A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

SULFIDESThe thermochernistry of CeS, along with other Ln sulfides, has been studied [6] because ofits possible role in steel treatment by mischmetal. It has one of the greatest - most negative - freeenergies of formation for sulfides and has been proposed as a containment material for veryreactive molten metals such as uranium and titanium.Possible preparation methods for Ln sulfides include :• direct reaction between the elements,• high temperature sulfidation of anhydrous salts by H 2 S,• low temperature sulfidation in oxygen-free organic media,• disproportionation between Ln metal and lead sulfide.One potential problem is the formation of the very stable oxysulfide, e.g. Ce 2 O 2 S due to water oroxygen contamination in the starting reactants. The oxysulfide content can be reduced by hightemperature reduction with carbon.Many ternary sulfides, M x Ln y S z ,, are known[1] where M can be mono-, di-, or higher valent.The compound, CaLa 2 S 4 , and similar materials have been extensively studied[7] because of theiroptical transparency from the visible out to 14 µ in the infrared. They are physically robust and arepotential windows for use with i.r. sensors. This type of ternary sulfide can be prepared by, e.g. :• firing in H 2 S of mixed oxides and carbonates,[8] or• reaction of alkoxides with H 2 S in organic solvents[9].[6] Thermochernistry of The Rare Earth Carbides, Nitrides and Sulfides for Steelmaking, KA.Gschneidner etal., Report IS-RIC-5, publ. 1971, Rare-Earth Information Center, Iowa State University, Ames, IA, availablefrom Molycorp[7] Physical Properties of Ternary Sulfide Ceramics, D.L.Chess et al., Mat.Res.Bull., 1984, 19, 1551 New FarInfra-red Window Materials -from Zinc Sulphide through Calcium Lanthanum Sulphide to Diamond,J.A-Savage, Glass Technoly, 1991, 32(2), 35[8] Processing Ternary Sulfide Ceramics : Powder Preparation, Sintering and Hot-Pressing, D.L.Chess et al.,J.Am.Ceram.Soc., 1983, 66(l), 18[9] Preparation of Calcium Lanthanum Sulfide Powders via Alkoxide Sulfurization, Y.Han and M.Akinc.,J.Am.Ceram.Soc., 1991, 74(11), 281545