V. V. Skorokhod

Gas atomized powders of hydride-forming alloys and their application in rechargeable batteries

Abstract Gas atomized powders of LaNi 4.5 Al 0.5 and LaNi 2.5 Co 2.4 Al 0.1 alloys were prepared and separated into fractions with different particle sizes. The dependence of morphology, oxygen content and crystal structure of the powders on particle size have been analyzed by means of XRD, SEM and EDS. The hydriding and electrochemical properties of different fractions were also evaluated. All fractions had a similar particle morphology and X-ray lattice parameters. EDS of the gas atomized alloys indicated that the surface of the smaller particles was less contaminated by oxygen than course particles. At the same time the fractions with particle sizes below 50 μm had poor activity both for gas hydrogenation and electrochemical charging. On the DTA curve of the small particles fraction an additional exothermal peak was observed, which may be attributed to a thermal-induced crystallization of the more developed amorphous component of the small particles structure. Gas atomized powders having large particle sizes display hydrogen and electrochemical capacity similar to those of arc-melted alloys.

Solid-phase sintering of ultrafine W(Mo)-Cu composite powders

ConclusionsThe solid-phase sintering of W-Cu composites can be markedly intensified by using ultrafine starting powder charges, the degree of intensification being a maximum with charges produced by reduction of oxide mixtures subjected to prior annealing in air. In this way it is possible to obtain virtually nonporous W-Cu composites with copper contents of 10–35%. The composition dependence of shrinkage in the solid-phase sintering of ultrafine W(Mo)-Cu powder composites is nonmonotonic in character. An anomaly is observed which would appear to be linked with the phenomenon of zonal isolation.

Sintering of tungsten-copper composites of various origins

ConclusionsIn the presence of a liquid phase the most active sintering was exhibited by W-Cu composites produced from copper tungstate (43% Cu) and from an oxide mixture annealed in air (20% Cu). The reason for this was that air-annealing preceding reduction completely (composite 2) or partially (composite 4) transformed the mechanical mixtures of oxides into homogeneous compounds. Under these conditions the tungsten and copper were “mixed together” at an almost atomic level, which imparted a high degree of homogeneity and dispersion to the W-Cu charges after reduction. In compacts from such a charge a disperse structure with a copper matrix readily forms in the initial stage of sintering, and it is this structure that ensures a high rate of densification. The dependence of the degree of homogeneity of a W-Cu charge on method of preparation was found to be reflected in an increase in the mean pore size in the initial stage of sintering. As expected, the mean pore size grew only negligibly in the initial stage of sintering of compacts from the most homogeneous charges (composites 2 and 4), while in composites 5 and 6 the increase in pore size constituted a serious obstacle to macroscopic shrinkage.

XPS and transmission electron microscopy of the multicomponent hydride-forming alloys for electrochemical applications

Abstract Photoelectron spectra of the Ce4d, Ni2p, Ni3p, Co3p, Al2p, O1s, C1s in Mm(Ni,Co,Al) 5 and Zr3d, Ti2p, V2p, Ni2p, O1s, C1s in Zr 1− X Ti X (Ni,V,Co,Cr) 2 alloys have been obtained. In the surface layer, about 2–2.5 nm of both alloys, the main part of the nickel atoms are in the metallic state (Ni 0 ) and only a third of them in oxidized states (Ni +2 , Ni +3 ). At the same time the concentration of nickel in surface layer of Zr-content alloy is much smaller when compared with Mm-content alloy. The chemical state of the Co and V atoms is similar to the Ni atoms state, but their concentrations, especially of V, in the surface layer is smaller than that of nickel. The results of XPS have been compared with the data of transmission electron microscopy of the thin foils of La- and Zr- based alloys. Dark field microphotographs of the oxidized alloys indicate the presence of two different phases, which, according to electron microdiffraction, are nickel-based alloy and oxide. In the first stage of oxidation on the surface of the foil, fine nickel particles (about 10 nm) and an amorphous oxide phase appear. Complete oxidation of the foil leads to the formation of a eutectic like structure consisting of a mixture of metallic and oxide phases. Some difference in the oxidized layer structure of the investigated alloys has been observed.

