The corrosion behaviors of ceramics (Si-SiC, SiC, Si3N4, Al2O3, ZrO2) were examined in boiliing 95 wt% sulfuric acid by measuring weight change, concentration of dissolved ions in the sulfuric acid, 4-point bending strength and apparent hardness calculated from Load-Depth curve obtained by Micro- Indentation technique. The corroded surface and the fracture surface of the specimens were analyzed by SEM and EPMA. The corrosion behaviors of these ceramics were divided into 3 types; (1) Si-SiC and SiC showed excellent corrosion resistance because of protective oxide films which developed during immersion, (2) the bending strength, apparent hardness of Si3N4 and Al2O3 decreased with increasing immersion time because of corroded layers produced during immersion, and (3) the bending strength of ZrO2 decreased with remarkable weight loss. The thickness (T) of oxide films and corroded layer produced on Si-SiC, SiC, Si3N4 and Al2O3 was evaluated from the depth (d) which was determined by the slope change on Depth-Load/Depth curve. The relationship between T and d was described as T≈10d. The bending strengths of Si3N4 and Al2O3 were evaluated from thickness (T) of corroded layer and KIc obtained before immersion. As a result, the bending strengths of Si3N4 and Al2O3 could be determined with both the KIc and the equivalent crack length (ae) to 20d.
