Kyowa Carbon collaborated with the Osaka Industrial Technology Laboratory of the Institute of Industrial Technology to first develop impermeable graphite that can withstand a maximum operating temperature of 1000°C. The biggest feature of this graphite product is that it has a heat resistance three times that of current resin-impregnated carbon. The company has now built a sample production facility at its affiliated Okayama plant and is developing markets for bearings, current collectors, continuous casting nozzles, heating elements, etc. Because of this, graphite has attracted attention as a new type of graphite.
At present, the artificial graphite electrodes used in steelmaking electric furnace electrodes, electrode brushes, heating elements, etc. are all made of petroleum coke. Nowadays, coal coke is mostly used, mixed with tar, asphalt, etc., and then formed and calcined. During the manufacturing process, due to the scattering of volatile matter, it has 15~30% pores. Water and air penetrate into these pores, so the initial vaporization temperature of graphite materials in the atmosphere is generally 520~560°C.
The impermeable graphite that has been successfully developed is a product in which 15 to 30% of the pores of the molded material are permeated with borosilicate glass. When it was oxidized at a temperature above 520°C, no pore oxidation was found. When the temperature reaches above 620°C, the borosilicate glass softens and covers the surface of the carbon material, inhibiting the oxidation of the surface of the carbon itself. In this state, the temperature rises to 1000°C, and even if heated for 10 hours, the oxidation consumption does not exceed 80%. Its oxidation rate is approximately one-third of that of untreated graphite at 800°C.
This graphite product has good wear resistance. When sliding pressure is 4 kilograms per square centimeter, its wear can be reduced by about 20% compared to untreated graphite. Bending strength 196 kg per square millimeter. Resistor 780 micro ohms. The elastic modulus is 1809 kilograms per square millimeter. The porosity is 15.3%.
In the past, in order to block the pores and make them impermeable, the use of resin or metal was considered. However, because the heat resistance of the resin is only 300°C and the price of metal is high, it cannot be widely used.
The main uses of impermeable graphite products that can withstand 1000°C include:
① Mechanical bearings, bushings, mechanical seals, and sliding materials.
②Electrical current collector.
③Metallurgical crucibles, boats, and low-temperature heating elements.
④ Nozzle for continuous casting, etc.
Of course, with the advancement of industrial technology, its uses will rapidly expand, and the demand for impermeable graphite that can withstand 1000°C will also grow rapidly.