Influences of NiCO<Subscript>3</Subscript> content on the microstructure and magnetic properties of Ni<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by SHS

Stoichiometric Ni_0.5Zn_0.5Fe₂O₄ powders were produced by self-propagating high temperature synthesis (SHS). The effects of NiCO₃ content in the raw materials on the microstructure and magnetic properties of Ni-Zn ferrite powders were systematically studied. The Ni_0.5Zn_0.5Fe₂O₄ powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetic properties of the powders were evaluated by vibrating sample magnetometry (VSM). The results show that the introduction of NiCO₃ into reactants improves the conversion percentage and refines the Ni_0.5Zn_0.5Fe₂O₄ particles. The increase of NiCO₃ content enhances the magnetic properties of Ni_0.5Zn_0.5Fe₂O₄. Particularly, the saturation magnetization reaches the maximum when the NiCO₃ content is 3 at.%.     

A simple thermal decomposition-nitridation route to nanocrystalline boron nitride (BN) from a single N and B source precursor

Nanocrystalline boron nitride (BN) was synthesized via a simple thermal decomposition-nitridation route by the reaction of hydrated ammonium tetraborate (NH₄HB₄O₇·3H₂O) and metallic magnesium powders in an autoclave at 650 °C. The crystal phase, morphology, grain size, and chemical composition of the as-prepared products were characterized in detail by X-ray powder diffraction (XRD), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The products were also studied by FT-IR and the thermogravimetric analysis (TGA). Results revealed that the as-synthesized nanocrystalline were h-BN, and they had diameters within 100 nm. They had good thermal stability and oxidation resistance in high temperature.     

液料等离子热喷法制备Fe3+/TiO2纳米粉末

通过对液料等离子热喷前驱物添加掺杂成分实现了液料等离子热喷TiO2纳米粉末的掺杂改性,并利用TEM,XRD及XPS对其进行表征.结果表明,采用液料等离子热喷法可以制备Fe3 掺杂TiO2纳米粉末,所制备粉末形貌基本呈球形或近球形,粒径分布为10～35 nm,掺杂量小于2.0%时粉末为锐钛矿及金红石相混晶,Fd3 掺杂促进锐钛矿向金红石相的转变,掺杂量为10.0%时析出了Fe2Ti3O9相.Fe3 掺杂不会引起TiO2粒径的大范围波动.粉末中含有O,Ti,Fe和C等元素,Fe元素在TiO2中仍为 3价.     

An Investigation into the Nature of the Oxide Layer Formed on Kovar (Fe–29Ni–17Co) Wires Following Oxidation in Air at 700 and 800 °C

This work provides new insight and evidence that challenges and extends the accepted view of the oxidation behaviour of Kovar (ASTM-15). Specimens of 2 mm diameter Kovar wire were oxidised in air at 700 or 800 °C for 10 min. The resulting oxide layers were analysed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, scanning transmission electron microscopy and Raman spectroscopy. Oxide layers of approximately 2 and 4 µm thickness were formed at 700 and 800 °C, respectively. These were found to contain iron, cobalt and traces of nickel. The combination of analysis techniques revealed that the oxide contains Fe₂O₃ in addition to (Fe, Co, Ni)₃O₄, a spinel oxide, in contrast to the combinations of Fe₃O₄, Fe₂O₃ and FeO that are typically reported. The oxide layer was found to be complex, consisting of multiple layers with different compositions, which is overlooked in the existing literature.     

Oxidation of Fe–22Cr Coated with Co3O4: Microstructure Evolution and the Effect of Growth Stresses

The oxidation behavior of a commercially available Fe–22Cr alloy coated with a Co₃O₄ layer by metal organic—chemical vapor deposition was investigated in air with 1% H₂O at 1,173 K and compared to the oxidation behavior of the non-coated alloy. The oxide morphology was examined with X-ray diffraction, electron microscopy, and energy dispersive X-ray spectroscopy. Cr₂O₃ developed in between the Co₃O₄ coating and the alloy, while alloying elements of the substrate were incorporated into the coating. Particular attention was devoted to possible sources of growth stresses and the effect of the growth stresses on microstructure evolution in the scales that developed on the non-coated and the coated Fe–22Cr alloy. Microstructural features suggested that scale spallation on coated Fe–22Cr occurred as a result of superimposing thermal stresses during cooling onto the growth stresses, that had developed during oxidation.     

