Anaori Carbon Co., Ltd.

Carbon materials are raw materials with base materials such as petroleum coke or coal pitch coke and are combined with materials such as coal tar pitch or coal tar.

The base materials are pre pulverized and sifted, and then a compound is made from the required amounts of each material. For 100 parts of the base material, 25-100 parts of the compounding materials are added, heated to 140-170℃ and then kneaded. The compound is molded while it is about the dampness and consistency of clay. For extrusion molding, the material is pressed out from the head of the cylinder mold or angular mold or for pressed molding the mold is filled and pressed.

Anisotropy (fibers differing in vertical and horizontal direction) occurs in products due to factors such as strength and thermal expansion coefficient for extrusion molds and pressed molds.

When we want to make the product stronger in order to prevent anisotropy, CIP molding (cold isostatic press or “rubber press”) can be used with extrusion molds and pressed molds.? A rubber mold is used to cover the extrusion or press molded product, placed in a tank of water, and clamped with equal directional pressure.?? These CIP molded items are called isotropic carbon and have been increasing recently.

When the mold is finished, it is sent to the calcination process. For calcination, a binding agent such as tar is used to bond the base materials to each other in order to carry out carbonization. Many molded items are placed into the brick kiln with packing such as coke powder around them in order to prevent oxidation and deformation and then they are fired at 700-1,300℃ using fuel oil for normally 10-20 days. After that, they are cooled for 5-10 days and the calcination process is complete.

During calcination when the binding agents are carbonized, the organic substances or anything other than carbon molecules dissipate from the binding agents and the carbonized bound areas can have a porosity of 40%. Depending on the material, in order to increase the density of the porosity, items that have been calcinated are immersed in binding agent liquid and then calcinated again.

Material in which the calcination process has been completed is ready to be shipped as carbonaceous carbon, however, the vast majority is sent on to the graphitization process in which the materials are heated to about 3,000℃ and then they become graphite grade carbon.

For graphitization, after the materials have been fired in a rectangular brick walled kiln, they are lined up, the gaps are filled with packing, and an electrical current is passed directly from both ends heating the materials due to the electrical resistance.? It is usually heated for 2-4 days and then cooled for 1-2 weeks.

Carbon materials in which crystallization does not progress during the graphitization processing become graphite carbon with increased graphite crystals.? Graphite carbon has more thermal stability than regular carbon materials.? Another property of graphite carbon is that it undergoes higher purification processing.? Even if only the graphitization process is carried out, most of the impurities are vaporized because it is fired at high temperatures; however, impurities of about 500 PPM still remain.? In order to decrease these impurities, the materials are treated with chemicals such as chlorine gas or halogen gas while they are fired to 2,500℃ in a high purification kiln.? The impurities are then decreased to less than 20 PPM.? Recently, high purity carbon materials are rapidly increasing for use in semiconductor manufacturing.? The molding method is shown in the figure on the right.