Magnetite Samples Research Articles

Size-controllable synthesis of Fe3O4 nanoparticles through oxidation–precipitation method as heterogeneous Fenton catalyst

Abstract

Magnetic signatures of serpentinization at ophiolite complexes

AbstractWe compare magnetic properties of 58 variably serpentinized peridotites from three ophiolite complexes (Pindos, Greece; Oman; Chenaillet, France) and the mid‐Atlantic Ridge near the Kane fracture zone (MARK). The Pindos and Oman sites show low susceptibility and remanence (K < 0.02 SI; Ms < 0.4 Am2/kg), while the Chenaillet and MARK sites show instead high susceptibility and remanence (K up to 0.15 SI; Ms up to 6 Am2/kg), regardless of serpentinization degree. Petrographic observations confirm that Pindos and Oman samples contain serpentine with very little magnetite, while Chenaillet and MARK samples display abundant magnetite in serpentine mesh cells. Bulk rock analyses show similar amounts of ferric iron at a given serpentinization degree, suggesting that iron is oxidized during the serpentinization reaction in both cases, but that its distribution among phases differs. Microprobe analyses show iron‐rich serpentine minerals (5–7 wt % FeO) in low‐susceptibility samples, while iron‐poor serpentine minerals (2–4 wt % FeO) occur in high susceptibility samples. The contrasted magnetic properties between the two groups of sites thus reflect different iron partitioning during serpentinization, that must be related to distinct conditions at which the serpentinization reaction takes place. We propose that magnetic properties of ophiolitic serpentinites can be used as a proxy to differentiate between high temperature serpentinization (>∼250–300°C) occurring at the axis (i.e., Chenaillet, similar to serpentinites from magmatically poor mid‐ocean ridges), from lower temperature serpentinization (<∼200–250°C), likely occurring off axis and possibly during obduction (i.e., Pindos and Oman). At both settings, serpentinization can result in significant hydrogen release.

Quantitative analysis of Fe and Co in Co-substituted magnetite using XPS: The application of non-linear least squares fitting (NLLSF)

Quantitative analysis of Co and Fe using X-ray photoelectron spectroscopy (XPS) is of important for the evaluation of the catalytic ability of Co-substituted magnetite. However, the overlap of XPS peaks and Auger peaks for Co and Fe complicate quantification. In this study, non-linear least squares fitting (NLLSF) was used to calculate the relative Co and Fe contents of a series of synthesized Co-substituted magnetite samples with different Co doping levels. NLLSF separated the XPS peaks of Co 2p and Fe 2p from the Auger peaks of Fe and Co, respectively. Compared with a control group without fitting, the accuracy of quantification of Co and Fe was greatly improved after elimination by NLLSF of the disturbance of Auger peaks. A catalysis study confirmed that the catalytic activity of magnetite was enhanced with the increase of Co substitution. This study confirms the effectiveness and accuracy of the NLLSF method in XPS quantitative calculation of Fe and Co coexisting in a material.

Ultrasound and UV assisted Fenton treatment of recalcitrant wastewaters using transition metal-substituted-magnetite nanoparticles

In this study, the degradation and mineralization of two dyes were investigated through heterogeneous Fenton using modified magnetite nanoparticles (Fe3−x−yNbxMoyO4). The Nb and Mo substituted magnetite samples were prepared by co-precipitation method and characterized by BET, XRD, TEM, XPS, VSM and chemical experiments. The emphasis was primarily on examining the effects of external energy sources on the activity of the Fe2.79Mo0.13O4, Fe2.79Nb0.19O4 and Fe2.79Nb0.171Mo0.023O4 nanoparticles in Fenton reaction. Methylene blue (MB) and methyl orange (MO) were chosen as the model cationic and anionic dyes. All samples showed exceptional activities in Fenton reaction under the influence of UV and ultrasound (US) energy compared to unmodified magnetite sample. The incorporated Nb and Mo significantly accelerated the MB degradation in US/Fenton followed by UV-B/Fenton and UV-A/Fenton reactions. However, the UV-B/Fenton was more effective in degradation of MO compared to other oxidation systems. Under all the studied conditions, co-doped Nb-Mo-magnetite nanoparticles showed highest activity in comparison to single Nb- and Mo-substituted magnetite samples. MB degradation through both UV and US/Fenton reactions were well described by pseudo-first-order equations in kinetics. The employed catalysts showed acceptable stability under the influence of UV and US irradiations. Although, the amount of leached Nb was relatively higher than Fe and Mo in acidic condition and under UV irradiation, the loss in the performance of the samples was insignificant. The results obtained from this work indicated that it is possible to treat wastewaters effectively by developing nano-catalysts with slight modification in naturally available compounds and using the existing advanced oxidation system.

