FORMATION AND STRUCTURE OF REACTION LAYERS IN SIC GLASS AND SIC/SIC COMPOSITES/

The structure and composition of interlayers between the fibre and mat rix in Nicalon/borosilicate glass and Nicalon/SiC composites depend st rongly on their formation mechanism. The applicability of existing mod els for interface reaction is limited, if the results of electron micr oscopic characterization are taken into account. The thermodynamic fun damentals illustrated by a volatility diagram of the Si-C-O system rev eal that variations in the pressures of O-2, SiO and CO, respectively, are responsible for the occurrence of various phases (carbon, carbon and silica, silica) between the fibre and matrix. The thermodynamic ap proach yields a four-stage model of layer formation including the acti ve oxidation of SiC.