[Music] [Music] lecture number 22 so today we will be looking into carbon carbon composite which is one of the star requirement in aerospace industry and automobile also slowly have started taking care of this carbon carbon composites carbon carbon composites are where in which the matrix is a carbon the reinforcing agent is also made out of carbon so in this lecture we will have a Content introduction to si si si then we will have different matrices then we will see the processing techniques advantages and applications these will be the content so here a composite you are trying to use fiber which is made out of which is made out of carbon material then you will also have a matrix which is made out of carbon material these two put together we try to get a carbon carbon composite the function of the filament here is to give high strength high stiffness and it also tries to give you low density the matrix it has to have good shear strength property and low density so you see here this is also low this is also low so naturally the composite what we get is going to have a very low density so it will have good shear strength property from the matrix high stiffness and high strength comes from the fiber what we use so we will use a fiber which is made out of carbon so it can be a single wire it can be a mat a 2 D or it can also be a 3 D so depending upon the requirements we choose a proper reinforcement matrix is made out of carbon and then we try to make composites so when I said matrix is made out of carbon so quickly since we have studied about the ceramic matrix composite what should come to your mind is we will try to use a polymer we will try to do pyrolysis and we get converted into carbon so this which should be the basic thought we will see the process whatever we have lined up here so matrix the matrix can be polymer matrix composite metal matrix composite ceramic matrix composite the most interesting and which is finding lot of applications are carbon carbon composites then we also have bulk metallic glass composites this is an extra field which is coming up which is called as BMG composites in this lecture we will more focused towards about CC composites so a matrix so what are the different types of carbon matrix they are thermoset resins can be thought of phenolic resins you have fluorine resins then oxidized Pyro's styrene we have then we have and resin then we have quali mean I'll lead in chloride so this and then etc you have many more resins which are available for these are all the possible matrix for carbon so you in the the carbon fiber can be made out of rayon based can be made out of fan based can be made out of pitch based so rayon pan pitch these three are the starting materials which are used for making carbon fiber even today that it is a state-of-the-art technologies are available only with few people for making highly pure carbon fibers up to nineteen ninety two percent or 95 percent it is easy to make a pure pure carbon fibers it is easy to make anything about that it's IP rights it's a proprietary item only very few companies across the globe hold the rights for making this carbon fiber they make it out of rayon pan or pitch these are the set of matrices where in which this can help in making a carbon matrix so matrix a reinforcement put together forms a carbon carbon carbon composites so it is a family of complex advanced materials that consist of carbon fiber embedded in a carbon matrix so carbon carbon composites are those special composites in which both the reinforcing fiber and the matter are made out of pure carbon they are made out of woven mesh of carbon fiber they are used for very high strength to modulus of rigidity they get and here they are they can withstand up to three thousand degree Celsius this is very very important this property makes CC composite quite usable in aerospace industries the Space Shuttle which comes back are nowadays made out of carbon carbon composites which are light and rate which can withstand very high temperatures and apart from that lot of filaments which are used for very high-temperature furnaces they are also nowadays made out of carbon carbon composite because they withstand very high temperatures so see see composite can be tailored to meet whatever is a customer requirement and today what has happened is they put carbon carbon fiber and then they have another material up and down so now see see composite is used also as a insert they are added in between sandwich so this assume this is a metal so you have two metals and then in between you have carbon carbon composites for required application again as I told you here it can be in the form of a woven mesh so this is a three dimensional version so in this is a preformed pair which is made out of carbon carbon carbon fibers and through which the carbon matrix is infused the carbon fiber which is used in the CC composite are tailored for to the mechanical properties of the final structure so for this the carbon fiber plays a very very important role so carbon fibers are having very high strength modulus and intermediate modulus fibres are also available in this in carbon fiber so this is a human hair this is a carbon fiber typically the human hair goes from 60 microns 60 microns to 100 microns this is the size of a human hair it varies in this range but you look at it this will be approximately five to ten microns so this is