Preparation Of Alumina Ceramic Hollow Microspheres By Spray Drying

Alumina ceramic hollow microspheres(ACHMs)have been regarded as a potential high temperature thermal protection material in the field of national defense due to their light weight,high strength,high temperature resistance,corrosion resistance and good physical and chemical stability.In this paper,ACHMs with a diameter of 5-30 μm were prepared by spray drying process using nano-alumina powder as raw material.The effect of microsphere properties was investigated,and hollow microspheres with completely dense surface were obtained by vacuum impregnation with polycarbosilane(PCS).The main research contents of the paper are as follows:Firstly,The synthesis of zirconium-oxygen organic-inorganic polymer(PNZ)was studied.Using zirconium acetate,acetylacetone,yttrium acetate,acetic acid and ammonia water as the main raw materials,the zirconium-oxygen polymer was synthesized by a controlled hydrolysis reaction,and deionized water was used as the solvent.The desired ceramic precursor is used as a binder for preparing alumina hollow microspheres.Secondly,in this paper,nano-alumina powder is used as the main raw material,silica sol(30-50 nm,solid content 18.42%)as filler,PNZ aqueous solution is used as binder,and polyethylene glycol(PEG,molecular weight 20000)is used as surfactant.Micron-sized alumina ceramic hollow microspheres were prepared by spray drying.The effects of spray drying process parameters and slurry formulation on hollow microspheres were studied.The results showed that: when the spray drying temperature was 130 ℃,the feeding rate was 2mL/min,alumina powder: PNZ aqueous solution: silicon When sol:surfactant:solvent water=10:5.86:16.64:1:90(mass ratio),the comprehensive performance of hollow microspheres is the best.At the same time,different alumina powder ratios will also affect the size and uniformity of the ceramic hollow microspheres.It is finally determined that the alumina powder with D50 of 300 nm and 100 nm is the mass ratio of 3:7,the obtained ceramic hollow microspheres The size and uniformity of the microspheres are the best.Thirdly,The effects of curing and sintering temperature on the properties of hollow microspheres were studied,and the results showed that the densest ceramic hollow microspheres were obtained when the curing temperature was 200 ℃ and the sintering temperature was 1000 ℃.The ceramic hollow microspheres were further vacuum-impregnated and sealed with polycarbosilane(PCS)to obtain alumina ceramic hollow microspheres with a completely dense surface.The final bulk density of the ceramic hollow microspheres is 1.8759g/cm3,the total porosity is 39.49%,and the compressive strength is 1.5 MPa,which can initially meet the relevant application requirements.In conclusion,this paper systematically studies the spheroidization factors of alumina ceramic hollow microspheres,and explores the effects of raw material formulation,spray process parameters,debinding and sintering temperature on the microscopic morphology and properties of ceramic hollow microspheres,and uses PCS vacuum impregnation.,After curing and sintering,ceramic hollow microspheres with completely dense surface are obtained.The research results of this paper have made a very useful exploration for the technical accumulation and progress of ceramic hollow microspheres for aerospace thermal protection.