N A S A TECHNICAL NOTE --- N A S A .-. TN D* ,

e /

SOLUBILITY OF IRON, NICKEL, AND COBALT IN LIQUID POTASSIUM AND EFFECT OF OXYGEN GETTERING AGENTS ON IRON SOLUBILITY

by James He Swisber

Lewis Research Center Cleueland, Ohio

-2734 -

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N W A S H I N G T O N , D. C . 0 M A R C H 1965

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TECH LIBRARY KAFB, NM

I111111 lllll lllll1111111111 Ill11 11111 Ill1 111 0079735

NASA T N D-2734

SOLUBILITY O F IRON, NICKEL, AND COBALT IN LIQUID POTASSIUM

ANDEFFECTOFOXYGENGETTERINGAGENTS

ON IRON SOLUBILITY

By James H. Swisher

Lewis Research Center Cleveland, Ohio

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

For sale by the Office of Technical Services, Department of Commerce, Washington, b.C. 20230 -- Price 61.00

~ . - - .. . . . .. -. . . . . . ..

SOLUBILITY O F IRON, NICKEL, AND COBALT I N LIQUID POTASSIUM

AND EFFECT OF OXYGEW GETI'ERING AGl3NTS

ON IRON SOLUBILITY

by James H. Swisher

Lewis Research Center

SUMMARY

The so lub i l i t y of iron, nickel, and cobalt i n potassium was studied i n the temperature range 941° t o 1328O K . 5 pa r t s per mil l ion a t the highest temperature. obtained fo r alpha i ron and nickel can be described by the following equa- t ions :

The cobalt so lub i l i t y w a s l e s s than Tke equilibrium so lub i l i t y

6166 log ppm alpha i ron = 8.193 - - T

3040 log ppm nickel = 3.89 - - T

where T i s the temperature i n OK.

The so lub i l i t y data were determined by sampling the potassium at the t e s t temperature using a dLssimilar metal cup. The equation for i ron w a s determined by using molybdenum sampling cups; however, t h e observed i ron so lub i l i t y w a s found t o be strongly dependent on the cup material . This dependence w a s cor- re la ted with the oxygen ge t te r ing a b i l i t y of various cup mater ia ls .

INTRODUCTION

The containment of l i qu id a l k a l i metals i s a serious problem i n the devel- opment of space power systems. Solubi l i ty data are needed t o a id i n the selec- t i o n of materials t ha t w i l l be compatible with l i qu id m e t a l heat-transfer media and working f lu ids . of iron, nickel, and cobalt i n potassium f o r the temperature range 941° t o 1328' K.

This report describes the determination of the so lub i l i t y

Previous work i n this area has been l imited primarily t o so lub i l i t y i n l i q u i d l i thium and l i q u i d sodium. The so lub i l i t y of several elements i n

I

Sam pli ng l i t h i u m i s reported i n reference 1. I n cup T

reference 2, t he ex is t ing data for niobium, tantalum, molybdenum, and tungsten i n l i t h - i u m and sodium are summarized. Additional data for the solvents l i thium and sodium are given i n references 3 t o 10.

The only avai lable data fo r the solu- b i l i t y of high-melting-point metals i n po- tassium are for the potassium-molybdenum

1352' K (1975' F) , t he so lub i l i t y of molyb- denum is reported t o be l e s s than 0 . 2 pa r t s per mil l ion for potassium containing about 50 pa r t s per mil l ion of oxygen.

(a) Normal position (b) Normal position system ( r e f . 11). For temperatures up t o before sampling. after sampling.

C 533428

Figure 1. - Schematic i l lustrat ion of test procedure. Reported

also, however, i s the f a c t t h a t the apparent so lub i l i t y of molybdenum increases l i n e a r l y

with the oxygen content of the potassium.

