Shape dependence of corrosion kinetics of Si3N4 ceramics in acids

The corrosion behaviour of Si3N4 ceramics with constant composition (Y2O3 - Al2O3 additives) but of different shapes - plate, cylinder and ball - was investigated in 0.5 mol/l H2SO4 at 90 °C. The corrosion kinetics were measured using weight losses and thickness of the corrosion layers. The investigation showed that the corrosion depends on the shape of the samples. The differences in corrosion kinetics cannot be explained by the shrinking core mechanism. They are caused by different formation rates of the passivating SiO2-rich layers in the corroded materials.