The high purity graphite generally refers to the amount of carbon containing more than 99.99% of graphite and in the organizational structure it can be divided into three categories: coarse grain structure, fine grain structure and ultra-fine grain structure. The basic material of the integrated circuit is mainly silicon single crystal chip, at present silicon single crystal growth process is mainly uses in Czochralski (CZ), Czochralski silicon accounted for about 80% of the total amount of silicon in the global electronics industry, the graphite piece in Czochralski silicon furnace is a consumable,we use the high purity graphite material to process the Czochralski silicon furnace heating system.
Another important use of high purity graphite is process various kinds of crucibles which are used for the production of precious metals, rare metals or high pure metal, non-metallic materials. The graphite electrode used in sectral analysis is also a kind of high purity graphite, which can be used for the spectral analysis of all elements except for carbon. The extrusion method is used for the graphite electrode for spectrum analysis ,the impurities of finished product should be not more than 6*10-5 ,in spectrum analysis in preparation of standard sample and catching impurities set required spectral pure carbon powder or spectral pure graphite toner by chemical method. These two kinds of high purity materials of impurity content requirements are in 6*10-5; in some application,it need the carbon content up to 99.9995% and total ash content less than 5 * 10-6. The molding methods of high purity graphite include three kinds of forming methods, such as extrusion, molding, and isostatic pressing.
2). The Graphite Material Used in Nuclear Power
The graphite is one of the materials used in the construction of nuclear reactors and one of reflective materials,the early reactors are graphite reactor. The graphite as the structural material of nuclear reactor is more strict and expensive in the selection of raw materials, process control, product inspection than the graphite electrode, the grphite used in a nuclear reactor must have the following properties: the little absorption for slow neutron , good high temperature strength, high thermal shock resistance, the good deceleration performance for the fast neutron, stable dimension under irradiation, impurity content rarely. For Boron, Cadmium and other easy absorb elements in the neutron ,we must control the content strictly. The nuclear graphite must have higher bulk density, The bulk density is one of the main indicators of nuclear graphite, The porosity and permeability must be reduced to a certain level. The mechanical strength of graphite is also related to its bulk density. The bulk density of graphite used in the normal graphite reactor is 1.7-1.75g/cm3.
3).The Homogeneous Graphite
Although the definition of homogeneous graphite need to be defined in the world, the general is measuring the diameter direction and lengthwise direction of some physical properties of the index and calculate the ratio, some with thermal expansion coefficient ratio, the most simple one is expressed as a ratio of the resistivity, the difference to referred to in ~ 1.1 range for isotropic products, more than 1.1 called the anisotropy product. Japan and other industrial technology advanced countries use static pressure molding method of large-scale production of isotropic graphite and the diameter can reach 1.5m, length of 3%, the volume density reached 1.95-2.0g/cm3, the anisotropy ratio reduced to 1.05. In addition to the use of general petroleum coke, the use of modified pitch coke, natural pitch coke, oxidized petroleum coke, calcined petroleum coke, natural graphite, etc., are also used in the manufacture of homogeneous graphite.
