The effect of pH of silica sol on its performance
Silica sol can be divided into alkaline silica sol (pH=8-11), neutral silica sol (pH=6-8), and acidic silica sol (pH=2-5) according to its pH range.
The storage stability of silica sols with different pH ranges varies, and generally speaking, alkaline silica sols have the longest storage stability, up to several years. This is because the surface of nano silica particles in alkaline silica sol has a silicate structure with negative charges and a high zate potential. Therefore, there is mutual repulsion between nano silica particles, which makes it difficult to agglomerate and can maintain good stability.
Neutral silica sol belongs to the category of silica sol that contains a small amount of alkali metal ions or ammonium ions. The zate potential on the surface of nano silica particles is smaller than that of alkaline silica sol, and its storage period is shorter than that of alkaline silica sol.
The surface of nano silica particles of acid silica sol is silicic acid structure, which contains rich silicon hydroxyl groups. The condensation reaction between hydroxyl groups will gradually occur during storage, so the acid silica sol will gradually produce gel, which shows that its viscosity will gradually increase with the storage time, and finally the gel will be jelly like. During the drying process of acidic silica sol, the binding force between nano silica particles is greater than that of alkaline silica sol or neutral silica sol due to the condensation reaction between silica hydroxyl groups. Therefore, it will play a better bonding role as a high-temperature binder.