First principle MD study on the structural and electronic properties of liquid and amorphous NI81B19 and NI80P20 alloy

Atomic and electronic structures of liquid and amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys were simulated by ab initio molecular dynamics. Pair correlation function, bond pair analysis, electronic population analysis, and density of states were calculated. It was found that amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys can be prepared by rapid quenching, and their structures are similar to those of liquid alloys. Bond pair analysis indicated that the environment of each atom in Ni₈₁B₁₉ system is dominated by icosahedral and distorted icosahedral inherent structures; however, in Ni₈₀P₂₀ system, the tetrahedral order is preponderant. Strong interactions occur between the d‐electrons of Ni and the p‐electrons of B (or P), which leads to the covalent interactions between Ni and B (or P) atoms. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Effects of Ti and Co on the Electrochemical Characteristics of MgNi-Based Alloy Electrodes

Mg-based hydrogen storage alloys MgNi, Mg0.9Ti0.1Ni and Mg0.9Ti0.1Ni0.9Co0.1 were successfully prepared by means of mechanical alloying （MA）. The structure and the electrochemical characteristics of these Mg-based materials were also studied. The results of X-ray diffraction （XRD） and scanning electron microscopy （SEM） show that the main phases of the alloys exhibit amorphous structures, and trace of Ni co-exists. The charge-discharge cycle tests indicate these alloys have good electrochemical active characteristics. And the cycle stability of Ti and Co doped alloy was better than that of MgNi alloy. After 50 cycle charge-discharge, the discharge capacity of the Mg0.9Ti0.1Ni0.9Co0.1 alloy was much better than that of MgNi and Mg0.9Ti0.1Ni alloys. The discharge capacity of Mg0.9Ti0.1Ni0.9Co0.1 was 102.8% higher than that of MgNi alloy, and 45.49% higher than that of the Mg0.9Ti0.1Ni alloy. During the process of charge-discharge cycle test, the main reason for the electrode capacity fading is the corrosion of Mg to Mg（OH）2 on the surface of alloys. The Tafel polarization test indicates Ti and Co improve the anticorrosion in an alkaline solution. The EIS results suggest that proper amount of Ti and Co doping improve the electrochemical catalytical activity on the Mg-based alloy surface significantly.     

The site preference and doping effect on mechanical properties of Ni3Al-based γ′ phase in superalloys by combing first-principles calculations and thermodynamic model

The fundamental aspects of site preference of alloying elements on sublattice of the strengthen γ′ phase with L1₂ structure have not been well understood, which hinders the optimized design of advanced Ni-based high-temperature alloys. In this contribution, the temperature- and composition-dependent site occupying preferences of the binary, ternary, and quaternary of Ni₃Al-based γ′ phase alloyed with M_i where M_i represents the additional transitional metals Co, Cr, Cu, Fe, Mn, Mo, Re, Ta, Ti, V, or W atoms (arranged in alphabetical order) chosen frequently, were studied using a two-sublattice thermodynamic model (Ni, Al, M_i)_1a(Ni, Al, M_i)_3c. The site occupying fractions (SOFs) were calculated based on a thermodynamic database established in this work, where the thermodynamic data of the end-members involved were obtained using first-principles calculations and phonon spectrum calculations. The calculated SOFs results show that there is an obvious site preference for stoichiometry binary Ni₃Al, and its site configuration changes from (Al)_1a(Ni)_3c at room temperature to (Al_0.9984Ni_0.0015)_1a (Al₀Ni_0.9994)_3c at 1273 K. For the γ′ phase with the composition 78Ni-26Al-4M_i (atom ratio and x_Ni/x_Al = 3:1), Mo atoms always preferred to occupy the 1a sublattice (Al site), Co, Mn, and Ti atoms always prefer the 3c sublattice (Ni site) in the whole temperature range, while the site preference of Cr, Cu, Fe, Re, Ta, V, or W atom is affected by temperature. For example, when the heat treatment temperature is lower than 700 K, Cr, Cu, Fe, Ta, V, and W atoms occupy the 1a and 3c sublattice randomly, and Re atoms prefer to 3c sublattice, while when the heat treatment temperature is higher than 1273 K, Cr, Cu, and W atoms prefer 3c sublattice, Fe and Ta atoms prefer to 1a sublattice, while all Re atoms occupy the 3c sublattice exclusively, and all V atoms occupy the 1a sublattice exclusively, respectively. Likewise, the site preference of the quaternary system with selective compositions 78Ni-26Al-2 M₁-2 M₂ was also predicted. Based on calculated SOFs results, the mechanical and thermodynamic properties were studied at the ground state. It has been revealed that Cr, Re, and V doping can improve the microhardness of Ni₃Al alloys; in particular, the effect of Cr is extraordinary; and all elements, except Mn, Mo, and Ti, would enhance the bulk modulus of Ni₃Al-based γ′ phase, in which Mn have the greatest influence on reducing the bulk and shear modulus, respectively. Furthermore, all the B/G ratios of the computed Ni₃Al-based γ′ phase are >1.75, showing inherent ductility. Only Cr doping significantly enhances the Debye temperature of the Ni₃Al-based γ′ phase.     

