Iron-cobalt Alloys Research Articles

Optimal Magnet Design for Lorentz Force Eddy-Current Testing

We propose a procedure to determine optimal magnet systems in the framework of the nondestructive evaluation technique Lorentz force eddy-current testing (LET). The underlying optimization problem is clearly defined considering the problem specificity of nondestructive testing scenarios. The quantities involved are classified as design variables, and system and scaling parameters to provide a high level of generality. The objective function is defined as the absolute defect response signal (ADS) of the Lorentz force resulting from an inclusion inside the object under test. Associated constraints are defined according to the applied force sensor technology. A numerical procedure based on the finite-element method is proposed to evaluate the nonlinear objective and constraint functions, and the method of sequential quadratic programming is applied to determine unconstrained and constrained optimal magnet designs. Consequently, we propose a new magnet design based on the Halbach principle in combination with high saturation magnetization iron–cobalt alloys. The proposed magnet system outperforms currently available cylindrical magnets in terms of weight and performance. The corresponding defect response signal is increased up to 180% in the case of small defects located close to the surface of the specimen. The combination of active and passive magnetic materials provides an increase of the ADS by 15% compared with the magnet designs that are built solely from permanent magnet material. The proposed procedure provides a highly adaptive optimization strategy in the framework of LET and proposes new magnet systems with inherently improved characteristics.

Measurement of Density of Fe-Co Alloys Using Electrostatic Levitation

The density of a series of five different iron-cobalt alloys was measured using electrostatic levitator processing. Each sample was processed through multiple thermal cycles and the liquid density was measured, while the superheated sample was cooled down to its undercooled state. The volume of the sample was estimated by analyzing captured high-speed video data of the projected shape of the sample. The mass change during the melt cycle was also tracked using Langmuir’s equation of mass evaporation. The density was then calculated as a function of temperature based on these measurements of volume and mass. Density values obtained showed higher precision than existing data from the literature obtained using a variety of different techniques, although the accuracy was consistent.

TEM observations of particles based on sampling in gas and soil at the Dongshengmiao polymetallic pyrite deposit, Inner Mongolia, Northern China

Forty-two samples of particles that were carried by the ascending gas flow and forty-two corresponding soil samples were captured from Quaternary sediments overlying the Dongshengmiao polymetallic pyrite deposit in the Province of Inner Mongolia, North China. The category, size, shape, chemical composition and structure of these particles were analyzed by transmission electron microscopy (TEM) technique. The observations indicated that most of the particles carried by the ascending gas flow were sub-circular, elliptical or irregular in shape, with sizes ranging from 5nm to 400nm; their primary components were dominated by the metallogenic elements Fe, Cu, Zn and Pb, and their highest weight percentages were up to 80.2%, 82.5%, 49.1% and 59.6%, respectively. We determine that a large number of metal sulfides and oxides/hydroxides (such as PbS, Fe3O4, Sb3O2 and Fe(OH)3), native metal alloy (such as native vanadium–platinum–iron–cobalt alloy), nonmetallic oxides (such as SiO2), chlorides (primarily NaCl), nonmetallic hydroxides (such as KOH) and sulfate (primarily BaSO4) particles, as well as precious metal elements (such as Au and Pt) bearing particles and rare earth elements (such as Y) as observed in the samples, exhibited a good correspondence with the concealed ore bodies and the wall rock. A number of the particles that were carried by the ascending gas flow were found in elemental associations S–Cu, S–Zn, S–Pb, S–Mo, S–Fe–Zn, S–Fe–Cu, S–Fe–Cu–Mo, S–Fe–Zn–Pb and Cr–Mn–Fe, which were consistent with previous studies on the mineral assemblages of this deposit. The particles carried by the ascending gas flow and soil particles have a common origin, that is, the ore body. Different particles carried by ascending gas flows come from different types of deposits, without interference from the properties or thickness of the overlying layer, suggesting that geogas prospecting could be used to explore for different types of ore deposits. An analysis of the particles carried by the ascending gas flow along the 14th exploration line demonstrates a good spatial correlation with the known concealed ore bodies. Additionally, Pt-bearing and rare earth element bearing particles were first found in the ascending gas flow from the Dongshengmiao deposit.

