Amorphous Fe73 Research Articles

Effect of Hydrogen Absorption on the Composition of the Amorphous Alloys Surface Layers

Hydrogen absorption leads to redistribution of the components of the surface layer of the amorphous alloy Fe73.8Si12.7B9.4Nb3.2Cu noncontact side, while the amorphous structure of this layer is preserved. The type of the micro-groups Fey Six changes in such a way that the ratio y: x decreases (to less than 1) and the chemical bond polarity decreases, as well. After degassing, the surface layer composition becomes similar to those before hydrogenation. The loss of the mechanical stability of the amorphous ribbon is accompanied by the formation of the micro-groups Fey Six with a decreased ratio of y: x.

ЕЛЕКТРОКАТАЛІЗ З УЧАСТЮ АМОРФНИХ МЕТАЛЕВИХ ЕЛЕКТРОДІВ

The effect of chemical composition of amorphous metal electrodes with different elemental composition (i.e. Al87.0Y5.0Ni8.0, Fe80.0Si6.0B14.0, Fe78,5Ni1.0Mo0.5Si6.0B14.0, Fe81,0Ni1.0Nb0.5Mo0.5Si3.0B14.0, Fe73,1Cu1.0Nb3.0Si15.5B7.4) on their electrocatalytic activity in the reactions of the decomposition of peroxide –O–O– bonds in hydrogen peroxide H2O2 and organic oligoperoxide compounds based on vinyl acetate, 2-tert-butyl peroxy-2-methyl-5-hexen-3-yne and maleic anhydride was studied. The electrochemical reduction of H2O2 and organic oligoperoxsde on AMA-electrodes by cyclic voltammetry is investigated. The dependencies of the rate of electrocatalytic processes on the concentration of supporting electrolyte, the rate of scanning of potential, the concentration of depolarizer and the duration of the initial spontaneous (in the absence of external potential) interaction of the peroxides compounds with the electrode surface were investigated. The rate constants of the decomposition of –O–O– bonds in peroxides of different structure were determined. In the case of the electrocatalytic AMA electrode Al87.0Y5.0Ni8.0, the process of dissociation of –O–O– bonding by the reductive mechanism is the most probable: In the case of AMA electrodes based on Fe (especially Fe73,1Cu1.0Nb3.0Si15.5B7.4) the decomposition of –O–O– bonds follows preferential oxidation mechanism: . Due to their high absorption ability, oligoperoxide molecules can undergo conformational changes on the surface of the electrode. This affects the stability of the peroxide bond significantly. The functional groups of oligoperxides show affinity to localized electrons on the electrode surface. This leads to the elongation of the –O–O– bond and facilitates the fragmentation of the oligomers. The amorphous alloys Fe73,1Cu1.0Nb3.0Si15.5B7.4 and Fe81,0Ni1.0Nb0.5Mo0.5Si3.0B14.0 have a higher catalytical activity in decomposition of H2O2.

Effect of Co Content on Structural Stability and Soft Magnetic Properties for (Fe1 – xCox)86Hf7B6Cu1 Amorphous Alloy

Amorphous (Fe1–xCox)86Hf7B6Cu1 ribbons were prepared by using the single-roller melt-spinning technique. The microstructure, crystallization activation energy, soft magnetic properties and structural defects of the samples have been investigated by XRD, TEM, DTA, VSM and positron annihilation lifetime spectra. The results show that the as-quenched alloy ribbons are structurally amorphous. The positron annihilation technique results show that for the (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloy, the annihilation lifetime τ1 is 149.0 ps in the monovacancy-like free volume. The annihilation lifetime τ2 is 344.5 ps in the microvoid. The values of τ1 and τ2 of (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloy are the Minimum in all of the samples, which indicates that the volumes of the monovacancy-like free volume and the microvoid in this alloy is the smallest. Combined with DTA results, the structural stability of (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) is the best. The VSM results show that (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloys display more excellent soft magnetic property.

