2001 Volume 8 Issue 295 Pages 434-440
Changes in mechanical strength of magnesium oxide (MgO) ceramics (relative densities ≥99.0%) with average grain sizes of 34.8 μm, 12.8 μm, and 0.65 μm under repeated heating and cooling have been examined. The heating and cooling of MgO ceramic with diameter of 20 mm and thickness of 1.5 mm were repeated between base temperature (TB : 900°C) and lower limit temperature. The temperature difference (ΔT) between TB and TL was changed from 100°C to 500°C; the heating-cooling rate of these MgO specimens was either 100°C·min-1 or 200°C·min-1. Appreciable decreases in residual flexural strength of MgO specimen with average grain size of 0.65 μm were observed as ΔT, the number of heating-cooling cycles, or the heating-cooling rate increased. The thermal damage of MgO specimen was less severe compared to the thermal shock resistance (water-quench test) but the trends were similar to one another.
