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This present work concerns the effect of ternary addition of non‐metallic and diamagnetic silicon on the metastable solubility of the immiscible silver‐cobalt system during the course of ball milling, annealing of the ball milled samples and the corresponding magnetic properties. It should be noted that silicon has a smaller goldsmidt radius (111 pm) than silver (144 pm) and silicon+4 has more valence electrons than silver+1. Keeping the objectives of the current study in mind, silicon may thus be considered as an option for ternary addition, in contrast to metallic components. An attempt has been made to examine the phase changes that occurred in the 50 silver‐40 cobalt‐10 silicon (atom percent) system during ball milling and the subsequent isothermal annealing of the ball milled product. Phase evolution during mechanical alloying and isothermal annealing is identified by means of x‐ray diffraction, differential thermal analysis, high resolution transmission electron microscopy and magnetic measurements. The addition of silicon facilitates cobalt‘s formation of a metastable alloy with copper after 50 hours of ball milling. Annealing significantly improves the magnetic characteristics of materials that have been ball milled; the optimal combination of magnetic properties was obtained after an hour of annealing at 550 °C. [ABSTRACT FROM AUTHOR]

Strong green-emission is observed in the new Tb3+ activated Sr6Y2Al4O15 nanocrystalline material series fabricated via solution combustion methodology. A monoclinic crystal framework with space group I4/mcm (140) having irregularly shaped grains with an average size of 49 nm is formed. Morphological aspects are examined via scanning and transmission electron microscopy (SEM and TEM). On near-UV excitation, the photoluminescence spectrum presents a fair green-light production at 18382 cm-1 wavenumbers reliable with the 5D4→7F5 electronic transition. The energy transfer phenomena are also discussed. The highest luminous intensity is observed for 5.0 mol% of Tb3+ composition with 282 nm excitation wavelength. d-d exchanges authorized the presence of the concentration quenching phenomenon. Diffuse reflectance spectroscopy was taken into use to explore the energy band gap which lies in the semiconductor domain. The CIE coordinates lay in the greenish zone of the chromaticity scheme, thus confirming their latent contention in pc-WLED fabrication and other advanced photonic applications. Strong green-emission is observed in the new Tb3+ activated Sr6Y2Al4O15 nanocrystalline material series fabricated via solution combustion methodology. A monoclinic crystal framework with space group I4/mcm (140) having irregularly shaped grains with an average size of 49 nm is formed. On near-UV excitation, the photoluminescence spectrum presents a fair green-light production at 18382 cm-1 wavenumbers reliable with the 5D4→7F5 electronic transition. The CIE coordinates lay in the greenish zone of the chromaticity scheme, thus confirming their latent contention in pc-WLED fabrication and other advanced photonic applications. [ABSTRACT FROM AUTHOR]

The present work explores the pioneering use of different fuels for the synthesis of CaFe 2 O 4 (CF) nanopowder through auto-ignition synthesis (AIS) with potential application in the acid fuchsine (AF) dye removal. The results showed significant alternation in structure, morphology, and magnetic properties depending on fuel type. The morphology of the CaFe 2 O 4 nanopowders changed from a rock-like appearance for dextrose to a porous, thick-walled network structure for sucrose. All synthesized particles showed superparamagnetic behavior, with a crystallite size of 9 nm to 16 nm. The different adsorption process parameters, including the solution pH, adsorbent amount, and contact time, were studied and optimized. The Langmuir isotherm well explains the adsorption of AF, and the maximum monolayer capacity of CF-dextrose, CF-xylitol, CF-sorbitol, and CF-sucrose was found to be 788, 1024, 1125, and 1297 mg/g, respectively. The pseudo-second-order (PSO) kinetic model describes the adsorption data and the value of rate constant (k 2 = 2.36E-05 for CF-dextrose, 3.11E-05 for CF-xylitol, 2.70E-05 for CF-sorbitol, and 5.36E-05 for CF-sucrose) explain fast adsorption process. Furthermore, the CF nanopowder exhibits better regeneration and reusability capacity after multiple consecutive cycles, and magnetic separation aptitude makes it more convenient to isolate the adsorbent after the adsorption process. [Display omitted] • Manipulation of morphology of CF pertaining to fuel in auto-ignition synthesis. • Pseudo-second-order and Langmuir's models well-described AF uptake on CF samples. • Langmuir isotherm evaluates superior uptake of AF dye on CF reaches up to 1297 mg/g. • High regeneration-reuse performance of magnetic CF for treating AF dye. • AF adsorption followed by Yoshida, dipole H-bonding, and ion-complexing mechanism. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Synthesis of Mg 0.5 Zn 0.5 Mn 1.95 (Fe/Co/Ni) 0.05 O 4 by auto-combustion method. • Structural, morphological, optical, dielectric analysis on the prepared samples. • High dielectric constants and low losses are suitable for communication devices. This work aimed at synthesizing Mg 0.5 Zn 0.5 Mn 1.95 (Fe/Co/Ni) 0.05 O 4 nanoparticles using sol–gel auto-combustion method. Structural studies (XRD, Rietveld, Raman) confirmed the tetragonal spinel structure with I41/amd space group and average crystallite size ranged between 18–22.8 nm. The morphologies and compositions of these nanoparticles were studied using SEM and EDX. UV–Vis spectra demonstrated significant enhancement in the absorbance values. The estimated optical band gaps vary between 1.6 to 1.77 eV. Frequency-dependent dielectric and impedance spectroscopic studies (at room temperature) reveal exciting results. Thus, tailoring of dielectric properties and optical band gaps of these transition metals doped Mg-Zn manganite nanoparticles may find potential applications in optoelectronics devices. [ABSTRACT FROM AUTHOR]

