Study On Thermal Conductivity And Compression Performance Of SiO₂-based Fibrous Insulation

Ceramic fibrous insulation is the main materials used in metallic thermalprotection system. The insulations have many advantages, such as a low thermalconductivity, reusable, etc.In present paper, the numerical model of the heat transfer process in ceramicfibrous insulation has been established, so it is possible to analyze the changes of theeffective thermal conductivity. It is found that heat transfer processes includes gasconduction, solid conduction and radiation heat transfer. The gas thermal transfermaterial is the main factor at low temperatures, while radiation heat transfer becomesan important factor at high temperatures. Compared with the test results, the calculatedthermal conductivity has the same changes. It is found that density and pressure are themost important factors for the effective thermal conductivity, and should be noticedduring the actual application process.Ceramic fibrous insulation materials were used for the SEM observation toanalysis the characteristics of fiber distribution. It is found that the fibers randomlydistribute in the horizontal direction inside the ceramic fibrous insulation, and thefibers stack layer by layer in the vertical direction. The layer spacing, pore size arerelated to the density. Increasing density will leads to an increasing number of fibers,reducing fiber pore size, increasing number of fiber nodes, reducing spacing betweenadjacent layers.Samples with different sintering conditions have been done the compression testsand SEM observation, in order to study the relation between mechanical properties andsintered conditions. It is found that the sintering conditions and number of fiber nodesdirectly affect the mechanical properties of the insulations, and appropriate sinteringprocess lead to best mechanical properties. Stress-strain curve includes linear elasticstage, yield plateau stage and densification stage; and the over-burning is most harmfulto the material's application.Insulation's microstructure is modeled by software GeoDict. The pore sizedistribution and related thermal, mechanical properties of the model are calculated bythe GeoDict software. It is found that fiber pore size shows roughly normal distribution.Besides, greater the model's density, the smaller the pore size, and more uniformdistribution. It is found that there is difference between the calculated mechanicalproperties of the model and the actual results, but the trends are same, and needs further parameters optimism.