SAPPHIRE IS HIGHLY ROBUST AT EXTREME TEMPERATURES:
A supported sapphire window can be taken to 1950℃ with no change to its shape and minimal reduction to mechanical performance. Sapphire windows are the perfect material for high temperature combustion chambers, gas processing and lamp shields.
Sapphire flats are ideal for furniture, boats and standoffs in high temperature furnace systems. Sapphire flats remain flat and dimensionally "perfect" up to 1700℃. Because of sapphire's extreme chemical resistance many materials will not stick to sapphire in spite of high temperatures.
Sapphire windows and flats maintain the highest temperature rating of all optical materials in both oxidizing and inert atmospheres.
Sapphire windows can withstand considerably higher temperatures than the closest runner up material, fused silica, with zero degradation. Fused silica will degrade and devitrify over time at temperatures almost half the maximum operating temperature of sapphire