Silicified graphite is a kind of composite material which is coated with silicon carbide layer on the surface of graphite material. The hardness of silicified graphite is actually the hardness of SiC, which is only inferior to that of diamond, boron nitride and boron carbide, which is higher than that of tungsten carbide and three aluminium oxide two. The production methods of silicified graphite are 3 methods, such as chemical vapor deposition (CVD), chemical vapor reaction (CVR) and liquid silicon infiltration reaction.

　　Chemical vapor deposition (CVI) method

　　The gas containing silicon and carbon is decomposed by high temperature graphite matrix, and SiC is deposited on the surface of graphite matrix. The raw material is three methyl silane (CH3SiC 3), four silicon chloride, hydrogen, silicon vapor and so on. The deposition temperature range is wide, from 1175 to 1775. The SiC layer produced by this method is very dense, uniform in thickness and approximately 0.1 to 0.3mm in thickness. But the combination of SiC and graphite as pure mechanical bonding and weak binding force in the blast temperature when SiC layer is prone to cracking and spalling.

　　Chemical vapor reaction (CVR)

　　The raw material is coke powder and excess quartz sand or amorphous silica powder. When heated to 2000 DEG C, a chemical reaction is generated to produce SiO vapor. SiO vapor reacts with the carbon matrix to form SiC. The SiC layer and the carbon substrate two has no obvious interface, are firmly combined, can not drop in temperature change and high load, but CVR method is SiO gas penetrated into the carbon based body reaction, therefore, still retain a porous carbon matrix, are used as sealing material, filling with resin impregnated or CVD method the pore.

　　Liquid silicon infiltration method

　　This method is also a kind of CVR. Under the vacuum condition, the carbon matrix is directly immersed in molten silicon liquid when heated to 800 DEG C. The liquid silicon gradually enters the carbon matrix and reacts to form SiC. Raw material is 99.9999% pure silicon. The thickness of SiC layer is up to 3.5mm. After reaction, the carbon matrix contains about 17% of the free silicon, filling the pores of the matrix, so that the matrix becomes dense and impermeable. However, the presence of free silicon reduces the corrosion resistance and high temperature oxidation resistance of silicified graphite.

　　The process of graphite impregnation is to fill the pores of carbon graphite materials with different forms of carbon. The purpose of the dense and impregnated graphite impregnation process is to produce high density products,

　　High density of liquid penetration. However, the densification is limited, it is impossible to require all the pores of dense products, but only A layer that is not dense enough for the product. Deposited on the surface of the graphite carbon covered layer, can significantly change the performance of another, because

　　The deposited carbon layer becomes another working surface. The characteristics of the dense carbon layer will be described below. Two, the need to dip the product of 1 small size graphite electrode and joint blank, a variety of graphite anode. These products have a high density and strength, low resistivity, so the first half of the finished product is soaked with coal tar and then graphitized. After coal asphalt impregnated a product the product volume density from 1.55 g / M 3 to about 1.65 g / cm 3, porosity decreased from 25 ~ 32 to 22 ~ 25%, the compressive mechanical strength can be increased to around 9.8 MPa, the resistivity can be decreased by about 10%.

　　For the requirements of high strength and high density products after two, three or four times (after repeatedly dipping roasting, baking again after impregnation), can make products to capture the high volume density of 1.85 g / cm'3, porosity decreased 116% compression! Strength increased to 39.2 MPa. 2 the production of high quality graphite anodes used in diaphragm salt solution electrolysis cells. After impregnation with coal tar graphite anode, the general can make the kitchen 8--9 months, not impregnated graphite anode can only be used for 5 - 6 months. The main reason is the influence of graphite anode life to the anode electrolyte penetration hole, and hydroxyl ions, sulfate ions and hypochlorite ions in the electrolyte in the anode discharge produces nascent oxygen.

