Lithium silicates

Fusion of sand with lithium chloride yields the orthosilicate, Li₄SiO₄, the metasilicate, Li₂SiO₃, and an acid silicate, Li₂O,5SiO₂. When the chloride is replaced by the carbonate, the same substances are formed, also another acid silicate, Li₂O,2SiO₂, and a subsilicate, Li₈SiO₆. A study by Niggli has proved the system lithium carbonate-silica to have the equilibrium indicated by the scheme

2Li₂CO₃+Li₄SiO₄ ⇔ Li₈SiO₆+2CO₂.

The monohydrate of the metasilicate, Li₂SiO₃,H₂O, is obtained as an almost insoluble, white, granular precipitate by the interaction at 80° to 90° C. of a solution of sodium metasilicate and the equivalent amount of lithium chloride in presence of normal lithium hydroxide. It is also produced by dissolving silicic acid dried below 100° C. in twice the theoretical proportion of twice-normal lithium hydroxide at the ordinary temperature, and subsequently heating the solution to 80° C. A readily soluble modification has also been prepared.

Several investigators have studied the properties of the silicates of lithium, but there is considerable divergence between the results obtained. Wallace has described the orthosilicate as forming strongly double-refracting crystals, melting-point 1168° C., and D=2.61. van Klooster mentions slight double refraction, and gives the melting- point as 1243° C., the density at 15° C. as 2.346, that of water at 15° C. being taken as unity, and the hardness (Mohs's scale) as 3.4. Rieke and Endell found for the melting-point 1215° C., and observed that water causes complete decomposition. More recent work by Jaeger and van Klooster gives the melting-point as 1256° C., and the density at 25° C. as 2-392. Dana and Foote found the melting-point to be 1255° C. Schwarz and Haacke regard the melting-point as being 1249° C., and the density as 2.28. The heat of fusion is 62 Cal.

The metasilicate melts at 1180° C. (Rieke and Endell), or 1188° C. (van Klooster), or 1201.8° C., or 1202° C., or 1209° C. For the density at 24.9° C., Jaeger gives 2.5203; and for the heat of fusion Schwarz and Sturm give 80.2 Cal. In an earlier paper van Klooster gave its density at 15° C. as 2.258, water at 15° C. being taken as unity, and its hardness (Mohs's scale) as 3. Friedel describes it as forming crystals of density 2.529 at 15° C., and as being decomposed by boiling water or dilute hydrochloric acid.

In aqueous solution the silicates of lithium undergo extensive hydrolytic dissociation. Double silicates of lithium and other metals have been described by Wallace.