The graphite heater is the electric heating body parts which made of graphite materials. The Graphite has good electrical and thermal conductivity, and it is commonly used in special industrial furnace as a heating element. The graphite electrode was the heating body in the early selection of industrial furnace , and the high density and power electrode was used as heating element later (smelting quartz glass also used graphite electrode as the heating element). In semiconductor industry development and refining silicon, single crystal germanium, gallium, indium, indium and other materials,the high-purity graphite with fine structure and homogeneous graphite were used as graphite heating in the heating furnace . The carbon cloth or graphite cloth were useing in some special industrial furnace and experimental furnace as the heating body.
The graphite heater has good high temperature strength,the strength of graphite is far worse than metal at normal temperature,but as the temperature increases, the strength gradually increases and it will exceed all oxides and metals.the graphite has some properties of metals and ceramics, with good electrical and thermal conductivity, and a pupil and a small thermal expansion coefficient, so the graphite is one of the best thermal shock resistance of materials.
The graphite heater requirements generate stable thermal field used in the heating furnace, so the graphite should be homogeneous and has stable resistivity. For the graphite heater of manufacturing single crystal , it require special clean graphite to avoid the effect of impurities crystal purity and the total ash content should be less than 20 X 10 - 6, and some require up to 5 x 10 - 6.
The graphite heating body often appear deformation phenomenon in the process of using , this is due to the creep caused by graphite. At normal temperature, the graphite creep is very small, when the temperature rises to 1700 degrees Celsius or higher, the creep can be observed after a few hours, when the stress is eliminated, the residual strain in the material, resulting in plastic deformation of graphite heating body. Reflected in the actual use of graphite deformation caused by thermal field is not uniform, the larger the size,the deformation smaller, smaller particles larger than the particle size of the graphite deformation. To prevent the graphite heating body deformation approach is the first empty burning a (first ohmic heating) heating body which support by bracket before we use it ,the air sintering temperature should be greater than the actual use temperature of 100 to 200 DEG C. In order to eliminate the thermal stress caused to graphite heating element deformation, some manufacturers will be use the graphite heating which the maximum graphite particles in 0.075mm expanding to 0.5 ~ 1mm, and it achieved good results.
