Effect of nanoscale powders and microwave sintering on densification of alumina ceramics

Nanoscale alumina (Al2O3) powders with an average size of 100, 200, or 300 nm were sintered to investigate the effects of the initial powder size on the densification behavior under the application of microwaves (2.45 GHz, 2 kW). The sintering was performed using microwave-assisted sintering (MWS) and conventional sintering (CS) methods in the temperature range of 1100–1600 °C for 0–180 min. The Al2O3 samples prepared with the 100-nm-sized powders using MWS exhibited a relative density (RD) of over 90% when sintered at 1200 °C for 10 min; the same RD was achieved at 1500 °C when the sintering was performed for the same time using CS. However, a sintering temperature difference of ~100 °C for a RD of ~90% was observed between the MWS and CS methods for the 300-nm-sized powders. Nano-grained (~290 nm) Al2O3 ceramics with a high density of ≥90% were obtained from nanoscale powders (~100 nm) using MWS methods. The response of the nanoscale powders to microwaves was more significant as the initial powder size decreased from 300 to 100 nm.