X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel–copper spinel manganites

The surface of non-stoichiometric nickel and nickel–copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p_3/2 core levels (M=Ni, Cu, Mn). In particular, both Cu²⁺ and Cu⁺ were evidenced in the structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p_3/2 region, which was explained by the displacement of some Ni²⁺ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel–copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value.     

Shear stress measurement in nickel and nickel–60 wt% cobalt during one-dimensional shock loading

The shear strength of pure nickel (Ni), and its alloy, Ni–60Co (by wt%), has been determined during one-dimensional shock loading in the impact stress range 0–10 GPa. The influence of the reduced stacking fault energy (SFE) for the Ni–60Co has been investigated. The shear strength (τ) and the lateral stress (σ _y ) both increase with the impact stress for each material. The shear stress has been found to be higher in the nickel than in the alloy. The progressive decrease of the lateral stress behind the shock front indicates an increase of the shear strength. A more complex mechanism of deformation has been found for the alloy since twin formation has been observed in the microstructure, while none has been seen in nickel. It is thought that mechanical twinning plays a predominant role in the deformation mechanism of the alloy resulting in the reduction of the material strength.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

Magnetic,dielectric and nonlinear optical absorption studies of nickel–zinc ferrite with Mg2+ doping

Journal of Materials Science: Materials in Electronics - Ni0.5?xMgxZn0.5Fe2O4 (x&nbsp;=&nbsp;?0.00, 0.05, 0.10 and 0.15) samples were prepared by the sol–gel method. The...     

Field-activated,pressure-assisted combustion synthesis of tungsten carbide–nickel composites

The field-activated, pressure-assisted combustion synthesis (FAPACS) process, which combines the simultaneous synthesis and densification of materials, was utilized to produce WC–10 wt.% Ni composites from reactant mixtures of W, Ni, and different carbon sources. The product composition, density, and microhardness of WC–Ni composites fabricated through the FAPACS process were investigated. The results show that the Vickers microhardness and toughness were 1287 kg/mm² and 7.8 MPa m^1/2 for the product made with activated carbon, and 1424 kg/mm² and 5.9 MPa m^1/2 with carbon black.     

Synthesis,characterization and optical properties of neodymium doped nickel ferrite nanoparticles prepared by novel sol–gel method

Neodymium doped nickel ferrite nanoparticles were successfully synthesized by novel sol–gel method with the aid of nickel(II) nitrate, iron(III) nitrate, neodymium(III) nitrate and lactose without adding external surfactant. Moreover, lactose plays role as capping agent, reducing agent, and natural template in the synthesis of NiFe_2?xNd_xO₄ nanoparticles. The as-synthesized NiFe_2?xNd_xO₄ nanoparticles were characterized by means of several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and UV–Vis diffuse reflectance spectroscopy. The magnetic properties of as-prepared NiFe_2?xNd_xO₄ nanoparticles were also investigated with vibrating sample magnetometer. To evaluate the photocatalyst properties of nanocrystalline NiFe_2?xNd_xO₄, the photocatalytic degradation of methyl orange under ultraviolet light irradiation was carried out.     

Synthesis of nickel–rubber nanocomposites and evaluation of their dielectric properties

Nanocomposites based on natural rubber and nano-sized nickel were synthesized by incorporating nickel nanoparticles in a natural rubber matrix for various loadings of the filler. Structural, morphological, magnetic and mechanical properties of the composites were evaluated along with a detailed study of dielectric properties. It was found that nickel particles were uniformly distributed in the matrix without agglomeration resulting in a magnetic nanocomposite. The elastic properties showed an improvement with increase in filler content but breaking stress and breaking strain were found to decrease. Dielectric permittivity was found to decrease with increase in frequency, and found to increase with increase in nickel loading. The decrease in permittivity with temperature is attributed to the high volume expansivity of rubber at elevated temperatures. Dielectric loss of blank rubber as well as the composites was found to increase with temperature.     

Oxidized nickel–titanium foams for bone reconstructions: chemical and mechanical characterization

This work examines NiTi foams that have been treated using a new oxidation treatment for obtaining Ni-free surfaces that could allow the ingrowth of living tissue, thereby increasing the mechanical anchorage of implants. A significant increase in the real surface area of these materials can decrease corrosion resistance and favour the release of Ni. This chemical degradation can induce allergic reactions or toxicity in the surrounding tissues. This study determines the porosity, surface characteristics, phase transformation, mechanical properties, corrosion behaviour and Ni release into the simulated body fluid medium of foams treated by a new surface oxidation treatment that produces Ni-free surfaces. These foams have pores in an appropriate range of sizes and interconnectivity, and thus their morphology is similar to that of bone. Their mechanical properties are biomechanically compatible with bone. The titanium oxide on the surface significantly improves corrosion resistance and decreases nickel ion release, while barely affecting transformation temperatures.     

