We have studied the effect of addition of titania, as a sintering agent, to alumina on the dielectric characteristics of the ceramic composites obtained. The dielectric properties of the titania-alumina composites were studied by use of impedance spectroscopy and the Hakki-Coleman method in the radiofrequency and microwave regions, respectively. The temperature coefficient of the resonant frequency (s f ) was also studied. Dielectric permittivity (e¢) was increased and the dielectric loss (tan d) was improved by addition of titania, as a result of better sintering; addition of 10 wt.% titania resulted in e¢ = 12.68 and tan d = 8.23 9 10 À4 in the microwave region. Increasing the concentration of TiO 2 led to inversion of the s f signal; values were positive when the concentration of TiO 2 was >7.5 wt.%. The ceramic composites were evaluated as antennas; for all samples the return loss (S 11 ) was <À10 dB and the gain was approximately 3 dBi. Addition of 7.5 wt.% titania to the Al 2 O 3 improved antenna performance. In conclusion, addition of the TiO 2 to alumina improves its dielectric properties, resulting in the possibility of use of such composites as dielectric resonator antennas (DRA).
Considerando-se a grande produção de resíduos de cerâmica vermelha (RCV) e os impactos ambientais associados ao descarte inapropriado destes resíduos no meio ambiente, e o alto teor de emissão de CO2 associado à produção da cal, este trabalho analisa o impacto da substituição da cal por RCV nas propriedades do estado endurecido de argamassas mistas. Para isso, foram feitas substituições nos teores de 20%, 40% e 60%, além de um traço de referência, para verificar a influência destas propriedades por meio dos seguintes ensaios: resistência à tração na flexão, resistência à compressão, absorção de água e índice de vazios. Os resultados obtidos foram satisfatórios para a maioria das propriedades mecânicas e físicas das argamassas, para todos os teores de substituição analisados, tendo no teor de 40% os resultados mais satisfatórios, demonstrando o potencial desta substituição.
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