The coating of silicon carbide heater for different environment

Vapor and Moisture

Service life shortened 20% than in   dry air

New furnace or old furnaces not work   long time, to dry at low temperature completely and then heat up

A coat

Nitrogen gas

Above 1400℃, nitrogen will   react with SiC to form silicon nitride, elements will become fragile and   service life shortened. The effect by dew point is same as H2

The recommended furnace temperature   not higher than 1300℃, surface loading as low as possible

B coat

Hydrogen

The mechanical strength decreasing   when elements temperature exceeds 1350℃, and also service   life much depends on intensity of moisture.

Operation temperature lower than   1300℃,   surface loading less than 5W/ CM2

Ammonia

Same as hydrogen and nitrogen

Operation temperature lower than   1300℃,   surface loading less than 5W/ CM2

B coat

Disassociated gas

（Mixture   of N2，CO，CO2，H2，CH4）

Carbon black from decomposed   hydrocarbon on elements surface will cause silicon carbide heater loose.

Introducing air into furnace   frequently to burn up additional Carbon. At side of furnace design, keep   enough space between elements to prevent short circuit.

（S、S2）

Above 1300℃, surface of   elements will be corroded and resistance increasing rapidly.

Keep silicon carbide heating   elements temperature lower than 1300℃

Vacuum

SiO2 protect film will not be   formed, SiC decomposed itself and service life shortened.

Using in pressure over 0.13Pa and   furnace temperature under 1100℃

Others

Various substances from treated   materials, such as Pb, Sb, alkali metal react with elements, which may   shorten elements service life.

To get rid of these substances in   advance, design gas outlet in furnace in order to decrease the effect.

C coat