First, the definition of electrician grade magnesium oxide: it refers to the fused crystalline magnesium oxide block broken and matched with different particle sizes or numbers in a certain proportion, directly or modified for tubular electric heating elements as insulation medium for heat conduction at high temperatures.

Second, electrical grade magnesium oxide classification: according to the production method and main use can be divided into the following four categories,

1), ordinary type, low temperature moisture-proof type, medium temperature moisture-proof type, high temperature type

Third, the performance requirements of magnesium oxide;

1, when the working temperature of magnesium oxide, it should have high thermalconductivity, so that the heat can be quickly transferred to the surface of the tube, so that the resistance wire and the wall temperature is closer;

2, when the operating temperature is within 1100℃, magnesium oxide should have good insulation performance;

3, magnesium oxide must have a certain granularity, the shape is generally round rather than the current production of sheet, because the round filling density, good mobility, and has a certain percentage of particles, the extra time is not easy to damage the heating wire, to ensure that there is no difficulty in filling;

4. Magnesium oxide should not corrode heating wire materials and pipes at room temperature or high temperature.

5, the water absorption rate of magnesium oxide shall not be higher than the following provisions: ordinary type ≤1.5%, low temperature moisture proof type ≤0.05%, medium temperature moisture proof type ≤0.10%, high temperature type ≤0.10%

6. The resistivity of magnesium oxide shall not be lower than the value specified in the following table.

4, electrical grade magnesium oxide particle size analysis;

Because magnesium oxide ore after crushing, the size of the particle size is different, if according to a certain amount of ratio has the following advantages.

1) can increase the density, reduce the working temperature of the resistance wire, thereby improving the life of the electric heating element;

2) Can overcome the "screening" effect; Improve the utilization rate of magnesium oxide;

5. State analysis of magnesium oxide under heat condition;

The porosity of the compressed magnesium oxide in the tubular heating element is 15% under normal circumstances, that is, the density of magnesium oxide is: the true density of magnesium oxide minus the porosity, that is, 3.85*(1-15%)=3.05 g/cm 3. If the temperature of the electric heating element is sufficiently high, then the oxygen in the stomata interacts with the resistance wire and pipe, and because of this reaction, the partial oxygen pressure is reduced, and the partial oxygen pressure of the final state determines the affinity between the oxygen and the metal parts of the element. According to data, partial oxygen pressure may drop to 10-13~10-19 ATA. At such a low oxygen pressure, the properties of the fine particles of fused magnesium oxide change, that is, the common magnesium oxide turns black, under oxidation conditions, magnesium oxide is mainly evaporated in molecular form at high temperature and does not decompose, and magnesium oxide may be partially reduced under reduction conditions.

It can be seen that when the pressure in the electric heating element drops 10-19~10-13ata at 800~1000 ° C, magnesium oxide has the conditions for reduction and decomposition. Only by adding a "reducing atmosphere", the necessary conditions are sufficient for the reduction and decomposition of magnesium oxide, so that magnesium oxide begins to black, if the cross-sectional area of the heating element is affected, the insulation of the heating element decreases and deteriorates, so the leakage current increases. Some sources also suggest that this reaction is reversible. If annealed in 900℃ air, the original properties will be restored.