Isostatically pressed graphite is a new type of graphite material developed in the 1960s, which has a series of excellent properties. For example, isostatically pressed graphite has good heat resistance. As the temperature rises in an inert atmosphere, its mechanical strength not only does not decrease, but increases, reaching the highest value at around 2500℃. Compared with ordinary graphite, it has a fine, dense structure and good uniformity. It also has a low thermal expansion coefficient and excellent thermal shock resistance, as well as a good isotropy, chemical corrosion resistance, thermal conductivity and electrical conductivity. It is also easy to machine.
It is precisely because of these excellent properties that isostatically pressed graphite is widely used in the fields of metallurgy, chemistry, electrical engineering, aerospace, and atomic energy industry. With the development of science and technology, its application fields are expanding.
Heaters for silicon crystal growth in both the CZ-monocrystalline and Multi-crystalline silicon ingot furnaces are made of isostatically pressed graphite. The components for isostatically pressed graphite include crucibles, heaters, electrodes, thermal shields, seed holding fixtures and rotating pedestal assembly, round plates, heat reflectors, and about 30 varieties of parts. Among them, 80% of isostatically pressed graphite is used to manufacture crucibles and heaters. In recent years, the requirement for the diameter of the single crystal rod has become larger, with the production of 300mm wafers becoming increasingly mainstream. Correspondingly, the diameter of the heating zone of the single crystal furnace is mostly 800mm, and the graphite crucible in the furnace has a diameter of 860mm to protect the quartz crucible. The heater has a diameter of about 960-1000 mm, and the diameter of some other components can reach up to 1500mm. Since 2003, people's awareness of protecting the living environment on Earth has gradually increased, and people increasingly prefer natural energy sources that do not emit carbon dioxide. In this trend, the production of solar cells has surged. In the process of manufacturing multicrystalline silicon wafers for solar cells, it is necessary to first melt the multicrystalline silicon pieces into an ingot. The heater of the ingot furnace needs to be made of isostatically pressed graphite.
Isostatically pressed graphite is also used to make diamond tools and hard alloy sintering molds, the thermal field parts of the optical fiber drawing machine (heaters, insulation tubes, etc.), the thermal field parts of the vacuum heat treatment furnace (heater, bearing frame, etc.), as well as precision graphite heat exchangers, mechanical seal components, piston rings, bearings, rocket nozzles, etc. Due to its excellent properties such as thermal conductivity, thermal stability, self-lubrication, resistance to wetting and chemical inertia, isostatically pressed graphite is an irreplaceable material for making crystallizers.