Determination of the polymerization degree of various alkaline solutions: Raman investigation

Alkaline silicate solutions are used for different industrial applications. Structural studies of these solutions performed by fourier transform infrared and nuclear magnetic resonance spectroscopies have shown the presence of cyclic species. However, these techniques do not allow determining the variations of chain and ring size depending on the content of alkali cations and water. The objective of this study was thus to use Raman spectroscopy to obtain additive information, such as variations of ring and chain size to evaluate the reactivity of the silicate solutions. For this, several solutions were prepared according to different preparation methods (commercial or laboratory) with different cations and Si/M ratios (M = Na and/or K). The structural results obtained by Raman spectroscopy showed that the preparation method has an effect on the variation of the amount of rings with 3 and 4 tetrahedra. It has also been demonstrated that the cation had a stronger influence on the variations of these rings for commercially available solutions compared to their laboratory-made counterparts. Moreover, in the case of mixed solutions (M = Na + K), the alkali cation influenced the formation of this type of rings. Then, the effect of the Si/M ratio on the different species was highlighted and, in particular, the formation of rings at the expense of chains. Finally, this study has demonstrated that Raman spectroscopy is a crucial technique for understanding the structure of silicate solutions and their reactivity.