Preparation Of Hollow TiO₂ And Composite Microspheres And Their Thermal Insulation Performance

The thermal conductivity of hollow TiO₂ microspheres can be greatly reduced due to the large amount of air in its unique hollow structure.Therefore,it is regarded as a new generation of thermal insulation material with economic and environmental,which plays a vital role in implementing the policy of energy saving and emission reduction.In this paper,hollow TiO₂ microspheres were prepared by a solvothermal template-free method,and organic acids were used as structural inducers.Hollow TiO₂/SiO₂composite microspheres were prepared by using self-made hollow TiO₂ microspheres as templates and flower-shaped hollow TiO₂/SiO₂/TiO₂composite microspheres were synthesized by using carbon spheres as templates.The composite film with good thermal insulation performance was prepared by mixing the microspheres as thermal insulation filler with the economical and suitable polyacrylate by physical blending method.Using formic acid,oxalic acid,malonic acid and citric acid as structural inducers,the effects of structural inducers on the morphology of hollow TiO₂ microspheres were investigated,and the results showed that oxalic acid was the best structural inducer.Based on the reflectance index,the optimal synthesis process conditions for hollow TiO₂ microspheres were determined as follows:reaction temperature 180?,reaction time 18 h,30 m L oxalic acid,0.5 g TBT,and the reflectivity of hollow TiO₂ microspheres to visible light is above 90%.The hollow TiO₂ microspheres were characterized by XRD,SEM,TEM,BET and other characterization methods,the results showed that the hollow TiO₂ microspheres are anatase structure with a lot of mesoporous structures on the surface of the shell layer.The thermal conductivity experiment results showed that the thermal conductivity of the hollow TiO₂ microspheres/polyacrylate composite membrane is 0.1885 W/(m·K)lower than the pure polyacrylate membrane0.21W/(m·K),and the reflectivity of the hollow TiO₂ microspheres/polyacrylate composite film is increased to 65%,which is much higher than 12%of the pure polyacrylate film.Using self-made hollow TiO₂ microspheres as templates,hollow TiO₂/SiO₂composite microspheres were successfully synthesized by the sol-gel method,the particle size of TiO₂/SiO₂composite microspheres was in the range of 2?3?m.Hollow TiO₂/SiO₂composite microspheres were characterized by XRD,BET and other methods,it was found that hollow TiO₂/SiO₂ composite microspheres presented anatase type structure with a large number of pores on the surface of the microspheres.The influence of TEOS amount on the morphology and reflective performance of the microspheres was investigated.It was found that with the increase of the amount of TEOS,the amount of SiO₂coating increased,and the reflectivity of the composite microspheres to ultraviolet radiation increased.When the addition amount of TEOS was 0.5 m L,the ultraviolet reflectance of hollow TiO₂/SiO₂composite microspheres was increased by 100%compared with hollow TiO₂ microspheres.Homogeneous carbon spheres were prepared by a simple hydrothermal method,and characterized by SEM,FT-IR,TG-DSC and other methods.It is found that the size of carbon spheres is about 150 nm,and there is a large amount of-OH on the surface of carbon spheres,which is beneficial to the TiO₂coating.When the calcination temperature is 500?,the carbon balls can be completely removed.Flower-shaped hollow TiO₂/SiO₂/TiO₂ microspheres were successfully prepared by using carbon spheres as template.The effects of the reaction temperature,reaction time,and the amount of hexamethylenetetramine(HMTA)added on the morphology and light reflection properties of the composite microspheres were investigated.It is confirmed that the best synthesis process is:1.0 m L TEOS,reaction temperature200?,reaction time 24 h,4 mmol HMTA,calcination temperature 500?.Under these conditions,the flower-like hollow TiO₂/SiO₂/TiO₂composite microspheres have the most perfect flower-like structure.The reflectivity of TiO₂/SiO₂/TiO₂composite microspheres to visible light is nearly close to 100%.The reflectivity of several composite films was investigated.The experimental results showed that the reflectivity of flower-shaped hollow TiO₂/SiO₂/TiO₂composite microspheres/polyacrylate composite membrane as high as 79%>hollow TiO₂ microspheres/polyacrylate composite membrane 65%>hollow TiO₂/SiO₂composite microspheres/polyacrylate composite membrane 61%.