Graphite felt has good stability, the unit cost of large surface area, good permeability of the advantages of electrode materials used in direct methanol fuel cell flow, but because of its poor hydrophilicity, electrochemical activity is not high, which greatly limits its application. Therefore, we try to improve the electrochemical properties of carbon atoms by changing the electronic structure of carbon atoms. Although the nitrogen doped graphite felt has been reported sporadically, the research on the nitrogen doped graphite felt used as the cathode of direct flow methanol fuel cell is still in the blank.

　　With the energy and environmental problems become more and more prominent, the research and development of green, pollution-free new energy has been attached great importance by the enterprises and the government. Fuel cell is a kind of clean energy which can directly convert the chemical energy into electric energy.

　　The graphite felt has the advantages of good stability, large surface area per unit cost and good fluid permeability, but its application is limited because of its poor hydrophilicity and low electrochemical activity. Therefore, it is hoped that the surface treatment can improve its electrochemical performance. Commonly used acid treatment, heat treatment, electrochemical oxidation, rare earth ion modification methods.

　　The electrode material is one of the key factors to restrict the development of the liquid flow battery. It needs to meet the requirements of high conductivity, large surface area, high selectivity to a specific reaction, good electrochemical activity, good chemical stability and so on. The main researches are metal, composite and carbon. The metal electrode has good conductivity, excellent mechanical properties, high electrochemical activity, but the stability in the anode region is poor and expensive, it is not suitable for large-scale applications; composite electrode material is a polymer and conductive carbon mixing, drying and tabletting after prepared, while improving the conductivity, oxidation but the need to overcome the polymer at high temperature; carbon electrode mainly include carbon cloth, graphite, carbon fiber and graphite felt, good stability and low cost, but the graphite, carbon fiber and carbon cloth used as electrode, a few cycles, the electrode surface is damaged, only the graphite felt electrode is the present study is more and more widely used as electrode material.

　　The raw material of spherical graphite is the high quality natural flake graphite, the advanced processing technology is adopted to modify the surface of graphite, it’s the graphite product which is in different fineness and the elliptical spherical shape.

　　The spherical graphite processing, at first , we get the initial spherical graphite product by by coarse crushing, reconditioning, magnetic separation process from the dry fine graphite ore in graphite workshop, and then we get the spherical graphite (high purity)by high temperature purification in the workshop workshop .

　　Spherical graphite material has good conductivity, high crystallinity, low cost, high theoretical lithium capacity and other characteristics, its charging and discharging potential is low and flat, it’s an important part of anode materials for lithium ion batteries at present , it also is the update product of the cathode materials for lithium ion battery production at home and abroad. It exists with excellent electrical conductivity and chemical stability, high discharge capacity, long cycle life, green environmental protection.

　　The main index of measuring spherical graphite quality: the first is the physical properties including particle size (D50,μm), tap density (g/cm3), specific surface area (m2/g), water content(%), fixed carbon content (%); the second is the electrochemical performance including the coulombic efficiency (%), charge capacity (mAh/g), life cycle (cycles).

　　With the development of the electric vehicle industry, our company researches and develops the natural spherical graphite which is used as large power lithium battery cathode materials in automotive, wind power and other fields. This product has a uniform distribution of particles, it has reached the domestic advanced level in the terms of energy density, power density, safety and other performances .

　　Comparative analysis of the advantages and disadvantages of graphite heating and silicon molybdenum rod heating under the condition of long-term working temperature of 1750 degree vacuum

　　The heating temperature is generally higher than the working temperature of 200 DEG C according to the calculation, such as the title, heating the working temperature of 1950 degrees Celsius

　　The maximum working temperature of MoSi2 heating material is 1700 DEG c,

　　Graphite heater (rod, tube, plate) in the absence of air in the working temperature of up to 2500 degrees C.

