Search

The structural, magnetic, and dielectric properties of spinel Magnesium (Mg) doped Nickel chromite (NiCr 2 O 4) nanoparticles (NPs) have been studied in detail. The X-ray powder diffraction exhibited normal spinel phase formation of Mg x Ni 1-x Cr 2 O 4 (x = 0, 0.2, 0.4, 0.6, and 1) NPs with a maximum average crystallite size of about 44 nm for x = 0.2 composition. The FTIR spectra of these NPs revealed the characteristic Ni–O and Mg–O and Cr–O bands around 639 cm−1 and 497 cm−1, respectively which confirmed the spinel structure. Temperature-dependent zero field cooled and field cooled graphs of NiCr 2 O 4 NPs showed phase changes from ferrimagnetic to paramagnetic state at 86 K, while MgCr 2 O 4 NPs showed antiferromagnetic (AFM) transition at Neel temperature (T N) at 15 K due to corner-sharing of Cr3+ ions at a tetrahedral lattice site resulting in a highly magnetic frustrated structure. The field dependent magnetization (M − H) loops of Mg x Ni 1-x Cr 2 O 4 NPs confirmed the competing AFM interactions and ferrimagnetic interactions resulting in a sharp decreased saturation magnetization with Mg doping. Dielectric constant, dielectric loss, and ac conductivity of these NPs showed size-dependent variation and depicted maximum value at x = 0.2 Mg concentration. In summary, the magnetic and dielectric properties of Mg doped NiCr 2 O 4 NPs were modified by variations in the average crystallite size and magnetic exchange interactions, which may be suitable for different technological applications. [ABSTRACT FROM AUTHOR]

Nanoscale NiCr2O4 spinel powders were prepared by solution combustion synthesis (SCS) from aqueous solutions of chromium/nickel nitrates as oxidants, urea as a fuel, and nitric acid and characterized by SEM/EDS, XRD, and porosity measurements. The catalytic activity of synthesized powders in conversion of CO to CO2 was determined and compared with that of supported Pd catalysts. An optimized composition of starting solution afforded for preparation of powders containing 93% of NiCr2O4 spinel without additional calcining. This powder showed good CO-to-CO2 conversion in the temperature range 150–300°С and can be recommended for practical implementation. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of Mn doped Nickel Chromite (Ni 1-x Mn x Cr 2 O 4, x = 0, 0.2, 0.3, 0.4, 0.6, 0.8) nanoparticles (NPs) were studied in detail. The X-ray diffraction analysis affirms normal spinel structure for all the samples and average crystallite size was found in the range 31–58 nm. The spinel structure of these nanoparticles was also confirmed by Fourier transform infrared spectroscopy which revealed the formation of tetrahedral and octahedral vibrational bands in the range 607 -628 cm−1 and 486 - 491 cm−1, respectively. Transmission electron microscopy images depicts less agglomerated and non-spherical shaped NPs. The temperature dependent zero field cooled and field cooled magnetic measurements revealed a paramagnetic to ferrimagnetic transition T c at 87 K for NiCr 2 O 4 NPs, which is shifted to low temperatures by Mn doping. This effect was attributed to cationic distributions between adjacent sites produced by Mn doping. M − H loops of Ni 1-x Mn x Cr 2 O 4 NPs revealed enhanced saturation magnetization with increase in Mn doping which is attributed to a large magnetic moment of Mn ions. Ni 1-x Mn x Cr 2 O 4 (x = 0.6 and 0.8) NPs show steps in their M − H loops because of exchange interactions between two sites of these NPs. [ABSTRACT FROM AUTHOR]

NiCr2O4 normal spinel nanostructures were prepared via hydrothermal treatment at 180 °C for 12 h in the presence of cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and poly vinylpyrrolidone-25000 (PVP-25000) as capping agents and subsequent calcination process at 500 °C for 3 h . In this method, [Ni(en)2(H2O)2](NO3)2 and [Cr(en)3]Cl3.3H2O used as precursors and not utilized any alkaline or precipitating agent. Detailed characterization of the as-prepared nanostructures were carried out by Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS). XRD revealed the formation of pure nickel chromite spinel phase and SEM showed the formation of uniform sphere-like nanoparticles. Furthermore, the photocatalytic degradation of acid black 1 as diazo dye used in textile and dyeing water pollutants was Investigated.

The NiCr2-xFexO4, (x=0.1,0.3,0.5) samples have a cubic structure at room temperature. For the sample with x=0.1, the lattice constant is determined to be a0=8.319 Å with a cubic spinel (Fd-3m) structure. The ferrimagnetic Néel temperature (TN) of NiCr2O4 is determined to be 80 K by zero field cooled magnetization curves under the external field of 100 Oe. With increasing Fe substitution, TN increases, and for x=0.1, TN is determined to be 135 K. For the sample with x=0.1, the Mössbauer spectrum at 4.2 K was fitted to two magnetic components of the magnetic hyperfine fields Hhf=488 and 472 kOe and isomer shifts δ=0.29 and 0.28 mm/s. The electric quadrupole splittings (ΔEQ) were found to be nearly zero below the TN=135 K. For the spectrum at 295 K, the ΔEQ are observed with large values of 0.54 and 0.37 mm/s, respectively. The values of the isomer shifts show that for all temperature ranges, the states are ferric (Fe3+). The Mössbauer spectra below the TN show the line broadening with the Jahn-Teller distortion and accompanying relaxation effects, respectively. [ABSTRACT FROM AUTHOR]