Simulation of crystal growth in multicomponent metastable alloys

A method for predicting the regularities of crystal growth from metastable melts has been developed. The process of crystal growth from a multicomponent melt is described by the methods of nonequilibrium thermodynamics, taking into account the mutual influence of thermal and diffusion processes. The application of a new variational approach to the constructed system of equations made it possible to obtain expressions of the crystal growth rate from a multicomponent melt convenient for practical calculations. The obtained technique allowed us to analyze the features of crystal growth at high rate of crystallization front, which leads to “impurity capture” effect – deviation from equilibrium conditions at the phase interface. The developed mathematical model makes it possible to calculate the growth rate of new phase particles and to estimate the effect of metastable effects on deviation of the components’ concentration at surface of the growing crystal from equilibrium values. Thus, using the obtained method, a “metastable” phase diagram of the system under study can be constructed. The developed approach is applied to the calculation of growth of α-Fe(Si) nanocrystals during annealing of amorphous alloy Fe73,5 Cu1 Nb3 Si13,5B9. The calculation results were compared with the results of the experiment on the alloy primary crystallization. It is shown that the concentration of Fe at the surface of the growing crystal does not significantly deviate from the equilibrium values. On the other hand, silicon atoms are captured by the crystallization front, silicon concentration at the surface of the growing nanocrystal deviates significantly from equilibrium values. The calculation has shown that after the initial crystallization of the amorphous phase, occurring at a temperature of 400 – 450 °C, the deviation of silicon concentration from equilibrium value is about 2 %, while this equilibrium value is about 13.3 %.

Features of the Use of Equilibrium State Diagrams for Description of Crystal Growth from Metastable Melts

The crystallization of metastable metal alloys is characterized by a high rate of the crystallization front, which leads to the effect of "impurity capture" and deviation from the local equilibrium near the surface of the growing crystal. To calculate the growth rate of the crystalline nuclei, a method was developed for prediction of deviation of the components’ concentration near the crystal surface from the equilibrium values. A crystal nucleus was considered to be growing from the initial multicomponent phase, due to interphase transition of the components through its surface. It became possible to distinguish the equilibrium and non-equilibrium effect of the nucleus growth rate by decomposing the molar rate of the product formation near equilibrium, as a function of the molar concentration of the components in the Taylor series and limiting with the linear members. The practical calculations were carried out for the crystallization of the amorphous alloy Fe73,5Cu1Nb3Si13,5B9 of the FINEMET type. The local deviations were investigated for the silicon concentration from the equilibrium values at the surface of the growing crystal.

Measurement of the Stiffness of Spin Waves in Amorphous Ferromagnetic Microwires by the Small-Angle Neutron Scattering Method

The spin-wave stiffness of a ferromagnetic microwire in the form of an amorphous Fe77.5Si5.5B15 strand with a diameter of 10 μm in a glass shell has been measured by the method of small-angle scattering of polarized neutrons. According to the quadratic dispersion relation for the ferromagnet, neutron scattering by spin waves is concentrated inside a cone with a cutoff angle θC. The cutoff angle θC has been determined by comparing the antisymmetric contribution to the intensity of scattering of polarized neutrons and a model function for a magnetic field H varied from 3.40 to 41 mT. The cutoff angle θC decreases according to the formula $$\theta _C^2(H) = \theta _C^2 - \left( {g{\mu _B}H + \Delta } \right){\theta _0}/{E_i},\,\;\;{\rm{where}}\,\,{\theta _0} = \,{\hbar^2}/(2A{m_n})$$. The stiffness of spin waves and the energy gap in the spectrum of spin waves in the Fe77.5Si5.5B15 ferromagnetic microwire at room temperature determined from the field dependence are meV $$\theta _C^2(H)$$ are A =82(3) meV A2 and Δ=0.048(2) meV, respectively. It has been shown that this method for the measurement of the stiffness of spin waves can be successfully used in compact (with low and moderate fluxes) pulsed neutron sources based on accelerators.

