Recently, there has been a growing interest in heating and sintering of ceramics by the microwave energy.[48,49] The interest in the use of microwave processing spans a number of fields from food processing to medical applications to chemical applications. A major area of research in microwave processing of ceramics includes microwave material interaction, dielectric measurement, microwave equipment design, new material development, sintering, joining, and modeling. Therefore the microwave processing of ceramics has emerged as a successful alternative to conventional processing. Nevertheless, microwave method not only offers the advantages of a uniform heating at lower temperature and time than the conventional method, but also provides an economic method of processing. The microwave energy has been already successively utilized in the fabrication of ceramics as well as carbon fibers at low temperature and time. Varadan et al. and Sharma, Varadan, and Varadan have synthesized various electroceramics such as barium strontium titanate (BST) and lead zirconate titanate (PZT) by microwave. Fig. 10 shows the schematic diagram of a typical domestic microwave unit used by Sharma, Varadan, and Varadan These materials are observed to have improved mechanical, electrical, and electronic properties. Until recently, microcoiled carbon fibers with large surface area have also been fabricated by using microwave aid.
Fig. 11 shows a schematic diagram of a microwave chemical deposition unit used for the fabrication of carbon nanotubes and coils. It consists of microwave magnetron, circulator, four-stub tuner, waveguide, cavity, etc. The microwave power can be adjusted from 0 to 3000 W at a frequency of 2.45 GHz. The function of circulator was to prevent power reflected by the load, thus preventing overheating of the magnetron. The forward and reflected powers were determined
Fig. 10 Schematic diagram of microwave used for the powder.
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