How do halogen elements affect electric heating elements？
1. The effect of halogen elements on electric heating elements.
(1) Destroy the protective oxide film: the alloy surface oxide film of the electric heating element and the dried halogen gas will dissolve into acid, which will have a strong corrosive effect on the oxide film. Chlorine dissolves in water to form hydrochloric acid, which can react with Al2O3 and Cr2O3 in the oxide film at low temperatures to dissolve the dense protective film.
6HCl+Al2O3==2AlCl3+3H2O (1-1)
6HCl+Cr2O3==2CrCl3+3H2O (1-2)
The chloride formed by reaction formula (1-1) and formula (1-2) has a very low melting point and boiling point, and the protective oxide film is destroyed at high temperature.
(2) The halogen gas entering the alloy forms a highly volatile compound with the alloy elements, which destroys the electric heating element from the inside. At high temperatures, halogen gases have a strong affinity with iron, chromium aluminum, nickel and other elements. The following reactions will occur at high temperatures:
2Al+3Cl2==2AlCl3 (2-1)
Fe+Cl2==FeCl2 (2-2)
Ni+Cl2==NiCl2 (2-3)
2Cr+3Cl2==2CrCl3 (2-4)
2. Electric heating elements used in halogen gas medium
At lower temperatures, halogen gases can chemically corrode various electric heating alloys, especially in humid media. Fe-Cr-Al alloys cannot be used in chlorine-containing media due to their high aluminum content. Nickel-chromium alloys such as Cr30Ni70 and Cr20Ni80 are allowed to be used in chlorine-containing media that are dry below 500°C. Nickel-chromium-iron alloys have lower chlorine corrosion resistance than nickel-chromium alloys, and are generally less used.
