Complex Permittivity and Permeability of α-Fe2O3 and Fe1−xO Powders in the Microwave Frequency Range between 0.2 and 13.5 GHz

Abstract

Nowadays, CO 2 emission reduction and energy conservation are urgent tasks owing to the initiation of Kyoto Protocol adopted for the prevention of global warming. Since large fraction of CO 2 emission is attributed to the blast furnace-type iron making in Japan in spite of the fact that Japanese blast furnace technology has been already advanced, new iron making process should be invented based on innovative theories and mechanisms. We have focused on the microwave heating as a new heating source for iron making. 1-4)Ishizaki et al.2) have produced the highly-pure pig iron from the carbon composite iron ore pellet composed of the mixture of magnetite ore (Romeral) and coal (Robe River) powders by means of a 2.45 GHz microwave furnace. The temperature reached 1 350°C ca. 500 s after the onset of the heating, and subsequently the power was switched off. This study implies that iron making from powder raw materials using microwave heating could yield the low temperature operation and the highly-pure pig iron production: The production of highly-pure pig iron is considered to be relevant to the rapid heating of raw materials. 5)Microwave absorption of materials is caused by Joule loss, dielectric loss and magnetic loss, which are dependent on the electrical conductivity and imaginary parts of permittivity and permeability, respectively. Therefore, it is very important to measure these properties for raw materials and refractories as a function of microwave frequency. In the previous papers, 6) the effects of various factors such as relative density, microwave frequency and particle size of powder SiO 2 and Fe 3 O 4 samples on the complex permittivity and permeability has been investigated by using coaxial transmission line method using a network analyzer. It has been found that the e r Ј values of powder SiO 2 and Fe 3 O 4 samples with the relative density below 1 are smaller than the values estimated using the linear relation between e r Ј and the relative density, and larger than those estimated using the Lichtenecker's logarithm mixed law. It has also been found that the imaginary part of complex permeability of Fe 3 O 4 powder with a particle size of 50 nm-180 mm show the peaks in the frequency range of 706 MHz to 2.99 GHz, depending on the particle size. The imaginary part of complex permittivity of Fe 3 O 4 powder is quite large having a peak around 10 GHz.On the other hand, it is very important to measure the complex permittivity and permeability of a-Fe 2 O 3 because most widely used iron ore contains a-Fe 2 O 3 rather than Fe 3 O 4 . Moreover, it is also of industrial importance to measure the complex permittivity and permeability of wüstite (Fe 1Ϫx O) to evaluate the changes of the microwave absorption characteristics in the course of reduction reaction of raw materials. Fe 1Ϫx O is an nonstoichiometric compound and the value of x ranges from 0.05 to 0.15 depending on the temperature and the oxygen partial pressure. Therefore, it is scientifically interesting to elucidate the x value dependencies of these ...

High-resolution dielectric characterization of minerals: A step towards understanding the basic interactions between microwaves and rocks

“…It is not possible to directly compare Peng et al results with this study: the measurements that they performed with a powder density closer to that of a solid material were influenced by thermal effects. In Hotta, et al (2010), the open-ended coaxial probe technique was used on compressed powders of pure hematite crystals with different densities. As expected, the trend of the ε' and ε'' with the relative density was increasing; the exact values were still obtained by numerical calculations.…”

“…13, values of ′′ = [8 − 15] and = [1.5 − 2.6] / were obtained. We note that, in literature, the conductivity of the hematite was estimated to be within a range = [0.1 − 1] / (Nelson et al, 1989;Peng et al, 2012;Hotta et al, 2010).…”

“…As a starting value of the expected conductivity of the samples, loss tangent and conductivity values found in the literature (Nelson et al, 1989;Peng et al, 2012;Hotta et al, 2010) were used, after the samples were characterized by Raman and SEM-EDX techniques in terms of chemical and elemental composition. Since the tip-sample system can be considered as a lossy capacitor, with the main contributions to the capacitance and loss variations stemming from the sample portion right beneath the tip-sample contact, for semi-empirical estimations the following relationship can be applied:…”

Dehydration Behavior of Goethite Blended with Graphite by Microwave Heating

“…This trial mainly focuses on the pretreatment of poor iron ores involving limonite or pisolite as well as that of sludge in which hydroxides are dominant. Permittivity [17][18][19] of the mixture of FeO(OH) and graphite powder has been measured in the microwave frequency at 2.45 GHz to determine the efficiency to assess how deep microwave can penetrate with various conditions.…”

Shape Anisotropy of Electromagnetic Materials in Application of Microwave by Micro-sized Numerical Electromagnetic Field Calculation

“…One of the reasons is considered to be that its shape affected the electromagnetic characteristics. 15) In this paper, shape anisotropy of micro-structure is researched as the fundamental electromagnetic characteristics of microwave application to electromagnetic materials, as well as iron oxide. Micro-sized water bar, to which high © 2012 ISIJ frequency electromagnetic field is applied, is considered as an asymmetry micro-structure material here.…”