Graphite powder is soft, black and gray; it has a greasy feel and can contaminate paper. The hardness is 1~2, and the hardness can be increased to 3~5 along with the increase of impurities in the vertical direction. The specific gravity is 1.9~2.3. Under the condition of insulating oxygen, its melting point is above 3000 °C, which is one of the most temperature-resistant minerals. The chemical properties of graphite powder at normal temperature are relatively stable, insoluble in water, dilute acid, dilute alkali and organic solvent; the material has high temperature resistance and can be used as refractory material, conductive material and wear-resistant lubricating material.
It reacts with oxygen at different high temperatures to form carbon dioxide or carbon monoxide; in the halogen, only fluorine can directly react with elemental carbon; under heating, graphite powder is more easily oxidized by acid; at high temperature, it can react with many metals to form metal carbonization. The material can be smelted at high temperatures.
Graphite powder is a chemically sensitive substance. In different environments, its resistivity will change, that is, its resistance value will change, but one point will not change. Graphite powder is a good non-metallic conductive substance. One, as long as the graphite powder is kept uninterrupted in the insulated object, it will be energized like a thin wire. However, the resistance value is not. This value is not an accurate number because the thickness of the graphite powder is different. The graphite powder resistance will be different in different materials and environments. Graphite has the following special properties due to its special structure:
1. High temperature resistance type: The melting point of graphite is 3850±50°C, and the boiling point is 4250°C. Even if it is burned by ultra-high temperature arc, the weight loss is small and the coefficient of thermal expansion is small. The strength of graphite is enhanced with increasing temperature, and the strength of graphite is doubled at 2000 °C.
2. Conductivity and thermal conductivity: The conductivity of graphite is one hundred times higher than that of ordinary non-metallic minerals. Thermal conductivity exceeds metal materials such as steel, iron, and lead. The thermal conductivity decreases with increasing temperature, and even at very high temperatures, graphite becomes a thermal insulator.
3. Lubricity: The lubricating property of graphite depends on the size of the graphite scale. The larger the scale, the smaller the friction coefficient and the better the lubrication performance.
4. Chemical stability: Graphite has good chemical stability at normal temperature, and is resistant to acid, alkali and organic solvents.
5. Plasticity: Graphite has good toughness and can be joined into very thin sheets.
6. Thermal shock resistance: When graphite is used at normal temperature, it can withstand severe changes in temperature without damage. When the temperature is abrupt, the volume of graphite does not change much and cracks are not generated.
1. As refractory material: Graphite and its products have the properties of high temperature resistance and high strength. They are mainly used in the metallurgical industry to manufacture graphite crucibles. In steelmaking, graphite is commonly used as a protective agent for steel ingots and the inner liner of metallurgical furnaces.
2. For conductive materials: used in the electrical industry to manufacture electrodes, brushes, carbon rods, carbon tubes, positive electrodes of mercury positive flow, graphite gaskets, telephone parts, coatings for television picture tubes, etc.
3. For defense materials: graphite powder can be used as the main raw material for the manufacture of graphite bombs.
4. For wear-resistant lubricants: Graphite is often used as a lubricant in the machinery industry. Lubricating oils are often not used under high speed, high temperature and high pressure conditions, and graphite wear resistant materials can work at high sliding speeds at temperatures of 200 to 2000 °C without lubricating oil. Many equipments that transport corrosive media are widely used in graphite materials to make piston cups, seals and bearings. They do not need to be lubricated during operation. Graphite milk is also a good lubricant for many metal processing (drawing, drawing).
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