Adsorption of metal ions Pb(II), Cd(II) and Cu(II) are observed on chromium doped nickel nano metal oxide. Chromium doped nickel oxide was synthesized by combustion technique using glycine as a fuel. In this work, transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) are applied to study the composition and structure of chromium doped nickel oxide. Batch equilibrium experiments were performed to study the removal efficiency of heavy metal ions. The effects of different parameters such as contact time, pH and adsorbent dose on the adsorption process were investigated. The adsorption kinetics and adsorption isotherms studies were also performed. The formation of hydroxide on the surface of chromium doped nickel oxide could be the main factor of cations removal due to its high adsorption affinity for aqueous solutes. Chromium doped nickel oxide may offer a potential remediation method for the removal of metals from water and environment. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis, characterization and alcohol sensing applications of highly porous NiO nanodisks (NiO-NDs). The nanodisks were synthesized via hydrothermal method and were characterized in detail to examine their morphological, structural, compositional, crystalline and optical properties through different techniques. The typical thickness of the nanodisks was in the range of 15 ± 5 nm while the diagonal dimensions were about 100 ± 20 nm. The electrochemical sensing performances of the synthesized NiO-NDs for different alcohols were subsequently measured by fabricating carbon paste modified electrodes in alkaline medium (CPE/NiO-NDs). For excellent sensing results, the fabricated CPE/NiO-NDs electrodes were standardized for NiO composition, scan rate, the concentration of functional electrode materials etc . Various electroanalytical techniques such as cyclic voltammetry, linear sweep voltammetry and amperometry were employed at different applied potentials to examine the sensing performances of the fabricated sensors. The maximum sensitivity was recorded for CPE/NiO-NDs with 15% NiO composition after 40 scan rates in 0.15 M of NaOH/0.1 M KCl supporting electrolyte. The detailed sensing studies confirmed that the CPE/NiO-NDs (15%) electrode was more sensitive for ethanol as compared to other alcohols. Experimental limit of detection (LOD) and linear dynamic range (LDR) were observed to be 1 mM and 1–47 mM, respectively whereas; the sensitivity of the CPE/NiO-NDs (15%) electrode was recorded to be 3.51 μA mM −1  cm −2 towards ethanol. [ABSTRACT FROM AUTHOR]

Thermally sprayed hard metal coatings are the industrial standard solution for numerous demanding applications to improve wear resistance. In the aim of improving coating quality by utilising finer particle size distributions, several approaches have been studied to control the spray temperature. The most viable solution is to use the modern high velocity air-fuel (HVAF) spray process, which has already proven to produce high-quality coatings with dense structures. In HVAF spray process, the particle heating and acceleration can be efficiently controlled by changing the nozzle geometry. In this study, fine WC-10Co4Cr and Cr3C2-25NiCr powders were sprayed with three nozzle geometries to investigate their effect on the particle temperature, velocity and coating microstructure. The study demonstrates that the particle melting and resulting carbide dissolution can be efficiently controlled by changing the nozzle geometry from cylindrical to convergent-divergent. Moreover, the average particle velocity was increased from 780 to over 900 m/s. The increase in particle velocity significantly improved the coating structure and density. Further evaluation was carried out to resolve the effect of particle in-flight parameters on coating structure and cavitation erosion resistance, which was significantly improved in the case of WC-10Co4Cr coatings with the increasing average particle velocity. [ABSTRACT FROM AUTHOR]

It is of interest to study the magneto-structural coupling in geometrically frustrated antiferromagnets, where structural distortion elevates the ground state degeneracy, leading to a long-range magnetic order. In this regard a cubic spinel compound of the form AB 2 O 4 is currently drawing much attention, where A refers to tetrahedral and B to octahedral sites. In the particular case of NiCr 2 O 4 the material undergoes several structural phase transitions associated with the magnetic ordering. It is therefore necessary to study the magnetic behaviour of NiCr 2 O 4 by substituting either A or B sites, or both systematically with suitable cations. The current work therefore aims at the modification of magnetic properties of NiCr 2 O 4 by doping with Co 2+ at A sites. In order to achieve the afore mentioned, (Ni 1− x Co x )Cr 2 O 4 (0 ≤  x ≤  1) were prepared using chemical co-precipitation techniques. X–ray diffraction (XRD) results indicate that the samples are in the expected phase without any trace of Cr 2 O 3 impurities after calcination. Transmission electron microcopy (TEM) analyses of these samples show that the particles are mostly bi-pyramidal in shape, with sizes ranging from 50 nm to 100 nm. In the present study the ferrimagnetic transition temperatures ( T C ) of the various samples were determined utilizing magnetization as function of temperature measurements. T C for NiCr 2 O 4 and CoCr 2 O 4 was determined to be 82.4 ± 0.8 K and 99.5 ± 0.5 K, respectively. These values are higher than those previously reported in the literature for both these compounds. Substitution of Ni by Co, results in an increase in the T C , giving values of 89.2 ± 0.7 K and 90.6 ± 0.9 K for (Ni 0.5 Co 0.5 )Cr 2 O 4 and (Ni 0.25 Co 0.75 )Cr 2 O 4 , respectively. The (Ni 0.5 Co 0.5 )Cr 2 O 4 sample demonstrated a high coercivity of 3.6 ± 0.1 T and a shift in the hysteresis loop observed under field cooled measurement, not previously reported in literature. X–ray photoelectron spectroscopy (XPS) of (Ni 0.5 Co 0.5 )Cr 2 O 4 suggests that the oxidation states of Ni and Co are 2+, while that of Cr is 3+. In order to investigate the local structure around the cations, low temperature extended x–ray absorption fine structure (EXAFS) measurements were performed. From EXAFS it is confirmed that no redistribution of A and B site cations occur at low temperatures. Present findings demonstrate that the magnetic properties of NiCr 2 O 4 can easily and dramatically be modified by doping Co 2+ at A sites. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the microbial adherence to the surfaces of a nonprecious metal alloy after plasma nitriding. Materials and Methods: The plasma-nitriding process was performed to the surfaces of metals prepared from a nickel-chromium alloy. The microorganisms were labeled with technetium-99m. After the labeling procedure, 60 metal disks were treated with a microorganism for each use. Results: The results revealed that the amount of adherence of all microorganisms on surfaces was changed by plasma-nitriding process; adherence decreased substantially ( P< .05) and the differences in plasma nitriding time were not significant ( P> .05) Conclusion: With the plasma-nitriding process, the surface properties of nonprecious metal alloys can be changed, leading to decreased microbial adherence. [ABSTRACT FROM AUTHOR]

