Formation of composite powders and ceramics from beta -SiC-Cr sub 2 O sub 3 -C mixtures

The phase-formation process in the disperse beta -SiC + SiO sub 2 + Cr sub 2 O sub 3 + C system treated in vacuum at 1273, 1473, 1673, and 1873 K was studied by X-ray phase analysis, IR spectroscopy, EPR, and other methods. It was found that at treatment temperatures of 1273, 1473, and 1673 K, the major process is carbothermal reduction of Cr sub 2 O sub 3 and SiO sub 2 with the formation of chromium carbosilicide and chromium carbide (Cr sub 3 C sub 2 ). At T = 1873 K, on the surface of the SiC particles, metastable chromium silicate forms on the base of SiO sub 2 and Cr sub 2 O sub 3 . The reduction of Cr sub 2 SiO sub 4 by silicon carbide is accompanied by the formation of CrSi sub 2 , Cr sub 5 Si sub 3 , and chromium carbosilicide. The phase composition of the products of interaction and their distribution over the volume of the composite powder and ceramic material are determined by the dispersion composition of the starting SiC powder and by the degree of development of reduction processes in local volumes of the disperse and compacted material.