Application of coherent-optical methods in physical studies of evaporation

The application of the methods of laser and holographic interferometry to the problems of measuring evaporation rates is examined. Mass transfer accompanying evaporation in the region of extradiffusion monitoring is studied.Notation j_v specific mass flux of the vapor, kg/(m²·sec) - _c coefficient of condensation - _v coefficient of evaporation - D coefficient of diffusion - m²/sec, wetting angle - R radius of the vessel, m - time, sec - h height of the segment, m - wavelength of the laser radiation, m - N order of the interference fringe or the number of fringes passing through a given point - density of the matter, kg/m³ - length of the cell with the liquid of interest, m - T temperature, K - n refractive index of the medium - m mass - kg, V volume of the spheroidal segment, m³ - _liq and _g molar mass, kg/mole - C₀ and C_p concentration of vapor in the gas, kg/m³ - a and b semiaxes of the spheroid, m - _e ellipsoidal coordinate of a point on the surface, m² - c/n derivative along the normal - r coordinate of a point on the surface of evaporation, m - n change in the refractive index of the medium Indices st standard liquid - liq liquid - g gas - 0 starting state - p equilibrium pressure Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 605–611, October, 1988.     

Effect of Intense Self-Irradiation on the Phase Composition of Metallic Plutonium

The crystal structure of film samples of "high-level" (based on ²³⁸Pu) and low-level (based on ²³⁹Pu) metallic plutonium during their prolonged (up to 343 days) storage (self-irradiation) at room temperature was studied by X-ray diffraction. In the samples of high-level plutonium, the -Pu and -Pu lattices coexist. In the period of 40-60 days, the other known crystal modifications of plutonium (-Pu, -Pu, -Pu, and -Pu) are also present. Low-level plutonium had only the -Pu lattice. A possible origin of this phenomenon is discussed.     

Temperature effects on the properties of Ge thin films

The effects of substrate temperature (T_s) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10^–2 ohm-cm) and high mobility (280 cm²/V·s) films were obtained at T_s=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms.     

Differential-flow-induced instability in a cubic autocatalator system

The formation of spatio-temporal stable patterns is considered for a reaction-diffusion-convection system based upon the cubic autocatalator, A + 2B 3B, B C, with the reactant A being replenished by the slow decay of some precursor P via the simple step P A. The reaction is considered in a differential-flow reactor in the form of a ring. It is assumed that the reactant A is immobilised within the reactor and the autocatalyst B is allowed to flow through the reactor with a constant velocity as well as being able to diffuse. The linear stability of the spatially uniform steady state (a, b) = (µ^–1, µ), where a and b are the dimensionless concentrations of the reactant A and autocatalyst B, and µ is a parameter reflecting the initial concentration of the precursor P, is discussed first. It is shown that a necessary condition for the bifurcation of this steady state to stable, spatially non-uniform, flow-generated patterns is that the flow parameter > _c(µ, ) where _c(µ,) is a (strictly positive) critical value of and is the dimensionless diffusion coefficient of the species B and also reflects the size of the system. Values of _c at which these bifurcations occur are derived in terms of µ and . Further information about the nature of the bifurcating branches (close to their bifurcation points) is obtained from a weakly nonlinear analysis. This reveals that both supercritical and subcritical Hopf bifurcations are possible. The bifurcating branches are then followed numerically by means of a path-following method, with the parameter as a bifurcation parameter, for representatives values of µ and . It is found that multiple stable patterns can exist and that it is also possible that any of these can lose stability through secondary Hopf bifurcations. This typically gives rise to spatio-temporal quasiperiodic transients through which the system is ultimately attracted to one of the remaining available stable patterns.     

Thermodynamics of Rubidium Uranoniobate

The standard enthalpies of formartion of crystalline -RbNbUO₆, -RbNbUO₆, and RbNbUO₆·H₂O at 298.15 K were determined. The temperature dependence of the heat capacity of -RbNbUO₆, RbNbUO₆·H₂O, and -RbNbUO₆ was studied in the range 60-300 K. The thermodynamic functions and equilibrium constants of the reactions involved in synthesis of rubidium uranoniobates at various temperatures were calculated.     