The possibility of obtaining black pigment based on nickel chromite (NiCrO) is examined. The morphological, granulometric, x-ray structural, and optical characteristics of synthesized crystalline powders of chromium nickel spinel are investigated. Upon spontaneous crystallization at temperature 950°C nickel chromite crystallizes in the spinel structure Fd3m with crystals ranging in size from 1.29 to 84 μm (predominantly in the form of an octahedron). The diffuse reflection spectra showed high emissivity of NiCrO: the diffuse reflection coefficient ranges from 2.65 to 4.81% in the range 320 - 1080 nm. Black glazes based on nickel chromite were obtained; the optimal weight content of the pigment is 6 - 8%. [ABSTRACT FROM AUTHOR]

Temperature dependent fabrication of NiCr 2 O 4 is studied and the application of the as-prepared NiCr 2 O 4 in both half-cell with Li metal anode and full-cell with LiFePO 4 cathode are assessed. When mixing with natural graphite (NG), the NiCr 2 O 4 obtained at 550 °C can deliver initial charge and discharge capacities of 795 and 1275.5 mAh g −1 at a specific current of 150 mA g −1 , maintaining of 939 and 955 mAh g −1 after 140 cycles. In contrast, after 140 cycles at the same specific current, the NiCr 2 O 4 obtained at 450 °C and 650 °C can maintain charge/discharge capacities of 800/814 and 523/528 mAh g −1 , respectively. When matching with a LiFePO 4 cathode, The NiCr 2 O 4 /NG (obtained at 550 °C) electrode delivers initial discharge capacity of 285 mAh g −1 , which maintains of 106 mAh g −1 after 50 cycles at a specific current of 100 mA g −1 . [ABSTRACT FROM AUTHOR]

In the present work erosive and abrasive wear behaviour of HVOF deposited WC-12Co, WC–10Co–4Cr and Cr 3 C 2 −25NiCr coatings was investigated. The maximum wear rate was exhibited by Cr 3 C 2 −25NiCr coating under both solid particle erosion and abrasion. The coatings exhibited composite erosion response. The erosion response was rationalized on the basis of velocity exponents, erosion mechanisms and mechanical properties. Erosion damage parameter and severity of contact can be useful indicator of transition in failure modes. The wear mechanisms were influenced by microstructure of the coatings and the test conditions, involving fracture and pull out of carbides, removal of splats and subsurface cracking. The lowest coefficient of friction exhibited by Cr 3 C 2 −25NiCr coating was attributed to formation of tribo oxide film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of undoped NiCr 2 O 4 and Ce doped NiCr 2 O 4 materials using microwave method. • Structural, optical, magnetic and antibacterial properties were extensively analyzed. • The substitution of Ce ion into NiCr 2 O 4 particles which improves the properties. • The Ce doped NiCr 2 O 4 shows an excellent anti-bacterial performance than pure NiCr 2 O 4. We present a comprehensive study on optimization of microwave method routes for producing well-crystalline spinel chromite, nicr 2 o 4 and Ce-doped nicr 2 o 4. All samples were characterized by powder X-ray diffraction (XRD) and vibrational spectroscopy in order to evaluate their phase composition, particle size and micro-strain. Selected samples were investigated by adopting transmission electron microscopy (TEM) and optical spectra (absorption spectroscopy & photoluminescence, PL). The presence of large concentration of anion deficiency and its related defects, are reflected in the intense emission of PL spectra and in lowering the band gap value with respect to the bulk counterpart. As the Ce concentration increases, the size of the nanoparticles reduced from ∼33 to 22 nm. The effects of the cation distributions on geometrical variations of electronic and magnetic properties of nicr 2 o 4 can be interpreted as dominated by the local behavior of Ni2+ at octahedral and Cr3+ tetrahedral sites. In the present work, the results indicate that the substitution of Ce ion into nickel chromite particles, enhances effects of the magnetic, optical properties, and also enhances the antibacterial properties. [ABSTRACT FROM AUTHOR]

Examines the dimensionality of nickel (Ni)-chromium (Cr) multilayered structures from the variation of the temperature dependence of the saturation magnetization with the Ni layer thickness. Cr contained in NiCr alloys; Illustration of an ideal interface and the composition and magnetization profiles.