　　Temperature is not the most important factor, the actual long-term working temperature is about 1600 degrees

　　Contact with oxygen in the air, graphite heater easy oxidation, The workpiece will be placed in the high temperature ceramic tube, not directly contact with graphite.

　　Graphite can be divided into natural graphite and artificial graphite, the two structures are similar, similar physical and chemical properties, but there is a big difference in use. In many studies, some researchers did not notice the difference between the two and generally referred to as graphite. The result of the confusion between the two has caused a lot of misleading, even the wrong decision-making, resulting in a great waste of resources and economic losses. In this paper, from the perspective of the structure and properties of natural graphite and artificial graphite, the characteristics and differences between them are discussed.

　　1 Graphite classification and characteristics:

　　1.1 natural graphite

　　Natural graphite is carbon rich organic matter in the geological environment of high temperature and pressure for a long time under the action of the formation of the transformation, is the crystallization of nature. The technological characteristics of natural graphite mainly depend on its crystalline morphology. Crystalline forms of different minerals with different industrial values and uses. There are many kinds of natural graphite, according to different crystal morphology, will be divided into natural graphite industry compact crystalline graphite, graphite and aphanitic graphite three. Our country mainly aphanitic graphite flake graphite and two categories.

　　1.2 synthetic graphite

　　Multi crystal graphite is similar to the crystallographic. A wide variety of artificial graphite, different production processes. Broadly speaking, all organic compounds obtained by carbonization and then graphitised after high temperature treatment of graphite materials can be referred to as artificial graphite like carbon (graphite) fiber, pyrolytic carbon (graphite), graphite foam etc.. While in a narrow sense of artificial graphite usually refers to the impurity content of low carbon raw materials (petroleum coke and pitch coke etc.) as aggregate, coal tar as the binder, after mixing, kneading, molding and carbonization (industry called roasting) bulk solid material and graphite and other processes in the system. Such as graphite electrode, hot isostatic graphite etc..

　　2 natural graphite and artificial graphite

　　In view of the natural graphite as the raw material to prepare the general is the narrow sense of artificial graphite, only to analyze and discuss the difference between natural graphite and narrow artificial graphite.

　　2.1 crystal structure

　　Natural graphite: crystal development is more perfect, the scale graphite graphitization degree is more than 98%, and the natural microcrystalline graphite graphitization degree is usually below 93%.

　　Synthetic graphite: crystal growth depends on the raw materials and heat treatment temperature. In general, the higher the heat treatment temperature, the higher the degree of graphitization. At present, the industrial production of artificial graphite, the degree of graphitization is usually less than 90%.

　　2.2 organizational structure

　　Natural flake graphite is a kind of crystal structure is relatively simple, only the defects on Crystallography (such as point defects, dislocations, stacking faults, etc.) characterized by macroscopic anisotropy. The grain size of natural microcrystalline graphite is small, the grains are arranged in disorder and there are holes after impurity removal.

　　Artificial graphite: can be regarded as a kind of heterogeneous material, including petroleum coke and pitch coke and carbon particles into the coating, Shi Moxiang transformation in coal asphalt binder particles around the graphite phase, particles or coal asphalt binder formed by heat treatment such as pores.

　　2.3 physical form

　　Natural graphite: usually in the form of powder, can be used alone, but often combined with other materials after the use of.

　　Artificial graphite: more forms, both powder, but also fiber and block, and the narrow sense of artificial graphite is usually a block, the need to be processed into a certain shape.

　　2.4 physical and chemical properties

　　In terms of physical and chemical properties, natural graphite and artificial graphite have both generality and difference in performance. Such as natural graphite and artificial graphite is a good conductor of heat and electricity, but for the same purity graphite powder and particle size, natural flake graphite, conductive heat transfer performance and the best performance of natural graphite, artificial graphite minimum. The graphite has good lubricity and certain plasticity, development of natural flake graphite crystal is perfect, the friction coefficient is small, the best lubrication, the highest plasticity, and dense crystalline graphite and the aphanitic graphite, artificial graphite.

