Effect of aging pH value on the properties of porous SiC ceramics produced through coat-mix process

The core-shell structure precursor powder was synthesized through coat-mix process, and a small amount of Al2O3, SiO2 and Y2O3 composite additives were added. Porous silicon carbide ceramics were produced after molding, carbonization and sintering, and the crystalline phase, weight loss, porosity, bending strength, and thermal expansion coefficient were measured. The effect of aging pH value of coat-mix process on the characterization of porous SiC ceramics had been analyzed. The results indicate that the crosslink degree and curing rate of the phenolic resin is adjusted by changing the aging pH value, and the coating effect in the coat-mix process is improved. Thereby, the flexural strength, thermal expansion coefficient, porosity and pore distribution of the porous SiC ceramics could be adjusted according to the application requirements. When the pH value ranges from 3 to 5 or higher than 7, the phenolic resin shows a lower crosslink degree and char yield, while the ceramics show a higher porosity and a lower thermal expansion coefficient; and the flexural strength decreases as the aging environmental pH value increases.