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Peng Z.,Michigan Technological University | Hwang J.-Y.,Michigan Technological University | Kim B.-G.,Korea Institute of Geoscience and Mineral Resources | Mouris J.,Microwave Properties North MPN | Hutcheon R.,Microwave Properties North MPN
Energy and Fuels | Year: 2012

The microwave absorption capability of an eastern high volatile bituminous coal from West Virginia was investigated by measuring the dielectric properties from room temperature to ∼900 °C in ultrahigh purity (UHP) argon, at both 915 and 2450 MHz. The dielectric properties remain relatively constant below 500 °C. As the temperature continues to increase, however, the relative dielectric constant and loss factor increase dramatically. This is due to the release of volatiles, resulting in the increased electrical conductivity and higher microwave loss. The calculation of microwave penetration depth shows that the pyrolysis process significantly improves the microwave absorption capability of the coal at high temperatures. The calculated reflection losses of the coal sample suggest that the maximum microwave absorption with the reflection losses of -41.25 dB and -32.54 dB can be obtained for the coal having thicknesses of 0.14 and 0.20 m at 915 and 2450 MHz, respectively. The sample dimension has a significant effect on the overall performance of microwave absorption of coal during pyrolysis and thus on the efficiency of microwave coal pyrolysis. © 2012 American Chemical Society.


Donaldson A.A.,University of Ottawa | Hutcheon R.,Microwave Properties North MPN | Zhang Z.,University of Ottawa
Fuel Processing Technology | Year: 2011

The dielectric properties of 4,6-dimethyldibenzothiophene (DMDBT), hexadecane (HD), quinoline (QL), and HD/QL mixtures were investigated at six microwave frequencies (0.4, 0.9, 1.4, 1.9, 2.5 and 3.0 GHz) and temperatures ranging from 297 K to 624 K. While both DMDBT and HD exhibited limited response under these conditions, QL demonstrated high dielectric loss with a penetration depth comparable to that of water. Through the use of the Debye relationship and solvent mixing rules, a model is proposed to predict the dielectric constant and loss factor for HD/QL mixtures. Based on the observed dielectric behaviour of QL, microwave-assisted separation/conversion may be effective during upgrading of light cycle oil (LCO) for similar, difficult-to-remove nitrogen compounds. © 2011 Elsevier B.V.


Samouhos M.,National Technical University of Athens | Hutcheon R.,Microwave Properties North MPN | Paspaliaris I.,National Technical University of Athens
Minerals Engineering | Year: 2011

The use of microwave radiation as an energy source in mineral processing and extractive metallurgy has demonstrated both the instantaneous generation of heat by microwaves in a number of compounds and minerals, and the achievement of high temperatures for an efficient time period enable the heating and reduction of metallic oxides and ores. In the present study, the carbothermic reduction of copper oxide (CuO) and one malachite [Cu 2CO 3(OH) 2] concentrate were investigated. To explore feasibility, the dielectric constants [real (′) and imaginary (″) permittivities] of both materials were measured at the frequencies of 2.45 GHz and 912 MHz, in the temperature range from 25 to 800 °C using the cavity perturbation method. The high ″ values (between 1.9 and 36.3) observed in the case of CuO suggest strong microwave absorption, while the malachite concentrate values (between 0.1 and 0.4) indicate limited microwave absorption. Experiments showed the microwave heating rate of CuO was considerably higher than that of the malachite concentrate. The carbothermic reduction of CuO oxide was examined, and the effect of power supply, carbon source, carbon content and granularity of the reducing agent on the reduction rate was studied in detail. Using an 800 W power supply, and with addition of lignite as a reducing agent (with carbon content two times stoichiometric), almost complete reduction of 10 g of CuO was achieved in 4 min. The carbothermic reduction of one malachite concentrate was attempted with the same experimental procedure, but the reaction was not possible using only lignite as the reducing agent, since the poor microwave absorption of malachite concentrate-lignite mixture produced a maximum temperature of 200 °C. This difficulty was overcome by the addition of 5% by weight of graphite powder to the mixture. The rapid heating of the malachite concentrate-lignite-graphite mixture (800 °C after 2 min) resulted in sequential malachite calcination and CuO reduction reactions. After 8 min at a power supply of 800 W, the reduction degree of CuO produced by the calcination of malachite was about 90%. © 2010 Elsevier Inc. All rights reserved.


Peng Z.,Michigan Technological University | Hwang J.-Y.,Michigan Technological University | Mouris J.,Microwave Properties North MPN | Hutcheon R.,Microwave Properties North MPN | Huang X.,Michigan Technological University
ISIJ International | Year: 2010

A simplified equation for determining the transverse electromagnetic mode (TEM) power penetration depth of microwaves in materials having both magnetic and dielectric response was derived. The penetration depths for a magnetite concentrate were calculated using this "full-response" equation, and a significant difference is shown compared with the penetration depth obtained using only the dielectric response (i.e., assuming no imaginary part of complex relative permeability). The temperature dependence of the power penetration depth, up to 1 000°C, was determined using measured values of the real and imaginary parts of complex relative permittivity, εr′, εr″ and permeability, μr′, μr″. The accurate determination of penetration depths can help in optimizing the dimensions of a load in a microwave furnace, producing more uniform heating under microwave irradiation and avoiding thermal runaway. © 2010 ISIJ.


