With the development of graphite industry, the application of graphite has also been widely recognized. At present, the development of graphite in China mainly includes the following points: first, the status and development trend of graphite processing technology at home and abroad. China is a large country with natural graphite resources, and its reserves, output and export volume rank first in the world. However, due to insufficient investment in technology development
1、 Status quo and development trend of graphite processing technology at home and abroad China is a large country with natural graphite resources, and its reserves, output and exports rank first in the world. However, due to insufficient investment in technology development, the production and processing of flake graphite are still the main raw materials. Carbon graphite material is a promising emerging material, which is widely used in the high-tech field. Developed countries have invested manpower and financial resources in development and research. The deep processing technology of natural graphite has developed rapidly, and some new industries have been formed. [graphite, graphite rod, graphite powder, graphite products, graphite processing]
At present, the flexible graphite industry in the United States, Japan, Germany and France takes the lead. Japan is a leader in producing nuclear grade ultra-low sulfur (S & lt; 500ppm) and high purity (S & lt; 50ppm) products. Among them, only Japan can produce high-purity flexible graphite. The world's largest output of flexible graphite is more than 15000-20000 tons.

In terms of anode materials for lithium-ion batteries, because graphite has excellent capacity, modified graphite is used as anode materials for lithium-ion batteries in the United States and Japan, and has formed an industry.

At present, silicon impregnated graphite is only produced in Germany, the United States and Russia. This product is a new material with high hardness, high mechanical strength, wear resistance, corrosion resistance and good lubrication in a wide temperature range. Compared with silicon carbide products, the biggest feature is high yield and low price. As the replacement period of color TV is greatly shortened, the performance requirements of graphite emulsion for color TV tubes are also changing with each passing day. At present, foreign countries still attach great importance to the research and development of graphite emulsion for color TV tubes.

China's new flexible graphite industry is under construction and development. During the "Eighth Five Year Plan" period, a number of achievements in flexible graphite processing technology and equipment have been made, but it is still in the trial production stage. China's lithium-ion battery is still in the stage of small-scale test, but the anode material with stable structure has been developed from natural graphite. Its internal capacity density is 350 MAH / g. Through introduction, digestion and absorption, China has been able to produce five kinds of specifications of graphite emulsion for color TV tubes. At present, silicon impregnated graphite products are blank in China.

II. Development and application of flexible graphite and expanded graphite materials flexible graphite and expanded graphite are important graphite deep processing products. From the perspective of materials science, expanded graphite and flexible graphite are very different, they are two kinds of materials. Expanded graphite is a loose porous structural material with excellent isolation and sealing performance. With the development of technology and application of new materials, these two kinds of new materials have different application fields due to their different characteristics. This paper will discuss the application status and development trend of these two closely related materials with different characteristics in the chemical industry and other fields. [graphite, graphite rod, graphite powder, graphite products, graphite processing]

Since the United carbon company invented the flexible graphite manufacturing technology in the 1960s, the flexible graphite industry has developed for nearly 40 years. As an excellent sealing material, roulong graphite has gradually become familiar to the engineering community, and it has been given the title of "sealing king". Flexible graphite is processed from natural flake graphite. The key technology of preparation is to prepare natural flake graphite into graphite interlayer compound. In industrial operation, concentrated sulfuric acid is often used as interlayer insert, so it is also called acidified graphite (expandable graphite). However, the acidified graphite is washed and dried by water after the graphite reacts with acid, and most of the interlayer inserts have escaped, so it is actually a residual graphite interlayer compound. When most of the graphite interlayer compounds are heated rapidly, the interlayer inserts will vaporize, thus forming a high pressure and expanding the graphite particles along the c-axis. The very thin acidified graphite flakes look like worms after expansion, and the length can reach 1 ~ 2cm. Therefore, they are called worm graphite or graphite worms, which is commonly called expanded graphite. When the expanded graphite is pressed or rolled, the worms mesh with each other, and the expanded graphite is rolled into a graphite coil or plate, that is, flexible graphite. Since the intercalating agent sulfuric acid escapes in most areas during heating, the chemical composition of the soft graphite is basically the same as that of the flake graphite except for the residual sulfur of about 1000ppm, which is pure carbon.

