Synthesis and Characterization of Nanocrystalline Ni-Ti and Ni-Cr Powders by Mechanical Alloying

Nanocrystalline powders in the Ni-Ti and Ni-Cr systems were prepared by mechanical alloying (MA) of elemental crystalline powders in an inert atmosphere. The microstructure of the mechanically alloyed powders were characterized by XRD and TEM. The ball-milling process results in a drastic decrease of the crystallite size to the nanometer scale. X-ray diffraction analysis reveals that in the Ni-Cr system, no diffraction peaks from NiCr compound were observed even after 20 h of ball milling; while the lattice parameter of Ni increased with the milling time. In the Ni-Ti system, amorphous alloy was formed. Crystalline intermetallic compounds were obtained by post heat treatment of the amorphous alloy.The crystallization temperature of the amorphous NiTi alloy was obtained be DSC measurement.     

Studies of solid solutions of chromic oxide in nickel oxide

A method of preparation of solid solutions of Cr₂O₃ in nickel oxide has been described. The homogeneity of the solid solutions obtained was controlled by determining the nickel and chromium content polarographically in the course of the zone dissolution of the samples. The presence of chromium-nickel spinel was detected by the X-ray analysis. The limiting concentration of Cr₂O₃ in the solid solution in equilibrium with the spinel has been determined.     

The heat diffusivity of solid solutions of silicon and germanium in nickel

The concentration and temperature dependences are given of the heat diffusivity of solid solutions of silicon and germanium in nickel in the temperature range from 295 to 1400 K. The behavior of heat diffusivity is investigated for these systems in the neighborhood of the Curie point. The critical exponent, which describes the behavior of curvea(T), is shown to be sensitive to the presence of admixtures     

Evaluation of the thermodynamic properties of solid solutions of titanium,chromium, cobalt,and nickel in silicon using a two-sublattice model

We have evaluated the thermodynamic properties of solid solutions of titanium, chromium, cobalt, and nickel in silicon using a two-sublattice model. Our results demonstrate that the thermodynamic data obtained can be used in thermodynamic calculations.     

Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Using high-energy ball milling of Ni₈₇B₁₃ and Ni_{87 ? x} Nb _x B₁₃ component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni₈₇B₁₃ alloy contained stable phases of Ni and Ni₃B; the Ni₇₅Nb₁₂B₁₃ alloy contained a τ phase (Ni₂₁Nb₂B₆) and a metastable solid solution of Ni〈Nb〉.     

Shape deterioration and reversible shape-memory effect in Ni-Ti alloys

The effect of constraint heating on shape-memory properties in Ni-Ti alloys is studied. Specimens which memorized linear shape showed remarkable shape deterioration under constraint conditions above 1% bending surface strain and 100° C heating temperature. A reversible shape-memory effect was obtained after constraint heating, and shape change due to this was about 1.4% bending surface strain. These effects strongly depend on ageing temperatures during shape-memory treatment.     

Antiferroelectric-ferroelectric transition in binary systems of solid solutions based on sodium niobate

The dielectric properties of the (1−x)NaNbO_3−x KNbO₃ and (1− x)NaNbO_3−x PbTiO₃ systems are investigated. The antiferroelectric-ferroelectric transition regions are determined. It is established that in the (1−x)NaNbO_3−x KNbO₃ system the antiferroelectric phase is stable for x≤0.01 and the ferroelectric phase is stable for x≥0.0175; the transition from one phase into another occurs in the concentration range 0.01<x<0.0175. In the (1− x)NaNbO_3−x PbTiO₃ system the transition region lies in the range 0.07<x<0.11. Pis’ma Zh. Tekh. Fiz. 25, 1–5 (October 12, 1999)     

Al effect in transport properties of nickel oxide and its relevance to the oxidation of nickel

Transport properties of Al (0.11 at%)-doped Ni_1−xO, at equilibrium and in presence of a driving force of diffusion, have been studied to understand the oxidation behaviour of dilute Ni-Al (0.5 wt%) alloys. At T < 1000 °C, the alloy oxidizes slower than nickel, in agreement with a process mainly controlled by the outward diffusion of Ni²⁺, but faster at T ≥ 1000 °C, where the inner porous layer shows a low adhesion to the metal, with a greater amount of Al³⁺. The increasing oxidation rates at the higher temperatures are in discrepancy with experiments performed in the stability range of undoped and Al-doped Ni_1−xO single crystals. A formal treatment of transport processes under non-equilibrium conditions has allowed us to analyse the role played by doping. It has been found both that the Al³⁺ enrichment near the metal/oxide interface is largely due to kinetic demixing processes through the oxide scale and that the increasing alloy oxidation kinetics, at T ≥ 1000 °C, is largely due to oxygen molecules which penetrate the oxide scale along cracks or fissures. It is suggested that the fissure formation along grain boundaries is due to the influence of Al on the nickel ion mobility, leading to a localized oxide particle growth within the scale itself.     

