Carbon / composite material fights carbon coating of oxidation pottery and porcelain considers to make progress

2g/cm3) , if the hot property that has hold of place of material with carbon element not only is low temperature of conductance of hot coefficient of expansion, high fever, tall aerification and good heatproof shake performance, and be like,still is superior mechanical performance below high temperature quantity of high strenth, high standard, good rupture tenacity and wear-resisting function. More special is C/C composite material lifts instead along with the elevatory intensity of temperature, reach a lot of civil industry domains to get in aviation, spaceflight, nuclear energy consequently great fix eyes upon. Because be in 2000 ℃ above, c/C still can hold its exceedingly good mechanical property, the field uses in a lot of aerospace, the high temperature material that C/C is ideal [1-4] . At the beginning of 70 time, as a result of the need of space shuttle, the United States began hot structure to use the research work of C/C, make C/C prevents hot material to develop to hot construction material by burn. Box of ala of leading edge of the nose awl cap that C/C can use at lighting part of construction of gas turbine engine, space shuttle as hot construction material, wing, alula and airframe flap [5, 6] . These application want the job below the ambient conditions in high temperature and oxidation inevitably. However, carbon begins oxidation in the atmosphere having oxygen of 370 ℃ , prep above when 500 ℃ rapid oxidation, bring about C/C material annihilative destroy [7] . This one the heel of Achilles restricted the immediate application of C/C. This undertakes be fightinged suitably oxidizing protective to material with carbon element with respect to the requirement. Technology of antirust of C/C composite material has two kinds: (1) matrix handles a technology, include matrix macerate technology and add flame retardant grain of pottery and porcelain. Former it is macerate oxidation depressor, wait like borate, phosphate and halide; Latter is compound in matrix add fireproof material grain, wait like B2O3, B, SiC and B4C; (2) coating technology. Plant before if the method is not used with coating technology union, the ability of C/C antirust is finite, can be only commonly under 1000 ℃ , and because the meeting introduces salt in matrix kind or grain of pottery and porcelain makes the mechanical function of C/C and heat function drop. To realize prep above of 1000 ℃ fight oxidation protection, coating technology is logical choice [4, 7-10] . The article is right carbon / composite material fights carbon coating of oxidation pottery and porcelain considers to be summed up. 2C/C composite material fights oxidation to defend the main demand of pair of coating systems is designed reliable, the coating system that can implement to fight oxidation for long to defend, indispensible consideration a few main factors, these a few elements are summed up at the graph 1 in. From apparently look, what coating must offer effective barrier layer to prevent oxygen is inward diffuse. Additional, it must have evaporate lowly function flows in high speed gas with preventing its in excessive bright corrode. From the point of inside point of view, there should be better combinative performance between coating and matrix. Lining can prevent carbon to diffuse outwards and also must achieve at least prevent carbon and outer oxide contact produces carbon the degree of reductive reaction. Finally, all interfaces must have chemical consistence, there is good mechanical consistence between coating and matrix [7] . Should consider to choose appropriate oxygen to diffuse above all barrier layer material. According to experience, matrix of C/C composite material is the biggest weight loss late is unfavorable more than 1 ％ , effective working hours asks to be in 100 hours commonly above. Accordingly, c/C can permit rate of the biggest oxidation for 0.

H-1 of 01 ％ · . According to this standard, computation gives oxygen to diffuse the biggest oxygen of barrier layer material diffuses rate for 3 × 10-10g S-1 of · of · Cm-1. Graph 2 gave out the oxygen below high temperature of pottery and porcelain of a few common oxide diffuses rate. Visible, oxygen diffuses rate in 1000 ℃ - inside 1400 ℃ limits, do not exceed S-1 of · of · Cm-1 of 3 × 10-10g have A12O3 and SiO2[4] only. But oxide is unfavorable and direct besmear Fu serves as on C/C matrix fight oxidation Xu layer, because,this is, on one hand oxide pottery and porcelain should compare corresponding boride commonly or the hot coefficient of expansion of carbide wants tall, with C/C matrix heat expands break those who had matched congress to bring about coating to flake. Consider the issue of chemical consistence on the other hand, the carbon below high temperature and oxide pottery and porcelain produce reductive reaction. Generate aeriform production to make coating invalidation. If carbon and 2 oxidation silicon issue reaction to generate CO and SiO in 1450 ℃ , the vapour pressure of CO of child of the reaction below 1500 ℃ will is more than 0.

