ELABORATION, MICROSTRUCTURE AND REACTIVITY OF CR3C2 POWDERS OF DIFFERENT MORPHOLOGY

Cr3C2 powders have been prepared by heat-treatment of metastable chrom ium oxides of controlled morphology in H-2-CH4 atmosphere. Starting wi th these highly reactive oxides allows formation of Cr3C2 at 700 degre es C. The reaction is pseudomorphic and different grain shapes (needle s, rods, spheres and polyhedra) have been obtained. The size distribut ion is narrow and the grain size is generally of the order of a few te ns of micrometers, but the ''spheres'' are in fact made up of aggregat es of small platelets about 1.5 mu m wide and 0.7 mu m thick. The oxid ation in air of the carbides was studied by thermal analyses (TGA, DTG and DSC) and was found to proceed in four steps in the 250-700 degree s C range. The differences observed between the carbides are related t o their morphology and texture.