APPAFWTUS AND PROCEDURF:

The experimental method used w a s t o sample the potassium at the t e s t tem- perature using an inver t ib le so lub i l i t y capsule. A schematic diagram of the so lub i l i t y capsule i s given i n f igure 1, and the capsule par t s are shown i n f igure 2 . I n most cases, t he so lub i l i t y capsule w a s machined from the mater ia l whose so lub i l i t y w a s t o be determined, and the sampling cup w a s made of molyb- denum; however, a modification w a s required fo r the t e s t s with cobalt and with nickel at temperatures of 1144' K and above. Columbium capsules were used because of the poor f ab r i cab i l i t y of cobalt and the poor creep strength of nickel a t high temperatures. The potassium w a s equi l ibrated i n cobalt or nickel cups, and the samples were taken i n the lower section of the columbium cap- su les . For t h e modified procedure f igures l ( a ) and (b ) should be reversed.

To check f o r possible in te rac t ion e f f ec t s i n solution, other metals were subst i tuted fo r molybdenum as the sampling cup material i n a ser ies of i ron so lub i l i t y t e s t s . The other metals used were zirconium, columbiWn, tantalum, and nickel . Chemical analyses of the container materials used are given i n t a b l e I .

Pr ior t o the experiments, the so lub i l i t y capsules were f i l l e d with about 1 . 5 grams of potassium and sealed by electron-beam welding. Both s teps were accomplished without interrupt ion i n a s ingle vacuum chamber ( lom5 t o r r ) . potassium contained less than 20 pa r t s per mil l ion of oxygen, as measured by a mercury amalgamation method ( r e f . 1 2 ) .

The

The s o l u b i l i t y experiments were performed i n the vacuum furnace t o r r ) shown schematically i n f igure 3(a); a photograph of t he furnace

i s shown i n f igure 3(b) . holder t h a t aided i n minimizing temperature gradients i n the capsules. Be - liminary t e s t s showed t h a t the equilibrium so lub i l i t y was achieved i n a f e w

The capsules were held i n a c lose - f i t t i ng molybdenum

2

Capsule assembled for test

C-69052

C U P

Figure 2. - Solubility capsule

TABLE I . - CHEMICAL ANALYSES OF CONTAINER MATERIALS

[Dashes ind ica te no analysis was obtained f o r impurity element.] ~~ ~~~

Concentration of impurity i n container mater ia l , ppm Impurity

Iron T i ckel [olybdenum Columbium -

Carbon

Nitrogen Hydrogen Cobalt

Oxygen

Sulfur Phosphorus S i l i c o n Manganese Copper

160 40 20 400 700

Calcium Magnesium Tin Aluminum Iron

Nickel Chromium Tungsten Zirconium Columb i u n

Total 2048 <96 <303

3

/-----

n

m.

'\ G"I Moo--- ~~

i r on loo0 Q 0

a=- fa-- 400-

~~ \\

_ _ ~

7 Kanthal-wound resistance furnace

,- Radiation shields

Molybdenum capsule holder

Gamma-alpha - '\, transformation

\a, 1179' K -.

- Thermocouple

E, n

Vacuum manifold

To oil diffusion pumpA

-Open symbols denote use of ~~

molybdenum container - Closed symbols denote use of

columbium container

- (a) Schematic of vacuum furnace.

Figure 3. - Solubility apparatus.

Cobalt 2 1 . 7 .a

Nickel <

Alpha i ron 7 (b) Overall view.

Reciprocal temperature, 1IT. O K

I I I I I 1400 1200 1 loo loo0 900

Temperature, T, O K

Figure 4. - Solubility of iron, nickel, and cobalt i n potassium.

4

hours at the experimental temperature. platinum - platinum-13-percent-rhodium thermocouples positioned at the center of t he capsule holder. temperature f luctuat ion i n the hot zone of t he furnace w a s +lo K.

Temperatures w e r e measured with

The thermocouples were accurate t o w i t h i n 3O K, and the

Sampling at the t e s t temperature w a s accomplished by invert ing t h e fur- nace, which allowed the potassium t o flow i n t o the sampling cups. After cool- ing t o room temperature, the capsules were cut open and the potassium samples dissolved i n buty l alcohol. The sampling cups then were leached with hydro- c lo r i c acid t o remove the material t h a t had precipi ta ted during cooling. orimetric methods were used t o determine the concentrations of i ron, nickel, and cobalt ( r e f s . 713 t o 15) i n the alcohol and acid solutions; the amount of potassium present i n the alcohol solutions w a s determined gravimetrically.

