Crystallization Maps for SiCO Amorphous Ceramics

Abstract

Amorphous silicon–oxycarbide (SiCO) can retain large mole fractions of carbon when it is made from controlled pyrolysis of silicon‐based polymers. The crystallization resistance of these ceramics, which is quite remarkable, varies with the carbon content. In high‐carbon materials, crystallization is usually accompanied by weight loss (resulting from the carbothermal reduction of silica), whereas phase separation can lead to crystallization without significant weight loss in the low‐carbon materials. A simple graphical method is developed to estimate the composition of the crystallized material, and the concomitant weight loss. The results are presented as maps for a quick estimate of crystallization and weight loss for any composition. Experiments with a medium–high carbon SiCO are used to quantify the degree of crystallization and the associated weight loss at 1300°C and at 1350°C; these results show that, in the case of medium high carbon content, crystallization begins with phase separation but becomes quickly dominated by weight loss.