RESUMO
Clear evidence for the microwave effect has been observed during experiments in which a variety of materials have been heated using experimental systems that allowed both conventional and conventional-microwave hybrid heating. A hybrid single mode cavity has been used to investigate the microwave effect during phase changes in silver iodide, barium titanate and benzil, whilst a hybrid multimode cavity has been used to investigate the microwave effect during sintering and annealing of a range of ceramic materials with different dielectric properties. Although evidence for the microwave effect was not found in every case, where it was found the results could not be explained purely in terms of temperature gradients within the materials.
RESUMO
Microwave heating has a number of advantages over conventional heating due to the ability to heat specimens directly through specific interaction of electromagnetic radiation with the material. Thus it is possible to consider highly localised, rapid melting of thermoplastics using microwave radiation as a means of forming and welding. However, most polymers exhibit very low dielectric losses in the GHz region, which means that it is difficult to heat them efficiently by this means. We have therefore studied the use of fillers such as talc, zinc oxide and carbon black as a way of increasing the susceptibility of common polymers to microwave processing. Carbon black was found to be the most effective susceptor for high density polyethylene and its efficiency was directly proportional to its surface area and loading.
