Abstract
The methodology of multi-variables control in millimeter wave sintering is set up, in order to provide a route to the design and development on advanced materials of next generation such as bulk nanocrystalline ceramics. The 28 GHz microwave sintering system has an intelligent peripheral equipment with a specially designed displacement sensor necessary for the real-time measurement and the closed loop control of a linear shrinkage. The CIP'ed compact of amorphous ZrO2-20mol%A12O3 powder, as synthesized via mechanical alloying, can be sintered to a full density without any macroscopic crack by employing millimeter wave heating followed by holding at a relatively low temperature of 1523 K. The rapid densification of the nanocrystalline ZrO2-20mol%Al2O3 compact in heating under a high frequency electric field is fairly well expressed by an Arrhenius relation ofε=Aexp (-H/kT) with an apparent activation energy (H) of 198 kJmol-1. Furthremore, the apparent activation energy tends to increase with increasing relative density in the case of a constant densification rate control sintering.
