Study of 0.9Al ₂O ₃–0.1TiO ₂ ceramics prepared by a novel DCC-HVCI method

Abstract

In this paper, in-situ coagulation of 0.9Al ₂O ₃–0.1TiO ₂ suspension and microwave dielectric properties of 0.9Al ₂O ₃–0.1TiO ₂ ceramics prepared by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method were proposed. The 0.9Al ₂O ₃–0.1TiO ₂ suspension could be coagulated via controlled release of calcium ions from calcium iodate at an elevated temperature. The influence of tri-ammonium citrate (TAC) content, solid loading, and calcium iodate content on the rheological properties of the suspension was investigated. In addition, the influence of coagulation temperature on coagulation time and properties of green bodies was also studied. It was found that the stable 0.9Al ₂O ₃–0.1TiO ₂ suspension could be successfully prepared by adding 0.3 wt% TAC and adjusting pH value to 10–12 at room temperature. 0.9Al ₂O ₃–0.1TiO ₂ green bodies with uniform microstructures were coagulated by adding 8.0 g/L calcium iodate after treating at 70 ℃ for 1 h. 0.9Al ₂O ₃–0.1TiO ₂ ceramics, sintered at 1500 ℃ for 4 h and annealed at 1100 ℃ for 5 h, showed uniform microstructures with density of 3.62±0.02 g/cm ³. The microwave dielectric properties of 0.9Al ₂O ₃–0.1TiO ₂ ceramics prepared by DCC-HVCI method were: ${\epsilon }_{\text{r}}$ = 11.26±0.06, Q× f = 11569± 629 GHz, ${\tau }_f$ = 0.93±0.60 ppm/℃. The DCC-HVCI method is a novel and promising route without binder removal process to prepare complex-shaped microwave dielectric ceramics with uniform microstructures and good microwave dielectric properties.