Fabricação e caracterização de cerâmicas com propriedades multifuncionais à base de CaCu3Ti4O12 modificadas com magnésio

• Autor(a) principal: Lourenço, Carolina [UNESP]
• Data de Publicação: 2017
• Tipo de documento: Trabalho de conclusão de curso
• Idioma: por
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/203603; http://www.athena.biblioteca.unesp.br/exlibris/bd/capelo/2019-06-25/000916042.pdf
• topic: Ceramica (Tecnologia); Estequiometria; Varistores; Microscopia eletrônica de varredura

This work had as proposal a new stoichiometric system to be applied as varistor and dielectric, that is, the non - ohmic and dielectric properties were evaluated. A gradual replacement of the calcium element by magnesium was performed following the ratio: Ca1-xMgxCu3Ti4O12, in which x = 0.00; 0.05; 0.10; 0.50; 0.90 and 1.00. In addition to the proportion of magnesium, the influence of different sintering temperatures was also evaluated: 1000 °C, 1050 °C and 1100 °C, obtained from the study of the Dilatometry of the powders. The ceramics were prepared by reaction in the solid state and sintered in a chamber oven. In order to know the microstructure and the phases present in the new system, X-ray diffractometry (XRD) and scanning electron microstructure (SEM) techniques were used in both powders and disc-shaped pellets. Density and porosity, important parameters to keep the ceramic application viable, were studied through the Archimedes method and also by the gas pycnometry technique. In order to evaluate the properties of the pellets, direct current (DC) measurements were performed to study the varistor property of the compound by determining the following parameters from the E vs. J curves: nonlinearity coefficient (α), field electric rupture (Er) and leakage current (if), among others. Through the impedance / admittance spectroscopy technique (alternating current - AC), dielectric loss and permissivity were determined. Dense bulbs (average of 4.65 g/cm³) and excellent dielectric constant ε ~ 105 (when X = 0.10 sintered at 1050 °C were found, in addition to constant dielectric loss over a wide frequency range. Regarding the non-ohmic property, it was verified that only some compositions were able to demonstrate the defined behavior, with a limitation of the equipment. For those that demonstrated, it was possible to ... (Complete abstract click electronic access below)