At present, the electric contacts on high-pressure or ultra-high-pressure boilers are made of ultra-pure alumina porcelain tubes as insulators. Because alumina tube has high mechanical strength and excellent insulation properties, it also has strong high temperature resistance to acid and alkali corrosion. When used in high pressure and ultra high pressure boilers with good boiler water quality, the life can reach more than one year.
In addition, the ultra-pure alumina ceramic tube has poor thermal shock resistance, which can easily cause damage to the insulator and seals of the ceramic seals. Therefore, during use, the electrical contacts should be preheated as slowly as possible to prevent steam shock and temperature Sudden changes could damage the motor.

We know that most high-pressure sodium lamps are made of alumina tubes, and the luminous flux of high-pressure sodium bulbs is strongly related to the specific performance of alumina tubes. Relevant factors include:
1. The transmittance of alumina tubes is related to the level of transmittance. The current alumina tubes are polycrystalline alumina tubes with a transmittance of about 92% ~ 93%. The light rate can reach about 97%, but its performance is brittle and not resistant to vibration.
2. The pressure in the alumina tube.
3. Production process.
4. The electrode emission performance, ie the work of overflow, should be low.
At present, a large range of high-pressure sodium lamps are used to replace high-pressure mercury lamps. On the basis of increasing the luminous flux, energy consumption is also saved, so there is a good prospect for development.