how the carbon fiber is made so here is a comparison between human hair and carbon fiber the reinforcement the these fibers are okay the carbon fibers first are prepared from pits or plan the carbon atom bonded together to form a long chain so in pitch or pan what we do is we try to take it the carbon atoms are bonded together to form a long chain this super-strong material that also extremely lightweight is a carbon fiber they have five times stronger than steel two times stiffer and about 2/3 times less weight as compared to that of steel so this is a carbon fiber so fiber so you see this is an interface right fiber interface and this is the matrix carbon fiber has very good mechanical properties so how is the carbon fiber prepared so in a pan process we take pan and then we try to stretch the fiber pass this fiber through a thermoset and then we try to carburized it then grapha ties it then we try to do a surface treatment then epoxy sizing we do and then finally we mind it in a spool so about 90% of the carbon fiber which are produced today are made out of and process the 10% is made from rayon process and this is a very well-established process so because of this carbonizing and graphite icing we need a very high very high quality processing here so basically it has to be a furnace and then there has to be a gas carrier media which is there so these two should make sure that a proper output is given so rest all treatment are straightforward so pan-pan they will do you process through spools so the carbon 5 are stretched so they are brought to high strength and then it undergoes in a thermoset it expands and I that series of rollers then carburizing then graphite icing then you undergo this surface treatment epoxy sizing and then you dry to do with spool so the processing of carbon fiber so we have carbon fibers so these are carbon fibers which are there you can see rough laminates so these are carbon fibers which are with rough laminates you can also see with a smooth laminate you can also see with isotropic properties so these are the different processing of carbon fibers so with this you can see these are the micro structures which are made and then a carbon with laminate structure laminar structure this is the smooth structure and isotropic structure is possible so when you talk about carbon matrix the carbon matrix in CC composite basic function is to transfer the mechanical load between the fibres it has to bind the fibres these two are well known so it acts as a binder to maintain the alignment of the fiber fibers and the fiber bundle at the same time isolate the fiber from one another so this is the basic function of a carbon matrix the other important criterias for the selection of a polymer precursor to form a carbon matrix should be the there it has to have a very high carbon yield why is that because I have put a big list of polymers where in which you try to do a proper processing it gets converted into a carbon matrix so now what should be the selection criteria so that is what we have listed it here high carbon yield it should give it should have as minimal shrinkage during pyrolysis process it should be amenable with all type of polymer matrix composite when it follows a root of resin transfer molding or filament winding it should it should use low solvent content it should have the highest high degree of pre polymerization with low viscosity it should have the ability for multiple sources it should be low cost its part life then the storage lifetime should be very long so these are the condition which which are put in front of before choosing the polymer precursor if you look at it this is a composite carbon carbon carbon this is a carbon matrix and these are the fibers which are used if you generally the CC composite is is has a Norman clay Chur so this is the CCM it is written as it is carbon carbon composite it says one or four so one stands for continuous fiber four stands for chopped fiber so you can put that signature digit there then 90 is the orientation 0 90 the alignment can be put as 90 45 30 whatever it is so this is zero zero means to do random and if you put 90 it is zero 90 orientation you can also have 45 this c is represent this digit represents the heat treatment temperature C means it is processed at a temperature between two thousand to three thousand six hundred and thirty-two degree Fahrenheit if you put M then it is 2500 degree Celsius to four thousand five hundred and thirty-two degree Ferren Fahrenheit or it is two thousand degree Celsius I am miss 2500 degree Celsius so this H represents purity how pure is the carbon-carbon composite regular great H is purified great SH is super purified grade so these are the grades so CCM composites can this is a signature which it follows the first digit talks for reinforcement next digit talks for alignment next digit talks for heat treatment and the last digit talks for purity of the composite so you can see here in plain and cross plane so here this is the product okay so you can see in plane and this is also in claim this is cross plane so you can choose this in plane and cross plane depending upon your requirement or depending upon your final product you choose whether to go for in plane or you go for cross section so in claim and then you have cross section so structures are there so what is the advantage of carbon-carbon composite it is very light in weight