United States Patent 19 11, 3,748,095 Henderson Et Al
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United States Patent 19 11, 3,748,095 Henderson et al. (45) July 24, 1973 54). PRODUCTION OF HIGH PURITY RARE EARTH SULFDES OTHER PUBLICATIONS E75) Inventors: James R. Henderson, Los Angeles; Eastman et al., "Journal of the American Chemical So Donald M. Johnson, Malibu; Michiya ciety," Vol. 72, 1950, pp. 2248-2250. Muramoto, Santa Monica, all of Samsonov, “High-Temperature Compounds of Rare Calif. Earth Metals with Nonmetals,' Consultants Bureau, 73 Assignee: McDonnell Douglas Corporation, New York, 1965, pp. 252-259. Santa Monica, Calif. 22 Filed: June 17, 1968 Primary Examiner-Carl D. Quarforth Assistant Examiner-F. M. Gittes 21 Appl. No.: 737,770 Attorney-Max Geldin 52 U.S. Cl.................... 423/21, 4231254,423/252, 42313, 4231562 57 ABSTRACT 51) int. Cl........................ C22b 59/00, C01f 17700 Novel method for the production of high purity metal 58 Field of Search ................. 23/50, 53, 134, 204, sulfides, selenides, tellurides, and arsenides, particu 23/21,316, 347, 345, 206 larly those of high melting point greater than 1,000 C, e.g., such compounds of the rare earth metals. An an (56) References Cited hydrous metal, metal salt, metal oxide or mixtures UNITED STATES PATENTS thereof is contacted with a gas mixture, e.g., HS and 3,282,656 1 1/1966 Kruger et al.......................... 23.1347 CS, at a high temperature, e.g., in the range of about 3,334,974 8/1967 Fletcher et al........................ 23/345 1,250° C to about 1,325' C, in the substantial absence 2,980,500 4/1961 Miller............................... 23/134 X of water vapor and oxygen until the product has been 3,033,659 5/1962 Fischer............................. 23/134 X formed. The metal sulfides, tellurides, selenides, and 3,065,515 1 1/1962 Antes................................ 23/134 X arsenides thus produced are formed into single crystals 3,253,886 5/1966 Lamprey et al....................... 231134 which are useful as semi-conductors, transistors, etc. FOREIGN PATENTS OR APPLICATIONS 158,267 1/1964 U.S.S.R................................... 23/21 9 Claims, 3 Drawing Figures - --" --|-- 1. azaaaaaaaaaaaaaaaaaaaa. SA22 3,748,095 2 PRODUCTION OF HOGH PURTY RARE EARTH A third method is the direct reaction of the elemental SULFIDES metal with sulfur at 1,000°C. This process is potentially This invention relates to production of high purity explosive and is considerably more expensive than the metal sulfides, selenides, tellurides, and arsenides and two methods previously described. The purity of the the single crystals thereof, particularly the sulfides, product is limited by the purity of the starting materi selenides, tellurides and arsenides of the rare earth als, and the metals, especially in the case of the rare metals and the single crystals thereof. earth metals are too expensive to permit practical pro In recent years there has been considerable interest duction. (See U.S. Pat. No. 2,978,661 and "Rare Earth in semi-conductive materials having relatively high Compound Semi-conductors' J. F. Miller, F. J. Reid, melting temperatures which would permit operation of 10 and R. C. Himes, J. Electro Chem. Soc. 106,043 electronic devices beyond the melting temperatures of (1959); and also U.S. Pat. No. 3,174,939). today's most widely used semi-conductors. Rare earth A final method involves the reaction of the metal semi-conductive materials, particularly the sulfides, oxide with carbon disulfide heated to 1,100°C. The dis selenides, and tellurides showed great promise because advantages of this method are that the product is con of their high melting points. However, repeated at 15 taminated with oxycarbides and metal carbide impuri tempts to produce these materials in pure form resulted ties. (See L. Ya. Markovskii, E. Ya. Pesina and R. I. in failure. The impure materials produced exhibited a Smirnova, Zh. Prik. Khim, Fol. 28, 1956, page 441.); lack of constant electrical resistivity with a change in and also U.S.S.R. 158,267. temperature especially in the hoped for high tempera It has now surprisingly been found that pure sulfides, ture range. Moreover, the processes required extensive 20 tellurides, selenides and arsenides can be produced by and costly preparation methods. It was also found that a simple, inexpensive process according to the inven the impurity of these materials prevented their being tion, in such high purity that single crystals of the rare formed into single crystals. As a consequence, the rare earth metal compounds are easily drawn from a melt of earth semi-conductive materials have found limited these compounds. The single crystals have extensive commercial application. 