1MPa[ll] . Efficient way is to use data of blame oxide pottery and porcelain. The oxygen below high temperature is in before be being contacted with matrix carbon, can build oxidation skin surface layer with its reaction above all, prevent oxygen to diffuse further. Can oxidize the material of pottery and porcelain that makes SiO2 has SiC, Si3N4, MoSi2, WSi2 to wait. Can oxidize the material of pottery and porcelain that makes A12O3 has AIN to wait. Nextpage but above place is enumerated material of pottery and porcelain does not agree with to serve as coating directly. Because consider the issue of the mechanical consistence of coating and matrix even,this is. The stand or fall of mechanical consistence decided coating is applying neuter actually can foreground. If coefficient of expansion is heated up between coating and C/C matrix,had differred big, be in when C/C leave the job to the thermal shock condition of high temperature from room temperature or arrive from refrigeration of tall preparation temperature when room temperature, coating can have the risk that come off and falls off because of producing great thermal stress. From the graph 3 in the hot coefficient of expansion that can compare direction of fiber of material of fireproof pottery and porcelain and edge of high-powered C/C composite material [7, 12] . Compare Si, SiC, Si3N4 and C/C to having with phase of common and fireproof data it is thus clear that relative to better mechanical consistence. What still should notice finally is, should avoid Xu layer to implementation fights oxidation for long to defend excessive in air current of high temperature high speed ablation. Because of layer of Xu of this pottery and porcelain volatile want small. This are realizing prep above 1800 ℃ fight oxidation to defend in appear particularly important. Graph 4 show the vapour pressure that gave material of a few kinds of pottery and porcelain to fall in high temperature [7] . These data make clear ZrO2, HfO3, Y2O3 and ThO2 in prep above 2000 ℃ fall can stabilize existence for long. But these Taozhi material can diffuse in oxygen only after the problem that hold back is solved completely, serve as fight burn layer material, because their oxygen diffuses,lead too tall. As a whole, siC and material of Si3N4 pottery and porcelain from hold back oxygen to diffuse, the mechanical consistence with C/C matrix, fighting burn ability is idealer for these a few respects fight oxidation coating material. But material of these two kinds of coating be confined to is used below in 1800 ℃ . Prep above 1800 ℃ , the cent of aeriform reaction child is pressed between surface layer of SiO2 oxidation skin and ground floor be more than 0.

1MPa(1atm) , make coating rapid invalidation [7] . What still should notice additionally is, pottery and porcelain of this kind of silicon radical is met in the stability in containing melt salt, vapor or hydric environment drop. Melt salt for instance Na2SO4 and Na2CO3 can arise from the impurity in fuel, they lay layer of oxidation of OK and deliquescent SiO2 in high temperature. Vapor and SiO2 reaction generate aeriform production Si(OH)4, and H2 reductive SiO2 makes SiO gas. All these reaction can quicken coating invalidation. Accordingly, if C/C composite material is in slashing special environment atmosphere,work, need the arrange inflict with be adopted certain restricts above the happening of adverse reaction, if be on coating of silicon radical pottery and porcelain besmear Fu Ta2O5, ZrO2 or Si2N2O [13, 14] . Normally the circumstance falls, fight oxidation experiment to be in pure dry oxygen or undertake in air, did not consider the impact of these elements commonly so. 3 fight system of coating of oxidation pottery and porcelain 3.