Peng Z.,Michigan Technological University | Hwang J.-Y.,Michigan Technological University | Mouris J.,Microwave Properties North MPN | Hutcheon R.,Microwave Properties North MPN | Sun X.,Rensselaer Polytechnic Institute
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The temperature dependence of the microwave absorption of conventionally heated nonstoichiometric ferrous oxide (Fe0.925O) was characterized via the cavity perturbation technique between 294 K and 1373 K (21 °C and 1100 °C). The complex relative permittivity and permeability of the heated Fe0.925O sample slightly change with temperature from 294 K to 473 K (21 °C to 200 °C). The dramatic variations of permittivity and permeability of the sample from 473 K to 823 K (200 °C to 550 °C) are partially attributed to the formation of magnetite (Fe3O4) and metal iron (Fe) from the thermal decomposition of Fe0.925O, as confirmed by the high-temperature X-ray diffraction (HT-XRD). At higher temperatures up to 1373 K (1100 °C), it is found that Fe0.925O regenerates and remains as a stable phase with high permittivity. Since the permittivity dominates the microwave absorption of Fe0.925O above 823 K (550 °C), resulting in shallow microwave penetration depth (∼0.11 and ∼0.015 m at 915 and 2450 MHz, respectively), the regenerated nonstoichiometric ferrous oxide exhibits useful microwave absorption capability in the temperature range of 823 K to1373 K (550 °C to 1100 °C). © 2011 The Minerals, Metals & Materials Society and ASM International.


Samouhos M.,National Technical University of Athens | Taxiarchou M.,National Technical University of Athens | Hutcheon R.,Microwave Properties North MPN | Devlin E.,Institute of Materials Science
Minerals Engineering | Year: 2012

The use of microwave radiation as an alternative energy source in mineral processing and extractive metallurgy has been studied since the initial work of Worner at the Univ. of Wollongong in 1986. Microwaves deliver heat directly to the interior of a sample, avoiding the usual slow heating mechanisms of thermal and convective heat transfer. Furthermore, the depth to which the microwaves penetrate and the amount of heat deposited at depth is dependant on the complex dielectric constant of the material which means that by careful choice of materials, a microwave heating system can deliver heat to specific chosen materials, while much reducing the heating of others, such as thermal insulation and oven walls, and thus improving efficiency. In the current study, the carbothermic reduction of a hematitic nickeliferous laterite was investigated, both by large-scale microwave oven experiments, and by measuring the complex dielectric constant (real (′) and imaginary (″) permittivities) of small samples at 2.45 GHz over the temperature range 5-980 °C, using the cavity perturbation method. The microwave oven heating behavior of the laterite-lignite mixture was explored using a 2.45 GHz ThermWave 1.3, variable power, microwave furnace, fitted with an optical pyrometer and an infrared thermal camera. The carbothermic reduction of laterite (i.e. the reduction of hematite contained in laterite) was attempted, and the effect of heating time, power, carbon content and sample mass was studied in detail. Using twice the stoichiometric carbon content (i.e. double the amount of carbon required to fully reduce the hematite to metallic iron), about 70% reduction degree was achieved at temperatures somewhat above 900 °C. The use of scanning electron microscopy and Mössbauer spectroscopy gave evidence of a lack of microstructural homogeneity in the reduced samples and the presence of phases which are not stable in the same temperature ranges, indicating some thermal inhomogeneity. © 2012 Elsevier Ltd. All rights reserved.


Pilatos G.,Institute of Nanoscience and Nanotechnology | Samouhos M.,National Technical University of Athens | Angelopoulos P.,National Technical University of Athens | Taxiarchou M.,National Technical University of Athens | And 4 more authors.
Chemical Engineering Journal | Year: 2016

Dense multi-walled carbon nanotubes (CNTs) have been successfully fabricated on expanded perlite particles by the pyrolysis of a camphor-ferrocene mixture at 800 °C. Scanning electron microscopy images show that the CNTs' growth is strongly affected by the specific surface area of perlite samples and it is more efficient in the case of perlite particles with a coarse surface and a high value of specific surface, likely due to the homogeneous dispersion of the catalyst. The optimum synthesized nanotubes have uniform outer diameters ranging between 25 and 50 nm, and a length of ~40 μm. Transmission electron microscopy reveals a typical hollow nanotube structure with the majority of catalytic Fe particles located at the nanotube tips suggesting a tip-growth mechanism. HR-TEM images of individual nanotubes show that their external walls consist of about 50 carbon sheets. Finally, the synthesized CNTs were separated from the substrate, and the dielectric permittivity of a low density powder of nanotubes was measured at various temperatures and frequencies using the cavity perturbation method. © 2016 Elsevier B.V.

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