Development of an instrumented and automated single mode cavity for ceramic microwave sintering: Application to an alpha pure alumina powder

Highlights: • Original single mode cavity for direct microwave sintering of low dielectric loss ceramics without any susceptor. • Combination of technological innovations for direct and reliable comparison between conventional and microwave sintering. • Use of numerical modeling for designing the setup and predicting electric field distribution within the cavity. • Evidence of microwave effects in the first and intermediate stages of sintering of pure alumina. - Abstract: This paper describes the development of an instrumented and automated single mode microwave cavity for sintering ceramic powders. This setup includes an optical dilatometer and a motorized plunger to control heating cycles in a wide range of heating rates (from 5 °C ∙ min⁻¹ to 200 °C ∙ min⁻¹) up to 1600 °C and to allow reliable comparison with conventional sintering. The cavity and the sintering cells for both hybrid and direct microwave sintering were designed using finite element simulation. For accurate temperature measurement, an optical pyrometer calibrated with a specific protocol has been used. Microwave sintering of fine grained (< 100 nm) alpha alumina compacts was thus investigated and compared to conventional sintering. This pure alumina powder has been sintered by direct microwave heating, without any susceptor nor doping element to initiate heating as often achieved in the literature. The comparison of the densification kinetics along an identical thermal cycle evidenced a significant enhancement of sintering under microwaves during the first and intermediate stages.