Corrosion behavior and resistance of hot-dip Al−Cr coated steel sheet under a salt corrosive environment

The corrosion behavior and resistance of hot-dip Al and Al−Cr coated steel sheets (SS) were investigated via scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), electron probe micro analysis (EPMA), glow discharge light spectroscopy (GDLS), and X-ray diffraction patterns (XRD). The Al−Cr coated layer was composed of the following three phases. Al phase comprised the surface layer, Al₁₃Cr₂ the middle layer, and Al₁₃Fe₄ and Al₅Fe₂ phases the interfacial layer between the Fe substrate and the coated layer. The corrosion behavior of the Al−Cr coated layer showed different aspects compared with the Al coated layer. In the Al−Cr coated layer, Cr was observed at an intermediate layer having a band shape. From the analysis of the polarization curve, the initial corrosion current of the Al−Cr coated SS was 10 times lower than that of Al in the early stage, and the corrosion resistance was superior to that of Al. The Al coated SS formed an Al−Fe−Si IMC layer, and the coated layer was almost destroyed. Many cracks were produced, and the corroded parts were enlarged from the cracks. The upper part of the Al−Cr coated SS, an Al−Si coated layer, was corroded. In contrast, the Cr-rich intermediate layer was not destroyed. Consequently, the high corrosion resistance was attributed to the densely covered Al(OH)₃ and the intermetallic compound layer of Al₁₃Cr₂. These results significantly contribute toward attaining a detailed understanding of the corrosion behavior and resistance Al−Cr coated steel sheets.     

The structure and composition of iron nanoparticles stabilized by carboxymethyl chitin resulting from ultrasonic irradiation

The methods of sonochemistry and “green” nanotechnology were used to develop a single-stage process to transfer iron nanoparticles from their micellar solution in isooctane to aqueous solution of carboxymethyl chitin excluding an intermediate stage of producing iron nanoparticulate dispersion in water. The structure and dimensions of iron nanoparticles in a macromolecular system based on 6-O-carboxymethyl chitin were examined using X-ray microanalysis and selected-area electron diffraction analysis, transmission electron microscopy (TEM), and atomic force microscopy (AFM). According to TEM and AFM data, the sizes of ultradispersed particles were within the range of 2–4 nm. The X-ray investigations indicated that iron nanonoparticles in the carboxymethyl chitin–iron nanoparticles system consisted mainly of zero-valent alpha-iron particles (α-Fe⁰) and a number of magnetite Fe₃O₄ nanoparticles. Because both types of particles exhibit magnetic properties, these metal–polymer nanocomposites may have a wide range of applications in medicine, electronics, biotechnology, ecology, and catalysis.     

Synthesis, characterization, magnetic and electrical properties of the novel conductive and magnetic Polyaniline/MgFe2O4 nanocomposite having the core-shell structure

Conductive and magnetic Polyaniline/MgFe₂O₄ nanocomposite was successfully synthesized in the form of core-shell via in situ chemical polymerization of aniline in the presence of MgFe₂O₄ nano-particles. X-ray powder diffraction of ferrites indicated that the structure of the core material is having the spinel structure, and demonstrated the formation of PAni/MgFe₂O₄ nanocomposite. XRD and TEM photographs showed that the particle's size of the MgFe₂O₄ core-material were around 30-35 nm before coating with Polyaniline, and grown up to 45 nm in the core-shell nanocomposite after coating. Although PAni has a relatively smaller electrical field coefficient than the core-shell nanocomposite, the resistivity of the core-shell material decreased, and hence its conductivity increased after a certain threshold voltage of 0.98 V equivalent to threshold electric field value equals 5.5 V cm⁻¹. The magnetic hysteresis loops investigated with VSM indicated that coating MgFe₂O₄ with Polyaniline has an healing effect which covers the ferrite surface defects, thus decreasing the magnetic surface anisotropy of ferrite particles leading to a decrease of the saturated magnetization (Ms) from 21.33 emu/g to 5.905 emu/g and a decrease of the coercivity (Hc) from 88.66 Oe to 81.6 Oe for MgFe₂O₄ and the core-shell nanocomposite respectively due to the amount of Polyaniline added. TGA and DTA revealed improved thermal stability of the core-shell nanocomposite with respect to that of Polyaniline due to the incorporation of ferrites. Raman spectroscopy confirmed TGA, DTA and XRD studies, and revealed that pure PAni is less stable than the corresponding core-shell nanocomposite with respect to molecular changes which might occur during heating at elevated temperatures. Moreover, Raman study confirmed the interfacial interaction between the core and the shell materials, and lead to an assumption about the presence of different conjugation chain lengths and types, such as the presence of the semi-quinones aside the quinone rings in the polymer chain, which showed different response upon heating the sample.     