you look at it it is one point six to two grams per centimeter cube it has very high strength at very high temperatures for example cutting tools and all you look you can it they don't need strength at room temperature strength at room temperature strength at high temperature okay this this is very important today our requirement our strength at high temperature requirements room temperature you can see the strength will be good hardness will be good but very high temperatures the strength the material gets deformed moment it deforms then it loses its functional properties so high strength at high temperature is another big advantage edge for cc composite in in a non oxidized atmosphere then it has to have low coefficient of thermal expansion it has to have high thermal conductivity and it also have has to have high thermal shock resistance when we look that ceramic matrix composite we said two properties are very important one is the toughness property has to be enhance or fracture toughness property to be enhanced that is why we go from ceramics to ceramic matrix and the next is high thermal shock resistance for a ceramic matrix composite when you go for carbon carbon composite also we keep this as one of the biggest criteria or this is one of the biggest advantage for choosing carbon carbon composite it has very low weight it has very high strength at high temperatures it has very low coefficient of expansion it has very high thermal conductivity today people are looking forward for heat exchangers made out of carbon carbon composite but what are the disadvantages the disadvantages are the fabrication course is extremely high because all the processes need furnaces these furnaces have should have gases in the absence of oxygen that is one the temperature what it operates should be very high which cannot be normally you China in a column in a furnace where the heating coil is made out of steel or tungsten okay next the the process leads to lot of Cora cities this process is followed is very similar to that of ceramic matrix composite we will see that then it has poor oxidation resistance so when it is done when there is a few trace of oxygen immediately the carbon carbon composites the carbon matrix loses its functional properties it has very poor inter laminar shear strength so we have to be very careful before using it for structural applications it has low oxidation resistance it reacts with oxygen even as low at 500 degree Celsius it reacts and it forms different compounds so the major disadvantages cost porosity and oxygen presence puts this carbon-carbon composite into a into still a very difficult component for manufacturing so if you look at it Europe uses the max the North America uses maximum of 35 followed by Europe which they use carbon fiber to a large extent then we use Japan uses 15 percent and the rest of the world uses 20 percent so this is what is the consumption of carbon fiber in the global market so slowly slowly it has been used in Asian countries so the application of CC composites are it can be used for a braking system where there is going to be very high temperature it can be used as a refractory material it can be used as a hot pressed die for a turbojet engine components they are today made out of carbon carbon composite so wherever you can replace met ceramic matrix composite we go for carbon carbon composite ceramic has a fracture toughness property so here it does not have that but however making CC composite is also a challenge so heating elements are made out of CC composite because they can withstand very high temperature missile con tip because when it enters inside or when it goes outside the atmosphere it does a huge friction coming up so missile cones are made out of corn tips are made out of CC composite the rocket motor trots are made out of it leading edge of space shuttles are made out of it heat shielding's are made x-rays targets are made out of it aircraft baked this braking system is an automobile today even in bikes people have started using CC composites aircraft brakes re-entry vehicles biomedical implants engine piston because very high combustion if you want to have so the the temperature which has to be withstand by the piston should be very high so now there are started using CC composites then we have electronic sinks and other automobile and motorbike bodies are made out of carbon carbon composites if you look at Boeing Dreamliner 787 the composites are 50% made out of this and then we will have carbon carbon composites carbon laminate composites are used in the tail region it is also used in the wings the carbon sandwich composites are again used in the tails and as well as in the wings we can see and then it is also used in the turbocharged the casing is all made out of it so the components that are used for used uses the composite structure are almost the fuselage is made out of composite they are some are made out of glass fiber also but now they are replacing it with carbon fiber because of light weight then upper and the lower wings wing skin are made out of it raaah dome is made out of atom is in the front portion the wing flap elevators and the Ilan's are made out of it the vertical fins and the horizontal stabilizers so these are the horizontal vertical stabilizer which are made out of it so now the complete plane are moved towards carbon carbon are made out of carbon fiber composites