Kinetics of nucleation and halt-in-growth processes in a thin layer

The methods of determining the kinetic exponents in the equation, dX/dVex = (1 – X)2–, used for nucleation and halt-in-growth processes where X is the transformed fraction, Vex the KJMA extended volume fraction which is related to time t, and is the overlap factor which accounts for the overlap between a crystallite and a phantom crystallite, are presented. The applications of the Kolmogorov–Johnson–Mehl–Avrami plot ( = 1) and the Austin–Rickett plot ( = 0) to this process are inappropriate, because the overlap factor is 0 < < 1. The impingement exponent 2- and the time exponent are determined from the linear relation of In {[(1 – X) – 1 – 1]/(1 – )} versus In t. From the value of , the crystal shape and growth dimension can be estimated by referring to the mathematical value of . The methods of evaluating the activation energy, Q, are presented using the Arrhenius relation. The value of Q is not directly related to the overlap factor however, appears as a constant term in the expression for Q.     

Influence of rhenium on the microstructures and mechanical properties of a mechanically alloyed oxide dispersion-strengthened nickel-base superalloy

The influence of a 3 wt% Re addition on the creep strength and microstructure of a mechanically alloyed and oxide dispersion-strengthened nickel-base superalloy was investigated. Two alloys, Ni–8Cr–6.5Al–6W–3Ta–1.5Mo–6Co–1Ti–3Re–0.15Zr–0.05C–0.01B–0.9Y₂O₃ (3Re alloy) and a non-rhenium containing (0Re) alloy were prepared for this study.The 3Re alloy showed two-fold improvement in creep life compared with that of 0Re alloy, presumably due to a change in the mode of the precipitate-dislocation interaction. For the 3Re alloy, finer, more cuboidal and aligned precipitates are formed, which force the mobile dislocations at the – interfaces to cut precipitates in order to proceed. Shearing of precipitates is evinced by the existence of stacking faults and results in an increase of creep strength. In constrast, lower creep strength was observed for 0Re alloy because a dislocation looping mode is dominant with coarser and more irregularly shaped precipitates present in this alloy. Another possible explanation for an improved creep strength of 3Re alloy is related to the tangled dislocation structure formed by the interaction between glide dislocation and interfacial dislocation, which also acts as an effective barrier for further glide dislocation motion. A 3 wt% Re addition significantly retards coarsening kinetics. Rhenium acts as a rate-controlling species upon the volume diffusion-controlled coarsening process because it is a heavy elemenet and also it almost solely partitions to the matrix. X-ray diffraction experiments showed that the magnitude of the lattice mismatch between and increased with the 3 wt% Re addition from 0% to –0.26% at room temperature. Increased lattice mismatch for 3Re alloy causes the formation of more aligned and cuboidal precipitates rather than random and odd-shaped precipitates for 0Re alloy, and it also accelerates the coalescence between cuboidal precipitates.     

Corrosion of Iron in a Carbonate-Bicarbonate Solution. Part 1. Crystallographic Analysis of Passive Films

Visible passive films are formed on the surface of 1010 steel at 325K in a solution of 1N NaHCO₃ + 1N Na₂CO₃ at anodic potentials up to –320mV_NHE inclusively. For potentials below –400mV, they are dull and contain FeCO₃. For –(390–320)mV, the films are thin blackish bright. Most probably, the diffraction peaks are caused by Fe₃O₄–Fe₂O₃. For –(430–400)mV, the films are dull blackish. Probably, this color is caused by a composite of magnetite and siderite.     

Sintering Behavior of Hot-Pressed Ca–αSialon Ceramics

On the basis of phase relationships in the Ca–Si–Al–O–N system, a Ca––sialon ceramic was synthesized using the hot-pressing technique. The reaction sequences and densifications of the Ca––sialon vs. firing temperatures have been characterized in detail. The present experiments reveal a reaction sequence as follows: at 1250°C the reactant mixture started to soften, at 1300°C a gehlenite phase was produced, at 1500°C the gehlenite phase was resolved into a liquid phase and a Ca––sialon started to form, and at 1600°C the formation of Ca––sialon was complete. The product was stable and almost entirely single phase Ca––sialon. Accompanying to the above sequences, densification also proceeded via a liquid-phase sintering, particle rearrangement, solution–reprecipitation, and grain growth process. In the final microstructure elongated grains of Ca––sialon were obtained, improving the fracture toughness of this Ca––sialon ceramic.     