This study investigated the workability of a NiCr wire probe diagnostic under low temperature plasma operating conditions. The aim of the work was to design and fabricate a triple Langmuir probe with NiCr alloy for measurements in low temperature rf plasmas. The spatial distribution of electron temperature and number density were evaluated at different filling pressures in the range of 0.2–0.4 mbar and rf powers in the range of 200–400 W. The probe data revealed a linear increase in temperature and electron number density with rf power along the chamber centerline, whereas an inverse relationship was found between the given plasma parameters and filling gas pressure. The spatial distribution measurements showed a decreasing trend in plasma parameters at positions away from the chamber centerline. The probe I – V characteristics curve revealed a change in polarity of probe potential with an increase in current supply from the plasma discharge to the probe. Initially, the potential difference raised from highly negative values to zero volt, thereafter started increasing positively. It is found that the response of NiCr alloy as probe material was appreciably good under the proposed operating conditions. [ABSTRACT FROM AUTHOR]

The aim of the investigations was to compare the microstructure, mechanical, and wear properties of CrC-NiCr+Ni and CrC-NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr C -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr C -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed CrC-NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine CrC and CrC particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr C -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (CrC-NiCr+Ni) in wear conditions. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr 3 C 2 –25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr 3 C 2 than the feedstock powder, possibly due to the rebound of some Cr 3 C 2 -rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10 −6 mm 3 /(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10 −6 °C −1 in the 30–400 °C range) is sufficiently close to that of the steel substrate (14.23x10 −6 °C −1 ) to avoid macro-cracking. [ABSTRACT FROM AUTHOR]

In this paper an original numerical model, based on the standard Berg model, was used to simulate the growth mechanism of NiCrxOy deposited with changing oxygen flow during reactive sputter deposition. The effect of oxygen flow rate on the discharge voltage, deposition rate and the material elementary composition were investigated. The ratio of Ni and Cr content in the film was measured using energy-dispersive X-ray spectroscopy (EDX). EDX detected a decrease in the Cr concentration with the increasing of oxygen flow rate due to the preferential oxidation of Cr to Cr2O3. Results show a reasonable agreement between numerical and experimental data. [ABSTRACT FROM AUTHOR]

A novel sonochemical route was reported for the manufacturing of nickel oxide (NiO) nanoparticles. The synthesized NiO nanoparticles were characterized by UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-Ray analysis (EDX). Their size calculated by SEM was ranges between 35 to 117 nm. The ability of NiO nanoparticles to remove lead ions from aqueous solutions was investigated. Several parameters such as dosage of the adsorbent, pH, shaking time and the effect of temperature were studied systematically and optimum values were chosen for subsequent isotherm modeling. Adsorption data obeyed both Langmuir and Freundlich isotherm models but fitted better with Langmuir isotherm model with highest uptake capacity of 166 mg/g. The kinetics of the adsorption process followed pseudo-second-order rate equation. Thermodynamics studies illustrated endothermic nature of the process and its feasibility. The experimental results depicted that the NiO nanoparticles can likely be employed as an adsorbent for removing heavy metal ions from water. [ABSTRACT FROM AUTHOR]

NiCr2O4/Cr2O3 system with ferrimagnetic spinel and antiferromagnetic transition metal oxide has been firstly synthesized by a chemical co-precipitation method. Magnetic measurements on this system also exhibit the exchange bias (EB) and training effect for the first time. EB effect with evident shift of coercive field and remnant magnetization can be detected at low temperature after field cooling from 350 K. The EB field can reach about 2037 Oe and the magnetization shift is as large as 0.129 emu/g at 10 K. Furthermore, EB effect recedes gradually with temperature increasing and disappears at about 70 K. In this process, EB field decreases with a linear dependence on the magnetization shift. This EB behavior is discussed according to the disordered regions existed at the interface between NiCr2O4 and Cr2O3. In addition, we have analyzed the training effect, which indicates the coexistence of two distinct forms of training mechanism during cycle procedure. One is concerned with an athermal impact resulting in the abrupt single cycle training and the other is gradual reduction of EB field during the subsequent cycles due to the conventional thermal activation mechanism. [ABSTRACT FROM AUTHOR]

Pure nickel chromite (NiCr 2 O 4 ) nanostructures were prepared via a new coprecipitation–calcination route by using [Ni(en) 2 (H 2 O) 2 ](NO 3 ) 2 and [Cr(en) 3 ]Cl 3 ·3H 2 O as novel precursors. The as-prepared nickel chromite nanostructures were characterized by energy dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). Results of this study demonstrate that particle size and morphology of the nickel chromite can be controlled by setting main preparation parameters such as the precipitator, the speed of the reaction stirrer, reaction time, surfactant, reaction temperature and calcination temperature. Nickel chromite nanostructures with different particle size and morphology were successfully synthesized. The magnetic properties of as-prepared nickel chromite nanostructures were also investigated with vibrating sample magnetometer (VSM). [ABSTRACT FROM AUTHOR]

