Low thermal expansion coefficient LAS glass-ceramics with petalite as the main crystal phase

Abstract

Li₂O–Al₂O₃–SiO₂ (LAS) glass-ceramics have been explored for nearly 80 years, due to their special properties, such as low/negative thermal expansion and high ionic conductivity, thus having commercial significance in various fields. In this study, LAS glass-ceramics based on petalite crystals were developed, which have promising mechanical, thermal properties and compactness, making them potential for applications in hollowwares, tablewares, containers, and plate glass industries. With given ratios of Al₂O₃/SiO₂, the crystalline phase is mainly affected by the concentration of Li₂O, where the content of Li₂O must be sufficiently low to form petalite LiAlSi₃O₈, thereby avoiding the formation of spodumene LiAlSi₂O₆. For this reason, CaF₂ was selected as a nucleating agent to increase the crystallinity of petalite, while the crystallization behavior of LiAlSi₃O₈ crystals was analyzed in detail. The average transmittance of 3.0 ± 0.2 mm thick glass-ceramics in the visible light region and infrared light region (400–1200 nm) is higher than 85 %. After crystallization at about 770 °C, the crystal size in the glass-ceramics is 100–200 nm, which is relatively dense and has excellent near-zero expansion coefficient. The minimum CTE_{(25–325 °C)} is 1.0992 ppm/ °C, while the mechanical properties such as Vickers hardness, elastic modulus and flexural strength are significantly improved.