Structure/property relationship in silicon oxycarbide glasses and ceramics obtained via the sol-gel method

The high temperature mechanical properties and devitrification resistance of silica glass can be improved by the substitution of some oxygen by carbon atoms in the amorphous network. These SiCO glasses can be prepared by sol-gel process, followed by pyrolysis at 1000degreesC. The compositions studied here are typically SiCxO2((1-x)) with 0.1less than or equal to x less than or equal to0.35 with or without an additional phase of free C or free Si. After heat treatment, mechanical properties were measured to reveal the macroscopic behavior of these materials. The presence of carbon atoms inserted in the amorphous network was assessed by Si-29 NMR. This has a significant role on the mechanical properties of silicon oxycarbide glasses (improvement of 40% of Young's modulus) compared to pure silica. Simultaneously, a study of the short and medium range order in the glass was performed by the calculation of Radial Distribution Functions. The results are presented in an attempt to correlate the macroscopic features with the structure and composition of the silicon oxycarbide network.