WHAT IS SODIUM SILICATE
Sodium silicate is a clear, odourless, viscous liquid. This specific silicate has a molar ratio of 3.22 and a total solids content of 36.8%. It is produced by fusing sand (SiO2) with sodium carbonate which produces solid glass (cullet). The glass is then dissolved in water and steam under high pressure which produces the sodium silicate solution also known as water glass. It is widely used in industry as sealants, binders, deflocculants, emulsifiers and buffers.
- Synonyms: Sodium trisilicate solution; Water glass; Silicic acid, sodium salt; sodium hydroxy(oxo)silanolate; acide silicique, sel de sodium; Kieselsaure, Natriumsalz;
- Molar Ratio: 3.22 +/-0.5%
- SiO2: 27.8% +/-0.5%
- Na2O: 8.5% +/-0.3%
- Concentration: 36–37%
- CAS No: 1344–09–8
- EC No: 215–687–4
- Formula: Na2Si3O7
- Viscosity: 70–100cPs (20C)
- Density: 1.38 g/cm3 (40 Be)
- pH: approx 11.3
- Solubility: completely miscible in water
Uses for sodium silicate
Sodium silicate is used, along with magnesium silicate in muffler repair and fitting paste. When dissolved in water, both sodium silicate, and magnesium silicate form a thick paste that is easy to apply. When the exhaust system of an internal combustion engine heats up to its operating temperature, the heat drives out all of the excess water from the paste. The silicate compounds that are left over have glass-like properties, making a somewhat permanent, brittle repair.
Sodium silicate can be used to seal leaks at the head gasket. Rather than pull the head, a jar of “liquid glass” is poured into the radiator and allowed to circulate. The Waterglass is injected via the radiator water into the hotspot at the motor. This technique works because at 93 C the sodium silicate loses water molecules to form a very powerful sealant that will not re-melt below 815 C. This approach is often used by disreputable used-car salespersons to disguise a leaking head gasket.
A sodium silicate repair of a leaking head gasket can hold for up to two years and even longer in some cases. The effect will be almost instant, and steam from the radiator water will stop coming out the exhaust within minutes of application. This repair only works with water to cylinder or water to Air applications and where the sodium silicate reaches the “conversion” temperature of 93 C.
Sodium silicate has been widely used as a general purpose cement, but especially for applications involving cementing objects exposed to heat or fire. For example, sodium silicate has been provided in home first-aid kits and used in medical practice as a glue for holding human skin together at surface cuts. It has also been used as a general purpose paper cement.
Sodium silicate is used as a timber treatment to preserve wood from insects and possesses some flame-retardant properties.
Concrete and general masonry treatment
Concrete treated with a sodium silicate solution helps to significantly reduce porosity in most masonry products such as concrete, stucco, plasters. A chemical reaction occurs with the excess Ca(OH)2 in the concrete that permanently binds the silicates with the surface making them far more wearable and water repellent. It is generally advised to apply only after initial cure has taken place (7 days or so depending on conditions).
Water glass is a useful binder of solids, such as vermiculite and perlite. When blended with the aforementioned lightweight aggregates, water glass can be used to make hard, high-temperature insulation boards used for refractories, passive fire protection and high temperature insulations, such as moulded pipe insulation applications. When mixed with finely divided mineral powders, such as vermiculite dust (which is common scrap from the exfoliation process), one can produce high temperature adhesives. The intumescence disappears in the presence of finely divided mineral dust, whereby the waterglass becomes a mere matrix. Waterglass is inexpensive and abundantly available, which makes its use popular in many refractory applications.
Water glass is used as a water treatment in waste water treatment plants. Waterglass will bind to heavier molecules and drag them out of the water.
Water glass was used in the magic crystal garden toys from the 1980’s. When waterglass was combined with a selection of different metals in solution, the waterglass would cause the metals to precipitate. Each metal would precipitate separately causing a different color stalagmite.
Sodium silicate in the paper & pulp industry
In the peroxide bleaching process of the Pulp and Paper industry sodium silicate functions as a transition metal ion chelate, a pH buffer, a stabiliser, a surface active agent and penetrant and as a corrosion control agent
Health & safety
Risk phrases: R34 Causes burns. R37 Irritating to respiratory system.
Safety phrases: S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S36/37/39 Wear suitable protective clothing, gloves and eye/face protection. S45 In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).
For full details see MSDS for sodium silicate