The 11th International Conference on Ferrites, ICF 11, was successfully held on April 15–19, 2013, at the Okinawa Convention Center, Okinawa, Japan organized by The Japan Society of Powder and Powder Metallurgy. ICF 11 covered a broad range of topics related to the science and technology of ferrites and related materials.
Get-together, Banquet, and Technical Visit were held in the ICF 11 as social events. They warmed up the conference, promoted friendship of the participants, and made participants enjoy not only culture and traditions but also beautiful scenery and marine science of Okinawa. You can find further information on Okinawa culture by inserting underlined bold letter key words on internet search.
This article presents a review of some salient aspects of a broad class of functional materials, namely complex oxides. These materials, exemplified by the rare earth manganites, superconducting cuprates and more recently multiferroics such as bismuth ferrite, are characterized by a complex crystal chemistry, that is central to competing/cooperating spin, charge, orbital and lattice degrees of freedom. In addition to this, a fundamental defining feature of such materials is the complex nanoscale phase coexistence that appears to be central to the appearance of large responses. The emergence of pulsed laser deposition as a tool to create artificially engineered heterostructures has provided researchers with a powerful approach to create new states of matter at such heterointerfaces. This combined with modern xray, electron, neutron and proximal probes (such as conducting AFM, piezoresponse SPM, etc.) and ab initio theoretical studies has provided us with deep insight into the various physical phenomena that manifest themselves in such materials.
There have been considerable interests in recent years in ferrite-ferroelectric composites for dual magnetic- and electric field tunable microwave and mm-wave devices such as resonators, filters, and phase shifters. Low-loss spinel and hexagonal ferrites are used in high frequency devices and the tuning in general is with a magnetic field H. When the ferrite is replaced by a ferrite-ferroelectric composite, however, the piezoelectric strain due to an electric field E applied to the ferroelectric will manifest as an induced anisotropy in the ferrite and facilitate E-tuning of the device. This review focuses on recent efforts on voltage tunable ferrite filters. A related phenomenon of importance is the nature of magneto-dielectric resonance in ferrites and its potential for low-loss H-tunable dielectric resonators, filters, isolators, and phase shifters for the frequency range 18–110 GHz. Potential avenues for enhancing the E-tuning of ferrite devices are also addressed.
Bi1-xGdxFeO3 (0≤x≤1.0) nanoparticles with an average diameter of 18 to 47 nm were synthesized by a wet chemical method. The annealing temperatures were controlled to obtain single-phase Bi1-xGdxFeO3 nanoparticles. The crystal structures changed from rhombohedral to orthorhombic as Gd ions increased to around x=0.2. The behavior of magnetization curves of x=0.1 suggested canted antiferromagnetism and magnetization drastically increased compared with x=0 (BiFeO3). This suggests that the canting angle increased with the increase of Gd ion. The dielectric properties of x=0.1 showed that dielectric loss (tan δ) has been improved compared with that of x=0 (BiFeO3) to about 90%, while real dielectric constant ε′ decreased about 15%. The reason is considered to be that impurities are restrained and leakage current decreased.
We microscopically investigate chiral magnetic orders in the absence and presence of magnetic field in a chiral magnetic crystal CrNb3S6 by means of low-temperature Lorenz transmission electron microscopy and small-angle electron scattering method. Based on detailed analyses in both real and reciprocal space, we directly observe that chiral soliton lattice (CSL) emerges in small magnetic fields applied perpendicular to the chiral crystallographic axis. CSL develops from chiral helimagnetic structure (CHM) with increasing the spatial period from 48 nm toward sample size in rising magnetic fields. Chiral magnetic orders of CSL and CHM do not exhibit any structural dislocation, indicating their high stability and robustness. This is because chiral magnetic orders are macroscopically induced by monoaxial Dzyaloshinkii-Moriya exchange interaction that is allowed in hexagonal CrNb3S6 crystals belonging to noncentrosymmetric chiral space group. Present observations of periodic, nonlinear, tunable, and robust CSL will be the first step to explore fascinating functions of CSL for magnetic and spintronic device applications using chiral magnets.
