The influence of grain size and texture on the Young's modulus of nanocrystalline nickel and nickel–iron alloys

Hardness and Young's modulus were measured by nanoindentation on a series of electrodeposited nanocrystalline nickel and nickel–iron alloys. Hardness values showed a transition from regular to inverse Hall–Petch behaviour, consistent with previous studies. There was no significant influence of grain size on the Young's modulus of nanocrystalline nickel and nickel–iron alloys with grain sizes greater than 20?nm. The Young's modulus values for nanocrystalline nickel and nickel–iron alloys for grain sizes less than 20?nm were slightly reduced when compared to their conventional (randomly oriented) polycrystalline counterparts. The observed trend with decreasing grain size was found to be consistent with composite model predictions that consider the influence of intercrystalline defects. However, there was some notable variability of the measured values when compared to the model predictions. Three theoretical relationships were used to characterise the anisotropic elastic behaviour of these materials. As a result, texture was also considered to have an influence on the measured Young's modulus and used to explain some of the observed variability for the entire grain size range (9.8–81?nm).     

Controlled synthesis and magnetic properties of nickel phosphide and bimetallic iron–nickel phosphide nanorods

Nickel phosphide (Ni₂P) and bimetallic iron–nickel phosphides [(Fe _x Ni _y )₂P] nanorods were fabricated by a seeded growth strategy. This strategy utilized pre-synthesized Fe₃O₄ nanoparticles as seeds and the thermal decomposition of metal precursors by multiple injections in a solution containing trioctylphosphine and didodecyldimethylammonium bromide (DDAB). The nanorods were characterized by transmission electron microscopy, X-ray diffraction, and magnetic measurements were carried out using superconducting quantum interference device (SQUID). The rod length was tunable, ranging from 10 to 110 nm depending on the number of injections, whereas the diameter of the rods was nearly 6 nm. It was found that the rod size increased with the number of injections under the constant total injection concentration and reaction time. In addition, the effect of the DDAB quantity used as a co-surfactant was studied, which showed that an optimum quantity was required to achieve uniform nanorods. Magnetic characterizations were performed over the two kinds of nanorods to identify their respective magnetic phases. The results demonstrated that the Ni₂P nanorods were defined as a Curie–Weiss paramagnet, whereas the (Fe _x Ni _y )₂P nanorods exhibited superparamagnetic characteristics.     

The production of nickel–alumina composite coating via electroplating

A series of electroplating works have been conducted to investigate the best condition for the coelectrodeposition of nickel–alumina (Ni/α–Al₂O₃) composite coating. Co-electrodeposition was done onto mild steel as cathode at ambient temperature (27°C) with current density of 30 mA/cm² under α-Al₂O₃ concentration of 2 g/l and various agitation speeds of 50, 100, 150, 200, and 250 rpms. The cross-section of the composite coatings portrayed α-Al₂O₃ particles was co-deposited. Under field emission scanning electron microscopy analysis, the coating shows a coarse surface morphology, while cross-sectional microstructures shows a compact embedding of α-Al₂O₃ particle in the Ni matrix. Elemental analysis by EDX detected the presence of Ni and α-Al₂O₃. Vickers microhardness testing shows that the coating hardness increases almost 60% at the highest agitation speed, i.e., 250 rpm.     

Hydrogen storage characteristics of nanograined free-standing magnesium–nickel films

Free-standing magnesium–nickel (Mg–Ni) films with extensive nanoscale grain structures were fabricated using a combination of pulsed laser deposition and film delaminating processes. Hydrogen sorption and desorption properties of the films, free from the influence of substrates, were investigated. Oxidation of the material was reduced through the use of a sandwiched free-standing film structure in which the top and bottom layers consist of nanometer-thick Pd layers, which also acted as a catalyst to promote hydrogen uptake and release. Hydrogen storage characteristics were studied at three temperatures, 296, 232, and 180°C, where multiple sorption/desorption cycles were measured gravimetrically. An improvement in hydrogen storage capacity over the bulk Mg–Ni target material was found for the free-standing films. As shown from a Van’t Hoff plot, the thermodynamic stability of the nanograined films is similar to that of Mg₂Ni. These results suggest that free-standing films, of which better control of material compositions and microstructures can be realized than is possible for conventional ball-milled powders, represent a useful materials platform for solid-state hydrogen storage research.     

