Oxygen potentials in Ni + NiO and Ni + Cr2O3 + NiCr2O4 systems

The chemical potential of O for the coexistence of Ni + NiO and Ni + Cr₂O₃ + NiCr₂O₄ equilibria has been measured employing solid-state galvanic cells, (+) Pt, Cu + Cu₂O // (Y₂O₃)ZrO₂ // Ni + NiO, Pt (-) and (+) Pt, Ni + NiO // (Y₂O₃)ZrO₂ // Ni + Cr₂O₃ + NiCr₂O₄, Pt (-) in the temperature range of 800 to 1300 K and 1100 to 1460 K, respectively. The electromotive force (emf) of both the cells was reversible, reproducible on thermal cycling, and varied linearly with temperature. For the coexistence of the two-phase mixture of Ni + NiO, δΜ_{O 2}(Ni + NiO) = −470,768 + 171.77T (±20) J mol⁻¹ (800 ≤T ≤ 1300 K) and for the coexistence of Ni + Cr₂O₃ + NiCr₂O₄, δΜ_{O 2}(Ni + Cr₂O₃ + NiCr₂O₄) = −523,190 + 191.07T (±100) J mol⁻¹ (1100≤ T≤ 1460 K) The “third-law” analysis of the present results for Ni + NiO gives the value of ‡H ₂₉₈ ^o = -239.8 (±0.05) kJ mol⁻¹, which is independent of temperature, for the formation of one mole of NiO from its elements. This is in excellent agreement with the calorimetric enthalpy of formation of NiO reported in the literature.     

Notch effects on tensile behavior of Ni3AI and Ni3AI + B

Tensile tests have been carried out at room temperature on double-notched specimens of Ni₃Al and Ni₃Al containing boron to observe the effect of boron on the notched specimen tensile behavior of Ni₃Al. The results indicate that a predominantly intergranular fracture can be induced in the presence of a high constraint (notch), even in boron-doped Ni₃Al, although a finite elongation and transgranular tearing-type fracture near the notch root were also observed. Fracture initiation was observed to occur in a brittle intergranular fashion in regions ahead of the notch in notched specimens of both Ni₃Al and Ni₃Al microalloyed with boron. An increase in the intergranular fracture stress of Ni₃Al due to boron was noted from the semiquantitative analysis (based on existing finite element models) of the notched tensile specimen data.     

含Ni~(2+),Fe~(3+),Mg~(2+)的硫酸盐溶液萃取分离Cu~(2+)

采用Lix984作萃取剂,煤油作稀释剂混合而成溶液萃取的有机相,从含Ni~(2+),Fe~(3+),Mg~(2+)离子的硫酸盐溶液中萃取分离Cu~(2+).实验结果表明,在一定范围内,铜萃取率随萃取剂浓度的升高、相比的增加、萃取时间的延长、初始水相pH值的增加、萃取温度的升高以及搅拌时间的延长而增加.本实验的优化条件为萃取剂体积分数达60%,相比为O∶A=2∶1,萃取时间为16 min,萃取初始水相pH值为2.5,萃取温度在25~45℃之间,搅拌速度为240 r/min.在最佳条件下,铜萃取率高达95.55%.Fe~(3+)萃取率为8.82%,Ni~(2+)的萃取率为5.47%,Mg~(2+)的萃取率为2.36%.从而达到Cu~(2+)与其它金属离子有效分离的效果.     

Mechanisms of cyclic strain hardening in Ni3Al+B single crystals

The evolution of dislocation substructures and their correlation with strees response in Ni₃Al+B single crystals fatigued at room temperature has been studied. Fatigue was conducted at total-strain amplitudes of 0.05–0.2%. Cyclic strain hardening and a tension/compression flow stress asymmetry were observed. The magnitude of stress asymmetry was found to depend on the applied cyclic strain. A dislocation structure composed of jogged superdislocations and superdislocation dipoles was observed. The dislocation dipoles were mainly formed by nonconservative of jogged superdislocations. Dragging of jogs, interaction between dislocations, and impedance of dislocation motion by dislocation dipoles (point defect clusters) are considered to be the major contributors to cyclic strain hardening in Ni₃Al+B single crystals. The separation between superpartial dislocations of a paired superdislocation was found to fluctuate away from the equilibrium spacing during cyclic straining. The extent of the fluctuation became more pronounced as the applied cyclic strain increased. This phenomenon was intimately related to the cyclic-strain dependence of tension/compression flow stress asymmetry found in fatigued Ni₃Al+B single crystals.     