We have focused on the magnetic memories using parallel-aligned nanowires without mechanical moving parts, in order to achieve the ultra high transfer rate of more than 144 Gbps for Super Hi-Vision TV storage. In this memory using nanowires, the data is stored as the magnetic domains with up or down magnetization along magnetic nanowires, and domains are shifted by applying current along the nanowire direction for data writing and reading purpose. It is important for the magnetic nanowire memories, that all magnetic domains should be shifted precisely along nanowire by applied current.In this study, we have fabricated the [Co/Pd] multilayered nanowires with perpendicular anisotropy, and succeeded to drive multiple magnetic domains along the nanowire by application of one pulse current with 5 µs-width at current density range of 2.6–2.7×107 A/cm2. However, the magnetic state of domains was destroyed at higher current density by the induced high temperature due to Joule heating. In order to reduce Joule heating, we tried to apply one shorter pulse current with 500 ns-width, and we could confirmed the multiple magnetic domains shift at wider current density range of 2.6–2.9×107 A/cm2.
Magnetite (Fe3O4) is the original magnetic material and the parent of ferrite magnets, with modern applications ranging from spintronics to MRI contrast agents. At ambient temperatures magnetite has a cubic spinel-type crystal structure, but it undergoes a complex structural distortion and becomes electrically insulating below the 125 K Verwey transition. The electronic ground state of the Verwey phase has been unclear for over 70 years as the low temperature structure was unknown, but the full low temperature superstructure was recently determined by high energy microcrystal x-ray diffraction. There are 168 frozen phonon modes in the acentric (and hence multiferroic) low temperature magnetite structure. The ground state was found to be Fe2+/Fe3+ charge ordered and Fe2+ orbital ordered to a first approximation, but an unexpected localization of electrons in three-Fe ‘trimeron’ units was discovered. This description is supported by band structure calculations. This brief review will summarise recent progress on understanding the ground state structure of the Verwey phase of magnetite.
The E.p mechanism of superconductivity that gives Tc in agreement with the observed values for metals and alloys, ternary chalcogenides, borides and cuprates on the basis that in the time-reversed pair state at the Fermi surface the electron-nucleus repulsive E.p interaction vanishes and provides the binding energy of the pair is shown here to apply also to the iron superconductors.
The d0 ferromagnetism in oxide films and nanoparticles without 3d elements and long-range magnetic order at concentrations of magnetic cations below the percolation limit with Curie temperature exceeding 300 K is not explained on the present understanding of magnetism in solids. It is shown that these arise in nanostructure solids when two degenerate spin-polarized macro states of the system through coupling to zero-point phonon removes the degeneracy and increases the binding energy of the system by a small amount. The coupling through quantum tunnelling persists even in the presence of thermal fluctuations until the fraction of recoilless transitions in the ground state of the lattice vanishes. This accounts for its weak intensity, universality and existence over a wide temperature range.
We have conducted hard X-ray photoemission spectroscopy on FeTiO3 and FeTiO3–Fe2O3 solid solution in order to examine the electronic structure and electrical conduction mechanism of the compounds. The valence band spectrum of FeTiO3–Fe2O3 solid solution manifests a clear peak shift compared to FeTiO3, indicating that the electronic structure of FeTiO3–Fe2O3 solid solution consists of strongly mixed Fe 3d and O 2p components and that the electron correlation of the Fe 3d components is varied by the formation of solid solution between FeTiO3 and α–Fe2O3. We propose that insulating FeTiO3 is converted into semiconductor via this mechanism by the formation of FeTiO3–Fe2O3 solid solution, and the electron transfer between Fe2+ and Fe3+ in C-plane dominantly contributes to the electrical conduction in FeTiO3–Fe2O3 solid solution.
We synthesized a single crystalline sample of LaCo2P2 and measured its magnetization. We estimated parameters of spin fluctuations from Arrott plots and M4-H/M plots by using Takahashi’s itinerant-electron theory of spin fluctuations. From these plots, the magnetic properties of LaCo2P2 have been found to agree with the Takahashi’s itinerant-electron theory.
We report single crystal growth of the strontium hexaferrite SrFe12O19 by the traveling solvent floating zone (TSFZ) method using self flux. After improving various conditions, such as preparation of feed rods, atmosphere and pressure during crystal growth, growing speed, and the flux, we successfully obtained large single crystals. The crystals have cylindrical shapes with 4–5 mm in diameter and 40–60 mm in length. They grew along a direction nearly perpendicular to the c axis. It was demonstrated that the TSFZ technique provides large single crystals of SrFe12O19 of good quality.
NiZn ferrite with the different grain sizes has been characterized by Photoemission Electron Microscope (PEEM) measurements and the magnetic domain has been successfully visualized. Small grain induces small magnetic domain and it becomes larger when the grain is large. From these measurements, the domain wall across the grain boundary has been confirmed regardless of the grain size. This result suggests the possibility of the magnetic coupling between the grains providing a new knowledge about the effect of the micro-structure on the magnetic domain structure and the magnetization in NiZn ferrite.
