The natural graphite can be devided into two kinds,one is natural flake graphite powder,and another one is aphanitic graphite powder,the classification is according to the crystallization morphology. The crystal diameter of the graphite >1μm is called natural flake graphite, and it can be seen the crystal structure by naked eye or ordinary microscope;and another type with the crystal diameter of the graphite <1μm,and it’s hard to see the crystal structure under the microscope,so it’s called aphanitic graphite powder,and most aphanitic graphite powder sharp as the earth,so it is also called amorphous graphite.

　　According to the size of the scale,the flake graphite powder can be classified as different grade,the particle size>+0.3mm,+0.18mm and+0.15mm,it’s called large scale graphite powder,and the size below 0.15mm,it’s called fine scale graphite. The application and value of the large scale graphite is better than the fine graphite,so the industrial utilization value is better.

　　The dense bulk graphite is evolved from the coalfield,the ore is black colour,and the sharp is dense block. The main composition is graphite,and except for the graphite ,there will be some quartz, mica, limonite, pyrite and some clay minerals. And the fixed carbon is different,from 60%~80%,the lowest is 15% and the highest is 90%. It’s the main types of the aphanitic graphite.

　　The degree of crystallization,scale size is important to the process performance, industrial value and the use. So the economic value of the flake graphite is higher than the aphanitic graphite,for example,most graphite crucible is made from the large scale graphite,because the strength of the large scale graphite is higher, and the thermal resistance is better,so the service life of the crucible is longer. The fine size graphite powder is hard to process the expanded graphite,the expanded graphite must be made from the large scale graphite powder. However,the aphanitic graphite can be used in the lithium battery,and the performance is better than the large scale graphite powder.

　　Except for the degree of crystallization,the fixed carbon content is also important to the property of the graphite powder. The content >80% is widely used,and the content <80% can be only used as the casting paint. The fine size high purity graphite can be used as lubricant,but the content of the fixed carbon need to be >99%,the particle size is 2~10μm. The graphite powder used as pencil need a fixed carbon >95%, the particle size should be <10μm,it should be the natural flake graphite.

　The production technology of the isostatic graphite is different from the graphite electrode. The isostatic graphite need the raw material which has an isotropic structure property. It need to grind into finer powder,and use the cold press molding technology(the isostatic press molding is one kind of the the cold press molding) the baking cycle is very long,and for the high density,it need more times’ dipping and baking.and the graphitization cycle is more than normal graphite.

　　The main technology mainly includes:

　　1) raw material grinding

　　the particle size need to processed into 20 μm below. For now,the finest isostatic graphite particle size is 1μm,and it must need the superfine mill.

　　2) the kneading processing

　　make the powder and coal asphalt adhesive into fixed ratio,then put into the heating mixer to make it mixed,the purpose of this is to make the powder surface coated a layer of the pitch. After that get it out and cool it. Compared with the production of graphite electrode,the kneading time need longer,and the temperature need higher,and the QTY of the pitch need more.

　　3) second-grinding

　　The material after crushing,grinding,it will be screened into tens to hundreds of microns and mix it uniformly,then press it and mold it,prepare for the second-grinding.

　　4) molding

　　Defferent from the extrusion molding and molded pressing,the isostatic molding is belong to the cold pressed molding. Press the raw material and make it into the rubber mould, use the high frequency electromagnetic vibration to make the powder pressed,then make it vacuum,put it into the high-pressure container with water or oil,then make the pressure to 100~200Mpa,at last,make it as a cylindrical or rectangular product.

　　5) baking and dipping

　　As the isostatic graphite compact structure,the baking temperature should heating-up slowly,and the temperature inside the furnace should also be controlled well,the heating-up speed should not beyond 1℃ /h,and the temperature difference in the furnace should below 20℃,and during the baking processing, it will take 1~2 month to meet the requistment.

　　After the baking processing, the volatile of the pitch discharged,there are some pores on the surface of the material ,so it need to be dipped,and it usually need many times to bake and dip.

　　6) the most important processing it the graphitization.

