Microwave Absorption Behavior of Iron-Alumina Mixed Powder at Elevated Temperature

Abstract

Recently, it has been reported that metal powders can be heated by microwave irradiation and many attentions have been attracted on the research field. More effectively heating of iron powder in H field than E field has also been reported. From this result, it is supposed that microwave absorbability of iron powder may change at Curie temperature since iron losses magnetism at the temperature. The objective of this work is to reveal the microwave absorption behavior of iron powder around Curie temperature. For this purpose, microwave absorption behavior of iron–alumina mixed powder at elevated temperature was measured by using a circular wave-guide fixture and a microwave vector network analyzer. When iron powder was subjected to a measurement, compact body of iron powder became a reflector for microwave above 700°C, hence any change of absorbability around Curie temperature (780°C) could not be obtained. When iron(50mass%)–alumina(50mass%) powder was subjected to measurement, drastic change of microwave absorbability was observed at Curie temperature. From the absorbability change around Curie temperature, it was estimated that contribution ratios of magnetic loss is 72% and of dielectric loss is 28% on microwave absorbability for iron(50mass%)–alumina(50mass%) mixed powder.