Study On Wet Chemical Preparation And Thermal Insulation Properties Of Oxide Hollow Spheres

With the development of energy-saving and aerospace technology,higher performance coating insulation technic should be developed.The usage of porous structural coatings to improve thermal insulation is an important direction of current research.Inorganic oxide hollow spheres have outstanding advantages:low thermal conductivity,good monodispersity,adjustable morphology,accessible raw materials.Also,it can be put into large scale production,many surface modification methods can be applied to and.Thus,Inorganic oxide hollow spheres are the most used for porous thermal insulation coatings.The epoxy polysiloxane resin main chain has a relatively unique Si-O-Si skeleton structure with high thermal stability,good insulation and good weather resistance,and good compatibility with oxides.Therefore,this paper mainly uses alumina and silica hollow spheres as thermal insulation fillers and epoxy polysiloxane as coating matrix to develop a kind of thermal insulation coating with excellent comprehensive performance.In this paper,a class of alumina hollow microspheres with good dispersibility and high sphericity were prepared by PO-driven sol-gel method.The impact of aging time,water-alcohol ratio,the amount added propylene oxide,reaction temperature and the heat treatment temperature on the microstructure of alumina hollow microspheres has been studied.The microstructure and formation mechanism of alumina spherical particles were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).Silica hollow nanospheres with good monodispersity,high sphericity and adjustable wall thickness were prepared by template method and sol-gel method.Scanning electron microscopy(SEM),transmission electron microscopy(TEM)and particle size analysis were applied to as-synthesized nanospheres.The effects of the amount of polyacrylic acid,and ethyl orthosilicate added and the washing times on the microstructure and morphology of silica particles were studied.The composite thermal barrier coating of epoxy polysiloxane resin incorporating alumina and silica hollow spheres was prepared by a spray coating process.The comprehensive properties of the coating were studie by the contact angle tester,pencil hardness tester,thermal conductivity tester,spectrophotometer,and universal tester.Main research work includes:(1)Alumina hollow microspheres with good dispersibility and high sphericity were prepared by sol-gel-driven sol-gel method,and the formation mechanism was explored.The effects of water-alcohol ratio,aging time,propylene oxide addition,hydrothermal temperature and heat treatment temperature on microstructure were studied.It found that the reaction product gradually transforms from a solid sphere to a hollow sphere as the aging time increases.When the amount of aluminum chloride hexahydrate added was 4.35 g,the ratio of water to alcohol was 1:0.54,the amount of propylene oxide added was 7 mL,and the reaction temperature was 30 ?,urchin-like alumina hollow microspheres were obtained.The alumina hollow microspheres were incorporated into an epoxy silicone resin to obtain a composite thermal insulation coating.The performance of the thermal insulation coating including contact angle,hardness,thermal conductivity,reflectivity and adhesion were investigated experimentally.It was found that with the increase the amount of alumina hollow spheres,the coating contact angle was reduced from 96.6 ° to 70 °,the hardness remained at 4 H,and the thermal conductivity was reduced from 0.92 W/(m·K)to 0.32 W/(m·K),the near-infrared visible band reflectance increased from 44.64%to 61.03%,and the adhesion remained at around 31 MPa,indicating that the introduction of alumina hollow microspheres had an obvious effect on improving the coating performance.(2)Hollow silica nanospheres with good monodispersity,high sphericity and adjustable particle size and wall thickness were prepared by sol-gel method and soft template method.The regulation of the amount of polyacrylic acid,the amount of tetraethyl orthosilicate added,and the washing times on the morphology of silica spheres were studied experimentally.It was found that when the amount of polyacrylic acid added was 0.3 g,the amount of tetraethyl orthosilicate added was 1.75 mL,and the number of washings was 3 times,a hollow silica nanospheres with a particle diameter of about 100 nm and a wall thickness of about 17 nm,were obtained,and the product has a smooth surface and a high degree of sphericity.The silica hollow spheres were incorporated into an epoxy silicone resin to obtain a thernal barrier coating.The performance of the thermal insulation coating contact angle,hardness,thermal conductivity,reflectivity and adhesion were investigated experimentally.It was found that with the increase of silica hollow spheres,the coating contact angle was reduced from 96.6 ° to 76 °,the hardness was remained at 4 H,and the thermal conductivity was reduced from 0.92 W/(m·K).0.30 W/(m·K),the near-infrared visible band reflectivity increased from 44.64%to 63.39%,and the adhesion remained at around 17 MPa,indicating that the introduction of silica hollow microspheres had a significant effect on improving coating performance.