Thermal state of a plasma in a compressed layer

The results of an investigation of the thermal state of a plasma in a compressed layer under retardation conditions of the plasma flow of a coaxial Hall accelerator are reported and compared with analogous data for a free flow.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. 67, Nos. 1–2, pp. 108–111, July–August, 1994.     

Coarsening of precipitates and dispersoids in aluminium alloy matrices: a consolidation of the available experimental data

Experimental data on the coarsening of precipitates and dispersoids in aluminium-based matrices are reviewed. Available data are tabulated as K=(r ³–r ₀ ³ )/t where r ₀ is the initial particle radius and r is its value after time t at temperature T, and then plotted as log (KT) against 1/T for consolidation and assessment. The considerable body of data for -A₃Li in Li-containing alloys is well represented by K=(K ₀/T) exp (–Q/RT) with K ₀=(1.3 _–0.5 ^+3.0 ) × 10^–13m³Ks^–1 and Q=115±4kJ mol^–1. The relatively limited data for and in Cucontaining alloys are representable by the same relationship with K ₀4 × 10^–8 and — 4 × 10^–10 m³ Ks^–1, respectively, and Q — 140 kJ mol^–1. Available data for coarsening of L1₂ ^– Al₃(Zr, V) and related phases in Zr-containing alloys and of Al₁₂Fe₃Si and related phases in Al-Fe based alloys indicate (i) rates of coarsening at 375 to 475 °C (0.7 to 0.8T_m) five to eight orders of magnitude less than would be expected for , and in this temperature range, and (ii) high activation energies of 300 and 180 kJ mol^–1, respectively.     

Initiation of detonation in reflection of a shock wave from a concave curvilinear surface

The authors present results of investigating the possibility of initiating a detonation regime of combustion of reactive gaseous mixtures by focusing a plane shock wave in reflection from concave axisymmetric and two-dimensional surfaces.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk. Scientific-Production Company Prostor, Krasnoarmeisk, Moscow Region. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 66–72, July–August, 1994.     

Calculation of the Flow of a Weakly Compressible Viscous Gas Using a Multiprocessor Computer System

A method to calculate the flow of a weakly compressible gas on a multiprocessor computer system using the ( – ) iteration algorithm has been proposed. The problem of gas flow in a cavity with a moving cover has been considered as an example. The flow is described using Navier–Stokes equations in natural variables; MACtype spaced grids are employed. Calculations with the use of a monoprocessor version of the ( – ) algorithm and using its parallel implementation for the case of four processors have been carried out; the issue of the efficiency of multisequencing has been studied. Certain aspects of organization of remote access to the multiprocessor system have been discussed.     

Thermophysical Properties of Molten Germanium Measured by a High-Temperature Electrostatic Levitator1

Thermophysical properties of molten germanium have been measured using the high-temperature electrostatic levitator at the Jet Propulsion Laboratory. Measured properties include the density, the thermal expansivity, the hemispherical total emissivity, the constant-pressure specific heat capacity, the surface tension, and the electrical resistivity. The measured density can be expressed by _liq=5.67×10³–0.542 (T–T _m ) kg·m^–3 from 1150 to 1400 K with T _m=1211.3 K, the volume expansion coefficient by =0.9656×10^–4 K^–1, and the hemispherical total emissivity at the melting temperature by _{T, liq}(T _m)=0.17. Assuming constant _{T, liq}(T)=0.17 in the liquid range that has been investigated, the constant-pressure specific heat was evaluated as a function of temperature. The surface tension over the same temperature range can be expressed by (T)=583–0.08(T–T _m) mN·m^–1 and the temperature dependence of the electrical resistivity, when r _liq(T _m)=60·cm is used as a reference point, can be expressed by r _{e, liq}(T)=60+1.18×10^–2(T–1211.3)·cm. The thermal conductivity, which was determined from the resistivity data using the Wiedemann–Franz–Lorenz law, is given by _liq(T )=49.43+2.90×10^–2(T–T _m) W·m^–1·K^–1.     

Solid hydrogen and deuterium. I. Ground-state energy calculated by a lowest order constrained-variation method

The ground-state energy of solid hydrogen and deuterium is calculated by means of a modified variational lowest order constrained-variation (LOCV) method. Both fcc and hcp H₂ and D₂ are considered, and the calculations are done for five different two-body potentials. For solid H₂ we obtain theoretical results for the ground-state binding energy per particle from –74.9 K at an equilibrium particle density of 0.700 ^–3 or a molar volume of 22.3 cm³/mole to –91.3 K at a particle density of 0.725 ^–3 or a molar volume of 21.5 cm³/mole, where =2.958 Å. The corresponding experimental result is –92.3 K at a particle density of 0.688 ^–3 or a molar volume of 22.7 cm³/mole. For solid D₂ we obtain theoretical results for the ground-state binding energy per particle from –125.7 K at an equilibrium particle density of 0.830 ^–3 or a molar volume of 18.8 cm³/mole to –140.1 K at a particle density of 0.843 ^–3 or a molar volume of 18.5 cm³/mole. The corresponding experimental result is –137.9 K at a particle density of 0.797 ^–3 or a molar volume of 19.6 cm³/mole.     