Thermal Annealing Effect on Real Time Atomic Relocation of Iron-Cobalt Alloys Prepared by Electro-Deposition

Atomic structures of fabricated Fe-Co alloys were investigated real time by time resolved x-ray absorption spectroscopy (TRXAS) at annealing temperature of 400° C. The various compositions of Fe-Co alloy thin films were prepared by electro-deposition on indium-tin oxide glass substrate with iron sulfate and cobalt chloride electrolyte solutions. The current density of 80 A/m2was used to deposit Fe-Co thin film with varying the ratio of Fe and Co ion concentrations. The Fe-Co alloys with boron nitride powders were mixed, grinded and pressed in the pallet form in order to insert into environmental controlled sample holder for TRXAS measurement. The samples were annealed under 20% oxygen and 80% nitrogen atmospheric by increasing the temperature up to 400° C and then remaining for an hour. The influence of annealing temperature can modify the atomic structures of Fe-Co alloys as indicated in the variation of extended x-ray absorption fine structure (EXAFS) peaks. Most of the EXAFS peaks followed the temperature profile i.e. increasing or decreasing during the temperature rising and then maintaining about constant values during holding the temperature at 400° C. By transforming the EXAFS peaks into scattering radius space, the modification of relative scattering amplitude from each nearest neighbor position indicated the atomic relocation during annealing the samples. Some of scattering patterns from Fe and Co oxides can be found and their amounts changed during rising the annealing temperature. In addition, the atomic relocations extracted from the Co absorption edge was very much smaller than those of Fe edge probably due to relative more stable of Co atomic positions for this range of annealing temperature.

A model-based method for the characterisation of stress in magnetic materials using eddy current non-destructive evaluation

A precise knowledge of the distribution of internal stresses in materials is key to the prediction of magnetic and mechanical performance and lifetime of many industrial devices. This is the reason why many efforts have been made to develop and enhance the techniques for the non-destructive evaluation of stress. In the case of magnetic materials, the use of eddy current (EC) techniques is a promising pathway to stress evaluation. The principle is based on the significant changes in magnetic permeability of magnetic materials subjected to mechanical stress. These modifications of magnetic permeability affect in turn the signal obtained from an EC probe inspecting the material. From this principle, a numerical tool is proposed in this paper to predict the EC signal obtained from a material subjected to stress. This numerical tool is a combination of a 3D finite element approach with a magneto-mechanical constitutive law describing the effect of stress on the magnetic permeability. The model provides the variations of impedance of an EC probe as a function of stress. An experimental setup in which a magnetic material subjected to a tension stress is inspected using EC techniques is tailored in order to validate the model. A very good agreement is found between experimental and modelling results. For the Iron-Cobalt alloy tested in this study, it is shown that a uniaxial tensile stress can be detected with an error lower than 3 MPa in the range from 0 to 100 MPa.

Electro-infiltration: A method to form nanocomposite soft magnetic cores for integrated magnetic devices

This article introduces a scalable, process-integrable manufacturing method for creating microstructured, nanocomposite soft magnetic cores on planar substrates such as silicon wafers or printed circuit boards. To demonstrate this electro-infiltration process, maghemite (γ-Fe2O3) nanoparticles less than 50 nm are first evaporatively consolidated from suspension into photoresist molds on a silicon substrate, forming dimensionally defined porous microstructures. Next, a high-saturation soft magnetic iron cobalt alloy (Fe–Co) is electroplated up from a conductive layer on the substrate to fill in the void spaces of the consolidated particles. The result is a dense, two-phase nanocomposite, where the maghemite nanoparticles form an inclusion phase in the electroplated metal matrix phase. Improved high-frequency permeability is observed in the 100 MHz–2 GHz range.

Thermodynamics of the oxygen solutions in chromium-containing melts of the Fe-Co system

Thermodynamic analysis of the oxygen solutions in chromium-containing melts of the Fe-Co system is carried out. The equilibrium constants for the interaction of chromium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of various compositions are determined. The dependences of the oxygen solubility in the melts on the cobalt and chromium contents are calculated. Chromium in iron-cobalt melts is characterized by a fairly high oxygen affinity, which substantially increases with the cobalt content in a melt. The introduction of chromium into a melt in manufacturing ironcobalt alloys results in the final metal with a lower oxygen concentration. The solubility curves of oxygen in chromium-containing iron-cobalt melts pass through a minimum, whose position shifts toward low chromium contents as the cobalt content in a melt increases. Further chromium additives result in an increase in the oxygen concentration in a melt. The higher the cobalt content in the melt, the sharper the increase in the oxygen concentration after the minimum when chromium is added to the melt.

