Desenvolvimento e caracterização de vitrocerâmicas com nanopartículas de titanatos de cálcio e bário
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Data
2021-10-28
Autores
Silveira, Wagner da
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Universidade Estadual Paulista (Unesp)
Resumo
Os materiais vítreos e vitrocerâmicos funcionais vêm sendo extensivamente estudados nas últimas décadas devido às suas características interessantes, as quais podem ser exploradas em diversas aplicações, como em revestimentos impermeáveis, janelas inteligentes e até em biovidros. Partindo desta gama de aplicações e sabendo que ainda há espaço para o desenvolvimento de materiais funcionais inéditos, este trabalho propõe o desenvolvimento de vitrocerâmicas pelo processo de fusão, no qual possam ser nucleadas fases dispersas de BaTiO3, CaTiO3 e BaTiO3-CaTiO3 em uma matriz a base de SiO2. O processo de fabricação envolveu a mistura e fusão de óxidos precursores (SiO2, TiO2, Al2O3) e carbonatos (CaCO3, BaCO3) em cadinhos de alumina. Em seguida, com o material fundido foi obtido fritas e placas de vitrocerâmica que foram caracterizadas por Difratometria de Raios X (DRX), Análise Térmica Diferencial (DTA), Espectrometria de Fluorescência de Raios X (FRX), Espectroscopia de Raios X por Dispersão em Energia (EDS), micro-Raman, Microscopia Eletrônica de Varredura (MEV) e óptica, análise de impedância e dureza. Por meio da DTA, foi possível determinar as temperaturas de cristalização das vitrocerâmicas propostas: 960ºC para a amostra Ca-Si e Ba-Si, 1000ºC para a amostra BaCa-Si e 1120ºC para a amostra Ba-Si. Para avaliar o processo de cristalização nestas faixas de temperatura, foram utilizados tratamentos térmicos de 30 min, 2h, 4h e 6h. Por meio do Refinamento de estrutura pelo método de Rietveld, foi possível obter a porcentagem das fases cristalizadas. Para o vitrocerâmica Ba-Si com o tratamento térmico por 6 horas (1120 ºC) foi obtido como microestrutura final BaTiO3 (68,07%) Ba2TiSi2O8 (19,82%) e Ba2SiO4 (12,11%). Para a vitrocerâmica Ca- Si com o tratamento térmico por 6 horas (1120 ºC) foi obtido como microestrutura final CaTiO3 (79,21%) CaTiSiO5 (11,25%) e Ca8Si5O18 (9,54%). Para a vitrocerâmica BaCa-Si não foi possível realizar o refinamento de estrutura, porém foi observado a presença das seguintes fases de interesse: BaTiO3, CaTiO3 e BaCaTiO4. O teste de dureza Vickers foi realizado para identificar a dureza das amostras de vitrocerâmica, sendo observado o maior valor de dureza para a vitrocerâmica Ca-Si (831HV) e a menor valor para a vitrocerâmica Ba-Si (486HV). As medidas elétricas mostraram como a variação da capacitância pode ser correlacionada com o tempo de tratamento térmico. De modo geral, os resultados mostram que é possível obter vitrocerâmicas com as fases dispersas de BaTiO3 e/ou CaTiO3, e que suas propriedades podem ser modificadas pelo tratamento térmico.
