Estudo da preparação de vidros e vitrocerâmicas óxidas por meio de levitação aerodinâmica utilizando fusão a laser

Abstract

The study of new routes for the preparation of glass-ceramics has been gaining increasing prominence in science. The aerodynamic levitation technique allows the obtaining of glassy and glass-ceramic materials from compounds that would have difficulty vitrifying under conventional conditions and, due to the lack of contact with any surface, can reduce the possibility of heterogeneous crystallization. Aerodynamic levitation also enables the production of miniaturized elements with a high degree of finish, being essentially ready for use in devices (avoiding cutting and polishing steps). In this doctoral thesis, glasses and glass-ceramics from the BaO – TiO2 – SiO2 – Al2O3 system were studied with and without the substitution of 23 mol% of Ca in the Ba site, aiming to obtain the crystalline phases Barium Titanate (BT) and Barium Calcium Titanate (BCT). The aerodynamic levitation system used is a modification (patent pending) that allows better heat distribution in the sample and utilizes lower-cost materials, further reducing the production cost of the material. The amorphous condition of the produced glasses was confirmed by Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD). After thermal treatment, the presence of the BT and BCT phases was confirmed through XRD, Raman Spectroscopy, and Scanning Electron Microscopy (SEM). During the process development, it was noted that glasses without the presence of Al2O3 did not show the formation of the BT phase, a fact reported in the literature, but never systematically discussed or explained. Thus, various molecular dynamics simulations were performed to evaluate the structure of the studied glasses. From the molecular dynamics, it was also possible to obtain data that allowed the development of a thermodynamic model (unprecedented for non-stoichiometric crystallization) to explain the crystallization differences in the studied glasses, concluding that the residual glass plays an important role in the crystallization.