Properties of Va metal-B films prepared by r.f.-sputtering

Ta_100-x B _x alloy films were prepared by r.f.-sputtering in the chemical composition range 45 x 77. Ta_100-x B _x (45 x 58) films consist of the amorphous phase, while the TaB₂ crystal phase was observed in Ta_100-x B _x (66 x 77) films. A remarkable preferred orientation with the (001) plane of TaB₂ parallel to the film surface was observed in Ta₃₄B₆₆. The d.c. electrical conductivity of Ta_100-x B _x (45 x 77) films decreases with increasing boron content in the range 6.7 × 10³ to 1.3 × 10^3–1 cm^–1. The micro-Vickers hardness of Ta_100-x B _x (45 x 77) films was in the range 2200 to 2600 kg mm^–2.     

The existence of Taylor vortices and wide-gap instabilities in spherical Couette flow

Summary The flow of a viscous incompressible fluid in the gap between two concentric spheres was investigated for the case where only the inner sphere rotates and the outer one is stationary. Flow visualization studies were carried out for a wide range of Reynolds numbers (Re2·10⁵) and aspect ratios (0.080.5) to determine the instabilities during the laminar-turbulent transition and the corresponding critical Reynolds numbers as a function of the aspect ratio. It was found that the laminar basic flow loses its stability at the stability threshold in different ways. The instabilities occurring depend strongly on the aspect ratio and the initial conditions. For small and medium aspect ratios (0.080.25), experiments were carried out as a function of the Reynolds number to determine the regions of existence for basic flow, Taylor vortex flow, supercritical basic flow and furthermore, to give the best fit for the maximum number of pairs of Taylor vortices as a function of aspect ratio. For wide gaps (0.330.5), however, Taylor vortices could not be detected. The first instability manifests itself as a break of the spatial symmetry and non-axisymmetric secondary waves with spiral arms appear depending on the Reynolds number. For =0.33, secondary waves with an azimuthal wave numbern=six, five and four were found, while in the gap with an aspect ratio of =0.5 secondary waves withn=five, four and three spiral arms exist. Frequencies of these secondary waves were measured, the corresponding critical Reynolds numbers and the transition Reynolds numbers during the transition to turbulence were found. The flow modes occurring at the poles look very similar to those found in the flow between two rotating disks. Effects of non-uniqueness and hysteresis were determined as a function of the acceleration rate.     

Microstructural development in cast alloys based on the β-NiAl–β′-Ni2AlTi–γ′-Ni3Al–α-Cr system

An investigation of microstructural development in three arc-cast Ni–Al–Cr–Ti multiphase alloys derived from the B2 type -NiAl phase is presented. Detailed microstructural characterization of Ni–25 at % Al–20 at % Cr–15 at % Ti, Ni–26 at % Al–21 at % Cr–11 at % Ti and Ni–25 at % Al–24 at % Cr–15 at % Ti materials by transmission electron microscopy (TEM), is described. Microstructural development is examined in both the as-cast condition and after 140 h homogenization treatments at both 850 and 1100 °C. The formation of a eutectic between an L21-type phase (Heusler phase, with a nominal composition of Ni2AlTi) and elemental -Cr is examined. The precipitation of within () and vice versa, in both the inter- and intradendritic regions, is considered. The formation of L12-type (nominally Ni3Al) precipitates within the and -phases is discussed, as is the transformation of to two-phase / during ageing. © 1998 Chapman & Hall     

Electrostatic Spray Deposition of Perovskite-Type Oxides Thin Films with Porous Microstructure

The deposition of perovskite-type oxides thin films [La_0.8Sr_0.2MnO₃ and La_1–xSr_xCo_1–yFe_yO₃ (0 x 0.4 and 0 y 1)] was investigated using the electrostatic spray deposition (ESD) technique. Lanthanum nitrate, strontium chloride and manganese nitrate, or cobalt nitrate and iron nitrate were dissolved into a mixture of 33 vol% ethanol and 67 vol% butyl carbitol, which was used as precursor solution. The effect of process parameters, such as deposition temperature, deposition time and concentration of precursor solution, on the surface morphology and microstructure of thin films were examined with scanning electron microscope (SEM). The deposited La_0.8Sr_0.2MnO₃ and La_1–xSr_xCo_1–yFe_yO₃ thin films were amorphous at the used deposition temperature (573K). Subsequently, the samples were heated at 1173 K for 2 h and were studied using X-ray diffraction (XRD). As the result, the crystal structure of the samples transformed to the desired perovskite phase. The chemical analysis of the thin films was investigated using energy dispersion X-ray (EDX) analysis. The observed chemical compositions of the samples were in a fair agreement with the ones of the starting solutions.     