Thermal stability of the αZn–Mg2Zn11 and αZn–βAl eutectics obtained by Bridgman growth

The thermal stability of rod-like Zn–Mg2Zn11 and lamellar Zn–Al eutectics obtained by Bridgman growth of Zn–3.1 wt% Mg and Zn–5 wt% Al has been studied for soaking times up to 10 h at 300 and 350°C, respectively. Two-dimensional coarsening resulted for Zn–Mg2Zn11 grown at 0.5 and 1 mm s-1 while fault migration was operative for lamellar Zn–Al grown at 0.1 and 1 mm s-1. Hardness decreased with increased soaking time according to a Hall–Petch relationship with mean interphase spacing and the values H0 and kY accord well with the values obtained from the Hall–Petch relationship for HV of as-solidified Zn–Mg2Zn11 and Zn–Al with eutectic interphase spacing, respectively. © 1998 Chapman & Hall     

Linear heat transfer in a flow around a cylinder or a sphere

It is shown that the relation between the Nusselt and Reynolds numbers determined by the Reynolds analogy is linear with self-similarity of the hydrodynamic resistance coefficient.Special Design and Technology Office Element, Odessa, Ukraine. translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, May–June, pp. 395–396, 1995.     

Concentrational polarization in ultrafiltration in a plane channel

We investigated steady-state concentrational polarization in laminar ultrafiltration in a plane channel in relation to the selective properties of the membrane.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. 67, Nos. 3–4, pp. 235–239, September–October, 1994.     

Human endothelial cell a

Composite materials comprised of the electrically conducting polymer, polypyrrole, with a variety of biologically active molecules, e.g. proteins or polysaccharides, are emerging as a novel class of smart biomaterials. In the present work we have studied the utility of a heparin–polypyrrole composite as a substrate for human umbilical vein endothelial cell (HUVEC) growth. We found that the polymer composites were well suited to support cell attachment and growth; displaying low surface hydrophobicity (water contact angle of approximately 20°) and roughness, Rq of approximately 10–12 nm. Doubling times for HUVEC on heparin–polypyrrole were greater than observed for gelatin-coated tissue culture polystyrene (44 and 36 h, respectively), however, the cells did proliferate to cover the polymer in an even monolayer. The initial mechanism of attachment and subsequent proliferation of HUVEC on heparin–polypyrrole was critically dependent on the presence of the serum adhesion glycoprotein vitronectin. Polymers that were composed of polypyrrole and sodium nitrate were more hydrophobic than heparin–polypyrrole and they did not support HUVEC growth. Given the relative ease with which these polymer composites can be electrochemically synthesized, the diverse range of cellular signal agents, e.g. growth factors, that can be incorporated within them, and the high degree of control that can be achieved in the release–surface exposure of these agents, we suggest that polypyrrole composites could serve a useful role as smart biomaterials in the near future. © 1999 Kluwer Academic Publishers     

Effect of a peripheral gas supply on the hydrodynamics of a spouting bed

The results of experimental investigations of the resistance of a pyramidal spouting bed with a peripheral gas supply are discussed, including the rates at the beginning and end of the process of spouting and material entrainment from an apparatus. Data is generalized in the form of dimensionless relations.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. 67, Nos. 1–2, pp. 39–42, July–August, 1994.     

Temperature measurements using a birefringent sensor

An optical method for temperature measurements is proposed based on the use of an autocollimation polarimeter and a sensitive birefringent plate. The basic expressions that describe the operation of the system are presented. It is shown that with the use of a quartz plate 1.5 mm thick the device makes it possible to determine values of temperature in the region of –80 to +150°C.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 5–6, pp. 475–482, November–December, 1994.     

