Interaction between silicon carbide rod and gas medium:

The chemical composition of Jian carbon rod is close to that of silicon carbide, and its crystal structure is the same as that of carbonization. However, due to the different processing processes of silicon carbon rod, such as recrystallization temperature, product pressing density, surface coating and the effect of gas medium, the service life of silicon carbon will also be different. According to thermodynamic calculation, silicon carbide is very unstable in high temperature oxidation atmosphere, but it can be used for a long time in high temperature oxidation atmosphere, which is largely due to the protective effect of silicon dioxide film. Therefore, silicon carbon also works at high temperature with the performance of silicon carbide, usually at 600-1500 ℃.

When the silicon carbide rod interacts with the gas medium at high temperature, the structure of the silicon carbide rod is destroyed and the resistance value increases. This phenomenon is called the aging of the silicon carbide rod. The growth rate of resistance reflects the reaction rate between silicon carbide rod and gas medium. This is not only related to the gas medium, but also related to the surface heating temperature and surface electrical load of silicon carbon rod. The following is the effect of silicon carbon on the gas medium and the growth of resistance at high temperature.

1. Oxidation reaction of silicon carbide rod in dry air

Silicon carbon press oxidizes slowly in dry air at high temperature, and the resistance increases gradually. The oxidation reaction is as follows

SiC+202ー→SiO2+CO

The resistance increase rate of carbon rod after oxidation in air is related to the service temperature of silicon carbon rod. The higher the service temperature is, the more intense the oxidation is, and the greater the resistance increase rate is.

2. Reaction of water vapor with silicon carbide rod

The oxidation of trace steam and silicon carbide rod is very obvious. The reaction between water vapor and silicon carbide rod is quite strong at high temperature. The reaction equation is as follows:

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Sic+3H2O-→SiO2+CO↑+3H2↑

For the above reasons, the use of silicon carbide rod in steam increases much faster than that in air.

3. Reaction of nitrogen with silicon carbide rod

When the temperature is higher than 1400, the silicon carbide rod and nitrogen form a series of nitrides, which significantly increases the resistance of the silicon carbide rod. The application of silicon carbide rod in nitrogen shall be controlled below 1300 ℃.

4. Reaction of hydrogen with silicon carbide rod

When the temperature reaches 1200, hydrogen begins to react with silicon carbide rod, and the reaction equation is

Sic+ 2HSIH. + C

Silicon carbide rod shall be used in hydrogen, and the service temperature shall be controlled at 1200 ℃.

Ammonia (NH) decomposes into N2 and H2 at high temperature. The reaction of these two gases with silicon carbide rod has been described above. Silicon carbide rod shall be used in ammonia, and the temperature shall be controlled below 1200 ℃.

6. Reaction of silicon carbide rod with other media

Chlorine reacts with the silicon carbide rod at 500 ℃ and the SiC component constituting the silicon carbide rod can be completely decomposed at 1200 ℃. Sulfur and sulfur oxide react with silicon carbide rod at 1300 ℃ to corrode silicon carbide rod, so the temperature should be reduced to 1200 in application. Hydrofluoric acid and fluoride can destroy the SiO2 protective film on the surface of silicon carbide rod at room temperature and shorten the service life of silicon carbide rod.

3、 Action of silicon carbide rod with acid and alkali

The function of silicon carbide rod with acid and alkali is the same as that of silicon carbide. Due to the function of silicon dioxide protective film, silicon carbide rod has strong acid resistance; Poor alkaline resistance (SO2 is a weak acid oxide). When alkaline slag is encountered at high temperature (above 1000 ℃), it is easy to be eroded by molten alkali and alkaline earth metals. It has destructive effect on silicon carbide rod. Silicon carbide rods below 200 ℃ are generally not eroded by acid flux.