Effect of Initial Silica Content on the Phase Composition, Morphology, and Thermal Oxidation Kinetic of Novolac-based Carbon Aerogel Composites

Silicon carbide-reinforced carbon aerogel with highly porous structure was synthesized by incorporation of a silicon-containing phase in the novolac aerogel via the pressurized sol-gel polymerization and the following carbothermal reduction process. Different ratios of organic to inorganic phase were adjusted by changing the TEOS (Tetraethylorthosilicate) content in the initially prepared sol and it,s effect on the final obtained SiC content and thermal performance of the carbon aerogel composites were then investigated. The maximum production yield of the SiC phase component during the carbothermal reduction process obtained at the stoichiometric ratio of C to SiO2. The kinetic evaluation was conducted using the less speculative method of NPK (Non-Parametric Kinetic).The initial incorporation of the silica phase in the novolac aerogel and the following formation of the SiC phase  results in a considerable decrease (up to one order of magnitude) in the oxidation rate constant of the hybrid aerogel composite.  Moreover, the kinetic model changed from a Reaction-Order model for the neat carbon aerogel to a Nomen-Sempere model for the reinforced one.