Sapphire (Al₂O₃) is an incredibly hard crystal (HK1370kg/mm2), second only to diamond. It has high mechanical strength, thermal and chemical resistance and is scratch resistant, making it very desirable for operating in harsh conditions. Sapphire windows can be made thinner than alternative crystals thanks to its structural integrity and can operate up to 2030⁰C. The material transmits between the UV and IR at 0.15-5.5µm, and has a high refractive index of 1.75..q
Sapphire has applications where its strength and durability are required. This includes pressure optical windows, furnace viewports, submersible ROVs, gas and oil analysis, barcode readers and IR analytical devices.