Preparation Of Homogeneous Mullite Based Fibrous Ceramics By Starch Consolidation

High temperature thermal insulation has attracted broad attention both since last century.With the development of the high temperature thermal insulation material,the performance requirements of this material have become demanding in many countries.The interior and external three-dimensional structures of the fibrous porous ceramic directly influence the thermal conductivity,weight and mechanical properties of the spacecraft.In order to meet the overall performance requirements,this paper designed a new mullite fibrous porous ceramic with a uniform three-dimensional structure.In this study,mullite fibers were selected as the matrix material,silica sols were chosen as the high temperature binders and the mullite fibrous porous ceramic with homogeneous interior and external structures was prepared by starch consolidation.The study found that the cationic starch with positive charges,which could absorb with negative charged silica particles,would prevent silica sols from diffusing to sample's surface effectively during gelatinizing process at high temperature,consequently ensuring the uniform structure of porous ceramics.Furthermore,the cationic starch could also evaporate completely during the sintering process and ensure the high porosity of porous ceramics.The microstructure and energy dispersive analysis showed that both the interior and surface of the fibrous porous ceramics fabricated by starch consolidation owned excellent three-dimensional skeleton structure,meeting the structure requirements in actual engineering.The formulations and preparation techniques of starch consolidated fibrous porous ceramics were optimized and the effects of cationic starch content,silica sols content and sintering temperature on samples'porosity,density,thermal conductivity and mechanical properties were also investigated.The experimental results showed that the sample owned good three-dimensional structure,high porosity,low density and relatively high compressive strength when the cationic starch content and silica content were 15 wt%and 12.5 wt%,respectively.When the sintering temperature was1500 ~oC,the silica sols in the sample would melt completely and bond the fibers as a whole,which could resist the load and bear the pressure.