and they are also slowly moving towards carbon carbon composites so if you look at LCA our frame these LCA are frames they are made out of carbon composites you can see these are the portions which are made out of carbon composite and slowly slowly they are trying to replace this carbon composite with carbon carbon matrix composites so here it was carbon composites it was not carbon-carbon that means to say here only fiber was used and polymer was used and slowly when in the high-temperature engine and other places they are replacing this carbon composite with carbon carbon fiber composite so significant weight reduction is there significant reduction in the pot count also since it is going to composite complex shapes can be made and integration of inserts in the parts can be made so number of parts are gone down so the fasteners are reduced because basically when you use composite materials you can think of using additives rather than making a whole so when we look into machining you will understand when you drill a hole there will be a lot of denominations coming into so nowadays it has gone to addition bonding then fatigue life is improved because we try we try to choose proper interface between the matrix and the fiber so we try to enhance the fatigue life the crack growth can be arrested and to a large extent the signatures are reduced in the LCF frame so this is the carbon fiber composites 45% it is tried using so this is the rocket nozzle tip which is made out of carbon carbon composite so this withstands very high temperature so a Space Shuttle nose tip are made out of carbon carbon composites yes of very high temperature so now slowly let's get into the fabrication methods of making CC composites so here there are four methods which are predominantly used okay four routes sometimes a combination of the two routes are also used see in manufacturing there is nothing called as a unique solution so depending upon the availability resources depending upon the output required a combination is always thought of and we try to get the required output so here there we have the four so one is impregnation and pyrolysis using thermoset resin impregnation and pyrolysis using thermoplastic pitts precursor and then we have a CVI route we have CVD route so fabrication method here is a schematic diagram which is given so the schematic mechanism of pore filling and pore blocking by liquid impregnation and CVD process so here what we do is we these are the pores pore entry entrance diameter okay this is a cross-section of a single pore so this is pitch impregnated so what we have is this is Pritz impregnated pore is there so then what we do is we try to graph a theis this pitch coke we try to do it so what we do is we take this pitch impregnated then we heat it to 2500 degree Celsius so then the resin is impregnated then this pyrolytic carbon is formed and then the gas impregnation early stage is like this okay so then what we do is graphitization of the pyrolytic carbon happens and after heating at 2500 degrees Celsius there is a graphite iced pyrolytic carbon which is getting formed on the gas impregnation final stage after heat treatment to 2500 degree Celsius we make a carbon-carbon composite by this process so here is a poor is a cross-section of a pore so this can be done by three roots so of one we try to put the pitch here and the pitch is impregnated here right and then what we do is here we try to graph at eyes the pitch coke then how do we get this done we heat it to whatever it is we heat it to two thousand we heat it to a higher temperature 2500 degree Celsius then we it forms like this and then we try to pitch coke is formed then here what we do is we try to use a cured resin right and then this cured resin is graph'it eyes pyrolytic carbon is pushed into so we get something like this so then pyrolytic carbon is like this and this is the early stage of impregnation and this gas impregnation final stage after two thousand five hundred degrees we get the required carbon carbon composite so the fabrication method generally each of the three processes are carried out at a temperature between 800 degree Celsius 2500 degree Celsius the final heat treatment goes up to 3,000 degree Celsius these three methods lead to different microstructures in the composite partially because of the difference in the method of the formation of carbon from the three different types of precursors but mainly because of the formation of carbon forms having different structures and properties for different precursors so these are the three pretty precursors with this precursors we are trying to get different different types of CC composites the thermostatic resin based processor for carbon carbon composite the resin are usually dissolved in an organic solvent with a catalyst /a curing agent before in filtration the resin in the impregnated composite is cured and then pyrolized by heating it to a temperature of 350 to 800 degree Celsius frequently hot pressing at high pressures up to 10 mega Pascal's and the temperature from 150 to 350 degree Celsius for a period of 10 hours it is done to get intense density in the curing process then the final pyrolysis of the composite is subsequently graph'it iced at thousand degrees Celsius we get a CCC composite okay so in this if you see very clearly time pressure and temperature are very important and then here in the absence