　　Heating-up to 3000℃,and it will take 1~1.5 month to make it. After this,the density,electricity conducting,thermal conducting and the erosion resistance will be improved better.

　　Graphite/resin composite bipolar plate has aroused wide public concern due to its good moldability, high flexural strength and electrical conductivity, good corrosion resistance. In this paper, carbon nanofibers's high strength,high electrical and thermal conductivity as well as excellent surface size effect was utilized to enhance the performance of graphite / resin composite bipolar plates.

　　Expanded graphite is widely used as the conductive filler, polyimide and benzoxazine as binder. The mixing method of expanded graphite and resin with large density difference was studied and the effect of resin content, molding temperature and pressure, holding time were also investigated. Using artificial graphite as the conductive filler and the above two kinds of resin as the binder, the paper investigated the effect of resin content, molding pressure and holding time on the properties of composite bipolar plate. The experiment focused on flexural strength, through-plane conductivity, in-plane conductivity and corrosion rate of the composite bipolar plate.

　　The catalyst was prepared by incipient wetness impregnation. Carbon nanofibers/graphite composite material was synthesized by the method of catalytic chemical vapor deposition through in-situ growth of carbon nanofibers on the surface of expanded graphite and artificial graphite. After mixing the composite material with the resin, the composite was shaped by thermal molding technique. The effect of carbon nanofibers under different catalyst loading and growth time of carbon nanofibers on the performance of the composite bipolar plate were studied. The results showed that appropriate amount of carbon nanofibers on the surface of expanded graphite could enhance the through-plane conductivity, however,the in-plane conductivity decreased significantly and flexural strength changed slightly. Artificial graphite/resin composite bipolar plate has high performance in many aspects, but the performance declined after carbon nanofibers were grew on the surface of artificial graphite.

How to use the graphite crucible in a right is important.

　　The first time to use it,we should heat the crucible under a 1300~1500 centigrade,and after 2~3 times,the surface of the crucible could form a sinter layer,so the service life will be longer. If we use it without the sinter layer for the first time, and melting the fusible metal,such as tin,vanadium,aluminum etc,the crucible will be broken quickly,and the graphite will be fire when it reach 700 centigrade.

　　The crucible should be put onto the special base,and the Dia of the base should be the same as the crucible. And there should be some graphite powder and coal powder on the base. And the material of the base should also be graphite material,it doesn’t allow to put the crucible onto other material base.

　　It must be very careful to fill in the crucible,and it doesn’t allow to throw the metal into the crucible. And the crucible should not be very full of the metal, coz the metal will expand during the melting process,and the metal material should not be too close to each other.

　　During the melting process,it should not put the metal in times.

　　It doesn’t allow to put the crucible into the high-temperature furnace,coz the crucible will crack because of this,and before putting the metal into crucible,the metal must be baked to dry. The wet metal should not be put into the crucible. The temperature of the heating should be heating-up slowly,it’s better to make the same graphite cover on the crucible ,coz it can reduce the losing of the metal.

　　The crucible should not be put onto the furnace for a long time,coz it can reduce the service of the crucible.the pliers which used for the crucible should be the circle shape.

　　The service life of the graphite crucible is mainly affected by the way of using. Many customers say that their crucibles will be broken or crack after several times, and they think the problem is from the crucible quality, however,if we could use it in a better way or a right way,the service life will be longer.

　　1、the storage of the graphite crucible.

　　The graphite crucible is easy to be wet,because it’s easy to absorb the moisture of in the air,so it’s better to store the crucible in a dry place,it should not be in the wet place.

　　2、Drying of crucible

　　Before using each type of the crucible,it must be dry,and it should be put as bottom up display,the crucible should not be baked by flame. It should be in an indirect heating way to warm up or use the warm wind to bake.

　　The temperature must be rise up little by little,the start temperature should be 60~80 centigrade,and the final temperature should be 150~200 centigrade.and the time to bake it should be 5~7days.

