Microwave Heating for Metallurgical Engineering (pp. 203-238)
Authors: (Jingjing Yang, Ming Huang, Jinhui Peng, Wireless Innovation Lab, School of Information Science and Engineering, Yunnan University, Kunming, People’s Republic of China, and others)
Abstract: As a sort of electromagnetic waves ranging from 300MHz to 3000GHz, microwaves have been widely used in wireless communication, radar, heating and sensing. Microwave heating is best known for heating food in the kitchen, and in the last two decades it has emerged as a ubiquitous tool in chemistry. Despite its broad technological importance, microwave heating remains an unpredictable tool because the detailed physics of the interaction between microwave and substance is poorly known. In this Chapter, we revisit the reflection and transmission of microwave by conducting medium. We show that when a large piece of metal is milled into particles and flours, it becomes a good microwave absorber. To reveal the mechanism behind this phenomenon, firstly, three models based on effective media theory, i.e., qusi-static model, equivalent parameter model and RC network models are studied. Then, a new equation is introduced to characterize the Debye and non-Debye relaxations under microwave irradiation. Some new physical phenomena including local field enhancement and temperature dependent relaxation time, etc., which exist in non-Debye materials can be explained by this equation. Finally, we show that the local field enhancement is a ubiquitous and nonlinear phenomenon in granular materials, which is relative to microwave power, boundary condition, constituent and micro-structure of the materials, etc., and this is the main reason that microwave assisted chemical reactions can take place at a much lower average temperature compared with conventional heating. Examples about the application of microwave heating in metallurgy engineering are given. These works lay a solid foundation for the development of microwave metallurgical engineering.
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