Improved adhesion between nickel–titanium SMA and polymer matrix via acid treatment and nano-silica particles coating

Shape memory alloy (SMA) composites are the desirable candidate for smart materials that used in intelligent structures. However, the overall mechanical performance of SMA composites depends immensely on the quality of the interaction between SMA and polymer matrix. Therefore, it is necessary to find out an approach to enhance the interfacial property of this composite. In this paper, we modified nickel–titanium SMA wire with nano-silica particles before and after acid treatment. The modification effect on the interfacial strength between SMA and epoxy resin was evaluated. Contact angle analysis, scanning electron microscopy (SEM) observation, and single fiber pull-out test were carried out. The bonding characteristics between modified wire and liquid/cured resin were investigated. We then embedded SMA wire into woven glass fabric/epoxy composite laminates, and manufactured this hybrid composites via vacuum assisted resin transfer molding processing. Three-point-bending test of the hybrid composites was performed to validate the modification effect. Fiber pull-out experiment demonstrates that the interfacial shear strength increases by 6.48% by nano-silica particles coating, while it increases by 52.21% after 8 h acid treatment and nano-silica particles coating simultaneously. For hybrid composites, flexural strength of the two specimens increases by 19.8 and 48.2%, respectively. In SEM observation, we observed large debonding region in unmodified composites, while interfacial adhesion between modified wire and epoxy keeps strong after flexural damage.     

One-pot synthesis of nickel oxide–carbon composite microspheres on nickel foam for supercapacitors

Using glucose and Ni(NO₃)₂ as precursors, the nickel oxide–carbon (NiO–C) composites are directly formed on the nickel foam by a one-pot hydrothermal method. The product presents a spherical morphology with the carbon component in the composite being a non-graphitic phase. The presence of NiO provides additional pseudo-capacitance for the electrode materials and the composites exhibit superior specific capacitance to the pure carbon materials formed on the nickel foam. Apart from that, compared with the nickel sheet substrate, the utilization of the nickel foam benefits for the achievement of higher performance and stability owing to its unique 3D structure. The highest specific capacitance for the NiO–C–nickel foam electrode of 265.3 F g⁻¹ is obtained at a discharge current density of 0.25 A g⁻¹.     

Influence of annealing on texture and magnetic properties of 18% nickel, 2400 MN m−2grade maraging steel

Abstract

The texture incorporated during cold rolling of maraging steel persists even when the samples are annealed at temperatures close to the melting point. The texture influences the microstructural developments observed following aging, which in turn affects the magnetic properties of maraging steel. The maximum coercive field, observed after aging at about 700°C, increased from about 11 140 A m^?1 in the as rolled and aged condition to about 14 720 A m^?1 in the specimen annealed at 1000°C before aging. The corresponding saturation magnetisation values also increased from about 1·040 to about 1·300 T. The prior annealing affects the morphology of the precipitates as well as the reverted austenite.

MST/3129     

Colloidal nanometric particles of nickel deposited on γ-alumina: characteristics and catalytic properties

The present paper deals with supported nanoparticles of metallic nickel prepared by impregnation of an organometallic colloidal precursor (NiRC complex) on -alumina. The obtained supported materials (NiRCS complex) were characterized by STEM, EELS, XRD and TGA and tested in the hydrogenation reaction of benzene and styrene both in the gas and liquid phases. EELS and STEM studies showed that the metallic nickel nanoparticles of the NiRC precursor were well dispersed (1–3 nm) on the support, without size variation during the impregnation step. However, particle growth in NiRCS was observed in samples used after reaction tests. On the other hand, TGA experiments showed that the nickel phase was inserted in an organic matrix which remained in the supported material after impregnation. This organic matrix should be partly removed or totally decomposed by washing with an appropriate solvent or thermal treatment above about 250°C under N₂, H₂ or air atmosphere respectively. The supported nickel particles were active in the gas phase hydrogenation of benzene in the temperature range of 150–200°C and their activity was enhanced by partial removal of the organic matrix with an organic solvent (e.g. ethanol) or by its total thermal decomposition. They were also found very active in the gas phase hydrogenation of styrene at room temperature. Finally, the supported nickel particles exhibited good hydrogen reservoir properties in organic solvent media.     

