Timothee Nsongoa
,
Guoliang CHEN
,
Xiaodong NI
材料科学技术（英文）
The embedded atom method was used to theoretically analyze the effect of the lattice parameter variation on the order-disorder transformation in binary alloys. The simple model was considered in which the configuration energy E as function of the lattice parameter a and the long-range order parameter sigma was given by Taylor expansion at sigma =0. The following results were found for AB alloy, at T=0 K, the stable state exists in the completely ordered phase which was also found in the case of A(3)B or AB(3) compounds The order-disorder was found to be a second-order transition. Only one kind of order-disorder was found for AB alloy. Three groups of order-disorder transformation can be observed for the A(3)B or AB(3) compound. For the group I when the temperature is below the critical temperature, the order-disorder is a first order transformation. For the group II, the order-disorder transformation is a first order transition. For the group III, the order-disorder transformation is found to be a second order transition. The lattice parameter variations have a significant effect on E-2 coefficient, which is related to the ordering energy. These results are, in a good agreement with those obtained by using EAM (embedded atom method) and CVM (cluster variation method), calculations.
关键词:
材料科学技术（英文）
Structure and magnetic properties of Ni nanoparticles and Ni(C) nanocapsules were studied. The carbon atoms hardly affect the lattice of Ni to form Ni-C solid solution or nickel carbides. The large thermal irreversibility in zero-field-cooled and zero-field magnetization curves indicates magnetic blocking with a wide energy barrier. Saturation magnetization, remanent magnetization and coercivity of Ni(C) nanocapsules decrease with increasing temperature.
关键词:
nanoparticles;nanocapsules;magnetic properties;particles;carbon
Feng XIAO
,
Liang FANG
,
Kiyoshi NOGI
材料科学技术（英文）
Surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys was measured at the temperature range of 1773~1873 K using an improved sessile drop method with an alumina substrate in an Ar+3%H2 atmosphere. The error of the data obtained was analyzed. The surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys decreases with increasing temperature. The influence of Co on the surface tension of Ni-Co alloys is little in the studied Co concentration range.
关键词:
Nickel
,
null
,
null
,
null
Nanostructured Materials
Ultrafine Ni particles have been obtained by evaporating pure Ni in methane gas atmosphere of 100 Torr, and in a mixture of H-2 and Ar of 760 Torr, respectively. The distinct characterization of the layers on two kinds of Ni particle surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and oxygen determination. The morphology and mean particle size were determined by transmission electron spectroscopy (TEM) and subsequent image analysis. The structure of ultrafine Ni particles were identified by X-ray diffraction (XRD). The effect of oxide and carbon layers on magnetization of the particles were studied by vibrating sample magnetometer (VSM). It was observed that a carbon-rich and an oxide of Ni2O3 layers were formed on the surface of Ni particles obtained in methane gas, and in a mixture of H-2 and A(r) gas atmosphere, respectively, it was shown that the methane gas makes resistance to oxidization during evaporating Ni in this gas atmosphere and no nickel carbides or Ni-C solid solution formed. (C) 1998 Acta Metallurgica Inc.
关键词:
magnetic-properties
Mir Ghasem HOSSEINI*, Mehdi ABDOLMALEKI, Sajjad ASHRAFPOOR
催化学报
doi:10.1016/S1872-2067(11)60464-6
A Ni-Zn binary metal coating was electrochemically deposited on a copper electrode that was coated with nickel (bottom layer). This was then etched in concentrated alkaline solution (30 wt%NaOH) to produce a nanoporous Ni electrocatalytic surface for borohydride electro-oxidation in alkaline solution. The bulk and surface compositions of the coating before and after alkaline leaching were determined by atomic absorption spectroscopy and energy dispersive X-ray analysis. The surface morphology was investigated by scanning electron microscopy. The characterization showed that the leached Ni/Zn-Ni coating has a nanoporous structure. Electrocatalytic activity for boro-hydride electro-oxidation was assessed by cyclic voltammetry and electrochemical impedance spectroscopy. The improved activity of the electrode was related to the removal of corrosion products and the formation of nanopores and cracks during alkaline leaching. Cyclic volt-ammetry studies confirmed that the alkaline leaching process improved the activity of the Ni/Zn-Ni coating in comparison to that of a smooth Ni deposit, and it gave an anodic peak current density that was 21 times higher.
关键词:
Acta Materialia
The effects of B, C, N, O, H, P and S impurities on the Ni/Ni3Al interface cohesion have been investigated by employing first-principles electronic structure calculations based on the discrete variational method. The binding energy, bond order, difference electron density, orbital occupations and density of states have been calculated to study the impurity-induced changes in the energetics and electronic structure. The impurities promote the Ni/Ni3Al interface cohesion and prefer to occupy the interface interstitial sites in the order S < P < H < O < N < B < C. The impurity-nickel covalent-like bonds form mainly due to impurity-p/Ni-d hybridization (except H-s/Ni-p hybridization in the H case). Meanwhile, the Ni-Ni bonding becomes weaker because of charge depletion on Ni atoms and bond misorientation resulting from the more homogeneous electron redistribution. In the order B, C, N and O, the impurity-metal bond varies from being homopolar to being much more heteropolar with increasing ionicity percentage, which results in decreasing p-d hybridization effects. (C) 1997 Acta Metallurgica Inc.
关键词:
grain-boundary embrittlement;cluster model;nickel;ni3al;segregation;fracture;sulfur
Xianxia YUAN
,
Yindong WANG
,
Feng ZHAN
材料科学技术（英文）
Effects of various Co species added by mechanically mixing with Ni(OH)(2) on the performance of Ni electrode were studied and the results were interpreted by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that CoO, Co and CoO+Co all can improve the performance of Ni electrode to some extent and the effect of CoO was the most obvious. This could be attributed to several causes: all three forms of additives increased the reversibility of Ni(II)/Ni(III) redox reaction, enhanced the oxygen evolution polarization, improved the charging efficiency of Ni electrode, improved the lattice imperfection of Ni hydroxide and made it more beneficial to charge transfer and H+ diffusion processes.
关键词:
Applied Surface Science
The optimal geometries, mechanical and thermal properties, and electronic structures of the three low index (0 0 1), (1 1 0), (1 1 1) Ni/Ni(3)Al thin film were studied using first principle calculations. Simulated results indicated that Ni and Al atoms in gamma' phase preferred to place in the hollow site of Ni atoms in g phase. In hollow sitemodels, electronic states affected by interface localize within 2 atomic layers. While the top site model, electronic states localize within 3 atomic layers. It is also found that hollow site (1 1 0) interface has the best mechanical properties. Hollow site (0 0 1) interface is the most easily formed interface, which has the best thermodynamic properties. (C) 2008 Elsevier B. V. All rights reserved.
关键词:
First-principle;Interface;Electronic structure;metallic multilayers;gamma'-phase;energy;ni;al;mechanisms;crystal
