Study On Drying Parameters And Anti-oxidation Codting Of Reticulated Vitreous Carbon Foam Filled With Al₂O₃Aerogel

The research of lightweight insulation composite material is an important topic ofthe thermal protection system in the domain of space. Al₂O₃aerogels and reticulatedvitreous carbon foam are two kinds of important lightweight thermal insulationmaterials, but both of them have shortcomings. Al₂O₃aerogel is completely transparentto infrared radiation and is of low mechanical strength and high brittleness, it cannot bedirectly used as heat insulation material; In the research, the porous structure ofreticulated vitreous carbon foam determins that it can be used as the mechanicalenhancement structure of Al₂O₃aerogel, Therefore, in this subject Al₂O₃aerogel isfilled into the pore of reticulated vitreous carbon foam, to make up the shortness of eachother, thus develop a composite material of higher mechanical strength, lighter weightand excellent heat insulation property.Through lots of experiments, the subject studied drying parameters of reticulatedvitreous carbon foam filled with Al₂O₃aerogels and the preparation of anti-oxidationcoating on the carbon foam surface.The atmospheric pressure drying method and freeze-drying method were studied respectively, and in the study of freeze-drying method,twosolvents were used:water and tert-butanol.The observation of the composite materials under scanning electron microscopy（SEM） shows that the product made by atmospheric pressure drying method is filledwith Al₂O₃aerogels but seriously shrinkage, the aerogels present a crack plate shape,strip with the structure of carbon foam, and lose the original porous features of aerogel.Products prepared by freeze-drying method show a structure of dendritic morpholoy,with space of sheets about10um, thickness of skeleton about5um.The aerogel betweenthe carbon foam is holisticly; there is a physical adhesion effect between aerogels andbubbles of carbon foam.The results of the compressive performance test show that the composite materialshares a similarly compression curve characteristics with the carbon foam, both of themshow the characteristics of sag curve.The major load-carrying structure of the compositematerial is the skeleton of carbon foam.Thermal analysis was carried out on the products, and the results show that the heatinsulation performance of the composite material is greatly improved after filled with alumina aerogel, especially the products made by freeze-drying method. Three carbonfoam templates were used to prepare the products, the reduced amplitude of threetemplates products made by freeze-drying method respectively are23.52%,23.58%,3.74%.After filling alumina aerogels,the density of the composite material is improved bydefferent extent.The products made by freeze-drying method are respectively improvedby93.77%、66.60%、71.86%,and atmospheric pressure drying method by60.78%、52.66%、58.82%.The anti-oxidation coating is made by four components,they are SiO2、B2O3、MoSi2、SiB4. In the research, the mothed of paint and sintering is used to close the poreof carbon foam.The observation of coating under scanning electron microscopyillustrates that the surface of coating is uneven due to the skeleton of carbon foam.Theoxidation rate of the composite materials under high temperature is inhibitory,Theweightlessness of the products is reduced from81.78%to22.24%.