Reactivity of α-tricalcium phosphate

The reactivity of -tricalcium phosphate (-TCP) in forming hydroxyapatite (HAp) at 37°C was investigated. The effects of synthesis route, HAp seeding and the presence of calcium salts on the mechanism and extent of HAp formation were examined by pH measurements and/or isothermal calorimetric analyses. A synthesis temperature at the lower end in the temperature range of 1100–1300°C and the reaction of -TCP with a high specific surface area greatly improved rate and extent of HAp formation. The time for complete reaction decreased from 18 h to 14 h, when the reaction was carried out in the presence of 1 wt% of HAp seeds; the hydrolysis mechanism did not change. At HAp seeds proportion of 5 wt% and 10 wt%, transformation occurred without a nucleation period. The calcium salt additives studied were anhydrous and dihydrate form of dicalcium phosphate (CaHPO₄ and CaHPO₄ · 2H₂O), calcium carbonate (CaCO₃), and calcium sulfate hemihydrate (CaSO₄ · 1/2H₂O). All the additives delayed HAp formation as determined by the isothermal calorimetric analyses. Their retarding effects in decreasing order are CaCO₃, CaSO₄ · 1/2H₂O, DCPD, DCP. CaCO₃ almost completely retarded HAp formation. After 24 h, hydrolysis was complete only for pure -TCP and for the -TCP-DCP blend. Reaction was complete in other formulations before 48 h except for the CaCO₃-containing blend. In all mixtures conversion to HAp occurred without forming any intermediates. However gypsum formed in the mixture containing CaSO₄ · 1/2H₂O. All the -TCP-additive mixtures, excluding -TCP-CaCO₃, reached nominally the same strength value after 24 h of reaction as governed by the transformation of -TCP to HAp. For phase-pure -TCP, the average tensile strength changed from 0.36 ± 0.03 MPa to 7.26 ± 0.6 MPa. Upon hydrolysis only the CaSO₄ · 1/2H₂O-containing mixture exhibited slightly higher strength averaging 8.36 ± 0.9 MPa.     

Elastic energy of the vortex state in type II superconductors. I. High inductions

The elastic properties of the flux line lattice (FLL) in type II superconductors are calculated from the linearized Ginzburg-Landau (GL) theory for large inductionsBH _c2 . They appear to be strongly nonlocal, i.e., the elastic modulic ₁₁ andc ₄₄ for homogeneous deformations do not apply if the strain field varies over distances /(1–B/H _c2 )^1/2 d ( is the penetration depth,d is the FL distance). For smaller strain wavelength,c ₁₁ andc ₄₄ are smaller by factors (1–B/H _c2 )²/2 ² and (1–B/H _c2 )/ 2 ² , respectively. The order parameter and local field of a deformed FLL exhibit the expected spatial frequency modulation, but also a pronounced amplitude modulation whose degree of modulation increases with the strain wavelength. The results of further calculations avoiding the linearization of the GL theory are given.     

Microstructural study of two LAS-type glass-ceramics and their parent glass

The two glass-ceramics studied here derive from the complex system (MgO,ZnO,Li₂O)-Al₂O₃-SiO₂ and are obtained by controlled devitrification of the same parent glass. Although they have the same chemical composition, one is a -quartz (or -eucryptite) type while the other one is a -spodumene glass-ceramic. A detailed microstructural analysis of these materials has been performed at different scales by several complementary characterization methods (SEM, TEM, DTA, XRD and FTIR). This extensive study has shown the great microstructure difference (grain distribution, grain size, nature of vitreous and crystalline phases) between these two glass-ceramics obtained from the same parent glass.     

Thermal diffusivity of inhomogeneous systems

The possibility of analyzing the nonsteady temperature fields of inhomogeneous systems using the quasi-homogeneous-body model is investigated.Notation t, t_I, t_i temperature of quasi-homogeneous body inhomogeneous system, and i-th component of system - a, , c thermal diffusivity and conductivity and volume specific heat of quasi-homogeneous body - a_{i i}, c_i same quantities for the i-th component - q heat flux - S, V system surface and volume - x, y coordinates - macrodimension of system - dimensionless temperature Fo=a/² - Bi=/ Fourier and Biot numbers - N number of plates - =h/ ratio of micro- and macrodimensions - _V, volumeaveraged and mean-square error of dimensionless-temperature determination - time - m_i i-th component concentration Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 126–133, July, 1980.     