　　3 natural graphite and artificial graphite

　　Graphite has many excellent properties, so it is widely used in metallurgical, mechanical, electrical, chemical, textile, national defense and other industrial sectors. The application fields of natural graphite and artificial graphite have overlapping parts and different places.

　　3.1 metallurgical industry

　　In the metallurgical industry, natural flake graphite because of good oxidation resistance can be used for production of refractory materials and aluminum carbon brick and magnesia carbon brick. The artificial graphite can be used as the electrode of the steel making, and the electrode made of the natural graphite is difficult to be used in the electric furnace with the harsh conditions.

　　3.2 mechanical industry

　　In the mechanical industry, graphite materials are usually used as wear-resistant and lubricating materials. Natural flake graphite has good lubricity and is often used as additive in lubricating oil. The equipment used for conveying corrosive medium is made of synthetic graphite made of piston ring, sealing ring and bearing. Natural graphite and polymer resin composite material can also be used in the field, but not as good as artificial graphite.

　　3.3 chemical industry

　　Synthetic graphite has the advantages of corrosion resistance, good thermal conductivity, low permeability and so on. It is widely used in chemical industry, such as heat exchanger, reaction tank, absorption tower, filter and so on. Natural graphite and polymer resin composite material can also be used in the above fields, but the thermal conductivity, corrosion resistance as artificial graphite.

　　The utility model relates to a graphite electrolytic cell, which relates to an electrolytic cell used for smelting rare earth metals. The main is to solve the problems of rare earth metal graphite electrolytic bath existing contact air directly on the inside of the upper part of rare earth metal smelting, under the condition of high temperature oxidation burning problem of. The invention is mainly in the rare earth metal graphite electrolytic bath with high temperature resistant upper inside protection metal cover, protective cover on the outward along the graphite cell volume will cover the upper, high metal protective cover is approximately equal to the depth of 1/3 graphite cell. The advantages of upper inside of the graphite electrolytic tank and air insulated, which is not oxidation under high temperature conditions, can prolong the service life of 3-4 times.

　　Electrolytic cell

　　The main equipment of electrolytic tank, can be divided into two types: diaphragm electrolyzer and diaphragm cell. Diaphragm electrolyzer can be divided into to the membrane (asbestos), ion-exchange membrane and solid electrolyte membrane (such as beta -Al2O3) form; non membrane electrolytic cell is divided into mercury electrolyzer and oxidation electrolytic tank.

　　Electrolyzer used in industry by tank, electrolyte, anode and cathode. The most used diaphragm separates the anode chamber and a cathode chamber. According to the difference of the electrolyte, it can be divided into three kinds: the water electrolysis cell, the molten salt electrolysis cell and the non-aqueous solution electrolysis cell. When the direct current passes through the electrolytic cell, the oxidation reaction occurs at the interface between the anode and the solution. It is the key to improve the current efficiency, reduce the voltage and save the energy consumption to optimize the structure of the cell and select the electrode and the diaphragm material.

　　Graphite carbon plate adopts high quality graphite carbon material, and the organic compound with strong acid resistance is added. By high pressure molding, vacuum impregnation, high temperature heat treatment

　　The process is refined, has the special acid resistance and the temperature resistance performance, is the chemical industry phosphoric acid reaction trough, the phosphoric acid storage tank and so on equipment ideal lining material.

　　Excellent corrosion resistance

　　Products using carbon graphite material quality, adding organic compound with strong acid, effectively reducing the product porosity increases, the bulk density of the products, so the product has strong corrosion resistance and excellent wear resistance.

　　Stable performance, strong durability

　　The product is made of high strength organic glue as binder, and the high and new technology additive is introduced at the same time. Therefore, the product has the advantages of high strength, good wear resistance and stable structure, and the structure of the product does not change with the change of temperature.