System of 1 monolayer coating is narrated like preamble place, it is idealer that material of silicon radical pottery and porcelain is like SiC and Si3N4 fight oxidation coating material. Use SiC of CVD law preparation and Si3N4 coating normally. Deposit temperature is controlled in 1100 ℃ [15, 16] . Because CVD law technology is sophisticated and cost is high. Grew a few low cost in recent years replace craft. WuTsung, Ming studies diffuse agglomeration craft [17, 18] , use what liquid state Si and carbon of C/C surface layer fall in 1600 ℃ to diffuse coating of reaction preparation SiC. Chen, ChiM. The person such as Ma developed reaction agglomeration technology. This craft mixes pink of right amount silicon and epoxy resin and besmear Fu gets carrying coating on the head on C/C matrix, use beforehand the coat of reaction preparation SiC that pink of the silicon in coating and hot solution of colophony of oxygen of 1800 ℃ firing temperature runner band get carbon [19] . If WSi2, MoSi2 and HfSi2 also are had,silicon changes thing fight oxidisability goodly, because below high temperature they and oxygen reaction generate SiO2 oxidation layer to be able to prevent farther combustion,this is. But differ as a result of as hot as C/C coefficient of expansion big, silicon changes content not to suit to serve as coating directly. Scholar of domestic and international research turns silicon content and other and difference of C/C matrix hot coefficient of expansion material of little pottery and porcelain is complex can solve this one problem as coating material. H. S. The Si that the person such as Hu studies, coating of Hf-Cr frit oar, disperse HfSi2 in Yu Gui [10] . The person such as Cheng Laifei of university of industry of our country northwest used similar technology to develop Si, Mo, Si, W coating [21. 22] . The person such as Ceng Bianrong disperses MoSi2 the ability that fights oxidation for long at containing the coating that packet of earning that bury a law uses to arrive in Si glass photograph to have 1500 ℃ [23] . But common monolayer coating comes true very hard to arrive from temperature of C/C oxidation threshold of the total temperature limits of high temperature fight oxidation to defend, because these craft are finished below high temperature, the hot coefficient of expansion that compares direction of C/C edge fiber as a result of material of these coating of pottery and porcelain is big, should cool from excellent equipment temperature room temperature, generation of Xu layer interior pulls stress, make coating appears crackle. Crackle becomes the passageway that oxygen diffuses to make oxygen and C/C matrix contact produce oxidation then. Because this should take certain step,close crackle. Nextpage3.

2 multilayer coating system is close the crackle of onefold Xu layer, commonly used method is layer of other pottery and porcelain introduces to rise to close in the surface layer of SiC or Si3N4 or ground floor the action of crackle. Developed to make coating of great layer pottery and porcelain defend on this foundation system. Its fight oxidation to defend the feature is shown 5 times like the graph [10] . Limits of inherent antirust temperature is to show the temperature that beginning to produce crackle and coating limit use the range between temperature. Inside this temperature limits, the place of oxidation surface layer that crackle is shut by mechanical ground or is produced by reaction closes. Be in early 1934, a kind of material with carbon element mentions in a patent of company of completely beautiful carbon fight oxidation to defend coating system, this system is by CVDSiC ground floor and surface layer of B2O3 glass ceramics are formed. Surface layer of B2O3 glass ceramics rises to close the action of crackle. P2O5 and SiO2 also had been mentioned in patent, but the effect that is inferior to B2O3 is good. Hot structure C/C fights oxidation to defend begin about at 70 time metaphase, crackle closes the choice of coating material basically is centered in ceramics of these 3 kinds of glass [7] . These crackle close of coating apply what improved whole coating system on certain level to fight oxidation function, but did not realize prep above of 1000 ℃ fight oxidation for long to defend. B2O3 is very sensitive to vapor, the water member that joins below microtherm is when temperature is higher release, bring apparent bulk change, make B2O3 layer flakes. Additionally B2O3 is in what 1000 ℃ meet prep above evaporate to restrict B2O3 to fall in higher temperature thereby in great quantities to use [24] . P2O5 restricted it to be able to be in only as a result of problem of evaporate ask a question quite small temperature area is valid. And the viscosity below SiO2 low temperature is tall, cannot rise to close in microtherm area the action of crackle. Can from close to crackle layer material modified and close in crackle on the layer again two respects solve the coating outside deposit above problem. F. J. Buchanan and J. A.

