Preparation of silicon dioxide nanoparticles and Study of eliminating hydroxide

摘要

Taking ammonia as catalyst and propanol as solvent, white deposition was synthesized via hydrolysis and polycondensation reactions by hydrolyzing tetraethylortho-silicate, then washing it with distilled water until it is neutral and washing it two times with ethanol, finally silicon dioxide nanoparticles were gained after baking. The experiments study the reactants and reaction conditions such as reaction temperature, concentration of ammonia and stirring intensity etal.. The results show that the particle size increases immediately when the concentration ammonia, the reaction temperature and the stirring intensity are increased, and the size of the silicon dioxide particle is subjected to the changes of these preparation parameters. Scanning electron microscope show the prepared nanoparticles take on inerratic sphericity and the granularity distributes uniformity. The experiments discover that hydrolysis of tetraethylortho-silicate is rapid and the polycondensation response is the controls step under ammonia as the catalyst by taking samples in reaction process. Because the radius of OH- is small as 0.09nm, which directly attacts Si atom of tetraethylortho-silicate, as a result, Si atom with negative electric charge causes excursion of -C2H5, the Si-O chemical bond was weakened and finally ruptured. And once the first -C2H5 was substituted by OH, the nest step is easier to carry on, lastly the hydrolysis was completed. The SiO2 content is only 86.72% in prepared sample, the infrared spectrum analysis show there is much hydroxide. The experiments of eliminating hydroxide were carried on for purifying SiO2, which are baking the sample in muffle under different temperature. The sample does not lose weight after 800℃ and the agglomeration phenomena appear when the temperature achieves 900℃, when the SiO2 is noncrystal all the same. The SiO2 content is up to 99.92% in the sample after eliminating hydroxide via analyzing by Liaoning province academy and analytic sciences. The TG-DTA tests show that the sample loses weight apparently in the ranges of 80-150℃ and 480-550℃, homologous there are two endothermal peaks; around 1200℃ appears the third endothermal peak with no losing weight, which is the transformative peak of crystal, and the XRD analysis prove it. According to , the activation energy of the endothermal peak for eliminating hydroxide was obtained by adopting Doyle-Ozawa, Kissinger and Coats-Redfern calculational methods, the reaction order and frequency factor were determined by making use of Kissinger method, finally the kinetic equation was deduced.