2.1 preparation of expandable graphite at present, there are two processes for the production of expandable graphite in China: chemical method and electrochemical method. Except for the oxidation process, the two processes are the same in other processes such as deacidification, water washing, dehydration and drying. The quality of the products of most manufacturers adopting chemical methods can reach the indexes specified in gb10698-89 expandable graphite standard, and meet the requirements for the production of bulk flexible graphite sheets and export supply standards. However, it is difficult to produce products with special requirements of low volatile content (& lt; 10%) and low sulfur content (& lt; 2%), and the production process is not up to standard. Strengthening technical management, carefully studying the intercalation process, mastering the relationship between process parameters and product performance, and producing expandable graphite with stable quality are the keys to improve the quality of subsequent products. The electrochemical method does not use other oxidants. The natural flake graphite and the auxiliary anode form an anode chamber, which is immersed in the concentrated sulfuric acid electrolyte. After direct current or pulse current is applied and oxidized for a certain time, it is taken out. After water washing and drying, it is expandable graphite. The biggest feature of this method is that it can control the graphite reaction degree and the product performance index by adjusting the electrical parameters and reaction time, with low pollution, low cost, stable quality and excellent performance. How to solve the stirring problem in the intercalation process, improve the efficiency and reduce the power consumption are the urgent problems to be solved. After the above two processes are deacidified, the mass ratio of sulfuric acid wetted and adsorbed by graphite interlayer compounds is still about 1:1, the consumption of intercalating agent is large, and the washing water consumption and sewage discharge are high. Moreover, most manufacturers have not solved the problem of wastewater treatment, which is in a state of natural discharge and serious environmental pollution, which will restrict the development of the industry.

2.2 progress in processing methods of expanded graphite

2.2.1 research literature on laser expansion method (3) studies how to use laser to expand expandable graphite. Laser has the highest energy density, and graphite also has good absorption to laser, and its absorption rate can reach more than 95%, which just meets the requirement of rapid temperature rise for graphite expansion. The laser used in the literature is medium infrared light with a wavelength of 10.6 microns. For graphite flakes with a thickness of only a few tens of microns, the penetration depth of infrared light is about the same as its wavelength. It has the effect of volume heating for graphite flakes. Hgl-81 CO2 gas laser made in China was selected in the experiment. The laser expansion device used in the experiment is shown in Fig. 1-1. Due to the high energy concentration of the laser and the propagation mode of the heat in the expansion process, the decomposition speed of the residual compound is greater than the propagation speed of the microcrack where it is located. A large amount of gas generated rapidly bends the upper and lower surfaces of the crack, resulting in violent expansion. In addition, the high energy of the laser increases the expansion of the small residual compound Island domain inside the scale, preventing the expansion of the adjacent large island domain from suppressing it. For these two reasons, all laser expansion has a very high expansion ratio.

2.2.2 research on microwave expansion of square graphite powder patent document (4) reports a method for producing expanded graphite worms, and the device is shown in Fig. 1-2. The expansion device is characterized in that expandable graphite particles with a certain thickness (up to 10mm thick) are laid flat on the conveyor belt. Expandable graphite is expanded after passing through a radiation zone. The minimum flux density amount in the radiation area is 500kW / m2. The radiation source can be infrared light source, microwave, laser beam [graphite, graphite rod, graphite powder, graphite products, graphite processing]

