Study On Preparation Of Silica Microspheres By Stober Method

Silica microsphere was targed for electronic encapsulation with the stober method in this thesis. We summerized the broad application of silica in order to find its potential applications. The origin of stober method was introduced and its extended research work, and the growth model based sub-particle agglomeration and monomer addition were also summarized.In the one-pot method, the effect of reaction time, temperature, concentration of ethyl silicate, water concentration and ammonia concentration on particle morphology, particle size and distribution of microspheres were studied. With the increase of water concentration, the particle size increased. And the reaction is more rapid, in one to two hours, the reaction has been basically completed. The higher the reaction temperature, the smaller the particle size, and the loss of monodispersity. With the increase of water concentration, the particle size increased first and decreased later, and it reached the maximum at 12mol/L. The higher the concentration of ethyl silicate, the greater the particle size. When the ammonia concentration increased from 0.5mol/L to 3mol/L, the particle size increased and the uniformity was very good.In order to decrease the number of nucleation in the initial nucleation stage and enlarge the size of microsphere, the continuous drop method was developed to obtain the desired numer of nuclei in the hydrolysis and condensation solution of the silica on source. The scanning electron microscopy images demonstrated that the lower the stirring rate, the better uniform the microspheres obtained, and the microspheres showed a multi-scale distribution at high stiring rate. The particle size distribution was detected by laser particle size analyzer in the circumstance of low stirring rate, and the distribution showed a good monodispersity. In order to reduce the number of nuclei further, potassium chloride was added to the hydrolysis solution to decrease the surface potential of the subparticles and accelerate the agglomeration of the subparticles. In the circumstance of the added rate 0.834ml/min, the particle size increases and thhe distribution is more uniform when the concentration of potassium chloride was from 0m M to 6m M. The more slowly the drop, the large the particle size and the better monodispersity. A lower water composition in mixture solvent will get a better monodisperse.