Nucleation and crystallization behavior of glass-ceramic materials in the Li 2O–Al 2O 3–SiO 2 system of interest for their transparency properties

Abstract

We investigated the nucleation and crystallization behavior of multi-phase glass-ceramic materials (in the Li 2O–Al 2O 3–SiO 2 system to which low amounts of oxides such as TiO 2, ZrO 2, P 2O 5, BaO, Sb 2O 3 and ZnO were added), with interest in their transparency properties as glazes for industrial tiles with high scratch resistance. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. XRD showed that the nucleating oxides produce, during the nucleation stage (at 953 K for 20 h), an orthorhombic ZrTiO 4 phase, which maintains a similar crystallite size (about 4 nm) during the subsequent crystallization processes. We succeeded in determining the concentration of nuclei by using XRD data only. This quantity resulted close enough to the corresponding one, determined using the classical TEM method. The formation of each crystalline phase, developed during the crystallization stage, as a function of the thermal treatment, was quantitatively measured using the Rietveld method. In particular, the isothermal transformations at 1003 and 1023 K of the characteristic main phase, i.e., β-eucryptite s.s., which is richer in silica with respect to the relevant stoichiometric phase, into β-spodumene s.s., also richer in silica, were found to be consecutive solid state reactions. Moreover, this preliminary investigation aims at improving knowledge of the mechanisms leading to the development of transparent/opaque materials during the thermal treatment of Li 2O–Al 2O 3–SiO 2 glass-ceramics.