Investigation of the influence of nickel content on the correlation between the hydrogen equilibrium pressure for hydrogen absorbing alloys and the capacity of MH electrodes in open and closed cells

Two series of overstoichiometric AB_2.4 alloys [(Zr_0.35Ti_0.65)(V_1.33Cr_0.4Fe_0.27)_{2– x} Ni_{0.4+ x} and (Zr_0.5Ti_0.5)(V_0.8Mn_0.8Cr_0.4)_{2– x} Ni_{0.4+ x} ], differing in the Zr to Ti ratios in group A and the presence of Mn or Fe in group B, were examined to consider the influence of various amounts of nickel on the structural parameters following the sorption of hydrogen. To predict the electrochemical behaviour of the prepared alloys as negative electrodes for Ni-MH cells, the pressure-composition isotherms (PCT) determined for the gas/solid phase system were correlated with the electrochemical pressure-composition (EPC) isotherms estimated from the rest potential of the alloy electrode. For preliminary assessment of the practical usefulness of the prepared samples, the electrodes made of all the alloys were subjected to charge/discharge measurements in a half-cell in 6 M KOH solution and the discharge capacities were estimated. Of the alloys with Fe and Mn components, the samples (Zr_0.35Ti_0.65)(V_0.93Cr_0.28Fe_0.19Ni_1.0) and (Zr_0.5Ti_0.5)(V_0.68Mn_0.68Cr_0.34Ni_0.7) provided the highest capacities. These alloys were chosen for testing the charge/discharge cycleability in closed Ni-MH cells. The reversibility of the cell with the former sample decreased significantly around the 25th cycle, whereas the discharge capacity of the cell with the latter sample remained almost unchanged during 100 cycles of testing. Electronic Publication     

Effect of annealing in a reductive environment on the magnetic properties of barium ferrite nanoparticles doped with Ti4+ and Co2+

It was found experimentally that the annealing of BaFe_10.6Co_0.7Ti_0.7O₁₉ and BaFe_10.2Co_0.9Ti_0.9O₁₉ complex magnetic oxide nanoparticles in paraffin vapor irreversibly increases their coercive force H _c and saturation magnetization M _s to the H _c and M _s values for barium ferrite BaFe₁₂O₁₉. The annealing of these nanoparticles, and of particles of magnetic oxides CrO₂, γ-Fe₂O₃, and BaFe₁₂O₁₉ in air and in paraffin vapor, has not been shown to affect their H _c and M _s values. An explanation in terms of diffusion self-purification of nanoparticles from ion impurities activated by chemical processes on their surface is offered.     

Crystal chemistry of the G-phases in the {Ti, Zr, Hf}-Ni-Si systems

Ternary compounds M₆Ni₁₆Si₇ (M=Ti, Zr, Hf) have been investigated by X-ray powder/single crystal and neutron powder diffraction. Compounds with Zr and Hf crystallize in the ordered Th₆Mn₂₃ type (Mg₆Cu₁₆Si₇-type, space group ), whereas Ti₆Ni_16.7Si₇ contains an additional Ni atom partially occupying the 24e site (M2 site, x=0.4637,0,0; occ.=0.119) inside a Ti octahedron; Ti atoms occupy a split position. Ti₆Ni_16.7Si₇ represents a new variant of the filled Th₆Mn₂₃ type structure. Ab initio calculations confirm the structural difference: additional Ni atoms favour the 24e site for Ti₆Ni_16.7Si₇, however, for the Zr and Hf-based compounds the unoccupied site renders an energetically lower ground state. Enthalpies of formation of Ti₆Ni₁₇Si₇, Zr₆Ni₁₆Si₇, and Hf₆Ni₁₆Si₇ were calculated to be −68.65, −74.78, and −78.59 kJ/(mol of atoms), respectively.     