The topic is the interpretation of measured values, a theoretical model and the investigation of critical parameters affecting stress sensitive permeability. The computer aided biaxial compression testing device allows the determination of the permeability, while at the same time the applied stress is measured. Compressive stress vertical to magnetisation is an equivalent to tensile stress parallel to magnetisation and vice versa. The rise of permeability can be found in a crystal anisotropy which is partly compensated by increasing magnetostrictive energy density. After reaching a maximum, the rising magnetostrictive energy leads to a monotonous decrease of permeability. The composition of ferrite and direction of stress strongly affects the stress sensitivity. Structural defects such as microcracks and rough edges result in giant local stress, which drastically reduces the initial permeability. A stress insensitive iron deficit MnZn ferrite is found (μi=500). Furthermore, stress induced μ(σ)-hystereses are measured and theoretically explained.
The partial substitution of Ni with Cu in NiZn-ferrites has many economical advantages in bulk magnetic component manufacturing and additional densification advantages in multilayer chip inductor manufacturing. However, the detailed mechanism through which the presence of Cu influences the densification of NiZn-ferrites has not been outlined in literature. In this article the mechanism of NiCuZn-densification has been explained on basis of point defect chemistry and changes in the type of major defects that dominate ion transport through sintering. Although the densification of NiZn-ferrites is mainly dictated by the Fe content and is restricted at Fe excess, in the presence of Cu this limitation does not hold any more because of the additional anion vacancies introduced due to Cu2+ to Cu+ reduction at elevated temperatures. In addition, further Cu reduction, through the usage of reductive atmospheres, enhances the densification even further and this provides an extra processing parameter for tuning densification. There is no evidence for liquid phase sintering due to the formation of liquid phases ought to the presence of Cu or associated eutectic mixtures.
Magnetization of a single grain is detected with an accuracy of about 10% by observing its translation through an area of microgravity; here translation was caused by an attractive field-gradient force produced by a static magnetic field. The above measurements were performed on paramagnetic pyroxene (MgFe)SiO3 grains as well as two different types of ferrite grains. It was experimentally confirmed that the obtained value of magnetization was independent to the value of sample mass, which indicated that translation of a grain was uniquely controlled by a field-induced potential. Magnetization of a single magnetic grain is measurable irrespective of its size, because mass measurement of sample is unnecessary in the proposed method. The measurement is not interrupted by a signal emitted from sample holder. The present method to measure magnetization is applicable in identifying the material of a small magnetic grain in a nondestructive manner.
It has been shown that by regulating excess iron content in spinel zinc ferrite it is possible to enhance its gas response. In this work relationships between structural properties and gas response of the non-stoichiometric zinc ferrites are studied. Stoichiometric and excess iron spinel zinc ferrite nanomaterials were synthesized by using sol-gel combustion. Rietveld refinement of site occupancies from powder XRD data shows that excess iron zinc ferrites contain vacancies on oxygen positions, Fe2+ on octahedral crystallographic B sites, and Fe3+ on the A site. As revealed by complex impedance spectra, with increasing oxygen vacancy concentration the depletion layer width decreases. At the same time, increasing oxygen vacancy concentration increases oxygen adsorption for reaction with a test gas, thus increasing the gas response of spinel zinc ferrite. Long term stability of the non-stoichiometric excess iron spinel zinc ferrite gas sensors will be discussed in this work.
The structural refinement using X-ray powder diffraction data was performed on the highly textured rectangular SrFe12O19 bar (M-type hexagonal ferrite) which was prepared by a conventional ceramic process. The difference between calculated and observed intensities in the X-ray patterns due to the preferred orientation was minimized by the generalized spherical harmonic function. The finally converged weighted R-factor (Rwp) for the longitudinal and the horizontal sections was 13.72% and 13.56%, respectively. Refined lattice parameters of the rectangular SrFe12O19 bar were a(=b)=5.8901(2) Å, c=22.9982(2) Å for the longitudinal, and a(=b)=5.8865(2) Å, c=22.9537(2) Å for the horizontal section, respectively. Other crystallographic data were well in accordance with those of randomly oriented synthesized-powder of SrFe12O19.
