Nano silica belongs to inorganic non-metallic nanomaterials,with particle sizes ranging from 1-100nm.It has strong adsorption,good plasticity,high magnetoresistance,and low thermal conductivity,and has been widely used in the electronic metallurgy,aerospace,and pharmaceutical and health industries.Moreover,due to its specific advantages such as small particle size,high chemical purity,and good dispersibility,it has become the most promising new inorganic material,providing a high-quality material foundation and technical support for the development of many related industries.Its broad commercial prospects and economic value have become a hot topic in scientific research,including its preparation,purification,chemical reactions,and properties and applications.
　　1.1 Chemical properties of nano silica
　　Nano silica is an important member of nanomaterials,which is a white amorphous powder,non-toxic,odorless,and pollution-free non-metallic material.Its microstructure is flocculent or network like quasi particle structure,and it is spherical.
　　Nano-SiO2,as a nano powder,its volume effect and quantum tunnel effect make it penetrate into the vicinity of theπbond of the polymer compound,overlap with the Electron cloud of the polymer compound,and form a spatial network structure,thus greatly improving the mechanical strength,toughness,wear resistance and aging resistance of the polymer material.Therefore,people often use the special structures and properties of nano SiO2 to modify plastics and coatings or prepare organic SiO2 composite materials to improve the comprehensive performance of organic polymer materials.
　　1.2 Optical properties of nano silica
　　As a nano powder,nano SiO2 has different optical properties from conventional materials due to its small size effect and surface interface effect.By using a spectrophotometer to test nano SiO2,it was found that its reflectivity in the short wavelength range of 200-280nm ultraviolet light is between 70%and 80%;For the UV mid band with wavelengths of 280-300nm,the reflectivity is above 80%;The light reflectivity of nano SiO2 materials reaches 85%between wavelengths of 300-800nm;The reflectivity of near-infrared light with wavelengths ranging from 800 to 1300nm also reaches 70-80%.
　　This special structure endows it with unique properties:nano silica has a reflectivity of up to 70%to 80%for ultraviolet radiation within a wavelength of 490nm.Adding it to polymer materials can achieve the goal of resisting ultraviolet and thermal aging.
　　1.3 Other properties of nano silica
　　The small size effect and macro quantum tunneling effect of nanometer silicon dioxide make it produce silting effect,which can go deep into the vicinity of the unsaturated bond of the polymer chain and interact with the Electron cloud of the unsaturated bond to improve the thermal,optical and chemical stability of the polymer material,thus improving the anti-aging and chemical resistance of the product.Moreover,it not only has specific advantages such as small particle size,high chemical purity,and good dispersibility.It also has the advantages of strong adsorption,good plasticity,high magnetoresistance,and low thermal conductivity[2].
　　2.The processing technology of nano silica
　　2.1 Preparation of nano silica
　　The process for preparing silica is divided into dry method and