Temperature Sensors operating above 1100°C normally use ceramic protection sheaths and insulators. The most useful ceramics for temperature sensors are Recrystalised alumina and Aluminous Porcelain.

Recrystalised Alumina Ceramic

Recrystalised Alumina is commonly called RA, Alsint ^®, RUBALIT ^®  , AluSIK-99 ZA ^®, 

RA is the higher temperature grade, with applications up to 1700°C. The specification most usually referred to is DIN 799. A similar grade DIN 710 is now no longer readily available, but it is still seen on older thermocouple specifications sheets. DIN 799 grade is minimum 99.7% Al₂O₃. Some ceramic shape manufacturers claim 99.8%. My understanding is that the basic raw material before extrusion is 99.8%.… Read more