Iron oxide microtubules produced by a species of iron-oxidizing bacteria, Leptothrix ochracea, have been expected to be useed as unique multifunctional materials such as catalysts scaffolds, pigments, and magnetic materials. However, their structural characteristics and formation mechanism are still ambiguous. The detailed features of the microtubules were characterized through electron microscopies, X-ray diffractometory, and energy dispersive X-ray spectroscopy. We found that the microtubules have hierarchical microstructures with aggregates of amorphous iron oxide nanoparticles. Statistical analysis of distributions of the tubule diameters and the wall thicknesses suggested that the tubule layer could grow from outside to inside.
ZnxFe3-xO4 spinel ferrite nanoparticles were prepared by the coprecipitation technique. This research studied the effects of the x value and electric reduction on the electrochemical properties of ZnxFe3-xO4 spinel ferrite electrodes. Results showed the pseudo-capacitances of ZnxFe3-xO4 electrodes decreased with an increase in the x value and these capacitances increased after electric reduction at the −0.7 V vs. Ag/AgCl reference electrode. In addition, the pseudo-capacitance after electric reduction decreased with repetition of the charge-discharge cycles. However, pseudo-capacitance increased again due to the re-treated electric reduction.
Magnetotactic bacteria are microorganisms that produce magnetic particles surrounded by a lipid bilayer membrane with proteins. Since the size and morphology of these particles are uniform, it is thought that magnetic particles are morphologically controlled within the bacteria. The Mms6 protein was isolated from the surface of cubo-octahedral magnetic particles formed in the Magnetospirillum magneticum strain AMB-1. By using Mms6, cubo-octahedral magnetic particles were synthesized in vitro. Furthermore, the analysis of the mms6 gene-deletion mutant of magnetotactic bacteria indicated that Mms6 plays a role in the in vivo regulation of magnetic crystal morphology during crystal growth. Thus, Mms6 can be used to synthesize morphologically controlled magnetic materials under normal temperature and pressure conditions.
L10-phase iron-platinum (FePt) nanoparticles (NPs) are an excellent magnetic material which is expected to be utilized for ultra-high density magnetic storage media because of their superior magnetic properties. Meanwhile, fcc-phase FePt NPs are also expected to be a high-performance nanomagnet for magnetic medicine, including magnetic hyperthermia, magnetic resonance imaging, magnetic cell/protein/organelle separation and magnetofection, because they present a superparamagnetic behavior with high saturation magnetization and high chemical stability. We outline the effectiveness of fcc-phase FePt NPs for some medical applications in comparison to superparamagnetic iron oxide (SPIO) NPs. In addition, some recent developments regarding magnetic-fluorescent and magnetic-plasmonic dual functional core-shell NPs are presented.
Biosensing based on magnetic labels (superparamagnetic beads (SPBs) consisting of polymer matrices embedded with iron oxide nanoparticles) offer unique advantages over conventional fluorescent markers and labels. In particular, SPBs can be manipulated and assembled at specific locations on functionalized surfaces by the application of external magnetic field gradients, and then disassociated by switching off the magnetic field. Also, suitably functionalized SPBs can be manipulated by the application of electric field gradients, thereby enabling a further degree of freedom in applications of the SPBs for biosensing and medical diagnostics. Here, we describe our research on protocols for biosensing based on the exploitation of the magneto-optic properties of SPBs for point of care treatment.
Two kinds of iron oxide particles—spherical cobalt-containing iron oxide particles with spinel structure and platelet γ-Fe2O3 particles—were synthesized for medical applications. The particle size of the spherical cobalt-containing iron oxide particles was about 20 nm regardless of the coercive force that was varied in the range of about 4.0 to 39.0 kA/m by varying the Co content. The size and coercive forces of the platelet γ-Fe2O3 particles were in the range of about 30 to 100 nm and about 7.6 to 13.5 kA/m, respectively. The temperature-raising properties were evaluated for water dispersion of these particles under different AC magnetic fields and frequencies to apply hyperthermia or thermoablation using hysteresis-loss heating of ferrimagnetic particles. Heat generation in spherical cobalt-containing iron oxide particles was based on both hysteresis-loss and Brownian relaxation. Platelet γ-Fe2O3 particles showed heat generation completely based on hysteresis-loss.
The balanced temperatures of La0.676Sr0.358Mn0.922Cu0.044O3 perovskite at 56 Oe amplitude of alternating magnetic field of different frequencies were investigated. The balanced temperatures at 600, 800 and 1000 kHz were 38.0, 39.0 and 39.7°C, respectively. Heating powers of the perovskite were also estimated from minor hysteresis loops data, which were measured at various temperatures under different amplitudes of magnetic fields (14, 28, 42, 56 and 70 Oe). The estimated heating powers under alternating field of different frequencies at the respective balanced temperatures were 0.06 W. This result shows that heat dissipation from the experimental system used in the heating ability experiment is 0.06 W. When the perovskite is set in the part where heat dissipation is known, we can estimate the balanced temperature in arbitrary frequency and magnetic field strength.
