Electrochemical corrosion of silicon-infiltrated silicon carbide ceramics in aqueous solutions

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Nevertheless, under certain conditions electrochemical corrosion is observed. Hence, in the present work a SiSiC ceramic and a composite material containing SiC as well as free carbon and Si were investigated in terms of microstructure and electrochemical corrosion behaviour. The SiC grains in the SiSiC exhibited a core-rim structure. The core and rim were formed from primary and secondary SiC, respectively, and had different corrosion stabilities due to the higher electrical conductivity of the rim. In contrast to the behaviour observed with pure chemical corrosion, under electrochemical conditions the Si showed a higher stability than the SiC in NaOH. Also, thicker protective SiO2 layers were formed in H2SO4 on the SiC grains than on the Si grains.