　　。 2.2.3 research on plasma expansion method

Document (5) introduces a method of expanding fluorographite interlayer compounds by using induction coupled plasma (ICP). The experimental apparatus is shown in Fig. 1-3. The fluorine graphite interlayer compound is continuously injected into the argon plasma torch with a high temperature of 5000 ~ 8000K, and the expanded graphite worm is obtained through the collection system. The analysis of graphite worms by scanning electron microscopy and Raman spectroscopy shows that the expanded graphite produced by this method has a carbon nanotube structure. The article believes that this expansion method may become a promising technology for preparing carbon nanostructures in the future. 2.3 development and traditional application of flexible graphite due to its gas-solid two-phase structure, flexible graphite has good sealing performance and has a broad market as a sealing material. In particular, asbestos, the traditional sealing material, is banned due to environmental pollution, which provides a development opportunity for flexible graphite. Many new brands of high-grade flexible graphite have been developed internationally according to different requirements of users. Nuclear power and fine chemical industry require low sulfur and high-purity flexible graphite. Generally, the sulfur content of nuclear grade flexible graphite is below 500ppm; The nuclear island part has higher requirements for it. In order to prevent the corrosion of the sealing metal surface in petrochemical industry, especially in fine chemical industry, corrosion inhibition flexible graphite is required. Generally, molybdate and other corrosion inhibitors are added to the flexible graphite. In addition, in order not to stop production when the pipeline leaks, there are injection flexible graphite fillers for plugging with temperature and pressure. The production of flexible graphite materials in China is dominated by six flexible graphite production lines for paper and plate introduced from Japan, the United States and Canada from the late 1980s to the mid-1990s (two in Shandong Binzhou flexible graphite factory, one in Shandong Qingdao Heilongjiang Li graphite company, one in Inner Mongolia Linhao flexible graphite company, one in Hubei Yichang graphite industry company and one in Shandong Qingdao advanced sealing material Co., Ltd.). The actual production capacity of each line is 100-150t, The total output is 600 ~ 800t. The quality of the flexible graphite sheet produced is generally the same as that of the foreign grade 2 and grade 3 products. After 1992, Shanxi Institute of coal and chemical industry, Tsinghua University, Zhejiang University and other units, drawing on foreign equipment and combining production experience, designed and manufactured a continuous flexible graphite plate production line with a width of 250 ~ 1000mm. The production capacity of domestic equipment is about 300t. Only 1 / 3 of the total output is made up of plates with grade 1 and grade 2 quality, and most of them are only at grade 3 or below. The function of the production system and the manufacturing accuracy of the equipment are important factors affecting the quality of the plate. The system functions of the imported flexible graphite production line are basically the same, from expansion, feeding, calendering, shearing to coiling, all of which are continuous and automatic. The number of online monitoring points is small, and the feedback function of detection information is lacking, which restricts the improvement of plate quality. Another aspect of the development of flexible graphite sealing materials is the development of low index flexible graphite. Japan has a kind of flexible graphite with a minimum carbon content of 90%, which reduces the cost and price. In fact, it is unnecessary to use high-grade flexible graphite for some equipment, such as agricultural machinery and extensive chemical machinery. Low grade flexible graphite has better sealing performance than asbestos, can meet the requirements of process technology, and has low cost, so it has strong competitiveness in the low-end product market, thus promoting the development of the industry. In addition, flexible graphite, as a sealing material, has not been well solved in terms of technical innovation and testing equipment from users to manufacturers in the quantitative test of sealing leakage rate. Foreign countries attach great importance to the technical research in this area. Germany has formulated standards in 1995, specifying the testing technology and equipment, requiring that the nitrogen leakage rate of flexible graphite plate strip and composite plate is less than 0.1mg/m * s (din28091) China should also carry out more work in this regard to improve work efficiency, product quality and use level of flexible graphite sealing materials in China. With the wide application of flexible graphite products in modern engineering, the world's demand for flexible graphite materials is increasing year by year. Most of the flexible graphite produced abroad is used for seals such as cylinder gaskets and inlet and outlet gaskets of automobile engines, followed by seals in petrochemical, chemical and power generation departments. There are controversies about the limitation of asbestos in China, which restrict the application of flexible graphite in internal combustion engine seals. The main market is still in the chemical, petrochemical, power generation and other industries. The main seals are packing rings (directly pressed with flexible graphite paper), spiral wound gaskets, general packing and asbestos products used in metal materials, which can all be replaced by flexible graphite. Based on the excellent performance of flexible graphite materials, the highland of asbestos sealing materials means a huge potential market of flexible graphite materials to a large extent. Flexible graphite materials cannot completely replace asbestos sealing materials in the short term, and its potential market capacity is huge.