Combination of ultrasonic and Fenton processes in the presence of magnetite nanostructures prepared by high energy planetary ball mill

High energy planetary ball milling process was used to prepare magnetite nanostructures from natural magnetite. The natural and ball-milled magnetite samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FT-IR). The results of EDX indicated the presence of main elements including Fe and O in the structure of both unmodified and milled magnetite samples. The specific surface area of catalyst increased from 0.9116m2/g to 28.692m2/g after ball-milling process. The catalytic activity of prepared magnetite nanostructures was evaluated towards degradation of Acid Blue 185 (AB185) in ultrasonic assisted heterogeneous Fenton reaction. 6h ball-milled catalyst exhibited the higher catalytic activity in degradation of AB185. The high degradation efficiency was obtained at initial pH of 3. Increasing the concentration of H2O2 from an optimum value of 15mM led to decrease in degradation efficiency because of scavenging effect of H2O2 on hydroxyl radicals. The optimized catalyst concentration was obtained 1.5g/L. Increasing initial dye concentration from 20 to 120mg/L led to decrease in degradation efficiency from 99 to 88%. The prepared magnetite nanostructures exhibited good stability in repeated cycles. The produced intermediates of the degradation of AB185 in ultrasonic assisted heterogeneous Fenton process were monitored by GC–MS analysis.

Hydrostatic pressure effect on magnetic hysteresis parameters of pseudo‐single‐domain magnetite

AbstractThis paper reports the first in situ magnetic hysteresis measurements of pseudo‐single‐domain (PSD) magnetite under high pressure up to 1 GPa. The magnetic hysteresis measurements of stoichiometric PSD magnetite samples under hydrostatic pressure were carried out using a piston‐cylinder high‐pressure cell, and the pressure dependence of the hysteresis parameters of PSD magnetite was calculated from the hysteresis curves. It was found that coercivity (Bc) increases with increasing pressure as a quadratic function up to 1 GPa by ∼90%, which is different from the pressure dependences of Bc of multidomain and single‐domain magnetites. Coercivity of remanence also increases as a quadratic function, and saturation remanence (Mrs) increases with pressure up to 0.5 GPa by ∼20% until reaching saturation. In contrast, saturation magnetization is constant up to 1 GPa. The approximate demagnetizing factor calculated from the ratio Bc/Mrs increases with increasing pressure, suggesting that the number of lamellar domains increases with increasing pressure. The number of lamellar domains and domain wall width are theoretically estimated to increase under high pressure due to the changes in magnetostriction, elastic, and magnetocrystalline anisotropy constants, and these changes in magnetic domain structure should relate to the changes in the magnetic properties of PSD magnetite.

Optical properties and crystallization behaviour of some MnO and/or Fe2O3-containing silicate glasses and glass-ceramics

Glass and glass-ceramics with the compositions 1Fe2O3-99SiO2 (1Fe), 2Fe2O3-98SiO2 (2Fe), 1MnO-99SiO2 (1Mn), 2MnO-98SiO2 (2Mn), 1MnO-1Fe2O3-98SiO2 (2MnFe), 2MnO-2Fe2O3-96SiO2 (4MnFe) (mol%) were prepared using the sol-gel method. The gel samples were heat treated between 120 and 1000°C. Thermogravimetric and differential thermal analysis (TG-DTA), ultraviolet, visible and near infrared spectrophotometry (UV–Vis-NIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (SEM-EDS) were used to study the structural changes that occur during the gel to glass and glass-ceramic conversions. Many of the prepared glass and glass-ceramics present brown or black colorations. These dark colorations are due to the presence in the samples of maghemite-C, magnetite, hematite, Mn3O4 (bixbyite) and Mn2+(Mn3+)14SiO24 (braunite) or simultaneously more than one of these crystalline phases. These nanoparticles give to the samples very interesting magnetic and optical properties of great importance in several medical fields. Furthermore, the study contributed to understanding the formation mechanism of some MnO and/or Fe2O3-containing silicate glasses and glass-ceramics prepared by the sol-gel method.