Geometrical factors for parts of an infinite cylindrical surface

A method is described for calculating geometrical factors, allowing for attenuation of radiation by the medium, and computing radiative heat transfer between coaxial strips forming part of a cylinder.Notation mean generalized geometrical factor - local generalized geometrical factor for a closed infinite cylindrical surface - F surface area - l length of ray between elements dF_m - D and H diameter and length of cylinder - k ray attenuation coefficient - equivalent solid angle [1] determined from the condition _mm=1 at =0 for a closed surface - f () indicatrix of the specific radiation intensity (a quantity analogous to the specific luminous intensity [1]) - angle between the normal to an element of surface and the ray linking the surface elements - and angles in a section of the surface - angle between the radius and the chord subtending the projections of dF_mon the section - angle between the radius and the chord subtending the projection of element dF_mon the section and the edge of the surface - acute angle between rayl and the generator of the cylinder - ₀ half subtended angle for the arc of a section of the surface - S₂ and M generalized local geometrical factors in the notation of [2] (s₂ and is shown in Table 2 - M local factor for an infinite cylinder with a semicircular cross section for a point in the middle of the plane part of the surface; a table of values of M is given in [2]) - n number of strips     

On the analysis of tunneling data for A15 superconductors

We examine the applicability of the standard McMillan inversion of Eliashberg's equations for superconductors with a nonconstant electronic density of statesN(). We do this usign simple models forN() and a realistically shapedN() taken from recent band structure work for Nb₃Sn. It turns out that peak structure inN() near _F may lead to gross errors in the derived Eliashberg function ²F() when the energy dependence ofN() is omitted in the inversion procedure. For Nb₃Sn, this leads to a 40% overestimate of when ²F() is evaluated via the standard McMillan program.     

Barium titanate fabricated from fur-fibres

Long-fibrous barium titanate (BaTiO₃) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K₂O·11TiO₂·3H₂O) and barium hydroxide (Ba(OH)₂). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K₂O·4TiO₂, 1–10 mm long and 1–100 m in diameter, were obtained by heating a mixture of K₂CO₃ and TiO₂ powders at 1000 C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K₂O·11TiO₂·3H₂O). Long-fibrous BaTiO₃, with fibres 100m–1mm long and 1–10 m in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)₂ (Ba/Ti ratio of 1) at 150 C for 24 h. As-prepared long-fibrous BaTiO₃ was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 C, but heat treatment at 1300 C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO₃ powder at a low temperature of 150 C.     

Numerical calculation of a generalized thermal model of radio-electronic apparatus

A method is proposed for numerical calculation of the temperature field of a generalized model of electronic equipment with high component density.Notation x,y,z,x,y spatial coordinates, m - time, sec - L_x, L_v, L_z dimensions of heated zone, m - _x, _y, _z effective thermal-conductivity coefficients of heated zone, W/m·deg - ₂ thermal conductivity of chassis, W/m·deg - a _z thermal diffusivity of heated zone along z axis, m²/sec - c₁ effective specific heat of heated zone, J/kg·deg - ₁ effective density of heated zone, kg/m³ - c₃, ₃, c₂, ₂ thermophysical characteristics of cooling agent and chassis, J/kg·deg·kg/m³ - q_v(x, ), q(x, y) volume heat-source distribution, W/m³ - q_s (x) surface heat-source distribution, W/m² - p number of cooling agent channels - Fo Fourier number - Bi Biot number - Uⁱ coolant velocity in i-th channel, m/sec - T₁(x, ), T₂(x, ), T₃(x, ) temperature distribution of heated zone, chassis, and coolant, °K - T₃₀, T₁₀(x), T₂₀(x) initial temperatures, °K - T_3in coolant temperature at input to channel, °K - T_T(x) effective temperature distribution of heat loss elements, °K - T_C temperature of external medium, °K - dimensionless heated zone temperature - _v(x) local volume heat exchange coefficient, W/m³·deg - ₁₂(x), _1C(x), _1T(x) heat liberation coefficients - W/m²·sec; ₂₁(x, y), _2c(x, y), _2T(x, y) volume heat-exchange coefficients of chassis with heated zone, medium, and cooling elements, W/m³·deg Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 876–882, May, 1981.     

Application of inert radioactive gases in the study of solids

The behaviour of different iron salts (FeSO₄.7 H₂O, FeC₂O₄.2 H₂O, Mohr's salt, and basic iron carbonate) was studied by means of the emanation method, DTA and dilatometry. The salts were heated within the temperature range of 20 to 1100 C, under identical conditions. The results obtained are compared and the process of thermal decomposition of the different salts is discussed.The activity of ferric oxide obtained by decomposition of various iron salts is estimated, and it is suggested that the low activity of the sulphate-derived ferric oxides is related to a low thermal annealing rate, while the higher activities of the other two resultant ferric oxides are similarly related to higher thermal annealing rates.     

