Hydrogen diffusion constants in stainless steel and Pd60Ag40 alloy, and permeability of diaphragms made of these metals

Hydrogen permeability through diaphragms made of 12X18H12T stainless steel and Pd₆₀Ag₄₀ alloy under electrolytic hydrogen saturation has been studied with an electrolytic cell with a vacuum chamber. Hydrogen diffusion constants D _H = 3.86 × 10⁻¹⁰ cm² s⁻¹ for stainless steel and D _H = 4.36 × 10⁻⁸ cm² s⁻¹ for Pd₆₀Ag₄₀ alloy have been determined at a temperature of 40°C using the Berrer relations.     

Dual-beam laser analyzer for inhomogeneities in active regions of multielement photodetectors

We describe equipment and a procedure for measuring inhomogeneities in active regions of solar cells, photoelectric transducers, and multielement photodetectors, based on a computer-controlled dual-beam laser scanner including a Pentium III personal computer, an HP-34401A digital multimeter with RS-232 serial interface;, a platform movable along the Y coordinate with the sample multielement photodetector to be tested and a microprobe device for picking up the photocurrents, an optical head with laser photodiodes in the visible (λ₁ = 0.68 μm) and IR (λ₂ = 0.82 μm) ranges scanning along the X coordinate, and a control unit for focusing the laser beams λ₁, λ₂, stabilizing the laser radiation power, and controlling the step motors for the X,Y coordinates. The equipment and procedure enable laser scanning of sample multielement photodetectors, with external dimensions 10 × 10 μm2 to 150 × 150 mm², along the X, Y coordinates at a maximum rate of 100 mm/sec; minimum radiation power of the laser diodes, 10 mW; range of laser beam diameters, 2–50 μm; range of scanning steps along the X, Y coordinates, 5–100 μm; current sensitivity 1·10⁻⁸ A, voltage sensitivity 1·10⁻⁷ V; measurement and analysis accuracy at least 0.5%; storage of color plots of the inhomogeneities in the active regions of the multielement photodetectors on the hard disk of the personal computer, with output of analysis results to a monitor and color printer, 32 color gradations. Software written in Delphi 7.0. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 277–280, March–April, 2006.     

Synthesis of Cr-based mixed oxides by reactive ion beam mixing of Cr/X interfaces (X=Al or Si)

The 3 keV O₂⁺\mathrm{O}_{2}^{+} reactive ion beam mixing of Cr/X interfaces (X=Al or Si) has been used to synthesize Cr-based mixed oxide thin films. The kinetics of growth, composition, and electronic structure of those films has been studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and factor analysis. Initially, for low ion doses, Cr₂O₃ species are formed. Later, with increasing the ion dose, Cr₂O₃ species are first transformed into Cr³⁺–O–X species, and subsequently, those Cr³⁺–O–X species are transformed into Cr⁶⁺–O–X species. This sequential transformation, Cr₂O₃→Cr³⁺–O–X→Cr⁶⁺–O–X, is accompanied by a slight increase of the oxygen concentration and a decrease of the Cr/X ratio in the films formed leading to the synthesis of custom designed Cr-based mixed oxides. The changes observed in the valence band and Auger parameters further support the formation of Cr–X mixed oxide species. Angle resolved X-ray photoelectron spectroscopy shows that for low ion doses, when only Cr₂O₃ and Cr³⁺–O–X species coexist, Cr³⁺–O–X species are located nearer the surface than Cr₂O₃ species, whereas for higher ion doses, when only Cr³⁺–O–X and Cr⁶⁺–O–X species coexist, the Cr⁶⁺–O–X species are those located nearer the surface.     

Mechanisms of creation and destruction of polyhalide V centers in irradiated AHC

The mechanisms of creation and destruction of polyhalide V centers in AHC were modeled by the MNDO semiempirical quantum-chemical method. It is shown that X ₃ ⁻ molecules dissociate from the ground state into X ₂ ⁰ and X⁻ and from the triplet state into X ₂ ⁻ and X⁰, whereas X ₅ ⁻ and X ₇ ⁻ molecules dissociate into X ₃ ⁻ and X ₂ ⁰ and X ₅ ⁻ and X ₂ ⁰ , respectively. At room temperatures, X ₃ ⁻ or larger aggregates, which consist only of X ₃ ⁻ centers, form stable polyhalide V centers. It is shown that the thermal stability decreases when going along the series X ₃ ⁻ , X ₅ ⁻ , and X ₇ ⁻ . The radiation-induced instability of stable F centers in AHC at room temperatures is associated with the destruction of X ₃ ⁻ centers and the thermal instability of X ₅ ⁻ and X ₇ ⁻ centers. E. A. Buketov Karaganda State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 50–54, March, 2000.     

