Microwave heating of soda-lime glass by addition of iron powder
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Haichuan Wangb) Department of Metallurgy, Anhui University of Technology, Ma-Anshan, Anhui, People’s Republic of China
Ken-ichi Mashiko Tohoku University, Sendai, Japan 980-8579; and Graduate School of Environmental Studies, Tohoku University, Sendai, Japan 980-8579
Shoji Taniguchi Graduate School of Environmental Studies, Tohoku University, Sendai, Japan 980-8579 (Received 3 September 2007; accepted 17 December 2007)
Experimental studies were conducted to investigate the microwave (MW) heating behavior of soda-lime glass beads with added iron powder. These studies were intended to obtain fundamental knowledge for vitrification solidification and for the fabrication of metal-reinforced glass-matrix composites. The glass beads (0.2 mm diameter) did not heat very well by themselves at temperatures greater than 200 °C within 600 s in a multimode applicator at a power of 0.67 W. The addition of iron powder (average 70 m, volume fraction 18%) made it possible to heat the glass beads above 700 °C within 60 s. At lower fractions of 3–11 vol%, however, a sudden temperature rise [thermal runaway (TRW)] occurred after the incubation time period. A single-mode MW applicator was used for clarifying the electric (E)-field and magnetic (H)-field contributions to the heating of each material and their mixtures. The results of this study demonstrated that the H-field contributed to the heating of the iron and then triggered the heating of the glass. The E-field component is necessary for heating the glass to a temperature higher than 800 °C. The factors determining the threshold values of the volume fraction causing TRW are discussed. I. INTRODUCTION
As a solution to major environmental pollution problems caused by hazardous materials, the immobilization of heavy-metal-containing materials such as fly ash and radioactive waste by glass solidification1–4 has been proposed. Microwave (MW) heating has been used as a method for melting glasses.5,6 However, all glasses are not necessarily good MW absorbers; for that reason, in most cases they are not heated easily. Some substances are usually added to the glasses for heating and melting. Metal pieces or powders were selected for use as heatingignition elements.7,8 On the other hand, some recent studies8,9 have reported the fabrication of glass/metal composite materials by MW processing (i.e., metal wires). Alternatively, particles are added not only as fillers for strengthening the
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Address all correspondence to this author. e-mail: [email protected] b) On leave. DOI: 10.1557/JMR.2008.0190 1564 J. Mater. Res., Vol. 23, No. 6, Jun 2008 http://journals.cambridge.org Downloaded: 02 Apr 2015
materials; it is also expected that the metal contents of the mixture will act as igniters of the glass heating by raising the temperature and increasing the permittivity of glasses.10 Although this ignition effect created by metal additives has been described in many MW studies, few fundamental studies have examined this phenomenon of MW heating of metal/glass mixture from the per
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