The throat material now is made from carbon carbon composite material,and the main material is 4D C/C, the acupuncture and puncture knitting process is the main direction. The throat is one of the most important parts of the engine,and the throat material must meet the technology requirement of the missile engine.

　　The material of the missile throat used to made from polycrystalline graphite, re-crystallized graphite,pyrolytic graphite etc. now the carbon carbon composite material is used for this parts.

　　Carbon carbon composite material is made from carbon fiber and carbon matrix material,it’s more strengthful than graphite material, thermal shock resistance property is better than graphite material,and it can be designed. Now the carbon carbon composite material has become the most appropriate material of the throat. C/C preform material has 2D,3D 4D,5D,7D even 11D, polar weave etc.and the 4D is widely used for many military products,such as : tomahawk cruise missile, anti submarine missile, anti tank missile etc.

　　The structure of the perform is also important to the carbon carbon composite material performance, the acupuncture and puncture knitting process can meet the high strength in the axial,and can meet mass production. Mmulti dimensional braided perform is not easy to make ,it need manual molding, complex process,expensive cost.

　　acupuncture and puncture knitting process have more fiber content than the whole felt,and compared with the weave C/C material,the process is more simple. And it’s more convenient to densify with CVI and easy to mass production in this way,so the cost will decrease.

　　In the future, the 4D acupuncture and puncture will be used mostly for the missile throat. It can improve the fiber content, mechanical properties and reduce the cost and make the mass production come true.

　　1、Determination of temperature in the process of graphitization

　　The temperature of carbon carbon composite material graphitization is one of the most important index during the processing. For a long time,it is basically determined by experience. In the old days,people think the temperature is the higher the better,but it’s wrong. To any carbon composite material,there is always a ideal temperature,to the resin carbon,the best temperature is 2480℃,as for the CVD carbon,pitch carbon and mixed matrix carbon,the ideal temperature is influence by the relative content,mix form and the different type and property of the carbon fiber,and the application is also need to be considered. Usually, the resin carbon can be partly graphitized at about 2500℃,as for the pitch carbon,it’s easily to be graphitized,so the 2200℃ is enough.

　　2、High pressure impregnation and carbonization process

　　During the carbon carbon composite material processing,many condition need to be considered,

　　such as temperature control,pressure control,the matching between temperature and pressure,the type of pitch etc.as the production cycle is very long during the processing,and so many parameters, each parameter can have a big influence on the production structure,property. The comprehensive influence is complex.

　　3、The relationship between content, arrangement of carbon fiber and the mechanical properties

　　We can choose different types of the carbon fiber according to the pressure of the parts. In a particular direction,if the fiber content is the same,the mechanical properties will be better when the fiber distribute uniformity.

　　4、The relationship between the density and property of the carbon carbon composite.

　　All the properties of carbon carbon composite material is closely related to the density.

　　So the density is also a key point during design,production and using. People think the higher density means higher properties,but it’s not true.as for the density,there is a ideal density,if the density is higher than it,the cost and production cycle will be higher and longer,on the other hand,it may have a negative effect to the properties of carbon carbon composite material.

　　With the development of solar energy Photovoltaic industry, the traditional graphite material is difficult to meet the needs of large-scale production equipment. However the carbon carbon composite material has a good thermo physical properties,it has a great advantage over the graphite material. The carbon carbon composite insulation parts,structure parts and heating unit will be more and more important to silicon single crystal furnace and poly-silicon ingot furnace. There are also some problems to the carbon carbon composite material,now,the best way is to use the SiC coating to increase the effective and service life.

　　The carbon carbon composite material is to do some reinforce treatment on the basis of carbon fiber,it forms under the 2000~2500℃,it can withstand the high temperature of 2000 ℃,after multiple heat treatment,the strength of C/C material is 3~5times than the graphite material,the parts will not break even drop off,and it’s also easy to process,good heat resistance, corrosion resistance, friction resistance,the service like is 3 times longer than the graphite material,and the price is about 2times than the graphite material.

　　The service life of silicon single crystal furnace is about 50 times,and the service life poly-silicon ingot furnace is about 100 times,however, the service of silicon single crystal furnace with carbon carbon composite material is more than 50times.

　　The bigger size of the C/C material means the higher cost performance. It can weave any shape and size perform,then use the densification process to make the CFC material,so the bigger size the cheaper price it will be. If use the graphite material,it needs to assemble with piece by piece together,the cost from processing is also expansive.

　　The service life of the C/C material with SiC coating is longer than the material without coating. Overall consideration,no mater the cost or property,the carbon carbon composite material is better than graphite material.

　　The carbon carbon composite material which used in the medical domain,is made of 3D carbon fiber perform and impregnated furfural resin, carbonization, chemical vaporized infiltration(CVI). It has all the good properties of carbon material,and also has a good biocompatibility and the similar modulus of elasticity as human skeleton,stable chemical property,high strength,light weight etc. but the disadvantage of carbon carbon composite material used for human skeleton is that the surface carbon particles of the CFC material will fall off,it’s not a small problem.the small partical will assimilated by macrophage or lymphocyte,however,the bigger particle will flow with the body fluid,and will be deposition at the body surface,and this situation will lead to the “black skin”. So it’s very important to produce and design the CFC material as per requirements for clinical applications to reduce the pollution to the body and increase the stability.

　　In general, scholars use SEM and Shore hardness tester to observe the micro morphology and test the surface hardness. They also need to do plant experiment in animal to research the CFC biological property,and study the feasibility of human bone tissue replacement.

　　Carbon carbon composite material as a new type carbon material,the material has an apparent similarity with the human bone. Traditional bone repair materials,such as metal, macromolecule, ceramic etc. to a certain extent,it can meet the effect of bone repair,but because of limitations of a single material,it hard to solve the patient suffering.

　　Compared with the metal material,the surface hardness and modulus of elasticity is better than the metal ones. Now the problem is to solve the biological activity of the surface and carbon partical falling off. And the process optimization of carbon carbon composite material producing and surface modification are also important issues to be solved.

　　Carbon carbon composite material can be used in the national defense industry and aerospace industry.

　　C/C composite material is made of PAN pre-oxidized fiber,use CVI and resin impregnation processing.it has a high specific strength,erosion resistance, thermal shock resistance,high temperature resistance,etc. After analogue simulation to the CVI processing of carbon carbon composite material and optimization of CVI processing,we could meet Computer automatic control of CVI processing and carbonization process,and reach the international advanced level.

　　In the early days,the solid rocket motor nozzle is made of graphite material and high strength steel or aluminium alloy,the weight of them increased costs and reduce the working efficienfy of the engine.with the rapid development of composite materials,the carbon carbon composite material replace the graphite material. The C/C composite material is light in weight and high strength,high temperature resistance,the developing trend in future is to make full carbon nozzle which means using carbon carbon composite material as integration structure material of the nozzle.

　　The throat is the main part of solid motor nozzle,the structure of it is sample,however,it’s the key parts. Among all the nozzle parts,the throat is in the worst environment,so the throat is easiest to be erosion. At present, high performance, large solid rocket motor nozzle general use carbon carbon composite material to make the throat.

　　The carbon carbon composite throat is now used in apogee kick rocket engine, medium range missile engine and II stage engine of long-range strategic missile,after the developing of multi direction weaving C/C composite throat,the I and III stage engine of long-range strategic missile can also made of it.

　　The failure behavior of carbon carbon composite throat is also important,the main factors include thermal contact resistance and ablation boundary, under the action of thermal stress, the fracture of the throat is broken.

　　The carbon carbon composite material has a big difference to the superalloy and ceramic materials. Under inert conditions,even the temperature reach 20000C,the strength of the C/C material can still remain unchanged situation,the strength will not reduce.

　　The carbon carbon composite material have a good resistance to thermal shocks and excellent mechanical properties. However, the fatal weakness of CFC material is the low oxidation resistance.although the C/C material has a high specific strength, high specific stiffness and high temperature stability,as one attractive structure material,when the temperature reach 4000C,the carbon carbon composite material start to oxidize. So the most researches on the C/C composite is how to avoid or reduce the degree of oxidation,and also many researches on the processing of the material,structure and the activity, quantitative relationship and the comparison between the C/C with protective layer and without protective layer. One of the most important results is that the physical properties have a big influence to the carbon carbon composite material activity.

　　The flow chart of C/C material below：

　　The different processing between carbon cloth and carbon felt can lead to the different C/C composite material,although they have the similar structure and graphitization degree and same heating treatment,they still have the different properties,the main reason is the oxidation direction,as the two different carbon fiber,they have the different surface area and pore volume.

　　So before using the carbon cloth or carbon felt to make C/C composite material,it’s also important to research the different fiber physical property.

　　C/C composite material is carbon matrix reinforced by carbon fiber. The whole system is made up of carbon element. So the carbon structure which is formed by carbon element will have a big influence on the mechanical properties, thermal performance, friction and wear properties of the composite material.the degree of graphitization is one of the most important indexes to characterize the carbon carbon composite material.most researches show that the higher degree of graphitization which has a better combination properties to the carbon carbon composite material.

　　According to the different kinds of raw materials,the carbon fiber can be divided into three kinds: polyacrylonitrile base(PAN) fiber,pitch base fiber and rayon base fiber. Generally speaking,the PAN base fiber is harder to be graphitization than pitch base,the rayon base is easier to be graphitizatioin than ordinary pitch base fiber.the difficult degree of graphitization is affected by the presoma.

　　The technology of matrix carbon mainly includes pyrolytic carbon,resin carbon,pitch carbon, in general,the pitch carbon is easier to be graphitization,and the resin carbon is hard to be graphitization,the difficult degree of pyrolytic carbon is depanding on the different structure,the rough laminar is easiest to be graphitization,the smooth laminar is harder than the RL,and the isotropic is the most difficult to be graphitization of all.

