Sol–Gel Synthesis and Characterization of Gelswith Compositions Relevant to Hydrated Glass Alteration Layers

摘要

During the processes associated with glass corrosion, porous hydrated glass alteration layers typically form upon exposure to aqueous conditions for extended time periods. The impacts of the alteration layer on glass durability have not been agreed upon in the glass science community. In particular, the formation mechanisms of hydrated glass alteration layers are still largely unknown and require further investigation, but these layers often require months to years to develop and are often too thin to adequately characterize. Meanwhile, sol–gel-derived silicate gels are relatively easy to synthesize in bulk with custom compositions relevant to hydrated glass alteration layers. If alteration layers and synthetic silicate gels demonstrate physical and chemical properties that are sufficiently similar, synthetic silicate gels could be used as analogues for hydrated glass alteration layers in future studies. However, synthetic gels must first be prepared and evaluated before comparisons between glass alteration layers and synthetic silicate gels can be made. This work focuses entirely on the synthesis and observed physical propertiesof synthetic silicate gels. A future work will compare the characteristicsof synthetic gels described in this work with altered waste glassformed in similar pH environments. In this study, synthetic gels weremade with custom compositions at various pH values to evaluate theeffect of pH on gel structure and morphology. Several other variableswere examined also, such as composition, drying, and aging. Gels wereproduced by sequential additions of organometallic precursors in asingle container. Gels were analyzed with several techniques includingsmall-angle X-ray scattering, gas adsorption, and He pycnometry todetermine the effects of the variables on physical properties. Resultsshow that gels prepared at pH 3 consistently contained fewer primaryparticles with diameters larger than 7.2 nm and fewer pores with diameterslarger than 30 nm compared to gels synthesized at pH 7 and 9. Compositionwas shown to have no discernable effect on primary particle and poresizes at any pH.