NiCr 2 O 4 is successfully prepared via hydrothermal pretreatment and subsequent sintering, which shows excellent electrochemical performance as a new anode material for lithium ion batteries with natural graphite adding and sodium alginate binder. At a specific current of 70 mA g −1 , it delivers charge and discharge capacities of 465.5 and 919.8 mAh g −1 in the initial cycle, which gradually increases along with cycle number owing to an electrochemical reconstruction in cycling. After 100 cycles, the charge and discharge capacities are 582.9 and 592.5 mAh g −1 , respectively. Furthermore, it is testified that natural graphite adding can effectively improve the electronic conductivity of the NiCr 2 O 4 electrode, and an appropriate amount of natural graphite is beneficial to improve the specific capacity and cycle stability of the electrode owing to a coordinated electrochemical reconstruction between NiCr 2 O 4 and natural graphite in cycling. [ABSTRACT FROM AUTHOR]

The present work shows that some mechanical properties of CrC-25NiCr coatings processed by HVOF thermal spraying such as elastic modulus, hardness, fracture toughness, and wear resistance are closely linked to selected processing parameters as well as to chemistry, structure, and morphology of the feedstock material. Optimization of processing parameters was based on oxygen concentration measurements inside the flame, studied by a contour plot, and curvature data recorded during spraying. The increase in velocity of in-flight particles strongly affected the interfacial fracture toughness of the coatings, as a maximum K of 3.71 MPa m was reached when particle velocity increased to ~765 m/s. The micro-hardness of CrC-25NiCr coatings was widely varied by changing the HVOF spray conditions, i.e., the amount of reinforcing phases and inter-splat adhesion were quite sensitive to any modification of the processing parameters. It was also found that coatings having a high inter-splat adhesion and/or low degradation of reinforcing hard phases showed reduced weight loss during erosive wear tests. Finally, from the experimental evidence reported in this work, a correlation between the elastic bending modulus of coatings and indentation crack length was also found. [ABSTRACT FROM AUTHOR]

The behavior and mechanism of NiCr-HfB cermet coating oxidation at 1,000, 1,100 and 1,200 °C in pure oxygen were investigated using thermogravimetric equipment, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Analyses of the oxidation kinetics confirmed that the parabolic rate law was followed at each temperature and the activation energy of oxidation was 284 kJ/mol. The oxidation layers were detected to be composed of NiO, NiCrO, CrO. The cross-sectional morphologies indicated that the oxidation layer consisted of three parts: Ni-rich oxide layer, spinel NiCrO layer and a thin layer of CrO. The oxidation process was controlled by the outward diffusion of the oxide-forming elements Ni, Cr and inward penetration of oxygen, by which the interaction mechanisms between the microstructures was clarified. On the basis of the experimental results and fundamental analyses, the NiO/NiCrO/CrO multi-layer oxidation mechanism was accordingly established to illustrate the oxidation behaviors. [ABSTRACT FROM AUTHOR]

Nanocrystalline nickel chromium ferrite (NiCrFeO, x = 0.1, 0.2) have been prepared by the chemical co-precipitation method. Half of the samples have been sintered at 620C and the other at 1175C. Then polypyrrole (PPy)-NiCrFeO composites have been synthesized by polymerization of pyrrole monomer in the presence of NiCrFeO nanoparticles. The structure, morphology and magnetic properties of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometer. Also, the initial magnetic permeability measurements as functions of temperature and frequency have been performed. The XRD and FT-IR studies have confirmed the well crystalline phase of ferrite nanoparticles, and the presence of amorphous PPy in the composite samples. The SEM and TEM images have obviously clarified the coating of ferrite nanoparticles by PPy in the composite samples. The hysteresis loop of the samples has proved that the samples are soft magnetic material because of their low coercivity. [ABSTRACT FROM AUTHOR]

The analytical research results of replacement possibility of expensive high-alloy nickel-chromium steels by sparingly alloyed nickel-free ones alloyed by nitrogen are shown. The interrelation of increase of operational steel properties for the grate bar of the roasting and sinter machines is shown. [ABSTRACT FROM AUTHOR]

Single phase sample of NiCr 2 O 4 crystallized in a tetragonal structure of I4 1 /amd space group was prepared. Ferrimagnetic transition at T C =73 K along with a large irreversibility has been observed from the magnetization measurement. The sample exhibits exchange bias phenomenon and it is explained by considering the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic moment. Presence of training effect is also observed. The exchange bias field ( H EB ) is found to decay exponentially with increase in temperature and however, the coercive field ( H C e f f ) follows the empirical relation H C e f f = H C e f f 0 1 − T T C ' 2 . The maximum experimental values of H EB and H C e f f are found to be 313 Oe and 4839 Oe respectively. [ABSTRACT FROM AUTHOR]

The nanocrystalline nickel chromite ( NiCr 2 O 4 ) with particle size of ∼20 nm was prepared by auto-combustion method. The nanocrystals were characterized by powder X-ray diffraction, vibrational spectroscopy and magnetic measurements. The expected structural phase transitions (cubic–tetragonal–orthorhombic) were studied by methods of temperature-dependent X-ray powder diffraction and vibrational spectroscopy. The evolution of the Raman spectra and X-ray diffraction patterns collected from 350 K down to 4 K confirmed the cubic-to-tetragonal distortion at ∼250 K, whereas the tetragonal-to-orthorhombic transition was not confirmed in the nanocrystalline sample. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this in-vitro study was to evaluate the effect of topical fluoride on surface of cast titanium and nickel-chromium. Materials and Methods: Thirty-nine rectangular specimens of titanium (grade 2) and 39 rectangular specimens of nickel-chromium were cast in equal dimensions and divided into three groups of 13 samples each. Group one specimens of titanium and nickel-chromium were placed in 2% neutral sodium fluoride (NaF) solution for 16 minutes. Group two specimens of titanium and nickel-chromium were immersed in 1.23% acidulated phosphate fluoride (APF) gel for eight minutes. Group three specimens of titanium and nickel-chromium were immersed in distilled water for 16 minutes. The surface roughness of the specimens was evaluated and the data were analyzed using two-way ANOVA and post-hoc comparison test with the level of significance set at 5% (P< 0.05). The surface of the specimens was further analyzed using a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Results: Group two titanium specimens showed a statistically significant increase in surface roughness (P<0.05); but no statistically significant increase was noted in the surface roughness of nickel-chromium specimens in groups one, two and three (P>0.05). Qualitative SEM and EDS analyses further revealed the surface corrosion of titanium (group two) and localized mild corrosive pitting of nickel-chromium specimens (group two). Conclusion: Topical fluoride with acidic pH affects the surface roughness of titanium and to a certain extent, nickel-chromium. Neutral NaF solutions cause no significant change in corrosion resistance of titanium or nickel-chromium. [ABSTRACT FROM AUTHOR]

