High temperature behavior of a gel-derived SiOC glass: Elasticity and viscosity

The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in- situ ultrasonic echography measurements. Temperature induced changes includ e structural relaxation and densification from 1000 to 1200 degrees C, and crystallization to form a fine and homogeneous beta-SiC/glass-matrix nanoco mposite with 2.5 nm large crystals above 1200 degrees C. Young's modulus me asurements clearly reveal a consolidation of the material upon annealing be low 1200 degrees C. Crystallization is almost complete after few hours at 1 300 degrees C and results in a significant increase in Young's modulus. The viscosity of the oxycarbide glass is much higher than that of fused silica , with two orders of magnitude difference at 1200 degrees C, and the glass transition temperature ranges from 1320 to 1370 degrees C.