Functional vitreous and glass-ceramic materials have been extensively studied in recent decades due to their interesting characteristics, which can be exploited in various applications, such as waterproof coatings, smart windows and even bioglass. Based on this range of applications and knowing that there is still room for the development of novel functional materials, this work proposes the development of glass-ceramics by the fusion process, in which dispersed phases of BaTiO3, CaTiO3 and BaTiO3-CaTiO3 can be nucleated in a matrix SiO2 base. The manufacturing process involved the mixing and fusion of precursor oxides (SiO2, TiO2, Al2O3) and carbonates (CaCO3, BaCO3) in alumina crucibles. Then, with the molten material, frits and glass-ceramic plates were obtained, which were characterized by X-Ray Diffractometry (DRX), Differential Thermal Analysis (DTA), X-Ray Fluorescence Spectrometry (FRX), X-Ray Dispersion Spectroscopy in Energy (EDS), micro-Raman, Scanning Electron Microscopy (SEM) and Optical Microscopy, impedance and hardness analysis. Through DTA, it was possible to determine the crystallization temperatures of the proposed glass ceramics: 960ºC for the Ca-Si and Ba-Si sample, 1000 ºC for the BaCa-Si sample and 1120ºC for the Ba-Si sample. To evaluate the crystallization process in these temperature ranges, heat treatments of 30 min, 2h, 4h and 6h were used. Through structure refinement by the Rietveld method, it was possible to obtain the percentage of crystallized phases. For the Ba-Si glass-ceramic with heat treatment for 6 hours (1120ºC) the final microstructure was BaTiO3 (68.07%) Ba2TiSi2O8 (19.82%) and Ba2SiO4 (12.11%). For the Ca-Si glass-ceramic with heat treatment for 6 hours (1120ºC) the final microstructure was CaTiO3 (79.21%), CaTiSiO5 (11.25%) and Ca8Si5O18 (9.54%). For the BaCa-Si glass-ceramic it was not possible to carry out the structure refinement, but the presence of the following phases of interest was observed: BaTiO3, CaTiO3 and BaCaTiO4. The Vickers hardness test was performed to identify the hardness of the glass-ceramic samples, with the highest hardness value being observed for the Ca-Si glass-ceramic (831HV) and the lowest value for the Ba-Si glass-ceramic (486HV). Electrical measurements showed how capacitance variation can be correlated with heat treatment time. In general, the results show that it is possible to obtain glass ceramics with dispersed phases of BaTiO3 and/or CaTiO3, and that their properties can be modified by heat treatment.
Functional vitreous and glass-ceramic materials have been extensively studied in recent decades due to their interesting characteristics, which can be exploited in various applications, such as waterproof coatings, smart windows and even bioglass. Based on this range of applications and knowing that there is still room for the development of novel functional materials, this work proposes the development of glass-ceramics by the fusion process, in which dispersed phases of BaTiO3, CaTiO3 and BaTiO3-CaTiO3 can be nucleated in a matrix SiO2 base. The manufacturing process involved the mixing and fusion of precursor oxides (SiO2, TiO2, Al2O3) and carbonates (CaCO3, BaCO3) in alumina crucibles. Then, with the molten material, frits and glass-ceramic plates were obtained, which were characterized by X-Ray Diffractometry (DRX), Differential Thermal Analysis (DTA), X-Ray Fluorescence Spectrometry (FRX), X-Ray Dispersion Spectroscopy in Energy (EDS), micro-Raman, Scanning Electron Microscopy (SEM) and Optical Microscopy, impedance and hardness analysis. Through DTA, it was possible to determine the crystallization temperatures of the proposed glass ceramics: 960ºC for the Ca-Si and Ba-Si sample, 1000 ºC for the BaCa-Si sample and 1120ºC for the Ba-Si sample. To evaluate the crystallization process in these temperature ranges, heat treatments of 30 min, 2h, 4h and 6h were used. Through structure refinement by the Rietveld method, it was possible to obtain the percentage of crystallized phases. For the Ba-Si glass-ceramic with heat treatment for 6 hours (1120ºC) the final microstructure was BaTiO3 (68.07%) Ba2TiSi2O8 (19.82%) and Ba2SiO4 (12.11%). For the Ca-Si glass-ceramic with heat treatment for 6 hours (1120ºC) the final microstructure was CaTiO3 (79.21%), CaTiSiO5 (11.25%) and Ca8Si5O18 (9.54%). For the BaCa-Si glass-ceramic it was not possible to carry out the structure refinement, but the presence of the following phases of interest was observed: BaTiO3, CaTiO3 and BaCaTiO4. The Vickers hardness test was performed to identify the hardness of the glass-ceramic samples, with the highest hardness value being observed for the Ca-Si glass-ceramic (831HV) and the lowest value for the Ba-Si glass-ceramic (486HV). Electrical measurements showed how capacitance variation can be correlated with heat treatment time. In general, the results show that it is possible to obtain glass ceramics with dispersed phases of BaTiO3 and/or CaTiO3, and that their properties can be modified by heat treatment.
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Palavras-chave
CaTiO3, BaTiO3, Vitrocerâmicas, Propriedades elétricas, Dureza, Vidro, Glass-ceramics, Electrical properties, Hardness