Chemical and electrolytic etching procedures are employed for most metals and for some applications for ceramics however plasma etching is the most effective etching technique for ceramics. Plasma etching makes it easy to distinguish between silicon carbide and silicon nitride by introducing CF4 gas to the sample in a partial vacuum environment. Tetrafluoromethane gas reacts with the silicon nitride producing SiF gas, nitrogen gas and solid carbon while the silicon carbide and glass remain unchanged. The newly formed carbon deposited over the remaining silicon nitride allows the phases to be distinguished due to their difference in atomic number.
Above: Plasma etcher running, typically 10 minutes at 100 watts for Si3N4 (top left). Sample as polished (top right), old etch (bottom left), plasma etch (bottom right).