Original paper(Vol.48 No.7 pp.746)

Abstract:The corrosion behaviors of ceramics (Si-SiC, SiC, Si₃N₄, Al₂O₃, ZrO₂) were examined in boiling 95wt% 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 K_IC obtained before immersion. As a result, the bending strengths of Si₃N₄ and Al₂O₃ could be determined with both the K_IC and the equivalent crack length (a_e) to 20d.

Key Words:Corrosion, Si-SiC, SiC, Si₃N₄, Al₂O₃, ZrO₂, Sulfuric acid, Apparent hardness, Parameter B, Micro-Indentation, Protective oxide film, Corroded layer, Equivalent crack length