Simulation of Crystal Growth in Multicomponent Metastable Alloys

A technique is developed for predicting the patterns of crystal growth from metastable melts. Using nonequilibrium thermodynamics methods, a crystal growth process from a multicomponent melt is described, which considers the interaction between thermal and diffusion processes. The application of a new variation approach to the constructed equation system has made it possible to obtain expressions for the crystal growth rate from a multicomponent melt, which is convenient for practical calculations. The developed technique has made it possible to analyze the crystal growth features at a high motion speed of the crystallization front, which leads to an “impurity capture” effect, i.e., the deviation from the equilibrium conditions at the interface. The developed mathematical model makes it possible to: calculate the growth rate of new phase particles, as well as evaluate the influence of metastable effects upon the deviation of component concentrations near the growing crystal’s surface from equilibrium values. Thus, with the use of the developed method, a “metastable” phase diagram of the system under study can be constructed. The approach under development has been applied to the calculation of the α-Fe(Si) nanocrystal growth in the course of the annealing of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy. The calculation results are compared with the experiment results on the alloy’s primary crystallization. It has been shown that the iron concentration at the growing crystal’s surface insignificantly deviates from the equilibrium values. On the other hand, silicon atoms are captured by the crystallization front; the silicon concentration at the growing nanocrystal’s surface significantly deviates from the equilibrium values. After the primary crystallization of the amorphous phase occurring in the temperature range from 400 to 450°C, calculations show that the silicon concentration’s deviation from the equilibrium value should be about 2%, whereas the equilibrium concentration value amounts to about 13.3%.

Adsorption-enhanced reductive degradation of methyl orange by Fe73.3Co10Si4B8P4Cu0.7 amorphous alloys

Cobalt alloying for Fe83.3Si4B8P4Cu0.7 amorphous alloy can enhance the decolorization performances of azo dye wastewater. Co substitutions in amorphous Fe83.3-xCoxSi4B8P4Cu0.7 (x = 0, 10, 20 and 40 at.%) alloys play a positive role in improving the decolarization efficiencies of methyl orange azo dyes (MO). Amorphous Fe73.3Co10Si4B8P4Cu0.7 alloy has better abilities to break –N=N– bonds of MO than Fe83.3Si4B8P4Cu0.7, Fe63.3Co20Si4B8P4Cu0.7 and Fe43.3Co40Si4B8P4Cu0.7 alloys, and is able to degrade MO to mainly form sulfanilic acid anions with trace amounts of intermediate products with higher complete degrees. The rate determining step of MO degradation is the surface adsorption on amorphous Fe43.3Co40Si4B8P4Cu0.7 alloy, and the intermediate degradation products with –N=N– bonds are dominantly formed with small amount of sulfanilic acid anions. The highest surface-area normalized rate constant (kSA) of MO degraded by Fe73.3Co10Si4B8P4Cu0.7 ribbons is confirmed to be 0.69, 3 times higher than that of zero-valent Fe powders and Fe83.3Si4B8P4Cu0.7 ribbons. The degradation pathways of MO by amorphous Fe73.3Co10Si4B8P4Cu0.7 alloy different from those by Fe83.3Si4B8P4Cu0.7 and Fe43.3Co40Si4B8P4Cu0.7 alloys have been clarified on basis of the UV–Vis and HPLC-MS data. The experimental results manifest that the degradation performances are enhanced by Co substitutions due to the sharp decrease of reaction activation energies and the improvements of adsorption performances. The mechanism changes from reduction degradation to adsorption-determined degradation modes with increases of Co concentrations. MO degradations on amorphous Fe73.3Co10Si4B8P4Cu0.7 alloy are governed by adsorption-enhanced reductive degradation mechanism.

Effect of the partial substitution of FeCo by Ge on the magnetic properties of nanocrystalline (Fe0.8Co0.2)72.7Al0.8Si17.5Nb3Cu1B5 alloy

Nanocrystalline soft magnetic ribbons, with a composition of (Fe0.8Co0.2)72.7-xAl0.8Si17.5Nb3Cu1B5Gex (x = 0, 0.5, 1), were synthesized by melt spinning and subsequent crystallization. Special attention was focused on the microstructure, crystallization process and initial permeability. The crystallization process and microstructure were examined by using differential scanning calorimetry and X-ray diffractometry, respectively. The temperature dependence of initial permeability was presented in combination with the effect of the Ge substitutions. As a result, the Curie temperature of amorphous (Fe0.8Co0.2)72.7Al0.8Si17.5Nb3Cu1B5 alloy was enhanced by Ge addition, which implied improved soft magnetic properties at elevated temperatures. The (Fe0.8Co0.2)71.7Al0.8Si17.5Nb3Cu1B5Ge1 alloy annealed at 640 °C for 0.5 h exhibited superior magnetic softness at room- and high-temperatures with respect to the Ge-free alloy.