Microstructure and topological analysis of Co : Al2O3 nanocermets in new FCC and BCC metastable Co-structures

Co : Al₂O₃nanocermets are synthesized by co-reducing Co²⁺-cations dispersed in a mesoporous AlO(OH) · H₂O matrix (amorphous) in a pure H₂atmosphere at 850–1150 K. The dispersed Co²⁺-cations in pores co-reduce to separated Co-particles of controlled size, as small as 50 nm, encapsulated in thin Al₂O₃films, which are formed in-situ by molecular decomposition of the matrix, 2AlO(OH) · H₂O Al₂O₃+ (2 + 1)H₂O. The Al₂O₃film which coats Co-particles has an amorphous structure. This is possible only if it is extremely thin limited to a thickness of t< 2r _c, with r _c 1.9 nm the critical size of its nucleation and growth into a stable crystallite. The thin Al₂O₃surface film supports the formation and existence of Co-particles in a modified FCC or BCC crystal structure. As a result, unusually, large crystallites of an average 100 nm diameter could be observed. Normally, such large particles of pure Co-metal exist in an HCP structure which undergoes a reversible martensitic transformation to FCC structure at 695 K. The results are analyzed and discussed in terms of microstructure, x-ray diffraction and XPS studies of nanocermets prepared under selected conditions.     

Specific heat near the lambda point in 4He and 3He-4He mixtures: Test of universality of the critical exponent and the amplitude ratio,and observation of the critical-tricritical crossover effect

The specific heat under saturated vapor pressure of pure ⁴He and of six ³He-⁴He mixtures up to X = 0.545 was measured in the temperature range 3 × 10^–6 <¦T-T ¦ <10^–2 K. The critical exponents and along the path = are independent of X up to X = 0.545, where (= ₃ – ₄) is the difference between chemical potentials. If we take account of higher order terms, the exponent (= ) and the amplitude ratio A /A are independent of X up to X = 0.545. The values of and A /A are –0.023 and 1.090, respectively. The critical-tricritical crossover effect was observed for X = 0.545 and the boundary of crossover region closest to the critical region was at /T = (1–2) × 10^–4, where is the distance ¦T – T ¦ along the path = . This value is in good agreement with the estimated value by Riedel et al. But, remarkably, in the case of X = 0.439 this effect was not observed.     

Investigation of the thermal and electrical transport properties of niobium and niobium films at temperatures between 9 and 50 K

The thermal conductivity and the electrical conductivity of niobium crystals and niobium films have been investigated in the normal state from 9 to 50 K. The deviations from the Matthiessen rule, w=/T+T², have been studied in detail for the thermal case. The investigation shows a slight dependence of the electron-phonon scattering coefficient upon the impurity content of the sample. With the specific electrical residual resistivity ₀ as the measure for the impurity content, the following correlation can be formulated: =1.2×10^-2[₀/-cm)]^0.04, being obtained in cm/W K. Above 20 K an additional scattering mechanism occurs. The temperature dependence of the additional resistance W between 20 and 50 K is proportional to T ^5.5 ··· T ⁴. Possible causes of this phenomenon are discussed. For the discussion, all the data available in the literature on the thermal conductivity of niobium in this temperature region are used.     

A note on the similarity solutions for free convection on a vertical plate

Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x and when the (non-dimensional) surface heat flux is –x are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value ₀, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >₀, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as ₀ and as –1, and the natures of these singularities are discussed.     

Dielectric Properties of Melt-Grown Cd1 – xZnxTe Crystals

The real (") and imaginary (") parts of the complex dielectric permittivity of Cd_{1 – x} Zn _x Te (x= 0.1–0.2) crystals are measured as a function of temperature and frequency. The "-vs.-temperature data show a maximum, and " rises rapidly at about the same temperature. This behavior is interpreted in terms of compositional fluctuations, structural defects, and the associated internal electric fields.     

γ ? α2 Phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%)

The ₂ phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. ₂ and phases were found at grain boundaries. ₂ layers that suspended in layers and interfacial ledge higher than 2d ₍₁₁₁₎ at /₂ interfaces were observed in the lamellar grains. These facts indicated that ₂ phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced ₂ phase transformation and dynamic recrystallization resulted in the presence of particles at grain boundaries. A structural and compositional transition area between deformation-induced ₂(or ) and its adjacently original (or ₂) phases was found by HREM and EDS and is suggested as a way to transform between and ₂ phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms.