Study On Preparation Of Silica Nanoparticles And Rheological Property Of Dispersion

In this paper, two parts, including preparation, characterization of silica nanoparticles and rheological property of silica dispersions were investigated.1. A method was proposed for the preparation of silica nanoparticles using inexpensive material of sodium silicate (Na₂SiO₃) and carbon dioxide (CO₂) by pressured carbonation, in which carbon dioxide acted as a precipitating reagent. Microstructure and size analyses of the precipitated silica nanoparticles were carried out using transmission electron microscope (TEM), scanning electron microscope (SEM), N2 adsorption (BET), X-ray diffraction (XRD) and (laser particle size analyzer) DLS. The average particle size, size distribution and yield of silica nanoparticles were affected by reaction time, temperature and concentrations of surfactant and sodium silicate solutions. The particle size of silica nanoparticles increased with reaction temperature and concentration of sodium silicate, and the yield of silica nanoparticles increased with increasing reaction time. The size distribution of silica nanoparticles was affected by concentration of surfactant. The optimal preparation condition was obtained through orthogonal experiment method. Silica nanoparticles with nanometer size, narrow size distribution, sphere in shape, high yield and purity was prepared under optimum condition.2. In this experiment, preparing silica nanoparticles by hydrolysis of silicon tetrachloride under alkaline solution where the silicon tetrachloride was obtained from the byproduct of polysilicon production. Microstructure and size analyses of silica nanoparticles were carried out using transmission electron microscope (TEM), scanning electron microscope (SEM), N₂ adsorption (BET), X-ray diffraction (XRD) and (laser particle size analyzer) DLS. The effects of the types of alkaline solution, its concentration, postproduction processes and surfactant on the properties of silica nanoparticles were studied in this article. The average particle size and tapping density size distribution were affected by the types and concentration of alkaline solution, while the DBP of silica nanoparticles were affected by post-processing and surfactant. The optimal preparation conditions were experimentally determined for obtaining the silica nanoparticles with nanometer size, narrow size distribution, high DBP value, high BET specific area value and high purity without sodium chloride and surfactant.3. The influence of suspending medium of water (H₂O), glycol (EG), polyethylene (PEG), glycerol (GL) and temperature on the stability and rheological properties of silica dispersions were studied with a stress controlled rheometer. The results showed that the stability of the systems increased as the viscosity increasing, and the systems had reversible shear-thinning and shear-thickening behaviors. Moreover, the microstructure and property of silica nanoparticles had main effect on stability and rheological properties of their dispersions. The storage modulus G', loss modulus G" and tgδhave also been studied through oscillation stress shear. The magnitude of G" was larger than that of G' and tgδ>1 for all of the systems in the range of stress studied, which showed that the systems mainly possess the viscous properties. The dominate influence on viscosity of systems was temperature, and with the increasing of temperature, the viscosity decreased.