Structural study of the effect of mineral additives on the transparency, stability, and aging of silicate gels

This work evaluates the structural evolution of silicate gel over time with mineral additives. A comparison between fresh and aged silicate gel synthesized from silica and potassium hydroxide was carried out using FTIR, Raman, and(29)Si MAS-NMR spectroscopies. Then, different additives, including NaOH, AlOOH, Li2B4O7, and HCl, were incorporated into the silica solution. The effects of these additives on the aspect, transparency, Q(n)polymerization, and stability of the silicate gels were studied. Structural studies showed that the quantification of Q(n)species was difficult using FTIR and Raman spectroscopies because of the existence of several contributions in the same spectral region of silicate species. More precise information was provided by(29)Si NMR spectroscopy, which demonstrated the increase in Q(3)species to the detriment of Q(4), revealing the depolymerization of the structure over time. Further study of the effect of additives revealed that HCl, AlOOH, and Li(2)B(4)O(7)did not improve the stability of the gel due to the formation of several networks. However, promising stability and transparency results were obtained using NaOH with a silicate/modifier molar ratio of 2.52.