Study On Mullite Reinforced Aluminum-chrome Phosphate High Temperature Composite Ceramics Prepared By Cold Isostatic Pressing

High temperature wave-transparent materials are mainly used to prepare radome and antenna window of aircrafts,ensure the normal electromagnetic signal transmission of internal antenna system in pneumatic environment with aircraft flying at high speed.As the requirements for aircraft operation become higher and higher,phosphate composites reinforced with siliceous fiber can not meet the requirement for aircraft high-speed flying.Combining with the research status of high temperature wave-transparent materials,ideal high temperature wave-transparent materials integrated with mechanical properties,dielectric properties and thermal shock properties have not been found yet.In terms of aluminum-chrome phosphates substrate materials with fine dielectric properties,high temperature performance and low mechanical properties,introduction of high strength mullite particles or whiskers improves the mechanical properties and thermal shock properties of aluminum-chrome phosphates substrate materials.Mullite particles or whiskers can match the chemical and physical compatibility of aluminum-chrome phosphates substrate materials,and mullite has high thermal stability and low dielectric constant.Meanwhile,in order to take full advantage of the good dielectric properties and high temperature performance of aluminum-chrome phosphates substrate materials,multiphase composite ceramics technology is employed to prepare mullite reinforced aluminum-chrome phosphate composite ceramics.Therefore,this thesis studies preparing mullite reinforced aluminum-chrome phosphate composite ceramics by isostatic pressing molding technology with mullite particles functioning as reinforcement.This thesis mainly studies the effect of milling time,mullite contents,molding pressure,sintering temperature and holding time on mechanical properties,dielectric properties,thermal shock properties and microstructure and morphology of composite ceramics.Research results show the best technical parameters:milling time of raw material is 24h;mullite design content is 400%,among which the contents ratio of SiO2 and Al2O3 is 1 and 2;isostatic pressing molding pressure is 150MPa;sintering temperature is 1500? and holding time is 4h.On this condition,mullite reinforced aluminum-chrome phosphate composite ceramics are obtained,whose porosity,density,flexural strength,Vickers hardness,critical thermal shock temperature difference,dielectric constant and dielectric loss are 2.83%,2.719g/cm-3,178MPa,570Hv,350 ?,<4.0 and<0.05(8?12GHz)respectively.And composite ceramics with fully dense and uniform structure are obtained,in which the uniform distribution of spherical aluminum chromium phosphates and short columnar-shape mullite are clearly visible.