　　3、the new crucible should not be used in the furnance under a very high temperature.it must be dried as the way above,then put it into the cold furnance,heating it slowly.keep it 1~2 hours(it depands on the size of the crucible),then heat the crucible to red colour,if no crack or broken under this situation,so there is no need to take it out,and we can put the metal inside under that situation,and the metal must be dry and pre-heated ones.(the coal used to heat the crucible is also dry).

　　When the temperature reach 1300~1500 centigrade,the crucible will melt,and it will form sinter layer on the surface of the crucible,so the crucible can be used for a long time even under the low temperature.

　　Making graphite,SiC,clay,silicon powder etc.as the raw material to process the graphite SiC crucible,the below are some results about the oxidation resistance from different factors such as:the raw material constitution,firing temperature,the method of forming and the different coating on the surface.

　　1) The firing temperature has a big influence on the density,and the density will lead to the service life of the crucible. When the temperature reach 1150 centigrade,the porosity of the graphite-SiC crucible is the lowest,and the density is the best.

　　2) The content of the SiC is also very important to the oxidation resistance of the graphite crucible,with the content of the SiC increasing,the porosity of the crucible is reducing,and the performance of the oxidation resistance will be better. The content between 35~50%,the porosity and weight loss rate are the best,when the content of SiC reach 50%,the density will be the highest,and the oxidation resistance is the best.

　　3) The silicon powder also has influence on the graphite-SiC crucible oxidation resistance,and with the different contents of the silicon powder changing,it can improve the the porosity,density and the oxidation resistance performance. When the silicon powder reach 15% content,the oxidation resistance performance is the best.

　　4) Different methods of forming also have different influence on the performance of the graphite-SiC crucibles. After the comparison between machine molding and isostatic molding,we could found that the way by isostatic molding is better than the machine molding ,because of the better density,lower weight loss rate,so it can tell that the oxidation resistance performance is better than the isostatic molding.

　　5) The coating on the surface of the crucible and the wall thickness also have influence on the oxidation resistance performance. When the thickness of the coating is the same,the crucible with B2O3 can reduce the weight loss rate of the crucible,and at the same time it can improve the oxidation resistance performance,and when the content of the coating is the same,the multi-storey coating is better than the single-storey on the density and the weight loss rate,and increase the oxidation resistance performance.

　　Graphite heat exchanger is a heat transfer device made of graphite. The graphite in the manufacture of heat exchanger should be non transparent, and is often used in the non - permeable graphite and graphite.

Structure

　　The graphite heat exchanger can be divided into 3 types: block type, tube shell and plate type according to its structure. A piece of hole: a plurality of bulk graphite assemblies that are formed by a plurality of holes. Shell and tube type: tube shell type heat exchanger in graphite for heat exchanger occupies an important position, according to the structure is divided into two kinds of fixed and floating head. Plate: made of graphite bonding plate heat exchanger. In addition, there are immersion, spray type and sleeve type, etc. (see snake tube heat exchanger, sleeve type heat exchanger). Graphite heat exchanger has good corrosion resistance, heat transfer surface is not easy to fouling, heat transfer performance is good. However, the graphite is easy to crack, the bending and tensile strength is low, and it can only be used for the low pressure, even though the pressure is the best piece of porous structure, the working pressure is generally only 0.3 ~ 0.5 mpa. Graphite heat exchanger with high cost, large size, use is not much. It is mainly used in the heat transfer of corrosive media such as hydrochloric acid, sulfuric acid, acetic acid and phosphoric acid, such as the condenser of acetic anhydride and acetic anhydride.

　　Graphite tubes are divided into synthetic resin impregnation, water glass impregnation, and pitch impregnation according to their different materials.

Characteristic

　　Graphite heat exchanger has good corrosion resistance, heat transfer surface is not easy to fouling, heat transfer performance is good. However, the graphite is easy to crack, the bending and tensile strength is low, and it can only be used for the low pressure, even though the pressure is the best piece of porous structure, the working pressure is generally only 0.3 ~ 0.5 mpa.