　　Under the right temperature (>1600C0),the carbon will transform into the graphite,and the changing process will be finished until the temperature reach 3000C0.

　　The graphitization processing of carbon carbon composite material takes advantage of heating to activate the amorphous carbon into graphite,so the degree of graphitization is not only depanding on the material structure but the heating temperature,pressure,the time of atomic rearrangement.

　　Carbon carbon composite material will occur oxidation in the circumstance of temperature above 450 C°,the rate of oxidation will increase rapidly with the temperature raising.some researches show that the strength of the carbon carbon composite material will reduce 10% with the oxidation loss 1%.the oxidation can not only cause the material loss,but also have the security risks on the material itself. So it’s important to do some protection of the C/C composite material.

　　The method of antioxidant treatment mainly divided into two categories.one is matrix modification to be antioxidant, and another one is surface coating to be antioxidant.the matrix modification way is to treat the CFC material during the preparation process,by using the CVI, impregnation or chemical reaction synthesis etc to add into the matrix or form antioxidation particles,such as Si,SiO2,B,B4C,MoSi etc.

　　However,it will make the CFC material can not be continuous with carbon,so it will change the thermophysical and strength properties(if too much antioxidation particles). During the friction process of the carbon carbon composite material,the antioxidation particles will wear and tear(because of the hard phase),so it will have a big influence on the carbon carbon composite material during the friction processing.the CFC material will start to oxidation when 370 C°,after mixing the antioxidation particles,the starting temperature of the oxidation can be increase to　600 C°.

　　The surface coating method need to confirm the oxygen barrier agent. The agent need to isolate the composite material and the oxygen circumstance. In addition,the agent must have low volatility,because it can avoid excess loss during the high velocity air.The coating must also have a good adhesiveness with the carbon matrix,and can prevent carbon from leaking out.

　　Si3N4,SiC,are some good oxygen barrier agent,they have a high temperature resistance,meanwhile,the SiO2 (forming of the surface)can be oxidation resistance.

　Compared with metal materials,the carbon carbon composite material has outstanding features.

　　1、Quality light

　　The density of carbon carbon composite material is only 1/4 of the steel,after using the carbon carbon composite material,it can can greatly reduce the quality of the aircraft. For example,it can reduce 816.5kg of Boeing 747-400,and can reduce 998kg of A340.

　　2、Energy load

　　Energy load is the index of absorbing the kinetic energy of the brake device,it’s usually indicated by the heat load ratio of the friction surface,the unit is J/cm2.As the heat capacity of C/C composite braking material is much higher than the powder metallurgy metal base material,so the energy load of carbon carbon composite material is 3 times higher than the powder metallurgy metal base material.

　　3、High temperature resistance, no deformation and no bonding phenomenon.

　　Because of the high strength under the high temperature,high thermal conductivity and low coefficient of thermal expansion,so the seismic performance is much better than the metal base braking material,and in the course of using, the deformation will not occur.

　　4、Good friction and wear,long service life.

　　Some researchs show that:during the brake processing,the friction coefficient of the carbon carbon composite material is stable,the curve of moment and the time is smooth,under the different conditions of speed, specific pressure and energy load,the property of friction is very stable;if ander the same conditions,it will show a good repeat performance,although under a high energy load,the moment will reduce little.

　　The carbon carbon composite material will have a good self-lubricating property after appropriate graphite processing,the friction rate will be 1/5 of the metal base material,so the service life will be longer,the surface of the friction will be smooth and bright. In addition,the C/C composite material can be used in overload condition.

　　C/C composite material was used for braking in the airplane for the first time in 1973,and now,over 60% of the carbon carbon composite material still be used for the airplane braking material,meanwhile, C/C composite material is also used for rocket nozzle, missile nose cone,parts on for re entering the atmosphere, racing car,high speed rail,tank etc.

　　When the plane take off and land,the kinetic energy is very large,the kinetic energy of Boeing 767 aircraft is about 670MJ.the function of the brake disc is to make the airplane,with high kinetic energy and high momentum,slow and stop. The dynamic and stationary disc of aircraft will rub against each other to absorb the huge kinetic energy.the C/C composite material belong to the brittle materials,the energy generated during the friction can not transform into other form through plastic deformation,so it can only transform into thermal energy,so the temperature of the surface between dynamic and stationary disc is very high,it can reach 2000℃ at the moment. So that could have massive significance to do the research of C/C composite material.

　　The influence of thermal conductivity of the C/C composite material is very complex. Different kinds of fibers and volume fraction,different kinds of matrix carbon and weave pattern,all these factors can lead to the thermal conductivity with a big difference. For example,there are different fiber type,such as: Nylon base,PAN base, isotropic pitch base and mesophase pitch base; The matrix carbon has thermosetting resin carbon, thermoplasticity pitch carbon and pyrolytic carbon vapor deposition;the weave pattern has fiber felt, non weft fabric,3D weave and 2.5d weave and 2d lamination etc. One of so many factors changed can have a big influence on the carbon carbon composite material.