Microwaves as an Energy Source for Producing Magnesia - Alumina Spinel

This work describes the production of magnesia-alumina spinel using microwaves as energy source. The microwave energy was supplied by means of an 800 W magnetron operating at 2.45 GHz. The microstructure and the mineral composition were studied by means of SEM and X-Ray diffraction respectively. The resultant product shown sintered zone and incipient smelting of the reagents meaning that microwave processing could be a practical form for spinel production. INTRODUCTION One of the most important properties of ceramic materials is that they retain their structural properties at high temperatures, they usually present a high melting point and this property makes difficult the process of this kind of materials, because it is necessary to achieve high temperatures. Traditionally, these materials have been produced using gas burners or electric resistance elements. Since the development of the microwave devices there has been an upsurge of interest, within the scientific community, on the possible applications of microwave radiation as an energy source for the processing of materials. There are some discussions about the mechanism that governs the absorption of microwave energy, some of these mechanisms are dipolar losses, ion jump relaxation and ohmic loss effects [Binner, 1993], but in many materials the transfer mechanism is still unknown. If the ceramic that is being processed takes enough energy for conducting a process, it would be feasible to carry out processes that, for now, are limited to be smelted in an electric arc furnace. There are several papers on sintering processes with microwaves [Boch et. al., 1992]; [Brandom et. al., 1992]; [Freim et. al., 1994] and [Cheng et. al., 1994], but in this work the aim is to have reactions that produces spinel. The objective of this work focuses on production of magnesia-alumina spinel, presenting a summary of the results of tests conducted at temperatures close to melting point, lower than those encountered in the electric arc furnace.