Magnetic separation-sulphuric acid leaching of Cu–Co–Fe matte obtained from copper converter slag for recovering Cu and Co

Cu–Co–Fe matte obtained from copper converter slag by reductive-sulfidizing smelting was treated by magnetic separation-sulphuric acid leaching (MS-SAL) process to recover the metal values, copper and cobalt. The MS-SAL process was proposed on the basis of mineralogical analysis of matte, which showed that the main copper-bearing phases were bornite and chalcocite (non-magnetic substances), and the main cobalt-bearing phase was cobalt–iron alloy (magnetic substances). The matte sample was crushed, wet ground and then magnetic separated to produce magnetically susceptible concentrate (mainly Co–Fe alloy). 95.75% of cobalt was recovered by magnetic separation and 87.8% of copper and 44.39% of iron remained in the tailings. The concentrate was leached further by sulphuric acid. Under the optimum conditions of 1.15 times the stoichiometric amount of sulphuric acid, 1h of leaching time and temperature 80°C, 99.81% of cobalt in concentrate was selectively leached into the solution while the 99.86% of copper remained in residue. The tailings containing mainly bornite and chalcocite and the leaching residue containing mainly metal copper were treated by ore proportioning with copper concentrate and fed to the copper smelting furnace. In this process, cobalt in matte was selectively extracted and the copper was almost entirely recovered for copper smelting rather than extracted from leaching liquor as in existing copper matte leaching technologies. Recovery yields of cobalt and copper by MS-SAL were 95.57% and 99.98%, respectively.

An EQCM study on the influence of saccharin on the corrosion properties of nanostructured cobalt and cobalt-iron alloy coatings

Nanostructured cobalt (Co) and cobalt-iron (CoFe) alloy coatings were electrodeposited from sulfate solutions in the presence and absence of saccharin. The effects of saccharin on the corrosion behavior of Co and CoFe alloy coatings were investigated using the electrochemical quartz crystal microbalance (EQCM) technique coupled with cyclic voltammetry (CV) measurements. Saccharin was added to the electrolyte as a grain refiner and brightener. Interestingly, opposite corrosion behaviors were found for all nanostructured coatings in 0.1 M H2SO4 and 0.1 M NaOH. The use of saccharin as an additive in the plating solution accelerated the anodic reaction for all deposits in acidic medium. The mass decreases while dissolution rate increased with higher saccharin concentration. Meanwhile, formation of a thick passive film on the Co electrode surface were enhanced while a hindering effect was observed for CoFe alloy coatings deposited in the presence of saccharin in alkaline solution. The anodic and cathodic curves obtained from potentiodynamic polarization experiments were also in agreement with the EQCM results.

The heating effect of iron-cobalt magnetic nanofluids in an alternating magnetic field: application in magnetic hyperthermia treatment

In this research, FeCo alloy magnetic nanofluids were prepared by reducing iron(III) chloride hexahydrate and cobalt(II) sulfate heptahydrate with sodium borohydride in a water/CTAB/hexanol reverse micelle system for application in magnetic hyperthermia treatment. X-ray diffraction, electron microscopy, selected area electron diffraction, and energy-dispersive analysis indicate the formation of bcc-structured iron-cobalt alloy. Magnetic property assessment of nanoparticles reveals that some samples are single-domain superparamagnetic, while others are single- or multi-domain ferromagnetic. The stability of the magnetic fluids was achieved by using a CTAB/1-butanol surfactant bilayer. Results of Gouy magnetic susceptibility balance experiments indicate good stability of FeCo nanoparticles even after dilution. The inductive properties of corresponding magnetic fluids including temperature rise and specific absorption rate were determined. Results show that with increasing of the nanoparticle size in the single-domain size regime, the generated heat increases, indicating the significant effect of the hysteresis loss. Finally, the central parameter controlling the specific absorption rate of nanoparticles was introduced, the experimental results were compared with those of the Stoner-Wohlfarth model and linear response theory, and the best sample for magnetic hyperthermia treatment was specified.

Implementation of non-equilibrium vertex corrections in KKR: transport through disordered layers

The theoretical description of modern nanoelectronic devices requires a quantum mechanical treatment and often involves disorder, e.g. from alloys. Therefore, the ab initio theory of transport using non-equilibrium Green’s functions is extended to the case of disorder described by the coherent potential approximation. This requires the calculation of non-equilibrium vertex corrections. We implement the vertex corrections in a Korringa–Kohn–Rostoker multiple scattering scheme. In order to verify our implementation and to demonstrate the accuracy and applicability we investigate a system of an iron-cobalt alloy layer embedded in copper. The results obtained with the coherent potential approximation are compared to supercell calculations. It turns out that vertex corrections play an important role for this system.

