Characteristics of sodium silicate
The main characteristics of sodium silicate solutions, which determine their high versatility in different application fields, are following:
- ability to give rise to siloxane polymeric chains (consisting of an alternation of silicon and oxygen atoms) with the single units of sodium silicate. This characteristic is the basis of the adhesive and inertizing properties of sodium silicate;
- high buffering power against pH. Sodium silicates derive from the neutralization of silicic acid with sodium hydroxide. Due to the incompleteness of salification, in solution always coexist discrete quantities of silicic acid, very weak, and caustic soda, a very strong base, which gives basic character to all sodium silicate solutions. The buffering power derives from the fact that if a strong acid is added to a sodium silicate solution, it is neutralized by the NaOH present in the sodium silicate, with the release of silicic acid which, due to its weakness, is not able to significantly lower the pH. Conversely, if a strong base is added to the sodium silicate, it is neutralized by the excess SiO2 without being able to increase the pH further.
- unlimited solubility in water of sodium silicate; water is in fact the only solvent for sodium silicate and can be used to dilute the solutions in any proportion you want. For heating purposes, sodium silicate solutions only release water vapour.
- low toxicity if swallowed, so much to be used to purify and treat water destined for human consumption and the American FDA (Food and Drug Administration) and several European countries have approved their use for bonding food packaging.