In the present work, NiCr–BaMoO 4 self-lubricating composites have been fabricated by hot pressing to evaluate their tribological properties at elevated temperatures. Hydrothermal synthesis method has been used to prepare fine BaMoO 4 spherical powders with a size of 500 nm by adjusting different technological parameters. The synthesized BaMoO 4 powders have a good thermal stability in air after calcining up to 1100 °C for 5 h. The friction and wear properties of NiCr–BaMoO 4 composites were investigated by using a ball-on-disk friction and wear tester in sliding against Si 3 N 4 ball up to 600 °C. As contrasted with unmodified NiCr alloy, the composites incorporated with 10 wt% or 20 wt% BaMoO 4 exhibit distinct improvements in effectively reducing friction and wear at elevated temperatures. NiCr–BaMoO 4 composites have low friction coefficients of 0.26–0.30 and small wear rates in the order of magnitude of 10 −5 –10 −6 mm 3 /Nm at elevated temperatures. A dense oxidized surface layer is formed on the worn surface of NiCr matrix composites incorporated with BaMoO 4 . Tribo-oxidation reaction during high temperature wear tests is responsible for the formation of dense oxidized surface layer containing BaMoO 4 , NiCr 2 O 4 , NiO and Cr 2 O 3 . The coupled Si 3 N 4 ball is covered with a transfer layer containing BaMoO 4 , which effectively reduces the friction and wear. [ABSTRACT FROM AUTHOR]

This paper summarizes 0 to 0.6 GPa neutron diffraction measurements of a nickel hexacyanochromate coordination polymer (NiCrPB) that has the face-centered-cubic, Prussian blue structure. Deuterated powders of NiCrPB contain ≈100-nm-sided cubic particles. The application of a large magnetic field shows the ambient-pressure, saturated magnetic structure. Pressures of less than 1 GPa have previously been shown to decrease the magnetic susceptibility by as much as half, and we find modifications to the nuclear crystal structure at these pressures that we quantify. Bridging cyanide molecules isomerize their coordination direction under pressure to change the local ligand field and introduce inhomogeneities in the local (magnetic) anisotropy that act as pinning sites for magnetic domains, thereby reducing the low-field magnetic susceptibility. [ABSTRACT FROM AUTHOR]

The hot-corrosion behavior of detonation-gun sprayed CrC-NiCr coatings with and without 0.4 wt.% CeO additive on Ni-based superalloy inconel-718 is comparatively discussed in the present study. Hot-corrosion studies were carried out at 900 °C for 100 cycles in NaSO-60%VO molten salt environment under cyclic heating and cooling conditions on bare and coated superalloys. The thermo-gravimetric technique was used to establish kinetics of hot-corrosion. XRD, FESEM/EDAX, and EDX mapping techniques were used to analyze the corrosion products of bare and coated samples. The results indicate that CrC-NiCr-CeO-coated superalloy showed better hot-corrosion resistance as compared to bare and CrC-NiCr-coated superalloys. The addition of CeO has improved micro-hardness, porosity, and surface roughness values of CrC-NiCr-CeO coating. The overall weight gain and parabolic rate constant of CrC-NiCr-CeO-coated superalloy were found to be lowest in the present study signifying that the addition of CeO in CrC-NiCr powder has contributed to the development of adherent and dense oxide scale on the coating at elevated temperature. [ABSTRACT FROM AUTHOR]

In order to achieve a desired dense structure for coatings employed in high temperature corrosion conditions, thermal spray process optimization with diagnostic tools can be applied. In this study, NiCr (51Ni-46Cr-2Si-1Fe) and FeCr (Fe-19Cr-9W-7Nb-4Mo-5B-2C-2Si-1Mn) powders were sprayed with HVOFGF (gas-fueled) and HVOFLF (liquid-fueled) systems, and the spray processes were monitored with diagnostic tools, including SprayWatch for measuring the temperature and velocity of the spray stream, and in situ coating property (ICP measurement) for measuring the stress state. Various spray parameters were applied to attain the best coating characteristics for high temperature applications. Selected coatings were exposed to high temperature corrosion conditions both in laboratory and actual power plant. The coatings were analyzed by microscopic means and mechanical testing. The application of process-structure-properties-performance methodology with the process monitoring, analysis of the coating characteristics, and results of corrosion performance are presented in this paper. [ABSTRACT FROM AUTHOR]

