Preparation and high-frequency soft magnetic property of FeCo-based thin films

A series of FeCo-based thin films were prepared by magnetron sputtering without applying an induced magnetic field.The microstructure,electrical properties,magnetic properties and thermal stability of FeCo,FeCoSiN monolayer thin film and[FeCoSiN/SiN_x]_n multilayer thin film were investigated systematically.When FeCo thin film was doped with Si and N,the resistivity and soft magnetic properties of the obtained FeCoSiN thin film can be improved effectively.The coercivity(H_c),resistivity(ρ) and ferromagnetic resonance frequency(f_r) can be further optimized for the[FeCoSiN/SiN_x]_n multilayer thin film.When the thickness of FeCoSiN layer and SiN_x layer is maintained at 7 and 2 nm,the H_c,p and f_r for[FeCoSiN/SiN_x]_n multilayer thin film are 225 A·m~(-1)392 μΩ·cm~(-1) and 4.29 GHz,respectively.In addition,the low coercivity of easy axis(H_(ce) ≈ 506 A·m~(-1)) of[FeCoSiN/SiN_x]_n multilayer thin film can be maintained after annealing at 300 ℃ in air for 2 h.     

Deformation mechanisms in Cr20Ni80 alloy at elevated temperatures

The mechanisms of plastic deformation of Cr20Ni80 nichrome with an initial grain size of 80 μm were studied in the temperature range 600–950°C and the strain-rate range 1.5 × 10^?6?5 × 10^?2s^?1. Nichrome is shown to exhibit anomalously high values of stress exponent n and a high deformation activation energy Q. These unusual properties were found to be caused by “threshold” stresses below which deformation does not occur. An analysis of the deformation behavior with allowance for threshold stresses reveals the regions of hot, warm, and cold deformation in nichrome. At normalized strain rates \(\dot \varepsilon \) kT/D _{1 Gb} < 10^?8, the true values of n and Q are ～4 and 285 ± 30 kJ/mol, respectively. In the normalized-strain range 10^?8?10^?4 n ～ 6 and the deformation activation energy decreases to 175 ± 30 kJ/mol. This change in the deformation-behavior characteristics is explained by the transition from high-temperature dislocation climb, which is controlled by lattice self-diffusion, to low-temperature dislocation climb, which is controlled by pipe diffusion, as the temperature decreases. At \(\dot \varepsilon \) kT/D _{1 Gb} = 10^?4, a power law break-down takes place and an exponential law (which describes the deformation behavior in the range of cold deformation) becomes operative.     

Creep correlations of metals at elevated temperatures

Creep data for pure metals at temperatures above those at which rapid recovery occurs (above about 0.45 the melting temperature) are correctable by means of the equations ? = f (te^?ΔH/RT, σ) and σ = f (?&#x0307 _s e^ΔH/RT). These correlations were applied successfully to data for aluminum, iron, nickel, copper, zinc, platinum, gold, and lead as well as for simple alloys. For a given metal, ΔH is a constant about equal to the activation energy for self-diffusion.     

Adsorption of hexane and benzene on fluorinated silicas: The effect of the perfluoralkyl chain length

By means of the gas chromatography and a static adsorption method, the extent of fluorination of the carrier surface, determined by the length of the grafted radical chain, affects the adsorption properties of silicas with perfluorohexyl, perfluoropropyl, and trifluoromethyl coatings. The analysis of data on the original carrier and chemically hydrophobized silicas, including a sample with grafted octyl groups used as the reference, shows that modification leads to the decrease in both the adsorption (a at 298 K and the Henry constants (K _H ) in a wide temperature range for hexane and benzene. However, in contrast to silicas with perfluoropropyl or perfluorohexyl coatings, the a and K _H values on trifluorometylsilica became equal (n-alkanes) or even somewhat lower (aromatic hydrocarbons) than those observed on the non-polar octylsilica surface. Irrespective of the degree of fluorination of the silica surface, the substitution and screening of silanol groups in silica lead to weakening the polarity of polyfluoroalkylsilicas as compared with the original carrier.     

Description of methane adsorption on microporous carbon adsorbents on the range of supercritical temperatures on the basis of the Dubinin–Astakhov equation

Temperature dependences of parameters n and E are calculated according to the adsorption equation of Dubinin–Astakhov for methane adsorption on eight active carbons in the range of supercritical temperatures of 170–340 K and pressures of 0–20 MPa. At temperatures above ~240 K, characteristic adsorption energy E of methane grows linearly at an increase in temperature. The temperature coefficients of characteristic energy of methane adsorption on active carbon tend to decrease at an increase in standard characteristic adsorption energy E₀. The average value of parameter <n> for the studied adsorbents tends to grow at an increase in standard characteristic adsorption energy E₀.     