Biosorption performance,combustion behavior,and leaching characteristics of olive solid waste during the removal of copper and nickel from aqueous solutions

Several researchers have proved that agricultural by-products constitute good adsorbents for removing heavy metals from aqueous solution. However, few investigations have identified efficient strategies for the adsorbent′s regeneration. Hence, a global methodology for the removal of copper and nickel metals from wastewater including metal biosorption, thermal treatment and residual ash landfill is proposed. In order to validate this strategy, olive solid waste (OSW), provided by an olive oil mill from Tunisia, were used to remove copper and nickel on batch experiments. Copper and nickel were adsorbed on a monolayer of OSW surface with maximal adsorption capacity (q _max) of 3.6 and 1.7 mg g^?1, respectively. Contaminated OSW with copper and nickel were combusted at 850 °C in an electrical furnace. About 96 % of each metal was recovered in residual ashes that present a good secondary raw material for copper and nickel production. Low leaching transfers (≤4 %) were observed for copper and nickel from residual ashes leading to the possibility to be landfilled. Therefore, the suggested process can be used as an alternative to the classical technologies for effluent decontamination.     

Chloride induced pitting corrosion of nickel in alkaline solutions and its inhibition by organic amines

Cyclic voltammetry, potentiodynamic and potentiostatic anodic polarization techniques complemented by SEM investigation are used to study the initiation and inhibition of pitting corrosion of nickel in NaOH solutions. The presence of Cl⁻ ions locally destroys the passive film formed on the nickel electrode at the pitting potentials, E_p, which are more active the higher the concentration of the Cl⁻ ions. E_p varies with the logarithm of Cl⁻ ions concentration according to sigmoidal S-shaped curves.     

镍渣机械力化学效应及其对反应活性的影响

为提高镍渣的反应活性,根据机械力化学原理,采用高能球磨技术处理镍渣并采取蒸压工艺制备镍渣制品.通过粒径分析、X射线分析以及扫描电镜分析等手段研究不同高能球磨时间下镍渣的粒径、结构和形貌变化以及镍渣的反应活性变化.结果表明:高能球磨可以进一步细化镍渣,使大颗粒块状粉体破裂、表面粗糙化并提高镍渣的反应活性,长时间球磨可使水化样品诱导期和加速期两个阶段的水化放热量显著增大;高能球磨4 h时镍渣蒸压试块的强度最大,可达24.4 MPa,是未高能球磨时的4.5倍,球磨4 h后蒸压试块水化产物的X射线谱图中出现了硬硅钙石、托勃莫来石和镁水化物等衍射峰.     

Synthesis, size reduction, and delithiation of carbonate-free nanocrystalline lithium nickel oxide

Lithium-based oxide nanoparticles have recently shown significant advantages as cathode materials for lithium ion batteries, showing higher ion exchanging rates related to the high surface area. Among them, LiNiO₂ has been considered an attractive candidate due to its relatively low cost, high discharge capacity, reversibility, and low toxicity. However, the synthesis of nanosized LiNiO₂ typically favors the formation of Li₂CO₃ and NiO phases, which critically affect the performance of the cathode nanoparticles. In this work, we describe the synthesis of lithium nickel oxide nanoparticles using a modified polymeric precursor method. As the formation of NiO and Li₂CO₃ was unavoidable, high temperatures would be required to obtain a carbonate-free LiNiO₂. In order to avoid large coarsening of the particles associated with those treatments, samples were treated at lower temperatures and cleaned from surface Li₂CO₃ contaminants using acidic washing. The procedure successfully removed the carbonate, and also resulted in crystallite size reduction (28.1–15.2 nm) and controlled delithiation, simulating the lithium deficient conditions during electrochemical lithium displacement.     

The dry friction effect under high-strain-rate plastic deformation of solid solutions

The movement of dislocations in the field of chaotically distributed point defects and Guinier–Preston zones under high-strain-rate deformation of solid solutions has been studied. It has been shown that, under definite conditions, the dynamic hindering of dislocations by the Guinier–Preston zones can occur similarly to dry friction and have a significant effect on the plastic deformation process.     

Structures of gismondine,cymrite, anorthite,and celsian solid solutions

This paper presents a comparative analysis of existing structural models for AAl₂Si₂O₈ · xH₂O (A = alkaline-earth element, 0 ≤ x ≤ 5) solid solutions and highlights their advantages and drawbacks. Water molecules are shown to play an important role in the formation of a zeolite structure, as exemplified by changes in the structural framework of gismondine during its dehydration.     

Compositions of gismondine,cymrite, anorthite,and celsian solid solutions

This paper presents a three-dimensional geometric analysis of the homogeneity regions of gismondine, cymrite, anorthite, and celsian solid solutions with the use of two composition tetrahedra: AO–BO_0.5–AlO_1.5–SiO₂ and AO–AlO_1.5–SiO₂–H₂O (where A = alkaline-earth element and B = alkali element). The main general aspects of the extension of the homogeneity regions are elucidated. The position of the homogeneity regions in the composition tetrahedra suggests that increasing the percentage of SiO₂ should lead to a gismondine–cowlesite phase transition and that a few phase transitions should be expected in the course of gismondine dehydration, which will lead to the formation of a solid solution with the anorthite structure after all of the water will be removed.