Some experimental data on a gas discharge between a flowing electrolyte and a metal electrode

Experimental data on a gas discharge obtained for comparatively high currents (4–11 A), powers (5–15 kW), and current density at a liquid cathode (0.8–1.0 A/cm²) are presented. As the electrolyte, a solution of sodium salt in distilled water was used. The losses on the liquid cathode were significantly diminished by decreasing its electric resistance. Regimes in which the thermal efficiency of a discharge apparatus is equal to ∼80% have been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 109–115, May–June, 2006.     

Hydrogen as a working atmosphere for manufacturing permanent magnets based on rare-earth metals

The phase compositions and magnetic properties of permanents magnets of the systems Sm – Co and Nd – Fe – B are analyzed. Features of the hydrogenation–disproportionation–desorption–recombination (HDDR) process in the Nd₂ Fe₁₄ B intermetallic are considered. Using the Dd – Fe – B system as an example, we assess stages of manufacture of commercial permanent magnets and show the prospect of using hydrogen as a working atmosphere for the manufacture of magnetic powder. It is established that the HDDR of Dd – Fe – B alloys leads to their homogenization, grain refinement to a grain size of 0.2 to 0.5 μm, and an increase in the volume content of the main ferromagnetic phase Dd₂ Fe₁₄ B. By optimizing such a treatment, we managed to increase the magnetic energy (by 10%) and the lift force (by 25 – 27%) of Dd – Fe – B commercial permanent magnets.     

Study of thermodynamic properties of liquid binary alloys by a pseudopotential method

On the basis of the Percus–Yevick hard-sphere model as a reference system and the Gibbs–Bogoliubov inequality, a thermodynamic perturbation method is applied with the use of the well-known model potential. By applying a variational method, the hard-core diameters are found which correspond to a minimum free energy. With this procedure, the thermodynamic properties such as the internal energy, entropy, Helmholtz free energy, entropy of mixing, and heat of mixing are computed for liquid NaK binary systems. The influence of the local-field correction functions of Hartree, Taylor, Ichimaru–Utsumi, Farid–Heine–Engel–Robertson, and Sarkar–Sen–Haldar–Roy is also investigated. The computed excess entropy is in agreement with available experimental data in the case of liquid alloys, whereas the agreement for the heat of mixing is poor. This may be due to the sensitivity of the latter to the potential parameters and dielectric function.     

Wettability of NiAl by a liquid Ni–Si–B alloy

An investigation of the wettability of the intermetallic compound NiAl by a liquid Ni–4.5 wt% Si–3.2 wt% B filler metal is presented in this paper. Dynamic observations of spreading of Ni–Si–B droplets, conducted using hot-stage light microscopy, are correlated with post-cooling microscopy and analysis. The paper examines the influence of the oxide layer on the NiAl substrates, on the progression of spreading of the Ni–Si–B liquid. Termination of spreading of the Ni–Si–B droplets by the onset of isothermal solidification at the spreading front is considered. Spreading of the Ni–Si–B droplets was found to be rapid until the onset of isothermal solidification at the spreading front. However, once isothermal solidification commenced, negligible further spreading was observed. The Ni–Si–B filler metal was observed to spread by undermining of the substrate oxide. However, a marked reaction occurred between the substrate oxide and the Ni–Si–B filler metal. This reaction served to remove the substrate oxide layer. The paper contrasts the mechanisms of substrate oxide undermining and isothermal solidification of liquid Ni–Si–B droplets on NiAl with those occurring during the spreading of the same liquid on pure nickel and Ni–Cr alloys. This revised version was published online in November 2006 with corrections to the Cover Date.     

Reduction of aluminum oxide in a nonequilibrium hydrogen plasma

A new method is proposed and experimental investigations are carried out aimed at reducing aluminum oxide in a nonequilibrium hydrogen plasma of a combined glow discharge (CGD) at a pressure of 1315.8–13,158 Pa, a discharge current of 5·10⁻²–3 A, and a hydrogen flow rate of 10⁻⁶–10⁻⁴ nm³/sec. A high degree of conversion of the aluminum oxide (60%) with an energy consumption of 20 kW·h/kg of Al₂O₃ is attained. Reduction of metals from oxides and other compounds in a CGD nonequilibrium hydrogen plasma can be used for producing rare-earth and high-purity metals. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 73, No. 3, pp. 580–584, May–June, 2000.     