• Compaction of amorphous and crystalline Nanomet by spark plasma sintering. • Maximum permeability can be controlled by flake size. • TEM analyze of Nanomet microstructure. Nanocrystalline soft magnetic materials with high saturation polarization and low losses have a high potential in motor applications. Thus, toroidal cores were compacted by spark plasma sintering of flakes of the melt-spun Nanomet alloy Fe-Si-B-P-Cu. The thermal properties of the ribbons were analyzed by DSC to determine the crystallization temperatures. The influence of the initial powder and of the compacting parameters such as maximum temperature and dwell time on the density and the magnetic properties in DC and AC were investigated. An optimum temperature range of approximately 50 K was determined for good soft magnetic properties. An effect of the dwell time was not recognized in the observed range. By compacting flakes of different sizes, the maximum permeability can be adjusted in the range of up to 7000. The microstructure was observed by means of XRD and TEM in order to confirm the amorphous and nanocrystalline state, respectively. Using the Lorenz mode of the TEM, it was possible to calculate the magnetic domain wall width for the samples and compare the resulting calculated magnetic properties with the experiments. [ABSTRACT FROM AUTHOR]

Multilayer composites have recently attracted considerable attention due to their ability to take advantage of the benefits of various metallic materials simultaneously. The present study is the first to use parallel tubular channel angular pressing (PTCAP) as a severe plastic deformation method to fabricate a bimetal Al/Mg tube. This process was applied on commercially pure aluminum along with an AM60 magnesium alloy at the temperature range of 250-400 °C. According to the microstructural and mechanical tests, there is a strong bond between layers besides the grain refinement after the process. Additionally, microhardness examinations showed that there is an excellent homogeneity in addition to the dramatic increase in the hardness of bimetallic PTCAP processed Al/Mg tube. Scanning electron microscope and energy-dispersive x-ray spectroscopy analyses in the interface between the layers and also the results of the shear strength test showed that by increasing the temperature, the diffusion rate at the interface increases. For instance, the significant bonding strength of 30 MPa was achieved after the PTCAP specimen at 400 °C. Therefore, these investigations substantiate that the PTCAP process can be used as an appropriate cladding technique for obtaining simultaneous severe plastic deformation microstructures and sufficient bonding strength in the production of bimetallic tubes. [ABSTRACT FROM AUTHOR]

The objectives of this work were to investigate the crystallization kinetics of Yttrium Iron Garnet (Y3Fe5O12, YIG) using the thermal analysis. The Differential Scanning Colorimetric (DSC) analysis confirmed that crystallization begins to form the YIG from the nitrates of the YIG gel product at the melting temperature of 337 °C. Two weight losses were discovered from the nitrates of the YIG gel product using simultaneous thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), in the temperature range of 70 to 130 °C and 760 °C, indicating the amorphous state to change the crystalline state formation. A thermo magnetization analysis (TMA) was performed on the synthesized YIG calcined at 850 °C, and the Curie temperature results were thoroughly examined. The Williamson-Hall (W-H) plots and transmission electron microscope (TEM) analysis were used to study the crystalline strain and crystalline formation of the as-prepared YIG particles at 850 °C calcined temperatures.