Magnetic Properties of Co-Fe Nanowires Electrodeposited in Pores of Alumina Membrane

Abstract The nanowires of Co66-Fe34 alloy were obtained in the process of the electrodeposition in the pores of alumina membrane. With the use of the X-ray diffraction analysis the structure of cobalt-iron alloy wires was determined. The wires have the regular Body Centred Cubic structure (BCC). The influence of membrane parameters, an external magnetic field, and the annealing temperature on the magnetic properties of alloy wires was investigated. The obtained nanowires show a high shape anisotropy in the direction perpendicular to the membrane surface of anodic alumina. It was found that the highest influence on the magnetic properties of the wires has their geometry (height, diameter, and the distance between them). The use of an external magnetic field directed perpendicular to the sample surface during the electrodeposition process and additional thermal treatment (annealing) causes a slight increase of the coercive field, remanence, and volume energy density.

Electrochemical properties of electrodeposited nanocrystalline cobalt and cobalt–iron alloys in acidic and alkaline solutions

Nanocrystalline Co and CoFe with varied iron contents ranging from 5 to 25 wt% Fe were electrodeposited from a sulfate bath. The average grain sizes of the coatings obtained were measured using Scherrer equation and calculated to be in between 16 and 65 nm. Electrochemical corrosion behavior of electrodeposited nanocrystalline cobalt (Co) and cobalt–iron (CoFe) alloys was investigated in both acidic (0.1 M H2SO4) and alkaline solution (0.1 M NaOH). This study investigates the corrosion behavior of electrodeposited CoFe alloy coatings using polarization tests, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy techniques. The nanocrystalline Co and CoFe showed active behavior for all alloy coatings in acidic condition, while an active–passive–transpassive behavior was seen for all coatings in alkaline condition.

Pyrohydrolysis synthesis of an iron-cobalt alloy

Pyrohydrolysis synthesis of an iron-cobalt alloy

Ternary Metastable Nitrides ε-Fe2TMN (TM = Co, Ni): High-Pressure, High-Temperature Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

High-pressure, high-temperature synthesis gives access to ternary metastable nitrides ε-Fe2TMN (TM = Co, Ni) as bulk materials for the first time. Both ε-Fe2CoN and ε-Fe2NiN crystallize isostructural to ε-Fe3N as evidenced by X-ray powder diffraction data. The lattice parameters of the new compounds are slightly smaller than those of ε-Fe3N owing to the reduced atomic radii of the metal atoms. Energy-dispersive X-ray spectroscopy of metallographic samples show homogeneous metal ratios corresponding to compositions Fe1.99(6)Co1.01(6)N and Fe1.97(2)Ni1.03(2)N. Extended X-ray absorption fine spectra indicate that cobalt and nickel occupy iron positions. Thermal analysis measurements reveal decomposition of both ternary nitrides above 920 K. ε-Fe2CoN disintegrates into N2 and iron–cobalt alloy, while ε-Fe2NiN decays into N2, iron–nickel alloy as well as α-Fe. The replacement of iron by cobalt or nickel essentially lowers the saturation magnetization from roughly 6.0 μB/f.u. for ε-Fe3N to nearly 4.3 μB/f.u. for ε-Fe2CoN and 3.1 μB/f.u. for ε-Fe2NiN. In parallel, the Curie temperature decreases from 575(3) K for ε-Fe3N to 488(5) K for ε-Fe2CoN and 234(3) K for ε-Fe2NiN. Calculations of the formation enthalpies illustrate that the phases ε-Fe2TMN (TM = Co, Ni) are thermodynamically unfavorable at ambient conditions which is consistent with our experimental observations. The substitution of one Fe by Co (Ni) yields one (two) more electrons per formula unit which reduces the magnetic interactions. First-principles analysis indicate that the replacement has a negligible influence on the electron occupation numbers and spin moments of the N and unsubstituted Fe sites, but decreases the local magnetic moments on the substituted Fe positions because the extra electrons occupy the minority-spin channel formed by states of the TM atoms.