Well-posedness of domain integral equations for a dielectric object in homogeneous background

An analysis of the mapping properties of three commonly used domain integro–differential operators for electromagnetic scattering by an inhomogeneous dielectric object embedded in a homogeneous background is presented in the Laplace domain. The corresponding three integro–differential equations are shown to be equivalent and well-posed under finite-energy conditions. The analysis allows for non-smooth changes, including edges and corners, in the dielectric properties. The results are obtained via the Riesz–Fredholm theory, in combination with the Helmholtz decomposition and the Sobolev embedding theorem.     

Numerical and physical modeling of a low-velocity air flow in a channel with a circular vortex cell

Based on a numerical solution, by the finite-volume method, of two-dimensional Reynolds equations that are closed using Menter’s two-parameter turbulence model and on physical modeling in a wind tunnel the authors analyze flow in a channel with a cylindrical vortex cell of circular cross section. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 346–353, March–April, 2000.     

Intragranular formation of austenite during delta ferrite decomposition in a duplex stainless steel

A Fe–22.5%Cr–4.53%Ni–3.0%Mo duplex stainless steel was solution treated at 1,325 °C for 1 h, quenched in water and isothermally treated at 900 °C for 5,000 s. The crystallography of austenite was studied using EBSD technique. Intragranular austenite particles formed from delta ferrite are shown to nucleate on inclusions, and to be subdivided in twin-related sub-particles. Intragranular austenite appears to have planar-only orientation relationships with the ferrite matrix, close to Kurdjumov–Sachs and Nishyiama–Wassermann, but not related to a conjugate direction. Samples treated at 900 °C underwent sparse formation of sigma phase and pronounced growth of elongated austenite particles, very similar to acicular ferrite.     

Wear characteristics of a new type austenitic stainless steel

In order to solve the problem of the poor wear resistance in conventional austenitic stainless steels, a new type austenitic stainless steel was designed based on Fe–Mn–Si–Cr–Ni shape memory alloys in this article. Studies on its wear resistance and wear mechanism have been carried out by comparison with that of AISI 321 stainless steel using friction wear tests, X-ray diffraction, scanning electron microscope. Results showed that the wear resistance of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was better than that of AISI 321 stainless steel both in dry and oily friction conditions owing to the occurrence of the stress-induced γ → ε martensitic phase transformation during friction process. This article also compared the corrosion performance of the two stainless steels by testing the corrosion rate. Results showed that the corrosion rate of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was notably lower in NaOH solution and higher in NaCl solution than that of AISI 321 stainless steel.     

Heat treatment of organic polymers in a flow of a gaseous heat carrier

Processes of heat and mass transfer are studied during heat treatment of organic polymers in a superheated-steam flow. Promising environmentally safe engineering processes of treatment of plant biomass, plastics, and rubber wastes that contain petroleum products of sludges and soils are described. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus,” Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 6, pp. 1021–1025, November–December, 1966.     

Lower frequency of free-field calibration of hydrophones in emission of tonal signals in a non-anechoic water tank

An approach to estimation of the lower free-field calibration frequency as well as the required magnitude of the water tank for calibration of hydrophones in a specified frequency range from the cepstrum of a segment of the amplitude response of the electroacoustic system, projector – hydrophone – non-anechoic water tank – measurement path of standard facility, is proposed. Estimates of the lower calibration frequency of hydrophones in a water tank with minimal dimension of 6 m in the case of radiation of quadrature-added harmonic signals are presented.     

Energy characteristics of a newly formed and hydrogenated metal surface in a corrosive medium

We determine the strength of contacting steel specimens in a corrosive medium using the modified chemical potentials Φ of the conduction electrons. The potentials are related to integral physical quantities that characterize the hydrogen content in the surface layers of the plates and are evaluated by an experimental procedure based on measurement of the surface tension and energy. A new strength criterion involving the potentials Φ is constructed. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 34–38, March–April, 1998.     

