v e t o t h e l i t h i u m content of t h e bismuth. Metallographic examination of samples from t h e molybdenum loop revealed small amounts of d i s s o l u t i o n and deposition of molybdenum i n t h e h o t and cold l e g samples respectively. I n t e r g r a n u l a r corrosion occurred t o depths less than 0.0005 i n . (Fig. 22). Mechanical p r o p e r t i e s (Table 14) of s e l e c t e d specimens from t h e hot l e g w e r e , on t h e average, more d u c t i l e and weaker than those from t h e cold leg. However, t h e p r o p e r t i e s of a l l specimens f a l l w i t h i n a normal range f o r t h i s material.

31 QRNL-DWG 79-10735

SAMPLE NUMBER 2.4

8 -2.4 ~

BOTTOM OF HOT LEG 6 0 0 . C

-32

-4.0

f 0

TOP'OF HOT LEG 700. C 4

BOTTOM OF COLD LEG 6 - i . ~

TOPOF COLD LEG 670. C

42 46 20 40 44 48 52 DISTANCE FROM BOTTOM OF HOT LEG (in.)

60 80

Fig. 21. Weight Changes in Molybdenum Samples Exposed to Bi-2.5% in Thermal Convection Loop Test CPML-2.

29 0.

Hot Lcg

Fig. 22.

N,IICO;S INCHES

79 Po03

Cold Leg

Metallographic Appearance of Molybdenum Samples From CPML-2.

Table 14. Room Temperature Mechanical P r o p e r t i e s of Molybdenum Exposed t o Bi-2.5% L i f o r 8700 h r i n Thermal-Convection Loop T e s t

Sample

Location

Temperature

Hot

("C)

Elongation (% i n 1.125 in.)

Ultimate Tensile Strength

0.2% Offset Yield Strength

700

15.1

100,800

98,300

680

12.5

104,100

103,700

650

13.6

97,700

93,400

630

17.5

93,900

80,900

620

Average

15.2

96,700

87,700

14.8

98,600

92,800

600

8.5

120,000

110,900

615

8.4

117,600

109,100

Hot Cold

13 15

630

8.1

113,100

108,200

17 19

640

9.8

118,900

113,100

650

10.4

111,100

106,100

9.0

116,100

109,500

Average

Cold

SUMMARY AND CONCLUSIONS Unalloyed molybdenum and two tantalum a l l o y s (T-111 and Ta-10% W) have e x c e l l e n t compatibility with bismuth-lithium s o l u t i o n s up t o 7OOOC even under temperature g r a d i e n t conditions. The mass-transfer corrosion rate of molybdenum a t 600-7OO0C w a s q u i t e low and decreased with time (up t o 10,000 h r ) . The mass-transfer rate increased with i n c r e a s i n g concentrations of l i t h i u m i n bismuth, but t h e maximum depth of corrosion t h a t w a s observed w a s always less than 0.0005 in. and w a s confined t o t h e g r a i n boundaries of fine-grain s i z e s u r f a c e grains. The room temperature mechanical p r o p e r t i e s of molybdenum appeared t o be unaffected by exposure t o bismuth o r bismuth-lithium s o l u t i o n s . The tantalum a l l o y T-111 a l s o has e x c e l l e n t compatibility with bismuth-lithium s o l u t i o n s , but w a s severely embrittled by 100-200 ppm 0 2 when oxygen contamination occurred i n t h e 600-7OO0C range. This embrittlement severely l i m i t s t h e p o t e n t i a l of T-111 as a MSBR chemical processing construction material. The mechanical p r o p e r t i e s of t h e a l l o y Ta-10% W w e r e not as s e n s i t i v e t o oxygen contamination as T - l l l ; a l s o Ta-10% W showed e x c e l l e n t compatib i l i t y i n tests with Bi-O.Ol% L i f o r 3000 h r . Unalloyed tantalum had a corrosion rate about t e n t i m e s t h a t of t h e above materials when i t w a s exposed t o bismuth o r Bi-O.Ol% L i . Unalloyed tantalum w a s n o t t e s t e d with Bi-2.5% Li. I n a d d i t i o n , unalloyed tantalum i s r a p i d l y corroded21 by l i t h i u m a t t h e s e temperatures i f t h e oxygen concentration of t h e tantalum exceeds approximately 100 ppm; t h e r e f o r e , tantalum seems less s u i t a b l e f o r processing a p p l i c a t i o n s than t h e above materials=

Iron, niobium, and s e v e r a l of t h e i r a l l o y s w e r e found t o be unacceptable materials f o r containing bismuth under temperature gradient conditions. Although t h e s o l u b i l i t y of these elements i n bismuth i s low, r a p i d k i n e t i c s of d i s s o l u t i o n and deposition l e d t o plugging of quartz thermal convection loops a f t e r only a few hundred hours of operation. Molybdenum samples brazed with iron-based a l l o y s (Fe-C-B, and Fe-Mo-C-B) r e s i s t e d mass t r a n s f e r , but t h e braze a l l o y s were attacked by bismuth. An a l l o y of Fe5X Mo completely dissolved by mass t r a n s f e r i n bismuth a f t e r only a few hundred hours i n a quartz thermal convection loop. ACKNOWLEDGMENTS

The work described i n t h i s r e p o r t w a s supported by t h e Molten S a l t Reactor Program and w a s c a r r i e d o u t over a period of several years. Construction and operation of t h e quartz thermal convection loops w a s c a r r i e d out under t h e d i r e c t i o n of L. R. T r o t t e r . R. E. McDonald provided considerable a s s i s t a n c e during f a b r i c a t i o n of t h e T-111 and molybdenum thermal convection loop components. Joining these loop components w a s t h e r e s p o n s i b i l i t y of A. J. Moorhead and J. D. Hudson. B. W. McCullun, J. W. Hendricks, and J. L. G r i f f i t h w e r e responsible f o r construction and operation of t h e test loop f a c i l i t i e s . George G r i f f i t h e d i t e d and Susan Hanzelka prepared t h i s manuscript f o r reproduction. These experiments were p a r t of an o v e r a l l materials program t h a t w a s c a r r i e d o u t under t h e d i r e c t i o n of H. E. McCoy. Special thanks are due him f o r t h e general and t e c h n i c a l guidance t h a t was provided. REFERENCES

1. M. E. Whatley and L, E. McNeese, Molten Salt Reactor Program Semiar#r. Prog. Rep. Feb. 29, 1968, O m - 4 2 5 4 . 2.

L. E. McNeese e t al., Program P h for Devebpment of Molten-Salt

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(October

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