　　According to the relevant information, some of the oil impregnated anode service life doubled. But too much oil will cause the deterioration of the operation of the electrolyzer, the use of high current density of the mercury electrolytic tank, but there is no oil immersed anode 3 chemical equipment requirements of impermeable graphite. Graphite is porous material, so the liquid and vapor can penetrate, available organic resin (such as phenolic resin, furfural acetone resin impregnated graphite products processing) in advance well, and after immersion in the appropriate temperature curing of the resin, can make liquid and gas of graphite products to low permeability in fact, the degree of harm, but also improve the mechanical strength of several times, and products, thermal conductivity is not reduced. This corrosion resistance, good thermal conductivity of the impermeable graphite chemical equipment is widely used.

　　The refractory material , graphite and graphite products have the properties of high temperature resistance and high strength. They are mainly used to make graphite crucible in metallurgical industry. Commonly it’s used as a protective agent for steel ingot in steel making.

　　Graphite is often used as lubricant in mechanical industry. The lubricating oil often can not be used under the condition of high speed, high temperature and high pressure, but the graphite wear resistant material can be operated at a temperature of 200~2000 DEG C at a high sliding speed without lubricating oil. The piston cup, sealing ring and bearing which are made of graphite material are used in a lot of equipment conveying corrosive medium widely, they do not need to add lubricating oil. Graphite grease is the good lubricant in many metal processing.

　　The conductive material , graphite is used for manufacturing the electrode, carbon nanotubes, carbon brush, and the positive electrode of the mercury rectifier,graphite gasket, telephone parts, TV tube coating etc.in the electrical industry .

　　Graphite has good chemical stability, the graphite products after special processing with corrosion resistance, good thermal conductivity, low permeability, it is widely used in the manufacturing of the heat exchanger, the reaction tank, condenser, combustion tower, absorption tower, cooler, heater, filter and pump equipment in petrochemical industry, hydrometallurgy, acid and alkali production, synthetic fiber, paper and other industrial sectors, it can save a lot of metal materials.

　　Casting, molding and high-temperature metallurgical materials because the graphite thermal expansion coefficient is small, and the capability of cold and hot change, it can be used as a mold of the glass, the use of graphite after black metal castings get precise size, smooth surface, high rate of finished products, it can be used without processing or minor processing, thus saving a lot metal.

　　Graphite rupture disk is the rupture disk which is impregnated by resin After a lot of molding and can withstand the high corrosion.The graphite rupture disk is a special type of safety device, it is mainly used in high corrosion condition and can bear any invasion from the strong corrosive chemicals.

　　The rupture disk utility model is a non closed pressure relief device composed of a blasting piece (or a bursting sheet component) and a clamping device (or a support ring). When it is under the given blasting temperature and the pressure difference between the two sides of the bursting disc reaches the preset value, the rupture disk instantly moves (breaks or falls off) and releases the fluid medium. There are two kinds of common graphite type rupture disk: flat-type and concave-type.

　　The graphite rupture disk size: conventional size 25mm--1000mm,bursting disc pressure: 0.001MPa--2MPa, applicable medium: gas, liquid and mixed medium, no insulation layer maximum temperature 200℃,80% operation rate, the highest manufacturing standards.

　　The graphite rupture disk is a safety device when we use acid, alkali and organic solvents and other corrosive fluids.It ruptures rapidly when the pressure is too large so as to ensure the safe. Our graphite rupture disk was produced with homogeneous graphite as the basic material, the machining setting pressure,its precision is high when the working pressure below 75% of the preset failure pressure .

　　The features of graphite rupture disk: corrosion resistance and excellent chemical weathering sleep, most media outside of the strong oxygen gasification has corrosion resistance, the probation period (1 years) no material degradation phenomenon; no plastic deformation phenomenon, the special properties of graphite is different from the metal materials, it almost has no plasticity until rupturing . That is to say, it damages facing the over pressure immediately, opening out the pressure of 100% ; a wide range of uses:it also be used in low pressure and the failure pressure characteristics of long-term stability.