Non-isothermal Primary Crystallization Kinetics of the Amorphous Fe85.3B11P3Cu0.7 Alloy

In the present research, the primary crystallization kinetics of the amorphous Fe85.3B11P3Cu0.7 alloy was analyzed using non-isothermal DSC measurements. The average and local activation energies, Ea, were determined by different isokinetic and isoconversional methods. The results obtained for activation energy in this research, show that due to the complexity of the primary crystallization process in this alloy, isoconversional methods are more suitable than the isokinetic ones. The Avrami exponents lie between about 1 and 2 in a wide temperature range of 370˂T≤410˚C. This indicates that one dimensional growth of nuclei with a decreasing rate of nucleation is the main mechanism during non-isothermal primary crystallization process of the amorphous Fe85.3B11P3Cu0.7 alloy which is a new finding for this alloy. Study of magnetic properties in the amorphous and nanocrystalline states revealed that annealing the amorphous ribbons at 440˚C for 10 minutes gives rise to a significant increase in saturation magnetization, Ms, i.e. from 144 in as-spun to 201 emu/g in annealed states. This amount of Ms makes this material a good candidate for different applications, especially in transformer cores.

Field and Current Controlled Domain Wall Propagation in Twisted Glass-Coated Magnetic Microwires

The torsion effect on the field and current driven magnetization reversal and the associated domain wall velocity in cylindrical amorphous and nanocrystalline glass-coated microwires is reported. Samples from three representative compositions have been investigated: (1) amorphous Fe77.5Si7.5B15 with positive magnetostriction, λ ≅ 25 × 10−6, (2) amorphous Co68.18Fe4.32Si12.5B15 with nearly zero negative magnetostriction, λ ≅ −1 × 10−7, and (3) nanocrystalline Fe73.5Si13.5B9Cu1Nb3 (FINEMET) with small positive magnetostriction, λ ≅ 2.1 × 10−6, all having the diameter of the metallic nucleus, d, of 20 µm and the glass coating thickness, tg, of 11 µm. The results are explained through a phenomenological interpretation of the effects of applied torque on the anisotropy axes within the microwires with different characteristics. Among all the complex mechanical deformations caused by the application of torque on magnetic microwire samples, the most important are the axial compression – for axial field-driven domain wall motion, and the circumferential tension – for electrical current/circumferential field-driven domain wall motion. The Co68.18Fe4.32Si12.5B15 microwire, annealed at 300 °C for 1 hour and twisted at 168 Rad/m exhibits the optimum characteristics, e.g. the lowest switching current (down to 9 mA~2.9 × 10−3 A/cm2) and the largest domain wall velocity (up to 2300 m/s).

Shifting from Ising model to Heisenberg model critical behavior and the departure from these models in Fe73.5−Cr Cu1Nb3Si13.5B9

Abstract The universality classes of amorphous alloy system Fe73.5−xCrxCu1Nb3Si13.5B9 with x = 0, 2, 4, 6, 8, and 10 are studied by determination of the static critical exponents (β, γ, δ), and critical temperatures from magnetization measurements using two independent methods, namely the Kouvel-Fisher method and the Berger-Campillo et al method. The found values for these critical exponents depend on the content of Cr and interestingly vary from values that correspond to universality classes of standard models (Ising (sample with x = 0), XY (sample with x = 2), and Heisenberg (sample with x = 4)) with short-range interactions to universality class of mean field model (samples with x = 6, 8, and 10) with long-range interactions. The critical temperature decreases quasi linearly with the increase of Cr content. The possible mechanisms leading to such universality classes and shift including the spin-orbit interaction, shape anisotropies, direct exchange and itinerant exchange are analyzed. In addition, X-ray diffraction and Mossbauer spectroscopy studies performed on this alloy system reveal that it has a heterogeneous structure.

