Creep viscosity and stress relaxation of gel-derived silicon oxycarbide glasses

The temperature dependence of the viscosity and stress relaxation kinetics of sol- gel-derived SiOC glasses that contain up to 14 at.% carbon have bee n characterized in the temperature range of 1000 degrees -1400 degreesC, Th e viscosity, as determined from relaxation experiments, is in good agreemen t with the creep viscosity and is typically two orders of magnitude higher than the viscosity of vitreous silica, However, materials suffer from parti al crystallization at > 1150 degreesC, and the precipitation of beta -SiC n anocrystals induces a flow-hardening behavior and results in a dynamic incr ease in viscosity, especially at > 1200 degreesC and for glasses with a hig h carbon content.