Probing the Limits of Electron and Ion Transport over Multiple Length Scales

As the demand for large scale batteries has grown, considerations such as earth abundance, cost, and toxicity have assumed a greater significance. Metal oxides such as magnetite (Fe3O4) are worthy of evaluation as active materials for electrochemical energy storage due to its earth abundance, low cost, environmentally benign iron metal centers and high theoretical capacity, 926 mAh/g. Implementation in the future will require understanding of the fundamental electrochemical reduction-oxidation mechanisms of the electroactive materials is required, coupled with characterization at the mesoscale to understand the underlying contributors to localized resistance which must be addressed in order to achieve significant improvements to current capability and reversibility. An emerging paradigm for the implementation of close-packed materials in higher current applications is the tuning of the materials crystallite dimensions, where the reduction of crystallite size should minimize the path length for ion transport upon discharge, resulting in a reduction of both internal cell resistance and the resultant structural strain associated with lithium insertion. The electrochemical impact of controlled crystallite size of magnetite will be described. In addition to the crystallite size of the electroactive material, a complete study of an electroactive nanomaterial in the complex mesoscale environment of a composite battery electrode should also consider the level of electroactive particle agglomeration, and agglomerate distribution within the battery electrode. Nanocrystalline magnetite (Fe3O4) powders and composite electrodes with different crystallite sizes were prepared, characterized, and electrochemically evaluated. Transmission electron microscopy (TEM) examination of cross-sectioned electrodes was used to quantify the aggregate size of the Fe3O4 active material. Notably, although the crystallite sizes of two magnetite samples Fe3O4 are different (28 and 9 nm), the observed sizes of the aggregates and aggregate distribution within the electrodes were similar, see TEM images of sectioned electrodes fabricated with the 28 nm (A,B) and 9 nm (C,D) sized Fe3O4 in the Figure. Transmission x-ray microscopy (TXM) combined with x-ray absorption near edge spectroscopy (XANES) at the National Synchrotron Light Source (NSLS) were used to determine the distribution of the iron oxidation states within the electrodes before and after electrochemical testing. The impact of both crystallite size and agglomeration on electrochemical performance were assessed. Figure 1

Fluidized-bed Fenton-like oxidation of a textile dye using natural magnetite

Degradation of Acid Orange 7 (AO7) as a model azo dye was investigated in a recirculating pilot fluidized-bed reactor by a Fenton-like process using natural magnetite (NM) and potassium persulfate (K2S2O8). Scanning electron microscopy was performed to characterize the magnetite sample. The heterogeneous Fenton-like process (NM/\({\text{S}}_{2} {\text{O}}_{8}^{2 - }\)) is a modified method owing to its enhanced mass transfer. It can be operated reliably and simply by reducing the produced iron oxide sludge in the conventional Fenton process. Degradation efficiency (DE %) of AO7 by NM/ \({\text{S}}_{2} {\text{O}}_{8}^{2 - }\) process was affected by operational parameters. The DE % of 75 % was obtained for the AO7 treatment (15 mg/L) at the desired conditions, such as pH 5, 0.2 mM \({\text{S}}_{2} {\text{O}}_{8}^{2 - }\), and 0.5 g/L NM after 120 min of reaction time. The dye degradation rate in all the experiments followed the pseudo-second-order kinetic with high correlation coefficients (R2 ≥ 0.98). The low released iron concentration, successive reusability at milder pH and the recirculation mode with the proper mixing are the significant advantages of the NM/\({\text{S}}_{2} {\text{O}}_{8}^{2 - }\) process.

Modified natural magnetite with Al and La ions for the adsorption of fluoride ions from aqueous solutions

Abstract Natural magnetite ore (Fe 3 O 4 ) was modified with aluminum and lanthanum ions to increase the fluoride removal efficiency from aqueous solutions. The modified and unmodified magnetite samples were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), infrared spectroscopy (IR), surface area (BET) and zeta potential ( ζ ). The adsorption and stability of fluoride on magnetite were investigated using modified magnetite in batch systems. The SEM results indicate the formation of a lanthanum oxide layer around the magnetite and that aluminum oxide is dispersed between the particles. Al and La were deposited as hydroxides (IR), which increased the surface area by 7.5 and 9.5 times higher than natural magnetite and shifted the surface potential toward positive values. The IR results indicated that fluoride replaces a hydroxyl group from the aluminum hydroxides whereas no such replacement was detected for materials with La. Batch tests showed that adsorption increased from 30 to 90% and 96% for the aluminum and lanthanum modified materials, respectively.

