Electromagnetic-wave sintering of alumina ceramics from nano-sized particles: possible material for high-pressure cell for millimeter-wave electron spin resonance

Abstract

Electromagnetic-wave sintering of alumina ceramics using 28 GHz gyrotron has been performed aiming for a high fracture toughness value in order for use as pistons for pressure cells of high-frequency electron spin resonance (ESR) measurements. We have tried to improve the fracture toughness by using nano-sized alumina powder (140 nm in average particle size) having smaller particle size than our previous work (400 nm in average particle size). Rapid densification was observed around the sintering temperature of 1200 °C. We obtained the relative density over 99 % above 1400 °C. It was found that alumina ceramics made in this work at sintering temperatures have smaller grain size and higher density simultaneously as compared to the previous work. These results suggest that alumina ceramics made from powder of smaller particle size sintered by electromagnetic-wave sintering possibly have high fracture toughness which can be used as materials for the pressure cell for ESR.