Infiltration of C/SiC composites with silica sol-gel solutions: Part I. Infiltration by dipping

Oxidation resistance of ceramic matrix composites (CMC) of SiC reinforced w ith C fibers (C/SiC) can be improved by filling the residual porosity. The aim of this work was to design and analyze a dipping infiltration process u nder ambient conditions (1 atm pressure and room temperature) with silica s ol-gel solutions prepared from tetraethyl orthosilicate. Different substrat es and solutions have been studied. Thermal treatments. i.e., curing or sin tering between infiltrations, increase the efficiency of the process since the densification of infiltrated silica opens up the remaining porosity. In creasing viscosity and/or concentration of the solution lead to greater wei ght gains. Weight gains are higher in the initial stages of the process bec ause larger diameter porosity remains unfilled. As the process advances, th e average pore size decreases, and only the lower viscosity solution can en ter the residual porosity.