Multi component modelling of an air classifier

This paper focusses on investigating the classification behaviours of the components having different densities and flow characteristics then developing preliminary model structure where these properties are considered. Such a study can improve the prediction accuracy of the existing models since material characteristics are of crucial importance. Within the scope of this study, laboratory scale experimental tests were undertaken on clinker, copper ore, magnetite and coal samples, at different operating conditions. The results concluded that, increasing the density decreased the cut size in the meantime increased the bypass of the classification operation. In addition, the sharpness and the fish hook parameters were found to be correlated with the flow characteristics of the material e.g., the higher the fluidity the higher the sharpness and the lower the fish-hook. As a conclusion of the study, the correlations presented in the paper were integrated into an existing air classifier model and preliminary multi component model structure for air classifiers was developed.

Blackening of fault gouge by comminution and pyrolysis of carbonaceous materials during earthquake slip

Black fault gouges sometimes develop, mainly in sedimentary rocks, but the cause of the color transformation is not well understood. Here we demonstrated the blackening of synthetic mixtures of montmorillonite and bituminous coal and of montmorillonite and magnetite in milling, heating, and friction experiments. Mixed samples with a higher volume fraction of coal or magnetite before the experiments showed lower L* values (lightness index; lower values indicate darker blacks), because coal and magnetite are intrinsically black. The milling and heating experiments showed that the L* values of mixed samples of montmorillonite and coal drastically decreased with longer milling times and higher temperatures. The L* values of mixed samples of montmorillonite and magnetite also decreased with longer milling times, but no notable change was observed in the samples after the heating experiments. Because comminution by milling induces granulation of the constituent materials, blackening of the experimental samples was primarily caused by dispersal through the sample of fine black particles such as coal and magnetite, but it could be strengthened by adsorption onto host particles of organic gases produced by pyrolysis of carbonaceous material at high temperature. The friction experiment with mixed samples of montmorillonite and coal produced the remarkably low L* values. Friction induces both comminution and heating of samples, so the blackening could be greater than after either milling or heating alone. Therefore, relatively black fault gouges, compared with the surrounding host rocks, might have experienced comminution and heating, probably related to earthquake slip. Thus, black coloration could be one of the important information on fieldwork.

Determination of multi-element concentrations at ultra-low levels in alternating magnetite and pyrite by HR-ICP-MS using matrix removal and preconcentration

This work presents a solid phase extraction (SPE) method for pre-concentration of 28 elements at ultra-level in magnetite and pyrite samples prior to their analysis using ICP-MS. The TRUspec resin and AG1-X8 anion resin were employed for the precise and accurate determination of Cr, Co, Ni, Cu, Zn, Ge, Rb, Sr, Ba, Cs and Li, Be, Sc, Cs, REEs, respectively. The recoveries for all the analytes were 100%±5% with low procedural blanks. The method was validated by Iron Formation reference material (FER-2), showing good agreement with literature value. The proposed method was employed for the analysis of magnetite and pyrite samples from alternating magnetite-rich and pyrite-rich mesobands. The obtained high quality data can be used to establish the genetic relationship between these two types of deposits.

Reduction of magnetite to metallic iron in strong alkaline medium

This work focuses on assessing the feasibility of cathodic iron extraction from the magnetite based precursors. For this, electrochemical processes at Fe3O4/alkaline electrolyte interface were screened by cycling voltammetry. Based on these results, one obtained guidelines for selecting the conditions (i.e., potential and temperature) where efficient direct electrochemical reduction of magnetite ceramics to metallic iron occurs. Electrochemical conversion of relatively dense magnetite samples yields a polycrystalline Fe scale, formed at the surface of the magnetite pellet in direct contact with the bulk electrolyte. Still, the onset of slightly open porosity results in formation of intermediate layers with coexisting magnetite and metallic Fe; this is ascribed to gradual development of additional porosity, which promotes sample impregnation with the electrolyte, extends the effective electrochemically active area, and facilitates dissolution of soluble species in the inner pores. This is clearly demonstrated by transient response behavior, with remarkable increase in the current density. The key roles of porosity and effective Fe3O4/electrolyte area are also emphasized by the enhanced kinetics of electrochemical reduction observed for highly porous magnetite samples, with nearly homogeneous distribution of reactant (Fe3O4) and product (metallic Fe), without a clear surface scale of metallic iron. In this case, the final product is very porous and fragile. The conversion of highly porous magnetite samples also proceeds with much higher Faradaic efficiency compared to nearly dense ceramics.

