Abstract
In this paper, in-situ coagulation of 0.9Al2O3–0.1TiO2 suspension and microwave dielectric properties of 0.9Al2O3–0.1TiO2 ceramics prepared by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method were proposed. The 0.9Al2O3–0.1TiO2 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 0.9Al2O3–0.1TiO2 suspension could be successfully prepared by adding 0.3 wt% TAC and adjusting pH value to 10–12 at room temperature. 0.9Al2O3–0.1TiO2 green bodies with uniform microstructures were coagulated by adding 8.0 g/L calcium iodate after treating at 70 °C for 1 h. 0.9Al2O3–0.1TiO2 ceramics, sintered at 1500 for 4 h and annealed at 1100°C for 5 h, showed °Cuniform microstructures with density of 3.62±0.02 g/cm3. The microwave dielectric properties of 0.9Al2O3–0.1TiO2 ceramics prepared by DCC-HVCI method were: εr = 11.26±0.06, Q×f = 11569±629 GHz, τf= 0.93±0.60 ppm/°C. 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.
Highlights
IntroductionThe application of Al2O3 ceramics was limited by high f ( 60 ppm/ °C ) and sintering temperature (> 1600 °C) [5]
With the rapid development of microwave communication technology, the demand of microwave dielectric ceramics with low dielectric constant ( r ), and relative low dielectric constant ( r = 10) [2,3,4]
The results above indicates that tri-ammonium citrate (TAC) improves the replusive force between 0.9Al2O3–0.1TiO2 particles, which is beneficial to the stable dispersion of the particles in the alkaline region
Summary
The application of Al2O3 ceramics was limited by high f ( 60 ppm/ °C ) and sintering temperature (> 1600 °C) [5]. Ohishi et al [7] and Miyauchi et al [8] found 0.9Al2O3–0.1TiO2 ceramics had a near-zero f , while a detrimental Al2TiO5 secondary phase could form during the sintering process, which could decrease the quality factor of ceramics. Ohishi et al [7] reported good dielectric properties of 0.9Al2O3–0.1TiO2 ceramics with r = 12.4, Q×f = 117000 GHz, f = +1.5 ppm/°C after annealing at 1000 °C for 2 h. Miyauchi et al [8] obtained a higher dielectric property of 0.9Al2O3–0.1TiO2 ceramics with r = 12.4, Q×f = 148000 GHz, f = + 1.5 ppm/°C after annealing at 1100 °C
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
