What is Water Glass?
Water glass, also known as sodium silicate or alkali silicate glass, is a glassy solid made up of sodium oxide (Na2O) and silica (silicon dioxide, SiO2) that has the benefit of being soluble in water. Water glass is available in the form of solid lumps or powders, as well as a smooth, syrupy liquid. Many industrial goods use it as a sodium source, as a builder in laundry detergents, as a binder and adhesive, as a flocculant in water-treatment plants, and a variety of other uses.
Water Glass Formula
Let us take a look at the chemical formula of water glass.
Water Glass Formula -(Na2O)x·(SiO2)y
Which Compound is Known as Water Glass?
Water glass has been made since the 19th century, and the basic concepts for manufacturing "silicate of soda" have not changed. Water glass is typically made by roasting different amounts of soda ash (sodium carbonate, Na2CO3) and silica sand (a natural source of SiO2) in a furnace at temperatures between 1,000 and 1,400 °C (approximately 1,800 and 2,500 °F), a method that produces CO2 and sodium silicate(alkali silicate glass) (Na2SiO3):
x Na2CO3 + SiO2 → (Na2O)x·SiO2 + CO2
This roasting produces cullet, which is fused glassy lumps that can be cooled and sold whole or ground up and sold as powders. The resulting lump or groundwater glass may then be fed into pressurized reactors to dissolve in hot water. The solution is cooled to a viscous liquid and sold in jars, containers, and tanks of different sizes.
2NaOH + SiO2 → Na2O∙SiO2 + H2O
Alkali metal silicates were formed at 4 million tones in 1990. The higher the ratio of SiO2 to Na2O and the higher the concentration of both ingredients in either production path, the more viscous the solution. The formation of silicate polymers, in which silicon (Si) and oxygen (O) atoms are connected by the covalent bonds into large negatively charged ring or chain structures that include positively charged sodium ions and water molecules, results in viscosity. Spray-drying highly viscous solutions produce glasslike hydrated sodium silicate beads. The beads can be packed for commercial use in the same way that ground cullet can, but they dissolve faster than anhydrous water glass.
Physical Properties of Water Glass
Sodium silicates are white powders or colourless glassy or crystalline solids. They are water-soluble, with the exception of the silicon-rich ones, and produce alkaline solutions.
In both neutral and alkaline solutions, sodium silicates are stable. Silicate ions react with hydrogen ions in acidic solutions to form silicic acids, which decompose into hydrated silicon dioxide gel. The effect of heating silica gel to force off the water is a strong transparent material called silica gel, which is commonly used as a desiccant. It can withstand temperatures of up to 1100 degrees Fahrenheit.
Uses of Water Glass
The most common use of sodium silicate solutions in cement is the manufacture of cardboard. The sodium silicate joint, when used as a paper cement, has a tendency to break after a few years, at which stage it no longer keeps the paper surfaces cemented together.
Sodium silicate is often used in drilling fluids to help strengthen borehole walls and prevent them from collapsing. When drilling through argillaceous formations containing swelling clay minerals like smectite or montmorillonite, it's especially useful.
Most masonry products, such as concrete, stucco, and plasters, can be treated with a sodium silicate solution to minimize porosity. While this effect helps to minimize water penetration, it has no effect on water vapour transmission or emission.
In wastewater treatment plants, sodium silicate is used as an alum coagulant and an iron flocculant. Colloidal molecules bind to sodium silicate, forming larger aggregates that fall to the bottom of the water column.
Solids such as vermiculite and perlite may be bound with water glass. Water glass can be used to create rigid, high-temperature insulation boards for refractories, passive fire safety, and high-temperature insulations, such as moulded pipe insulation applications, when combined with the aforementioned lightweight aggregates.
When doing sand casting of iron or steel, it is used as a sand binder. By moving CO2 through a mixture of sand and sodium silicate in the mould box, which hardens it almost immediately, allows for the rapid development of a solid mould
Did You Know?
Water glass has had a lot of success as an egg preservative, particularly when refrigeration isn't accessible. Freshly laid eggs are submerged in a sodium silicate solution (water on glass). They were removed from the solution and allowed to dry after being soaked in it. The eggs have a permanent airtight coating on them. The majority of bacteria that would otherwise cause them to spoil are kept out and their moisture is kept in if they are then stored in a suitable setting.
This can keep treated eggs fresh for up to five months. When boiling eggs that have been preserved in this way, the shell is no longer permeable to air, and the egg can crack unless a hole is made in the shell (e.g. with a pin) to allow steam to escape.
FAQs on Water Glass
1. What exactly is water glass in chemistry, and what is its general chemical formula?
Water glass, also known as sodium silicate or alkali silicate glass, is a compound made from sodium oxide (Na₂O) and silica (SiO₂). Unlike regular glass, it is notable for its solubility in water. Its general chemical formula is written as (Na₂O)x·(SiO₂)y, where the ratio of x to y can vary, leading to different properties.
2. How is water glass prepared on an industrial scale?
Water glass is commercially produced by heating soda ash (sodium carbonate, Na₂CO₃) and silica sand (SiO₂) in a furnace at very high temperatures, typically between 1,000°C and 1,400°C. This high-temperature reaction releases carbon dioxide and produces fused glassy lumps of sodium silicate, which can then be dissolved in water under pressure to form a viscous liquid solution.
3. Why is water glass often described as a syrupy liquid with variable viscosity?
The syrupy nature and variable viscosity of water glass solutions are due to the formation of silicate polymers. In water, silicate ions form large, negatively charged chain or ring structures. The viscosity depends on the ratio of SiO₂ to Na₂O and the overall concentration; a higher proportion of silica leads to more complex polymerisation and thus a more viscous, thicker solution.
4. What are the main chemical properties of a water glass solution?
The key chemical properties of sodium silicate solutions include:
- Alkalinity: They are soluble in water and form alkaline solutions.
- Stability: The solutions are stable in neutral and alkaline conditions.
- Reaction with Acids: In acidic solutions, they react to form silicic acid, which subsequently decomposes into a hydrated silicon dioxide gel. This gel, when heated, becomes silica gel, a powerful desiccant.
5. What are some of the most important industrial applications of water glass?
Water glass has a wide range of industrial uses due to its unique properties. Some major applications include:
- Detergents: It acts as a builder in laundry detergents.
- Adhesives and Binders: It is used as a binder for paper products like cardboard, in cement, and for sand in metal casting.
- Water Treatment: It serves as a flocculant to help remove suspended colloidal particles from wastewater.
- Construction: It is used to reduce the porosity of masonry products like concrete and stucco.
- Fire Protection: When mixed with materials like perlite, it creates high-temperature insulation boards.
6. How does sodium silicate act as a binder in applications like sand casting?
In sand casting, water glass is mixed with sand to create a mould. Its binding action is chemically triggered. When carbon dioxide (CO₂) gas is passed through the mixture, it reacts with the alkaline sodium silicate. This reaction rapidly forms silicic acid, which dehydrates to silica gel, almost instantly hardening the sand mixture and creating a strong, solid mould for casting molten metal.
7. From a chemical standpoint, why was water glass effective for preserving eggs before refrigeration was common?
Water glass was used for egg preservation because of its ability to create an airtight seal. When fresh eggs were dipped in a sodium silicate solution and allowed to dry, the solution filled the microscopic pores of the eggshell and hardened into a glassy, impermeable layer. This coating prevented bacteria from entering the egg and moisture from escaping, thus keeping the eggs fresh for several months.