Optical and electronic properties of heusler Cu<Subscript>2</Subscript>MnAl alloy with shape memory effect

A ferromagnetic Heusler Cu₂MnAl alloy with a shape memory effect has been studied in the wide spectral region of 0.25–2.80 μm (0.44–5.35 eV) at room temperature using spectral ellipsometry methods. Dispersion dependences for optical constants n(hν) and κ(hν), dielectric permeability ε(hν), and optical conductivity σ(hν), which is proportional to the interband density of electronic states, have been analyzed. Optical conductivity spectra have been calculated by mathematical modeling based on data for the electronic state densities in both subbands of electrons with spins oriented along and against the magnetization direction. A model of indirect transitions based on the Berglund–Spicer formula has been shown to describe the experimental spectrum only in general terms. The main contribution to the conductivity in the high-frequency spectral region is due to direct transitions of electrons in the vicinities of L, X, and Γ points of the Brillouin zone coupled with Cu atoms whereas low-energy anomalies in the absorption spectrum σ(hν) are caused by electrons coupled with Mn and Al atoms.     

Rapid solidification of Al-Cu-Ag ternary alloy under the free fall condition

The rapid solidification of Al-30%Cu-18%Ag ternary alloy is investigated by using the free fall method. Its solidified microstructure is composed of θ(Al₂Cu), α(Al) and ξ(Ag₂Al) phases. The liquidus temperature and solidus temperature are determined as 778 and 827 K, respectively. The alloy melt undercooled amounts up to ΔT _Max=171 K (0.20T _L). Its microstructural evolution is investigated based on the theoretical analysis of undercooling behavior and nucleation mechanics. It is found that the undercooling increases with the decrease of the diameter of the alloy droplet. When ΔT<78 K, the primary θ(Al₂Cu) phase of the alloy grows into coarse dendrite. When 78 K⩽ΔT⩽171 K, its refined θ(Al₂Cu) phase grows alternatively with α(Al) phase. Once ΔT⩾171 K, its microstructure is characterized by the anomalous (θ+α+ξ) ternary eutectic. Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105)     

Electrical studies of surface reconstruction resulting from chalcogen evaporation at the Ag2±δX/Vacuum interface (X=S, Se)X/Vacuum interface (X=S, Se)

We have investigated the dissociation rates of nonstoichiometric semiconductors Ag_2±δX (X=S, Se) to the vacuum by means of solid-state electrochemical technique. The values of chalcogen fluxes from the sample’s surface were measured versus compound’s composition and temperature. There has been obtained experimental evidence of the surface reconstruction of silver chalcogenides when the exact phase composition δ_cr.(T) is reached. This critical value δ_cr. correlates with the order-disorder transition in the silver sublattice for the Ag_2±δX/vacuum interface.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

Calculation of radiative transition probabilities and radiative recombination rate coefficients for H2, OH, H 2+ and OH+ molecules

A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B → X) and Werner (C → X) band systems of H₂ and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between H₂⁺ (X) and H₂(X), and between OH⁺(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated as a function of temperature in the range 1500–15 000 K.     

Growth and structure of a combinatorial array of mixed-phase magnesium–aluminum thin-film alloys

Combinatorial gradient-controlled sputter deposition has been employed to produce a library of 100 separate thin films with a wide range of Mg–Al alloy compositions. We have successfully isolated the β (Mg₁₇Al₁₂) phase in polycrystalline films for investigation. The importance of understanding the physical properties of the β phase becomes apparent when one realizes the contrary effects associated with its existence in these alloys. The presence of the β phase has been found to be desirable for increasing corrosion resistance; however, in structural components under tensile loading and/or at elevated temperatures, the β phase precipitates undergo coarsening which induces poor creep behavior in several common alloys. We have also synthesized amorphous Mg–Al and mixed-phase compositions as identified by X-ray diffraction measurements. We have observed various degrees of surface oxidation which appear to be correlated with the presence of each particular phase. Details of the growth procedure as well as structural and compositional characterization are presented. PACS 61.10.Nz; 61.43.Dq; 61.82.Bg; 68.55.-a; 68.55.Nq     

