Synthesis, Properties And Structure Of Large Particle Size And High Concentration Silica Sol

Silica sol is a stable dispersion of the amorphous SiO2 particles in water. As one kind of important inorganic polymer materials, it is widely applied in precision casting, paper industry, paint and so on owing to its excellent qualities in dispersion, adhesion and film formation. Silica sol in industry has small particle size (10-20 nm) and relative low concentration (< 30%), which can not satisfy the requirements in some special fields. In order to enlarge the application ranges, nowadays, how to obtain large particle size and high concentration of silica sol attracts increasing research interests.In this thesis, the activated silicon acid is obtained through hobility ion-exchange process, whereby the 10% water glass was employed as the raw materials. Based on the activated silicon acid, large particle size and high concentration silica sol have been prepared successfully by two different processes which are ion exchange processⅠand combined ion exchange process with silicon hydrolysis processⅡ. Furthermore, the reaction conditions (the concentration of sodium silicate, reaction temperature, reaction time, pH etc.) and procedures, have been optimized and described briefly as following.(1)The activated silicon acid was heated at 100℃for 0.5 h. After poly(ethylene glycol) is added to the activated silicon acid. The value of pH of 50 mL activated silicon acid was adjusted to 9.5 by sodium hydroxide solution. The parent solution was obtained. Then,1500 ml (30 times) activated silicon acid was added into the above parent solution, the value of pH was kept at 9.5. The reaction was performed at 100℃for 6 h, so the systemⅠwas prepared. With the same procedure,50 mL of the system I was reacted with 1500 mL activated silicon acid, and the value of pH was kept at 9.5. The reaction was performed at 100℃for 6 h, so the systemⅡwas synthetized. Then 50 mL of the systemⅡwas reacted with 1500 ml activated silicon acid. By this means, the result of experiment showed that particle diameter of silica sol is 35 nanometers, the concentration of silica sol can reach 35%.(2)The activated silicon acid was heated at 100℃for 0.5 h.50 mL activated silicon acid was mixed with the surfactants of sodium dodecyl benzene sulfonate (0.02g), KH-550 (0.15mL), poly(ethylene glycol) (0.2g). The activated silicon acid was adjusted to 9.5 by sodium hydroxide solution. The parent solution was prepared. At 100℃,2g silica was added into the parent solution, and the parent nuclide was prepared after 8h. Then, the parent nuclide solution is concentrated to 15%, and 5g silicon powder was added in gradually, which reacted with 80 times volume of activated silicon acid for 8h. Its optimal reaction temperature was 100℃, and the value of pH was 9.5. Through condensation, the large particle size and high concentration silica sol was synthetized.The structures and physical properties of the large particle size and high concentration silica sol had been characterized by IR and SEM spectrum. The results showed that the silica sol particle size could reach up to 50 nanometers under the optimum technological conditions, which were much larger than those produced in industry. The concentration of silica sol could reach 40%.