　　Precise dimension

　　The product is of high quality and precise shape, and can produce special products according to the requirements of users.

　　Graphite carbon plate has the characteristics of wear resistance, temperature resistance, pressure resistance, corrosion resistance, creep resistance, oil-free self lubrication, small expansion coefficient, and excellent sealing property.

　　Use: pump, valve, fan, compressor, mixer, reactor, hydraulic pneumatic, electrical components, glass instrument, rotary joint, mechanical seal, pipe flange, petrochemical equipment, drying equipment, finishing equipment, chemical equipment, chemical machinery, rubber machinery, food machinery, machinery, machinery and other rotating fluid separation and the sealing member.

　　High purity graphite: graphite content of more than 99.9% of graphite called high pure graphite. Is an ideal inorganic non metal crucible boat, crystal furnace heater, EDM graphite, sintering mold, tube anode, metal coating, semiconductor technology with graphite crucible, electron tube, thyratron and mercury arc rectifier with graphite anode, grid etc..

　　High purity graphite has the advantages of small resistance coefficient, high temperature resistance, corrosion resistance, oxidation resistance, good thermal shock resistance, electrical conductivity, thermal conductivity, small coefficient of expansion, self lubrication, easy machining precision and so on.

　　1) high temperature resistant graphite melting point of 3850 - 50 DEG C, the boiling point of 4250 DEG C, even after the ultra high temperature arc ignition, the weight loss is very small, the thermal expansion coefficient is small. The graphite strength increases with the increase of temperature, and at 2000 DEG C, the graphite strength is doubled.

　　2) conductivity, thermal conductivity: the conductivity of graphite is one hundred times higher than the general non-metallic minerals. Thermal conductivity of steel, iron, lead and other metal materials. The thermal conductivity decreases with the increase of temperature, even in high temperature, graphite as insulator. Graphite is able to conduct electricity because each carbon atom in graphite has only

　　3 covalent bonds with other carbon atoms, and each carbon atom retains 1 free electrons to transfer the charge.

　　3 lubrication: graphite lubrication performance depends on the size of the graphite flake, the larger the size, the smaller the friction coefficient, the better the lubrication performance.

　　4) chemical stability: graphite has good chemical stability at room temperature, acid and alkali corrosion resistance to organic solvents.

　　At present, the domestic production of graphite felt is mainly used to make thermal insulation material, and its conductivity and electrochemical activity can not meet the requirements of the use of battery electrode materials, therefore, it needs surface treatment on the for graphite felt .Commonly used surface treatment methods include heat treatment, acid treatment and electrochemical oxidation treatment.

　　The operation of heat treatment in air atmosphere, and the heat treatment after carbon fiber conductive ability has been improved, but there is no deep research on revealing fiber structure changes and conductive ability of the report.

　　The surface morphology and structure of carbon fiber felt changed before and after heat treatment, and the conductivity of the carbon fiber felt was also affected. The mass loss of carbon fiber felt was slow at the beginning, and gradually increased when the temperature exceeded 450 degrees celsius.

　　This is because oxygen started contact with graphite felt when exposed to only the surface of some active substances, the reaction is slow; with the reaction, oxygen gradually exposed to the fiber body, which is also affected by the oxidation erosion, the integrity of the fiber was damaged.

　　In the heat treatment of graphite felt, if the temperature is too low, with active keys C-O and C=O activity were lower than the proportion of the surface area, leading to electrochemical active carbon fiber felt low, unable to meet the requirements of use as electrode materials; but if the heat treatment temperature is too high, it will cause the carbon fiber mat surface etching is serious, excessive oxidation, fiber breakage and breakage, resulting in the electrical conductivity and mechanical properties decreased sharply, seriously affecting their life.

　　There is no surface of carbon fiber graphite felt after heat treatment. The texture is clear, can be observed in some small, parallel to the fiber axis etching grooves and other defects, these defects are mainly due to the formation of polyacrylonitrile carbon fiber precursor phase is used in wet spinning caused by the storm.

