THE CHEMISTRY OF THE RARE EARTH SILICIDES

Journal Article · Sat Dec 01 04:00:00 UTC 1962 · Uspekhi Khimii (U.S.S.R.) For English translation see Russ. Chem. Rev. (Engl. Transl.)

OSTI ID:4761372

Samsonov, G V

The physical and chemical properties of the silicides can be varied over wide limits because of the simultaneous presence of covalent bonding between the silica atoms, and metallic bonding between the metal and silica atoms. Available data on the rare earth silicides including the scandium and yttrium silicides are summarized. The structure, lattice parameters, melting points, electrical resistance, Hall coefficients, and thermal emf' s are presented in tabular form. The heat of formation was estimated as plus or minus 25 plus or minus 10 kcal/ atom of Si, or about 50 kcal/mol. The variation in properties with temperature is presented. For example, LaSi/sub 2/ is a metallic, n-type conductor from 20 to 500 deg C, but becomes a p-type, semiconductor above 500 deg C. Preparative methods can be grouped as follows: direct reaction of the rare earth metal with silicon metal, reduction of a rare earth oxide with silicon metal, and electrolysis of a fused salt containing a rare earth metal and silicon. Direct synthesis of the silicide from the elements must be carried out in an inert atmosphere due to the high affinity of rare earth metals for oxygen and nitrogen. Reduction of a rare earth oxide with silicon metal is the most widely used method. The reaction is ordinarily carried out in an aluminum oxide crucible which is heated in a graphite resistance furnace. The electrolysis method is hardly used, because it is difficult to obtain the pure silicides by this method. The available data on the silicides of Sc, Y, la, Ce, Pr, Nd, Sm, Eu, Gd, Dy, and Yb are given in separate sections. (33 references.) (TTT) means of determination of thorium or molybdate solutions at suitable concentrations and pH ranges. H/sup +/ ion concentration plays an important role in the aggregation process. (auth)

• Research Organization: Inst. of Cermets and Special Alloys, Ukrainian Academy of Sciences, SSR
• NSA Number: NSA-17-012297
• OSTI ID: 4761372
• Journal Information: Uspekhi Khimii (U.S.S.R.) For English translation see Russ. Chem. Rev. (Engl. Transl.), Journal Name: Uspekhi Khimii (U.S.S.R.) For English translation see Russ. Chem. Rev. (Engl. Transl.) Vol. Vol: 31; ISSN USKHA
• Country of Publication: Country unknown/Code not available
• Language: Russian

Related Subjects

ALUMINUM OXIDES
BINDING ENERGY
CERIUM COMPOUNDS
CHEMICAL REACTIONS
CHEMISTRY
CRUCIBLES
DYSPROSIUM COMPOUNDS
ELECTRIC CONDUCTIVITY
ELECTRIC POTENTIAL
ELECTROLYSIS
EUROPIUM COMPOUNDS
FURNACES
FUSED SALTS
GADOLINIUM COMPOUNDS
GRAPHITE
HALL EFFECT
HEATING
INERT GASES
LANTHANUM COMPOUNDS
LATTICES
MELTING POINTS
NEODYMIUM COMPOUNDS
OXIDES
PRASEODYMIUM COMPOUNDS
PREPARATION
RARE EARTHS
REDUCTION
SAMARIUM COMPOUNDS
SCANDIUM COMPOUNDS
SEMICONDUCTORS
SILICIDES
SILICON
SILICON OXIDES
THERMODYNAMICS
YTTERBIUM COMPOUNDS
YTTRIUM COMPOUNDS