Microwave Absorbing Ferrite Thin Films for Microwave Heating of Microstructured Reactors
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1222-DD05-09
Microwave Absorbing Ferrite Thin Films for Microwave Heating of Microstructured Reactors Pengzhao Gao1, Evgeny V. Rebrov1, Jaap C. Schouten1, Richard Kleismit2, John Cetnar2, Guru Subramanyam3 and Gregory Kozlowski2 1
Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Physics Department, Wright State University, Dayton, OH 45435, USA 3 Department of Electrical and Computer Engineering, University of Dayton, Dayton, OH 45469, USA 2
ABSTRACT Nanocrystalline Ni0.5Zn0.5Fe2O4 thin films have been synthesized with various grain sizes by sol– gel method on polycrystalline silicon substrates. The morphology and microwave absorption properties of the films calcined in the 673–1073 K range were studied by using XRD, AFM, near–field evanescent microwave microscopy, coplanar waveguide and direct microwave heating measurements. All films were uniform without microcracks. The increase of the calcination temperature from 873 to 1073 K and time from 1 to 3h resulted in an increase of the grain size from 12 to 27 nm. The complex permittivity of the Ni-Zn ferrite films was measured in the frequency range of 2–15 GHz. The heating behavior was studied in a multimode microwave cavity at 2.4 GHz. The highest microwave heating rate in the temperature range of 315–355 K was observed in the film close to the critical grain size of 21 nm in diameter marked by the transition from single– to multi–domain structure of nanocrystals in Ni0.5Zn0.5Fe2O4 film and by a maximum in its coercivity. INTRODUCTION Microwave heating has become an important method for chemical reactor heating and materials processing. The concept of microwave heating enables optimal control of the rate of heat transfer in a microstructured reactor by eliminating conductive and/or convective heat transport resistances. In this way the controlled heating of a microreactor can be achieved using selective microwave absorption into a functional thin films (i.e. with a thickness
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