Li₂O-MgO-CaO-Al₂O₃-SiO₂-F系ガラスの結晶化と結晶化物の性質

抄録

Studies on the crystallization of the glasses and the properties of crystallized glasses having the composition {Li₂Ca (Mg_5-xAl_x) (Al_xSi_8-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 c_hex, so that from the value of lattice constant c_hexof 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 c_hex 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 c_hex 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.