Effects of phosphorus on creep behaviour of nickel and Ni–20Cr and on creep and strength of Nimonic 80A

Abstract

The influence of P on the creep behaviour of Ni, Ni–20Cr (wt-%), and Nimonic 80A was investigated by carrying out creep tests under various loads and at different temperatures. After creep fracture the samples were investigated using optical, scanning electron, and transmission electron microscopy. The grain boundary segregation was examined using Auger electron spectroscopy (AES). It was found that P segregates to the grain boundaries in all the materials investigated. The creep rate of Ni–20Cr and Nimonic 80A is decreased by the addition of P. Grain boundary segregation of P and its influence on strength was also investigated using AES for specimens aged between 600 and 700°C after fracture by a tensile test inside an ultrahigh vacuum chamber. Maxima of tensile strength are observed to be time dependent as a result of carbide precipitation, which is affected by the P segregation.

MST/1679     

Experimental study on capillary and mechanical properties of a porous nickel–copper composite

A novel porous nickel–copper composite was designed and fabricated by sintering a mixture of a high-porosity open-cell copper foam plate and fine nickel powder. The microstructure of the porous nickel–copper composite was characterised by the scanning electron microscope. The effects of sintering temperature and dwelling time on the sintering shrinkage, sintered porosity, capillary performance and mechanical properties of the porous composite and monoporous sintered nickel powder were investigated experimentally. The nickel–copper composite presented significant lower sintering shrinkage, higher porosity, lower tensile strength and better capillary performance than the sintered nickel powder under all sintering conditions. The sintering temperature has more influence than the dwelling time on both the capillary performance and tensile strength of the sintered composite.     

Hydrogen production of nickel–scandia-stabilized zirconia and copper/nickel–scandia-stabilized zirconia catalysts through steam methane reforming for solid oxide fuel cell operation

In this study, the catalytic activities of the steam methane reforming (SMR) reactions with two catalysts, including nickel–scandia-stabilized zirconia (Ni–SSZ) and copper/nickel–scandia-stabilized zirconia (Cu/Ni–SSZ), were examined and compared. The microstructure and crystallinity of the as-prepared catalysts were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Mass spectrometer was applied in the outlet streams, in order to simultaneously monitor the time-dependent kinetics in the reactor for an activity test and conversion examination. Finally, thermogravimetric analysis (TGA) and Raman spectrometer were implemented for further verification of carbon residuals on the catalysts. It was found that the incorporation of Cu on Ni–SSZ imposed significant constraints on the growth of nickel crystallites from NiO during the annealing process in reducing atmospheres. The methane conversion of Ni–SSZ and Cu/Ni–SSZ catalysts (annealed at 300 °C for 2 h) was 36.2 and 26.0%, respectively. However, the amount of carbon residuals on Cu/Ni–SSZ catalyst (300 °C for 2 h) was 18.6%, which is lower than that of the Ni–SSZ catalysts (33.2%) from TGA results. Further Raman experiments revealed that more graphite-like carbon residuals and less defects or amorphous carbons (I_G/I_D?=?2.0) were found in the case of Cu/Ni–SSZ catalysts (300 °C for 2 h). Among the catalysts in this study, the Cu/Ni–SSZ catalyst (300 °C for 2 h) is considered as a promising catalyst for SMR reaction, since it has a fair methane conversion, and characterized higher CO₂ selectivity and lower CO selectivity without compromising the hydrogen purity. More importantly, the least amount of carbon residuals was found in Cu/Ni–SSZ catalyst (300 °C for 2 h), which assured a better lifetime.     

Titanium diboride–nickel graded materials prepared by field-activated, pressure-assisted synthesis process

The formation of four-layered functionally graded material (FGM) samples of TiB₂–Ni/TiB₂–Ni₃A + Ni/Ni₃Al/Ni by field-activated, pressure-assisted synthesis process (FAPAS) was investigated. The microstructure, phase composition of the interfaces, and mechanical properties of the graded material were characterized. Elemental concentration profiles across interfaces between layers showed significant interdiffusion, indicative of formation of good bonds. The measured microhardness values of the sample increased monotonically from the nickel substrate to the surface layer (TiB₂–Ni). The values ranged from about 360 to over 3500 HK over a distance of 2 mm. The results of this investigation demonstrate the feasibility of the FAPAS process for rapid formation of FGMs with good diffusion bonds.     

Electrical and optical properties of single crystalline α-Al2O3 doped with nickel

Nickel, substituting for aluminium in α-Al₂O₃ acts as an acceptor with a level ∼2.46 eV above the conduction band if a large polaron model applies, ≅ 2.57eV−H(μ _h) above the band if a small polaron model applies. It is present as Ni³⁺ at high, and as Ni²⁺ at low, oxygen pressures, the concentration of Ni³⁺ being reduced to one-half of its high value at =1 Pa. Analysis of the data provides proof that the native defect compensating the charge of Ni²⁺ (=ni _al ^′ ) is V _O ^2. , Al _i ^3. being a minority species; H _F,Al−1/2H _s=121 kJ mol⁻¹.