Atmosphere | Impact on Element | Solution | Coating |
Vapor and moisture | The service life is about 20% shorter than that in the dry air. | New furnaces or furnaces unused for a long time should be thoroughly dried at low temperature before heating. | A coating |
Nitrogen | Nitrogen reacts with SiC above 1,400℃, producing silicon nitride, making elements fragile and shortening the service life of elements. This is affected by dew point in the same way as H2. | The recommended furnace
temperature is not higher than 1300℃ with surface loading as low as possible. | B coating |
Hydrogen | When elements are heated to above 1,350℃, their resistance will increase rapidly and their mechanical strength will decline, furthermore, the service life of elements varies greatly, depending on the moisture content of gas. | The recommended furnace
temperature is not higher than 1300℃ with surface loading lower than 5W/cm2 | C coating |
Ammonia | Same as hydrogen and nitrogen | The recommended furnace
temperature is not higher than 1300℃ with surface loading lower than 5W/cm2 | B coating C coating |
Disassociated gas（N2，CO，CO2，H2，CH4）
(N2, CO, CO2, H2, CH4) | Decomposed Carbon black attach to body of heating elements to make elements loose. | Convey air into furnace
frequently to burn up additional
Carbon. For furnace design,
keep enough space between
elements and elements to prevent short circuit. | |
Sulphur （S、S2） | When elements are heated to 1,300℃, their surfaces will be eroded, leading to a sharp increase in resistance. | Control the element temperature to below 1,300℃. | |
Vacuum | SiO protective film will not be formed in high vacuum, and Silicon carbide will be decomposed itself, then service life of elements will be shortened. | Furnaces temperature lower than 1000℃ with pressure above 0.13Pa. | |
Others | Various substances from treated materials, such as Pb, Sb and alkali metal, react with elements, which may shorten the service life of elements. | To get rid of these substances in advance, set up a gas exhaust in furnace to reduce the impact. | D Coating |