Grain boundaries (GBs) in polycrystalline and nanocrystalline materials are rarely flat, and their curvatures often evolve dynamically in three-dimensional (3D) GB network under thermomechanical stimulations. However, the complexity of polycrystalline microstructure greatly hinders our understanding of GB kinetics with 3D crystallographic clarity, especially at atomic scale. Here, we reveal a disconnection-based mechanism of GB kinetics in 3D space, by combining atomic-resolution in situ nanomechanical testing and atomistic simulations. Upon loading, GB can gradually adjust its curvature in 3D via sequential nucleation, propagation and annihilation of curved disconnections, where anisotropic mobilities of different disconnection segments induce a dynamic GB curving in 3D. Such curved disconnection-mediated GB curving and migration can coordinate among multiple GBs, and contribute to 3D grain growth/annihilation in GB networks. This curved disconnection-based 3D GB kinetics elucidates a long-elusive perspective in GB deformation, significantly advancing current knowledge of GB-mediated plasticity in metallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Deformation-induced grain-growth in nanocrystalline materials is a widely-reported phenomenon that has been attributed to grain boundary (GB) processes. In this paper, we report on the opposite phenomenon, wherein a stable nanocrystalline (NC) Cu-Ta alloy undergoes a further refinement of the nano-grains during severe plastic deformation (SPD). SPD up to 250% results in a significant grain-size reduction despite the 350°C increase in temperature caused by the deformation process. Experiments and atomistic-simulations show that this unexpected grain-refinement is a direct result of well-dispersed Ta-nanoclusters throughout grain centers and along GBs acting as kinetic-pinning agents and suppressing GB processes that occur during recrystallization. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Controlling the phases and structure of nanostructured rare-earth-based permanent magnets is essential to develop magnets with high performance in clean energy technologies. Importantly, simultaneously controlling the texture and morphology of nano-grains can lead to both high coercivity and high maximum energy product in the nanostructured magnets. Here, we demonstrated the use of electron-beam exposure (EBE) as a rapid heating technique to control the crystallization of the Pr-Fe-B magnet. Due to the effect of the extremely high heating rate, EBE can be adapted to control the phase, grain size, and morphology of the amorphous precursor as well as the texture of Pr-Fe-B nano-grains. A quasi-texture nanostructure with optimal magnetic exchange interactions is thus achieved, leading to a record-high coercivity of 29.1 kOe at room temperature. We further applied the Landau model and Coble-Creep model to explain the positive impact of the EBE on the crystallization and microstructure of the Pr-Fe-B magnet. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study investigated the mechanisms and temperature dependence of the R phase variant reorientation deformation in a nanocrystalline NiTi wire by means of in-situ synchrotron high-energy X-ray diffraction technique during tensile deformation. The NiTi wire exhibited a single stage B2 → R transformation upon cooling with the R → B19′ martensitic transformation completely suppressed down to the liquid nitrogen temperature. The R phase variant reorientation deformation in tension was revealed to proceed in a Lüders-manner, as evidenced by sudden changes of diffraction peak intensity and increases of lattice elastic strains of the R phase during the deformation. The variant reorientation obeys the principles to yield maximum crystallographic strain in the direction of the applied load. Thus, the variants with larger d -spacing values aligned to the axis of tension grew at the expense of those of lower d -spacing values. The increases of lattice elastic strains are attributed to the internal load transfer among the different crystallographic variants during the R phase reorientation. The crystallographic strain of R phase reorientation was found to increase with decreasing the deformation temperature. This corresponds directly to the continued evolution of the structure of the R phase of increased structural distortion relative the B2 phase with decreasing the temperature. This reflects the second order nature of the R phase. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report our findings on the influence of composition and reaction temperature on the phase composition and structure of nickel-based microspheres prepared by combining exothermic synthesis and spray pyrolysis from a glycine–nitrate solution. It has been shown that, at the optimal reductant-to-oxidant ratio and reaction temperature, the microspheres consist of Ni, Ni3N, and NiO, and the nickel content reaches 98%. The synthesized material has the form of microspheres 0.5 to 1.5 μm in average diameter and 10 to 15 nm in crystallite size. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Diffusion kinetics, processing, and microstructures of alumina ceramics have been of great scientific and technological interests. Here we reported the sintering kinetics and microstructure evolution in high-purity dispersed ultrafine α -Al 2 O 3 nanoparticles with superior sinterability. An extremely fine grain size of 34 nm with 99.6 % theoretical density and a uniform microstructure can be produced by two-step pressureless sintering. Systematic kinetic analysis further points out to a surprising insensitivity of α -Al 2 O 3 nanocrystalline ceramics to Fe and other impurities, which contrasts with prior reports in the literature. We propose this insensitivity is originated from extensive grain boundaries in nanocrystalline ceramics, which allows segregation of impurities and lowers their concentrations at grain boundaries. [ABSTRACT FROM AUTHOR]