　　Graphite heat exchanger with high cost, large size, use is not much. It is mainly used in the heat transfer of corrosive media such as hydrochloric acid, sulfuric acid, acetic acid and phosphoric acid, such as the condenser of acetic anhydride and acetic anhydride. Mainly used in the chlor alkali chemical industry, petroleum chemical industry, fluoride salt, titanium dioxide, zirconium, chloroacetic acid, chlorinated paraffin, monocrystalline silicon fluorine chemical industry.

Classification

　　A piece of hole: a plurality of bulk graphite elements are assembled in a plurality of holes.

　　II tube shell type: tube shell type heat exchanger in graphite for heat exchanger occupies an important position, according to the structure is divided into two kinds of fixed and floating head.
　　The panel: made of graphite plate bonded plate heat exchanger. In addition, there are immersion, spray type and sleeve type, etc. (see snake tube heat exchanger, sleeve type heat exchanger).

　　Shell and tube heat exchanger (shell and tube heat exchanger) is also called tubular heat exchanger. Is to close the bundle in the shell wall as heat transfer surface heat exchanger. The structure of the heat exchanger is simple and reliable, and can be made of various structural materials (mainly metal materials), and can be used in high temperature and high pressure.

　　Heat exchanger is a metal sheet with a corrugated shape by a series of stacked a new high-efficiency heat exchanger. A thin rectangular channel is formed between the plate and plate, and the heat exchange is carried through the half piece. Heat exchanger is an ideal heat exchange equipment for liquid - liquid, liquid - vapor. It has the characteristics of high heat transfer efficiency, small heat loss, compact structure, small size, convenient installation and cleaning, wide application, long service life, etc.. Under the same pressure loss, the heat transfer coefficient is 3-5 times higher than that of tubular heat exchangers, and the area of the tube type heat exchanger is 1/3, and the heat recovery rate can be as high as 90%.

　　Although the definition of isotropic graphite in the world needs to be further defined, it is generally to measure some physical properties of the product's diameter and length. The ratio of the thermal expansion coefficient is expressed as the ratio of the resistivity. The large scale graphite diameter of the advanced countries and other industrial technology has reached 1.5 m, the length is 3%, the bulk density is g/cm 1.95-2.0, the anisotropy ratio is reduced to 1.05. In addition to the use of ordinary petroleum coke, the use of modified asphalt, tar, coke, oxidized petroleum coke, petroleum coke, natural graphite, etc..

　　And other static pressure graphite by high pure graphite pressed. Static pressure graphite is a new product developed in the last 50 years, which is closely related with the modern technology. Do not only in the civil field, occupies an important position in the national defense, is a new type of material, attract people's attention. It is the production of single crystal furnace, metal continuous casting graphite mold, electric spark machining with graphite and other non alternative materials, but also the production of rocket nozzle, graphite reactor of the material and the material of the reflection material.

The graphite material and parts are already widely used in all kinds of industries for almost 50years,as the many good properties,such as :electricity conducting,corrosion resistance and good thermal conductivity,it is widely used for electrode,electro-chemical power,carbon brush on the motor and the gasket etc. However,the mechanical properties of graphite material is weak,easy to break and crash,limit the range of use.

　　The graphite material impregnated with phenolic resin can improve the mechanical properties. The phenolic resin has several good properties such as high thermal stability, structural integrity etc,and making it as one of the binders of graphite is a good way to reduce the opening rate and improve the mechanical properties. Now the graphite impregnated phenolic resin is one of the most common use graphite products among all the graphite chemical products,the graphite tube impregnated phenolic resin is widely use for heat exchanger.

　　Some Scholars’testing showed that the impregnated graphite under 160℃ condition of cure has the best performance(the highest weight gain rate, the lowest porosity,the highest shore hardness)and the flexural strength under temperature 140℃ is the best,and it has the best thermal stability. The thermal stability is better during 0~450℃,but then the temperature reach 450℃ above,the phenolic resin will be decomposition,and the performance will be lower.

　　The temperature has a big influence on the phenolic resin impregnated graphite material. The reason weight gain rate under 160℃ is the highest is because when the temperature below 160℃even lower,the phenolic resin can not full diffusion in the graphite material and lead to the overall uneven,and if the temperature is too high,the viscosity of phenolic resin will be reduction,and lead to lack of binder, can not reach the desired effect.