Col-

RESULTS AND DISCUSSION

Experimental

The so lub i l i t y data fo r i ron, nickel, and cobalt i n potassium are shown i n figure 4. Least squares calculations l ed t o the following analyt ical equa- t i ons fo r the i ron and nickel data:

6166 log ppm alpha i ron = 8.193 - - T

3040 log ppm nickel = 3.89 - - T where T i s the temperature i n OK.

In f igure 4 the data points fo r i ron t h a t correspond t o the highest t e s t temperatures of 1257' and 1328' K do not f a l l on the l i n e drawn through the other points. Although a change i n slope of the so lub i l i t y l i n e i s t o be ex- pected a t the alpha t o gama transformation temperature, t h i s change should be too s m a l l t o be observed i n the experimental p lo t . (The enthalpy change accompanying the transformation i s only 0.2 kcal/mole as shown i n r e f . 16, p. 397.) An explanation of t h i s anomaly in the iron data w i l l be presented l a t e r i n connection with an oxygen get ter ing e f f ec t .

From the solubility-temperature dependence, the apparent heats of solution of alpha i ron and nickel i n potassium were found t o be 28.220.3 and 13.922.1 ki localor ies per mole, respect ively. Standard deviations i n so lub i l i t y values averaged over the experimental temperature range were 22 .3 percent for alpha i ron and 227 .8 percent fo r nickel . The large uncertainty i n the nickel values w a s mainly due t o a blank correction for t he leaching s tep. The blank weight of 15 micrograms w a s nearly as la rge as the t o t a l weight of nickel i n the sam- p le s . In the cobalt t e s t s , the concentrations of cobalt were detectable, but the analyses were not suf f ic ien t ly accurate t o specify values f o r the cobalt so lub i l i t y .

The concentrations of i ron, nickel, and cobalt obtained i n the so lub i l i t y t e s t s a re typ ica l of data reported f o r a l k a l i m e t a l solvents ( r e f s . 1 t o 11)

5

I

TABm 11. - RELATIVE SOLUBILITIES OF IRON, NICKEL,

AND COBALT I N POTASSIUM, SODIUM, AND LITHIUM

[Comparisons made on atomic rather than weight bas i s . I

(a) Relative so lub i l i t y i n d k a l i m e t d solvents

Solute I A l k a l i metal solvent I I

Nickel 1 Cobalt Iron

Potassium > sodium > l i t h i u m L i t h i u m > sodium > potassium Potassium sodium

(b) Relative so lub i l i t y of iron, nickel, and cobalt

I Alkali metal solvent I Solute

Pot ass ium Sodiuma Lithium

Iron > nickel > cobalt I r o n = cobalt > nickel Nickel > i ron

aDisagreement ex i s t s between investigators on reported values for i ron and nickel i n sodium ( r e f s . 5, 6, and 8).

TABLE 111. - EFFECT O F VARIOUS CONTAINER MATERIALS

ON OBSERVED SOLUBILITY OF IRON I N POTASSIUM

Sampling cup material Observed i ron so lub i l i t y a t 1144' K,

PPm

N i eke1 Molybdenum Columbium Tantalum Zirconium Molybdenum with zirconium coupon5

3540 639, 655

194, 257, 358 117 44

77, 129

but very low i n comparison t o other l i qu id metal solvents, such as copper, t i n , and aluminum ( r e f . 1 7 ) . recognized e f f ec t s t h a t govern so lub i l i t y (atomic s ize , electronegativity, and valency) a re unfavorable for producing high so lub i l i t y i n a l k a l i metals ( r e f . 16 , p . 7 9 ) .

The r e s u l t s are not unexpected because the generally

It should be noted t h a t the r e l a t ive s o l u b i l i t i e s of iron, nickel, and cobalt i n potassium, sodium, and l i t h i u m a re not the same. A comparison i s given i n t ab le 11. This difference i n r e l a t ive s o l u b i l i t i e s i s not consistent with current theore t ica l pr inciples ( r e f . 1 6 , p . 7 9 ) .

