TANTALUM AND NIOBIUM the final operating temperature of 500” C., involves the formation of tantalum pentoxide, tantalum and niobium trichloride, niobium tetroxide, and, possibly, tantalum and niobium nitrides, or even elemental tantalum and niobium, by the action of ammonia, hj-drogen, and nitrogen. The next step, chlorination, is truly the means whereby the separation is actually achieved. I n the chlorination all lower chlorides, lower oxides, nitrides, and metal ~ o u l dform volatile compounds and would be driven off, leaving essentially pure tantalum pentoxide as residue. Conclusions
A method has been described for separating tantalum and niobium. T h e procesr, is based on a selective chlorination which follows a heat treatment of partially hydrolyzed tantalum and niobium chlorides with ammonia or a n ammonium compound. Hvdrolysis is the factor t h a t determines the purity of the compounds obtained. T h e method presented does not effect a quantitative separation. However. i t offers a rapid process for obtaining pure tantalum and/or niobium rompounds. The method employs low cost material and simple procedures and equipment. Literature Cited
Atkinson, R. H., Steigman, J., and Hiskey, C. F., A n a l . CAem., 24,447 (1952). Burstall, F. H., Swain, P., and associates, A n a l y s t , 77, 1497 (1952). Cunningham, T. R . , and Price, R. C., U. S. Patent 1,908,473 (May 9,1933). Curvelliez, F., Brit. Patent 644,544 (Oct. 11, 1950); U. S. Patent 2,429,671 (Oct. 28, 1947). Ephraim, F., “Inorganic Chemistry.” p. 626, Interscience, KewYork. 1948. Foote, H. IT., and Langley, R. W., Am. J . Sci., 30, 401 (1910). Fowler, R. hl., U. S. Patent 2,481,584 (Sept. 14, 1949). Fowles, G., and Pollard, F. H., J . Chem. Soc., 1952, p. 4938. Friend, 3. X., “A Textbook of Inorganic Chemistry,” Vol. VI, Part 111, p. 141, Charles Griffin, London, 1936. Ibid.,Part V, pp. 64, 163. Golibersuch, E. W., and Young, R. C., J . Am. Chem. Soc., 71, 2402 (1949). (12) Jenness; L. G., U. 9. Patent 1,834,622 (Dec. 1, 1931). (13) Kraus, K. A , , and Moore, G. E., J . A m . Chem. Soc., 71, 3855 (1949). (14) Krbll, W.J., and Bacon, F. E., U. S. Patent 2,427,360 (Sept. 16,1947).
Ibid.,2,443,254 (June 15, 1948). Leddicotte, G. W., and Moore, F. L., J . Am. Chenz. Soc., 74, 1618 (1952). RIarignac, J., Ann. chim. p h y s . , 8 , 5 (1868); 9, 249 (1886) (as reported by J. Newton Friend in “.L Textbook of Inorganic Chemistry,” Vol. VI, Part 111, p. 128, Charles Griffin, London, 1936). Mellor, J. W., “A Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. IX, pp. 475, 664, Longmans, Green, London, New York, Toronto, 1947. Merrill, H. B., J. A m . Chem. Soc., 43, 2378 (1921). Illortimore, D., Romans, P., and Tews, J., A p p l . Spectroscopy, 8, No. 1,24 (1954). Moureu, H., and Hamblet, C. H., J . Am. Ciiem. Soc., 59, 33 (1937). Pierce, D. D., Ibid., 53, 2810 (1931). Pierce, D. D., and Yntema, L. F., J . Phys. C h e m . , 34, 1822 (1930). Ruff, O., and Thomas, F., 2. anorg. u. allgem. Ciiena.. 156, 213 (1926). Schaefer, H., and Pietruck, C., Ibid.,266, 151 (1951). Schoeller, W.IX., “ilnalytical Chemistry of Tantalum and S i o bium,” Chapman and Hall, London, 1937. Sears, G . W., J . Am. Chem. Soc., 48, 343 (1928). Societ6 gen6rale nietallurgique de Hoboken, Belg. Patent 470,891 (February 1947). Ibid.,470,892 (February 1947). Societe g6n6rale mBtallurgique de Hoboken. French Patent 834,602 (Nov. 25, 1938). Stevenson, P. C., and Hicks, H. C., A n a l . Chem., 25, 1517 (1953). Sue, E’., Bull. SOC. c k i m . France, 149, P t . 1, Ser. 5 , Vol. 6, Pt. 1, p. 823 (1939). Tarasenkov, D. N., and Komandin, A. V., J . Gem Chem. (C.S.S.R.),10,1319 (1940). Tikhomiroff, N.. Compt. rend., 236, 12, 1283 (March 23, 1953). Titan Co.. Brit. Patent 649,342 (Jan. 24, 1951). Uspenkaya, T. d.,and Chernikhov, Y u . X.,Compt. rend. acad. Sci. U.R.S.S., 28, 800 (1940). Weinland, R., and Stortz, L., Z. anorg u. allgem. Chem., 54, 223 (1907). Weiss. L., and Landecker, AI., Ger. Patent 221,429 (April 25, 1909). Wernet, J., 2.a i z o ~ g .u. allgem. Chem., 267, 213 (1952). Werning, J., and associates, IKU.ENG.CHmr., 46, 844 (1984). Yntema, L. F., T r a n s . Am. Electrochem. Soc., 55, Preprint No. 8 (1929). RECEIVED for review April 11, 1954.
