Fundamentals of Microwave-Material Interactions and Sintering

Abstract

ABSTRACTBasic interaction mechanisms are shown to depend strongly on the dielectric and magnetic properties of a process material. This causes a strong dependence of power absorption on frequency, material particle size, shape, temperature, and density. Sintering dynamics cause the microstructure of the treated material to change resulting in a change in microwave (1W) heating uniformity and rate. The concept of dielectric mixtures is introduced to predict the dielectric and heating properties of a host material with its inclusions in the form of shells, ellipsoids, spheres, disks and needles. Simplified models are described to give a process designer some insight into the behavior of MW sintering. Microwave power, by its very nature, gives better heating control and efficiency and provides internal heat to aid the material transport during sintering. No inherent temperature limit exists for MW sintering although refractory materials used to contain the process material create an artificial upper limit. It is shown that very high (1500–2000°C) temperatures in small samples can be readily achieved using commercial microwave ovens if appropriate MW transparent sample holders are used.