Fe–O stable isotope pairs elucidate a high-temperature origin of Chilean iron oxide-apatite deposits

Iron oxide–apatite (IOA) ore deposits occur globally and can host millions to billions of tons of Fe in addition to economic reserves of other metals such as rare earth elements, which are critical for the expected growth of technology and renewable energy resources. In this study, we pair the stable Fe and O isotope compositions of magnetite samples from several IOA deposits to constrain the source reservoir of these elements in IOAs. Since magnetite constitutes up to 90 modal% of many IOAs, identifying the source of Fe and O within the magnetite may elucidate high-temperature and/or lower-temperature processes responsible for their formation. Here, we focus on the world-class Los Colorados IOA in the Chilean iron belt (CIB), and present data for magnetite from other Fe oxide deposits in the CIB (El Laco, Mariela). We also report Fe and O isotopic values for other IOA deposits, including Mineville, New York (USA) and the type locale, Kiruna (Sweden). The ranges of Fe isotopic composition (δ56Fe, 56Fe/54Fe relative to IRMM-14) of magnetite from the Chilean deposits are: Los Colorados, δ56Fe (±2σ)=0.08±0.03‰ to 0.24±0.08‰; El Laco, δ56Fe=0.20±0.03‰ to 0.53±0.03‰; Mariela, δ56Fe=0.13±0.03‰. The O isotopic composition (δ18O, 18O/16O relative to VSMOW) of the same Chilean magnetite samples are: Los Colorados, δ18O (±2σ) = 1.92±0.08‰ to 3.17±0.03‰; El Laco, δ18O=4.00±0.10‰ to 4.34±0.10‰; Mariela, δ18O=(1.48±0.04‰). The δ18O and δ56Fe values for Kiruna magnetite yield an average of 1.76±0.25‰ and 0.16±0.07‰, respectively. The Fe and O isotope data from the Chilean IOAs fit unequivocally within the range of magnetite formed by high-temperature magmatic or magmatic–hydrothermal processes (i.e., δ56Fe 0.06–0.49‰ and δ18O=1.0–4.5‰), consistent with a high-temperature origin for Chilean IOA deposits. Additionally, minimum formation temperatures calculated by using the measured Δ18O values of coexisting Los Colorados magnetite and actinolite separates (630°C) as well as Fe numbers of actinolite grains (610–820°C) are consistent with this interpretation. We also present Fe isotope data from magmatic magnetite of the Bushveld Complex, South Africa, where δ56Fe ranges from 0.28±0.04‰ to 0.86±0.07‰. Based on these data and comparison to published Fe and O stable isotope values of igneous magnetite, we propose extending the magmatic/high-temperature δ56Fe range to 0.86‰. Considering that the Chilean IOAs and Kiruna deposit are representative of IOA deposits worldwide, the Fe and O stable isotope data indicate that IOAs are formed by high-temperature (magmatic) processes.

Mechanosynthesis, structural, thermal and magnetic characteristics of oleic acid coated Fe3O4 nanoparticles

Oleic acid coated iron ferrite-magnetite nanoparticles (Fe3O4) have been synthesized via a new combined route, ceramic method and subsequent wet mechanical milling, starting from a stoichiometric mixture of the easily accessible Fe and Fe2O3 precursors. In the first step, the magnetite has been obtained in well crystallised state by heat treatment of precursor's mixture. In the second step, the as obtained magnetite powder has been wet milled in a high energy planetary ball mill using oleic acid as process control agent. Using the same conditions dry milled magnetite samples have been obtained for comparison. The as obtained powders have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), magnetic measurements M = f(H), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). According to XRD analysis two different processing mechanisms are observed for dry and wet milling modes. The magnetite mean crystallite size is 19 nm according to XRD after 240 min of wet mechanical milling. The High Resolution SEM confirmed that the powder consists in nanoparticles that have particles with the size up to 30 nm. The bond of the oleic acid to the magnetite nanoparticles has been observed by FTIR and DSC investigations. The presence of free and bonded oleic acid is revealed and the free oleic acid can be removed controlled by heat treatment. The magnetisation of the milled samples is lower as compared to the magnetisation of the un-milled sample due to several causes such as disordered structure, finite size effect and powder contamination. A powder contamination with iron occurs during milling and this leads to the formation of a wüstite-FeO phase for the dry milled samples. In the case of the wet milled samples, due to an oleic acid layer the FeO phase formation is prevented.

