Under normal circumstances, alumina tubes have high mechanical strength and excellent insulation properties, as well as strong high temperature resistance to acid and alkali corrosion. It is often used in discharge tubes. The sodium and mercury filled in the discharge tube is actually a solid substance of sodium and mercury. We know that mercury and its compounds are toxic. After evaporation, mercury will be more adsorbed on furniture and walls. If it is left for a long time, it will make people Poisoning, causing danger. The discharge tube is a specially made transparent polycrystalline alumina ceramic tube. The polycrystalline alumina tube can withstand high temperature and high pressure, and has a stable resistance to sodium corrosion against sodium vapor under high pressure. 
In addition, alumina tubes can also be used for thermocouple temperature measurement. The most common type of thermocouple structure in the industry is the common plug-in type, which consists of thermal electrodes, insulating sleeves, protective sleeves, and junction boxes.

Alumina tube

Nufco thermocouple ceramic protection tube: 
Material: 99.5% AL2O3 
Structure: Trigonal 
Temperature range: 1600 ° C-1800 ° C 
Density 3.9-4.0g / cm3 
Melting point 2050 ° C 
Boiling point 2980 ° C 
Insulation sleeves in thermocouples are mostly oxidized Aluminum tube or industrial ceramic tube. Protective sleeve is set according to temperature conditions, the measured temperature of 1000 ℃ generally metal tube, while measuring the temperature above 1000 ℃ even multi industrial ceramic aluminum oxide protective sleeve .