Sapphire is an oxide crystal with a high thermal conductivity comparable to that of stainless steel at room temperature. It is widely used as a unique heat-dissipating material due to its light transmitting properties, heat resistance, and corrosion resistance. In particular, its extremely high thermal conductivity at low temperatures makes it an excellent material for heat dissipation in cryogenic environments. A typical example of this feature is the mirrors of the gravitational wave telescope “KAGRA”.
【Reference】G. K. White & M. L. Minges, International Journal of Thermophysics volume 18, pages1269–1327(1997)
Sapphire has a large linear thermal expansion coefficient around room temperature (≈5.5×10-6/K), and is known to be not very resistant to thermal shock. φ50×3t (mm) on the c-plane was subjected to a thermal shock test in which a heated sample was thrown into 10°C water. No cracks were observed up to 200°C, but cracks were observed in the sample heated to 250°C.
