Study On Preparation And Modification Of Silica Sol By Aluminium Salt

Silica sol is a kind of colloid solution well dispersing corpuscles of silica in water. It is a stable and dispersive system as amorphous SiO₂ particle in water. As an important inorganic polymer material, it has been widely used in the area of chemical engineering, casting, textile, paper making, coating, food, electron, ore dressing and so on.Using sodium hydroxide and sodium silicate as catalyst, silica sol was prepared by the reaction of silicon powder with water through dissolving method in this thesis. The effect of various conditions, such as temperature, time, usage of silicon powder and catalyst on preparation of silica sol was investigated, and properties of silica sol were also analyzed. The structures of silica sol that prepared at the most effective reaction conditions were identified.Using sodium hydroxide as catalyst, the most effective reaction conditions were: 25g silicon power and 0.16g sodium hydroxide in 200mL water, at 90℃continuously was reacted 8h, then silica sol was obtained: viscosity was 5.3mpa·s , and Beaume degree was 15, and pH was 8.5. Using sodium silicate as catalyst, the most effective reaction conditions were: 30g silicon powder and 2.34g sodium silicate in 200mL water, at 90℃continuously was reacted 8h, then silica sol was obtained: viscosity was 5.9mpa·s, Beaume degree was 20 and pH was 9.0.As starting material, sodium silicate was used to prepare silica sol through dissolution, acidification, alkalization, maturation. Modified silica sol separately was obtained by aluminum sulfate, aluminum nitrate and aluminum chloride. Parameters change of silica sol was discussed, when the ratio of Al/Si was from 0.05 to 0.25. Three modified silica sol were obtained in the condition of most effective technique, and theirs structures were analyzed.The stability of silica sol and modified silica sol that were prepared according above methods was discussed. When pH was between 8.5-10 in the alkaline condition, silica sol was the most stable; when pH was between 3-4 in the acidic condition, silica sol was also stable; when pH was 7, silica sol was the lest stable. The modified effect of low concentration silica sol was stable, however, the modified effect of high concentration silica sol was less stable. When the ratio of Al/Si was 0.15, the most stable modified silica sol was prepared by aluminum sulfate in three aluminum salts under the most effective reaction conditions.