High purity graphite
Graphite with a graphite content of more than 99.9% is called high-purity graphite. It is an ideal crucible boat for inorganic nonmetal, heater for single crystal furnace, EDM graphite, sintering mold, electron tube anode, metal coating, graphite crucible for semiconductor technology, graphite anode and grid for emission electron tube, thyristor and mercury arc rectifier.
High purity graphite - Characteristics of high purity graphite
High purity graphite has the advantages of low resistance coefficient, high temperature resistance, corrosion resistance, oxidation resistance, good thermal shock resistance, low conductivity, thermal expansion coefficient, self lubrication, and easy precision machining.
High purity graphite graphite related composition
Graphite, diamond, carbon 60, carbon nanotube and so on are all simple substances of carbon element, which are allotropes of each other.
Graphite soft, black gray; It has a greasy feeling and can contaminate the paper. The hardness is 1-2, and the hardness can increase to 3-5 with the increase of impurities in the vertical direction. The specific gravity is 1.9 ~ 2.3. The specific surface area is concentrated in the range of 1-20m2 / g (measured by f-sorb2400 specific surface area meter BET method). Under the condition of isolating oxygen, its melting point is above 3000 ℃, and it is one of the most temperature resistant minerals.
There is no pure graphite in nature, which often contains impurities such as Si02, A1203, Fe0, Cao, P2O5 and Cu0. These impurities often appear in the form of quartz, pyrite, carbonate and other minerals. In addition, there are gas parts such as water, asphalt, CO2, H2, CH4 and N2. Therefore, in the analysis of graphite, the content of volatile matter and ash must be determined at the same time in addition to the content of fixed carbon.
High purity graphite graphite process characteristics
Mainly determined by its crystalline form. Graphite minerals with different crystal forms have different industrial values and uses. In industry, natural graphite can be divided into three categories according to different crystal forms.
1. Dense crystalline graphite
Dense crystalline graphite is also called block graphite. Such graphite crystals are obvious and visible to the naked eye. The particle diameter is greater than 0.1mm, and the specific surface area is concentrated in the range of 0.1-1m2 / g (measured by the BET method of f-sorb2400 specific surface area meter). The crystal arrangement is disordered and in a dense block structure. This kind of graphite is characterized by high grade, generally with a carbon content of 60-65%, sometimes up to 80-98%, but its plasticity and smoothness are not as good as flake graphite. The research on the specific surface area of graphite is very important. The specific surface area detection data of graphite can only be true and reliable if it is detected by BET method. At present, many instruments in China can only be detected by direct comparison method, and now they are also eliminated in China. At present, the multi-point BET method is adopted for the specific surface area test at home and abroad. The specific surface area measurement standards formulated at home and abroad are all based on the bet test method. Please refer to the Chinese national standard (GB / t19587-2004) - Method for measuring the specific surface area of solid substances based on the principle of gas adsorption bet. The specific surface area detection is actually a time-consuming work. Due to the different adsorption capacity of samples, the testing of some samples may take a whole day. If the testing process is not fully automated, the tester can't leave at all times, and must concentrate on observing the dashboard and operating the knob. A little carelessness will lead to the failure of the testing process, which will waste a lot of valuable time of the tester. Only fully automated and intelligent specific surface area tester products can meet the international standards of the testing instrument industry. All similar international products are fully automated, and manually operated instruments have been eliminated in foreign countries. Truly fully automated and intelligent specific surface area analyzer products liberate testers from repetitive mechanical operations, greatly reduce their work intensity, simplify training, and improve work efficiency. The truly fully automatic and intelligent specific surface area tester greatly reduces the error caused by human operation and improves the test accuracy. The f-sorb2400 specific surface area tester is an instrument that can truly realize the detection function of BET method (with direct comparison method). More importantly, the f-sorb2400 specific surface area tester is the only fully automated and intelligent specific surface area detection equipment in China so far. Its test results are highly consistent with international standards and have good stability. At the same time, it reduces human errors and improves the accuracy of test results.
2. Flake graphite
Graphite crystal is scaly; It is metamorphosed under high-strength pressure and can be divided into large scale and fine scale. This kind of graphite ore is characterized by low grade, generally between 2-3%, or 100-25%. It is one of the best floatable ores in nature. High grade graphite concentrate can be obtained through multiple grinding and separation. This kind of graphite has better floatability, lubricity and plasticity than other types of graphite; Therefore, it has the greatest industrial value.