Microwave Power Absorption in Materials for Ferrous Metallurgy

The characteristics of microwave power absorption in materials for ferrous metallurgy, including iron oxides (Fe₂O₃, Fe₃O₄ and Fe₀.₉₂₅O) and bitumite, were explored by evaluating their dielectric loss (Q _E) and/or magnetic loss (Q _H) distributions in the 0.05-m-thick slabs of the corresponding materials exposed to 1.2-kW and 2.45-GHz microwave radiation at temperatures below 1100°C. It is revealed that the dielectric loss contributes primarily to the power absorption in Fe₂O₃, Fe_0.925O and the bitumite at all of the examined temperatures. Their Q _E values at room temperature and slab surface are 9.1311 × 10³ W m^?3, 23.7025 × 10³ W m^?3, and 49.5999 × 10³ W m^?3, respectively, showing that the materials have the following heating rate initially under microwave irradiation: bitumite > Fe_0.925O > Fe₂O₃. Compared with the other materials, Fe₃O₄ has much stronger power absorption, primarily originated from its magnetic loss (e.g., Q _H = 1.0615 × 10⁶ W m^?3, Q _H/Q _E = 2.4185 at 24°C and slab surface), below its Curie point, above which the magnetic susceptibility approaches to zero, thereby causing a very small Q _H value at even the surface (Q _H = 1.0416 × 10⁵ W m^?3 at 880°C). It is also demonstrated that inhomogeneous power distributions occur in all the slabs and become more pronounced with increasing temperature mainly due to rapid increase in permittivity. Characterizing power absorption in the oxides and the coal is expected to offer a strategic guide for improving use of microwave energy in ferrous metallurgy.     

Inverse magnetocaloric effect in the uniaxial paramagnet with non-Kramers ions

It has been shown that, in a uniaxial paramagnet with non-Kramers ions with a spin of S = 1 and single-ion anisotropy of the easy-plane type (DS _Z ² ), there is a low-field (μ₀ H ≤ D) and low-temperature (k _B T < 0.68D) region in which the isothermal magnetization along the hard direction H||OZ increases the magnetic entropy by ΔS _M (T, ΔH = H _f - H _i > 0) > 0 and the adiabatic magnetization along the same direction reduces the sample temperature by ΔT _ad(T, ΔH > 0) < 0 (inverse magnetocaloric effect (MCE)). The main features of the inverse MCE in uniaxial paramagnets with large spins (S = 2, 3, …) of the non-Kramers ions have been discussed.     

The influence of methylcellulose (MC) on solubility of calcium hydroxyapatite (HA) crystals in HA/MC nanocomposites

The influence of methylcellulose ([C₆H₇O₂(OH)_3–x(OCH₃)_x]_n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)₂–H₃PO₄–[C₆H₇O₂(OH)_3–x(OCH₃)_x]_n–H₂O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca²⁺ and PO₄^3- ions).     

Specific features of magnetic order in a multiferroic compound CuCrO<Subscript>2</Subscript> determined using NMR and NQR data for <Superscript>63, 65</Superscript>Cu nuclei

Results of studying the paramagnetic and ordered phases of a CuCrO₂ single crystal using nuclear magnetic and nuclear quadrupole resonances on ^63,65Cu nuclei are presented. The measurements have been carried out in wide ranges of temperature (T = 4.2–300 K) and magnetic-field strength (Н = 0–94 kOe), with the magnetic fields being directed along a and c axes of the crystal. The components of the electric-field gradient tensor and the magnetic-shift tensor (K _a,c) have been determined. The temperature dependences K _a(H || a) and K _c(H || c) for the paramagnetic phase are described by the Curie–Weiss law and reproduce the behavior of the magnetic susceptibility (χ_a,c). The hyperfine field on a copper nucleus has been determined, which is equal to h _hf ^a,c = 33 kOe/μB. Below the temperature Т _N = 23.6 K, nuclear magnetic resonance and nuclear quadrupole resonance spectra for ^63,65Cu nuclei have been recorded typical of helical magnetic structures, which are incommensurable with the lattice period.     

The effect of the precipitation conditions on the morphology and the sorption properties of CuS particles

The effect of the nature of the copper salt precursor anion and the pH of a solution on the morphology and the phase composition of CuS particles has been studied upon precipitation from thiourea solutions. It has been established that, irrespective of the precipitation conditions, generation of the CuS phase and the chalcanthite impurity phase CuSO₄ ? 5H₂O is recorded according to the X-ray diffraction analysis data. At pH 8 and a c((NH₂)₂CS): c(Cu²⁺) ratio of 1: 1, from nitrate solutions a fine powder is formed that consists of spherical particles smaller than 100 nm in size. An increase in the c((NH₂)₂CS): c(Cu²⁺) ratio and in the precipitation pH results in coarser particles of up to 1.5 μm in size. The replacement of the salt precursor anion by SO₄^2- facilitates the decrease in the spherical particle size to 1 μm and that by Cl^– to 0.7 μm. The synthesis conditions of the CuS sorbent that control the latter’s morphological properties have an effect on the sorption of cadmium from aqueous solutions.     

