Leaching behaviour of silicon nitride materials in sulphuric acid containing KF

The leaching behaviour of gas-pressure-sintered silicon nitride materials with different grain boundary phases was studied in 1 N sulphuric acid at 90 °C with varying additions of KF. The progress of corrosion was investigated in terms of mass loss and thickness of the corroded layer. Also SEM micrographs were taken from the samples and EDX analyses were conducted upon the corroded samples. The corrosion resistance of the materials was found to be sensitive to KF additions as small as 0.01 wt.%. The formation of different corroded sublayers caused by different leaching rates of the single components of the grain boundary phases was shown. It was found that the corrosion behaviour depends strongly on the composition of the grain boundary phase.