Effect of Oxygen Impurity on Solubi l i ty

The so lub i l i t y da ta f o r i ron obtained by using various sampling cups are A var ia t ion of two orders of magnitude w a s observed i n the given i n tab le 111.

so lub i l i t y of i ron at 1144' K (1600O F) as the sampling cup metal w a s varied

6

I

I I I I I I t t 1 I I I I I I I I I I I I I I I I I I I I I I I

4

I I I I -85

I lm I I I I I I I c Potassium-potassium oxide (K-K20)

I/ I I I I

L I

E I I

I I I I I I I I I I I I I I I

I I I I I I I 1

1

on-ferrous oxide (Fe-FeO)

I I I I I I

\

A A

0 h

0

\

4 Nickel-nickel oxide (Ni-NiO) Molybdenum-molybdenum oxide (Mo+l0O2) Columbium-columbium oxide (Cb-Cb02) Tantal u m-tantalu m oxide (Ta-Ta205) Zirconium-zirconium oxide (Zr-ZrO,)

0

0

s \ \ \

-110 -135 -160 -185 -210 -235 Standard free energy of formation AFo for sampling cup metal oxides,

kcall mole oxygen

Figure 5. -Effect of oxygen ettering agents on observed solubility of iron in potas- sium. Temperature, 1144 8 K (16000 F).

through the following se r i e s : nickel, molybdenum, columbium, tantalum, and zirconium. These r e s u l t s can bes t be explained by assuming tha t t he so lub i l i t y of i ron i s a function of t he oxygen concentration i n the potassium, which i n tu rn i s controlled by the ge t te r ing act ion of the cup mater ia ls .

A general correlat ion w a s made i n f igure 5 between the observed i ron solu- b i l i t y and the standard f r e e energy of formation (AFo, a measure of ge t te r ing poten t ia l ) of t he sampling cup metal oxides ( r e f . 18) . The so lub i l i t y of i r o n can be seen t o increase i n a regular manner with decreasing -mo of the sampling cup metal oxides. The use of standard free-energy da ta w a s considered va l id because, even though complete saturat ion of t he sampling cups with oxygen did not occur, t he surfaces of t h e cups were believed t o be saturated during the course of t he tests, and the pr inciple of l o c a l equilibrium w a s believed t o apply ( r e f . 19).

A n i n t e re s t ing p a r a l l e l can be seen i n dynamic corrosion tests of s t e e l s with sodium, where it w a s found t h a t t h e corrosion r a t e varied with the oxygen content of t h e sodium (ref . 20). fe r ra te , (Na~0)2*FeO, i so la ted i n the sodium-iron-oxygen system ( r e f . 21 ) ,

It w a s subsequently proposed tha t a sodium

7

could ac t as an intermediary species i n the i ron mass-transfer process. A comparable en t i t y , potassium fe r r a t e , could be the species t h a t accounts for the dependence of the so lub i l i t y of i ron i n potassium. on oxygen content.

Figure 6 shows the potassium corner of a proposed potassium-iron-oxygen phase diagram. Here the oxygen concentration i n the potas- sikum, established by a par t icu lar ge t te r ing agent, i s represented by l i n e 1 , which in-

extended. I ron w i l l dissolve along l i n e 2 u n t i l sa turat ion i s reached a t point x . Since the posi t ion of l i n e 2 var ies with each ge t te r ing agent, the observed so lub i l i t y

w i l l a l so vary. In the event t h a t more than one ge t te r ing agent i s present, t he posi t ion of the l i n e w i l l be governed by the most e f fec t ive ge t te r ing mate- rial present.

Potassium I ron - t e r sec t s t h e i ron apex of the diagram when

Figure 6. - Potassium corner of proposed potassium-iron- oxygen phase diagram at constant temperature.

This l a t t e r contention w a s t e s t ed i n two i ron capsules with molybdenum sampling cups and zirconium coupons placed i n the potassium. i s a poorer ge t t e r than zirconium, the i ron so lub i l i t y should be the same as t h a t obtained when using a zirconium cup ( tab le I11 and f i g . 5 ) . The values obtained were 77 and 1 2 9 pa r t s per mill ion, compared t o a value of 44 pa r t s per mil l ion resu l t ing from the or ig ina l t e s t with the zirconium cup. Qualita- t i v e agreement w a s obtained because the values were closer t o the zirconium value i n f igure 5 than t o the molybdenum values. A n oxide f i l m observed on the zirconium coupons a f t e r t h e t e s t could have reduced the effectiveness of the zirconium get ter ing agent by reducing t h e r a t e of t ransport of oxygen i n t o the metal. r i u m concentration of oxygen i n the potassium.