Superconducting cellular MgB<Subscript>2</Subscript>

A new composite superconducting material in the form of a cellular structure consisting of large Mg grains surrounded by thin MgB₂ layers has been prepared. The superconducting properties of such a cellular structure were found to depend on the thickness of the superconducting layer d _s. As d _s decreases from ～30 to 1 μm, the critical temperature decreases by more than 10 K. The derivative of the upper critical field with respect to the temperature (dH _c2/dT) near T _c increases from ～0.2 T/K at high d _s to ～0.35 T/K at d _s ～6 μm. The critical current density of the cellular samples calculated for the area of the superconductor section is above 10⁵ A/cm² (T = 4.2 K and H = 1 T).     

Determination of Johnson–Cook Plasticity Model Parameters for Inconel718

In order to simulate foreign object damage (FOD) phenomenon in aircraft high-pressure compressor blades made of a nickel-based super-alloy, Johnson–Cook (J–C) plasticity model was used. For prediction of material’s plastic behavior at temperature of 400 °C (working temperature of the blades) in the range of strain rates associated with the FOD phenomenon (in order of 10⁶ s^?1), material parameters of A, B, C, n and m for the J–C plasticity model had to be determined experimentally. Parameters of A, B and n with values of 1108, 699 MPa and 0.5189, respectively, were obtained from quasi-static tensile tests. Moreover, m was determined to be 1.2861, also through quasi-static tensile tests with a strain rate of 1 s^?1 at three temperatures of 475, 550 and 625 °C. However, in order to determine C, firstly a steel ball was impacted on the surface of a flat specimen made of a precipitation-hardening alloy, and then, the impact site was 3D scanned to obtain the induced crater profile. Finally, the impact test (ballistic) was simulated using Abaqus, and a C value of 0.0085 was determined by comparing the actual crater profile with the one obtained from the simulation through a trial-and-error approach.     

Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10^?2, 10^?2, 5 × 10^?4 and 10^?4 s^?1. The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg₁₇Al₁₂ particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.     

Equilibrium adsorption of stilbenoids at metal oxides

The isotherms of adsorption of trans-hydroxystilbenes (stilbenoids) and hydroxybenzenes (phenols) from n-hexane-ethyl acetate (1: 1) at nanodispersed aerogels of aluminum and titanium oxides were measured under static conditions. The adsorption isotherms can be approximated well by the Freundlich equation for the model of localized adsorption at energetically heterogeneous solids. It was found that the adsorption value of both stilbenoids and phenols is improved with an increase in the number of OH groups in their molecules, being sensitive to the chemistry of the adsorbent surface. trans-Hydroxystilbenes adsorb at TiO₂ better than do the corresponding phenols. The opposite pattern was observed for Al₂ O₃. The adsorption of trans-hydroxystilbenes at TiO₂ is irreversible and accompanied by the formation of colored surface compounds.     

Investigation of the Corrosion Inhibition of CTAB and SDS on Carbon Steel Using an Experimental Design Strategy

The corrosion inhibition performance of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) on carbon steel was investigated in sodium chloride solutions. Using an experimental design strategy pH, chloride concentration, SDS/CTAB concentrations, and temperature were optimized by conducting only 30 experiments. The optimum value of each factor was obtained from the designed matrix of the experiments based on the lowest log I _corr value calculated for each experimental condition. The 3D surface plots of the electrochemical response (log I _corr) against each factor were constructed. The optimum conditions in which the lowest log I _corr can be achieved were found as follows: pH 12, [Cl^?] ≈ 1 M, [SDS] ≈ 200 ppm, [CTAB] ≈ 20 ppm, and T ≈ 10 °C.     

Experimental Investigation of Newly Synthesized Gemini Cationic Surfactants as Corrosion Inhibitors of Mild Steel in 1.0 M HCl

Three Gemini cationic surfactants named N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-octanamidopropyl) propane-1,3-diaminium bromide (C8-S3-C8), N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-dodecanamidopropyl) propane-1,3-diaminium bromide (C12-S3-C12) and N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-hexadecanamidopropyl) propane-1,3-diaminium bromide (C16-S3-C16) were evaluated as corrosion inhibitors for mild steel in 1.0 M HCl. The corrosion rate of mild steel in 1.0 M HCl at three different temperatures 25, 45 and 60oC was investigated gravimetrically. The corrosion rate of mild steel was confirmed electrically at 25oC. The corrosion inhibition efficiency directly proportionally with the hydrophobic chain length of inhibitors. The inhibition efficiency exhibit a positive trend with raising the solution temperatures. The potentiostatic polarization study revealed that the tested gemini cationic surfactants act as mixed type inhibitors with predominant control of cathodic reaction. The Villamil isotherm provide the best describing of the adsorption process on the selected steel in 1.0 M HCl. The adsorption of the tested inhibitors on the steel surface is a mixture of chemical and physical adsorption.     