The CVDSiC/ square spar that Little studies / CVDSiC is multilayer in the system [25, 26] , in adding Na2O B2O3, be opposite with reducing B2O3 the sensitivity of vapor. And add SiO2 to be able to restrain what B2O3 falls in high temperature to evaporate. Document [mention in 27] in close B and SiC grain are added in the agent, raise coating fight oxidation to defend function. Its coating system is CVDB/CVDSiC/ contains layer of boracic pink glass / contain SiC glass layer. Since B2O3 issued a large number of evaporating to restrict the service life that Xu layer leaves in high temperature in high temperature, can close in glass so CVDSiC of Fu of layer surface besmear is in what high temperature falls to evaporate with reducing B2O3. But the layer of methodological deposit SiC that uses CVD on B2O3 directly is considered as improper, because sink high to accumulate temperature and evaporate ceaselessly,meet when SiC [25] . Because this can choose B, B4C and ZrB2,close as crackle layer. They can oxidize the action that forms B2O3 to remove crackle to close then. S. Goujard and L. The CVDSiC/Si-B-C that Vandenbulcke builds or B4C/CVDSiC are multilayer coating system, the course is right of each ply after optimizing a design, can realize 1500 ℃ to fight oxidation for long to defend [11, 28] . 3.

The coating system that 3 Xie escape penetrable crackle to arise is multilayer coating defends the system closes as a result of use crackle technology, make preparation technology sophisticated, rose to make cost. To reduce cost, improve the performance that fights oxidation coating at the same time, developed not to need to use crackle to close in recent years the does not have perforative crackle coating system of coating. From the following 4 respects can realize those who do not have perforative crackle to fight oxidation to defend coating. (Coating of gradient of function of coating of 1) function gradient adopts the successive change that part organizes in coating, implementation heats up gradient of coefficient of expansion to distributing, achieve alleviation thermal stress to avoid the end that crackle produces. Although did not advance the idea of functional gradient coating clearly,scholar of a few research is in in research, but they distributing gradient of coating composition composition, the thermal stress with alleviation coating interior [29-35] . 1995, w. Kowwbel and J. C. Withers uses CVD and CVR technology, successfully preparation flawless C/SiC function gradient transfers coating. Compare with photograph of common CVDSiC/Si3N4 coating, have C/SiC function gradient to pass the system of two kinds of coating that crosses a layer, namely layer of CVRC/SiC function gradient / Si layer / Si3N4 layer and layer of CVDC/SiC function gradient / SiC layer / Si3N4 layer, fight oxidation function and heatproof shake function to rise significantly. This coating system oxidizes via isotherm of 2 hours of 1650 ℃ experiment, arise without crackle of perforative and whole coating, oxidation weightlessness can be ignorred; Via 20 1650 ℃ (10 minutes) to 600 ℃ (20 minutes) circular oxidation experiment, weightlessness is led under 1 ％ [36] . (Coating of pottery and porcelain of 2) answer photograph adds the composite material of pottery and porcelain of pliable but strong with the grain such as ZrO2, SiC, its rupture tenacity rises somewhat than material of onefold pottery and porcelain. The mechanism that add pliable but strong basically has refine matrix grain, crackle to change direction to change with the photograph of bifurcate and ZrO2 add pliable but strong [37] . Same, in coating of pottery and porcelain the grain such as dispersion ZrO2 or SiC can rise to prevent the action with patulous crackle, implementation does not have the coating system of perforative crackle. Be in early L990 year, d. The generation that the person such as Kehr points out to SiC of deposit of chemical on coating of poor ZrO2 oar makings gas phase will reduce CVDSiC coating crackle [38] . Dan Wenzhong does not have this coating defy oxidation test result. 