Effect of glass-removal on the magnetostriction and magnetic switching properties in amorphous FeSiB microwires

Abstract Results on the influence of glass-removal on the magnetostriction, magnetic switching properties and domain wall propagation in amorphous Fe77.5Si17.5B15 microwires are reported. Glass removal releases high thermoelastic stresses originated by the difference in thermal expansion coefficients of glass and metal, which reduces the coercivity, increases the domain wall mobility and decreases the local nucleation fields and their distributions. Evening the distribution of nucleation fields and eliminating the local surface defects due to glass removal increase the field range of single domain wall propagation regime. It was also found that the saturation magnetostriction coefficient significantly decreases after glass removal, which strengthens the impact of the reduced magnetoelastic anisotropy. The effect of glass removal on magnetostriction was previously observed only in Co-rich microwires with small negative magnetostriction. Understanding the factors that control the magnetic switching and domain wall dynamics is of interest for practical applications in sensing, storage and logic devices.

The Microstructural Changes due to the Heating Treatment of Magnetic Amorphous Fe81(PtRh)5Zr7Nb1Cu1B5 Alloy

The Microstructural Changes due to the Heating Treatment of Magnetic Amorphous Fe₈₁(PtRh)₅Zr₇Nb₁Cu₁B₅ Alloy

Modifying the transition temperature, 120\u2009K\u2009\u2264\u2009Tc\u2009\u2264\u20091150\u2009K, of amorphous Fe90\u2212xCoxSc10 with simultaneous alteration of fluctuation of exchange integral up to zero

Amorphous (a-) Fe90−xCoxSc10 alloys have been produced by rapid quenching from the melt. The Curie temperature, TC, was determined using both mean field theory and Landau’s theory of second-order phase transitions in zero and non-zero external fields. The dependence of TC on the atomic spacing can be explained by the empirical Bethe-Slater curve. The value of TC of a- Fe5Co85Sc10, determined by the above theoretical approaches is 1150 K, which is the highest TC ever measured for amorphous alloys. The flattening of the measured normalized magnetization, M(T)/M(0), as a function of the reduced temperature, T/TC, is explained within the framework of the Handrich- Kobe model. According to this model the fluctuation of the exchange integral is the main reason for the flattening of M(T)/M(0). In the case of a-Fe90Sc10 without Co, however, the fluctuation of the exchange integral is dominant only at zero external field, Bex = 0. At Bex = 9 T, however, the fluctuation of the exchange integral has no conspicuous effect on the reduction of the magnetization. It is shown that at Bex = 9 T the frozen magnetic clusters control the behaviour of the reduced magnetization as function of T/TC. In contrast to other ferromagnetic alloys, where the flattening of M(T)/M(0) is characteristic for an amorphous structure, the a- Fe5Co85Sc10 does not exhibit any trace of the fluctuation of the exchange integral.

Mechanism of Transformation of Ferrocene into Carbon-Encapsulated Iron Carbide Nanoparticles at High Pressures and Temperatures.

A mechanism was established for the formation of nanosized iron carbide particles encapsulated in carbon shells via the processes of ferrocene thermal conversions at high pressures. At a pressure of 8.0 GPa, products of ferrocene decomposition were studied as a function of temperature by X-ray diffraction, Raman and Mössbauer spectroscopy, scanning and transmission electron microscopy. It was shown that the mechanism of formation of the carbon-encapsulated iron carbide nanoparticles at high pressures and temperatures differs qualitatively from the known mechanism of their formation in the gas-phase processes of laser pyrolysis or photolysis of ferrocene. At high pressures and temperatures, the formation of iron carbide nanoparticles occurs not due to the primary growth of pure iron particles and the subsequent dissolution of carbon in iron. Nanoparticles are formed due to the direct fusion of iron-carbon clusters, which are formed at intermediate stages of ferrocene thermal destruction. Then, obtained amorphous iron carbides Fe1- xC x with a high carbon content start to crystallize. Two crystalline carbon-encapsulated forms of iron carbide (Fe7C3 and Fe3C) are the main products of crystallization of the amorphous Fe1- xC x depending on the temperature of the ferrocene treatment.

