Corrosion Behavior of Sintered Silicon Nitride Ceramics in Acid and Alkaline Solutions
Masatsugu Arai, Akiomi Kohno
Silicon nitride ceramics were corroded in boiling 35wt% HCl and boiling 30wt% NaOH aqueous solutions. The corrosion resistance was evaluated by measuring weight loss and bending strength of the specimens before and after corrosion. The corroded and fractured surfaces of specimens were observed by SEM. When soaked in 35wt% HCl solutions, the corroded layer where the grain boundary was dissolved grew with soaking time. Bending strength dropped with soaking time. When soaked in 30wt% NaOH solutions, grain boundaries were dissolved slightly, and Si3N4 particles were dissolved and then dropped out. Close agreement was obtained between the measured bending strength and the bending strength predicted with the KIc of the silicon nitride ceramics and crack length. In this prediction the corroded layer thickness of the specimens soaked in 35wt% HCl solutions was considered to be the diameter of the semi-circular surface crack, and that of the 30 wt% NaOH solutions was considered to be the maximum depth of surface edge crack.