The surface charge of silica particles in most silica sols is negative. The surface of silica sol particles is mainly composed of silanol groups, with a structural formula of -Si-OH. Under alkaline pH conditions, the surface of the particles carries anionic charges, and the stability of the silica sol needs to be maintained by combining with cationic substances (such as Na+, K+, NH4+). Silica sol remains relatively stable in the pH range of 8-10.5, and will not produce gelation and sedimentation. It has been reported in the literature that under acidic pH conditions, when pH>2, the surface of the particles carries anionic charges, and when pH<2, the surface of the particles carries cationic charges. The content of -Si-OH in the particle structure of acidic silica sol is rich, and it is easy to condense with each other to make the silica sol gel. Therefore, the storage stability period of acidic silica sol is shorter than that of alkaline silica sol.