Study On The Preparation Technology Of Ultrafine Silica By Silicon Tetrachloride Gas Phase Hydrolysis Method

As a clean and sustainable regeneration energy resource,solar energy has been received close concern from worldwide in the condition of the resource crisis becomes more and more serious. Solar-grade multicrystalline silicon is an important raw material for preparing solar cells,and the demand of it has been increasing year by year. At present,the world’s70%-85%poly silicon was produced by using improved Siemens method.During this process,a lot of poisonous and harmful byproduct silicon tetrachloride was generated.Effective treatment of silicon tetrachloride directly affect the healthy development of poly silicon industry. Ultrafine silica prepared by silicon tetrachloride was one of the methods of realize silicon tetrachloride harmless, resource and scale treatment. As a kind of important fine chemical, silica is widely used in the fields of rubber,coating,cosmetics because of it’s good reinforcing ability,thixotropy and thickening property.A new process of preparing ultrafine silica by gas phase hydrolysis method has been proposed in this paper. The process use polysilicon byproduct silicon tetrachloride and water glass as raw material. It’s simple operation,safety and high economic benefits relative to other way of treating silicon tetrachloride.In engineering test,several reaction factors such as the ventilation rate of silicon tetrachloride, the concent of water glass,the reaction temperature,the concent of additive,the pH at the reaction ending,the stirring rate and surfactants were investigated on the physical and chemical properties of the ultrafine silica.Integrated single factor experiment, response surface methodology design experiment and surfactants using experiment, the experiment results showed that the optimum process conditions for the preparation of ultrafine silica by silicon tetrachloride gas phase hydrolysis method were confirmed as follows:ventilation rate of silicon tetrachloride was150ml/min when the reactive system was100ml, the concent of water glass was8.6%,the reaction temperature was76℃,the concent of additive was2.7%,the pH at the reaction ending was7,the stirring rate was250r/min,aging temperature and aging time were76℃and9h respectively and the addition amount of LQ-03was2%. The micro-morphology, structure and particle size of samples which were made at the optimum process conditions were made by several detection methods such as infrared spectrum, X-ray diffraction, TEM, specific surface area measuring instrument and particle size measurement. The sample was amorphous silica with good dispersivity and characterized in various aspects as follows:average particle size was215nm, treated surface area was119.99m2·g-1,DBP was3.05ml·g-1, apparent density was0.13g·mL-1, silica content(dry basis) was98.25%, heating loss was6.52%,roasting loss was5.84%and pH was6.9.