Improving the soft magnetic properties of the Fe73.5Si13.5B9Nb3Cu1 nanostructured ribbons by annealing in the hydrogen atmosphere

The nanocrystallization stage was performed in a reductive hydrogen atmosphere to prevent surface oxidation and improve the soft magnetic properties of the amorphous, Fe73.5Si13.5B9Nb3Cu1 alloy through annealing. Both the amorphous and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 ribbons were characterized by differential scanning calorimetry, transmission electron microscopy, X-ray diffraction, alternative gradient field magnetometry, and AC susceptometry techniques. To reduce the processing cost, commercially available industrial gas sources were used at the atmospheric pressure, instead of high purity inert gas or high vacuum ambient. The surface oxidation completely stopped after using a 70% Ar–30% H2 mixture of such gases, also the period of the nanocrystallization stage decreased. Moreover, it was observed that the soft magnetic parameters of the nanocrystalline samples depend on the annealing time. Both the in-plane permeability and coercive field of the ribbons improved through nanocrystallization and the optimum annealing time was determined.

Structure modification and recovery of amorphous Fe73.5Si13.5B9Nb3Cu1 magnetic ribbons after autoclave treatment: SAXS and thermodynamic analysis

The structure, crystallization kinetics and magnetic property of as-quenched Fe73.5Si13.5B9Nb3Cu1 amorphous ribbon (R0) as well as ribbons after autoclave treatment at 100 °C and 150 °C (R1 and R2) have been systematically studied by various techniques. With increasing autoclave treatment temperature, the measured structural, kinetic and magnetic parameters of samples increase firstly, i.e. R0 < R1; and then decrease or recover to the as-quenched sample, i.e. R2 < R1 or R2 ≈ R0. These results indicate that the SROs in R1 samples increased by transforming from fcc to bcc structure during the autoclave treatment and that the autoclave treatment can decrease the large radius (rM) MRO (medium range order), but increase the small rM MRO. The measured structural, thermal and magnetic parameters of R2 sample have a tendency to recover toward as-quenched R0 sample. The thermal and magnetic parameters of samples after solely annealing treatment at higher temperature have no obvious recover phenomenon. The uneven actions of pressure and temperature in autoclave treatment may be helpful for us to search a new method to improve the magnetic properties of Fe-based glasses.

Modeling of stress relaxation kinetics of amorphous Fe0.7Nb0.1Zr0.1Ti0.1 alloy powder: A novel approach based on differential thermal analysis

In this study, the stress relaxation of amorphous Fe0.7Nb0.1Ti0.1Zr0.1 alloy was investigated by differential thermal analysis (DTA) to enhance the soft magnetic properties. Amorphous Fe0.7Nb0.1Zr0.1T0.1 alloy was produced by mechanical alloying technique using the mixture of pure elements and without adding metalloids. It was found that the stress relaxation process follows the Johnson-Mehl-Avrami model and the mechanism was volume diffusion control with three dimensional growth of the nuclei. The relation of stress relaxation progress (α), with time was proposed as: dαdt=βdαdT=3.04exp−4312RT1−α−ln1−α0.37. The final achieved microstructure leads to higher saturation magnetization and lower coercivity that are favorable for soft magnetic applications.

Improvement of soft magnetic properties of Fe0.7Nb0.1Zr0.1Ti0.1 amorphous alloy: A kinetic study approach

In this paper, the crystallization kinetic of amorphous Fe0.7Nb0.1Zr0.1Ti0.1 was studied by differential thermal analysis to produce an appropriate amorphous/nanocrystalline microstructure for improving the soft magnetic properties. Amorphous Fe0.7Nb0.1Zr0.1Ti0.1 alloy without metalloids was prepared by mechanical alloying of pure elements. The results showed that Johnson-Mehl-Avrami model was able to explain the crystallization kinetic of products as: dαdt=βdαdT=4.86×109exp−186776RT1−α−ln1−α0.24. Moreover, volume diffusion control with three dimensional growth of the nuclei was the predominant mechanism of crystallization. The simulation results confirmed that by employment of kinetic model, it was possible to control the microstructure as combination of amorphous/crystalline phases and enhance the saturation magnetization from 59 to 142 A·m2/kg and reduce the coercivity from 2.05 to 0.14 kA/m by controlling of crystallization progress at specific predefined α value.