The Effect of Lithium on Crystallization and Microstructure of Glass-Ceramics in Soda-Lime Silicate System

Abstract

This study investigated the crystallization of soda-lime silicate (NCS) system by re-melting soda-lime silicate glass cullet with Al2O3 CaCO3 and Li2O. The Li2O was added as a nucleating agent. The effect of the nucleating agent on crystallization was investigated in order to study the possibility for use as a parent glass for glass-ceramics. Soda-lime silicate cullet was the main raw material and its chemical composition by weight was 68% SiO2 2% Al2O3 9% Na2O 9% K2O 3.5% CaO 2.5% MgO 1.2% TiO2 3% SrO and 2% ZnO. Glass batches with composition (%wt) of (65-x) Cullet:13Al2O3:22CaCO3:x(Li2O) (x = 0, 1, 2, 4, 6 and 8) were melted at 1500°C for 3 hours and annealed at 600°C. All glasses added with Li2O were clear except x = 8. The crystallization was investigated by Differential Scanning Colorimetry technique (DSC). The results exhibited the exothermic peak of crystallization (TpI and TpII). The glasses with added Li2O exhibited decreasing crystallization temperature with increasing Li content. The glasses were heated at temperatures around the crystallization temperature (700, 750 and 800°C). After heat treatment, the crystalline phase in the glasses was determined by X-ray diffraction technique (XRD). The microstructure was investigated by optical microscope and Scanning Electron Microscope (SEM). The phases of Nepheline (Na,K)AlSiO4 and Wollastonite (CaSiO3) were found. The crystallization depended on the heat treatment temperature. The thermal expansion of the glasses was determined by the dilatometric method to indicate the characteristics of the glass-ceramics. In conclusion, Li2O had a strong effect on the crystallization in soda-lime silicate system. The result could be applied for the production of glass-ceramics from soda-lime cullet.