The production of liquid water glass
Water glasses are produced presently by using two basic methods
a) The production from “PKS/D” (solid sodium and potassium silicate SSS/SPS)
SSS/SPS is produced from sand (silica 70-75 %) by melting in glass bath furnace at the temperature of 1400-1600 °C using the help of alkaline fluxing agents – sodium (sodium oxide) or potash (potassium oxide), i.e. substances, which make melting of sand easier. Molten glass is cooled intensely to crack it in the smallest parts possible (visually similar to pieces of ice) thus making subsequent dissolving as easy as possible. Input material prepared in such a way is dissolved to fluid water glass in an autoclave (heated sealable pressure container) using potassium hydroxide or sodium hydroxide, water, temperature and pressure. In this way, it is possible to manufacture all types of water glass.
b) Hydrothermal reaction
Silica sand is directly dissolved using the help of hydroxide, water, temperature and pressure in an autoclave (heated sealable pressure container). By using this method, it is possible to manufacture only some types of sodium water glass.
It is possible to upgrade the parameters and properties of water glasses by adding organic or inorganic agents into the process of dissolving in autoclave.
Properties of water glass
The composition of water glass is most often characterized by siliceous module M, which is the molar ratio of SiO2
O for sodium glass or of SiO2
O for potassium glass. The value of the silicic module of commonly manufactured types of water glass lies usually within the range of 1,6 – 4,1. Apart from the module, it is the density of water glass that is most often used to characterize it. Furthermore, viscosity and the value of pH is also used. Viscosity of water glass depends on its concentration and on the value of silicic module of the initial glass. During the comparing of data on viscosity, it is necessary to take into account that water glass behaves as Newtonian fluid and the value of viscosity thus depends on the method of measuring. The value of pH is also a function of chemical composition and concentration of water glass. Water glasses as solutions of salts of intense alcali and weak acids are considerably alkaline.
Hardening of water glass
Hardening of water glass is caused by gel production of silicic acid, in most cases due to the reaction of alkaline silicate with carbon oxide, or carbonic acid, based on the following schematic layout.
• n H2O)
By-product of the hardening reaction is, according to the type of water glass, either sodium or potash.
The application of water glass
Sodium water glass is used as an addition into degreasing agents and detergents as binding material in the production of welding rods or sand moulds in foundries. It is used as a remover of heavy metals in water cleaning facilities, as a bonding agent in paper-making industry, or as an activating agent in the production of geopolymeric materials. In construction industry, potassium water glass is used for the production of organic coating, sealants, dry mortar compounds etc. For demanding applications such as industrial floors, special fire-resistant materials, paint etc., less known water glasses such as lithic, sodium-lithic and potassium lithic water glasses are used.