Carbothermal synthesis of vanadium and chromium carbides from solution-Derived precursors

Vanadium and chromium tartrate precursors prepared from aqueous solutions have been used as preceramic materials for carbothermal reactions with and without simultaneous nitridation. Their thermal behaviour has been investigated by TG/DTA, X-ray diffraction and measurement of surface areas. Under pyrolysis up to about 600°C, reactive composites consisting of intimately mixed carbon and amorphous M 2O 3 oxides are formed by salt decomposition. The subsequent processes of crystallization of oxides and carbothermal reduction render both the composites and the reduction products porous. The carbothermal reactions leading either to V 8C 7, a V(C,N,O) solid solution, and Cr 3C 2, respectively, proceed at moderate temperatures between 800 and 1100°C. The final products result as assemblages of fine carbide or carbonitride particles, however, with extensive heat treatment the particles grow and the surface areas diminish. Air oxidation of the final products has been studied by simultaneous TG/DTA.