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

Vanadium and chromium tartrate precursors prepared from aqueous solutions h ave been used as preceramic materials for carbothermal reactions with and w ithout simultaneous nitridation. Their thermal behaviour has been investiga ted by TG/DTA, X-ray diffraction and measurement of surface areas. Under py rolysis up to about 600 degrees C, reactive composites consisting of intima tely mixed carbon and amorphous M2O3 oxides are formed by salt decompositio n. The subsequent processes of crystallization of oxides and carbothermal r eduction render both the composites and the reduction products porous. The carbothermal reactions leading either to V8C7, a V(C,N,O) solid solution, a nd Cr3C2, respectively, proceed at moderate temperatures between 800 and 11 00 degrees C. The final products result as assemblages of fine carbide or c arbonitride particles, however, with extensive heat treatment the particles grow and the surface areas diminish. Air oxidation of the final products h as been studied by simultaneous TG/DTA. O 1998 Elsevier Science Limited. Al l rights reserved.