硼的添加对Ti0.26Zr0.07V0.24Mn0.1Ni0.33贮氢合金结构和电化学性能的影响

Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33Bx(x=0~0.10)系列合金均有V基固溶体相和C14型Laves相两相组成。添加B可提高Ti_0.26Zr_0.07V_0.24 Mn_0.1Ni_0.33合金的放电容量, Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33B0.1合金电极在60 mA·g^-1电流放电时的放电容量达到476.7 mAh·g^-1.B的添加不同程度地降低了合金的高倍率放电性能, 使合金电极表面上电化学反应的电荷转移电阻(R_ct)显着增加, 交换电流密度(I₀)显着降低。添加B可显着改善Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金电极的高温放电性能, Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33B_0.025合金电极在343 K高温下其放电容量达到525.6 mAh·g^-1.     

Mg0.9Ti0.1Ni1－xCox (x＝0.05, 0.1, 0.15, 0.2)合金的合成及电化学性能研究

采用机械合金化法合成了Mg_0.9Ti_0.1Ni_1－xCo_x (x＝0.05, 0.1, 0.15, 0.2)系列四元合金, 并对该系列合金的结构和电化学性能等方面进行了研究. 球磨100 h的该系列合金, XRD结果表明, X射线衍射峰均呈现宽化趋势, 基本呈非晶态. 充放电结果表明, 该系列合金具有较好的活化性能, 它们的循环稳定性明显好于MgNi合金, 其中Mg_0.9Ti_0.1Ni_0.8Co_0.2最大放电容量最高, 为427.5 mAh•g^－1. 在充放电循环过程中, Mg在合金表面形成了Mg(OH)₂是合金电极衰减的主要原因. 腐蚀曲线的测试结果表明, Co的添加可以提高合金电极在碱液中的抗腐蚀能力, 从而提高了电极的循环稳定性.     

硼的添加对Ti0.26Zr0.07V0.24Mn0.1Ni0.33贮氢合金结构和电化学性能的影响

Ti0.26Zr0.07V0.24Mn0.1Ni0.33Bx(x=0~0.10)系列合金均有V基固溶体相和C14型Laves相两相组成。添加B可提高Ti0.26Zr0.07V0.24Mn0.1Ni0.33合金的放电容量,Ti0.26Zr0.07V0.24Mn0.1Ni0.33B0.1合金电极在60 mA·g-1电流放电时的放电容量达到476.7 mAh·g-1。B的添加不同程度地降低了合金的高倍率放电性能,使合金电极表面上电化学反应的电荷转移电阻(R ct)显著增加,交换电流密度(I0)显著降低。添加B可显著改善Ti0.26Zr0.07V0.24Mn0.1Ni0.33合金电极的高温放电性能,Ti0.26Zr0.07V0.24Mn0.1Ni0.33B0.025合金电极在343 K高温下其放电容量达到525.6 mAh·g-1。     

Oxidation behaviour and kinetic properties of shape memory CuAlxNi4 (x=13.0 and 13.5) alloys

Although the copper-based shape memory alloys (SMA) have some important problems such as controlling of the kinetic properties in the shape memory ability, they have relatively more advantages when compared to nitinol, such as lower price and simpler production technology. In order to determine the kinetic properties and oxidation rates of shape memory CuAl_xNi₄ (x=13 and 13.5) alloys with polycrystalline forms, the alloys have been homogenized in β-phase field at 930 °C for 30 min and immediately quenched in iced-brine water at −3 °C. The transformation temperatures in a period of three thermal cycles which include heating and cooling processes have been determined through Shimadzu DSC-50 differential scanning calorimeter. Activation energies of forward and reverse martensitic transformations have been calculated by using the Kissenger method. Thermogravimetric analysis with Shimadzu TGA-50 have been carried out for the determination of mass changes of alloys during heating and cooling cycles with two temperature rates selected as 10 and 30 °C/min up to 900 °C. It has been shown that increasing aluminium content reduces the oxidation rates of the alloys. It has also been established that CuAlNi shape memory alloys have a good stabilization in martensitic phase.     

Influence of chemical composition on martensitic transformation of MnNiIn shape memory alloys

The most extensively studied Heusler alloys are those based on the Ni–Mn–Ga system. However, to overcome the high cost of Gallium and the generally low martensitic transformation temperature, the search for Ga-free alloys has been recently attempted, particularly, by introducing In, Sn or Sb. In this work, two shape memory alloys, Mn₅₀Ni_50?xIn_x (x = 7.5 and 10), were obtained by rapid solidification. We outline their structural and thermal behaviour. The structural austenite–martensite transformation was checked by calorimetry. The transformation temperatures decrease as In content increases. The same pattern is reflected in entropy and enthalpy changes linked to transformation. The control of the valence electron by atom (e/a) determines the transformation temperatures range in this kind of alloys, and it is possible to develop alloys that can be candidates in applications such as sensors and actuators. In addition, X-ray diffraction was performed to verify the crystalline structure at room temperature.