Since molybdenum

Thus, the tes t . time may not have been long enough t o reach the equi l ib-

In f igure 5, the point obtained using the n icke l sampling cup should be independent of the aF0 of N i O . Since potassium and i ron are stronger get- t e r ing agents than nickel, the oxygen content of the potassium and hence the observed i ron so lub i l i t y should depend primarily on the t o t a l oxygen content of the system. In other words, l i n e 2 i n f igure 6 cannot be f ixed by the cup mater ia l when it is a weaker get ter ing agent than potassium or iron.

The apparently anomalous high-temperature i ron points presented e a r l i e r i n f igure 4 can a l s o be explained i n terms of the oxygen impurity e f f ec t . these points it i s suggested that there w a s not su f f i c i en t oxygen present i n the system t o reach the p a r t i a l pressure of oxygen tha t would be i n equilib- r i u m with the ge t te r ing material a t the t e s t temperature. The i ron so lubi l i ty , therefore, would correspond t o a lower than equilibrium concentration of oxygen i n the potassium and the solut ion process would follow a l i n e 2 ' ( f i g . 6),, which l i e s below l i n e established by the ge t te r ing agent used (molybdenum).

For

2

8

It should be noted (see f i g . 4, p . 4) t h a t t he so lub i l i t y of nickel i n potassium appeared t o be independent of t he container mater ia l . and columbium were used.) Thus, fo r nickel, it may be inferred tha t the oxygen in te rac t ion e f fec t i s s m a l l . T h i s behavior i s consistent with oxygen-catalyzed mass-transfer r e s u l t s obtained fo r nickel i n sodium, which yielded lower values than those for i ron i n sodium ( r e f s . 22 t o 24).

(Molybclenum

CONCLUDING REMARKS

The r e s u l t s of this invest igat ion indicate t h a t i ron-r ich al loys could have l imited use as containment materials for l i qu id potassium. A s ignif icant amount of mass-transfer of i ron could occur i n a l i qu id metal loop because the the l i qu id i s circulated through a temperature gradient. The experimentally determined fac tors t h a t support this conclusion are the r e l a t ive ly high i ron so lubi l i ty , the high temperature coeff ic ient of so lubi l i ty , and the enhancement of so lub i l i t y with oxygen contamination. The successful use of iron-base al loys would depend t o a la rge extent on how well the oxygen l e v e l i n the potassium i s controlled. On the other hand, t he da ta determined for nickel and cobalt i n potassium indicate t h a t t h e i r use i n space power systems should not be seriously l imited by so lub i l i t y c r i t e r i a when potassium i s the heat-transfer medium or working f l u i d .

Lewis Research Center, National Aeronautics and Space Administration,

Cleveland, Ohio, January 5, 1965.

REFERENCES

1. Leavenworth, H . W . ; and Cleary, R . E . : The Solubi l i ty of N i , C r , Fe, T i , and Mo i n Liquid Lithium. Acta Met., vo l . 9, no. 5, 1961, pp. 519-520.

2 . DiStefano, J . R . ; and Hoffman, E . E . : Corrosion Mechanisms i n Refractory Metal - Alkali Metal Systems. Rept . N o . ORNL 3424, Oak Ridge N a t l . Lab., Sept. 1 6 , 1963.

3. Bychkov, Yu. F.; Rozanov, A . N . ; and Yakovleva, V. B. : Determination of t he Solubi l i ty of Metals i n Lithium. Soviet J. Atomic Energy, vo l . 7 , no. 6, Apr. 1961, pp. 987-992.

4. Bagley, K . Q.; and Montgomery, K . R . : The Solubi l i ty of Nickel i n Lithium. Rept. N o . IGR-TN/C-250, Culcheth Labs., Culcheth, Lanes (England), Sept. 30, 1955.

5 . Baus, R . A . , e t al.: The Solubi l i ty of S t ruc tura l Materials i n Sodium. Proc. I n t . Conf. on Peaceful Uses of Atomic Energy, Vol. 9, 1956, pp. 356- 363.

