Almost fully dense pure alumina could be prepared by fast firing (FF) at a high temperature (greater than 1689 °C) and a high heating rate (～350 °C/s) with a whole sintering cycle in approximately 2 min without pressure. Dynamics of the ultrafast densification was explored by comparing the densifying characters of FF sintering and conventional sintering. Results show that overlapping of surface/grain boundary diffusion and lattice diffusion caused by the high heating rate, as well as rapid migration of nanoscale particles caused by the high heating rate and the sufficiently high sintering temperature, leads to the ultrafast densification, which differs from conventional time-cost material diffusion. The ultrafast densification dynamics is expected to be helpful for understanding or developing new fast sintering methods for ceramics.
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