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 very high mechanical strength and excellent insulation performance, but also has a strong high temperature acid and alkali corrosion resistance, used for high pressure and ultra-high pressure boiler furnace water quality is good, the life can reach more than
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 very high mechanical strength and excellent insulation performance, but also has a strong high temperature acid and alkali corrosion resistance, used for high pressure and ultra-high pressure boiler furnace water quality is good, the life can reach more than one year.
In addition, the thermal shock resistance of the ultra-pure alumina porcelain tube is poor, which is easy to cause the insulator and porcelain sealing parts to leak due to damage. Therefore, in use, the electrical contact should be preheated as slowly as possible to prevent the motor from being damaged by steam flow impact and sudden temperature change.
We know that most high-pressure sodium lamps are made of alumina tubes, and the luminous flux of high-pressure sodium bulbs is closely related to the specific properties of alumina tubes.
Relevant factors include:
1.The light transmittance of alumina tube is related to the level, the alumina tube in use are polycrystalline alumina tube, the light transmittance is about 92%~93%, if the use of single crystal alumina tube its light transmittance can reach about 97%, but its performance is brittle, vibration resistance.
2. Air pressure in alumina tube.
3. Production process.
4. The emission performance of the electrode, that is, the overflow power should be low.
At present, high pressure sodium lamp is widely used to replace high pressure mercury vapor lamp, which not only increases the light flux but also saves the power loss, so it has a good development prospect.
| Properties | Unit | Value |
| Main Composition | % | AL2O3;SiO2:1.5%~3.5%;
CaO:1.2%~2.8%;MgO:0%3.5% |
| Color | – | White |
| Bulk Density | g/cm³ | 3.6 |
| Possion’s Ratio | – | 0.22~0.23 |
| Water Absorption | % | – |
| Flexural Strength | Mpa | 300~340 |
| (HV)Hardness | Gpa | 312.2~13.5 |
| Young’s Modulus of Elasticity | Gpa | 280~320 |
| Coefficient of linera Thermal Expansion | 25℃~500℃，x10-6 mm/℃ | 7.3-7.2 |
| Thermal Conductivity | W/(m.k) | 16~23 |
| Specific Heat | X10 3 J/(Kg·K） | 0.78 |
| Dielectric Constant(1MHZ) | – | 9.0~9.4 |
| Dielectric Loss Angle | ×10-4 | 5~10 |
| Dielectric Strength | X10 6 v/m | 14~15 |
Alumina Ceramic Tube
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