Today, graphite heating and you talk about the characteristics of hot pressed graphite. In graphite crystal, the carbon atoms in the same layer form covalent bonds by SP2 hybridization. Each carbon atom is connected with the other three atoms by three covalent bonds. Six carbon atoms form a positive six connected ring on the same plane, and extend into a lamellar structure. Here, the bond length of C-C bond is 142pm, which belongs to the bond length range of atomic crystal.
Therefore, for the same layer, it is an atomic crystal. The carbon atoms in the same plane still have one p orbital each, and they overlap each other. Electrons are relatively free, equivalent to free electrons in metal, so graphite can conduct heat and electricity, which is the characteristics of metal crystal. Therefore, it is also classified as metallic crystal. The distance between layers of graphite crystal is 340 PM, which is combined by van der Waals force. That is to say, the layers belong to molecular crystal. However, due to the strong combination of carbon atoms on the same plane layer, it is very difficult to destroy, so the melting point of graphite is also very high, and its chemical properties are stable. In view of its special bonding mode, it can not be considered as atomic crystal or molecular crystal. According to the modern expression, graphite is considered as a mixed crystal.
Hot pressed graphite is characterized by high density and high strength, and its density can reach about 2. It has excellent erosion resistance and erosion resistance. It is an important candidate material for rocket and missile nozzles and warheads. Excellent heat conduction and conduction function, good heat stability function and heat shock resistance with low linear expansion coefficient, chemical corrosion resistance and hard reaction of most metals. The strength increases with the increase of temperature at high temperature (above 800 ℃ sintering temperature of most copper matrix). With outstanding smoothness and wear resistance, it is easy to process and has good machining function. It can be made into hot pressing mould with disordered shape and high precision. In view of the above characteristics, graphite materials have been widely used in diamond sintering mold. Due to the highly disordered arrangement of fibers, good isotropy, high density, low ablative performance and excellent erosion resistance.
