The changes in lead silicate glasses induced by the addition of a reducing agent (TiN or SiC)

Abstract Foam glasses can be prepared from lead silicate glasses through reaction with a reducing agent such as TiN or SiC. The environmental impact and specific characteristics of the final product (e.g., density, porosity, and thermal and mechanical properties) depend on the reaction processes that occur during expansion. The mechanisms of foam glass formation are determined in this study from experimental results, which we also use to determine the structural differences between the bulk (lead silicate glass before treatment) and foam glass (after heating the lead silicate glass with a reducing agent). This paper also presents measurements of the variation of the concentration of the divalent cation Pb(II) in the vitreous network (which initially contains 2–5 mol% PbO) during the expansion process. These results were obtained with various methods, including X-ray diffraction, differential scanning calorimetry, photoelectron spectroscopy, and scanning electron microscopy with energy dispersive spectrometry. Our results show that a small proportion (about 20%) of the initial Pb(II) in network modifying sites is reduced to Pb metal, and the remaining proportion is present in the vitreous network as Pb(II) with another particular environment. Increasing the amount of SiC or TiN results in increased reduction of Pb(II). The quantity of the reducing agent can be optimized with respect to the temperature, pressure, and reaction rate.