Microstructural Uniformity and Homogeneity in Alumina Sintered by Microwave (Hybrid) Heating at 2.45 GHz

Abstract

Microwave (hybrid) heating (MHH) is a unique combination of microwave (MW)-material interaction and conventional radiant heating/conduction mechanisms that facilitates the attainment of very high heating rates in a 2.45 GHz multimode MW cavity. Microstructural uniformity and homogeneity of cold-pressed green samples of pure, undoped, as-received alumina, fired by MHH vis-à-vis conventional fast firing (CFF) has been investigated. The synergism of the twin heating mechanisms (with MHH) results in an improved parity in temperatures across the sample cross-sections vis-à-vis CFF and stand-alone MW (SMW) sintering; this enhanced parity in temperatures (with MHH) can be premised to be responsible for the better microstructural homogeneity and enhanced mechanical properties relative to CFF. Sintering of larger (20 gm vs 6 gm) samples with MHH shows evidence of a definitive mass dependence on the MHH phenomenon. Larger masses show a better parity in temperatures between the surface and the interior of the sample. Consequently, this culminates in further enhancements in the homogeneity of the microstructure, and improved and more uniform mechanical properties relative to the smaller MHH and CFF samples.