Film forming mechanism and application characteristics of potassium silicate in coatings

The appearance of potassium silicate is a blue-green, brown, or colorless transparent solid or viscous liquid. Among them, the colorless transparent liquid is of superior quality. Potassium silicate contains various components: amorphous silica, hydrate, hydroxide, orthosilicic acid, and polysilicate anions. Among them, the type and content of anions are related to the modulus and pH value, and the water glass is usually strongly alkaline. The higher the modulus, the greater the viscosity; if the modulus is the same, the greater the density and the thicker it is.
The main body of the film forming of potassium silicate is colloidal silicon dioxide (also known as silicic acid), and the film eventually formed by potassium silicate is a network structure composed of colloidal silicon dioxide with Si-O-Si as the main skeleton and the crystals of metal ions or other salts are dispersed in the network structure.
Potassium silicate is placed in the air, absorbing carbon dioxide in the air, forming amorphous silicate, and gradually drying and curing. After slow curing, the water resistance of the film is relatively poor. Appropriate curing agents are usually added to reduce the curing time. The curing agent can promote the condensation of SiO2 colloids into water-resistant coatings and react with alkali metal ions to produce insoluble substances. This method uses alkali metal ion immobilization technology, also known as water glass curing technology.

Potassium silicate as a coating base material mainly has the following characteristics.
(1) High bond strength
Potassium silicate has a good bonding ability and strong bonding force with inorganic substrates. The silicic acid gel is precipitated when hardened, blocking capillary voids and preventing water leakage.
(2) Good heat resistance and weather resistance
Potassium silicate is non-combustible, smokeless, and does not produce toxic gases and smoke in the event of a fire. And it has good weather resistance to ultraviolet and ozone. The higher the temperature, the stronger the drying of silicone gel, while the strength not only does not decrease and even slightly increases, the heat resistance temperature is generally 500~600℃. Because of its good heat resistance, potassium silicate has been widely used in heat-resistant concrete, heat-resistant cement, heat-resistant mortar, etc.
(3) Good acid resistance
In addition to hydrofluoric acid, superheated phosphoric acid above 300 ° C, advanced fatty acids, oleic acid, and potassium silicate can almost withstand all inorganic and organic acids. The good acid resistance of potassium silicate makes it widely used in acid-resistant concrete, acid-resistant mastic, acid-resistant mortar, etc.
(4) Strong functionality
It has a proper moisture-regulating effect, anti-condensation, and anti-mildew; mold is not easy to grow and has a certain anti-insect effect. Compared with organic coatings, it has certain electrical conductivity and does not absorb much dust due to static electricity.
(5) Rich resources and environmental protection
Soluble in water, easy to treat, and rich in resources, with no environmental harm.
(6) Poor water resistance and alkaline resistance
After adding sodium fluosilicate, the potassium silicate’s hardening is still incomplete, and a part of the potassium silicate remains. Potassium silicate is soluble in water and alkali, so potassium silicate water resistance and alkali resistance are poor. The water resistance of hardened potassium silicate can be improved to some extent by pickling with a medium-concentration acid solution.
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