Estudo da cinética de nucleação e crescimento de cristais na matriz vítrea TeO2 – WO3 – Bi2O3

Abstract

The technological advance of the last decades has provided significant advances both in obtaining and in the applications of glass. These materials have fundamental aspects, which put them as viable alternatives for applications in optics, in primary mirrors of telescopes and even photonic devices fibers in nanometric scale. The glasses of tellurium oxide base are an option to replace or enhance the characteristics of conventional vitreous systems such as silicate glasses. Optical and structural properties of tellurite glasses have directed research for various applications. In this work, samples of tellurite glasses were obtained from the matrix 80TeO2•(20 – x)WO3•(x)Bi2O3(mol%) prepared by the method of melting/cooling. These samples were characterized by thermal and structurally in order to study the control and size distribution of crystals in the glass matrix by two-step heat treatment, study the nucleation process and growth of crystals and study induced crystallization in the glass. Using two-step heat treatment was obtainedglass-ceramics with uniform distribution of crystal sizes. With the differential thermal analysis (DTA) associated with Matusita method, the results indicated that the samples were nucleated during annealing used to remove the remaining mechanical stresses of the melting/cooling process. The induced crystallization was studied using X-ray diffraction (XRD). It was possible to observe the formation of two crystalline phases after the heat treatment at 400°C, the δ–Te0,95W0,05O2,05 and δ–Bi2O3 phases.With subsequent treatments were also formed the α–TeO2 and γ–TeO2 phases. The induced crystallization of the study was accompanied by Raman spectroscopy, which allowed the identification of vibrational modes of polymorphs of TeO2.