Microwave sintering of ZnO at ultra high heating rates

In this paper, a unique processing approach for producing a tailored, exter nally controlled microstructure in zinc oxide using very high heating rates (to 4900 degreesC/min) in a microwave environment is discussed. Detailed d ata on the densification, grain growth, and grain size uniformity as a func tion of heating rate are presented. With increasing heating rate, the grain size decreased while grain size uniformity increased. At extremely high he ating rates, high density can be achieved with almost complete suppression of grain growth. Ultrarapid microwave heating of ZnO also enhanced densific ation rates by up to 4 orders of magnitude compared to slow microwave heati ng. The results indicate that the densification mechanisms are different fo r slow and rapid heating rates. Since the mechanical, thermal, dielectric, and optical properties of ceramics depend on microstructure, ultrarapid hea ting may lead to advanced ceramics with tailored microstructure and enhance d properties.