Study of 0.9Al_2O_3–0.1TiO_2 ceramics prepared by a novel DCC-HVCI method

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: ε_r = 11.26±0.06, Q×f = 11569± 629 GHz, τ_t = 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.