Distribution of temperature in a plate with a single-layer coating subjected to intense heating

We establish the distribution of temperature formed under conditions of abrupt changes in the surface temperature near the adhesional contact between the base and the coating in a plate of infinite length made of molybdenum or niobium both sides of which are covered with silicide coatings. The problem of heat conduction for a multilayer plate subjected to thermal cycling is solved by the method of finite integral transformations. It is shown that a silicide coating with a thickness of 60–100 μm leads to the formation of a significant temperature gradient in the base material under conditions of cyclic variation of temperature. This work was partially supported by the Soros International Program in the Field of Exact Sciences (ISSEP), Grant No. PSU 062034. Translated from Problemy Prochnosti, No. 3, pp. 128–133, May–June, 1998.     

Generalization of volt-ampere characteristics of the electric arc in a double-jet plasmatron with tubular single-chamber electrode units

On a double-jet plasmatron with cylindrical single-chamber electrode units, an experimental study of volt-ampere characteristics of the electric arc is conducted at current 105–550 A, voltage 400–1320 V, total flow rate of the plasma-forming gas (air) (0.76–9.83)∙10⁻³ kg ⁄ s, angle between the cathode and anode parts 45–62°, distance between the cathode and anode axes at the outlet from nozzles 0.07–0.2 m, and outlet pressure of ~0.1 MPa. Correlations for these characteristics are obtained.     

Experimental study of friction stress on the wall of a cylindrical tube in an oscillating turbulent flow of a liquid

Results of experiments where the nonstationary friction stress in an oscillating flow in a cylindrical tube was measured by a mechanical sensor within rather wide ranges of frequency (1–160Hz) and Reynolds number (1.7·10⁴–1.2·10⁵) are presented. A technique is suggested for calculating dynamic characteristics for the friction stress within three ranges of frequency, for which quasistationary and quasilaminar models of flow and a model for the intermediate frequency range are applicable. On the basis of experimental data, an approximation relation for the transmission ratio of the friction stress as a function of the dimensionless frequency is suggested. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 704–711, July–August, 2000.     

Effect of polymers on the nanostructure and on the carbonation of calcium silicate hydrates: a scanning transmission X-ray microscopy study

This study investigated the effects of organic polymers (polyethylene glycol and hexadecyltrimethylammonium) on structures of calcium silicate hydrates (C–S–H) which is the major product of Portland cement hydration. Increased surface areas and expansion of layers were observed for all organic polymer modified C–S–H. The results from attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopic measurements also suggest lowered water contents in the layered structures for the C–S–H samples that are modified by organic polymers. Scanning transmission X-ray microscopy (STXM) results further supports this observation. We also observed difference in the extent of C–S–H carbonation due to the presence of organic polymers. No calcite formed in the presence of HDTMA whereas formation of calcite was observed with C–S–H sample modified with PEG. We suggest that the difference in the carbonation reaction is possibly due to the ease of penetration and diffusion of the CO₂. This observation suggests that CO₂ reaction strongly depends on the presence of organic polymers and the types of organic polymers incorporated within the C–S–H structure. This is the first comprehensive study using STXM to quantitatively characterize the level of heterogeneity in cementitious materials at high spatial and spectral resolutions. The results from BET, XRD, ATR–FTIR, and STXM measurements are consistent and suggest that C–S–H layer structures are significantly modified due to the presence of organic polymers, and that the chemical composition and structural differences among the organic polymers determine the extent of the changes in the C–S–H nanostructures as well as the extent of carbonation reaction.     

Closure of a Longitudinal Crack in a Shallow Cylindrical Shell in Bending

We study the two-dimensional problem of contact interaction of the lips of a longitudinal crack in a cylindrical shell subjected to bending under the assumption of contact along a line. The influence of the surface curvature and crack closure on the stressed state and limiting equilibrium of the shell is analyzed. The numerical results are compared with the asymptotic solution of the problem. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 2, pp. 45–48, March–April, 2005.     

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.     

Dynamic stresses in the vicinity of a crack along the cylindrical surface

By using the method of boundary integral equations combined with the method of small parameter, we solve the problem of low-frequency loading of a shallow crack along a cylindrical surface in an infinite elastic body. The distributions of the modes I–III stress intensity factors along the contour of the defect are obtained for different values of crack curvature and wave numbers. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 108–113, July–August, 2006.