Antioxidant Methods of Spherical Graphite Materials
Surface coating method:
Coating method that is sprayed on the surface of graphite material coated with a layer of oxidation resistance, the general coating varies according to the coating, the coating process is different, the characteristics of the products produced are not the same. (a) Spraying of metal, carbide, silicide and other materials are metal, carbide, silicide and a mixture of the above materials in the graphite electrode surface sputtering or fusion of a layer of aluminum-based cermet, often used coating process Aluminum and refractory on the electrode surface of the "alternate spray a melting method", can be antioxidant coated graphite electrode, anti-oxidation coating must meet the following requirements: 1) can withstand low temperature without melting, coating decomposition temperature in 1850 "C above; 2) good with the electrode surface, and a similar heat shrinkage coefficient; 3) conductive ability higher than the graphite electrode matrix;
Vapor deposition method:
Pyrolytic carbon and pyrolytic graphite have good resistance to high temperature and corrosion resistance, so in the Spherical Graphite material surface by chemical vapor deposition method to deposit a certain amount of pyrolytic carbon or pyrolytic graphite, can improve the oxidation of Spherical Graphite material However, the most serious drawback of pure pyrolytic carbon coatings is that the anisotropy is large and is prone to peeling in practice. In the process of pyrolytic carbon accumulation, the axial shape of the crystal is perpendicular to the base surface of the pyrolytic carbon, and the anisotropy of the pyrolytic carbon can be reduced. c axial strength, improved other functions, such as swelling, etc. In addition, the vertical inlaid needle-like silicon carbide destroyed the layered structure of pyrolytic carbon, thereby adding a layer of pyrolytic carbon.
The leaching method is to impregnate the graphite material with the oxidation resistant material, reduce the porosity of the graphite products, so as to achieve the purpose of reducing the contact surface of carbon and oxygen, and improve the oxidation resistance of the graphite material. In order to achieve satisfactory results, should be based on the details of the impregnation agent, using different impregnation method (a) immersion phosphate solution _l "This process is complicated and easy, the resulting Spherical Graphite products, the oxidation temperature of 760 Or higher. The specific method is to soak the graphite product in a phosphoric acid-containing phosphoric acid solution for about 10 minutes.Then the soaked product is then heated to at least 500 to about C for about 5 to 10 minutes. By 680 "C and The oxidation test of 800 ~ C shows that the oxidation resistance of soaked Spherical Graphite products is obviously stronger than that of non-soaked graphite products. (b) immersion borosilicate glass 0 borosilicate glass in the impregnation device in the stainless steel actinium crucible, vacuum melting and melting, into the graphite products, the import of ammonia to maintain a certain effort to melt the glass immersed in graphite products in. Impregnated graphite products than the impregnated graphite products before the performance greatly improved. Among them, the compressive strength is doubled, the flexural strength is more than doubled, the porosity is clearly reduced, and the resistivity is almost unchanged. The oxidation resistance is enhanced and the oxidation loss is clearly reduced.
Spherical Graphite is a carbonaceous element crystalline mineral, its crystalline frame for the hexagonal layered structure. The interval between each network layer is 3.40, the distance between the carbon atoms in the same network layer is 1.42A. Is a hexagonal system, with a good layer of cleavage. Cleavage surface to the main molecular bond, the molecular attraction is weak, so the natural floatability is very good. Spherical Graphite soft, dark gray; a sense of light, can purify the paper. Hardness of 1 to 2, along the vertical direction with the addition of its hardness can be increased to 3 to 5. Specific gravity of 1.9 to 2.3. In the isolated oxygen conditions, the melting point of more than 3000 ℃, is one of the most resistant minerals.
Nature in the pure Spherical Graphite is not, which often contains Si02, A1203, Fe0, CaO, P2O5, Cu0 and other impurities. These impurities often appear in quartz, pyrite, carbonate and other minerals. In addition, there are water, asphalt, CO2, H2, CH4, N2 and other local gas. Therefore, the analysis of Spherical Graphite, in addition to determining the fixed carbon content, but also must be measured volatiles and ash content. The process characteristics of the Spherical Graphite are secondary to its crystalline appearance. Crystalline shape of different Spherical Graphite minerals, with different industrial value and usefulness. Industrial, according to the crystal shape is different, the natural Spherical Graphite is divided into three categories.