1997, a. Joshi and J. S. Lee is in Si, on the foundation of Hf-Cr monolayer coating, what what Si contains in using black lead grain and coating is former a reaction, siC grain even ground dispersion is in Si, in coating of Hf-Cr frit oar. Research shows SiC grain rises to refine the grain, action that prevents crackle to expand, raise coating to fight oxidation function thereby, the craft sex that raised preparation coating greatly [39] . The MoSi2 that the bag buries craft preparation, coating of pottery and porcelain of SiC answer photograph, because face of MoSi2/SiC phase boundary can reduce the stress with most advanced crackle to center, make crackle preferential again face of edge phase boundary is patulous, crackle is patulous path is tortuous, form penetrable crackle not easily [40] . (Coating of deposit of 3) low temperature is general the main reason that the tall preparation temperature of coating system is coating generation crackle. If use deposit temperature to oxidize under C/C the preparation craft of threshold temperature, can come true to arrive from room temperature of the total temperature limits of high temperature fight oxidation to defend, and need not use crackle to close technology. Because difference in temperature is small,this is, coating pulls stress in-housely to be able to 't make coating produces crackle possibly; Or although have crackle generation, also can heat up coefficient of expansion to be more than the hot coefficient of expansion of matrix because of coating, when temperature of deposit of temperature prep above (also temperature of threshold of prep above oxidation) when, crackle closes automatically. Document [18] points out through analysis of thermal stress computation, the preparation temperature when SiC coating under 1000 ℃ when, coating can avoid the generation of crackle. But H. T. Tsou and W. The research of Kowbel makes clear, the SiC coat that lays deposit at 300 ℃ with PACVD technology still has crackle to exist. But the crackle of the SiC coat that this crackle wants to compare preparation of common CVD craft is small much. And the amount that PACVDSiC ground floor reduced crackle of the coating outside CVDSiC/Si3N4 [41] . They still use PACVD technology preparation BlC/BN is flawless coating [42] , with PACVDB4C/CVOSi3N4 coating [43] . Two kinds of systems protect hold to fight oxidation function goodly with 1300 ℃ in 900 ℃ respectively. (The coating with 4) and little difference of C/C matrix hot coefficient of expansion makes the prime cause of common coating occurrence crackle is coefficient of expansion heats up between coating and matrix do not match. If choose difference of as hot as C/C matrix coefficient of expansion,the fireproof material of likeness of rule of small, change regards coating as material. But from go up at all avoid crackle generation. DineshK. The research of the person such as Agrawal makes clear as a result, [NZP] , NaZr2P3O12 kind some material can be satisfied in material above requirement. The Ca0 in this kind of material.

5Sr0.

5Zr4P6O24(CSZP) , SrZr4P6O24(SZP) and Bal. 75Zr4P5. 65Si0. 35O24(BS17) is optimal await select material to expect. They can stabilize existence for long in air below 1500 ℃ . The method that uses hot pressing agglomeration will [NZP] kind on C/C of material Xu Fuyu, what can realize 1200 ℃ is long fight oxidation to defend [21] . In chlorine atmosphere, the CVD(B+Si)N coating of hour of L of 1500 ℃ heat treatment and C/C matrix heat expand rate is adjacent, it is compact consequently flawless, can realize 1500 ℃ to fight oxidation for long to defend [44] . 4 conclusion Si base material of pottery and porcelain is used as C/C extensively to fight oxidation coating material like SiC and Si3N4. As a result of the existence of crackle, common and onefold coating realizes total temperature limits very hard fight oxidation to defend. Use crackle to close the technology can solve this one problem, but can make cost of complex, preparation improves preparation technology. The coating system that does not have perforative crackle can make defend function rises, reduce coating preparation cost. CNC Milling