Sodium silicate

Sodium silicate is a solid or white glassy or colorless crystalline powder. All of them, except the rich silicones, dissolve easily in water and form an alkaline solution. Sodium silicate is stable in alkaline and neutral solutions. In acidic solutions, silicate ions react with hydrogen ions to form silicic acid, which tends to decompose into a hydrated silicon dioxide gel. When heated to expel water, it produces a hard, translucent substance called silica gel, which is widely used as a desiccant. It can withstand up to 1100 degrees Celsius.

The main uses of sodium silicate are detergents, paper, water treatment and construction materials.

The biggest use of sodium silicate solution is cement for making cardboard. When used as a paper cement, sodium silicate joints eventually crack within a few years, at which point the paper surface cannot be cemented. The sodium silicate solution can also be used as a rotary adhesive layer to bond glass to glass or silicon wafers coated with silicon oxide to each other. Sodium silicate glass-to-glass bonding has the advantage of being a low-temperature bonding technique, unlike fusion bonding. It also requires less processing than glass-to-glass anodic bonding, which requires an interlayer such as SiN to act as a diffusion barrier for sodium ions. The deposition of such layers requires a low-pressure chemical vapor deposition step. However, the drawback of sodium silicate bonding is that it is very difficult to remove air bubbles. This is also because this bonding technique does not require vacuum bonding and does not use field aids such as anodic bonding. This lack of field assistance can be useful because it can create an attractive force between the wafers high enough to bend a thin wafer and cause it to collapse onto a nanofluid cavity or MEMS device.

Sodium silicate is mostly used in drilling fluids to stabilize the borehole wall and prevent the collapse of the borehole wall. This is especially useful when drilling a hole through clay formations containing swollen clay minerals such as smectites and montmorillonite.

Concrete treated with sodium silicate solution helps to reduce porosity in most masonry products such as concrete, plaster and plaster. This effect helps to reduce water infiltration, but its effectiveness in reducing water vapor infiltration and emission is not known. It chemically reacts with excess calcium (OH)2 (portlandite) in the concrete to form a permanent bond between the silicate and the surface, greatly improving the durability and water repellency of the concrete. This treatment is usually applied only after initial healing (up to 7 days, depending on the condition). These coatings are known as mineral silicate paints. An example of sodium silicate and calcium hydroxide in concrete reacting to form calcium silicate hydrate (or CSH) gel, the main product of hydrated portland cement.

Water glass is useful as an adhesive for solid materials such as vermiculite and perlite. Mixed with the lighter weight fraction of the latter, water glass can be used to produce rigid high temperature insulating boards used in high temperature insulation such as refractories, passive fire protection, and molded pipe insulation applications. When mixed with finely divided mineral powders such as vermiculite powder (a common scrap from the exfoliation process), high temperature adhesives can be produced. In the presence of finely divided mineral dusts, the swelling disappears, thus turning the water glass into a matrix. Because of its cheap and abundant availability, water glass is popular for use in many refractory applications.

It is used as a sand binder in iron and steel sand casting. Strong molds can be produced rapidly by passing CO2 through a mixture of sand and sodium silicate in the mold box, which hardens the mold almost immediately.

Sodium silicate is used in muffler repair and installation pastes along with magnesium silicate. Sodium and magnesium silicates dissolve in water and form thick pastes that are easy to use. When the exhaust system of an internal combustion engine is heated to operating temperature, the heat will remove all excess moisture from the paste. The remaining silicate compound has glass-like properties and provides a brittle temporary restoration.