Electrolyte impact on the passive layer formation of SSiC at high potentials

Owing to their outstanding hardness, solid-state sintered silicon carbide ceramics (SSiC) are extremely difficult to machine with mechanical technologies. Therefore, electrochemical machining (ECM) might be a promising alternative to machine workpieces of such ceramic. The prerequisite, a sufficient electric conductivity of the cerami is realized by using sinter additives, e.g. AI, which are incorporated into SiC and act as dopants. The feasibility in principle of the ECM of SSiC is evidenced in alkaline electrolytes. However, in contrast to the thermodynamics expactations, the anodic dissolution takes place via passive layer formation at very high potentials. In the present work the authors focus on the passive formation at high anodic potentials under alkaline, neutral, and acidic conditions as well as the effect of various anions. The electrochemical study is supplemented by scanning electron microscopy. It will be demonstrated that the effect of different anions is clearer than the different pH-value.