Studies of the mechanism of formation of calcium silicate compounds by titration based on emission and atomic absorption spectroscopy

In this paper, the inhibition effect of silicate on emission or absorption of calcium was used for an investigation of the mechanism of formation of calcium silicate compounds. For that purpose, calcium chloride solutions were continuously titrated with a standard solution of sodium silicate (Na₂SiO₃), with simultaneous aspiration of the titrand into an air-hydrogen flame. During the titration, changes in the emission of the CaO-band at 622 nm and the CaOH-band at 554 nm were registered automatically on the recorder. Changes in the absorption of calcium were also registered at 422 nm. Thus curves of the same shape were obtained, with the same number of characteristic points, in which the SiO₂/Ca ratio is constant, when the concentration of silicate in the titrant varies. This fact suggests that calcium reacts with silicate to form compounds with a constant composition.Curves of the same shape were obtained by titration of a standard solution of sodium silicate, with a calcium chloride solution, while monitoring the changes in the absorption of calcium at 422 nm and changes in the emission of the CaO-band at 622 nm. In this case, the mole ratios SiO₂/Ca at the characteristic points of the curves were the same as in the case of the titration of calcium chloride solution with the silicate solution.On the basis of the mole ratios SiO₂/Ca at the characteristic points on the titration curves, which amount to 0.21, 0.33 and 0.50, the mechanism of formation of calcium silicate compounds was represented by chemical equations.It may be concluded that in the process of evaporation of spray droplets a chain of reactions take place, resulting in compounds that can be represented by the general formula xCaO·SiO₂.