ACCEPTEDAugust 9, 1964. Presented before the Division of Physical and Inorganic Chemistry a t the 126th hfeeting, h r E R I C A N CHEUICAI, SOCIETY.x e w York, N. Y
Ductile Tantalum by Kroll Process H. A. JOHANSEN’ U.
S. Bureau
AND
S. L. MAY
o f Mines, Albany, Ore.
P
RESENT commercial method of production of tantalum metal
is by a batch electrolytic process. Annual production of tantalum metal is low and the high cost limits its use. High cost is due principally to scarcity of high grade ore (a minimum of 60% combined tantalum-niobium oxide content is required) which is obtained exclusively from foreign sources, difficult purification, particularly from niobium, and the involved process of converting the electrolytic product t o dense metal by vacuum and powder metallurgy. Furthermore, the scarce and valuable niobium is not recovered with much success by the Msrignac separation method which is still used although i t is about 100 years old. T h e research effort at this laboratory has aimed, therefore, a t finding new separations techniques for the relatively abundant 1
Present address, Univeisity of Oregon, Eugene, Ore
December 1954
domestic low grade ores) recovery of niobium in high purity, and improved reduction process for the pure metals. All phases of this research have shown success. Ores n-ith as low as 20% combined tantalum and niobium oxides have been processed t o high purity compounds. TKOdifferent methods for separation of tantalum and niobium that have been developed-by solvent extraction and by selective hydrolysis and chlorination of the anhydrous chlorides-are described in t,he accompanying paper. This paper reports the production of ductile t’antalum meta.1 by a new method which may have industrial application. T h e laboratory scale production of tantalum and niobium (columbium) metal powders by t’he method of von Zeppelin (8) has been reported (4). I n this method the anhydrous pentachloride was packed int,o a st,cel container with magnesium chips and a carrier salt of potassium chloride. The mixture was fired
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT by heating and the resulting cake was leached t o obtain the metal product. The extreme fineness of the powders was cited as an advantage over the electrolytic method from the standpoint of powder metallurgy. The Kroll process ( 6 ) , which has already been used for the large scale production of titanium, zirconium, and hafnium, may be briefly described as the magnesium reduction of a n anhydrous chloride under inert atmosphere of helium or argon. The reaction product may be water leached, but theusual and preferable practice is to vacuum distil the ma.gnesium chloride and excess magnesium t o leave a sponge metal product. The vacuum distillation has advantages over water leaching in that the metal particles are not oxidized or contaminated by the action of water or acids, and the high temperatures of the distillation process frequently enable a densification and sintering of the product, t,hus diminishing the surface area exposed. I n practice, the Kroll process has distinct advantages over the von Zeppelin method in t h a t the rat,e of reduction may be regulated by cont,rolling the volatilization of the anhydrous chloride, whereas the von Zeppelin process has t,he hazards implicit in a bomb process. Experiments indicate l a r g e Scale Reductions of Tantalum Pentachloride Are Possible
Tantalum pentachloride was produced by direct chlorination
of tantalum scrap, or tantalum carbide produced by reduction of tantalum pentoside with carbon. Since the Kroll process depends on volatilized chlorides, hydrolysis of the anhydrous tantalum chloride should not contaminate the product as in the von Zeppelin process. I n practice, however, hydrolysis occurred because of exposure t o the atmosphere during transfer from the chlorination furnace t o the reduction furnace. This represented a certain loss of efficiency and hence exposure to the air was minimized. The c!iloride was placed in a silica boat which was inserted in a horizontal 2-inch borosilicate glass t,ube with three heated zones. A flon-ing helium