Sodium and Potassium Silicates

Properties and Applications

Sodium, potassium and lithium silicates are important inorganic binders and additives. These resins when added to concrete and other masonry products increase resistance to heat, wear, oil, water and acids.

Sodium silicate solutions (Na Si), also called water glass or liquid sodium silicate, are the largest volume silicate products. These resins readily polymerize when the pH is lowered to about 10 or lower. At these conditions, concentrated solutions polymerize to form a gel whereas relatively dilute solution form a sol when acidified. The degree of polymerization of silicate anions depends on the alkali silicate concentration, pH value, temperature, and concentration of other (multivalent) ions present in solution. Fastest gelation is observed between pH 5 and 8.¹
Potassium silicate solutions (K Si) have similar properties to sodium silicate solutions but are somewhat more viscous than at equal concentration. They also have a higher hydration number due to the larger ionic radius. Due to their greater chemical stability (less carbonate whitening) they are often preferred for decorative paint applications. They are also more soluble and compatible with other (dissolved) chemicals.
Lithium silicate solutions (Li Si) have a lower alkalinity and viscosity than Na Si and when dried, they are less water soluble than Na Si and K Si. They are also more reactive and dry faster. Furthermore, their addition to Na/K Si can boost adhesion to various substrates.² However, due to their much higher cost and their lower stability, they are less frequently used.

Silicates are used for a wide range of masonry applications including concrete and brickwork sealing, chemical-resistant mortars, and clay slip casting. The addition of silicates lowers the viscosity of slurries and thereby reduces the casting time.¹ The addition of silicates also reduces firing time, sinter shrinkage, and increases the strength of the final masonry product. When added to cement, silicates increase temperature and acid resistance, reduce sag and slump, and lower the porosity of the final masonry product.¹

Sodium silicates in liquid form (water glass) are used as functional additives, modifiers, film formers, and as reactive resins in numerous products and applications including detergents³, pulp & paper products, industrial and municipal water treatment (coagulant), drilling fluids (corrosion prevention & emulsion breaking) and, on a somewhat smaller scale, textile processing (dye fixation), food preservation, plant nutrient, natural plant fungicide, adhesives, sealers, paints and coatings.

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