3. Cryptocrystalline graphite
Hidden quality graphite is also known as amorphous graphite or earthy graphite. The crystal diameter of this kind of graphite is generally less than 1 micron, and the specific surface area is concentrated in the range of 1-5m2 / g (measured by the BET method of f-sorb2400 specific surface area meter). It is an aggregate of microcrystalline graphite, and the crystal form can only be seen under the electron microscope. This kind of graphite is characterized by earthy surface, lack of luster and poor lubricity. High grade. Generally 60-80%. A few as high as 90%. Poor ore washability.
Graphite is widely used in industry and is used in almost every industry. Artificial graphite, or special graphite, is widely used in industry. According to its molding method, it can be divided into the following types.
1. Isostatic pressing graphite. That is, what many people call "three high graphite", but not three high is isostatic pressure.
2. Molded graphite
3. Extruded graphite, mostly electrode materials.
Among them, according to the particle size of graphite, it can also be divided into: detailed structured graphite (generally with a specific surface area of 10-20m2 / g, measured by f-sorb2400 specific surface area meter BET method), medium coarse graphite (generally with a particle size of about 0.8mm), and electrode graphite (2-4mm).
High purity graphite - special properties of graphite
1) high temperature resistant type: the melting point of graphite is 3850 ± 50 ℃, and the boiling point is 4250 ℃. Even if it is burned by ultra-high temperature arc, the weight loss is very small, and the coefficient of thermal expansion is also very small. The strength of graphite increases with the increase of temperature. At 2000 ℃, the strength of graphite is doubled.
2) conductivity and thermal conductivity: the conductivity of graphite is 100 times higher than that of general non-metallic minerals. Its thermal conductivity exceeds that of metal materials such as steel, iron and lead. The thermal conductivity decreases with the increase of temperature, and even at extremely high temperatures, graphite becomes an insulator. Graphite can conduct electricity because each carbon atom in graphite forms only three covalent bonds with other carbon atoms, and each carbon atom still retains one free electron to transfer charges.
3) lubricity: the lubricity of graphite depends on the size of graphite scales. The larger the scales, the smaller the friction coefficient, and the better the lubricity.
4) chemical stability: graphite has good chemical stability at normal temperature, and can resist acid, alkali and organic solvent corrosion.
5) plasticity: graphite has good toughness and can be rolled into very thin flakes.
6) thermal shock resistance: when graphite is used at normal temperature, it can withstand drastic changes in temperature without damage. When the temperature changes abruptly, the volume of graphite changes little and cracks will not occur.
High purity graphite - name source
It comes from the Greek "graphein", meaning "for writing". It was named in 1789 by A.G. Werner, a German chemist and mineralogist;
Chemical composition: there are few pure ingredients, often containing various impurities;
Category: natural elements - nonmetallic elements - Carbon Group
Crystal system and space group: hexagonal crystal system, p63 / MMM;
Unit cell parameters: A0 = 0.246nm, C0 = 0.670nm;
Morphology: single crystals are often in sheet or plate shape, but complete ones are rare. Aggregates are usually scaly, massive and earthy;
Color: iron black;
Streak: bright black
Transparency: opaque
Luster: semi metallic luster
Hardness: 1-2
Cleavage and fracture: parallel cleavage is extremely complete;
Specific gravity: 2.21-2.26g/cm3
Specific surface area: 5-10m2 / g (measured by f-sorb2400 specific surface area meter BET method),
Other properties: the sheet is flexible, slippery, easy to pollute hands, and has good conductivity;
Identification features: iron black, low hardness, a group of extremely complete cleavage, slippery feeling and hand dyeing;
High purity graphite - origin and occurrence
Graphite is formed at high temperature. The most widely distributed metamorphic deposit is graphite, which is formed by regional metamorphism of sedimentary rocks rich in organic matter or carbonaceous matter;
High purity graphite - main uses
Graphite is widely used in industry, such as making high-temperature crucibles in smelting, lubricants in machinery industry, electrodes and pencil leads; It is widely used in advanced refractory materials and coatings in metallurgical industry, stabilizers for initiating explosive materials in military industry, pencil leads in light industry, carbon brushes in electrical industry, electrodes in battery industry, catalysts in fertilizer industry, etc. After deep processing, flake graphite can produce graphite milk, graphite sealing materials and composites, graphite products, graphite antifriction additives and other high-tech products, and become important non-metallic mineral raw materials for various industrial sectors
New uses of high purity graphite graphite:
With the continuous development of science and technology, many new uses of graphite have been developed. Flexible graphite products. Flexible graphite, also known as expanded graphite, is a new graphite product developed in the s. The United States successfully developed flexible graphite sealing materials to solve the leakage problem of atomic energy valves. Subsequently, Germany, Japan and France began to develop and produce them. In addition to the characteristics of natural graphite, this product also has special flexibility and elasticity. Therefore, it is an ideal sealing material. It is widely used in petrochemical, atomic energy and other industrial fields. The international market demand is increasing year by year.
