Study On The Preparation And Properties Of Mullite-based Rigid Porous Insulation Materials

With the rapid development of hypersonic vehicle technology, the rigidinsulation material with high-temperature resistance has attracted more attention.High-tempeature rigid insulation materials have low density, low thermal conductivity,and low thermal expansion. In this paper, mullite-based ceramic fibers is chosen toprepare the rigid porous insulation materials via moulded drainage and pressurelesssintering. The processing technology, microstructure, coating and ablation behaviorwas investigated.In the test method part, the Archimedes method was used to measure the densityand porosity of the porous insulation materials. Compressive experiment of the porousfiber material is determined to evaluate its mechanical property. The microstructure isobserved and analyzed with scanning electron microscopy and the element analysis isstudied byb the spectrum analyzer. Lastly the oxyacetylene ablation test is performedto investigated the mullite-based porous fiber mateiral with high radiation coating.The experimental results showed that PAM (polyacrylamide) is the optimumdispersant in the slurry, and the quantity is about2wt%of the total fiber mass. Thefiber adhesive can be the mixture of silicon carbide and boron carbide. The optimummass ratio for SiC and B4C is1:1. The length of mullite fiber is about1~2mm and themoulding pressure is100KPa. The optimum parameter of the preparation technologyis as following: the green body is dried for24h at room temperature, and then placedin muffle furnace for sintering. During heating stage,the heating rate is2℃/min fromroom temperature to500℃, keeping temperature for120min. The heating rate is5℃/min to1200℃.The SiC and B4C for fiber adhesive can formed boron silicate glasss in hightemperature, and the boron silicate glasses is fludity and can hardly evaporate, whichcan bind the chopped ceramic fiber tightly. After sintering, it can be found thecompressive strength was influenced by the density to a great extent. The strenghincreased from0.84MPa to7.24MPa when the material density varied from0.43to0.79g/cm3.The high radiation coating layer is prepared via slurry spraying and sinteringmethod on the material surface to enhance the insulation performance. The Internalcoating for94wt%of silicon oxide and6wt%of boron oxide, the outer coating is50wt%of TaSi2,20wt%of MoSi2,2.5wt%of SiB6and27.5wt%of borosilicate glass,in order to improve the high radiation of surface in high temperature. The experiments show that after coating the mullite-based rigid porous insulation material is with goodinsulation properties, ablation300s under1600℃conditions, and the temperature ofthe back does not exceed80℃. Through the surface and cross section of the ablativematerial microstructure analysis showed that the microstructure of mullite fiber1.5mm below the surface keeps well under the protection of the coating. Overallmullite-based rigid porous insulation material with coating shows non-ablativecharacteristics. Analyze the mechanism of the protective surface coating on themullite-based rigid porous insulation materials.