| C/C composite is a novel material with high performances at high temperature in the new material fields.It plays an important role in the high technology fields such as aerospace,aeronautic and civil industry. However,C/C composite has the worse anti-oxidation performance in oxygen circumstance.It has been found that C/C composite occurs to have oxidation reaction over 370℃at oxygen ambience,its reaction speed also rapidly augments at 500℃,leading to destructive damage of materials. Therefore,it is very important that C/C composite has the reliable anti-oxidation protection at high temperature.Firstly,the oxidation kinetic model and mechanisms of C/C composite was studied.A system of high temperature oxidation resistance coating of SiC/Mo(Six,Al1-x)2 for C/C composite material was produced with a two-step solid reactions technique.Major components of the coating are SiC,Mo(Six,Al1-x)2 with trace of Mo4.8Si3C0.6.Chemical reaction thermodynamic analysis shows that the formation of the composite coatings is based on a two-stage mechanism:low and high temperature stages.During the low temperature stage(below 1750℃),the melted silicon impregnates in and reacts with carbon composites leading to the formation of SiC,which builds up a thicker inner layer of the coating; During the high temperature stage(～2000℃),complex multiphase chemical reactions occur among SiC,MoSi2 and Al2O3 leading to the formation of metal-ceramic Mo(Six,Al1-x)2 compound and a whisker SiC phase,which build up the top layer of the composite coatings. Thermodynamic and chemical reaction analyses fit completely to the experimental results.Additionally,a very dense composite coating was prepared with the raw powders composing of Si 10%,Al2O3 10%,SiC 54%and MoSi2 26%,the coating exhibits less sintering with the surrounding powders.The Mo(Six,Al1-x)2 material has the better anti-oxidation performance than MoSi2,so the Mo(Six,Al1-x)2 was selected as the sealing reagent of compound coatings.Add different content Al in the fixed quantity MoSi2 powder to prepare the material Mo(Six,Al1-x)2.With the incensement of Al, the peak intensity of Mo(Six,Al1-x)2 also increases.The results indicated the CL03 Mo(Six,Al1-x)2 had the better oxidation resistant performance by the comparison analysis of high oxidation experiments.Making use of CL03 Mo(Six,Al1-x)2 to cover the carbon/carbon composite's SiC/Mo(Six,Al1-x)2 compound coatings as sealing reagent,having anti-oxidation experiment. Be oxidized 2h,5h,10h,15h,20h respectively at 1500℃,the coatings had been oxidized,but the C/C composites hadn't lost weight,got promising oxidation resistant result.
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