Cross-section and rate coefficient calculation for electron impact excitation, ionisation and dissociation of H2 and OH molecules

The weighted total cross-section (WTCS) theory is used to calculate electron impact excitation, ionisation and dissociation cross-sections and rate coefficients of OH, H₂, OH⁺, H₂ ⁺, OH^- and H₂ ^- diatomic molecules in the temperature range 1500–15000 K. Calculations are performed for H₂(X, B, C), OH(X, A, B), H₂ ⁺(X), OH⁺(X, a, A, b, c), H₂ ^-(X) and OH^-(X) electronic states for which Dunham coefficients are available. Rate coefficients are calculated from WTCS assuming Maxwellian energy distribution functions for electrons and heavy particles. One and two temperature (θ_e and θ_g respectively for electron and heavy particles kinetic temperatures) results are presented and fitting parameters (a, b and c) are given for each reaction rate coefficient: k(θ) = a (θ^b)exp (-c/θ).     

57Fe Mössbauer study of ternary alloy systems Fe(Sb1−x Te x )2 for 0.5≤x≤1.0 at 4.2K

Summary We report on low-temperature (4.2 K)⁵⁷Fe M?ssbauer studies of the ternary alloy system Fe(Sb_1−x Te _x )₂ for 0.5≤x≤1.0. The M?ssbauer spectra are electric-quadrupole doublets for all the specimens, indicating a non-magnetic character. The quadrupole splitting decreases with the increase in tellurium concentration. FeTe₂ has also been studied in external magnetic fields up to 6T. These experiments show that the electric-field gradient in this alloy is negative and has an asymmetry parameter of η ≈0.7. Paper presented at the ICAME-95, Rimini, 10–16 September 1995.     

Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy nanoparticles embedded SiO<Subscript>2</Subscript> films: synthesis and structure

Cu–Ni fcc alloy nanoparticles (NPs) of tunable atomic ratios were generated in SiO₂ films. The films were prepared using the Cu(NO₃)₂ and Ni(NO₃)₂ co-doped inorganic–organic hybrid silica sols by single dipping. Transparent, crack-free, glassy SiO₂ films of 310 ± 10 nm in thickness embedded with high mol percent of Cu–Ni alloy NPs were yielded after annealing at 750 °C in 10% H₂-90% Ar atmosphere. Nominal compositions of the films were 20 mol% (Cu–Ni)-80 mol% SiO₂. Optical spectral study of the heat-treated films showed disappearance of Cu plasmon bands due to Cu–Ni alloy formation. Grazing incidence X-ray diffraction (GIXRD) studies revealed the formation of Cu–Ni alloy (2:1, 1:1 and 1:2) NPs inside the SiO₂ film. GIXRD showed a systematic shifting of the diffraction peaks with respect to the fcc Cu–Ni alloy composition, maintaining the nominal ratios. Transmission electron microscopy (TEM) studies of the representative Cu_0.5Ni_0.5-doped film showed existence of homogeneously dispersed Cu–Ni alloy NPs of average size 6.35 nm inside the SiO₂ matrix. The energy dispersive X-ray scattering (EDX) analysis of the individual NPs using the nano-probe (scanning TEM mode) confirmed the presence of both the Cu and Ni with the desired atomic ratio.     

Effect of nitrogen concentration on the electronic and vibrational properties of zinc-blende InNxP1-x(x < 0.01)

Taking into account the recent advances in the epitaxial growth of single-crystal InN leading to a drastic re-evaluation of its fundamental energy band gap, we have studied the electronic properties of InN_xP_1-x (x < 0.01) ternary alloy. Using the empirical pseudopotential method under the virtual crystal approximation, combined with the Harrison bond orbital model, the band gap at Γ, X and L points, the effective masses of the Γ valley and the electronic charge densities are calculated as a function of nitrogen composition. The fitted expressions of the energy band gaps indicate that the bowing parameter at Γ reached a broad value for very low nitrogen incorporation ( ). Furthermore, the band gap at Γ point decreases drastically with increasing nitrogen composition up to 1%. The elastic constants and the optical phonon frequencies are also reported. Our theoretical results provide a good agreement with the available data.     