Crystallization process and magnetic properties of Fe100−x,B x (10 ≦ × ≦ 35) amorphous alloys and supersaturated state of boron inα-Fe

Amorphous specimens of Fe_100–x B _x were prepared in the range 10 × 35 at % B by a single-roller method. The crystallization process and the boron concentration dependence of the Curie temperature were examined by differential scanning calorimetry, X-ray diffraction, Mössbauer spectroscopy and magnetic measurements. Two-step crystallization was observed in specimens with× < 17: amorphous amorphous + boron-supersaturated b c c phase (-Fe(B)) t-Fe₃B +-Fe. A single-Fe(B) phase was not observed. The transition temperature from t-Fe₃B to stable (-Fe + t-Fe₂B) sensitively depends on the boron content in the alloys. The crystallization temperature (T _x) of the amorphous alloys was almost unchanged for 17 × 31, but increased remarkably at high boron concentrations of× 33, where the decomposition products consisted of t-Fe₂B and o-FeB. The Curie temperature (T _c) of the amorphous phase was as low as 480 K at× = 10, increased with increasing boron content up to 820 K and then decreased in the high boron concentration alloys of× > 28. A single-Fe(B) phase was not detected in the as-quenched specimens of× = 8 and 10. The phase coexisted with the o-Fe₃B and amorphous phases. The lattice parameter of the phase was 0.2861₀ nm which was smaller than that of pure iron by 2/1000, indicating the substitutional occupation of boron atoms in the b c c lattice.     

Microstructure and crystallographic texture of rolled polycrystalline Fe3Al

An imperfectly B₂ ordered Fe₃Al aggregate was cast, thermomechanically hot rolled and finally annealed at 870 K. Subsequently, the specimen was rolled at 800–830 K to a strain of 80%. The microstructure and the crystallographic texture of the rolled polycrystalline sample was investigated within the range =20–80%. The microstructure consisted of flat, elongated grains. In numerous grains straight slip lines were detected. Even after =80% recrystallization was not observed. The rolling texture of Fe₃Al considerably deviates from that of non-ordered body centered cubic (b.c.c.) alloys and pure b.c.c. metals. The {111}uvw texture fibre (7-fibre) was very pronounced, while the {hkl}110 fibre (-fibre) was very weak. The {112}110 orientation which represents the strongest texture component in non-ordered b.c.c. alloys did not occur at all. The textures are discussed in terms of the {110}111, {112}111, {112}111 and {123}111 slip systems. The contribution of crystallographic slip of the various types of potential slip systems was simulated by means of the Taylor theory.     

Coupled heat and mass transfer in mixed convection over a VHF/VMF wedge in porous media: The entire regime

Summary The development of flow and heat transfer of a viscous electrically conducting fluid in the stagnation point region of a three-dimensional body with an applied magnetic field is studied when the external stream is set into an impulsive motion from rest and at the same time the surface temperature is suddenly raised from that of the surrounding fluid. This analysis includes both short time solution (Rayleigh-type of solution) and the steady-state solution as time tends to infinity (Falkner-Skan type of solution). The unsteady three-dimensional boundary layer equations represented by a system of parabolic partial differential equations are solved numerically using an implicit finite-difference scheme. For certain particular cases analytical solutions are obtained. In the absence of the magnetic field, the reverse flow occurs in the transverse component of the velocity in a certain portion of the saddle-point region (–1c<–0.4, wherec=b/a is the ratio of the velocity gradients in they- andx-directions at the edge of the boundary layer). The magnetic field delays or prevents the reverse flow. The surface shear stresses in the principal and transverse directions and the surface heat transfer increase with the magnetic field both in nodal point (0c1) and saddle point (–1c<0) regions. For a fixed magnetic field, the surface shear stress inx-direction and the surface heat transfer increase with time in nodal and saddle point regions, but the surface shear stress in the transverse direction increases with time for 0<c1 and decreases with increasing time for –1c<0.     

The Ni3Al-Ni3Cr-Ni3Ru section of the Ni-Cr-Al-Ru system

An investigation is reported of the 75 at% nickel section of the Ni-Cr-Al-Ru system at 1523 and 1273 K. Constitutional data obtained by electron probe microanalysis, X-ray diffraction and microscopical examination are presented as partial isothermal sections. At 1523 K, the major part of the section consists of phase, while the aluminium-rich region contains a and+ region; the extent of the solid solution of chromium and ruthenium in totals ~ 4 at%. The ruthenium-rich corner of the section shows a two-phase region consisting of + ruthenium-rich solid solution. At 1273 K the,+ and + ruthenium regions increase in extent. The/ mismatch values in the equilibrated alloys studied lie in the range ~ –0.08 to –0.39%. Constitutional features of as-cast alloys are also reported.     