2.4 expansion of the use of flexible graphite

Flexible graphite is not only used for sealing, but also has excellent characteristics such as conductivity, heat conduction, lubrication, high and low temperature resistance and corrosion resistance. Because of this, the use of flexible graphite has been expanding over the years. The electrothermal material made of its conductivity and easy processing can be used in some harsh working conditions. Of course, because of its low strength, it must be fixed and have a supporting structure. Examples that have been applied are electric heaters made of picture frames; It has also been reported that flexible graphite paper is used for electromagnetic shielding. In the fuel cell of new energy system, flexible graphite can be used as the collector plate material. It not only has good conductivity, but also resists the corrosion of electrolyte, and can easily press the complex guide groove system of fuel gas and oxidant gas. The excellent reflection characteristics of flexible graphite on heat radiation conduction can be used to make heat shielding (thermal insulation) components for high-temperature equipment. For radiation heat conduction (& gt; 850 ℃), flexible graphite is an excellent heat insulator with stable structure and performance. It has better shielding effect than tungsten, molybdenum and other metals. Graphite has long been used as a high-temperature lubricant, and flexible graphite foil is an excellent follower. When used in high-temperature die conditions such as die forging, it has excellent lubricity and can avoid lubrication dead point, with good effect. Other new uses are also being developed.

2.5 application of expanded graphite in environmental protection and biomedicine

The expanded graphite obtained by high-temperature expansion has rich pore structure, so it has excellent adsorption performance. Most environmental protection materials use the adsorption of pollutants to achieve the purpose of pollution control. Therefore, expanded graphite, a porous structure material, can be used as an adsorption material factory to develop and close the pores, with the pore volume accounting for about 98%. The porous structure material is different from the porous structure material, and it is a porous material with an epitaxial mesopore structure. Therefore, its adsorption characteristics are also different from those of activated carbon, and its adsorption performance in gas phase adsorption is far less than that of activated carbon; But the liquid phase adsorption is much larger than that of activated carbon. Macroporous structure is favorable for adsorption of organic and bioengineering macromolecules. Due to the nonpolarity of graphite surface, lipophilic and hydrophobic in liquid phase adsorption preferentially adsorb oil products. The experimental results show that LG expanded graphite can adsorb more than 80g of heavy oil. Therefore, it is a promising environmental protection material for removing oil pollution on water surface. In 1997, an oil tanker leaked off the coast of Fukuoka, Japan, and expanded graphite was tried to remove it, which achieved good results. Because of its lipophilic and hydrophobic characteristics, it is also very effective to remove trace oil pollution in water. In the wastewater treatment of chemical enterprises, many methods and materials are often used in environmental protection engineering. Expanded graphite is a good microbial carrier for commonly used microbial (bacterial) treatment, so it has a good application prospect in chemical water treatment, especially in the water treatment polluted by oil and fat organic macromolecules, and because of its chemical stability, it is relatively easy to regenerate and reuse after pollution treatment. Expanded graphite also has a wide application prospect in biomedical materials due to its adsorption characteristics on organic and biological macromolecules. Tsinghua University and others have developed expanded graphite to make medical dressings instead of gauze. Through animal experiments on more than 300 mice, rats, guinea pigs and military rabbits, it has been proved that it is non-toxic, has no side effects, has no stimulation to wounds, does not stain black, and promotes healing. 114 clinical experiments were carried out in four hospitals, including the burn department of the First Military Medical College's Nanfang Hospital. The results showed that the effect was better than that of traditional gauze drainage. It had obvious anti-infection, anti-bacterial and anti-inflammatory effects, and could replace 50 ~ 80% gauze. This achievement has obtained the invention patent (zl95115437.0) and is being industrialized. [graphite, graphite rod, graphite powder, graphite products, graphite processing]

