Microwave Sintering of Alumina at 2.45 GHz

Abstract

The sintering kinetics and microstructural evolution of alumina tubes (ϳ17 mm length, ϳ9 mm inner diameter, and ϳ11 mm outer diameter) were studied by conventional and microwave heating at 2.45 GHz. Temperature during microwave heating was measured with an infrared pyrometer and was calibrated to ؎10°C. With no hold at sintering temperature, microwave-sintered samples reached 95% density at 1350°C versus 1600°C for conventionally heated samples. The activation energy for microwave sintering was 85 ؎ 10 kJ/mol, whereas the activation energy for conventionally sintered samples was 520 ؎ 14 kJ/mol. Despite the difference in temperature, grains grew from ϳ1.0 m at 86% density to ϳ2.6 m at 98% density for both conventionally sintered and microwave-sintered samples. The grain size/density trajectory was independent of the heating source. It is concluded that the enhanced densification with microwave heating is not a consequence of fast-firing and therefore is not a result in the change in the relative rates of surface and grain boundary diffusion in the presence of microwave energy. Fig. 7. Grain growth trajectories of microwave-sintered and conventionally sintered samples.

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