Technological procedure for processing the quartz resources in order to obtain the assortment for water glass

Tests on quartz raw material from the deposit 'Bijela Stijena - Skočić' have included: grading, washing, grinding and magnetic separation. Test results have shown that the assortment of required sand quality can be obtained for water glass. The required quality condition for assortment of water glass, set by the company 'Alumina' Zvornik, is that Fe2O3 content does not exceed 0.04% and the grit of -0.4 + 0.05 mm. The results obtained after washing and grading starting sample used in these tests to a class of -0.4 + 0.05 mm showed that content of Fe2O3 from 0.131 % was reduced to 0.075%, and after treatment at high gradient electromagnetic separator at 0.038%. Microscopic analysis showed that the initial sample has: quartz, chalcedony, feldspar, mica, cherts, magnetite, limonite-goethite, shells, fossil remains, and that after the magnetic separation of magnetite sample was removed and most of the other carriers magnetic fraction. Based on this, a flow diagram is defined for procedure of obtaining the quartz sand for water glass on the basis of quartz raw materials from the deposit 'Bijela Stijena -Skočić'.

Determination of ferrous and total iron in refractory spinels

Accurate and precise determination of the redox state of iron (Fe) in spinels presents a significant challenge due to their refractory nature. The resultant extreme conditions needed to obtain complete dissolution generally oxidize some of the Fe(II) initially present and thus prevent the use of colorimetric methods for Fe(II) measurements. To overcome this challenge we developed a hybrid oxidimetric/colorimetric approach, using Ag(I) as the oxidimetric reagent for determination of Fe(II) and 1,10-phenanthroline as the colorimetric reagent for determination of total Fe. This approach, which allows determination of Fe(II) and total Fe on the same sample, was tested on a series of four geochemical reference materials and then applied to the analysis of Fe(Ni) spinel crystals isolated from simulated high-level-waste (HLW) glass and of several reagent magnetites. Results for the reference materials were in excellent agreement with recommended values, with the exception of USGS BIR-1, for which higher Fe(II) values and lower total Fe values were obtained. The Fe(Ni) spinels showed Fe(II) values at the detection limit (ca. 0.03 wt% Fe) and total Fe values higher than obtained by ICP-AES analysis after decomposition by lithium metaborate/tetraborate fusion. For the magnetite samples, total Fe values were in agreement with reference results, but a wide range in Fe(II) values was obtained indicating various degrees of conversion to maghemite. Formal comparisons of accuracy and precision were made with 13 existing methods. Accuracy for Fe(II) and total Fe was at or near the top of the group. Precision varied with the parameter used to measure it but was generally in the middle to upper part of the group for Fe(II) while that for total Fe ranged from the bottom of the group to near the top.

Ultrasonic probing of cohesive granular media at very low consolidation

In this work, we study sound propagation in different granular media made of magnetite particles, steel particles, and glass beads consolidated under their own weight. We used two ultrasonic non invasive methods, which are found in good agreement, to estimate the longitudinal wave velocity Vp. In the first one, the velocity is determined through the resonance peaks of the powder slab. The second method determines the velocity with the time of flight of a short pulse traveling through the medium. Magnetite and steel samples show dispersive properties below a frequency ∼ 10kHz. The increase of attractive forces between particles lead to two competing effects; on one hand the solid fraction decreases and on the other hand the contacts are stiffer. A decrease in solid fraction implies that the number of contacts decreases leading to a decrease in the wave propagation velocity. On the other hand stronger contacts on average lead to an increase of sound velocity. In our experiments an increase in powder cohesion (caused by a decrease of the bead diameter) leads to an increase in sound velocity even though the solid fraction decreases. The same behavior is found in glass beads. These results show the predominant role of cohesive forces on sound propagation in loosely consolidated dry fine powders as well as the accuracy of ultrasonic methods for powder characterization.

Possibility for Iron Production Using High-Power Millimeter Waves

Microwave (MW) technology is a promising alternative to conventional heating. It also resides in the new domain of materials science, namely, microscopic and strong thermal nonequilibrium systems. The application of MWs in the iron industry may be characterized by a high potential for an essential reduction of carbon dioxide emission. A series of experiments has been conducted to prove the effectiveness of rapid and high-purity refinement under an oxygen-containing environment by means of MW application, and achieved highly positive results. That has led to feasibility studies using a compact 30-GHz gyrotron system at the Karlsruhe Institute of Technology. Potential MW effects have been investigated. High-quality pig iron has been made from powder samples of mixed magnetite and carbon by 30-GHz millimeter-wave heating. This paper discusses the experimental results obtained recently and the estimated MW power for the iron production.