CrC-25(NiCr) coating is widely used in wear, erosion and corrosion applications. In the present study, D-gun-sprayed CrC-25(NiCr) coatings with and without 0.4 wt.% ceria incorporated were deposited on Superni 718, Superni 600 and Superco 605 substrates. Hot-corrosion runs were conducted in 40 %NaSO-40 %KSO-10 %NaCl-10 %KCl environment at 900 °C for 100 cycles. Corrosion kinetics was monitored using weight gain measurements. Characterization of corrosion products was carried out by field-emission scanning electron microscopy (FESEM)/energy-dispersive spectroscopy (EDS) and x-ray diffraction (XRD) techniques. It was observed that CrC-25(NiCr) coating with and without added ceria deposited on both of the Ni-based alloys showed resistance to corrosion under the given environment. Addition of ceria enhanced the adherence of the oxide to the coating during the corrosion run and reduced the overall weight gain. However, CrC-25(NiCr)-coated Superco 605 did not perform satisfactorily under this environment. [ABSTRACT FROM AUTHOR]

Thermal spraying of CrC-NiCr composites generates varying degrees of carbide dissolution into the Ni binder. During high-temperature exposure, the carbide dissolution zones precipitate high concentrations of small carbides which develop into finely structured networks. This raises the possibility of producing unique tailored carbide composite structures through the generation of controlled carbide dissolution and appropriate heat treatment. The first step in this process is to produce a supersaturated Ni-Cr-C solid solution from which the carbide phase could be precipitated. In a previous work, a broad range of plasma parameters were trialed to assess their effect on the degree of carbide dissolution at a fixed spray distance of 100 mm. The current two-part work builds on the most promising plasma parameters from those trials. Part 2 of this article series investigated the effect of spray distance on the compositional development in CrC-NiCr coatings during high-energy plasma spraying. The coating compositions were analyzed in detail and quantified through Rietveld fitting of the coating XRD patterns. Coating microstructural features were correlated with the observed variations in composition. The effect of the spray parameters and spray distance on the equilibrium coating compositions is discussed. [ABSTRACT FROM AUTHOR]

Thermal spraying of CrC-NiCr composites generates varying degrees of carbide dissolution into the Ni binder. During high-temperature exposure, the carbide dissolution zones precipitate high concentrations of small carbides which develop into finely structured networks. This raises the possibility of producing unique tailored carbide composite structures through the generation of controlled carbide dissolution and appropriate heat treatment. The first step in this process is to produce a supersaturated Ni-Cr-C solid solution from which the carbide phase could be precipitated. In a previous work, a broad range of plasma parameters were trialed to assess their effect on the degree of carbide dissolution at a fixed spray distance of 100 mm. The current two-part work builds on the most promising plasma parameters from those trials. In Part 1 of this two-part article series, the effect of spray distance on the extent of carbide dissolution and carbon loss during high energy plasma spraying was investigated. The effectiveness of solid shield and gas shrouding is contrasted, and the mechanisms by which they influence the degree of decarburization discussed. [ABSTRACT FROM AUTHOR]

The main goal of the present study is to explain synergistic extraction of nickel from simulated Cr-Ni electroplating bath solutions (SEBS) using 5,8-diethyl-7-hydroxydodecane-6-one oxime (LIX 63) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) as extractants by emulsion liquid membrane (ELM) technique. The importance of membrane composition and aqueous phase properties on nickel extraction percentage has been highlighted for the selective extraction of nickel. Some important parameters like acid concentration, stripping solution type and concentration, mixing speed, extractant concentrations, phase ratio, and surfactant concentration was studied to improve the extraction and stripping efficiencies. Higher than > 99% of nickel was recovered at optimum conditions within 6 min. The higher separation factors (βNi/Cr) were obtained as 580. As a result, the nickel extraction kinetic with D2EHPA has been defined as faster than LIX63. So, the kinetic transport of nickel mainly depends on LIX63 than D2EHPA. According to these results, D2EHPA behaves as a synergistic extractant in the present extraction mechanism. [ABSTRACT FROM AUTHOR]

Spinel nickel chromite nanoparticles were synthesized using a simple thermal treatment method. The effect of calcination temperatures on the final properties of obtained materials was carefully examined using various characterization techniques.The infrared spectra of nickel chromite (NiCr2O4) revealed the characteristic bonds of metal-oxygen for NiO and CrO bands around 600 and 470cm-1, respectively. The powder X-ray diffraction patterns exhibited the formation of normal spinel phase of NiCr2O4 in the calcination process at temperature between 550 and 850°C. From transmission electron micrographs, nanosized particles with average size of ~7-64nm were observed at calcination temperatures of 550-850°C, respectively. The calcined samples at 750 and 850°C exhibited paramagnetic behavior with g-factor values of 1.92 and 2.15, peak-to-peak line width of 25.59 and 117.02Oe and resonance magnetic field of 342.04 and 306.49Oe, respectively. Variation in the value of g-factor, peak-to-peak line width and resonance magnetic field can be attributed to the dipole-dipole and super exchange interactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] A study of the underwater performance of polymers in preventing leakage current shunting thin-film strain gauges. [•] Two-part silicone rubbers lead to very low underwater leakage currents even across gaps of 10μm. [•] The underwater leakage current amplitude can be linked to the cleanliness of the substrate prior to encapsulation. [Copyright &y& Elsevier]

