Alkali Metal and Alkali Earth Carbonates at Microwave Frequencies, II: Microwave Heating of Barium Carbonate

It has often been reported in literature that microwave processing of ceramics has produced results which indicate that phenomena, such as diffusion, occur faster than would be indicated by the process temperature:, Recent research has suggested that the strength of the electric field may be the critical parameter governing the magnitude of any microwave effect [Rowley and Wroe, 1995]. Although research suggests that microwave heating may influence diff usion and reaction rates, the authors are not aware of any reports of microwave influencing the temperature at which phase changes occur in crystalline solids.Barium carbonate undergoes a phase change at 811°C resulting in a step change in permittivity and loss factor. This sudden change should manifest itself as a discontinuity in the heating rate curve when a sample of barium carbonate was heated at a constant microwave power level. The temperature of the discontinuity in the heating curve should coincide with the temperature of the phase change.The present results suggest that the presence of a microwave field does not, in fact, shift the phase change temperature.