atmosphere was provided. T h e first zone served to sublime tlie chloride over a graphite boat containing magnesium (10% excess over t h a t required for reduction) in the center furnace zone which was heated to about 750" C. The third zone was unheated on the first pass but, upon completion of the initial sublimation, the helium gas flow \vas reversed, the first heating zone cooled, and the chloride which did not react on the first pass vias then returned through the reaction zone. Careful control of the rate of sublimation of chloride resulted in little or no chloride passing the reaction zone. After it was alloved t o cool, the crude sponge metal in the graphite reaction boat, was viit,hdraivn and placed in a vacuum furnace and distilled at 900' C. for 4 hours a t a vacuum of about 1 micron. Care Tvas exercised in the initial exposure of the distilled product to the air, as the sponge tended to be pyrophoric. Careful conditioning Tvith helium-air mixtures PIICcessfully avoided this difficulty. T h e distilled product n-as light gray to silvery in color, loosely coherent, aiid appeared t,o be deposited in layers. The sponge was broken up, bricjuettcd, and nielted directly in a n arc furnace with helium-argon atmosphrrc. -4 tungsten tip electrode was used. The but,toii required a light scalping t o remove a very hard layer, but the interior material v-as softer
(hardness Rockwell C 33), was free from porosity, and was readil) cold-rolled, about 10% reduction per pass, into sheet. The total reduction was about 93% from 0.250 to 0.016 inch. This sheet was easily bent with the fingers and after repeated bending showed no sign of cracking. A typical run was as follows: Chloride, Grams 135 T
Magnesium, Grams 33 54
Tantalum Metale, Gram? 61
Efficiencj ,
70
77.5
Spectrographic analysis of the cold-rolled sheet shox ed the following percentages of impuriticc: Aluminum Magnesium Iron Silicon Kiobiuni
0 01 0.001 ?;ot detected 0.1 0 1
Analytical determinations indicated that the Kroll process tantalum contained 0.016% carbon, compared to 0 . 0 1 4 ~ ofouirc! in cominercial tantalum sheet which vias arc-melted and coldrolled. +Ilarger scale reduction would produce soft,er material and mouId increase efficiency. Previous experience with the magnesium reduction of other refractory metal chlorides, such as zirconium, titanium, and hafnium, has shoxvn t h a t by increasing the scale of operat,ions, the over-all level of contamination can be reduced, thereby resulting in softer, more ductile metals. Vacuum arc-melting should also produce softer metal by elimination of the more volatile tantalum oxides. Rlaterials of construction for a larger design become a serious problem, however, since it was found that iron \vas seriously attacked by tantalum pentachloride at, reduction temperat,ures. The melting of tantalum metal by arc processes m s first a(!complished by von Bolton ( 1 , 7 ) . Tantalum, despite its high 50" C. (3),presents no problem in arrmelting point of 3000" melting on a \vat,er-cooled copper hearth, as \vas described for titanium by KroIl(5). While commercial tantalum is somewhat softer in arc-melted form (about Rockn-cll B 80), the extra hardness of tlie magnesium reduced product vas no deterrent t o cold-rolling, as evidenced by the 93yoreduction in thickness. It was also determined that tantalum powder made by the conventional electrolysis proceys ( 2 ) could be arc-melted and coldworked to ductile sheet.
+
literature Cited (1) Rolton, W.von, 2. Elektrociren~., 11, 45 (1905). ( 2 ) Driggs. F. H.. and Lilliendahl, IY. C . , IXD. ENG.CH 634 (1931).
(3) Geach, G. .i..aiid Summers-Siiiith. D., J . Inst. M e t a l s , 80, 143 (1951). (4) Isaza, J., Shaler, X., and Wulff,
J.* Melals Techlid., 14, Tech. Pub. 2277 (1947). ( 5 ) l i r o l l , W.J., T m n s . Electrochem. Soc., 78, 35 (1940). .J.. 1 7 . 3. Patent 2,205,854 (1950). ., i-aoaum, 2, 159 (19.52). ( 8 ) Zeppelin, H. van, Jlctall u . E m . 40, 252 (1943). 1ii:crIviiu f3r review March 3 0 , lil3i,
ACCEPTEDSeptember 3 , 19.51.
END OF TANTALUM AND NlOBlUM SECTION
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Vol. 46, No. 12
