Preparation of dense 0.9Al2O3−0.1TiO2 ceramics with highly improved microwave dielectric properties by a noncontaminated DCC method

Abstract

In this paper, dense 0.9Al2O3 − 0.1TiO2 ceramics with highly improved microwave dielectric properties were prepared by a noncontaminated direct coagulation casting (DCC) method. The suspension was destabilized and coagulated by consumption of the dispersant without introducing impurity ions. The effect of dispersant content, pH value and solid loading on the rheological properties of 0.9Al2O3 − 0.1TiO2 suspension was investigated. It was found that 0.9Al2O3 − 0.1TiO2 suspension with a high solid loading of 50 vol% and low viscosity of 0.7 Pa∙s could be prepared by adding 0.5 wt% TMAOH at the pH in the range of 10–12. The suspension was coagulated by adding 2 vol% GDA when it was treated at 60 ~ 80 °C for 40 ~ 60 min. Compared with dry pressing method, more homogeneous and denser microstructure could be obtained in 0.9A12O3 − 0.1TiO2 ceramics prepared by DCC via dispersant reaction which were sintered at 1550 °C for 3 h and annealed at 1100 °C for 5 h. The Al2TiO5 second phase in 0.9A12O3 − 0.1TiO2 ceramics prepared by DCC via dispersant reaction could be eliminated more easily by annealing treatment. After annealing treatment, only Al2O3 and TiO2 phases could be detected. Therefore, higher density and much better microwave dielectric properties with ρ = 3.81 ± 0.02 g/cm3, εr = 12.17 ± 0.02, Q × f = 25,637 ± 749 GHz, τf = 13.12 ± 1.62 ppm/°C were obtained by DCC via dispersant reaction, and the Q × f value almost improved by 25%. Without introducing impurity ions, it provides a new insight into preparing complex shaped function ceramics with high properties.