The morphology of platelet α-FeOOH, a precursor for synthesizing γ-Fe2O3 particles for use in cancer therapy by hysteresis-loss heating, was investigated with the aim of reducing the size of γ-Fe2O3 particles. The α-FeOOH particles were synthesized by the precipitation of ferric ions in alkaline solution containing ethanolamine, and crystals were grown via hydrothermal treatment. The particle length of α-FeOOH was reduced on lowering the precipitation temperature and maintaining it in the range from −3°C to 6°C, whereas the ratio of the long and short axes was maintained. The axial ratio of the α-FeOOH particles was remarkably affected by the precipitant's aging temperature in the range of 4–60°C, and became smaller when the aging temperature was lowered. The addition of Si was effective for reduction of the particle length of α-FeOOH. Platelet α-FeOOH particles with a particle length of ~40 nm and an axial ratio of ~1.5 were obtained by using Si as an addictive and employing precipitation, aging, and hydrothermal treatment temperatures of −3.5°C, 4°C, and 150°C, respectively.
Bio-labeling applications of quantum dots (QDs) have grabbed scientists' attention due to their numerous benefits to human life. The quality properties such as strong, narrow, tunable and size-dependent emission of broad absorption spectrum QDs, combined with water-solubility and non-toxicity, are needed for QDs to perform as excellent labeling tools in biological applications. Besides, predictable and reliable controls to achieve perfect and biologically safe QDs with excellent optical properties are expected. In this study, we managed to synthesize cadmium sulfide (CdS) QDs with a mean size of 8 nm by capping it with thioglycolic acid—which has hydrogen bonding—to make QDs soluble in aqueous solutions. Polyethilenimine has functioned to render the QDs to be water soluble and enhances photo-oxidation even in aqueous solution. It also acted as a ligand to modify CdS QDs to prevent surface trap and thus increase CdS QDs' quantum yield. Furthermore, improved stability of the QDs in polymer sphere and non-toxicity is needed. Therefore, the ideal bio-labeling QDs should be dense and equal in size and shape to achieve constant photoluminescence peak. Hence, the CdS QDs have been capsulated with poly(2vinylpyridine) (P2VP) homopolymers and apo-ferritin in order to compare which one is the best capsule for QDs with the desired properties for applications in bio-labeling.
A harmonic signal analysis of magnetic nanoparticles (MNPs) used as tracers in magnetic particle imaging (MPI) was conducted. The harmonic spectrum from three types of immobilized MNPs namely, Resovist, fluidMAG, and SupraBead, were measured at excitation fields of 1.4 mT and 28 mT with a frequency of 10 kHz. Resovist showed the richest spectrum, followed by fluidMAG and SupraBead. These different harmonic properties among samples were analyzed on the basis of the magnetic moment m and anisotropy energy EB of the MNPs. We show the conditions of m and EB required for harmonic signal generation. As m and EB are widely distributed within MNPs, a fraction of MNPs satisfies the m and EB conditions and contributes to the harmonic signals. Resovist shows the largest such fraction satisfying these conditions. This is reflected in the experimentally obtained rich harmonic spectrum of Resovist. The experimental data was found to agree well with the numerical simulation results based on the Landau–Lifshitz–Gilbert equation when the distributions of m and EB within the MNPs were taken into account. These findings may serve as an important basis in the optimization of MNPs for MPI.
Magnetic separation using permanent magnets and/or electromagnets has been increasingly used for purification and recycling of suspended solids and water since the mid 1970's. The objectives behind the development of such magnetic separation systems include purification of kaolin clay in the paper-coating industry, wastewater recycling in the steel industry, and recycling of glass-grinding sludge in the CRT-polishing industry. Due to direct, selective, high-intensity magnetic forces on particles to be separated, the filtering speed of High Gradient Magnetic Separation (HGMS) systems, developed in the 1970's, is now 15–300 times faster than conventional filtration systems. Consequently, magnetic separation is now being applied to a broad class of weak paramagnetic materials, down to submicron particle size. Such HGMS systems have been used for large-scale manipulation of colloidal materials (i.e., up to 50 kg/hr for drainage purification and reuse systems in steel mills). In the 1980's, large superconducting magnets were adopted for field coils of HGMS systems used for kaolin clay purification. After development in the 1990's of less expensive, liquid-helium-free superconducting magnets, national research projects were initiated in Japan, Korea and China to expand their application. A particularly pressing application is the environmental remediation of soil polluted with radioactive particles in Japan.