Solid hydrogen and deuterium. II. Pressure and compressibility calculated by a lowest-order constrained-variation method

The pressure and the compressibility of solid H₂ and D₂ are obtained from ground-state energies calculated by means of a modified variational lowest-order constrained-variation (LOCV) method. Both fcc and hcp structures are considered, but results are given for the fcc structure only. The pressure and the compressibility are calculated or estimated from the dependence of the ground-state energy on density or molar volume, generally in a density region of 0.65^–3 to 1.3^–3, corresponding to a molar volume of 12–24 cm³/mole, where = 2.958 å, and the calculations are done for five different two-body potentials. Theoretical results for the pressure are 340–460 atm for solid H₂ at a particle density of 0.82^–3 or a molar volume of 19 cm³/mole, and 370–490 atm for solid ⁴He at a particle density of 0.92^–3 or a molar volume of 17 cm³/mole. The corresponding experimental results are 650 and 700 atm, respectively. Theoretical results for the compressibility are 210 × 10^–6 to 260 × 10^–6 atm^–1 for solid H₂ at a particle density of 0.82^–3 or a molar volume of 19 cm³/mole, and 150 × 10^–6 to 180 × 10^–6 atm^–1 for solid D₂ at a particle density of 0.92^–3 or a molar volume of 17 cm³/mole. The corresponding experimental results are 180 × 10^–6 and 140 × 10^–6 atm^–1, respectively. The agreement with experimental results is better for higher densities.     

Deviation from Wiedemann–Franz Law for the Thermal Conductivity of Liquid Tin and Lead at Elevated Temperature

The thermal conductivities of tin and lead in solid and liquid states have been determined using a nonstationary hot wire method. Measurements on tin and lead were carried out over temperature ranges of 293 to 1473 K and 293 to 1373 K, respectively. The thermal conductivity of solid tin is 63.9±1.3 Wm^–1K^–1 at 293 K and decreases with an increase in temperature, with a value of 56.6±0.9 Wm^–1K^–1 at 473 K. For solid lead, the thermal conductivity is 36.1±0.6 Wm^–1K^–1 at 293 K, decreases with an increase in temperature, and has a value of 29.1±1.1 Wm^–1K^–1 at 573 K. The temperature dependences for solid tin and lead are in good agreement with those estimated from the Wiedemann–Franz law using electrical conductivity values. The thermal conductivities of liquid tin displayed a value of 25.7±1.0 Wm^–1K^–1 at 573 K, and then increased, showing a maximum value of about 30.1 Wm^–1K^–1 at 673 K. Subsequently, the thermal conductivities gradually decreased with increasing temperature and the thermal conductivity was 10.1±1.0 Wm^–1K^–1 at 1473 K. In the case of liquid lead, the same tendency, as was the case of tin, was observed. The thermal conductivities of liquid lead displayed a value of 15.4±1.2 Wm^–1K^–1 at 673 K, with a maximum value of about 15.6 Wm^–1K^–1 at 773 K and a minimum value of about 11.4±0.6 Wm^–1K^–1 at 1373 K. The temperature dependence of thermal conductivity values in both liquids is discussed from the viewpoint of the Wiedemann–Franz law. The thermal conductivities for Group 14 elements at each temperature were compared.     

Magnetic Dynamics in Condensed Oxygen: Recent Experimental Results

The spin dynamics in the condensed phases of ambient–pressure molecular oxygen (liquid, plastic–crystalline (–), magnetically disordered (–) and fully ordered –O ₂ ) iS investigated by means of the concurrent use of neutron scattering and muon–spin relaxation. Above the transition the magnetic dynamics is governed by fast paramagnetic fluctuations whose spectrum is determined from the S(Q,) dynamic structure factors accessible from inelastic neutron scattering. Such information is shown to provide a key to understand the non–trivial temperature dependence of longitudinal relaxation rates found in muon spin relaxation measurements. Recent neutron scattering measurements performed within the magnetically ordered –phase under high–resolution conditions reveal the presence of a low–energy excitation of magnetic origin, unnoticed in a previous polarized–neutron experiment, which corresponds to the continuation to longer wavevectors of the spin–wave mode detected in antiferromagnetic resonance (AFMR) experiments carried out by optical means.     

Analysis of Turbulence Models and Investigation of the Structure of the Flow in a Hydrocyclone

A numerical investigation of the structure of the flow in a hydrocyclone has been carried out on the basis of Reynolds equations with the use of various models of turbulence: the k– model, the k– RNG (ReNormalization Group) model, the k– model corrected for the Richardson number Ri, and the k– model. It is shown that the distributions of the velocities and pressure in a hydrocyclone obtained with the k– Ri model, in which the influence of the rotation of the flow on the processes of generation/dissipation of turbulence and the anisotropy of the turbulent pulsations are taken into account, coincide most closely with the experimental ones.