Methods of calculating heat transfer in metallurgical plants and control models

Modern deterministic approaches to constructing mathematical models and strategic and tactical control models for a production process with reference to metallurgy and labor activity are considered. Examples of using complete and simplified mathematical models to evaluate optimal conditions of production and technological processes are presented.Notation p medium density - t time - i medium enthalpy - thermal conductivity - T, temperature - q_v intensity of internal heat sources - q_rad vector of heat transferred by radiation; m and n, number of volume and surface zones - A radiation transfer coefficient - g convective transfer coefficient - Q_j heat sources - c heat capacity per unit volume - w_l.s velocity along the x-axis - x, y, z coordinates - q_s.t. source term - s layer thickness - u, v gas velocity components - c_p gas heat capacity at constant pressure - _t turbulent viscosity - Pr_t turbulent Prandtl number - q^ch heat release power due to chemical reactions - q^r heat by radiation - number of nodes - V volume of a zone or node - A _j ^j radiation to answer coefficient proportional to the intrinsic radiation flow leaving the zone h - C concentration of a reagent to be treated - C₂ equilibrium concentration - C _j initial concentration of a reagent in a treating medium - relative initial potential - L₀ theoretical reagent flow rate necessary for complete reaction - efficiency (effectiveness) - _s heat transfer efficiency - _ch physicochemical efficiency - W flow heat capacity - G mass flow - F_x surface - k_ch and k total heat and mass transfer coefficients - Z_ch and Z_enh enhancement density centers of heat and mass transfer processes - Q_L relative potential of the physicochemical and thermal interaction - generalized chemical-thermal efficiency - _t.ch. and _t final physicochemical and thermal efficiencies - q_ch and q_u useful energy expenditures for chemical and thermal processes - _ch and _t effective resistances determined by the extent of using chemical-thermal regeneration, thermal efficiency of an extra modulus and other factors - b_d.r. energy expenditures for direct use of a reagent - F_opt complex optimality criterion - Q_res resultant heat flux - K_non degree of heating nonuniformity - A, B weight coefficients - _loss and _loss coefficients of heat losses by the working space and under chemical and mechanical incomplete combustion - _r regeneration degree - J_F optimality criterion with respect to heat flow rate and capital expenses - b_f specific fuel flow rate - Q output (commercial products) - V₀ and V₁ effective labor potential and current potential per labor product - K labor activity intensity - F_e extensive factor of the labor activity (last labor) - g_out output - =N labor activity capacity - N pure products (national income) - q₁ relative magnitude of useful products - Q useful products - C cost - _ac labor activity effectiveness - complex coefficient of the labor potential effectiveness - complex extensive factor of the labor activity - _p.r. profit rate. Indices - i, j, s, m,l.s. zones transferring and absorbing the heat, surface, material, and lining-setting - b liquid or solid body (lining-setting material) - l laminar boundary layer at the zone-surface boundary - L_f, 1, 2, 0, , inlet temperature parameters of the heating medium, the medium to be treated, the treating medium and the surrounding medium at the inlet and outlet - ch chemical potential - fix assigned potential - node Ural Polytechnic Institute, Ekaterinburg, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 259–270, March, 1993.     

Heat Capacity Measurement of Oxygen-Dissolved V–Ti Alloys1

The heat capacities of (V_1–y Ti _y ) O _x alloys (x=0.13 to 0.18, y=0.06 to 0.23) were measured in the temperature range from 380 to 900K with a differential scanning calorimeter. A -type peak corresponding to the order–disorder phase transition was observed in the heat capacity curves of each (V_1–y Ti _y ) O _x alloy (x0.18, y0.09). The baseline of the measured heat capacity was estimated with the harmonic term and the anharmonic term of the lattice vibration. The entropy changes at the phase transition were determined by subtracting the baseline mentioned above from the measured heat capacities. The experimental entropy changes were in good agreement with those calculated theoretically, based on the arrangement of oxygen and the limited coordination number of oxygen around vanadium. There were no peaks in the heat capacity curves for the samples with compositions y0.16. Introduction of titanium, which has a larger ionic radius than that of vanadium, may disturb the ordering of oxygen around the metal.     

