A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Sodium Silicate

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Key Data

Formula: (Na₂O)_x(SiO₂)_y
CAS: 15859-24-2 (sodium silicate), 1344-09-8 (liquid sodium silicate), 6834-92-0 (sodium metasilicate)
Other names: waterglass, liquid glass
Appearance: White powder or clear liquid
Solubility in water: 222 g/l (25°C); 1606 g/l (80°C) for the metasilicate according to one source; 350 g/l (20°C) according to another

Solutions (e.g. 10g/l) can have a pH of 11.2 - 12.5, with a solution of about 25g hydrated sodium silicate per 1l of water. The lower the ratio of the ratio of SiO₂:Na₂O, the higher the pH.

It forms a medium strong base dissolved in water. Reacts with aluminium, copper, tin or zinc and compounds, giving off Hydrogen gas.

Note that in an acidic solution silicic acids are formed, which turn into silica gel on the loss of water.

Melting Point: 1089°C for the anhydrous metasilicate. Hydrated forms have much lower melting ponts, around 50 - 70°C depending on the formula and level of hydration.
Boiling Point: 100°C in water solution

Composition/Impurities

The strength of solutions is measured in degrees Twaddle (°Tw). To convert to specific gravity, SG=1+0.005t, where t is the °Tw value.
The most common compound is sodium metasilicate, where x and y are both 1.
In pottery supplies, CTM use x=1, y=3 for their 75°Tw liquid, and x=1, y=2.05 for their 120°Tw liquid. Other UK suppliers offer the same °Tw solutions, so this is probably common at least across the UK.
In industry, it is characterised by the ratio of SiO₂:Na₂O (by weight - multiply by 1.032 to convert to molar). This can be in the range of 1:2 - 3.75:1. Those below 2.85:1 are called alkaline; those above neutral (though the pH is still strongly alkaline). This would make the 75°Tw alkaline and 120°Tw neutral.

Uses

Used as a deflocculant (including in magic water and magic slip), and also to produce a crackle effect on the surface of clay. Acts as a binder, up to about 1000°C.

Exposure Routes

Skin and Eye Exposure

May cause redness and painful itching due to a reaction with the skin or eye. Although not a true allergy, this may trigger an allergic type anaphylactic reaction.
In solution may it cause skin burns and serious eye damage.

Skin Absorption

Not absorbed

Inhalation

Yes

Ingestion

Yes

Toxicity

Acute

Skin

See exposure

Inhalation

Inhalation of significant quantities may cause a cough and sore throat, but no lasting harm

Ingestion

Ingestion of significant quantities may cause nausea, diarrhoea and vomiting, but no lasting harm

Repeat Dose

Skin

Inhalation

No harm

Ingestion

No harm

Genotoxicity

No risk

Carcinogenicity

No risk

Reproductive Toxicity

No risk

Fire Hazard

Not combustible

Health and Safety Practice

Wear gloves (e.g. Nitrile) and safety glasses or face shield.
Spills are very slippery and, when dried, form a sharp glass which can cut.

Disposal

No specific risks to the environment, other than neutralise the solution before disposal. It will revert to silica.

Regulatory Requirements

Dust Limits

None