Infiltration of C/SiC composites with silica sol-gel solutions: Part II. Infiltration under isostatic pressure and oxidation resistance

Abstract

An infiltration process that uses silica sol-gel solutions was developed to protect C/SiC composites against oxidation. The infiltration is assisted using isostatic pressure. Different process parameters including substrate porosity and solution concentration and viscosity were varied to optimize the infiltration effectiveness. Applied pressure enhances penetration of solutions, reducing the importance of viscosity, an important process variable for dipping infiltration. The effectiveness of the isostatic pressure infiltration method, evaluated through the total weight gains and pore-size distribution of infiltrated samples, is compared with results of dipping infiltration. The oxidation behavior of the infiltrated samples, was evaluated by stepwise oxidation test as well as isothermal tests at 1200 and 1600 °C. The infiltrated SiO₂ protects the C/SiC substrate, reducing the burnoff rate of C fibers at low temperature and delaying the oxidation of SiC.