Magnetic properties of substitutional solid solutions of nickel and iron hexacyanoferrate–hexacyanochromate

In order to evaluate the influence of substitution at the central metal ion position in transition hexacyanometallates in some detail, the magnetic studies were carried out on a series of solid solutions of metal hexacyanometallates of the composition M[Fe^II(CN)₆]_{1? x} [Cr^III(CN)₆] _x , where M?=?Ni^II and Fe^III. The temperature and field dependences of magnetization were studied using a superconducting quantum interference device magnetometer. The field dependence of the samples at 5?K shows a hysteresis behaviour. For M?=?Ni^II, the transition temperature increases with increase in the substitution of low-spin Fe(III) by Cr(III) in the hexacyanometallate unit. The saturation magnetization was found to decrease with increase in the iron concentration. The observed variation in the magnetic properties, such as the value of T _C and the nature of magnetic ordering, is attributed to the variation in the composition of the transition-metal ion in the coordination sphere of carbon. On the other hand, for M?=?Fe^III, the transition temperature and saturation magnetization remained almost unchanged, indicating that substitution at the carbon coordination site did not produce any change in the magnetic interaction among the transition-metal ions through the cyanide ions.     

Magnetic anisotropy of Pm impurity in rare earth–nickel compound

Low-temperature nuclear orientation was applied to study hyperfine interactions of ¹⁴²Pr, ¹⁴⁷Nd and ^143,144Pm nuclei in Pr^0.5Nd^0.5Ni single crystal. Angular distributions, temperature dependence and external magnetic field effects on the γ-ray anisotropy are presented. A Nd-Pm exchange interaction seems to dominate the magnetic properties of Pm ions in this system. This revised version was published online in August 2006 with corrections to the Cover Date.     

The influence of nickel dopant on the microstructure and optical properties of SnO2 nano-powders

The microstructure and optical properties of Ni-doped SnO2 nano-powders are studied in detail. By Ni-doping, not only the grain size reduces, but also the grain shape changes from nano-rods to spherical particles. The crystallization becomes better with annealing temperature increasing. The band gap energy decreases as nickel doping level increases. The sp-d hybridization and alloying effect due to amorphous SnO2-x phase should be responsible for the band gap narrowing effect. Nickel dopant does not change the photoluminescence （PL） peak positions.     

Effects of nickel on the crystallization of Zr70Cu20Ni10 amorphous alloy

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are employed to investigate the effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy. We have found that the crystallization process of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is strongly influenced by the addition of nickel. Addition of 10 at% Ni to the Zr₇₀Cu₃₀ amorphous alloy makes the crystallization process proceed from a single-stage mode to a double-stage mode. The activation energy for crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is calculated to be about 388kJ·mol^-1 on the basis of the Kissinger equation. The effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy are discussed in terms of the genetics of metals.     

The effect of vacuum annealing on the remediation abilities of iron and iron−nickel nanoparticles

Zero-valent iron nanoparticles are effective remediators of uranium from solution. It is postulated that the improved core crystallinity and the migration of impurity phases to the nanoparticle surfaces induced by annealing may improve their corrosion resistance and reactive lifespan. The ability of annealed and non-annealed Fe and FeNi nanoparticles to remediate a U-contaminated effluent from AWE, Aldermaston was investigated. Nanoparticles (of diameter typically between 0 and 100 nm) were introduced to the effluent and allowed to react for 7 days during which the liquid and nanoparticulate solids were periodically sampled. In all the systems, the maximum U-uptake occurred within 1 h of introduction, with variable efficiency. The Fe nanoparticles removed 98% of the total U from solution, resulting in a final U-concentration of <4 μg/L. A rapid release of Fe into solution was recorded early in the reaction period: attributed to limited partial dissolution of the nanoparticles. Annealing the Fe nanoparticles did not affect their efficiency but the dissolution of Fe was significantly reduced and X-ray Photoelectron Spectroscopy indicated slower progressive oxidation. The performance of the FeNi nanoparticles was significantly improved by annealing, with U-uptake increasing from 50 to 94%. Although the dissolution of Ni was completely inhibited by annealing, the Fe dissolution increased compared to that observed for the non-annealed FeNi nanoparticles, in contrast to behaviour exhibited by Fe-annealed nanoparticles. In all the systems, U was reduced to U(IV) and retained on the surfaces of the nanoparticulate solids for up to 48 h; the U-stability was not affected by annealing the Fe or the FeNi nanoparticles before use.     

The interaction of dislocation loop and γ' precipitate in nickel based alloys

The nucleation and growth of interstitial loops during irradiation has a : ontrolling effect on the subsequent swelling behaviour of metals. In nickel based alloys containing ordered γ' precipitate (Ni₃Al, Ti), interactions occur between the nucleated loops and γ' particles. This effect has been studied in two nickel based alloys using a High Voltage Electron Microscope.

