Sodium Silicate: Structure, Properties & Uses

Sodium silicate is both the technical and common name for a mixture of compounds with the chemical formula Na_2xSi_yO_2y+x or (Na₂O)_x·(SiO₂)_y. Some compounds include sodium metasilicate Na₂SiO₃, sodium orthosilicate Na₄SiO₄, and sodium pyrosilicate Na₆Si₂O₇.

• Metasilicate is commonly known as waterglass, water glass, or liquid glass. 
• Sodium silicate is usually colourless translucent solids or white powders.
• The compound is soluble in varying amounts of water that will produce alkaline solutions.

Due to the presence of iron-containing impurities, the commercial product, which is available in water solution or solid form, is frequently greenish or blue.

• The anions in the compound are polymeric in nature.
• It is highly stable in alkaline and neutral solution.
• In the case of an acidic solution, the silicate ions react with hydrogen ions to form silicic acids.
• The substance has many applications, including cement formulation, passive fire protection, textile and lumber processing.

Na_2xSi_yO_2y+x or (Na₂O)_x·(SiO₂)_y

Key Terms: Sodium Silicate, Sodium Metasilicate, Sodium Orthosilicate, Sodium Pyrosilicate, Acidic Solution, Silicic Acids, Ions, Sodium Carbonate, Hydrogen, Alkanline Solution, Silicon

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What is Sodium Silicate

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Sodium silicate is an inorganic sodium compound that consists of silicate as a counter ion. The compound is also known as water glass or sodium metasilicate. 

• Sodium Silicate was first observed in 1500 by European alchemists.
• It is a solid powdered substance which forms a flaky mixture.
• The compound is made of sodium oxide (Na₂O) and silicon dioxide (SiO₂).
• When sodium silicate is heated at high temperatures, then it will form a hard, translucent substance called silica gel.
• The compound can withstand temperatures up to 1100°C.
• It comes under the category of desiccant. 

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Structure of Sodium Silicate

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Sodium Silicate is a crystalline solid that can be written in the form of Na₂OSiO₂. The compound is composed of sodium ions (Na⁺) and silicate ions (SiO²₃−).

• The structure of the compound is tetrahedral in shape.
• It will form a three-dimensional network with oxygen atoms.
• The oxygen atom serves as a bridge with silicon atoms.
• The silicate ions found in the compound have a central silicon ion, which is bonded to four oxygen atoms.

Sodium Silicate 

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Properties of Sodium Silicate

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The properties of sodium silicate is divided into two sections namely physical and chemical properties which are as follows:

Physical Properties of Sodium Silicate

The physical properties of sodium silicate are as follows:

• It is a white powder or colourless glassy or crystalline solid. 
• They are water-soluble, with the exception of the silicon-rich ones, and produce alkaline solutions.
• It is insoluble in alcohols and acids.
• The density of the compound ranges from 1.36 to 1.47 grams per cubic centimetre.
• It tends to exhibit high viscosity, which in turn depends upon the concentration of the solution.
• It can endure temperatures of up to 1100 degrees Fahrenheit.
• Sodium silicate is a hygroscopic substance with a pH of 11-13.

The physical properties of sodium silicate are tabulated below:

Chemical Properties of Sodium Silicate

The chemical properties of sodium silicate are as follows:

Hydrolysis 

Sodium Silicate will undergo a hydrolysis reaction when it reacts with water. The reaction will produce silicic acid and sodium hydroxide as by-products. 

Polymerization

The compound will undergo a polymerization reaction to form silicate compounds like sodium metasilicate and sodium orthosilicate. 

Thermal Decomposition 

Sodium silicate will undergo thermal decomposition on heating at high temperatures. On heating, it will form compounds like silica and sodium oxide.

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Preparation of Sodium Silicate

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In a reactor, a mixture of silica (typically quartz sand), caustic soda, and water is treated with hot steam to make sodium silicate solutions. The general consensus is that:

2x Na₂OH + SiO₂ → (Na₂O)x·SiO₂ + xH₂O

• Decomposition can also be used to make sodium silicates by dissolving silica SiO₂ in molten sodium carbonate.

x Na₂CO₃ +SiO₂ → (Na₂O)x·SiO₂ + CO₂

• Sodium sulphate with carbon as a reducing agent can alternatively be used to make the material:

2x Na₂SO₄+ C + 2 SiO₂ → 2 (Na₂O) x·SiO^₂ + 2 SO₂ + CO₂

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Uses of Sodium Silicate

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Sodium silicates are used mostly in detergents, paper, water treatment, and construction products. The multiple uses of sodium silicate are as follows:

Fluids for Drilling

Sodium silicate is commonly used in drilling fluids to help support borehole walls and prevent them from collapsing. When drilling through argillaceous strata, the compound containing expanding clay minerals like smectite or montmorillonite is especially effective.

Auxiliary Detergents

Detergent auxiliaries contain compounds such as complex sodium disilicate and modified sodium disilicate. A silicate layer gives the detergent granules their toughness.

Casting in Sand

It is utilised as a sand binder when making iron or steel sand casting. The mixture hardens instantaneously by flowing CO₂ through a mixture of sand and sodium silicate in the mould box.

• It enables the speedy production of a strong mould.

Treatment of Water

In wastewater treatment plants, sodium silicate is utilised as an alum coagulant and an iron flocculant. Colloidal molecules attach to sodium silicate, forming bigger aggregates that sink to the bottom of the water column. 

• The sodium silicate interacts with small negatively charged particles suspended in water. 
• This ionic strength increases with the addition of sodium silicate (doubly negatively charged anion accompanied by two sodium cations).
• This, in turn, causes the electrical double layer to collapse and coalesce. 
• The process is known as Coagulation.

Repairing Metal

In muffler repair and fitting paste, sodium silicate is combined with magnesium silicate. Both sodium silicate and magnesium silicate dissolve in water to form a thick paste that is easy to apply. 

• When an internal combustion engine's exhaust system reaches operating temperature, the heat pushes all of the extra water out of the paste. 
• The remaining silicate components have glass-like characteristics, resulting in a brittle, transient repair.

Construction of Safe

A mixture of sodium silicate and sawdust has been utilised between the double layer of some safes. This makes them more fire resistant, and the smoke emitted makes cutting them open with an oxyacetylene torch extremely difficult.

Medicine and Food

While sodium silicate and other silicates are not used medically, they are the main ingredients in "instant" wrinkle removal treatments, which tighten the skin momentarily to reduce the appearance of wrinkles and under-eye bags. 

• These creams can produce remarkable changes when applied as a thin coating and allowed to dry for a few minutes. 
• The impact is temporary, lasting anything from a few minutes to several hours. 
• It works like water cement, cracking and leaving white residues on the skin as the muscle begins to move.

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Health Hazards of Sodium Silicate

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The health hazards of sodium silicate are as follows:

• Eye contact with sodium silicate can cause extreme irritation, pain, and corneal burns, which can result in blindness.
• If the product comes into close touch with the skin, irritation may develop. 
• Inhaling sodium silicate mists can irritate the respiratory tract, causing symptoms like coughing, choking, and pain.
• On ingestion, it can cause nausea, vomiting and diarrhoea.
• It will cause dehydration when ingested in large amounts.  

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Things to Remember

• Sodium Silicate is a colourless compound which is composed of oxides of sodium and silica.
• The compound is a byproduct of the Bayer process.
• It is highly temperature resistant, meaning water evaporates and leaves behind a translucent substance called silica gel. 
• The compound is prepared by a combination of soda ash and sand.
• Detergents, paper, water treatment, and construction materials are some of the most common uses for sodium silicates.

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