Composições á base de aluinissilicatos e alumina para aplicações dielétricas.

Abstract

The ceramic materials are present in many applications of electronic components, highlighting mullite and mullite-based composites. The objective of this work was to study formulations containing aluminosilicates and alumina in order to obtain compositions suitable for dielectric applications. Initially, the precursors kaolin, ball clay and alumina were submitted to the characterizations: chemical, mineralogical and granulometric, and from the chemical composition it was defined the quantity of components in the masses. Specimens were produced ((50 mm x 15 mm x 5 mm) (50 mm x 3 mm)) by uniaxial pressing to 19, 6 MPa. The specimens were dried at 110 oC and sintered at temperatures of 1400, 1450 and 1500 °C, with heating rate of 5 °C/min and firing level of 60 minutes. Subsequently, the specimens were submitted to the characterizations: physicochemical, mechanical and dielectric. The relative dielectric constant (İr) and the tangent of losses (tan į) were evaluated for the frequencies of 0.1 kHz, 1 kHz, 10 kHz and 100 kHz at room temperature. It was observed the majority crystallization of the mullite phase for the studied temperature range, with morphology in the form of needles. Compositions containing higher content of fluxes presented lower porosity (~ 1.84) and water absorption (~0.74) and better flexural strength (~ 66 MPa). The dielectric constant values were close to those of mullite (İr = ~ 3,5 to ~ 4,5) in the frequency of 1 kHz, for the compositions sintered at 1400 °C. Lower dielectric losses (tan į ~ 0.01) were observed at 1400- 1500°C and 100 kHz.