Comparison of non-metallic heating elements
One. Silicon carbon rod (SiC): rod or tube
1. Recrystallization temperature: 1800 degrees Celsius
2. At normal temperature: high hardness, brittleness, high temperature resistance
3． Small deformation at high temperature, horizontal installation is more common
4． Good resistance to sudden changes in temperature (resistance to rapid changes)
5. Stable chemical properties, does not react with acidic materials
6. But at high temperatures, it will react with alkaline earth metals or low melting acid salts.
7. Contact with hydrogen will cause hydrogen embrittlement
8. Large resistivity
9. Since the resistance of each root is different, it must be selected when used to make the current three-phase balanced, and a voltage regulator must be equipped (the capacity of the voltage regulator is three times the working voltage)
10． Resistance characteristics: lowest resistivity at 800 degrees Celsius or 900 degrees Celsius
11. Surface load: design is generally 5W / CM2
12. At the exit of the heating element, generally at the sealing device to reduce heat loss
13. Electrical performance: There is a large specific resistance. When it is heated to 1200 degrees in the air, the error reaches plus or minus 50 degrees. Generally, intensive discharge is used during assembly. The error is reduced by radiation
14. Atmosphere impact:
A. Water vapor will affect it;
B. Use in hydrogen, the temperature should be less than 1200 degrees
C. Used in chlorine gas, at 500-600 degrees, the elements decomposed in NH3 will react with it
D. When used in a nitrogen / hydrogen mixture, the temperature should be less than 1250 degrees
E. In ammonia, SiN is generated at 1350 degrees, which affects the life
F. In sulfur, SO2 will be produced at 1300 degrees, and SO3 will corrode SiC, so it should be less than 1200 degrees
G. In CO, free carbon is generated, which reacts with silicon carbide to increase the current and burn out the transformer.
two. Silicon rhenium rod (MoSiO2) (mainly used in laboratory electric furnace)
1. Resistance to oxidation and high temperature (1200-1650 degrees)
2. The shape is "U", so there is enough expansion space at the bottom due to the consideration of installation
3． At room temperature, the strength is high and the brittleness is large. At 1350 degrees, it begins to soften. Low temperature oxidation occurs at 400-800 degrees
4． Applicable to air, nitrogen and inert gas, but not to be used in reducing atmosphere
5. At 1350 degrees, try to avoid sulfur and chlorine atmosphere. Matching refractory materials are acid or neutral materials
6. Compared with silicon carbon rod: high temperature, can be used in air, water vapor, nitrogen, carbon dioxide atmosphere to 1200-1650 degrees