Na2O content.
Sodium ions are the stabilizing ions of silica sol. Sodium ions come from sodium oxide. Therefore, sodium ions act as stabilizers in silica sol. However, since the colloid particles in silica sol preferentially adsorb sodium ions, a high sodium ion content will reduce the charge of the colloid particles and reduce the repulsive force between the colloid particles, which will indirectly lead to a decrease in the stability of the silica sol. Therefore, the sodium ion content cannot be too high, which is the basis for the low Na2O content in the silica sol parameters.