Adsorption properties of aluminum oxide modified with Co and CoO particles

Adsorption properties of γ-Al₂O₃ modified with Co (5 and 10 wt %) and Co (5 wt %) species are investigated by dynamic adsorption. N-hexane, n-heptane, n-octane, benzene, toluene, ethylbenzene, chloroform, and diethyl ether were used as test adsorbates. Adsorption isotherms were measured, and isosteric adsorption heats were calculated for the indicated sorbates. It was shown that the adsorption isotherms of all the adsorbates and at all the temperatures of measurements on γ-Al₂O₃ modified with Co (5 wt %) and CoO (5 wt %) nanoparticles located above that recorded for the initial γ-Al₂O₃ sample. It was established that the surface of modified γ-Al₂O₃ possessed mainly electron-accepting properties. The 5% Со/γ-Al₂O₃ and 5% СоO/γ-Al₂O₃ nanocomposites exhibited the greatest adsorption capacity relative to aromatic hydrocarbons.     

Magnetic and structural properties of rapidly quenched Nd-Fe-Co-Ge-B alloys

We have studied the magneto-resistive effect in bulk Y_3/4Lu_1/4Ba₂Cu₃O₇ + CuO composites prepared by the fast-sintering technique. It has been found that the composites exhibit large magnetoresistance in low magnetic fields (<100 Oe) in a broad temperature range (tens of kelvins below the critical temperature T _c). The HTSC-based composites exhibit a much higher sensitivity to weak magnetic fields at liquid-nitrogen temperature as compared to pure HTSC ceramics. By choosing a proper bias current j, it is possible to control the shape of the resistivity-magnetic field ρ(H) characteristic of the composites and to vary the parameter R ₀ = {R(H = 0) ? R(H)}/R(H = 0). Under the condition j > j _c (where j _c is the critical-current density), large values of the magnetoresistance R ₀, up to thousands percent, are obtained in the range of weak magnetic fields (tens of oersteds) at 77 K. This effect is attractive for practical applications of these composite materials as active elements of magnetic-field sensors. The sign of the magneto-resistive effect is positive in contrast to that of manganese oxides. This may be important for some devices.     

Short-range atomic order in Fe<Subscript>2</Subscript>B powders

The possibility of application of a local atomic displacement (LAD) model for describing the mechanism of formation of a low-field part (H _hf ≤ 23.6 T) of a hyperfine-field distribution P(H) in a Fe₂B alloy at early stages of grain refinement has been investigated. It has been found that the appearance of Mössbauer contributions, which are not typical of the tetragonal C16 structure, in the P(H) function of the Fe₂B alloy is induced by a decrease in the relative interatomic distances Δr _Fe-B/r _Fe-B to ≤0.18 for some configurations of iron and boron atoms in the unit cell.     

Size dependence of the melting temperature of metallic nanoclusters from the viewpoint of the thermodynamic theory of similarity

The generalized Thomson formula T_m = T_m^(∞)(1-δ)R for the melting point of small objects T_m has been analyzed from the viewpoint of the thermodynamic theory of similarity, where R is the radius of the particle and T_m^(∞) is the melting point of the corresponding large crystal. According to this formula, the parameter δ corresponds to the value of the radius of the T_m(R^-1) particle obtained by the linear extrapolation of the dependence to the melting point of the particle equal to 0 K. It has been shown that δ = αδ₀, where α is the factor of the asphericity of the particle (shape factor). In turn, the redefined characteristic length δ₀ is expressed through the interphase tension σ_sl at the boundary of the crystal with its own melt, the specific volume of the solid phase v_s and the macroscopic value of the heat of fusion λ_∞:δ₀ = 2σ_slv_s/λ_∞. If we go from the reduced radius of the particle R/δ to the redefined reduced radius R/r₁ or R/d, where r₁ is the radius of the first coordination shell and d ≈r₁ is the effective atomic diameter, then the simplex δ/r₁ or δ/d will play the role of the characteristic criterion of thermodynamic similarity. At a given value of α, this role will be played by the simplex Estimates of the parameters δ₀ and δ₀/d have been carried out for ten metals with different lattice types. It has been shown that the values of the characteristic length δ₀ are close to 1 nm and that the simplex δ₀/d is close to unity. In turn, the calculated values of the parameter δ agree on the order of magnitude with existing experimental data.