of oxygen is very very important so if you look at it following is a flow diagram for CC composite using thermoset resin you have a fiber preform this is resin is getting infinite rated into it then we do a curing the next stages you'd get a pre peg then stacking or the prepreg you do curing so prepackaged we're already polymer is fitted into the resin so you have a continuous fiber then resin impregnated we do filament winding and then we do curing so when all these things are cured you go to pyrolysis so pyrolysis is done up to a temperature of 800 degree Celsius then what we do is moment the pyrolysis is over then there might be some pores or some gap in between so again what we do is we try to do a resin infiltration and this process is repeated multiple times until you get the final required dimension strength or or thickness or whatever it is then once it is done then finally we do one more heating from thousand degrees to three thousand degree Celsius to get the required output through this processing route we try to get a carbon carbon composites manufactured using thermo septic resin so preform prepreg and then we use continuous to get the carbon carbon composite made so we can also use thermoplastic pitch based processing so for carbon carbon composites so the pits impregnated preform is subjected to two pyrolysis carburization in an inert atmosphere to convert the organic compound to coke and a high temperature treatment at thousand to two thousand degree Celsius for graphitization of the coke so first it forms pitch into a is converted into the organic component into coke then we try to do this coke to get Grapher taste of this coke to get the required output so the densification process is carried out at atmospheres at atmospheric oral at reduced pressure is repeated several times to get the desired density it is more efficient process the coke yield of our pitch increases from 50 percent to 85 percent by weight the pressures which are used are seventy mega Pascal's the pressures are also very high so this is what is the root flow chart for making it so fiber is taken in a preform okay and then we put the molten pitch infiltration is done fiber preform molten pits infiltration is done then pyrolysis is taken care the molten pitch infiltration happens then we do one more round of pyrolysis and we keep adding repeating these steps n number of times and then finally we do a final treatment at this D at two thousand to two thousand two thousand two hundred to two thousand seven hundred degree Celsius to get the required output by this way we try to make carbon carbon composites so basically the that resin is is taken to a very high temperature it's graphite iced to get the required output so this is for thermoplastic pitch based processing the next one is chemical vapour infiltration process in chemical vapour infiltration process the gaseous precursor is infiltrated into the fiber preform this is driven by either diffusion process or it is imposed by a external pressure so either you push it or there is some phenomena which sucks it capillary action you get it done the deposition filling fills the space between the fiber forming and the composite matrix in which the resin is the is the deposited material and the dispersed phase is a carbon phase the chemical vapour infiltration is a very similar process to that of chemical vapour deposition which we have seen in ceramic matrix composites so we use the precursor gas then we use a carrier media carrier gas and then what we get is CVD and this CVD is done on a substrate so on a substrate or on a fiber we try to get the required output so this is CV this is CVD process or CVI process here so what is the difference between the previous process and this process in the previous process what we do is we take a fiber we take a molten pitch which is infiltrated so all these things happen somewhere close to room temperature itself but here in CVI what we do is we try to take the precursor as the the precursor is a gracias precursor which is tries to pass through the recent fiber so as I told you last time in ceramic matrix composite we have an isothermal CVI process we have a thermal gradient CVI process we have a pressure gradient CVI process we also have a rapid CVI process for making carbon carbon composites so here through this the reactant gas is passed through here is the preform carbon fiber which is kept this gas goes into reacts and then makes a carbon carbon composite so one date reacts if whatever happens is only at a nascent stage or in a green stage then after this it has to undergo one or two times of more graphitization so that the carbon carbon composites is formed and here this vapors are infiltrated at regular intervals so that you try to have a proper densification of the carbon carbon composite so these are the induction coil for heating this is a hot region preform is used and this is a graphite holder so that the graphite can withstand very high temperature otherwise they would have gone for a metal one metal or a steel one so and here in the bottom they use a water jacket and then for cooling so what is a major advantage low fiber damage happens here then highest purification can be done low infiltration temperatures are required enhanced mechanical properties can be done good shock resistance happens increased creep and oxidation behavior comes interface can be deposited in