     

Structural chemistry of complex carbides and related compounds

Complex carbides formed in ternary systems of a transition element (M), a B-group element (M′), and carbon and having a formula M₂M′C (H-phase) or M₃M′C (perovskite carbide) occur frequently. This reflects the simple geometry of the atomic arrangement of the metals and the filling mode by an interstitial stabilizer such as carbon or nitrogen. The phase relationship of the ternary combinations {Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, and Ni}-aluminum-carbon was investigated. New complex carbides were found with the corresponding zirconium, hafnium, and tantalum combinations. The crystal structures in the case of Zr- and Hf-containing complex carbides can be characterized by a twelve-metal-layer sequence and by a ten-metal-layer sequence with carbon atoms again filling octahedral voids. The transition of structure types from TiC, Ti₂AlC, Ti₃SiC₂, ZrAlC₂, Zr₂Al₃C₅, to Al₄C₃ is also discussed.     

Ni添加对0.4Zr0.1V1.1Mn0.5Cr0.1合金的相结构和电化学性能的影响

本文通过XRD、SEM、EDS研究了Ti_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1Ni_x(x=0，0.2，0.4，0.6，0.8)合金的相结构和电化学性能。该合金系由BCC结构的V基固溶体主相和六方结构的C14 Laves第二相组成，Ni能够促进第二相的生成，Ni含量的增加导致了各相中的化学组成和晶格参数的变化，并通过电化学方法研究了Ni含量对_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1合金电极的最大放电容量、自放电性能、高倍率放电性能、循环稳定性能等的影响。     

Theoretical studies of hydrogen storage in binary Ti-Ni,Ti-Cu,and Ti-Fe alloys

Theoretical studies have been carried out to examine hydrogen storage in some binary transition metal alloys which include titanium as one of the alloying elements. Quantum mechanical calculations at the Extended Hückel level of approximation have been performed on numerous clusters of compositions Ti₁₈Ni₁₈, Ti₁₈Ni₁₈H, Ti₁₈Ni₁₈H₁₂, Ti₂₄Ni₁₂, Ti₂₄Ni₁₂H, Ti₂₄Ni₁₂Hi₁₂, Ti₁₆Cu₁₆, Ti₁₆Cu₁₆H, Ti₂₄Cu₂, Ti₁₆Fe₁₆, Ti₁₆Fe₁₆H₉, and Ti₁₆Fe₁₆H₃₂, to yield information on energetics, densities of states, charge distributions, and the effects of hydrogenation on these properties. In addition, ab initio calculations at the split valence level of approximation have been performed on several smaller clusters. The hydrogens have been shown to acquire a partially anionic character in all cases. Another conclusion is that the preference of H for certain types of sites (for example the tetrahedral Ti₄ sites in crystalline TiCu) is more likely to be related not to the intrinsically greater stability of a hydrogen atom located in such a site, but to more general topological and electronic considerations. Qualitative concepts related to the classification, spatial distribution, and sizes and shapes of hole sites which could become occupied by hydrogen atoms, have been shown to correlate with hydrogen storage capacity for crystalline materials. These qualitative concepts have been extended to amorphous materials and corroborate the observations that under optimized conditions amorphous alloys can be found with better reversible hydrogen storage properties than the crystalline or microcrystalline systems. Distorted tetrahedral and octahedral holes have been examined in detail, and parameters (volume, area, tetrahedrality, and octahedrality) have been introduced to describe their sizes and shapes. An algorithmic surveying technique has been introduced, and shown to provide useful information about the limiting amounts of hydrogen uptake.Camille and Henry Dreyfus teacher-scholar     