25 use as semi-conductors, photon sensors and narrow Until the present time, rare earth metal sulfides, sele band photon counters, transistors and thermal radia nides, tellurides and arsenides have been produced by tion detectors, and injection lasers. several methods. These methods will be discussed with The process of the invention while particularly suited reference to the sulfides, but it should be kept in mind for the production of the sulfides, selenides, tellurides, that the selenides, tellurides, and arsenides are similarly 30 and arsenides of the rare earth metals, considered to produced. include elements 39 and 57-71 of the periodic table, The first of these methods involves the reaction of has wide application in the production of the sulfides, selenides, tellurides, and arsenides of any metals anhydrous metal salts such as the chloride or sulfate wherein such compounds have a melting point of about with HS at about 1,000°C. A major disadvantage of 35 900°C or greater. As used herein and in the appended this process is that it is expensive since an elaborate claims, the term "metal' is meant to include any ele preparation and quality control of the anhydrous metal ment of the periodic table that in general is character salt raw material is required. Also, all water vapor must ized chemically by the ability to form cations by loss of be completely removed from the reaction chamber one or more electrons from each atom to form basic since reaction products, e.g., HCl in the case of the 40 oxides and hydroxides. chloride, will dissolve the metal sulfide product in the The process of the invention broadly comprises con presence of water. Even with all these precautions, the tacting a substance selected from the group consisting reaction never goes to 100 percent completion and the of substantially anhydrous metal, metal oxide, metal product is contaminated with oxysulfide and oxychlo salt, and mixtures thereof, with (a) a first substantially ride impurities. (See U.S. Pat. No. 2,978,661) 45 dry gas selected from the group consisting of H and Another method involves the reaction of a metal HZ, and with (b) a second substantially dry gas se oxide with HS at 1250°-1300°C in a graphite furnace. lected from the group consisting of CZ, and organic This method also requires a long reaction time and compounds of Z, wherein Z is selected from the group even then may never reach completion. Furthermore, consisting of S, Se, Te, and As, said reaction being con the furnace walls are destructively corroded by the HS 50 ducted at a temperature in the range of from about and the particles of corroded furnace wall contaminate 900'C to about 1,500'C, and in the substantial absence the product and limit production to a few cycles for a of oxygen and water vapor, for a time sufficient to set-up of expensive equipment. The graphite particles, allow substantially complete reaction. moreover, are impossible to repove and remain as an The method of the invention particularly comprises impurity. (Sec Picon and Cogne, Bulletin de la Societc 55 contacting a substantially anhydrous metal, metal salt, de Chimic, Paper, France No. 51, 1932, page 94; Mile. metal oxide or a mixture thereof with a mixture of dry M. Guittard, These de Doctorate en Pharmacic, Paris, gases selected from the group consisting of (a) one of France, i957; Jean Flahaut, Micheline Guittard and H, and HZ and (b) one of CZ and organic compounds Madelene Patrie. Bulletin de la Societe de Chimie, of Z, wherein Z is selected from the group consisting of France, Paper No. 180, 1958, page 990; M. Picon, L. 60 sulfur, selenium, tellurium, and arsenic. The gas mix Domage, J. Flahaut, M. Guittard, and M. Patrie, Bulle ture can have varying proportions of the (a) and (b) tin de la Societe de Chemie, France, Paper No. 2, 1960, components above, as more fully described below. The page 221; V. I. Marchenko and G. V. Samsonov, Neor reaction is conducted at a preferably uniform, high ganicheskie Materialy, Vol. 1, No. 1., 1965, pages temperature in the range of from about 900°C to about . 47-52; E. Eastman, L. Brewer, L. Bromley, P. Gilles, 65 1,500°C, preferably from about 1,100°C to about and N. Lofgren, Journal of the American Chemical So 1,350°C, and substantially in the absence of oxygen and ciety, Vol. 72, 1950, page 2248.) water vapor. Reaction time is sufficient to allow sub 3,748,095 3 Radium sulfide RaS stantially complete reaction to occur and is usually Ruthenium sulfide RuS decomposes at 1000 about 1 hour per 50-100 grams of starting material. At *Samarium sulfide SmS 780 the end of the reaction, the product in the form of a Scandium sulfide ScS Silicon sulfide SiS sublines at 940 powder is cooled to room temperature. Single crystals Sodium sulfide NaS 1180 can be formed from a melt of this powder. Strontium sulfide SrS >2000 Tantalum sulfide TaS > 1300 The invention provides rare earth sulfides, tellurides, *Terbium sulfide TbS > 1500 selenides, and arsenides of such great purity that they Thorium sulfide ThS 1925 are readily formed into single crystals.