　　Pyrolytic graphite is a new type of carbon material, is the high pure hydrocarbon gas in the furnace pressure in pyrolytic carbon of 1800 DEG C to 2000 C high crystallinity graphite matrix on the chemical vapor deposited, it has a high density (2.20g/cm), and the content of impurities (heat, electricity and magnetism and the anisotropy of mechanical properties. The vacuum degree of 10mmHg can still be maintained at about 1800℃

　　The process of decomposition of matter. Many inorganic substances and organic matter are heated to a certain degree of decomposition reactions will occur. The pyrolysis process does not involve the reaction of the catalyst, as well as other energy, such as UV radiation.

　　High temperature strength increases with the temperature increasing, the strength reached the highest value at 2750 C 3600 C sublimation. low elastic modulus, high thermal conductivity, low thermal expansion coefficient, good thermal shock resistance. good chemical stability, acid, alkali, salt and organic reagent of molten metal, slag and other corrosive media have no effect, in the atmosphere at a temperature below 400 DEG C oxidation is not obvious, the oxidation rate increased significantly at 800 C. do not put any gas at high temperature, at 1800 degrees Celsius or so to maintain the vacuum of 10-7mmhg.

　　Heat transfer process requires a large amount of heat absorption process. The heating method can be divided into self heating process and external heating process. For example, limestone pyrolysis to produce lime, temperature above 800 degrees Celsius, or even in the presence of oxygen does not affect the reaction process, so you can use the direct calcination of the industrial furnace for heating process. For the cracking of petroleum fractions, the reaction temperature is over 750 DEG C, and the lowest possible hydrocarbon partial pressure, is the product of combustible gas, so commonly used partition heat transfer mode (such as pyrolysis tube furnace) or by the carrier (such as direct heating regenerative furnace pyrolysis, sand furnacecracking, high temperature water vapor cracking). External thermal process. But can also be used to burn some of the raw materials for the self heating process, such as natural gas or heavy oil combustion pyrolysis of acetylene, carbon black, etc..

　　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 .

　　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.

　　(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

　　Manufaturing technique of refractory products is similar with that of common graphtie prodcut. The basic process are as follows:

　　Selecting Raw Material → Heating Raw Material → Smashing → Compounding → Molding Biscuit → Drying →Presintering Biscuit →Rough Machining →Sintering → Final Machining → Inspecting→ Finished Product.

　　1. Selecting Raw Material

　　When peolple are selecting raw material, they should take application into consideration. Most raw material is chemical material, only a few raw material is raw mineral materials. Usually, we can get raw material from market. And some special raw material should be compound by people themselves.

　　In general，the purity of raw material is very high. For example, when people produce magnesia carbon brick, content of magnesium oxide should exceed 95% and content of flake graphite should exceed 92%. From a material point then, the purity of raw material should be as high as possible. However, nothing is evidable. High purity means high cost.Like producing magnesia carbon brick, If people ensure the impurity of iron trioxide below 0.35%, the final product must will be qualified.

　　2. Heating Raw Material

　　The material which is applied to manufacturing graphite refractory products, especially oxidised raw material, need to be heated previously. Heating process can be divided into two aspects: the one aspect s calcine, which means burning raw material under a lower temperature that below final maching temperature, which aims at removing volatile impurities and inclusions, reducing contraction of briquettes, and promoting the transformation of allomorphic crystal form; the other aspect is electric smelting, the procedure of which is melting raw material with electric-arc furnace, smashing raw material after cooling, which can improve control on Dimension

　　3. Smashing

　　Smashing is a really important procedure in the course of producing refractory products, whose objective is to change granularity of raw material. As for benefit of smashing procedure， it can sactter raw material so evenly that biscuit can be molded more easyly. What ‘s more, it can make solid-phase reaction ,which avail sintering under a high temperature circumstance and decreace firing temperature, become more throughly. Furthermore, it can expose more impurity, which increase the purity of raw material.

　　(To be continued)