Determination of corrosion potential of coated hollow spheres

Copper hollow spheres were created on porous iron particles by electro-less deposition. The consequent Ni plating was applied to improve the mechanical properties of copper hollow micro-particles. Corrosion properties of coated hollow spheres were investigated using potentiodynamic polarisation method in 1 mol dm⁻³ NaCl solution. Surface morphology and composition were studied by scanning electron microscopy (SEM), light microscopy (LM) and energy-dispersive X-ray spectroscopy (EDX). Original iron particles, uncoated copper spheres and iron particles coated with nickel were studied as the reference materials. The effect of particle composition, particularly Ni content on the corrosion potential value was investigated. The results indicated that an increase in the amount of Ni coating layer deteriorated corrosion resistivity of coated copper spheres. Amount of Ni coating layer depended on conditions of Ni electrolysis, mainly on electrolysis time and current intensity. Corrosion behaviour of sintered particles was also explored by potentiodynamic polarisation experiments for the sake of comparison. Formation of iron rich micro-volumes on the particle surface during sintering caused the corrosion potential shift towards more negative values. A detailed study of the morphological changes between non-sintered and sintered micro-particles provided explanation of differences in corrosion potential (E_corr).     

The corrosion resistance of a Fe/Cu composite

A composite made from a mixture of iron and copper powders was produced and characterised. The Cu addition favours the production of sintered Fe in the powder metallurgy industry processes. The corrosion behaviour in different electrolytic solution (sodium chloride or hydrochloric, acetic or sulphuric acids) and the corrosion rates were obtained from the weight loss and potentiodynamic methods – intersection and linear polarisation resistance. The values in hydrochloric and sulphuric acid vary slightly with respect to the average value of 78 mV/decade. The values obtained in acetic acid and sodium chloride are higher probably due to the formation of a thin film layer over the metallic surface. The morphology was analyzed through the observation by optical and scanning electron microscopy. It has been determined the nature of the oxide layer, Fe₃O₄, by X‐ray photoelectron spectroscopy (XPS), isolating the composite from the atmosphere. Thus, this oxide layer acts as a corrosion protective surface.     

Carbon doped α-Al2O3 coatings grown by chemical vapor deposition

Alumina (Al₂O₃) coatings deposited by chemical vapor deposition (CVD) with different modifications and dopants are widely applied as wear resistant coatings on cemented carbide cutting tools. The aim of this work was to investigate the influence of CH₄ addition on the deposition of α-Al₂O₃ by low-pressure chemical vapor deposition (LPCVD). The coatings were deposited at 1005 °C on a TiN–TiCN base layer using a precursor gas mixture of AlCl₃, CH₄, CO₂, HCl, H₂S, and H₂. Coating characterization was conducted by scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), glancing angle X-ray diffraction (GAXRD), nanoindentation and tribological ball-on-disk tests against Al₂O₃ balls. Additionally, the ball-on-disk wear tracks were investigated by Raman spectroscopy.     

Corrosion behavior of NiCrFe Alloy 600 in high temperature, hydrogenated water

The corrosion behavior of Alloy 600 (UNS N06600) is investigated in hydrogenated water at 260 °C. The corrosion kinetics are observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 0.055 mg dm⁻² h^−1/2. A combination of scanning and transmission electron microscopy, supplemented by energy dispersive X-ray spectroscopy and grazing incidence X-ray diffraction, are used to identify the oxide phases present (i.e., spinel) and to characterize their morphology and thickness. Two oxide layers are identified: an outer, ferrite-rich layer and an inner, chromite-rich layer. X-ray photoelectron spectroscopy with argon ion milling and target factor analysis is applied to determine spinel stoichiometry; the inner layer is (Ni_0.7Fe_0.3)(Fe_0.3Cr_0.7)₂O₄, while the outer layer is (Ni_0.9Fe_0.1)(Fe_0.85Cr_0.15)₂O₄. The distribution of trivalent iron and chromium cations in the inner and outer oxide layers is essentially the same as that found previously in stainless steel corrosion oxides, thus confirming their invariant nature as solvi in the immiscible spinel binary Fe₃O₄-FeCr₂O₄ (or NiFe₂O₄-NiCr₂O₄). Although oxidation occurred non-selectively, excess quantities of nickel(II) oxide were not found. Instead, the excess nickel was accounted for as recrystallized nickel metal in the inner layer, as additional nickel ferrite in the outer layer, formed by pickup of iron ions from the aqueous phase, and by selective release to the aqueous phase.     

