Working Principle Of SIC Heating Elements

  The working principle of silicon carbon rods is based on the semiconductor characteristics and physical and chemical properties of its main raw material, high-purity silicon carbide. From the perspective of conductivity, silicon carbide is a wide bandgap semiconductor. At room temperature, there are few free carriers and high resistance. After power is turned on, electrons absorb energy and jump to the conduction band to form current. Lattice vibration assists electron migration to reduce resistance, and when the temperature rises, the bandgap width decreases. The increase in carrier concentration causes the resistance to change with a negative temperature coefficient. In terms of the heating mechanism, following Joule's law, when current passes through the silicon carbon rod, the collision between the carrier and the lattice generates heat.
  During the working process, different temperature stages show different characteristics: the resistance slowly decreases from room temperature to 400℃; the resistance decreases significantly from 400-700℃ and the oxidation rate accelerates, which requires rapid temperature rise to cross; above 700℃, a dense silicon dioxide protective film is formed on the surface, the oxidation rate slows down, and enters a stable working area. To ensure power stability, an adjustable transformer or thyristor power regulator is required to adjust the voltage in real time according to the temperature. In addition, the high thermal conductivity of the silicon carbon rod allows its heat to be quickly transferred to the surface, thereby heating the heated object through radiation and convection. The self-generated silicon dioxide protective film on its surface can prevent oxygen from penetrating and extend its service life. However, when the resistance increases abnormally, thermal stress causes mechanical fracture, or chemical corrosion destroys the oxide film, the silicon carbon rod will fail.