Service Life Effect on Structure and Phase Composition of DIN 14MoV63 Steel

Russian Physics Journal - The paper studies the structure and phase composition of steel 0.12C–1Cr–1Mo–1V–Fe (grade DIN 14MoV63) after a long-term operation using the...     

Role of the third component in the high-temperature hardening of Ni<Subscript>3</Subscript>Al phase

The high-temperature solid solution hardening of the ternary Ni₃Al + Me phase (Me is a metal) is analyzed. The hardening resulting from the alloying by refractory elements (Nb, Ta, Hf) is considered in detail. This phenomenon is established to have a multifactorial nature.     

Phase Composition of Ultra-Fine Grain Titanium After Aluminum Ion Implantation

Russian Physics Journal - The paper investigates commercially pure titanium VT1-0 (US analog Grade 2) in the ultrafine grain state after the aluminum ion implantation at a fluence of 1?1017,...     

Structure and Phase Composition of Heat-Resistant Ni–Al–Co Alloy After Annealing and Creep

Russian Physics Journal - The paper presents research into the structure and phase composition of Ni–Al–Co alloy modified by rhenium (~3 аt.%) alloying. Observations are carried...     

Diffusion layer thickness in a membrane system as determined from voltammetric and chronopotentiometric data

The thickness of the diffusion boundary layer (DBL) in solution near the surface of an ion-exchange membrane is compared at current densities (δ⁰) much less than the limiting value and at the limiting current density (δ_lim). The initial linear part of the current-voltage curve (CVC) of the membrane and the initial part of its chronopotentiogram are used to calculate δ⁰. Values of δ⁰ are found in a flow-through cell with an active membrane area of 2 × 2 cm² and 0.02 M NaCl solution for three membranes: AMX, Nafion-117, and MK-40. It is shown that δ⁰ is more than 20% less for Nafion-117 than for AMX and MK-40. Values of δ⁰ are close together for the latter two membranes and do not differ greatly from the value calculated from convective diffusion theory (the Leveque equation). In all cases, δ⁰ is significantly greater than δ_lim found from the value of the limiting current density by the method of intersecting tangents, which are drawn to the initial segment of the CVC and to the sloping plateau. The effects that determine the dependence of DBL thickness on not only hydrodynamic conditions, but also the state of the membrane surface, are discussed. The principal phenomenon responsible for the decrease in DBL thickness with increasing current is termed coupled convection, more likely, electroconvection. Among the significant properties of the surface are singled out its electrical heterogeneity and degree of hydrophobicity. The different rate of electroconvection near cation- and anion-exchange membranes is related to the Stokes radius of the counterions. The latter explains the well-known observation in the literature that the limiting current density in dilute NaCl solutions is approximately the same for cation- and anion-exchange membranes in spite of the fact that the mobility of Cl⁻ ions is approximately 1.5 times higher than that of Na⁺ ions.     

Model and experimental studies of gravitational convection in an electromembrane cell

The model and experimental studies of the effect of gravitational convection on transport processes in an electromembrane cell are carried out. A model of an unsteady process of binary electrolyte transfer in moderately dilute solutions in an electromembrane cell for underlimiting current modes with allowance made for the natural and forced convection is built in the form of a system of two-dimensional equations of Navier-Stokes, Nernst-Planck, thermal conductivity, and electric current continuity. The dynamics of the appearance and development of vortex structures that arise in response to operation of gravitational archimedian forces is considered as well as their effect on the transfer of salt ions. Chronoampero- and chronopotentiograms obtained in an experimental study of desalination channels in electromembrane systems are interpreted.     

Effect of anion-exchange membrane surface properties on mechanisms of overlimiting mass transfer

Four effects providing overlimiting current transfer in ion-exchange membrane systems are examined. Two of them are related to water splitting: the appearance of additional current carriers (H+ and OH- ions) and exaltation effect. Two others are due to coupled convection partially destroying the diffusion boundary layer: gravitational convection and electroconvection. Three anion-exchange membranes, which differ in surface morphology and the nature of ion-exchange sites within a surface layer, are examined. The ion transfer across these membranes in NaCl solutions is studied by voltammetry, chronopotentiometry, and pH-metry. By excluding the effects of water splitting and gravitational convection, it is shown that the main mechanism of overlimiting mass transfer in narrow membrane cells at low salt concentrations is electroconvection. The reasons explaining why water splitting suppresses electroconvection are discussed. The scenario of development of potential oscillations with growing current and time is compared with that described theoretically by Rubinstein and Zaltzman.     

Effect of the ion-exchange-membrane/solution interfacial characteristics on the mass transfer at severe current regimes

In the electrodialysis of dilute solutions, performed at intense current regimes, the membrane electrical conductance and diffusion permeability are no more crucial. Of more importance become the membrane properties that control increase in the overlimiting mass transfer of salt ions, as well as H⁺ and OH^? ions in membrane systems. In this work different methods of the improving of mass-exchange characteristics of commercial ion-exchange membranes intended for operation at intense current regimes are discussed. They are based on modern concepts of mechanisms of the electroconvection (which proceeds as electroosmosis of 2nd kind), as well as mechanisms of H⁺ and OH^? ions generation at the membrane/solution interface. Influence on the membrane electrochemical and mass-exchange characteristics is possible via (a) control of chemical nature of fixed groups at membrane surfaces, in order to weaken their catalytic activity with respect to water dissociation reaction, (b) increase in the surface hydrophobicity, and (c) design of electrical inhomogeneity of the membrane/solution interface; the purpose is the facilitating of intense development of electrical convection.     

Study of creep and features of the dislocation structure in single crystals of Ni3Ge alloy

Data from investigating the dislocation structure of Ni₃Ge alloy single crystals formed during creep are presented. The creep of the Ni₃Ge single crystals with the [001] orientation of the deformation axis was studied. It was found that a fragmented substructure with varying degrees of disorientation occurs in the areas of macrolocalized deformation. A polycrystalline substructure consisting of fragments with a low dislocation density is formed in the local areas.     

Reflection spectra of narcotic-containing plants and choice of spectral ranges for their detection

Journal of Applied Spectroscopy -