situ we want to enhance what are the disadvantages of this process it's a slow process it can take even several weeks to have it it has a half porosity is always part of the product so this porosity will try to give a very less or this will have to compromise a mechanical property it is capital intensive in CVI process this is how the CV a growth mechanism is there you have initial fiber which are erased these are initial fiber arrays these are initial matrix infiltration happens right and then what happens is this is first let's take this is one stage and in the next stage you keep on pumping it second time third time fourth time so you see that this in filter in initial matrix which was in filter the thickness increases and we are talking about the residual pores of ten to fifteen percent these are the pores which are there because completely this portion is locked so once it is locked the further gasses cannot go through so this portion is the residual pores which is prone to happen here in CVI process the best pour that means to say the lowest porosity what you can get is around about six percent which are reported in the research publication but generally it is ten to fifteen percent so what is isotherm which we were discussing there are four different types of CVI so what is isotherm see VA isotherm CVI is the most widely used process and it is very similar to that of a ceramic matrix composite so here the fiber preform are heated in a CVI reactor up to a in infiltration temperature in the range of 800 degrees 2200 degree Celsius so the infra the fiber preform is heated reactor up to an infiltration temperature where the temperature ranges from 800 degree Celsius 2200 degree Celsius or slower the position rate can be achieved by operating the reactor under reduced pressure and a lower temperature of thousand 50 degree Celsius so this is a isotherm CVI so you have process temperature of 10 50 degree Celsius the pressure is 50 milli bar the flow rate is 2.2 SLM and then the h2 is 2 MTS ratio is 10 is to 1 so here this is an isotherm we we push in gas inside the furnace and we start using it so if you look at the density evolution of CVA so over a period of time we see that 100% the the densification keeps on increasing so the process duration you see here it is almost 355 hours it it is it is done so that you try to get a final shape so this is the product which was supposed to be made so for making this process it is it takes 355 hours so the initial preform was around about 0.7 kgs the final preform mass was around about 4.8 it gets around about 5 kgs so there are 50 steps which are involved so every time what we do is we keep on pushing gas inside after every density 1 cycle we try to push the gas once again and then we start improving the densification so you can see the densities which is increased from 300 to 2 & 3 5 millimeter cube the thermal gradient CVI process in order to reduce the processing time so if you see here it takes isothermal it is around about 355 hours so in order to reduce that time what we do is the thermal gradient and the pressure gradient has been developed so in thermal gradient CVI is normally performed as a cold wall CVI process this process is very suitable for large carbon composites such as the rocket nozzle are made out of it the fiber preform is placed around a mandrel here and which is heated the outer surface is exposed to a cooler environment because the proximity of water cold cooling is possible here so this is what is the schematic diagram for thermal gradient CVI process this is a graphite mandrel so you place your preform the gas is flown from the top so the the heating is maintained in the furnace so this is a pre fiber preform this is a schematic diagram of thermal gradient CVI process the cooling jackets are here you can see the induction is given these circles are induction and then after that you will have cooling then you have a preform the fiber carbon fiber preform is the reinforced preform is there you have a mandala on which the preform is wound so now you pass gas through it so you try to get the carbon getting infiltrated into the preform so you produce a carbon carbon composites so you also have a pressure gradient which is a small variation modification of the isothermal CVI process so here a carbon fiber is placed in an isothermal II heated furnace with an outer graphite tool which only leaves a small gap for the forced gas to flow a forced gas of the precursor to flow through the pressure difference that forces the gas flow through the pores is created across the walls of this structure the process is also limited to the production of a single or a simple shape only done here this method may not be suitable for commercial production of CC composite parts for a large area so this method is not used so the schematic diagram is seen here so you have this is a fiber preform this is the gas in this is a gas out so you have heating coils and here it is airtight so that you try to make simple geometries out of it so there is a pressure gradient which is maintained such that you get the CVI done for making a carbon carbon composite the next process is called as a rapid CVI process a rapid CVI process technique developed by France this is still in a very very nascent stage can be rapidly for industries where in which the densification which is done is very good in this process at the precursor