Nucleation and crystallization behavior of glass-ceramic materials in the Li2O-Al2O3-SiO2 system of interest for their transparency properties

We investigated the nucleation and crystallization behavior of multi-phase glass-ceramic materials (in the Li2O-Al2O3-SiO2 System to which low amounts of oxides such as TiO2, ZrO2, P2O5, BaO, Sb2O3 and ZnO were added), with i nterest in their transparency properties as glazes for industrial tiles wit h high scratch resistance. X-ray diffraction (XRD) and transmission electro n microscopy (TEM) were used. XRD showed that the nucleating oxides produce , during the nucleation stage (at 953 K for 20 h), an orthorhombic ZrTiO4 p hase, which maintains a similar crystallite size (about 4 nun) during the s ubsequent crystallization processes. We succeeded in determining the concen tration of nuclei by using XRD data only, This quantity resulted close enou gh 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., beta -eucryptite s .s., which is richer in silica with respect to the relevant stoichiometric phase, into P-spodumene s.s., also richer in silica, were found to be conse cutive solid state reactions. Moreover, this preliminary investigation aims at improving knowledge of the mechanisms leading to the development of tra nsparent/opaque materials during the thermal treatment of Li2O-Al2O3-SiO2 g lass-ceramics. (C) 2001 Elsevier Science B.V. All rights reserved.