ABSTRACT
Silicon carbide and porous carbon are high-resistivity materials. Silicon carbide (SiC) can be made by heating a mixture of carbon and quartz grains to about 2500°C. Heating elements of SiC can be made by heating elements of carbon at about 1900°C in sand (SiO2). The resistivity depends on the manufacturing method and varies much more than for metallic materials. Below about 800°C it depends strongly on the amount of impurities. The resistivity increases with time of heating at a high temperature. When SiC is exposed to a high temperature, a protective oxide layer of SiO2 is formed on its surface. The material is used mainly for furnaces. However, its high resistivity and its oxidation resistance at high temperatures make the material interesting also for certain applications in the appliance industry. The high resistivity of the material is utilized. A perforated SiC tube is coated with catalytic material and equipped with electrodes at the ends for connection directly to the power supply.
