Studies on Crystallization of Glasses and Properties of Crystallized Glasses of System Li<sub>2</sub>O-MgO-CaO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>-F

Abstract

Studies on the crystallization of the glasses and the properties of crystallized glasses having the composition {Li2Ca (Mg5-xAlx) (AlxSi8-x) O22F2} were carried out. Those compositions were obtained by the isomorphous substitution of the F-richterite composition {Na⋅NaCa⋅Mg5⋅Si8O22F2}.The results obtained were summarized as follows:1) The crystallized glasses having the compositions of Li2Ca(Mg3Al2)(Al2Si6) O22F2+0.75, 1.0, 2.5mol Li2O heat-treated at 950°C for 2-3 hours had very large negative thermal expansion coefficients and their crystalline phases were mainly β-quartz (ss).2) Accoding to J. Petzoldt, the crystallized glass having the composition of eucryptite (LiAlSiO4) and heat-treated at higher temperatures has a larger negative thermal expansion goefficient (at 900°C α≈-10×10-7/°C at 1000°C α≈-70×10-7/°C). β-quartz (ss) precipitated at higher temperature in the glass having the composition of eucryptite has larger lattice constant chex, so that from the value of lattice constant chexof β-quartz (ss) the value of thermal expansion coefficient of β-quartz (ss) may be presumed. In this investigation, β-quartz (ss) precipitated at 900°C in the glasses containing more than 0.75mol excess Li2O had larger lattice constants chex than that of precipitated at 900°C in the glass having the composition of eucryptite, and β-quartz (ss) precipitated in the glass containing more than 1.0mol excess Li2O had nearly the same value of lattice constant chex as β-eucryptite.3) In the glass having the composition {Li2Ca(Mg4Al)(AlSi7)O22F2}, the crystallization started at the glass surface and the strength of the crystallized glasses, heat-treated at relatively lower temperature, increased with treating time.