Processing Materials Using Electromagnetic Radiation

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Copyright: La Robina, Michael
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Abstract
Although substantial work has been carried out using electromagnetic (EM) radiation in the form of radio frequency (RF) induction or microwave heating to process metals, alloys and cold crucibles for melting many difficult refractory and/or reactive materials using induction, none have so far provided a theoretical basis for using the technologies with insulators such as ceramics, glass-ceramics and conductors. In contrast to Joule melting, RF and microwaves provide a highly efficient technique for preparation of high-density and refractory materials using conductors or insulators. When one attempts to melt ceramics or glasses using induction heating, it becomes apparent that induction will not work. Some elements and most ceramics, glasses as well as some alloys are either good insulators or have very poor electrical conductivity. The usual way to melt these materials with an electromagnetic field requires the use of a high melting point conductor, called a susceptor that will couple with the EM field and heats up by induced eddy currents, in turn heating the sample. A solution to this problem is to invoke the MOTT Transition phenomenon which shows that the conductivity of a material is dependent of temperature. Simply stated an insulator can become conductive by increasing its temperature and reciprocally a conductor can become an insulator with increase in temperature. It is also well known that the EM penetration depth is a function of frequency of the EM field and the resistivity of the material. Melting of materials was carried out with and without a conductor to start the melting by using both induction low frequency heating and dielectric high frequency heating. This thesis presents both a theoretical explanation as well as results that show the advantages of the technology, as applied to processing and melting a wide range of materials using EM radiation in the form of induction or microwaves in a resonant cavity. Results from these studies are presented and a proposed variable frequency generator is presented that can allow the processing of any material, be it a conductor or insulator, by appropriate selection of frequency. Friction superheating observed during levitation experiments is also reported.
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Author(s)
La Robina, Michael
Supervisor(s)
Ferry, Michael
Sorrell, Charles
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Publication Year
2017
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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