　　(continuously last article )

　　4. Compounding

　　Mixing qualified manufactured raw material proportionally, adding binder and making preperation for molding of biscuit.

　　5. Molding Biscuit

　　Machining Biscuit into certian shape. With the developement of molding technology, more and more molding method are invented. Compression molding is the most common technique. No matter what mloding method are applied, the final product should comply with following requirement: the size, shape, and precision of product should be manchined as designed. And then, final product should be high in density, uniform in structure, stratification, low in porosity, outstanding mechanical strength. By the way, chemical- physical property also should be qualified.

　　6. Drying

　　Shaped biscuit neet to dry for a while in the air, then by putting it into oven or chamber to dry it throughly and to dislodge free water content, after which product can continue to suffer final firing. Sometimes, people straightly convey raw material into kiln. Firing raw material under 140 ℃, then final firing succeed..

　　7. Presintering and Rough Machining on Biscuitre

　　Before the final firing, product should be fired under a lower temperature to remove various organic binder, especially wax. After presintering, product start to own sufficent mechanical strength. At this time, the product can be rough machined, such as triming size, cutting or drillingd. Because, in the last, the product which have suffered final machining become very hard.At that time, rought machining become very tough.

　　8. Sintering

　　Sintering is the most important procedure. This procedure will decide thether the product can be produced successfully. Sintering have following function: first of all, it can exclude extra water content and organic in product; then, crystal form of product transform in allomorph way. Moreover, solid particles react with each other, which is called solid-phase reaction.. Next, stable product is manufactured.

　　9. Final Machining

　　Manufacturing procedure of graphite refractory products is complex. Under the influence of quality of raw material, manufacturing technique, operation, many errors exist among stable product. So, after sintering,the stable product should be machined advancely, which includes Cutting, cars, planing, drilling, milling, grinding, polishing, etc. Before the product leave factory, it should be inspected strictly.

　　According to different application of carbon and graphite product, diiferent physical-chemical standard indicators were stipulated to evaluate quality. Physical-chemical indicators of product is concerned not only with that of raw material, but also with manufacturing technology.There are some rules existing between raw material and manufacturing technology. If we want to keep product be qualified, we should ensure raw material is qualified, manufacturing technology is responsible. This article focus on introducing main physical-chemical indicators. There are six main indicators.

　　1. True density

　　True density means the weight of per unit volume of material excluding proportion,who is measured by g/cm³.Usually，we smash assay into 0.15mm, infiltrate assay with alcohol or distilled water, and weight the handled material via comparison weighing method.

　　By testing true density, we can acquaint basic particle degree and arrange degree of material. As for graphite product and natural graphite sample, true density can reflect the degree of graphite lattice structure.

　　2. Apparent density

　　Apparent density means the weight of per unit volume of material including porosity, which is measured by g/cm³ too.

　　3. Ash content

　　Most ash contained in Carbon material is Oxidized metal and nonmetal element. Among all kinds of ash, metallurgical coke content(12%-16%) is the highest, the second one is anthracite(7%-12%). Ash of pitch coke and petroleum coke is around 0.5%. The main compound in ash is ferric oxide, aluminum oxide and silicon dioxide, which account for over 80% of the total ash content.

　　4. Mechanical strength

　　In carbon and graphite products industry, we are often used to denote the mechanical strength by three indictors: compressive strength, tensile strength and bending strength. The relationship of these three indictors are as follows: compressive strength of graphite product is as twice larger as bending strength. And bending strength is as twice larger as tensile strength.

　　5. Specific resistance

　　Most carbon and graphite product appllied to electric conduction, so better the electrical property is, better the material is. That is the date of specific resistance should be as low as possible, lower speific resitance means higher current density.

　　If you want to learn more knowlegement about graphite and carbon product, welcome to our website:www.bjgreatwall.com