Microwave heating of narrow metallic powder streams

In this work the design of an on-air pre-heating system for very narrow metallic powder streams by means of microwave radiation is described. A dielectric characterization for the temperature range 20 - 800°C was performed by means of an inverse permittivity recovery method. The heating applicator consists of a short-circuited WR-340 waveguide, which is fed by a magnetron plus launcher. An isolator (circulator plus water load) is introduced between these two systems in order to avoid damages in the magnetron. The zone for the material processing is located in the centre lobe of the TE103 mode. Both static (powder inside a quartz tube ¿2mm) and dynamic tests were realized, monitoring the temperature reached at the powder container and obtaining SEM images for analysing the heating effect on the powder particles. Despite the almost empty conditions in the applicator, which leads to a very sharp resonance, good tuning was achieved and high heating rates were obtained in the powder.