Improving properties of Na2O–CaO–SiO2 glass by CdO, Fe2O3 addition and its crystallization for sealing applications

Abstract

The present work describes the preparation and characterization of new glass and glass-ceramic systems dependent on the Na2O–CaO–SiO2 composition which modified with partial CdO/CaO and Fe2O3/SiO2 substitutions. Typical temperatures for thermal analysis were examined by DTA and dilatometry measurements as a function of CdO and Fe2O3 contents. As well, the chemical stability and control crystallization of the newly established glasses and glass-ceramics were decided and discussed. The Tg and Tc temperatures decreased, while the CTE values increased with CdO and Fe2O3 contents. The produced glass-ceramics were dense and well-crystallized, including precipitation of the Na4Ca4Si6O18 phase with its derivative of the Na6Cd3Si6O18 phase, in addition to CaFeSi2O6 of the pyroxene type. The CTE of the prepared glasses and glass-ceramics is linearly increasing as a function of compositions. The values vary within the range of 33–72 × 10−7 °C−1 for the glasses, whereas they ranged from 57-104 × 10−7 °C−1 for their corresponding glass-ceramics. The results of the dissolution rate indicated that the DR ratio was increased by CdO/CaO replacements for the glasses and their crystalline samples. While the durability improved by Fe2O3/SiO2 substitutions. The DR and CTE values of the prepared materials are very close to or surpass the values of commercial sealing materials. The thermo-chemical properties showed that the prepared glass-ceramics, especially those with high Fe2O3/SiO2 replacement, are promising candidates as environmentally safe sealant materials for different applications, such as encapsulating photovoltaic cells and sensors used in unmanned systems in military applications.