of carbon fiber preform acts as a carbon susceptor and is fully immersed in a liquid hydrocarbon such as cyclohexane or a toluene so it is immersed inside and then we do the process out of the two hydro carbon the carbon yield is higher at toluene the complete densification of CC bricks can be achieved within 10 hours by this process so what we do is we try to take a porous carbon fiber preform which acts as a scepter and it is fully immersed inside a hydro liquid hydrocarbon and then you dry it you get the process done very fast so the other one is chemical vapor deposition so it is infiltration here it is the position infiltration is pushing through the position is you deposit on top of it okay so here the preparation of CC fiber preforms of a desired shape and structure is done the densification by the densification of the composite by seized by CVD techniques are pretty good the infiltration from the pressurized hydrocarbon gas is around 900 degrees 2200 degree Celsius the gas is spiralized from the deposition on a fiber surface the process Duras and depends upon the thickness of the preform the heat treatment increases the modulus of elasticity and strength this process gives high strength and modulus of elasticity when we use a CVD process in a CVD process we use gases and then we use a carrier gas it is passed through a furnace and where in which there is a maintain the temperature of 720 degree Celsius this is a quartz tube and there is a quartz boat which is there where in which the can sample is given by CVD the carbon is getting deposited and the fiber and we make a carbon carbon composite in this process this is quite a slow and second thing is here there is a possibility of other impurities coming form so there has to be a proper control on the output the limitation of this the hydrocarbon gas which is infiltrated into the inter filament surface and it also it it in fill it forms an inter fill a mental surface and a crack sometimes these gas deposits on the outer shell and leaves lot of pores the infiltration and the densification is required the it takes a long time to do this process so if you look at the properties of the ccc composite it has excellent thermal shock low coefficient of expansion high modulus high conductivity low density high strength high coefficient of very low coefficient of friction high resistance in non oxidized atmosphere high abrasion resistance electrical conductivity and non brittle fracture these are some of the properties which are good for carbon carbon composites so if you look at temperatures polymer matrix composite it can withstand thermoset can go up to 300 or 400 degree Celsius this can go up to 500 degree Celsius when you look at metal matrix composite it can go from 400 degree Celsius it can go depending upon your matrix requirement it can go up to thousand degree Celsius this is a service condition where it can work ceramic matrix composite it can go up to thousand three hundred degree Celsius it can be silicon nitride silicon carbide alumina can go up to a slightly higher temperature of thousand four 400 degree Celsius look at carbon carbon composite it can go up two thousand five hundred degree Celsius service condition easily a temperature around and when you do a graphitization when it is graphite it can go up to two thousand degree Celsius so this makes it a very very viable matrix for high-temperature applications so if you look at specific strengths at varying temperatures you can see that carbon carbon composite the specific strength is almost constant up to 2,000 degree Fahrenheit whereas aluminium there is a decline titanium you can see over a period of time it is decline in kernel for slightly higher temperature and nodular iron with also there is a decline which happens over a period of time so the carbon-carbon composite maintains the strength the specific strength to a higher for a very high temperature as constant so it also depends upon the orientation if you have this is a flux Ural strength for short fibres for cloth type and then for roving type plus minus 45 rowing type plus minus 15 unidirectional fiber carbon fiber we use and then we try to have multiple orientations we can go have a flexural strength as as high as 700 Newton per millimeter square so if you look into it this is as a climax for this carbon carbon composite so if you see here carbon fiber reinforced plastics strength versus temperature the carbon fiber falls here and moment you convert this matrix into a carbon so this is carbon fiber-reinforced this is carbon fiber-reinforced in a carbon matrix you can see here it works very nice from thousand four thousand to two thousand degree celsius it works excellently well there is no compromise in strength and in fact you see here this is the major advantage of carbon carbon composites used in very high service temperature conditions with this we come to an end of this carbon carbon composites fabrication and we have seen different properties so predominantly here we use thermo set matrix thermoplastic matrix then we use CVI in CVI we have seen four different variations to reduce the cycle time and to enhance the quality of the oak we can also do exclusively CVD but there is lot of limitation in this process so that is why we don't use CVD to a large extent we follow only CVI process to get the carbon carbon composites thank you very much [Music] [Music] [Music]