6 . Rodgers, S . J.; Mausteller, J . W . ; and Batut is , E . F.: I ron and Nickel Concentrations i n Sodium. Tech. Rept . No. 27, Mine Safety Appliances Co., June 30, 1954.

9

7 . Minushkin, B . : Solution Rates and Equilibrium Solubi l i ty of Nickel and I ron i n Liquid L i t h i u m . June 30, 1961.

NDA Rept . No. 2141-1, United Nuclear Corp.,

8. Kovacina, T . A.; and Miller, R . R . : The So lub i l i t y of Nickel i n Sodium by a Tracer Technique. Nuclear Se i . and Eng., vol . 10, no. 2, June 1961, pp. 163-166.

9 . Kovacina, T . A . ; Ewing, C . T . ; Stone, J. P. ; and Mil ler , R . R . : High Tem- perature Propert ies of Sodium and Potassium. Prog. Rept. No. NRL-5904, Naval Res. Lab., Jan. 31, 1963.

10. Grand, J . A . ; e t al. : The So lub i l i t y of Tantalum and Cobalt i n Sodium by Activation Analysis. J . Phys. Chem., vo l . 63, no. 7, Ju ly 20, 1959, pp. 1192-1194.

11. Blecherman, S . ; and Corliss, J . : PWAC Advanced Materials Program. Prog. Rept. Nos. 1004-1012, P r a t t and Whitney Aircraf t , Ju ly 1962-Dee. 1963.

1 2 . Dupraw, W i l l i a m A.; Graab, Judson W . ; and Gahn, Randall: Determination of Oxygen i n Potassium. Analytical Chem., Vol. 36, N o . 2, Feb. 1964, pp. 430-431.

13 . Penner, E. M.; and Inman, W . R . : Extraction and Determination of I ron as the Bathophenanthroline Complex i n High-Purity Niobium, Tantalum, Molyb - denum and Tungsten Metals. Talanta, vol . 9, 1962, pp. 1027-1036.

14. Bandemer, S. L. ; and Schaible, P. J . : Determination of Fe. Study of the o-phenanthroline Method. Ind. Eng. Chem., Anal. ed., vol . 1 6 , 1944, pp. 317-319.

15. Cheng, K. L.; and Goydish, B . L . : Spectrophotometric Determination of Micro Amounts of Nickel, Iron, and Cobalt i n Thin Films. Micro-chem. Jour . , vo l . 7 , no. 2 , 1963, pp. 166-178.

1 6 . Darken, L. S.; and G u r r y , R . W . : Physical Chemistry of Metals. McGraw- H i l l Book Co., Inc . , 1953.

1 7 . Hansen, M . : Consti tution of Binary Alloys. Second ed., McGraw-Hill Book Co., Inc . , 1958.

18 . Wicks, C . E . ; and Block, F. E . : Thermodynamic Propert ies of 65 Elements: Their Oxides, Halides, Carbides, and Ni t r ides . B u l l . No. 605, B u r . of Mines, 1963.

1 9 . Darken, L . S . : Role of Chemistry i n Metallurgical Research. Trans., AIME, v01. 221, 1961, pp. 654-671.

20. Epstein, L . F.: S t a t i c and Dynamic Corrosion and Mass Transfer i n Liquid Metal Systems. Chem. Eng. Prog., vol . 53, Symposium Ser . , No. 20, 1957, pp. 67-81.

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21. Horsley, G . W . : Mass-Transport and Corrosion of Iron-Based Alloys i n Liquid Metals. Reactor Tech., vo l . 1, Aug. 1959, pp. 84-91.

22 . Anon.: Metallurgy Division Annual Progress Report for Period Ending Octo- ber 10, 1957. Rept. No. ORNL-2422, Oak Ridge N a t l . Lab., Dee. 13, 1957.

23. Anon.: Metallurgy Division Semiannual Progress Report for Period Ending October 10, 1957. Rept. No. ORNL-2217, Oak Ridge N a t l . Lab., Nov. 4, 1959.

24. Anon.: Metallurgy Division Semiannual Progress Report for Period Ending April 10, 1956. Rept. No. Om-2080, Oak Ridge N a t l . Lab., Nov. 13, 1959.

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