Effect of irradiation on the microstructure and mechanical behavior of nanocrystalline nickel

The effect of 4.0 MeV proton irradiation on the microstructure and mechanical properties of nanocrystalline (nc) nickel was investigated. The irradiation damage induced in the sample was of the order of 0.004 dpa. Transmission electron microscopy of irradiated samples indicated the presence of dislocation loops within the grains. An increase in hardness and strain-rate sensitivity (m) of nc-Ni with irradiation was noted. The rate-controlling deformation mechanism in irradiated nc-Ni was identified to be interaction of dislocations with irradiation-induced defects. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Gibbs energy of formation of nickel orthosilicate (Ni2SiO4)

Two solid state galvanic cells:Pt, Ni + Ni2Si04 + Si02/(Y203)Zr02/Ni + + NiO, Pt (1) and Pt, Ni + NizSiOj + Si02/CaF2/Ni + + NiO, Pt (11) have been employed for the determination of the Gibbs' energy of formation of nickel orthosilicate(Ni2Si04) from nickel oxide and quartz. The emf of cell (I) was reversible and reproducible in the temperature range 925 to 1375K whereas emf of cell (11) drifted with time and changed polarity. From the results of cell (I), the Gibbs' energy of formation of nickel silicate is obtained as,2Ni0 (r.s.) + Si02 (quartz) + Ni2Si04 (olivine)Gibbs' energy of formation of the spinel form of Ni2Si04 is obtained by combining the data for olivine obtained in this study with high pressure data on olivine to spinel transition reported in the literature. The complex time dependence of the emf of cell (11) can be rationalised on the basis of formation of calcium silicates from calcium oxide, generally present as an impurity in the calcium fluoride electrolyte, and silica. The emf of cell (11) is shown to be the function of the activity of calcium oxide at the electrolyte/ electrode interface. The results provide strong evidence against the recent suggestion of mixed anionic conduction in calcium fluoride.

Solubility and activity of oxygen in liquid nickel in equilibrium with -Al2O3 and NiO.(1+x)Al2O3

The limiting solubility of oxygen in liquid nickel in equilibrium withα-alumina and nickel aluminate has been measured by inert gas fusion analysis of suction samples in the temperature range 1730 to 1975 K. The corresponding oxygen potential has been monitored by a solid electrolyte cell consisting of calcia stabilized zirconia as the electrolyte and Mo + MoO2 as the reference electrode. The results can be summarized by the following equations: log(at. pct O) = \frac - 10,005T + 4.944 ( ±0.015)log(atpctO)=T−10005+4944(0015) % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn DmO2 /4.606RT = log P O2 1/2 = \frac - 13,550T + 4.411 ( ±0.009)O24606RT=logPO212=T−13550+4411(0009) From simultaneous measurements of the potential and concentration of oxygen in melts, not in thermodynamic equilibrium with alumina and aluminate phases, information on the composition dependence of the activity coefficient and the standard free energy of solution of oxygen is obtained. For the reaction, $\frac{1}{2} O_2 \to \underset{\raise0.3em\hbox{$Missing close brace ΔG o = -72,930 - 7.11T (±840) J gr.at.–1 = + 0.216 at. pct OlogfO=T−500+0216atpctO where the standard state for dissolved oxygen is that which makes the value of activity equal to the concentration (in at. pct) in the limit as concentration approaches zero. The oxygen solubility in liquid nickel in equilibrium with solid NiO, evaluated from thermodynamic data, is compared with information reported in the literature. Implications of the results to the deoxidation equilibria of aluminum in nickel are discussed.

Kinetics of Sulphation of Nickel and Cobalt Ferrites with Na$O, Melt Containing F'e3+ Ions

It has been experimentally established that nickel and cobalt can be extracted from their ferrites with sodium sulphate melt containing femc ions. The kinetics of extraction from synthetic ferrites using a melt of sodium and ferric sulphates of eutectic composition has been studied as a function of the particle size of the ferrite and temperature in the range 900 to 1073 K. The divalent ions in the ferrite exchange with the ferric ion in the melt, leaving a residue of hematite.The rate of reaction conforms to the Crank-Ginstling-Brounshtein diffusion model. The reaction rate is governed by the counter-diffusion of ~ e an~d ~+i ' +(or co2+) ions in the hematite lattice. Analytical expressions for the rate constants have been derived from the experimental data as a function of particle size and temperature. The activation energy for the extraction of nickel from nickel ferrite is 154(+10) kJ mol-' and the corresponding value for cobalt is 142(+10)kJ mol;'. In sulphation roasting of minerals containing nickel, the yield of nickel is generally limited to 75% due to the formation of insoluble ferrites. The use of melts based on sodium sulphate provides a possible route for enhancing the recovery of nickel to approximately 98%.

