Crystallization, mechanical, and optical properties of transparent, nanocrystalline gahnite glass-ceramics

This paper describes the preparation of a transparent glass-ceramic from the SiO2-K2O-ZnO-Al2O3-TiO2 system containing a single crystalline phase, gahnite (ZnAl2O4). TiO2 was used as a nucleating agent for the heat-induced precipitation of gahnite crystals of 5-10 nm. The evolution of the ZnAl2O4 spinel structure through the gradual formation of Al-O bonds was examined by infrared spectroscopy. The dark brown color of the transparent precursor glass and glass-ceramic was eliminated using CeO2. The increase in transparency of the CeO2-doped glass and glass-ceramics was demonstrated by UV-visible absorption spectroscopy. EPR measurements confirmed the presence of Ce3+ ions, indicating that CeO2 was effective in eliminating the brown color introduced by Ti3+ ions via oxidation to Ti+4. The hardness of the glass-ceramic was 30% higher than that of the as-prepared glasses. This work offers key guidelines to produce hard, transparent glass-ceramics which may be potential candidates for a variety of technological applications, such as armor and display panels.