For the case of Nimonic 80A alloy containing 18% volume fraction : gamma;' precipitate, dislocation loop-particle interactions obeyed the developed isotropic elasticity theory.²'³'¹² Consequently, rather low dislocation densities were developed and the swelling resistance was high during electron irradiation. In Nimonic 115A alloy, loop nucleation and growth was dependent on the availability of interfacial dislocation surrounding the γ' particles.

With regard to the swelling behaviour of γ' hardened alloys, it : s concluded that several mechanisms contribute to make these materials resistant.

Coherency strains at the γ' particles reduce the density of : limbing dislocations.

The γ' precipitate affects the climb efficiency of the : ucleated dislocations by:

pinning the dislocation line, thus introducing a line tension force : hich opposes dislocation climb and reduces swelling;

reducing the available volume of material in which dislocation loops : an nucleate and grow.     

Effect of nickel segregation on CuΣ9 grain boundary undergone shear deformations

Impurity segregation at grain boundary(GB) can significantly affect the mechanical behaviors of polycrystalline metal. The effect of nickel impurity segregated at Cu GB on the deformation mechanism relating to loading direction is comprehensively studied by atomic simulation. The atomic structures and shear responses of Cu Σ9(114) 110 and Σ9(221) 110 symmetrical tilt grain boundary with different quantities of nickel segregation are analyzed. The results show that multiple accommodative evolutions involving GB gliding, GB shear-coupling migration, and dislocation gliding can be at play, where for the 2ˉ21ˉ shear of Σ9(114) 110 the segregated GBs tend to maintain their initial configurations and a segregated GB with a higher impurity concentration is more inclined to be a dislocation emission source while maintaining the high mechanical strength undergone plastic deformation for the 11ˉ4ˉ shear of Σ9(221) 110. It is found that the nickel segregated GB exerts a cohesion enhancement effect on Cu under deformation: strong nickel segregation increases the work of separation of GB, which is proved by the first-principles calculations.     

Sonocatalytic injury of cancer cells attached on the surface of a nickel–titanium dioxide alloy plate

The present study demonstrates ultrasound-induced cell injury using a nickel–titanium dioxide (Ni–TiO₂) alloy plate as a sonocatalyst and a cell culture surface. Ultrasound irradiation of cell-free Ni–TiO₂ alloy plates with 1 MHz ultrasound at 0.5 W/cm² for 30 s led to an increased generation of hydroxyl (OH) radicals compared to nickel–titanium (Ni–Ti) control alloy plates with and without ultrasound irradiation. When human breast cancer cells (MCF-7 cells) cultured on the Ni–TiO₂ alloy plates were irradiated with 1 MHz ultrasound at 0.5 W/cm² for 30 s and then incubated for 48 h, cell density on the alloy plate was reduced to approximately 50% of the controls on the Ni–Ti alloy plates with and without ultrasound irradiation. These results indicate the injury of MCF-7 cells following sonocatalytic OH radical generation by Ni–TiO₂. Further experiments demonstrated cell shrinkage and chromatin condensation after ultrasound irradiation of MCF-7 cells attached on the Ni–TiO₂ alloy plates, indicating induction of apoptosis.     

Precipitation of γ′ phase and helium bubbles during proton and α-particle irradiation of nickel–silicon

Segregation of silicon was induced by light-ion irradiation at elevated temperatures in Ni–8Si specimens. Its occurrence at external surfaces, helium-induced cavities, dislocation loops, coherent twin boundaries, grain boundaries, and precipitate-matrix interfaces has been investigated by transmission electron microscopy. Layers of ordered γ^′ (Ni₃Si) phase were formed at most of these point defect sinks. The behaviour of grain boundary precipitation was found to be exceptional in various respects. In particular, a high rate of precipitation distinguishes grain boundaries from all other kinds of point defect sinks investigated here. This phenomenon of rapid precipitation was found to be adjoined to precipitation-driven grain boundary migration and is attributed to a radiation-induced “discontinuous” precipitate reaction. Observations of helium bubble distributions created during α-particle irradiations at growing dislocation loops and at migrating grain boundaries are also briefly discussed.     

61Ni Mössbauer study of the surface hyperfine magnetic field in nickel

⁶¹Ni Mössbauer measurements have been performed at 4.2 K on spherical Ni particles with an average diameter of 100 and 30 Å, covered with a protective layer of SiO. Their spectra contain a surface component with a significantly reduced hyperfine magnetic field as compared with the field in the bulk. This result confirms recent theoretical predictions.     

