Preparation And Properties Of Yttrium Silicate Modified Lightweight Thermal Protection And Insulation Composites

Due to the increasing speed of reusable orbiters,the requirements for thermal protection materials are increasingly stringent.In this context,lightweight thermal protection and insulation composites arise at the historic moment,combining the advantages of light weight,high porosity and low thermal conductivity of the thermal insulation layer and high temperature resistance,good ablative resistance and oxidation resistance of the thermal protection layer,thus anti heat integration is realized.In this paper,the system design,process optimization and material preparation of the porous thermal insulation matrix and the dense thermal insulation layer are carried out,and a new method for the preparation of lightweight thermal insulation composite materials is proposed,which lays a foundation for the prFor thermal insulation layer,this paper optimized the carbon fiber woven body acupuncture as insulating substrate,and the carbon fiber surface C/SiO₂ composite coating was prepared in order to solve the problem of poor oxidation resistance.That is because SiO₂ coating has excellent oxidation resistance and low thermal conductivity,not only can inhibit the oxidation of carbon fiber in the high temperature aerobic environment,but also can lower the thermal conductivity of insulating layer,while C coating can prevent the carbon thermal reduction reaction of carbon fiber and SiO₂ coating at high temperature.How the mass fraction of glucose solution,water fluid temperature and the water thermal response time influence C coating micro-structure is explored,and the C coating was prepared on the carbon fiber surface with 30 wt.% glucose solution as the raw material,180? as the hydrothermal reaction temperature and 2h as the hydrothermal reaction time,on this basis,the effects of TEOS mass fraction,water/ethanol molar ratio and sol-time on the microstructure of SiO₂ coating were investigated,moreover,the SiO₂ coating was prepared on the carbon fiber surface containing C coating with 30 wt.% TEOS solution as reaction raw material,6:1 as water/ethanol molar ratio and 2h as sol-gel time,finally carbon fiber braid containing C/SiO₂ composite coating was obtained.The test and analysis results of the performance of braids of different components show that the introduction of C/SiO₂ composite coating on the surface of carbon fibercan reduce the weight loss rate of braids by 30% under the aerobic atmosphere of1200?,which indicates that it effectively improves the antioxidant performance of thermal insulation layer,meanwhile,the introduction of C/SiO₂ composite coating also significantly increases the compression strength of braids.For the thermal protection layer,the yttrium silicate with high temperature resistance,good ablative resistance and oxidation resistance is selected as the dense layer material.But its sintering temperature is higher,in order to prevent the structural damage of carbon fiber that occurs in high temperature sintering process,the following processes are proposed in this paper.By preparing SiO₂ coating on the surface of Y₂O₃ powder and introducing it into the surface layer of carbon fiber braid,the preparation technology of yttrium silicate dense layer is optimized,and the sintering temperature of the dense layer is reduced to a certain extent.After SiO₂ coating was prepared on the surface of Y₂O₃ powder by the sol-gel method after the process optimization,the influencing factors of sintering of Y₂O₃ powder containing SiO₂ coating were investigated,and the optimal sintering process parameters of yttrium silicate were determined.On this basis,the yttrium silicate dense layer was prepared on the surface of carbon fiber braided by slurry impregnation sintering method.The microstructure,oxidation resistance and ablative resistance of the composite with 2 and 5 times impregnation and sintering were investigated,the result shows that yttrium silicates dense layer can greatly enhance the antioxidant properties of composites,as the mass fraction remains as high as 80% even under 1200 ?aerobic condition,and the dense layer can protect the braid to a certain extent in aerobic ablation environment,especially the dense layer after 5 times of impregnation and sintering can provide effective protection of the substrate for up to 100 min under1000?.