Study On The New Preparation Process Of Silica Sol

A new preparation process of silica sol with good perspective and some value in production and application has been described, which adopted modified silicon dissolution method, prepared silica sol by hydrolyzing silicon powder with catalyst. The process, borrowing ideas from particle-growing method, fell silicon dissolution method into two steps of preparation of nuclear parent and colloidal particle growth and prepared large particle size stable silica sol with good evenness through repeating colloidal particle growth and colloidal particle finishing. This process could control freely colloidal particle size and produce series product of different sizes to satisfy require of diverse application fields.The effects of multiplicate technical factors on the properties of products, such as addition and adding style of silicon powder, SiO₂ concentration of mother solution reaction temperature, pH value and time, have been studied by way of single factor experiments and orthogonal design. And marked degree of each technical factor's effects on the properties of products was confirmed by the variance analysis of orthogonal experiment. It was prepared of series product with average diameter 10nm, 20nm, 40nm, 60nm, 80nm and 100nm, and the optimum technological conditions of every step were also screened out. After concentration, SiO₂ mass fraction of the products could reach to above 40%, with viscosity less than 10 mPa·s and good stability. It showed that the products have well size distribution by laser scattering particle size distribution analysis (LSPSDA) and TEM characterization.Colloidal particle finishing, which could be used to improve product uniformity, was put forward in the research, drawing the mechanism from grain ripening in crystallizing process; Along with the increase of silica sol size, the rate of silicic acid polymerization gradually reduced, which seriously affected preparation of large size silica sol, wherefore it was put forward to add silicic acid polymerization catalyst to improve the speed and the results showed that this method has obvious effect; At last, it was studied that silica sol was surface modified with blocking agent to improve the stability of the silica sol, and it was prepared of stable silica sol with neutral pH range, which could be applied in expanded field. It showed that the hydroxyl groups on the surface of colloidal particle were partly substituted for methyl group by FT-IR characterization.In addition, this paper also explored mechanism of silicon powder hydrolysis and polymenrization process on the base of previous theory and analysis experimental phenomenon and results. The mechanism can well explain why the pH value of system reduced in the silicon powder hydrolysis and polymenrization process, and why silicic acids were difficult to plotmerize under the alkaline condition. It can give some academic reference value to silica sol production.