This study presents a newly developed superconducting magnetic separation system capable of continuous operation without interruption of feed-water owing to its unique structure, consisting of a continuously rotating disk-type magnetic filter and solenoid-type superconducting magnet. The continuously rotating disk-type magnetic filter, which is installed outwardly from the center axis of the magnet bore, is mounted on the cryostat and the superconducting magnet is energized using a permanent current switch, which consumes less electric power. This structure enables provision of a continuous operation system with high-speed and energy-saving separation treatment. We carried out a field test for two years including continuous operation for 1,000 hours. The test plant constructed had a capacity of 500 m3/day in order to study the possibility of applying the system for the purification of polluted lake and river water. The results show that the system has good performance, evidenced by a phosphorous removal rate of more than 85% and a suspended solid removal rate of less than 5 mg/L at a separation speed of 0.1 m/s. This system was found to be capable of being used practically for water pollution purification.
On-site experimentation of high gradient magnetic separation (HGMS) to remove arsenic from geothermal water was conducted at the Kakkonda geothermal power plant in Shizukuishi, Iwate, Japan, from 2000 to 2005. By this HGMS method, the arsenic concentration in the geothermal water was reduced to less than the effluent standard of 0.1 mg/L but slightly higher than the environmental standard of 0.01 mg/L in Japan. To enhance the magnetic properties of arsenic-containing particles in geothermal water, we tried several pretreatment methods and found that the co-precipitation method using Fe(III) hydroxide generates suitable magnetized flocks for magnetic separation. Such treated geothermal water had a pH between 4.0 and 4.5 and a temperature higher than 90°C. The magnetic susceptibility of the resulting flocks was around 10−3, which is a typical value for paramagnetic materials. In the experiments we used a superconducting magnet to apply a magnetic field up to 2 T to a magnetic filter fabricated by packing 100 m-diameter ferromagnetic thin wires in a 50 mm ID paramagnetic stainless tube. With this HGMS system, the arsenic concentration was reduced from 3.25 mg/L to less than 0.07 mg/L at a flow velocity through the HGMS filter, 4.2 and 8.5 cm/s.
The principle and some examples of magneto-Archimedes separation of feeble magnetic materials have been introduced. Under magneto-Archimedes levitation condition, the stable levitation position depends on the materials because it is determined by the difference in volume magnetic susceptibilities and densities between objects and their surroundings. By using this feature, this novel magnetic separation technique was successfully demonstrated. When some powder mixtures composed of feeble magnetic materials were levitated, the initial mixture underwent separation into each kind of the ingredient particle aggregates immediately. It was also confirmed that this method is sensitive to both material density and magnetic susceptibility. This technique seems to be a beneficial way for the practical separation of feeble magnetic materials.
This study shows the development of a produced water treatment system using flocculation and magnetic separation, and the improvement of the prediction formula on floc residual rate to evaluate magnetic separation performance. Previously, magnetic separation conditions were determined based on a number of experiments on various types of influent that depends on wells. Therefore it took time substantially to design specifications for each system. A simple design process diagram has been established by considering influential factors to magnetic separation conditions and conducting simple experiments using synthetic water. The developed prediction formula can realize speedy and effective proposals on the system customized for each site.
We have devised the rapid elimination system for the contaminated radioactive cesium using magnetic nanocomposites. The Great East Japan Earthquake hit caused a serious meltdown of the overheated fuel rods and the release of radioactive chemicals into the environment. Until now, fuel rods have been cooled using seawater to control its temperature, therefore huge amount of waste water containing high concentrations of radioactive cesium have been continuously generated. On the other hand, radioactive cesium is easily condensed in the fly ash originating from incineration of garbage. The garbage incineration plant is overflowing with the fly ash which cannot be discarded (when the radioactivity of fly ash exceeds 8000 Bq/kg, we cannot discard it as a usual manner). Prussian blue is known as an effective eliminator of radioacitive cesium from seawater and fly ash slurry, however complete and rapid collection of Prussian blue dispersed in water is very difficult. Recently, we have developed a novel form of magnetically guidable Prussian blue coated magnetic nanocomposite clusters via the application of nanotechnology for drug delivery system. Using this type of nanocomposites under magnetic field, we have confirmed that 99.9% and over 80% of cesium were rapidly removed from seawater and fly ash, respectively.
