Effects Of Atmosphere Conditions On Silicon Carbide Heating Elements

Effects   Cause by Vapor and Moisture

Moisture   influences the quality of Sic heater tremendously, sometimes cutting its life   to less than one fifth of expected life under ordinary use.

It   is important to raise the temperature to purge moisture when initiating a new   furnace or restarting to use one after a long suspenstion.

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Effects   of Hydrogen Gas

Sic   heater 's resitance increases rapidly and its mechanical qualities   deteriorate quickly, if the temperature exceeds 1350 in a hydrogen gas   atmostphere. The life, however depends very much on the intensity of   moisture.

With   a dew point of -30°C, the recommended furnace chamber temperature is less   than 1300°C, with a want loading as less as possible. (The dew point is one   of the characteristics of the amount of vapor in gas. A lower dew point means   less vapor content.)

Effects   of Nitrogen Gas

Nitrogen   Gas reacts with silicone carbide and forms silicon nitride the temperature   exceeds 1400°C.

The   effects of the dew point are similar to those caused by hydrogen gas.

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Effects   of Disassociated Ammonia Atmostphere (Mixture of H2 75% and N2 25%)

As   with the case of hydrogen and nitrogen gas.

OPerating   temperature of less than 1300°C is recommendable. The effects of the dew   point are as same as in the case of hydrogen gas.

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Effects   of Disassociated Gas (Mixture of N2, CO, CO2, H2, and CH4)

Partial   decomposition of hydrocarbon by heating produces carbon, and short-circuiting   is caused by sooting.

It   is necessary to prevent inclusion of under composed carbohydrate in the gas   and at teh same time, to burn off accumulated free carbon by occassionally   introducing air into the furnace. The electric furnace should be designed   with wide spacing between EREMA elements to prevent potential   short-circuiting caused by sooting.

Effects   of Sulfur Gas (S and SO2)

The   surface of ehating elements will be damaged and resistance rapidly increased   if temperature of EREMA exceeds 1300°C in a sulfur gas atmostphere.

Use   the EREMA element under 1300°C.

Effects   of Vacuum

IN   the high vacuum, SiO2 protect film is not formed and silicon carbide   dissolves itslef. As a result, a service life will be shortened.

Avoid   usage pressure over 0.13Pa and temperature over 1000°C

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Effects   of Other Volatile Materials

Various   substances, emitted from processed materials during calcination, including   such halides as lead, antimony, alkali and alkaline earth, as well as oxides,   chemical compounds thereof may occassionally stick to heating elements and   corrode them.

If   the presence of volatile substances is suspected, it is important to remove   them beforehand or lessen their effects by installing an exhaust port.

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