As the carbonization reaction progresses, the silica gel content increases, followed by free water evaporation and dehydration of the silica gel into a solid to coagulate and harden.
1. Slow. Since the concentration of CO2 in the air is low, the carbonization reaction and the entire condensation and solidification process are very slow.
2. Volume shrinkage.
3. Low strength.
In order to accelerate the coagulation and solidification speed of water glass and improve the strength, it is generally required to use a curing agent sodium fluorosilicate in the use of water glass, and the molecular formula is Na2SiF6.
The amount of sodium fluorosilicate is generally from 12% to 15%. The dosage is small, the coagulation and solidification is slow, and the strength is low; if the amount is too much, the coagulation hardening is too fast, the construction operation is inconvenient, and the early strength after hardening is high, but the late strength is obviously reduced. Therefore, the amount of curing agent should be strictly controlled during use, and it should be appropriately adjusted within the above range according to the temperature, humidity, modulus and density of water glass. That is: the temperature is high, the modulus is large, and the lower limit is selected when the density is low, and vice versa.
Instant powdered sodium silicate is also known as instant saponin and hydrated sodium silicate. The product is white in appearance, powdery and has good uniformity. It is very convenient to transport, store and use, especially suitable for mechanization and automation. Widely used in metallurgy, electric power, petrochemical and building materials industries. It is used as a binder in unshaped refractories, industrial cleaners, preservatives, quick-drying agents and reinforcing agents in soap and acid-resistant cement, fine ceramics industry and precision casting industry. The instant powdered sodium silicate product also has all the properties and applications of liquid saponin. The instant powdered sodium silicate has a molecular formula of Na2O·mSiO2·nH2O, and the amount is generally between 280 and 350. Compared with the anhydrous powdered sodium silicate which is mechanically pulverized, the former has many valuable properties such as water dissolution rate and purity. The instant powdered sodium silicate is a fine chemical product, which is obtained by the dry process (the Glauber's salt method, the soda ash method), the saponin by chemical processing, filtration, mold adjustment, spray drying and the like.