What Is Sodium Silicate?

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  • Written By: Helga George
  • Edited By: Michelle Arevalo
  • Last Modified Date: 13 September 2019
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Sodium silicate is one of several chemicals that are composed of sodium, silica, and oxygen. The term is often used to indicate sodium metasilicate, which is also known as liquid glass. Sodium silicate melts at a very high temperature, making it useful for commercial fire-proofing.

A sodium silicate compound contains sodium oxide, Na2O, and silica, Si2O, or a mixture of these compounds. They can be associated with up to nine molecules of water, or lack water and be known as anhydrous. These compounds can be solid, or they can be liquids. The solid version is widely used to make silica gel — a common drying agent.

The combination of being liquid and being resistant to high heat makes these compounds useful for automobile repair. A sodium silicate solution is circulated from the radiator to seal leaks in the head gasket. This solution can also be used instead of motor oil to permanently disable a car engine prior to the auto's destruction. The liquid version is also useful to treat concrete to make it more water repellent.

Sodium silicate water solutions bind solids well, forming insulation boards that tolerate high temperatures. This property enables them to be used to as a refractory—retaining strength at high temperatures. Due to this, they can be used as linings in kilns and glass-making equipment. If water-proofed, they can be used as passive fire protection, such as being incorporated into the structure for plastic pipes, to form firestop devices.


Sodium metasilicate is a strong base that is used in a variety of detergents as a substitute for phosphates, which have been responsible for a great deal of water pollution, by causing algae blooms. It acts primarily by changing the pH of the water to inactivate water hardness. Technically, it is known as a builder.

Another sodium silicate compound is sodium aluminum silicate, which is also known as sodium aluminium silicate. It is composed of sodium, silica, oxygen, and aluminum. It can also be found in an anhydrous form, or combined with water.

Sodium aluminum silicate can form very attractive minerals, including jadeite, which comprises one form of the gemstone jade. Another mineral is albite. These minerals are anhydrous.

There is a synthetic, industrial form of sodium aluminum silicate that contains water. It is known as synthetic amorphous sodium aluminosilicate. This is a common food additive, used as an anti-caking agent that keeps powdered foods free of lumps.

Another commercial use for sodium aluminum silicate is in making synthetic zeolites. These are compounds that are highly porous minerals and are strongly absorbent. They are used commonly as a component of laundry detergents.


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