Redox behavior of tin in aluminosilicate melts: Implications for the fining process

Abstract

Aluminosilicate glasses are widely used in everyday applications and can be seen as building blocks of modern technology, from display screens to glass‐ceramics. However, due to their high viscosities, gas bubbles can only be removed from aluminosilicate melts at high temperatures, leading to significant energy costs. This fining process can be improved with the use of multivalent oxides such as SnO₂. In this study, extended x‐ray absorption fine structure (EXAFS) and Raman spectroscopy were used to determine the local environment surrounding Sn(II) and Sn(IV) ions in a sodium aluminosilicate glass. In situ XANES spectroscopy enabled the quantification of Sn redox state at high temperature, allowing for the determination of thermodynamic parameters governing the Sn reduction. Our results show that Sn(IV) is octahedrally coordinated and linked to network‐forming tetrahedra through corner‐sharing, whereas Sn(II) is in a lower coordination number. Comparing the modeled behavior of Sn with that of Fe and Ce, it appears that SnO₂ is a suitable fining agent for aluminosilicate glasses as it undergoes reduction when the viscosity is sufficiently low for bubbles to escape the melt. Conversely, the use of CeO₂ leads to substantial gas release at higher viscosities, resulting in foam formation within the glass.