Influence of Alumina Additions on the Physical and Chemical Properties of Lithium-iron-phosphate Glasses

Alumina improves the properties and depresses the devitrification of soda-lime-silicate glasses. Herein, the influence of alumina on the glass transition temperature, density, chemical durability, crystallization of lithium-iron-phosphate (LIP) glass has been investigated. As alumina was added to replace the iron oxide in a base LIP glass with the molar composition of Li2O:Fe2O3:P2O5=30:20:50, the alumina-containing glasses have increased Tg, densities and chemical stabilities than the base glass. When the amount of alumina is increased from 2 to 6 mol, the Tg value slightly increases, whereas the density decreases. However, the smallest weight loss is shown for the glass containing 3.2 mol of alumina. The variations of the properties with alumina are explained based on the infrared structure analysis results. In addition, it is found the either the base or the alumina-containing glasses have surface crystallization upon heat-treatments. Under the same treatment conditions, the base glass exhibits a thin layer of crystallization with LiFeP2O7 as the main phase. In contrast, alumina-containing glasses show much higher degree of crystallization, which is further increased with the amount of alumina. This trend is opposite to that of silicate glass. Besides the LiFeP2O7 main phase, Fe7(PO4) phase is also identified in the crystallized alumina-containing glasses.