The process of forming gel under appropriate conditions with a certain concentration of sol is called gelation.
In the gelation process of silica sol, the colloidal particles form a capillary network structure with hydrogen bonds in the early stage of drying, and the hydroxyl dehydration in the later stage of drying causes the hydrogen bonds to continuously form silicon-oxygen covalent bonds, and the colloidal particles grow three-dimensionally. However, due to the different cross-linking speeds in each direction, the cross-linking density will be different, and finally a heterogeneous gel with complex micro-regions and a dendritic polymer structure will be formed.