Graphite powder is a kind of mineral powder, the main component is carbon simple substance, soft, dark gray; it has a greasy feeling and can contaminate paper. The hardness is 1-2, and its hardness can increase to 3-5 along with the increase of impurities along the vertical direction. The specific gravity is 1.9-2.3. Under the condition of isolating oxygen, its melting point is above 3000°C, and it is one of the most temperature-resistant minerals. The chemical properties of graphite powder are relatively stable at room temperature, insoluble in water, dilute acids, dilute alkalis and organic solvents; the material has high temperature resistance and electrical conductivity, and can be used as refractory materials, conductive materials, and wear-resistant lubricating materials.
Material introduction
React with oxygen at different high temperatures to form carbon dioxide or carbon monoxide; among halogens, only fluorine can directly react with simple carbon; under heating, graphite powder is more easily oxidized by acid; at high temperatures, it can also react with many metals to form metal carbonization Substances that can smelt metals at high temperatures.
Material properties
Graphite powder is a chemically sensitive substance. Its resistivity will change in different environments, that is, its resistance value will change, but one thing will not change. Graphite powder is a good non-metallic conductive substance. One, as long as the graphite powder is kept uninterrupted in the insulating object, it will be energized like a thin wire. However, the resistance value is not an accurate number, because the thickness of the graphite powder is different. Use The resistance value of graphite powder will be different in different materials and environments. Due to its special structure, graphite has the following special properties:
1) High temperature resistant type: the melting point of graphite is 3850±50°C, and the boiling point is 4250°C. Even after being burnt by an ultra-high temperature arc, the weight loss is very small, and the thermal expansion coefficient is also very small. The strength of graphite increases with the increase of temperature, and at 2000°C, the strength of graphite doubles.
2) Electrical and thermal conductivity: The electrical conductivity of graphite is one hundred times higher than that of ordinary non-metallic minerals. Thermal conductivity exceeds that of metal materials such as steel, iron, and lead. Thermal conductivity decreases with increasing temperature, and even at extremely high temperatures, graphite acts as a thermal insulator.
3) Lubricity: The lubricating performance of graphite depends on the size of the graphite flakes. The larger the flakes, the smaller the friction coefficient and the better the lubricating performance.
4) Chemical stability: Graphite has good chemical stability at room temperature, and is resistant to acid, alkali and organic solvents.
5) Plasticity: Graphite has good toughness and can be connected into very thin sheets.
6) Thermal shock resistance: When graphite is used at room temperature, it can withstand drastic changes in temperature without damage. When the temperature suddenly changes, the volume of graphite does not change much, and no cracks will occur.
Applications
1. As a refractory material: Graphite and its products have the properties of high temperature resistance and high strength. They are mainly used to manufacture graphite crucibles in the metallurgical industry. In steelmaking, graphite is often used as a protective agent for steel ingots and as the lining of metallurgical furnaces.
2. As a conductive material: In the electrical industry, it is used to manufacture electrodes, brushes, carbon rods, carbon tubes, positive electrodes of mercury positive current devices, graphite gaskets, telephone parts, and coatings for TV picture tubes, etc.
3. As a wear-resistant lubricating material: Graphite is often used as a lubricant in the machinery industry. Lubricating oil often cannot be used under high-speed, high-temperature, and high-pressure conditions, while graphite wear-resistant materials can work at (1) 200~2000 °C at high sliding speeds without lubricating oil. Many equipments conveying corrosive media widely use graphite materials to make piston cups, sealing rings and bearings, and they do not need to add lubricating oil during operation. Graphite milk is also a good lubricant for many metal processing (wire drawing, tube drawing).
Industrial applications
Graphite has good chemical stability. Specially processed graphite has the characteristics of corrosion resistance, good thermal conductivity, and low permeability. It is widely used in the production of heat exchangers, reaction tanks, condensers, combustion towers, absorption towers, coolers, heaters, and filters. , Pump equipment. Widely used in petrochemical, hydrometallurgy, acid-base production, synthetic fiber, papermaking and other industrial sectors, it can save a lot of metal materials.
Casting, foundry, molding and high-temperature metallurgical materials: Due to the small thermal expansion coefficient of graphite and its ability to withstand rapid cooling and rapid heat changes, it can be used as a casting mold for glassware. After using graphite, black metal can be used to obtain castings with accurate dimensions, smooth surface and high yield. It can be used without processing or with a little processing, thus saving a lot of metal. In the production of powder metallurgy such as cemented carbide, graphite materials are usually used to make porcelain boats for molding and sintering. Crystal growth crucibles for monocrystalline silicon, regional refining vessels, bracket fixtures, induction heaters, etc. are all processed from high-purity graphite. In addition, graphite can also be used as graphite insulation boards and bases for vacuum smelting, high temperature resistance furnace tubes, rods, plates, grids and other components.
Principle of Conduction
Generally, rubber is insulated. If it needs to conduct electricity, then it needs to add conductive substances. Graphite powder has excellent conductivity and lubricating mold release. Processing graphite into graphite powder has excellent lubrication and electrical conductivity. The higher the purity of graphite powder, the better the electrical conductivity. Many special rubber product factories need conductive rubber, so can graphite powder be added to the rubber to conduct electricity? The answer is yes, but there is also a question, what is the proportion of graphite powder in rubber? Some enterprises use a ratio of no more than 30%. This type is used on wear-resistant rubber products, such as car tires, etc. There are also special rubber factories that use a ratio of 100%. Only in this way can they conduct electricity. The basic principle of electricity conduction It is a conductor that cannot be interrupted, just like a wire. If it is broken in the middle, it will not be energized. The conductive graphite powder in the conductive rubber is a conductor. If the graphite powder is cut off by the insulating rubber, it will not conduct electricity. , so the proportion of graphite powder is less, the effect of conductivity may not be good.
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