Heterojunction semiconductor SnO2/SrNb2O6 with an enhanced photocatalytic activity: The significance of chemically bonded interface

Heterojunction photocatalysts SnO₂/SrNb₂O₆ were synthesized by a milling–annealing technique. The powders were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflection spectroscopy (DRS). Their UV-induced photocatalytic activities were evaluated by the degradation of methyl orange and methylene blue. The results generally show that the binary semiconductors SnO₂/SrNb₂O₆, with matching band potentials, exhibit better photocatalytic properties than the single phase SrNb₂O₆ or SnO₂. The effective electron–hole separation both at the chemically bonded interface and in the two semiconductors is believed to be mainly responsible for the increased photocatalytic performance of composites. The formation of chemically bonded interfaces between SnO₂ and SrNb₂O₆ particles makes the interparticle charge transfer more spatially available and smoother, which is significant to enhance the photocatalytic activity.     

High-temperature oxidation of Permalloy in air

Hematite (α-Fe₂O₃) nanowires were observed through directly annealing Ni₈₁Fe₁₉ foils at 600 °C for 120 min in atmosphere. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterise the nanowires. The results indicate that the growing mechanism includes iron segregation to the surface combined with an internal stress induced by the oxidation process.     

Preparation of micro-nano hollow multiphase ceramic microspheres containing MnFe2O4 absorbent by self-reactive quenching method

Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching method which is integrated with flame jet,selfpropagating high-temperature synthesis(SHS),and rapidly solidification.The morphologies and phase compositions of hollow microspheres were studied by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectroscopy.The results show that the quenching products are regular spherical substantially with hollow structure,particle size is between few hundreds nanometers and 5 lm.Phase compositions are diphase of Fe3O4,Mn3O4,and MnFe2O4,and the spinel soft magnetic ferrite MnFe2O4 with microwave magnetic properties is in majority.Collisions with each other,burst as well as‘‘refinement’’of agglomerate powders in flame field may be the main reasons for the formation of micro-nano hollow multiphase ceramic microspheres containing MnFeOabsorbent.     

Cobalt Ferrite in YSZ for Use as Reactive Material in Solar Thermochemical Water and Carbon Dioxide Splitting, Part I: Material Characterization

The synthesis, characterization, and evaluation of different weight loadings of cobalt ferrite (CoFe₂O₄) in 8 mol.% yttria-stabilized zirconia (8YSZ) via the co-precipitation method are reported. Prepared powders were calcined at 1350°C for 36 h and 1450°C for 4 h in air. These powders were then formed into a porous structure using sacrificial pore formation via oxidation of co-mixed graphite powder. These formed structures obtained were then characterized using thermogravimetric analysis (TGA), x-ray diffraction, high-temperature x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Brunauer–Emmett–Teller surface area analysis was performed on the most promising of the structures before being subjected to 50 thermal reduction-CO₂ oxidation (redox) cycles using TGA. Together, these results indicate that CoFe₂O₄-8YSZ can provide a lower reduction temperature, maintain syngas production performance from cycle to cycle, and enhance utilization of the reactive material within the inert support in comparison to iron oxide only structures.     

Electrical and magnetic properties of magnesium ferrite ceramics doped with Bi2O3

The effects of concentration of Bi₂O₃ and sintering temperature on DC resistivity, complex relative permittivity and permeability of MgFe_1.98O₄ ferrite ceramics were studied. The objective of the study was to develop magneto-dielectric materials, with almost equal values of permeability and permittivity, as well as low magnetic and dielectric loss tangent, for the design of antennas with reduced physical dimensions. It was found that the poor densification and slow grain growth rate of MgFe_1.98O₄ can be greatly improved by the addition of Bi₂O₃, because liquid phase sintering was facilitated by the formation of a liquid phase layer due to the low melting point of Bi₂O₃. It was found that 3% Bi₂O₃ can result in fully sintered MgFe_1.98O₄ ceramics. The DC resistivities of the MgFe_1.98O₄ ceramics were increased as a result of the addition of Bi₂O₃, except for 0.5%. The exceptionally low resistivities of the 0.5% samples were explained by a ‘cleaning’ effect of the small amount of liquid phase at the samples’ grain boundaries. The electrical and magnetic properties of the MgFe_1.98O₄ ceramics exhibited a strong dependence on the concentration of Bi₂O₃. The 0.5% samples were found to have the highest dielectric loss tangents, which can be understood similarly to the DC resistivity results. The 2–3% Bi₂O₃ is required to attain low dielectric loss MgFe_1.98O₄ ceramics for antenna application. Low concentration of Bi₂O₃ increased the static permeability of the MgFe_1.98O₄ ceramics owing to the improved densification and grain growth, while too high a concentration led to decreased permeability owing to the incorporation of the non-magnetic component (Bi₂O₃) and retarded grain growth. However, the addition of Bi₂O₃ alone is not able to produce magneto-dielectric materials based on MgFe_1.98O₄ ceramics, and further work is necessary to modify the permeability using cobalt (Co).     