Tilted and Crossing Vortex Chains in Layered Superconductors

No Heading In presence of the Josephson vortex lattice in layered superconductors, small c-axis magnetic field penetrates in the form of vortex chains. In general, structure of a single chain is determined by the ratio of the London [] and Josephson [_J] lengths, = /_J. The chain is composed of tilted vortices at large s (tilted chain) and at small s it consists of crossing array of Josephson vortices and pancake-vortex stacks (crossing chain). We study chain structures at the intermediate s and found two types of phase transitions. For 0.6 the ground state is given by the crossing chain in a wide range of pancake separations a [2–3]_J. However, due to attractive coupling between deformed pancake stacks, the equilibrium separation can not exceed some maximum value depending on the in-plane field and . The first phase transition takes place with decreasing pancake-stack separation a at a = [1 – 2]_J, and rather wide range of the ratio , 0.4 0.65. With decreasing a, the crossing chain goes through intermediate strongly-deformed configurations and smoothly transforms into the tilted chain via the second-order phase transition. Another phase transition occurs at very small densities of pancake vortices, a [20 – 30]_J, and only when exceeds a certain critical value 0.5. In this case small c-axis field penetrates in the form of kinks. However, at very small concentration of kinks, the kinked chains are replaced with strongly deformed crossing chains via the first-order phase transition. This transition is accompanied by a very large jump in the pancake density.PACS numbers: 74.25.Qt, 74.25.Op, 74.20.De     

Streamline curvature effects in side-channel spillway flow

Summary Steady flow in side channel spillways is investigated, thereby accounting for the effects of the streamline slope and curvature on the free surface profile. The governing system of equations is linearized in order to discuss the main features of the solutions. Subsequently, the non-linear version is solved by an implicit numerical procedure; particular attention is paid to the stability of the chosen scheme. Finally, the solutions are compared to observations and an almost perfect agreement is found.Notation a reference flow depth - b channel width - F Froude number - g gravitational acceleration - h flow depth - J average energy gradient - K Strickler's roughness coefficient - L lateral inflow length - m root of characteristic polynomial - n Manning's roughness coefficient - p lateral inflow intensity per unit channel width - q lateral inflow intensity - Q discharge - R hydraulic radius - S specific momentum - S _f frictional slope - S ₀ bottom slope - V average cross-sectional velocity - x longitudinal coordinate - X normalized longitudinal coordinate - y normalized flow depth - factor, 01 - factor, 01 - perturbative change in flow depth - relative discharge intensity - relative specific momentum With 7 FiguresSeveral symbols may appear with indices u, d, N, c and then refer to the up-and downstream end of the lateral inflow zone, and to uniform and critical flow conditions, respectively. Primes indicate derivatives with respect to the longitudinal coordinate.     

Stability of metastable phases and microstructures in the ageing process of Al–Mg–Si ternary alloys

Precipitation behaviour of Al–Mg–Si alloys, with balanced (Mg/Si=2), excess silicon (Mg/Si<2) and excess magnesium (Mg/Si>2) compositions, were studied by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and Vickers hardness tests. Four significant exothermic peaks were observed in DSC curves which were attributed to metastable clusters, , and stable phases. The peaks corresponding to and were formed closely in the DSC curves but showed different behaviour in isothermal annealing. The additional peak verifying the precipitation of phases, which has recently been proposed by some workers, was not detected. Transmission electron microscope observations and Vickers microhardness tests showed that precipitates played a major role in improving the hardness, but not precipitates. © 1998 Chapman & Hall     

Precise measurements of critical parameters of sulfur hexafluoride by laser interferometry

A laser interferometry has been applied, in the present study, for determination of the critical temperature and critical exponents of sulfur hexafluoride (SF₆). By means of laser holographic technique by real-time method, a series of Fraunhofer diffraction patterns due to the density fluctuation of the sample fluid in the very vicinity of the critical point has been successively photographed and analyzed. A dual-thermostat system which was designed and constructed for the present purpose has made the sample temperature constant within 15 K for several days. We have obtained 107 data for ( _L– _v)/ _c along the vapor-liquid coexistence curve in the reduced temperature range 10^–6¦T ^*¦7×10^–5 and additional 34 data for the isothermal compressibility in the single phase region. By analyzing these measurements with the aid of the simple power law, the critical temperature and the critical exponents of SF₆ have been determined as T _c=318.708±0.001 K, =0.350±0.004, and =1.24±0.02, respectively.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Spray atomization of two Al–Fe binary alloys: solidification and microstructure characterization

The effect of solidification history on the resultant microstructures in atomized Al–3Fe and Al–7Fe powders is studied, with particular emphasis on the relationships between droplet size, undercooling and phase stability. The atomized Al–Fe powders exhibit four microstructural features, i.e. Al3Fe phase, Al + Al6Fe eutectic, -Al dendrite and a predendritic structure. The presence of these is noted to depend on a kinetic phase competitive growth mechanism, which was determined by the initial undercooling experienced by the powders. The results of scanning electron microscope analysis demonstrate that the content of Fe in the -Al phase increases with decreasing powder particle size, i.e. for Al–3 wt% Fe powders, the content of Fe in the -Al phase is 2.21 and 2.56 wt% corresponding to powder particle sizes of 90 and 33 m, respectively; for Al–7 wt% Fe powders, the content of Fe in the -Al phase is 5.51 and 5.98 wt% corresponding to powder sizes of 90 and 33 m, respectively. In the present study, homogeneous nucleation undercooling, corresponding to the -Al phases, is also estimated using an existing correlation.     

