ZnO-Al2O3-SiO2系ガラスから析出する準安定Indialite

It was found that an indialite-like crystal was precipitated on heat treatment of some glasses of the compositions near 2ZnO⋅2Al2O3⋅5SiO2. The formation and the thermal stability of this phase and some characters of the crystallized glasses containing this phase were examined and the following results were obtained.1) Zn-indialite (2ZnO⋅2Al2O3⋅5SiO2) was precipitated as a main phase when glasses of the compositions 2.17ZnO⋅2Al2O3⋅4.77SiO2, 2.16ZnO⋅2Al2O3⋅5SiO2, for example, were heated at 870°-1000°C.2) Zn-indialite was metastable, converting easily to a mixture of gahnite and silica above 1000°C.3) Long crystals (500μ) were formed at the block surface, perpendicular to it, when glass block was heated.4) The Zn-indialite precipitated in glasses was hexagonal or pseudohexagonal and in many cases optically uniaxial negative, having unit cell lengths a and c equaling 9.82A and 9.35A, respectively.5) The coefficient of thermal expansion of the Zn-indialite aggregate was 11×10-7/c, similar to that of indialite.