Solubility of water in molten alkali silicates

JSGT 1958 V42 T130-T144

The solubility of water in molten alkali silicates which are in equilibrium with an atmosphere of steam has been investigated as a function of temperature and alkali oxide content. A minimum at approximately 25 mol% alkali is observed in the solubility–composition curves for all three systems. This is interpreted in terms of two different mechanisms for the solution of water. One of these (Si–OH/OH–Si) results in a solubility which decreases with alkali oxide content while the other (Si–O–Si+2Na⁺+2OH^- or Si–O–H–O–Si) produces a system in which the solubility increases with alkali oxide content. The heat of solution of water in sodium and potassium silicates is negative but in lithium silicates is positive. This is attributed to the high field strength of the lithium ion which causes a weakening of the Si–O–Si linkages and results in the formation of weaker Si–OH bonds.

C. R. Kurkjian & L. E. Russell