Fabrication by Electrophoretic Deposition of Nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> 3D Structure on Carbon Fibers as Supercapacitor Materials

Core–shell nanostructured magnetic Fe₃O₄@SiO₂ with particle size ranging from 3 nm to 40 nm has been synthesized via a facile precipitation method. Tetraethyl orthosilicate was employed as surfactant to prepare core–shell structures from Fe₃O₄ nanoparticles synthesized from pomegranate peel extract using a green method. X-ray diffraction analysis, Fourier-transform infrared and ultraviolet–visible (UV–Vis) spectroscopies, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopy were employed to characterize the samples. The prepared Fe₃O₄ nanoparticles were approximately 12 nm in size, and the thickness of the SiO₂ shell was?~?4 nm. Evaluation of the magnetic properties indicated lower saturation magnetization for Fe₃O₄@SiO₂ powder (~?11.26 emu/g) compared with Fe₃O₄ powder (~?13.30 emu/g), supporting successful wrapping of the Fe₃O₄ nanoparticles by SiO₂. As-prepared powders were deposited on carbon fibers (CFs) using electrophoretic deposition and their electrochemical behavior investigated. The rectangular-shaped cyclic voltagrams of Fe₃O₄@CF and Fe₃O₄@C@CF samples indicated electrochemical double-layer capacitor (EDLC) behavior. The higher specific capacitance of 477 F/g for Fe₃O₄@C@CF (at scan rate of 0.05 V/s in the potential range of ??1.13 to 0.45 V) compared with 205 F/g for Fe₃O₄@CF (at the same scan rate in the potential range of?~???1.04 to 0.24 V) makes the former a superior candidate for use in energy storage applications.     

Preparation and magnetic property of multi-walled carbon nanotube/a-Fe2O3 composites

In order to attain new functional nanomaterials with good magnetic property, multi-walled carbon nanotubes/hematite (MWNTs/α-Fe₂O₃) composites were synthesized using the co-deposition method. MWNTs/α-Fe₂O₃ composites were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), Raman spectroscopy and vibrating sample magnetometry (VSM). The experimental results show that the structure and magnetic properties of the MWNTs/α-Fe₂O₃ composites are related to the heat treatment temperature. MWNTs are modified by α-Fe₂O₃ nano-particles and α-Fe₂O₃ nanorods with a diameter of 10?50 nm after being treated at 450 °C. When the heat treatment temperature exceeds 600 °C, MWNTs are only modified by Fe₃O₄ particles. Furthermore, the MWNTs composites treated at 450 °C and 600 °C have good magnetic behaviour.     

Synthesis and electrochemical performance of YF<Subscript>3</Subscript>-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials for Li-ion batteries

Spinel LiMn₂O₄ cathodes were coated with 1 mol% YF₃. X-ray diffraction (XRD) analyses showed that Y and/or F did not enter the lattice of the LiMn₂O₄ crystal. Transmission electron microscopy (TEM) showed that a compact YF₃ layer of 5–20 nm in thickness was coated onto the surface of LiMn₂O₄ particles. Scanning electron microscopy (SEM) observation showed that the YF₃ coating caused the agglomeration of LiMn₂O₄ particles. The cycling test demonstrated that the YF₃ coating can improve the electrochemical performance of LiMn₂O₄ at both 20 and 55°C. Moreover, YF₃-coated LiMn₂O₄ exhibited an improved rate capability compared with the uncoated one at high rates over 5C. The immersion test in electrolytes showed that YF₃-coated LiMn₂O₄ is more erosion resistant than the uncoated one.