Nanocrystalline Co 3 O 4 powders have been successfully prepared by using the precipitation method. The novelty in the present work is the comparative investigation of the influence of the calcination temperatures on the structural, morphological, optical, hemocompatible and antibacterial properties of nanocrystalline Co 3 O 4 powders. The Powder X-ray Diffraction (XRD) pattern result displays single phase Co 3 O 4 particles well crystalline in nature. The Scanning Electron Microscopy (SEM) result shows the agglomerated spherical Co 3 O 4 particles increasing with increase of calcination temperatures. The particle size and morphology of the Co 3 O 4 samples are characterized by using the Transmission Electron Microscopy (TEM) analysis. The optical absorption, optical band gap, and charge transfer between cobalt and oxygen are obtained from the UV–visible spectra. The fluorescence (FL) emission spectra reveal that strong visible emission peaks are observed at 402 and 414 nm for the Co 3 O 4 nanoparticles calcined at 450 and 600 °C, respectively. The hemolysis result reveals their highly hemocompatible nature. The antimicrobial activity of the samples against the gram negative bacteria Escherichia coli (E.coli) has been investigated. In addition, the possible mechanisms of hemocompatibility and antimicrobial activity of the Co 3 O 4 nanoparticles have been investigated in this current work. [ABSTRACT FROM AUTHOR]

[Display omitted] • Red-light emanating Eu3+ activated Ba 2 La 4 Zn 2 O 10 nanocrystals have been prepared via a simple urea-assisted solution combustion approach. • XRD, SEM, TEM, PL, DR, and EDAX characterizations are executed to explore numerous characteristics. • The fabricated nanophosphors have significant applications in numerous photonic and solid-state lighting applications. Strong red-emission is observed in the new Eu3+ activated Ba 2 La 4 Zn 2 O 10 nanocrystalline material series fabricated via solution combustion methodology. A tetragonal crystal framework with space group I4/mcm (1 4 0) having irregularly shaped grains with sizes between 33 and 62 nm is formed. Morphological aspects are examined via scanning and transmission electron microscopy (SEM and TEM). On near-UV excitation, the photoluminescence spectrum presents a fair red emission at 16129 cm−1 wavenumbers consistent with the electronic transition 5D 0 →7F 2. The energy transfer phenomena are also discussed. The highest luminous intensity is observed for 5.0 mol% of Eu3+ composition with 394 nm excitation. d-d exchanges authorized the presence of the concentration quenching phenomenon. Diffuse reflectance spectroscopy was taken into use to explore the energy band gap which lies in the semiconductor domain. The CIE coordinates lay in the reddish zone of the chromaticity plot, thus confirming their latent contention in pc-WLEDs and other advanced photonic applications. [ABSTRACT FROM AUTHOR]

This article reports an investigation into ferrite and nanocrystalline materials for the medium-frequency transformer of a dual active bridge DC-DC converter, which plays a key role in the converter’s efficiency and power density. E65 MnZn ferrite cores and toroidal and cut nanocrystalline cores are selected for the construction of 20-kHz transformers. Transformer performance is evaluated with a 1.1-kW (42–54 V)/400 V dual active bridge DC-DC converter with single-phase shift and extended phase shift modulations. The experimental results indicate that the toroidal nanocrystalline transformer had the best performance with an efficiency range of 98.5–99.2% and power density of 12 W/cm3, whereas the cut-core nanocrystalline transformer had an efficiency range of 98.4–99.1% with a power density of 9 W/cm3, and the ferrite transformer had an efficiency range of 97.6–98.8% with a power density of 6 W/cm3. A small mismatch in the circuit parameters is found to cause saturation in the nanocrystalline toroidal core, due to its high permeability. The analytical and experimental results suggest that cut nanocrystalline cores are suitable for the dual active bridge DC-DC converter transformers with switching frequencies up to 100 kHz.

• We have discussed the mechanisms influencing the depth resolution in 'on-axis' TKD. • Signals contributing to detectable Kikuchi bands in TKD originate from a volume of finite thickness (∼λ TDS) next to the bottom foil surface. • This existing surface sensitivity of TKD analysis can lead to the observation of different grain structures when opposite sides of a nano-crystalline foil are facing the incident electron beam. • A guideline for suitable sample thickness is suggested in order to achieve clear and indexable Kikuchi patterns for TKD analysis. In this paper, we have analyzed the depth resolution that can be achieved by on-axis transmission Kikuchi diffraction (TKD) using a Zr–Nb alloy. The results indicate that the signals contributing to detectable Kikuchi bands originate from a depth of approximately the mean free path of thermal diffuse scattering (λ TDS) from the bottom surface of a thin foil sample. This existing surface sensitivity can thus lead to the observation of different grain structures when opposite sides of a nano-crystalline foil are facing the incident electron beam. These results also provide a guideline for the ideal sample thickness for TKD analysis of ≤ 6λ TDS , or 21 times the elastic scattering mean free path (λ MFP) for samples of high crystal symmetry. For samples of lower symmetry, a smaller thickness ≤ 3λ TDS , or ≤ 10λ MFP is suggested. [ABSTRACT FROM AUTHOR]