First observation of lasing at 231 Å in neon-like nickel using the prepulse technique

We report lasing for the first time in nickel on the neon-like J=01, 3p3s transition at 231 Å as well as several weaker transitions including the J=2»1 lines at 298 Å and 304 Å. Amplification is seen only when the prepulse technique of using a low intensity prepulse before the main optical drive pulse is used to illuminate the nickel target. The prepulse technique is also shown to produce lasing in copper and dramatically improve the output of the germanium laser.     

Cation distribution by Rietveld,spectral and magnetic studies of chromium-substituted nickel ferrites

Ultrafine crystals of chromium-substituted nickel ferrite were prepared by wet chemical co-precipitation method using sulphates of respective metal ions. Formation of these materials has been confirmed by X-ray powder diffraction method. The fine crystal nature of these materials is evidenced from scanning electron microscope (SEM). Cation distribution has been investigated using X-ray diffraction technique. Cation distribution indicates that chromium occupy octahedral site for all the values of composition x. The saturation magnetization and magneton number both are decreasing with increase of chromium concentration x. The decrease in saturation magnetization and magneton number is attributed to the substitution of the Cr³⁺ ions. Curie temperature (T _C ) from susceptibility plot is found to decrease with Cr concentration x. Curie temperature of all the compositions are also obtained theoretically and it agrees with observed Curie temperature.     

Studies on the characteristics of Barkhausen emission and evaluation of the critical fields for domain wall notion in nickel

Acoustic Barkhausen Emission(ABE)and ElectromagneticBarkhausen Emission(EBE)have been measured.Explanations of the re-sponse of nickel to an applied magnetic field are considered using energydensity diagrams and critical fields deduced using Kersten's modifiedtheory.These theoretical models are correlated with ABE and EBEmeasurements,providing further confirmation of the origins of ABE beingnon-180°domain wall motion.This paper also shows that the motion ofdomain walls,on increasing the magnetising fields from saturation to satu-ration,follows the sequence of 71°-180°-109°.Values of criticalfields correponding to 71°,180°and 109°wall motions in nickel are de-termined using these techniques.     

Synthesis and characterization of nickel–manganese oxide via the hydrothermal route for electrochemical capacitors

Nano-sized and well dispersed manganese oxide and nickel–manganese oxide (Ni–Mn–O) powders are synthesized via the hydrothermal route. The addition of nickel ions significantly affects the morphology, particle size and the electrochemical properties of the obtained powders. Adding nickel ions results in a significant change in the shape of the powders from rod-like to plate-like. The electrochemical analysis of the electrode reveals that the specific capacitance of the synthesized powders is greatly increased with the addition of nickel ions. When the hydrothermal temperature is increased to 125 °C, the specific capacitance also increases to 284 F/g and decreases by about 4% after 1500 cycles of charge and recharge. Ni–Mn–O is considered to be a promising material for the electrodes used in electrochemical capacitors.     

The nature of the C-defects in nickel and their rôle in the interpretation of radiation damage in metals

In previous Perturbed-Angular-Correlation (PAC) studies of the - emission of ¹¹¹In probe nuclei in cold-worked or particle-irradiated nickel, it has been found that thermal annealing in the temperature regime of recovery stage III leads to the formation of so-called C-defects (Cubic defects). This is indicated by the occurrence of a new frequency of about 80 Mrad/s, in addition to the frequency (200 Mrad/s) that is due to ¹¹¹In on substitutional sites. Obviously, the C-defects are complexes consisting of ¹¹¹In and the intrinsic point-defect species that migrates freely in recovery stage III. Therefore, they have played an important rôle in the long-standing controversy on whether the recovery-stage-III defects are vacancies (one-interstitial model) or self-interstitials (two-interstitial model). The present paper reports on a novel experimental effort to reveal the nature of the C-defects by combining PAC studies on nickel samples differently pretreated in a systematic way, investigations of the Extended X-ray Absorption Fine Structure (EXAFS) on In-doped nickel, and measurements of the decay rate of ¹¹¹In nuclei in the Electron-Capture-Induced Decay (ECID). On the basis of the results of these experiments it is concluded that the defects trapped by substitutional ¹¹¹In atoms (In_s) in recovery stage III are self-interstitials (I), as expected according to the two-interstitial model. Moreover, there is evidence that the C-defects are In interstitials on tetrahedral sites (In_i) that form exclusively in the vicinity of the specimen surface from In_s – I pairs via the reaction In_s+I In_i.