Abstract
Abstract A comparative study between the conventional and 2.45 GHz microwave multimode sintering behavior of insulator (α-Al2O3) and semi-conductive ceramic (ZnO) was systematically investigated. The apparent activation energy of nonisothermal sintering was determined by way of the Arrhenius plot of densification data at constant heating rates (CHR) and the concepts of Master Sintering Curves (MSCs), respectively. During microwave densification process, the apparent activation energy was about 90 kJ/mol less than the value for conventional sintering of Al2O3 applying these two estimation methods. However, an opposite result was obtained in the case of ZnO, although its densification process had been also accelerated by microwave as well as Al2O3. The significant differences in activation energy give a good proof of the difference in diffusion mechanism induced by the electromagnetic field underlying microwave sintering.
Highlights
In order to achieve rapid heating, low sintering temperature and low processing cost, microwave-assisted process has received intensive interests for sintering various ceramic materials.[1,2,3] Thanks to the coupling between electromagnetic fields and materials, microwave sintering provides the possibility to heat volumetrically samples
Two set of samples were prepared respectively for the conventional and microwave multimode sintering. Both set of samples were shaped by uniaxial pressing at 110 MPa, followed by cold isostatic pressing (CIP) at 300 MPa
A common phenomenon is observed on both samples (ZnO and Al2O3) sintered in either conventional or microwave sintering techniques: the densification curves shift toward higher temperature with increasing heating rate
Summary
In order to achieve rapid heating, low sintering temperature and low processing cost, microwave-assisted process has received intensive interests for sintering various ceramic materials.[1,2,3] Thanks to the coupling between electromagnetic fields and materials, microwave sintering provides the possibility to heat volumetrically samples. The microwave energy is mostly absorbed within the bulk in many solids, leading to improved thermal efficiency and much higher heating rates. A homogeneous temperature distribution within the solid is subsequently achievable when microwave is used as a source of energy. High heating rates are useful to get low grain size and so to improve the properties of the products. Homogeneous temperature fields are beneficial to decrease the thermal stress into the sample being heat treated
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