This paper first presents an adaptive switching frequency modulation that optimizes the efficiency of the cascaded buck-boost (CBB) converter. Such bidirectional dc–dc CBB topology is typically deployed in PV-battery-device systems. A precise loss-model that accounts for component nonlinearities is developed to determine power-loss distribution. According to the loss model, optimal switching frequencies are selected that correspond to the lowest total loss in both the buck and the boost modes of the operation. Then, a small volume low-profile planar-nanocrystalline inductor is designed to further increase efficiency and power density. Finite element analysis method is used to evaluate the inductor design. A digital control system is designed to periodically adjust the optimal switching frequencies to modulate the pulsewidth modulation duty cycle and to take into account any load and line regulations. The objective of this paper is to achieve ultra-high efficiency (over 99%) for a well-known CBB converter. A 100 W CBB converter prototype was built to verify the proposed algorithm and designed nanocrystalline inductor. A California Energy Commission weighted efficiency of 98.87% with a peak efficiency of 99.31% was achieved for the buck mode and 98.58% with a peak efficiency of 99.25% was achieved for the boost mode, both at nominal voltage. Also, a power density of 3.67 kW/L was reported. [ABSTRACT FROM AUTHOR]

Abstract Nanocrystalline Nickel-based alloys were investigated as catalysts for the oxygen evolution reaction (OER) at industrial operation conditions for alkaline water electrolysis. Different alloys were prepared by rapid solidification and subsequent high-energy milling. Regarding OER activity, the best efficiency was obtained for a nanocrystalline Ni Fe alloy in 29.9 wt.-% KOH at 298 K. However, at elevated temperature (333 K), comparable activities were determined in short-term experiments for nanocrystalline Ni Fe and Ni alloys as well as for polycrystalline Ni. This initially incomprehensible outcome can be explained by the incorporation of Fe, which is present as impurity in the reagent grade KOH solution, into the NiOOH anode surface layer. However, after a long-term operation, the nanocrystalline Ni Fe alloy shows a significantly better activity, in particular, at altering current density of up to 1 A cm−2. As a result, the nanocrystalline Ni Fe alloy exhibits a very high efficiency and excellent long-term activity (375 mV overpotential at 0.3 A cm−2) after 95 h of operation at different loads. Highlights • Nanocrystalline Ni based alloys were investigated towards OER activity. • Both Fe in the alloy bulk and Fe impurities in the electrolyte affect the OER activity significantly. • Ni Fe alloys are excellent long-term stable catalysts at high current densities up to 1 A cm−2. • Fe-free Ni alloys show low OER activity with a high Tafel slope (b > 350 mV). [ABSTRACT FROM AUTHOR]

Abstract Nanocrystalline metallic materials with grain sizes of less than 100 nm exhibit high strength and unique characteristics, such as high levels of ductility and corrosion resistance. Mechanical milling techniques can be used to produce large amounts of nanocrystalline metallic powder. However, it is essential to perform a sintering treatment, which induces coarsening of the crystal grains, to form a bulk material from the mechanically milled powder. The cold spray technique is expected to effectively form a nanocrystalline metallic coating using the mechanically milled powder. This study focuses on pure iron coating, which is formed by a cold spray technique using mechanically milled pure iron powder. Pure iron powder, with crystal grains of ~100 nm, was obtained by a mechanical milling process, and was deposited onto a low-carbon steel substrate by cold spraying. It was confirmed that a dense, nanocrystalline coating with a hardness of over 300 HV can be achieved; however, the deposition efficiency of this coating was half of that of the coating formed using the as-received powder. The improvement of the deposition efficiency and properties of such coatings was attempted using powder mixtures comprising both milled and as-received powders. The results indicate that the deposition efficiency and microstructure, directly linked to the mechanical properties of the coating, can be controlled by varying the content of the as-received powder of the mixture. Highlights • The nanocrystalline pure iron coating can be obtained by employing mechanical milling combined with cold spraying. • The deposition efficiency and microstructure can be controlled using powder mixtures comprising both milled and as-received powders. • The milled and as-received powders in the mixture are deposited on the substrate independently without interaction with each other. [ABSTRACT FROM AUTHOR]