Button-cell for hearing aid apparatus based on gasatomized powders of hydriding alloy La-Ni-Co-Al

Gas atomized powders of LaNi2,5Co2,4Al0,1 alloywere prepared and used for the construction of nickel/metal hydride battery. The powdercharacteristics such as particle size distribution, morphology, oxygen content, crystal structure fordifferent fractions were analyzed. The hydriding and electrochemical properties were evaluatedtoo. All fractions have a similar particle morphology and only a slightly different X-ray determinedlattice parameters of the alloy. The fractions with particle size less than 50 μm have apoor activity at both gaseous and electrochemical hydriding. This phenomenon may be attributedto the presence of fine fractions of the amorphous component. Gas atomized powders of coarsefractions possess high corrosion resistance and display a similar hydrogen and electrochemicalcapacity as arc melt alloys.

X-ray diffraction investigation of the alloy formation process in the products of reduction of tungsten and molybdenum from a complex oxide

To obtain a homogeneous alloy through a solid-phase reaction in a mechanical mixture of pure tungsten and molybdenum powders, prolonged holding at temperatures of 1400-1500~ or higher is necessary [i, 2]. Activation of diffusion processes in mixtures of refractory metals can be achieved either by employing activating additions [1-3] or by increasing the contact surface between the reacting components. The simplest way of increasing the contact surface or phase interface of metal powders consists in their direct mixing and comminution. More effective, however, is the mixing of oxides, followed by their reduction [4].

Correlation Between Surface Chemical States and Electrochemical Activities of Alloys AB5 and AB2

The X-ray photoelectron La 3d, Ni 2p, Ni 3p, Al 2p, O Is and C 1s core-level spectra in LaNi4.5Al0.5 and the Zr 3d, Ti 2p, Ni 2p, Co 2p, V 2p, O 1s and C 1s spectra in Zr0.59Ti0.41Ni0.78V0.53Cr0.22Fe0.2Co0.27 and Zr0.9VCo0.55Ni0.55 have been obtained. Results of the XPS studies have been compared with data of polarization measurements as well as of the electrochemical behaviours of the alloys in the potential range -0.95 V ≤ E ≤ -0.2 V. A good correlation of data of the XPS and polarization measurements is established. The present study indicate that the alloy which contained on its surface the greatest amount of catalytic active centres observed by the XPS technique (e.q., segregation of the nickel atoms in the metalic state Ni°) possesses the more flat polarization curve in the range of small currents as well as the smaller potential at some cathodic currents. In the present work the such alloy was LaNi4.5Al0.5, which displayed higher electrochemical activity as compared with those of the Zr-containing alloys.

Structural mechanism and character of redistribution of tungsten and molybdenum in their reduction from a mixed oxide

ConclusionsAt temperatures of 600°C and higher the mixed oxide (W0.5Mo0.5)O3 is reduced with the starting uniform distribution of tungsten and molybdenum being retained in the end product, which is due to a single mechanism being operative in the process. As a result, a virtually homogeneous alloy is formed. At 400–600°C the reduction of tungsten and molybdenum from the mixed oxide involves two different structural mechanisms, which brings about a regrouping of the metals, disturbs their uniform starting distribution, and hence lowers the degree of homogeneity of the end product.

Some physicochemical properties of diamonds produced by a high-temperature explosion

Conclusions1.The product of the high-temperature synthesis contains, after chemical processing, ultrafine diamonds (single crystals of about 100-Å size) and various impurities (graphite, a carbon-base phase, unstable compounds condensing in the solid phase, and chemisorbed gaseous substances). Depending on synthesis and concentration conditions, the amount of impurities in ultrafine synthetic diamonds varies from 4 to 50 wt.%; it also grows with increasing defectiveness of the diamond crystal structure.2.Vacuum annealing at 500–600°C drives off almost all the chemisorbed impurities.3.The presence of chemisorbed impurities and crystal structure imperfection have a marked effect on the initial graphitization temperature of the finely divided diamond, which may range from 800 to 1000°C.4.Finely divided cubic diamond with a negligible amount of volatile impurities (less than 4 wt,%) and a practically undistorted crystal lattice is characterized by high thermal stability.

Electric erosion of the composite W(Mo)-Cu in electroerosion treatment of hard alloy in a carbon-containing liquid. I. Mechanism of wear of pseudoalloys W-Cu

ConclusionsThe discovered mechanism of erosion of tungsten-copper pseudoalloys in electrospark treatment of the hard alloy VK20 in a carbon containing liquid Is characterized by the formation of sections of high melting phase on the working surface, the phase consisting of a mixture of tungsten and its carbides, and by the predominant action of the electric discharges on these sections. As a rule, copper is removed along the perimeter of the sections of high melting phase. The amount of removed phase is determined (with constant pulse parameters) by the ratio between the components of the pseudoalloy. The concept was advanced of a dynamic surface layer of pseudoalloys during mass effect on them of electrlc discharges in a carbon containing liquid.