A new matched thermochemical diagram for vacuum refining of nickel and cupronickel alloys

Sulfur and oxygen dissolved in nickel and cupronickel melts can be remwed as gaseous oxides of sulfur by a vacuum treatment. Presented in this paper is a new matched thermcxhemical disgran~ that permit.. direct evaluation of the equilibrium partial pressure of SO, as a function of temperature wer an alloy of specified compition. The matched thermochemical diagram consists of a central plot which shows the integral Gibbs' energy of mixing for the binary system SO, at different temperatures. The central plot is flanked on either side by terminal plots of the chemical potentials of oxygen and sulfur, as functions of temperature, for different alloy compositions. By projecting the chemical wtentials of oxygen and sulfur from the terminal lots on to the central diagram, ihe equilibrium partial pressure of S0,can be directly ;cad on the nomograms on the central plot at different temperatures. The matched therrnochemical diagrams are useful in assuring the efficiency of vacuum refining.

Dislocation mechanisms for plastic flow of nickel in the temperature range 4.2 – 1200 K

The temperature ranges of thermal and athermal deformation behaviour of nickel are identified by employing the temperature-dependence of flow-stress and strain-rate cycling data. The results are used to present a unified view of dislocation mechanisms of glide encompassing the two thermally activated and the intermediate athermal regimes of plastic flow.In the low-temperature thermally activated region (<250 K) the strain rate is found to be controlled by the repulsive intersection of glide and forest dislocations, in accordance with current ideas. The athermal stress in this region can be attributed mainly to the presence of strong attractive junctions which are overcome by means of Orowan bowing, a small contribution also coming from the elastic interactions between dislocations. The values of activation area and activation energy obtained in the high-temperature region (> 750 K) negate the operation of a diffusion-controlled mechanism. Instead, the data support a thermal activation model involving unzipping of the attractive junctions. The internal (long-range) stress contribution here results solely from the elastic interactions between dislocations. This view concerning the high-temperature plastic flow is further supported by the observation that the Cottrell–Stokes law is obeyed over large strains in the range 750–1200 K.

Dioxomolybdenum reagents in organic synthesis: utility of redox capability to design reduction and oxidation

The usefulness of dioxomolybdenum reagents in oxo-transfer reactions have been reviewed. The redox ability of dioxomolybdenum reagent has been utilized in designing several synthetic methods, which are useful in organic synthesis. Several reactions such as oxidation of alcohols, sulfides, amines, azides olefins etc are accomplished by using dioxomolybdenum reagents. Similarly, it is also demonstrated that dioxomolybdenum complex is useful in performing reduction of aldehydes, ketones, esters, azides etc. A fine tuning of reaction conditions provides suitable conditions to perform either oxidation or reduction by using catalytic amount of reagents. The oxidation reactions are further simplified by employing the polymer supported molybdenum reagents.

Synthesis, Thermal stability and Mechanical Behavior of Nano-Nickel

Nanocrystalline materials exhibit very high strengths compared to conventional materials, but their thermal stability may be poor. Electrodeposition is one of the promising methods for obtaining dense nanomaterials. It is shown that use of two different baths and appropriate conditions enables the production of nano-Ni with properties similar to commercially available materials. Microindentation experiments revealed a four fold increase in hardness value for nano-Ni compared to conventional coarse grained Ni. An improved thermal stability of nano-Ni was observed on co-deposition of nano-Al2O3particles.

Nanostructured titanium-nickel alloys: a comparison of processing routes

Rapid solidification, mechanical alloying and devitrificaiton of precursor metallic glasses are all possible routes for the synthesis of nanocrystals and nanocomposites, though their efficacy is system dependent. In a comprehensive study of alloys across the Ti-Ni phase diagram, nanocrystals of Ti and Ni and nanocomposites of alpha -Ti and Ti sub 2 Ni, Ti sub 2 Ni and TiNi and beta -Ti and glass have been produced. By the addition of Al, devitrification of metallic glasses created by mechanical alloying led to nanocrystalline intermetallic compounds. The evolution of these nanocrystalline microstructures has been rationalized on the basis of thermodynamic and kinetic considerations involving the metastable phase diagram for this system.

Molybdenum trioxide catalyzed oxidative cross-dehydrogenative coupling of benzylic sp(3) C-H bonds: synthesis of alpha-aminophosphonates under aerobic conditions

Molybdenum trioxide (MoO3) catalyzed efficient oxidative cross-dehydrogenative-coupling (CDC) method for C-H functionalization of N-aryl tetrahydroisoquinolines has been explored. This user-friendly method of synthesizing alpha-aminophosphonates employs 1.1 equiv of dialkyl-H-phosphonate under aerobic condition. Formation of new C-P bonds from unfunctionalized starting materials under environmentally benign conditions provides an excellent avenue for the synthesis of biologically active alpha-aminophosphonates. (C) 2012 Elsevier Ltd. All rights reserved.

Bioactivity and mechanical properties of nickel-incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a-C : H) and nickel-incorporated hydrogenated carbon (Ni/a-C : H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni3C) only. The presence of Ni3C has increased the sp(2) carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a-C : H films shows very low friction coefficient with higher scratch-resistance behavior than that of pure a-C : H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone-like apatite layer on Ni/a-C : H films. Thus, the results have indicated the suitability of the films for bone-related implant coating applications. Copyright (C) 2011 John Wiley & Sons, Ltd.

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-nitrobenzoic acid with methyl carbazate as ancillary ligand. Crystal structure of the copper(II) complex

Divalent metal complexes of general formula M(2-nb)(2)(mc)(2)].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH2NHCOOCH3), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II) complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG-DTA. Emission studies show that these complexes are fluorescent.