2.6 other application prospects of expanded graphite

Expanded graphite has a large specific volume, a loose volume of 100 ~ 300ml / g, stable chemical properties, high oxidation temperature (& gt; 400 ℃), and high safety. Therefore, it is an ideal heat insulation (thermal insulation) and sound insulation material. The wall materials of some foreign high-end buildings and passenger ships are sandwiched with a layer of expanded graphite of a certain density, which plays the role of heat preservation and sound insulation, and in the event of a fire, it can prevent the spread of the fire. In foreign countries, expandable graphite has been added to the foam cushion and the cabin wall of the engine room seat. Once a fire breaks out, the expandable graphite expands rapidly, occupying the space and blocking the fire propagation channel. Although expandable graphite is used, the physical and chemical characteristics of expandable graphite are still used. Expanded graphite is pulverized into fine powder, which has good scattering and absorption characteristics for infrared waves. It is a good infrared shielding (stealth) material and plays an important role in photoelectric Countermeasures in modern wars. The structure, properties and applications of expanded graphite are in research and development.

III. goals and directions of future graphite processing R & D: for more than 20 years, flexible graphite sealing materials have been developing at a high speed at an annual growth rate of 10% ~ 15%. It is estimated that in 2000, the market demand will be more than 30000 tons, and the domestic market will be 4000 tons, of which more than 100 tons are flexible graphite for nuclear energy. China's annual demand for graphite emulsion for color TV tubes will reach 1500 tons during the Ninth Five Year Plan period. At present, China can only produce 500 tons. The development of lithium-ion batteries is extremely rapid. About 500 tons of graphite anode materials are needed for 100 million single cells, and it is estimated that 1500 tons will be needed in 2000; Silicon impregnated graphite materials, graphite environmental protection materials and graphite medical materials are completely new industries with greater market potential.

Graphite materials and their composites, as new materials in the 21st century, will undoubtedly have great development and be applied in many fields, and some new high-tech industries will appear accordingly. China is rich in graphite resources, and has a certain foundation and technical reserves in research and development; Through further technological development, industrialization will be realized soon and remarkable economic benefits will be obtained.

The development objectives of the national plan include: research and development of ultra-low sulfur and high-purity flexible graphite processing technology and equipment for nuclear energy, research and development of natural graphite anode material preparation technology and equipment for lithium-ion batteries, research and development of various brands of graphite emulsion urgently needed for domestic color TV tubes, and research and development of key equipment (special vacuum induction furnace) and auxiliary processing and equipment for silica impregnated graphite material production technology; Specifically, it includes the technology and equipment of nuclear grade flexible graphite and high-purity flexible graphite production line with an annual output of 20 tons; Anode materials for lithium ion batteries; Graphite anode material preparation technology, anode material industrial preparation equipment; Graphite emulsion for color TV tubes; Silicon impregnated graphite materials, development of molding processing technology and equipment.

If the development task of graphite deep processing technology can be successfully completed, a new high-tech new industry using China's abundant graphite as raw material will be built, and economic benefits of an annual output value of 250 million yuan and a profit and tax rate of 40% will be obtained. These products will make great contributions to China's technology and social economy in the fields of nuclear power, chemical industry, energy, electronics, environmental protection, metallurgy, machinery, medical treatment and so on. At the same time, they also have great export potential, change the structure of China's Graphite export products, and greatly improve the ability to earn foreign exchange. [graphite, graphite rod, graphite powder, graphite products, graphite processing]