Corrosion behavior of single-crystal alumina in argon, air, and water vapor atmospheres at 1700-2000°C

The results for the corrosion of alumina single crystals at 1700-2000 degrees C in argon, argon/water vapor, air, and air/water vapor for 10 h are reported. There were no obvious weight and volume changes after corrosion. White spots were observed on the surfaces of the specimens after corrosion tests. The initial temperature for the appearance of these white spots was 1800 degrees C for argon and air, 1900 degrees C for argon/water vapor, and 2000 degrees C for air/water vapor. These white spots were likely formed by internal impurities, which diffused outward to the surface and coalesced at high temperatures. There was no evidence of corrosion damage inside the specimens. The flexural strength of the specimens was clearly enhanced after the corrosion tests and showed no evident relation to the corrosion conditions. This increase in strength after corrosion was likely due to the healing of surface machining flaws. The surface flaw healing temperature for alumina crystals was higher than 1400 degrees C.