Contamination by oxygen and nitrogen during the high-temperature synthesis of rare earth element carbides and the hydrocarbon contents of their hydrolysis products

Abstract

Contamination of reaction mixtures of rare earth elements and carbon by air oxygen and nitrogen at high temperatures results in changes in the phase composition of the products, which in turn lead to changes in the composition of the hydrolysis gas. La, Ce, Pr, and Nd give carbide-oxides Ln2O2C2 of acetylide nature, in concentrations increasing with increasing extent of contamination. For the smaller rare earth elements from Dy, Ho to Lu, the contamination leads to methanide-type carbide-oxides (or nitrides) M(C, N, O, ). A slight contamination of mixtures of the metals with carbon which are somewhat carbon-deficient with respect to the 1 : 2 composition gives rise to a phase which evolves a gas containing C3 hydrocarbons in a high concentration (nearly 50%), while its methane content is very low. The stability of this allylenide phase, which is not the M15C19 carbide, increases in the direction towards Lu to an extent such that the phase forms even besides higher amounts of the carbide-oxide-nitride, i.e., also on extensive contamination.