Microstructural Evolution on Firing Soda–Lime–Silica Glass Fluxed Whitewares

Abstract

Density and microstructural evolution of porcelains containing 0–25 wt% soda–lime–silica (SLS) waste glass fired over a range of temperatures from 600° to 1400°C have been investigated. After firing 3 h at 1100°C, batches containing 6.25 wt% SLS glass and 18.75 wt% nepheline syenite flux system attained open‐pore closure and a bulk density of 2.40 g/cm3, comparable to results from commercial porcelain after firing at 1200°C. SLS glass softens and melts, conferring early densification and overfiring on porcelains fired at normal commercial firing temperatures. The microstructural evolution examined using XRD, SEM/energy dispersive spectroscopy (EDS), and TEM/EDS revealed formation of a variable composition plagioclase, rounded wollastonite particles, sodium silicates, and tridymite in batches containing SLS glass, in addition to primary and secondary mullites, partially dissolved quartz, and a glassy matrix as found in the waste‐free batch. Ca2+ and Na+ from the SLS glass migrate to regions containing the products of clay decomposition to form plagioclase, limiting the extent of mullite crystallization. The presence of a solution rim surrounding quartz and different glass compositions around wollastonite crystals indicate that the system is not in equilibrium, although phases predicted by the Na2O–CaO–SiO2 equilibrium diagram were formed.