Applications of sapphire
Single Crystal Sapphire's optical, electrical, chemical resistance, high thermal conductivity, and mechanical properties make it a superior choice over quartz, alumina and other ceramic materials for hundreds of applications ranging from optical sapphire windows for aerospace sensor systems.

Advantages of Sapphire
Excellent optical characteristics for UV to IR wavelength
High strength
Low electrical resistance(Insulation)
High thermal conductivity
High operating temperature (<1800°C)
High wear and scratch resistance
Chemically inert
Good Thermal Properties

Highly Recommended Sapphire Windows from Yutai Optics:
Optical Sapphire Windows
Sapphire Windows with Hole
Sapphire Windows with Step
Thin Sapphire Glass Sheet