Ti-V-Nb-Cr-Ni电极合金的微观结构及某些动力学性能研究

本文采用XRD，FESEM-EDS及电化学阻抗谱(EIS)等方法对V基固溶体Ti_0.25V_0.34Nb_0.01Cr_0.10Ni_0.30电极合金的微观结构及某些动力学性能，如交换电流密度(i₀)、氢的扩散系数(D)等进行了研究。XRD和FESEM-EDS分析测试结果表明：Ti_0.25V_0.34Nb_0.01Cr_0.10Ni_0.30电极合金由BCC结构的V基固溶体主相和少量的TiNi基第二相组成，其中，V基固溶体主相为树枝晶形状，TiNi基第二相呈网格状围绕着树枝晶。EIS及其等效电路分析结果表明，电极表面电化学反应的电荷转移电阻(R_T)随着温度的升高而降低，而交换电流密度和氢在合金本体中的扩散系数随着温度的升高而升高。在343 K时的交换电流密度分别为323 K和303 K的3.6倍和13.6倍，氢的扩散系数略有升高。电化学反应的表观活化能(Δ_rH)59.091 kJ·mol^-1远高于AB₅型合金的28.10 kJ·mol^-1。Ti_0.25V_0.34Nb_0.01Cr_0.10Ni_0.30合金电极的放电容量在303～343 K较宽的温度区间内随温度的升高而增加，且高温倍率放电(HRD)性能优于低温，当放电电流密度较大时，氢的扩散是放电过程的主要速度控制步骤。     

Das Dreistoffsystem Nickel—Chrom—Bor

The ternary system Ni?Cr?B was established at 1000°C by X-ray diffraction and metallographic examinations. Binary chromium resp. nickel borides and two ternary borides Cr₃NiB₆ and Cr₂Ni₃B₆ were confirmed. Differential thermoanalysis of binary Ni?B-alloys showed the possibility of a metastable solidification according the partial system Ni?Ni₂B up to 19 at % B. The melting temperatures of ternary alloys were established.     

Stability and crystal chemistry of the ternary borides M2(Ni21−xMx)B6 (M Ti,Zr, Hf)

A crystallochemical study was undertaken to investigate the structural stability and the compositional extent of the ternary borides M₂(Ni_21−xM_x)B₆ (M  Ti, Zr, Hf). This phase often occurs during the production of MB₂ joints by means of Ni–B brazing alloys. Samples with the nominal compositions M₂Ni₂₁B₆ and M₃Ni₂₀B₆ were synthesized by arc melting and characterized by optical and electron microscopy, and X-ray diffraction. Crystal structure refinements were performed by the Rietveld method. The compositional boundaries of the ternary phases were experimentally determined and found strictly related to the M/Ni size ratio. The stability of this structure is mainly determined by the capability of the structure to expand under the effect of the Ni substitution by the M atom. The CALPHAD modeling of the three M–Ni–B ternary systems in the Ni-rich corner of the phase diagram, performed on the basis of the obtained structural data, shows a good agreement with experimental results.     

Synthesis and structure of phosphates M<Subscript>0.5</Subscript>Ti<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phosphates M_0.5Ti₂(PO₄)₃ (M = Ni, Zn) were synthesized by the sol-gel method and characterized by the methods of X-ray diffraction, IR spectroscopy, and electronic microprobe analysis. Structures of Ni_0.5Ti₂(PO₄)₃ and Zn_0.5Ti₂(PO₄)₃ were studied by Rietveld method using the X-ray powder diffraction data.     

Effects of crystals on the mechanical properties of Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glasses

In this paper the mechanical properties of fully amorphous and partially cystalline Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ alloys were investigated. The changes in hardness and ductiity caused by the presence of crystals in the amorphous matrix is presented.     

A conjoint XRD-ND analysis of the crystal structures of austenitic and martensitic Ti0.64Zr0.36Ni hydrides

The crystal structures of the hydrides of austenitic and martensitic Ti_0.64Zr_0.36Ni alloy have been investigated by conjoint X-ray diffraction (XRD)-neutron diffraction (ND) analysis. Austenitic Ti_0.64Zr_0.36Ni alloy with cubic CsCl-type structure preserves its metal sublattice structure after deuteration. It forms a Ti_0.64Zr_0.36NiD_1.5 deuteride with D-atoms occupying half of the octahedrally coordinated 3d sites. On the contrary, the monoclinic TiNi-type structure of martensitic Ti_0.64Zr_0.36Ni alloy is modified after deuterium absorption. At and , two deuterides coexist with orthorhombic CrB-type structure for the metal sublattice and compositions Ti_0.64Zr_0.36NiD (β-deuteride) and Ti_0.64Zr_0.36NiD_2.6 (γ-deuteride). For the β-monodeuteride, deuterium atoms are tetrahedrally coordinated by (Ti,Zr) atoms. For the γ-deuteride, D-atoms fully occupy tetrahedrally coordinated (Ti,Zr)₃Ni 8f sites and partially occupy pyramidal (Ti,Zr)₃Ni₂ 4c sites. At higher pressures, deuterium solution occurs in the γ-phase with a partial occupancy of octahedrally coordinated (Ti,Zr)₂Ni₄ 4a sites.