An insight into anodic dissolution processes of carbides obtained by product analysis

The question of the dissolution products during the electrochemical machining of carbides is still under discussion in the literature. C0, C2+ and C4+-species are considerable. In this study, the authors took advantage of a precipitation reaction of carbon dioxide/carbonate (CO2/CO32-) with barium hydroxide (Ba(OH)2), forming insoluble barium carbonate (BaCOs), for a qualitative detection of these species directly during the anodic dissolution process. Potentiostatic experiments were performed in Ba(OH)2-electrolyte on solid-state sintered silicon carbide and tungsten carbide. It was shown that the precipitation of barium carbonate directly takes place on the surface of the carbides and led to a passivation of the surface. Additionally, complementary experiments were carried out on graphite and platinum. On graphite the oxygen evolution is the main reaction, only slight passivation was observed. This observation is consistent with the reactions on platinum, where the oxygen evolution takes place exclusively.