Combustion synthesis of Ni3Al and Ni3Al-matrix composites

The self-propagating mode of combustion synthesis (SHS) of Ni₃Al starting from compacts of stoichiometrically mixed Ni and Al powders readily forms fully reacted structures with about 3 to 5 pct porosity, if green density of the compacts is greater than about 75 pct of theoretical. SHS-produced Ni₃Al matrix composites with up to 2 wt pct A1₂O₃ whiskers also have relatively low porosity levels. Porosity increases rapidly with lower green densities, higher Al₂O₃, or SiC whisker contents, and the degree of reaction completeness diminishes. The SiC whiskers undergo reaction with the matrix, while Al₂O₃ whiskers are nonreactive. All of these observations correlate well with temperature measurements made during the course of the reaction. The SHS mode can be achieved with agglomerated particle size ratioD _Al/D _Ni ≥ 1, larger than the limit established from studies of the thermal explosion mode of combustion synthesisD _Al/D _Ni ≃ 0.3. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Combustion in Layered Ni + Al and Ti + Al + C Powdered Mixtures

Russian Journal of Non-Ferrous Metals - This study is devoted to the technology of producing cermet coatings using self-propagating high-temperature synthesis (SHS). The importance of the study is...     

A point defect model for fatigue crack initiation in Ni3Al+B single crystals

Transmission electron microscopy of boron-doped Ni₃Al single crystals, oriented for single slip and cyclically deformed at room temperature, revealed a high density of dislocation dipoles and point defect clusters. Observations of circular perfect dislocation loops, Frank loops, vacancy tetrahedra and spherical voids provide evidence of vacancy condensation during fatigue cycling at room temperature. It is suggested that lattice misfit develops between persistent slip bands (PSB) and matrix as a result of the generation and coalescence of excess vacancies in PSBs. The misfit strain at PSB/matrix interfaces is considered to increase with increasing cumulative plastic strain. Together with SEM observations of surface topography, it is suggested that fatigue damage in Ni₃Al single crystals is initiated by the formation of microvoids (microcracks) at PSB/matrix interfaces. The microvoids (microcracks) break down the coherency of the PSB/matrix interfaces and thereby relieve the accumulated misfit strain at the interfaces. A model of fatigue crack initiation based upon a surface energy criterion is proposed.     

The mechanical behavior of nonstoichiometric compounds Ni3Si,Ni3Ge,and Fe3Ga

The compression flow stress of the three kinds of nonstoichiometric Ll₂ compounds has been measured as a function of composition in the temperature range from 77 to 800 K. The effect of nonstoichiometry on the positive temperature dependence of strength and the defect strengthening in polycrystalline Ni₃Si, Ni₃Ge, and Fe₃Ga alloys are quite similar to those found previously in Ni₃Al and Ni₃Ga alloys. However, the more intensive positive temperature dependence of strength, the limited homogeneity range within the nickel-rich side of stoichiometry and the lattice contraction in forming Ll₂ ordered structure observed in Ni₃Si and Ni₃Ge are concluded to be characteristic nature of compounds containing 4B-subgroup elements as the minority component. The difference of the extent of homogeneity range in various Ll₂ compounds is explained by an asymmetric index deduced from the consideration of the shape of free energy curve in the vicinity of stoichiometry. All these characteristic natures are discussed in terms of the change in bond strength.     

Particle penetration during spray forming and Co-injection of Ni3Al + B/Al2O3 intermetallic matrix composite

Intermetallic matrix Ni₃Al + B/Al₂O₃ composite, with 11 vol pct of Al₂O₃ particles incorporated into the matrix, was synthesized using a spray atomization and coinjection method. The penetration behavior of ceramic particles into atomized droplets during spray atomization and coinjection of Ni₃Al + B/Al₂O₃ composite was investigated experimentally and numerically. It was found that the extent of incorporation of Al₂O₃ into Ni₃Al + B droplets depends on the solidification condition of the droplets at the time of droplet/particle interaction. Penetration was observed only in fully liquid droplets or partially solidified droplets. No penetration was observed for droplets smaller than ∼40 μm, because droplets in this size range were fully solidified at the point of coinjection, and penetration was not possible for fully solidified droplets. The distribution of penetrated Al₂O₃ in the Ni₃Al + B droplets was, in general, uniform, with no trends of segregation observed. However, it was noted that most Al₂O₃ particles were located at the grain boundaries inside the droplets, while some Al₂O₃ particles were trapped inside the droplets by primary dendrite arms resulting from a fast moving solidification front typically associated with rapid solidification processes such as spray atomization. Finally, it was believed that the Al₂O₃ particles facilitated nucleation upon penetration of the Ni₃Al + B droplets either by means of thermal gradients or compatibility of preferred growth planes.     

黄钠铁矾和硫化锰分步去除硫酸锰溶液中铁钴镍

采用黄钠铁矾和硫化锰沉淀法从软锰矿硫酸浸出液中分步去除Fe3+、Co2+、Ni2+。先采用黄钠铁矾法沉淀去除Fe3+,再采用硫化锰沉淀去除Co2+、Ni2+。单因素试验最佳工艺条件为：隔氧环境下,MnS添加量10 g/L、反应温度75 ℃、反应时间30 min、转速120 r/min,此条件下,Co2+去除率达99.2%,Ni2+去除率达99.81%。