      Carbon fiber and resin, metal, ceramics and other matrix composite, made of carbon fiber composite materials.

　　Fiber reinforced material has been the focus of people's attention. Since the advent of glass fiber and organic resin composite, carbon fiber, ceramic fiber and boron fiber reinforced composite materials have been successfully developed, and the performance of the composite materials has been improved. Let us know about the carbon fiber composite material with no special features.

　　Carbon fiber is a kind of special fiber which is made up of carbon. The carbon content of carbon fiber is different, and it is generally more than 90%. Carbon fiber has the characteristics of carbon materials, such as high temperature, resistance, electric conduction, heat conduction and corrosion resistance, but with the general carbon material is different, its shape has a significant anisotropy, soft, can be processed into a variety of fabrics, along the fiber axis show a high degree of intensity. Carbon fiber has a small proportion, so it has a high specific strength.

　　Carbon fiber is made of carbon fiber, which is made of artificial chemical fiber which is not melted during heat treatment, and is processed by heat stable oxidation, carbonization and graphite.

　　Carbon fiber is a new material with excellent mechanical properties. Its specific gravity is less than steel 1/4. The tensile strength of carbon fiber composite material is 7~9 times, it is 3500Mpa times of steel, and the tensile modulus of 23000~43000Mpa is higher than that of steel. So the CFRP strength than the material strength and density ratio to 2000Mpa/ (g / cm3) above, and A3 steel strength only about 59Mpa/ (g / cm3), the specific modulus also than steel.

　　The main purpose of carbon fiber is to make structural materials, such as resin, metal, ceramic, etc.. Carbon fiber reinforced epoxy resin composite, its specific strength and specific modulus, are the highest in the existing structure materials. In the field of density, stiffness, weight and fatigue properties, the carbon fiber composite material has advantages in high temperature and high chemical stability.

　　Carbon fiber is the 50's in the early time of the rocket, aerospace and aviation and other cutting-edge science and technology needs, and is now widely used in sports equipment, textiles, chemical machinery and medical fields. With the advanced technology of new material and technical performance requirements increasingly harsh, and promote scientific and technological workers to improve. In the early 80's, the high performance and ultra high performance carbon fiber appeared, which is a technological leap, but also marks the research and production of carbon fiber has entered a advanced stage.

　　The composite material made from carbon fiber and epoxy resin is a kind of advanced aerospace materials because of its small proportion, good rigidity and high strength. Because the weight of the space vehicle is reduced by 1 kilograms, it can be reduced by 500 kilograms of the carrier rocket. Therefore, the aerospace industry in the use of advanced composite materials. There is a vertical landing gear, which is used by the carbon fiber composite material has accounted for 1/4 of the total weight of the wing weight of 1/3. According to reports, the U.S. space shuttle on the key components of the 3 rocket propulsion and advanced MX missile launch tube, are made of advanced carbon fiber composite material.

　　Now the F1 (the world's first equation) car racing, most of the structure of the body is made of carbon fiber material. Top sports car, a big selling point is the use of carbon fiber body, in order to improve the aerodynamic and structural strength

　　Carbon fiber can be processed into fabric, felt, mat, tape, paper and other materials. In addition to the traditional use of carbon fiber in the use of insulation materials, the general is not used alone, and more as a reinforcing material to add to the resin, metal, ceramics, concrete and other materials, composite materials. Carbon fiber reinforced composites used as aircraft structural materials, electromagnetic shielding in electrical materials, artificial ligaments and other body substitute materials as well as for manufacturing the rocket shell, motor boats, industrial robots, automobile plate spring and drive shaft etc..

　　Advantage

　　1、 high strength (5 times the iron and steel)

　　2、 excellent heat resistance (can withstand 2000 degrees above the high temperature)

　　3、 excellent thermal shock resistance

　　4、 low thermal expansion coefficient (deformation is small)

　　5、 small heat capacity (energy saving)

　　6、the proportion of small (steel 1/5)

　　7、 excellent corrosion resistance and radiation properties