Magnetostrictive vibrator utilizing iron–cobalt alloy

In this paper, a novel magnetostrictive vibrator with a unique and integrated design is proposed and developed by using a kind of iron–cobalt alloy (Permendur). Permendur is a giant magnetostrictive material (GMM) with magnetostriction exceeding 70ppm, Young's modulus of 210GPa, high relative permeability and sufficient force for actuation, which shows a good performance as actuator material and has been drawn a lot of attention. The magnetostrictive vibrator has four legs around which the coils are wound. The legs can be pushed (expansion) and pulled (contraction) independently through controlling the input currents of the coils. The actuation principle of the magnetostrictive vibrator is illustrated. The lateral vibrating motion can be generated by using a pair of opposing coils, whereas 2D vibrating motion can be obtained by using two pairs of opposing coils. The finite element analysis (FEA) is adopted to analyze the vibration mode and assist the concrete design of magnetostrictive vibrator. Through some fundamental experiments, the characteristics of the magnetostrictive vibrator are evaluated. For the application, it has been successfully used as a vibrating polisher in the ultra-precision finishing of micro-optic molds.

Synthesis of Nanocrystalline Cobalt-Iron Alloys and Its Characterization

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Electroless synthesis of 3 nm wide alloy nanowires inside Tobacco mosaic virus

We show that 3 nm wide cobalt–iron alloy nanowires can be synthesized by simple wet chemical electroless deposition inside tubular Tobacco mosaic virus particles. The method is based on adsorption of Pd(II) ions, formation of a Pd catalyst, and autocatalytic deposition of the alloy from dissolved metal salts, reduced by a borane compound. Extensive energy-filtering TEM investigations at the nanoscale revealed that the synthesized wires are alloys of Co, Fe, and Ni. We confirmed by high-resolution TEM that our alloy nanowires are at least partially crystalline, which is compatible with typical Co-rich alloys. Ni traces bestow higher stability, presumably against corrosion, as also known from bulk CoFe. Alloy nanowires, as small as the ones presented here, might be used for a variety of applications including high density data storage, imaging, sensing, and even drug delivery.

Electrodeposited Cobalt-Iron Alloy Thin-Film for Potentiometric Hydrogen Phosphate-Ion Sensor

A cobalt-iron alloy thin-film electrode-based electrochemical hydrogen-phosphate-ion sensor was prepared by electrodepositing on an Au-coated Al2O3 substrate from an aqueous solution of metal-salts. The use of a cobalt-iron alloy electrode greatly improved the hydrogen-ion sensor response performance, i.e., the sensor worked stably for more than 7 weeks and showed a quick response time of several seconds. Among the cobalt and iron alloy systems tested, the electrodeposited Co58Fe42 thin-film electrode showed the best EMF response characteristics, i.e., the sensor exhibited a linear potentiometric response to hydrogen-phosphate ion at the concentration range between 1.0 × 10–5 and 1.0 × 10–2 M with the slope of –43 mV/decade at pH 5.0 and at 30℃. A sensing mechanism of the Co-based potentiometric hydrogen-phosphate ion sensor was proposed on the basis of results of instrumental analysis.

Synthesis and Characterization of Co-Fe Nanocrystalline Magnetic Films Electrodeposited From Electrolyte Solution Containing Sodium Saccharin

Cobalt-iron (Co-Fe) alloy thin films ( Co100-x-Fex with x=0 , 6, 11, 14 and 18) were electrodeposited on brass substrates from sulfate plating baths containing saccharin salt. The electrolyte in the synthesis process consists of mixtures of FeSO4.7H2O , CoSO4.6H2O , NaCl and H3BO3 . Various concentrations of FeSO4 were added to the plating solution to deposit films with different alloy compositions. Saccharin (C6H4CONHSO2) was also added as a grain refining agent to improve the quality of deposits. Energy dispersive X-ray spectroscopy (EDS) analyses showed that the compositions of the electrodeposits corresponded to the concentration of FeSO4 in the electrolytic bath. X-ray diffraction (XRD) results showed that the crystallographic structure of the films was dependent on the composition of the alloy. Calculation of crystallite size from X-ray peak broadening showed that the crystallite sizes were within the range of 10-99 nm. Scanning electron microscopy (SEM) results showed that films with higher Fe content exhibited irregular granule shapes. The thicknesses of the thin films were about 50 μm as determined by SEM measurements of the films' cross section. Atomic force microscopy (AFM) results showed rougher granular surfaces for Co-Fe films with higher Fe content. A similar behavior was observed by SEM. Magnetic force microscopy (MFM) showed that the domain pattern was stripe structure for Co and Co94-Fe6 films. The structure changed to granular domain structures with increasing iron content. The best soft magnetic properties with high saturation magnetizations and low coercivities were obtained when BCC and FCC phases of Co-Fe system coexisted.