Influence of pore volume on laser performance of Nd : YAG ceramics

For present study, 1.1 at% Nd-doped YAG ceramics with a controlled pore volume (150–930 vol ppm) were fabricated by a solid-state reaction method using high-purity powders. The scattering coefficients of Nd:YAG ceramics, obtained from Fresnel' equation, increased simply with increases in the pore volume. The cw laser output power of Nd:YAG ceramics was clearly related to the scattering coefficients of the specimens examined in the present works, which in turn were affected on the pore volume. The effective scattering coefficients of Nd:YAG ceramics with a pore volume of 150 vol ppm were nearly equivalent to those of a 0.9 at%Nd:YAG single crystal by Czochralski method. As the exciting power was increased under excitation by an 808-nm diode laser, however, the laser output power of the Nd:YAG ceramics exceeded that of the Nd:YAG single crystal because of the fairly large amount of Nd additives. The lasing performance of the Nd:YAG ceramics changed drastically with change in pore volume. On the other hand, lasing performance was not affected by the existence of grain boundaries in the polycrystalline Nd:YAG ceramics.     

Magnetic Properties of High-Resistivity CdTe〈In〉 and CdTe〈Cl〉 Crystals

The magnetic susceptibility of high-resistivity CdTeIn and CdTeCl crystals was measured between 4.2 and 300 K. The susceptibility was found to vary anomalously with temperature. Below 50 K, all the samples were paramagnetic. The observed anomalies are interpreted in terms of donor–acceptor pairs formed by native defects and dopant or uncontrolled impurity atoms. The effect of doping on the 300-K is related to the Van Vleck paramagnetic contribution resulting from the local electric fields of X_i–V _Cdand In_i–V _Cddefect complexes. In CdTeCl, this contribution is insignificant.     

Some electrical characteristics of lithium and yttrium sialons

Some electrical properties of hot-pressed lithium sialons, Li _x/8Si_6–3x/4Al_5x/8O _x N_8–x havingx<5 and an yttrium sialon were measured between 291 and 775 K; the former consisted essentially of a single crystalline phase whereas the latter contained 98% glassy phase. For lithium sialons, the charging and discharging current followed al(t) t ^–nlaw withn=0.8 at room temperature. The d.c. conductivities were about 10^–13 ohm^–1 cm^–1 at 291 K and rose to 5×10^–7 ohm^–1 cm^–1 at 775 K. At high temperatures electrode polarization effects were observed in d.c. measurements. The variation of the conductivity over the frequency range 200 Hz to 9.3 GHz followed the () ⁿ law. The data also fitted the Universal dielectric law,() ^n–1 well, and approximately fitted the Kramers-Kronig relation()/()– =cot (n/2) withn decreasing from 0.95 at 291 K to 0.4 at 775 K. The temperature variations of conductivities did not fit linearly in Arrhenius plots. Very similar behaviour was observed for yttrium sialon except that no electrode polarization was observed. The results have been compared with those obtained previously for pure sialon; the most striking feature revealed being that _d.c. for lithium sialon can be at least 10³ times higher than that of pure sialon. Interpretation of the data in terms of hopping conduction suggests that very similar processes are involved in all three classes of sialon.     

Influence of Multiple‐Scattering Processes on the Laser Probing of Biological Tissues

Theoretical aspects of multiplescattering processes in laser probing of biological tissues have been considered. The method of digital dynamic specklephotography has been described. The results of experimental studies of the nearsurface blood flow and stressedstrained states in a pinstructure–toothroot model are presented.     

Elementary excitations of4He clusters

The elementary excitations of⁴He clusters containingN atoms are investigated by solving the equations of the random phase approximation (RPA) with a phenomenological effective interaction. The calculations were done for 40N728. The effects of the RPA correlations are explicitly discussed. Important deviations from the predictions of the liquid droplet model (LDM) are found up toN500 for the breathing compression mode and up toN100 for surface excitations. Sum rules for compression and surface excitations are also derived and discussed.