Functions of sodium silicate
When used, silicates exert different functions among which the main ones are:
- Binding agent action through physical or chemical adherence;
- Clumping action;
- Filmogenic action, due to water evaporation and subsequent siloxane polymerization and to viscosity increase;
- Fireproof action, due to the formation of refractory and heat isolating films that prevent the close contact between fuel (wood, paper, cotton, etc.) and oxidizing agents (air), indispensable for combustion;
- Heat resistance, due to the inorganic nature and especially to the non-volatility of polymerized silicates;
- Resistance to acids, due to the insolubility and to the perfect chemical inertia of SiO2 in an acid environment, except for the hydrofluoric acid;
- Anticorrosive action on metals both due to the pH raising and to the interfacial chemical reaction with formation of a metallic silicate monolayer impervious to oxygen and that constitutes a great barrier to corrosion;
- Flocculant action on cations and polycations, with formation of large flakes easy to sediment;
- Deflocculant and fluidifying action of clayey sludges;
- Antisettling action: sodium silicate avoids the solid particles coagulation in suspension, not only for the electrostatic repulsion but also for the density and viscosity increase of the dispersing phase;
- Ion-exchange action: sodium silicate loses sodium ions and captures polyvalent metals ions. This explains the soothing properties of sodium silicate on hard water;
- Inertizing action: sodium silicate complexes and makes the metallic cations considerably toxic insoluble, by incorporating them in three-dimensional polymeric structures preventing to get back into solution;
- Buffer action on pH: sodium silicate, thanks to the silicic acid weakness and to the considerable potential acidity, exerts a remarkable buffer action on pH maintaining it at medium high values (10.5-12);
- Saponifying action: it exerts a saponifying action on fats, bringing them into solution and exerting this way function of detergent;
- Wetting action: sodium silicate, especially the most alkaline one, reduces the surface tension of water and increases the wettability of solids.
- Bactericidal action: in slightly diluted sodium silicate solutions bacteria are not found because of the alkaline environment, highly unfavourable for their development.