In this report, the magnetic behaviour of bulk and nanoparticles of NiCrO under different applied magnetic fields has been investigated extensively. Nanoparticles of NiCrO (12 nm) were obtained by mechanical milling of polycrystalline powder prepared by polyol method. FC-ZFC measurement of bulk at different applied magnetic fields has revealed the existence of a ferrimagnetic transition around 66 K followed by an antiferromagnetic transition close to 30 K. However, its nano counterpart has shown remarkable change in magnetic properties-a suppression of ferrimagnetic transition accompanied by strengthening low-temperature magnetic phase and observation of a new transition at 90 K ( T), which is weakly magnetic in nature. The frequency-dependent ac susceptibility data of nanoparticles have been fitted to the well-known de Almeida-Thouless equation and a H dependence of the low-temperature peak is observed with a resulting zero-field freezing temperature ( T) equal to 10.1 K. Further, the dynamical behaviour near freezing temperature has been analysed in terms of critical behaviour and the obtained fitted parameter values were found to be τ (relaxation time constant) = 3.6 × 10 s, T = 8.7 K and zν = 11.1. Moreover, Vogel-Fulcher law has been used to understand the nature of freezing transition, and the parameters after fitting are obtained as E/ k = 58.9 K, τ = 5.22 × 10 s and T = 8.03 K. Finally, the spin-glass phase is concluded. Moreover, in contrast to bulk, the H dependence of freezing temperature of nanoparticles sample (75 h) does support the 2D surface-like spin-glass nature. [ABSTRACT FROM AUTHOR]

The reaction between Ln(III) chloride and NiCl2·4H2O salts in presence of a multidentate sterically unencumbered ligand, (E)-2,2'-(2-hydroxy-3-((2-hydroxyphenylimino)methyl)-5-methylbenzylazanediyl)diethanol (LH4) leads to the synthesis of four isostructural pentanuclear hetereometallic complexes [Ni2Dy3(LH)4]Cl (1), [Ni2Dy3(LH)4]Cl (2), [Ni2Tb3(LH)3(LH2)]Cl2 (3), [Ni2 Ho3 (LH)3 (LH2)]Cl2 (4) with unprecedented topology. Here the two compounds 1 are 2 are monocationic and crystallize in chiral space group, P212121 whereas compounds 3 and 4 are dicationic and crystallize in achiral space group P21/n. The total metal framework, {Ni2Ln3} unit is held by four triply deprotonated ligands [LH]3- in 1 and 2 whereas in case of 3 and 4 three triply deprotonated [LH]3- and one doubly deprotonated [LH2]2- ligands are involved. In these complexes both the lanthanide ions and the nickel(II) ions are doubly bridged and the bridging is composed of oxygen atoms derived from either phenolate or ethoxide groups. The analysis of SQUID measurements reveal a high magnetic ground state and a slow relaxation of the magnetization with two relaxation regimes for 1. For the thermally activated regime we found an effective energy barrier of Ueff = 85 K. Micro Hall probe loop measurements directly proof the single-molecule magnet (SMM) nature of 1 with a blocking temperature of TB = 3 K and an open hysteresis for sweep rates faster than 50 mT/s. [ABSTRACT FROM AUTHOR]

The monofunctional proline dehydrogenase (ProDH) from Mycobacterium tuberculosis performs the flavin-dependent oxidation of l-proline to Δ1-pyrroline-5-carboxylate in the proline catabolic pathway. The ProDH gene, prub, was cloned into the pYUB1062 vector, and the C-terminal His-tagged 37 kDa protein was expressed and purified by nickel affinity chromatography. A steady-state kinetic analysis revealed a ping-pong mechanism with an overall kcat of 33 ± 2 s–1 and Km values of 5.7 ± 0.8 mM and 3.4 ± 0.3 μM for l-proline and 2,6-dichlorophenolindophenol (DCPIP), respectively. The pH dependence of kcat revealed that one enzyme group exhibiting a pK value of 6.8 must be deprotonated for optimal catalytic activity. Site-directed mutagenesis suggests that this group is Lys110. The primary kinetic isotope effects on V/KPro and V of 5.5 and 1.1, respectively, suggest that the transfer of hydride from l-proline to FAD is rate-limiting for the reductive half-reaction, but that FAD reoxidation is the rate-limiting step in the overall reaction. Solvent and multiple kinetic isotope effects suggest that l-proline oxidation occurs in a stepwise rather than concerted mechanism. Pre-steady-state kinetics reveal an overall kred of 88.5 ± 0.7 s–1, and this rate is subject to a primary kinetic isotope effect of 5.2. These data confirm that the overall reaction is limited by reduced flavin reoxidation in the second half-reaction. [ABSTRACT FROM AUTHOR]

Abstract: Raman and infrared spectroscopy were performed on synthesized spinel oxide powders of solid solution , over the full range of composition , to determine the dependence of the vibrational modes on the divalent cation, which occupies the tetrahedral site of the normal spinel lattice. X-ray diffraction shows a nearly linear change in the lattice parameter of the solid solution. Our data agree with literature values for the pure chromites, and . Solid solution data are reported here for the first time. All observed vibrational modes exhibit one-mode behavior and increase in wavenumber when nickel is replaced by magnesium. The wavenumbers of the highest-wavenumber Raman mode, , and the two higher-wavenumber infrared modes, and , do not significantly change with substitution of the divalent cation, while the lower-wavenumber Raman and infrared modes are affected by this cation substitution on the tetrahedral site. The and modes exhibit a nonlinear increase in wavenumber. [Copyright &y& Elsevier]