A magnetic separation technique has been conducted to recycle the nickel (Ni) element from the waste fluid of electroless Ni plating processes. The experiment was operated using the face-to-face type electromagnet generating 1.96 T and the data was compared to those in the case of the high temperature superconducting bulk magnet which generates 3.45 T. In the electroless plating processes, the plating fluid containing high concentration of Ni ions is disposed after several turns of the plating cycles when the concentration of phosphite ions exceeds a certain level. In order to extract the Ni element at first, we formed the coarse Ni-sulfate crystals with the sizes over 1 mm from the Ni-phosphite precipitates by controlling the temperature and the pH value. Next, the magnetic separation experiments were operated to collect the Ni-bearing precipitate which carried the weak magnetism. Although the performance of high temperature superconducting bulk magnet is superior to that of electromagnets, as a result, we succeeded in collecting Ni-sulfate crystals preferentially to the Ni-phosphite precipitates soon after the crystal growth began.
Hollandite-type AxFexSn8-xO16 (A: K, Rb, Cs) powder were prepared by conventional solid state reaction method for studying the correlation of nitrogen oxide (NO) adsorption mechanism on its surface. Observation of NO adsorption was performed by the diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS). After adsorbed NO gas on hollandite surface, absorption bands around 1350–1400 cm−1 and 1750 cm−1 were observed as KNO3. And, NO adsorption of AxFexSn8-xO16 surface was observed until 400°C, respectively. From the NO adsorption property on hollandite surface by DRIFT spectra, it was found that the presence of oxygen in carrier gas had a significant contribution for NO adsorption, and the active point was alkaline metal ions located at the end of one-dimensional tunnel.
Fe-included titania nanosheets were prepared by ionic-exchanging and acid-base reaction from lepidocrocite-type titanate. Obtained titania nanosheets were flocculated by reacting with potassium hydroxide solution. The flocculated nanosheets and the base material were evaluated nitrogen monoxide (NO) adsorption property using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). The flocculated titania nanosheets was better NO adsorption property than the base material.
Ferrites have the ability to exchange oxygen with the environment, depending on the partial pressure of oxygen and have been therefore considered as candidates for RedOx materials in both the Chemical Looping Combustion and the Thermochemical Water Decomposition Processes. In this article the feasibility of MnZn- and NiZn-ferrites as RedOx materials has been evaluated in the above processes. The Oxygen Transfer Capability, the methane decomposition activity as well as the catalytic activity towards H2 production by water splitting have been studied at temperatures 1173–1273 K.
The formation process of a ferrite oxide film, which can effectively suppress radioactive nuclide deposition on piping surfaces of BWR reactor water recirculation system, was evaluated from the viewpoints of scale-up from a 1 liter flask scale to a 10 m3 plant scale. To get a thin and closely packed oxide film, the pH and oxidation-reduction potential values should be maintained within the magnetite stability domain in the Pourbaix diagram of the iron-water system by controlling the hydrazine concentration. The selected film forming conditions were confirmed using the flow system apparatuses of 1/500 and 1/10 actual plant scales. This film formation process could be evaluated taking into consideration the charge balance and chemical equilibrium equations of each reaction involved in the film formation. The method was applied to an actual plant just after the chemical decontamination.
Different grades of spray roasted iron oxides are produced in form of chemical by-products at steel mills. Originating from the thermal decomposition of up-graded iron chloride solutions, these synthetic iron oxides became a strategic raw material source for the production of soft and hard ferrites, and a series of chemical, ceramic and metallurgical products. Manganese contents in the order of 0.25 up to 1.0 per cent limit their usage for some applications, which presently being serviced by iron oxides based on other precursors. Another fast growing market concerns olivine structured LiFePO4 cathode battery materials, which contain about 50 wt.% Fe2O3. Spray roasters have been designed to yield iron oxides exhibiting specific surface area data in the range of 0.5 up to 25.0 m2/g. Preferred BET-data are: 0.5 up to 4.0 m2/g for hard ferrites, 3.0 up to 5.5 m2/g for soft ferrites and 8.0 up to 12.0 m2/g for pigments. Washed iron oxides exhibiting total chloride levels in the order of 600 ppm Cl− are available. Further washing results in Cl− levels of 300 ppm and an additional thermal treatment, by means of a short treatment within a vertical un-obstructed furnace, yields iron oxides with <20 ppm Cl−.