High purity graphite - Graphite anecdotes
Diamond "flies" out of graphite powder.
When you mention diamonds, people will associate them with the dazzling and glittering scene, which shines with the owner's activities. But because of its high price, most people can only flinch. Nevertheless, people still yearn for diamonds. Do you know what diamonds are? Its chemical composition is carbon (c), and natural diamonds can only be called "Diamonds" after being polished. Natural diamonds are very rare. There are only two diamonds weighing more than 1000 carats (1g = 5 carats) in the world, and only a few diamonds weighing more than 400 carats. The largest diamond found so far in China weighs 158.786 carats, which is called "Changlin diamond". Rare things are more precious. Just because natural diamonds used as "Diamonds" are rare, people want to replace them with "artificial" diamond, which naturally reminds them of graphite, the "twin" brother of diamonds.
The chemical composition of diamond and graphite is carbon (c), which is called "allotrope". From this title, we can know that they have the same "quality", but their "shape" or "nature" are different, and they are very different. Diamond is the hardest material at present, while graphite is one of the softest materials.
The hardness difference between graphite and diamond is so great, but people still hope to obtain diamond by artificial synthesis, because graphite (carbon) is abundant in nature. However, it is not so easy to turn the carbon in graphite into the carbon arranged like diamond. Graphite at 50000-60000 atmospheres ((5-6) × 103mpa) and a high temperature of 1000 to 2000 degrees Celsius, and then using metals such as iron, cobalt and nickel as catalysts, graphite can be transformed into diamond.
At present, more than ten countries (including China) have synthesized diamonds in the world. However, due to its fine particles, this kind of diamond is mainly used as an abrasive for cutting and drilling bits for geology and petroleum. At present, 80% of the world's diamond consumption is mainly used in industry, and its output is far more than that of natural diamond.
The initially synthesized diamond particles are black, 0.5mm in size, and weigh about 0.1 carat (the smallest diamond used for gemstones generally cannot be less than 0.1 carat). At present, the large grain diamond developed in China is more than 3mm, and more than 6.1 carats of diamond have been produced in the United States and Japan. We say that diamonds have "flown" out of graphite, and gem grade synthetic diamonds will also be supplied to the market in the near future.
How can graphite replace copper?
In the 1960s, copper was widely used as an electrode material, with a utilization rate of about 90%, and graphite was only about 10%; In the 21st century, more and more users began to choose graphite as electrode material. In Europe, more than 90% of electrode materials are graphite. Copper, once the dominant electrode material, has almost lost its advantages over graphite electrodes. What caused this dramatic change? Of course, graphite electrode has many advantages.
(1) faster processing speed: in general, the machining speed of graphite can be 2-5 times faster than that of copper; The speed of EDM is 2 ~ 3 times faster than that of copper;
The material is less easy to deform: it has obvious advantages in the processing of thin rib electrodes; The softening point of copper is about 1000 degrees, which is easy to deform due to heat; The sublimation temperature of graphite is 3650 degrees; The coefficient of thermal expansion is only 1 / 30 of that of copper.
(2) lighter weight: the density of graphite is only 1 / 5 of copper. When large electrodes are used for electrical discharge machining, it can effectively reduce the burden of machine tools (EDM); It is more suitable for application in large-scale molds.
(3) less discharge consumption; Because spark oil also contains C atoms, during EDM, high temperature causes C atoms in spark oil to be decomposed, and then a protective film is formed on the surface of graphite electrode to compensate for the loss of graphite electrode.
(4) no burr; After the copper electrode is processed, it needs to be trimmed manually to remove burrs, while graphite has no burrs after processing, which saves a lot of costs and makes it easier to realize automatic production;
(5) graphite is easier to grind and polish; Since the cutting resistance of graphite is only 1 / 5 of that of copper, it is easier to grind and polish manually;
(6) lower material cost and more stable price; Due to the rise of copper price in recent years, the price of isotropic graphite is lower than that of copper. Under the same volume, the price of universal graphite products of Toyo carbon is 30% - 60% lower than that of copper, and the price is more stable. The short-term price fluctuation is very small.
It is this incomparable advantage that graphite gradually replaces copper as the preferred material for EDM electrodes
High purity graphite - Graphite origin
Famous origin: Ticonderoga, Madagascar and Ceylon in New York. Liumao in Jixi City, Heilongjiang Province is the largest origin in China.
Laixi City, Shandong Province is one of the important graphite producing areas in China. The proven reserves of graphite are 6.8711 million tons, and the current reserves are 6.3993 million tons.
