ON EXISTENCE OF CERIUM MONOCARBIDE - CERIUM NITRIDE CARBIDES

Re-examination of the binary system Ce-C gave no evidence for the existence of any phase structurally based on monatomic (methanide) anions, but the C22- anions of Ce2C3 appear to undergo reversible dissociation to methanide anions at high temperatures (1800-2000°C). The ternary system Ce-C-N is complex. Both tetragonal CeC2 and b.c.c. Ce2C3 showed evidence of substitutional replacement of C22- by N3-, with a significant composition range in the ternary diagram; their hydrolysis conformed to the pure acetylide type. One, or probably two, f.c.c. nitride carbides of variable composition were found: (a) in apparent equilibrium with the Ce2C3 phase, a nitride carbide Ce NxCy (x + y ≥ 0·8; 0·4 < x < 0·7; y < 0·4), which furnished CH4 as a primary hydrolysis product, and was regarded as a defect structure derived from CeN by partial substitution of C1 anionic units. (b) In the absence of the Ce2C3 phase a f.c.c. nitride carbide Ce NxCy with x + y ≥ 1 which yielded C2 hydrocarbons and must be regarded as of acetylide" type. Structural problems and the mechanism of reactions leading to the formation of nitride carbides are discussed. © 1969."