The combination of highly reactive raw materials with an optimized set of dopants results in high density Mn Zn ferrites. The use of non-calcined raw materials has the advantage of simplified processes and improved cost efficiency of the industrial realization. Lowest power losses and highest saturation flux densities could be achieved as a result of substantial investigations. Both properties require a dense and defect-reduced microstructure. The spinel formation and the grain growth were optimized due to the required grain size, the composition and the grain boundary thickness. Usual additive oxides like CaO, SiO2 and Nb2O5 were amended by V2O5 and SnO2 as eutectic control. Increased transport capability for the initial chlorine content of iron oxide at moderate temperatures could be enhanced by optimized shrinkage behavior. Consequently all results were adapted to commercial raw material qualities with the result of highest performance power transformer ferrites in the frequency range up to 300 kHz.
The synthesis of MFe2O4 (M: Co, Ni and Zn) spinel ferrites was studied by the use of hydroxides as starting materials, applying isostatic pressure of HIP process. Single phases of ZnFe2O4 and CoFe2O4 were obtained at 300°C. Single phase of NiFe2O4 was not obtained at 400°C from the mixture of NiO and FeOOH. However, the mixture of Ni(OH)2 and FeOOH with 20 mass% of water formed the single phase of NiFe2O4 at 400°C. These ferrites revealed high crystallinity and fine particle size of 50–400 nm. No reaction occurred in the mixtures of oxides, such as ZnO and Fe2O3. Although the addition of small amount of water to the oxide mixture promoted the reaction, single phase was not obtained at 400°C. In the conventional process, these ferrites were generally prepared at higher temperature of 800–1200°C. Water produced from the hydroxides played important role to form these ferrites at low temperature.
Especially in the production of MnZn- and NiCuZn-ferrites the purity of applied ferric oxide is of vital importance to achieve high quality products. Usually synthetic iron oxides produced by the spray roasting process of spent pickle liquor in flat carbon steel production are used. Spray roasting plants therefore have to be equipped with a pickle liquor purification process to remove elements like Ti, Al, Cr, P simultaneously by means of precipitation. Colloidal silica is bonded in parallel to a certain degree by means of adsorption on precipitated metal hydroxides. In recent years plenty of new steel grades have been developed requiring more and/or new alloying elements leading to an additional contamination of the pickle liquor and thus pushing the purification system to the limit. In order to overcome possible troubles additional treatment of spent pickle liquor prior to spray roasting has to be considered. In the case of Ni and Cu a removal of the pickle liquor by membrane electrolysis was investigated by operating a small pilot plant. Cu was removed completely and Ni removal was up to 20%. In case of Ni for quantitative removal also organic complex forming agents like Dimethylglyoxime can be applied.
New and emerging ferrite applications where significant power is involved (i.e. in automotive), impose stronger demands on the performance of magnetic cores, such as that the components should exhibit higher saturation flux densities at high temperatures, than those currently exhibited by existing components, with the lowest possible effects on other important magnetic properties (i.e. initial magnetic permeability, power losses). In this article the development of a MnZn ferrite polycrystalline material is reported with a saturation flux density of 642 mT at 10 kHz, 1200 A/m, 25°C and 550 mT at 100°C. The initial permeability is 1020 (10 kHz, 0.1 mT, 25°C) and the power losses 800 mW cm−3 (100 kHz, 200 mT, 100°C). The previous results place this material among the best in its class. The improvements have been realized through optimizations in the design of the antiferrimagnetic unit cell lattice as well as through optimizations on the processing and the microstructural evolution of the polycrystalline structure.
The present work deals with the effect of uniaxial compressive stress on the magnetic properties of MnZn-ferrite materials with permeability levels between 2000–12000. The investigation included the effects of several process operational or material structural parameters such as time and periodical stress application and removal, sintering partial pressure of oxygen, final density and grain size on the stress sensitivity of the polycrystalline material. It was found that stress sensitivity increases with permeability, while the high permeability grades show a permanent decrease of the permeability level under prolonged application of the applied stress. Regarding the power MnZn ferrite materials, a reduction of the secondary permeability maximum temperature by ~0.5°C MPa−1 and a subsequent reduction in magnetic flux density by ~1.4 mT MPa−1 upon the exertion of uniaxial compressive stress was measured. In addition, it was observed that there is an optimal partial pressure of oxygen during sintering, under which the stress sensitivity of the material becomes minimum. A mechanism of anisotropy field variations induced in the material in combination with the defect structure of the material and its dependency on the partial pressure of oxygen has been proposed.