Phase segregation in the Fe90Zr10 amorphous alloy under heating

A study of the changes in the structure of melt-quenched Fe₉₀Zr₁₀ amorphous alloys by x-ray diffraction, Auger spectroscopy, and transmission electron microscopy is reported. The samples were subjected to isochronous (for 1 h) and isothermal anneals at 100–650 °C. It is shown that an amorphous alloy annealed for one hour at 300–500 °C crystallizes with formation of a supersaturated solid solution of Zr in α Fe and the intermetallic compound Fe₃Zr. Isothermal anneal at 100 °C for up to 7000 h produces nanocrystallites 110–30 nm in size, with fuzzy interfaces between the grains. An alloy subjected to such an anneal contains two solid solutions of Zr in Fe, having a cubic and a weakly tetragonal lattice. Crystallization taking place during low-temperature anneals is preceded by phase segregation of the alloy within the amorphous state. The lattice periods of the solid solutions have been determined. The possibility of the alloy crystallizing by spinodal decomposition during prolonged annealing is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1769–1772 (October 1998)     

Solidification microstructure of AZ91D Mg alloy after laser surface melting

The solidification microstructure plays a critical role in determining the surface properties of laser-treated magnesium alloys. The purpose of this paper is to study the solidification microstructures of AZ91D Mg alloy following millisecond- and nanosecond-pulse Nd:YAG laser irradiation. The solidification microstructural evolution of laser-melt AZ91D Mg alloy was investigated using X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectrometer and transmission electron microscopy. Much refined α-Mg phase and β-Mg₁₇Al₁₂ intermetallics were observed in the microstructure after laser surface melting. Periodic and successive structure was observed in the millisecond irradiated surface and the melt depth was more than 100 μm. The solidification microstructure was mainly cellular/dendrite structures together with a large number of β-Mg₁₇Al₁₂ nano-particles. Micron holes were found in the nanosecond irradiated surface and the melt depth was shallow at 50 μm. Millisecond-pulse Nd:YAG laser was found to be more suitable for Mg alloy surface treatment due to sufficient melt depth.     

FCNC top quark decays in extra dimensions

The flavor changing neutral top quark decay t→cX is computed, where X is a neutral standard model particle, in an extended model with a single extra dimension. The cases for the photon, X=γ, and a standard model Higgs boson, X=H, are analyzed in detail in a non-linear R_ξ gauge. We find that the branching ratios can be enhanced by the dynamics originating in the extra dimension. In the limit where 1/R≫m_t, we have found Br(t→cγ)≃10^-10 for 1/R = 0.5 TeV. For the decay t→cH, we have found Br(t→cH)≃10^-10 for a low Higgs mass value. The branching ratios go to zero when 1/R→∞.     

Measurement and simulation of specific heat for metastable liquid Ni80Fe10Cu10 alloy

The specific heat of undercooled liquid Ni₈₀Fe₁₀Cu₁₀ alloy was experimentally measured by electromagnetic levitation drop calorimeter, and also numerically simulated by the molecular dynamics method. The achieved maximum undercooling is up to 252 K (0.15 T _L) in the experiments, and the measured result is 41.67 J mol⁻¹ K⁻¹. The simulation provides calculated data within 0∼702 K undercooling range, which is much broader than the experimental regime. The simulated value is 37.02 J mol⁻¹ K⁻¹. Although there exists a difference of 4.65 J mol⁻¹ K⁻¹ between them, the result is quite acceptable for simulation. Furthermore, the liquid structure of undercooled Ni₈₀Fe₁₀Cu₁₀ alloy is studied in terms of the total and partial pair distribution functions, which display that the ordered degree of atoms enhances from a normal liquid to metastable state.     

Novel fabrication and catalytic application of poly(ethylenimine)-stabilized gold–silver alloy nanoparticles

Novel synthesis of amine-stabilized Au–Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au–Ag alloy nanoparticles was readily controlled by varying the initial relative amount of HAuCl₄ and AgNO₃. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation problem of Ag⁺ in the presence of Cl⁻ from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl₄ and AgNO₃ salts were used for the fabrication of Au–Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include the co-reducing agents for HAuCl₄ and AgNO₃, the stabilizing agents for Au–Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use in catalysis, the Au–Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction of 4-nitrophenol in the presence of NaBH₄. As the Au content was increased in the Au–Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased from pure Ag to pure Au.