Influence of the carbon material on the synthesis of silicon carbide

The present work is focused on the study of the relevance of the structure and properties of carbon materials derived from petroleum and coal in the carbothermal reduction of silica to produce SiC. Four different types of petroleum cokes and three metallurgical cokes produced from bituminous coals of different rank have been characterized in terms of optical texture, porosity, CO2 surface area and ash composition. The SIC yield at 1400 and 1500 degrees C is affected by the degree of anisotropy and the size and crystallographic order of the anisotropic components in coke. Indeed, a good relationship between the SIC yield at 1500 degrees C from acid-demineralized cokes and the coke optical textural index (OTI) has been found. Moreover, from statistical analysis limited to petroleum cokes and metallurgical cokes it can be deduced that the dispersion of the catalytic metals in the cokes, specially Fe, and Ni, has a great importance for selecting the carbon material. A model employing the optical textural index (OTI) and the amount of metals (Fe and Ni) in ashes, as well is second-order parameter such as vanadium content, gave an excellent model for predicting SIC yield. For the raw carbon materials studied, experimental SIC yields at 1500 degrees C and those obtained from the equation fit a straight line of slope unity. (C) 1999 Elsevier Science Ltd. All rights reserved.