Based on classic Derjaguin, Landau, Verwey, Overbeek (DLVO) theory [17], particles repel each other at a pH above 11. As the pH is reduced or through charge screening and reducing the dielectric constant of the aqueous phase (by adding inorganic acid, inorganic salts or alcohol) [18], silicate species aggregate to form higher-order oligomers. The boric acid, as a kind of inorganic acid, could reduce the pH value of the sodium silicate solution.