Concentration dependence of thermodynamic,transport and surface properties in Ag–Cu liquid alloys

Thermodynamic, transport and surface properties of Ag–Cu liquid alloys have been investigated on the basis of a simple statistical model. The free energy of mixing, heat of mixing and entropy of mixing have been computed to understand the thermodynamic properties of Ag–Cu alloys in liquid state at 1,423 K. The concentration–concentration fluctuations in the long wavelength limit and the chemical short range order parameter have been determined to comprehend the microscopic and structural information of the alloy. The viscosity and surface tension of the alloy have been evaluated to analyze the transport and surface properties. The theoretical analysis reveals that the energy parameter is temperature dependent, and that Ag–Cu liquid alloy is a weakly interacting-phase separating system.     

Viscosity and diffusivity in melts: from unary to multicomponent systems

Viscosity and diffusivity, two important transport coefficients, are systematically investigated from unary melt to binary to multicomponent melts in the present work. By coupling with Kaptay’s viscosity equation of pure liquid metals and effective radii of diffusion species, the Sutherland equation is modified by taking the size effect into account, and further derived into an Arrhenius formula for the convenient usage. Its reliability for predicting self-diffusivity and impurity diffusivity in unary liquids is then validated by comparing the calculated self-diffusivities and impurity diffusivities in liquid Al- and Fe-based alloys with the experimental and the assessed data. Moreover, the Kozlov model was chosen among various viscosity models as the most reliable one to reproduce the experimental viscosities in binary and multicomponent melts. Based on the reliable viscosities calculated from the Kozlov model, the modified Sutherland equation is utilized to predict the tracer diffusivities in binary and multicomponent melts, and validated in Al–Cu, Al–Ni and Al–Ce–Ni melts. Comprehensive comparisons between the calculated results and the literature data indicate that the experimental tracer diffusivities and the theoretical ones can be well reproduced by the present calculations. In addition, the vacancy-wind factor in binary liquid Al–Ni alloys with the increasing temperature is also discussed. What’s more, the calculated inter-diffusivities in liquid Al–Cu, Al–Ni and Al–Ag–Cu alloys are also in excellent agreement with the measured and theoretical data. Comparisons between the simulated concentration profiles and the measured ones in Al–Cu, Al–Ce–Ni and Al–Ag–Cu melts are further used to validate the present calculation method.     

双温度氩-氮等离子体热力学和输运性质计算

获得覆盖较宽温度和压力范围内的等离子体热力学和输运性质是开展等离子体传热和流动过程数值模拟的必要条件.本文通过联立Saha方程、道尔顿分压定律以及电荷准中性条件求解等离子体组分;采用理想气体动力学理论计算等离子体热力学性质;基于Chapman-Enskog方法求解等离子体输运性质.利用上述方法计算了压力为0.1, 1.0和10.0 atm (1 atm=101325 Pa),电子温度在300—30000 K范围内,非局域热力学平衡(电子温度不等于重粒子温度)条件下氩-氮等离子体的热力学和输运性质.结果表明压力和非平衡度会影响等离子体中各化学反应过程,从而对氩-氮等离子体的热力学及输运性质有较大的影响.在局域热力学平衡条件下,计算获得的氩-氮等离子体输运性质和文献报道的数据符合良好.     

Phonon spectra and temperature variation of bulk properties of Cu,Ag, Au and Pt using Sutton–Chen and modified Sutton–Chen potentials

Three potentials of the Finnis–Sinclair type are studied with regard to their suitability for predicting bulk thermal and elastic properties of fcc metals Cu, Ag, Au and Pt over a wide temperature range. We start with a particular parametrization of the Finnis–Sinclair model known as the Sutton–Chen potential and a later version of the same, known as the quantum Sutton–Chen potential. The quasiharmonic lattice dynamics method is used to study the temperature variation of the thermodynamic properties. Both models are found to yield poor results for thermal expansion, which can be traced to rapid softening of transverse phonon frequencies with increasing lattice parameter. The form of the Sutton–Chen potential is modified here to seek improvement in the agreement between quasiharmonic calculations and experimental data. It is found that the modified potential better predicts bulk properties in nearly all cases studied. Significant improvement is seen over the Sutton–Chen potential, while lesser but still substantial improvement is observed over the Quantum-Sutton Chen potential.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.     

Effect of the burning temperature on the phase composition,photovoltaic response,and electrical properties of Ag/Pd resistive films

Silver-palladium (Ag/Pd) films were grown by thick-film technology using a resistive paste consisting of Pd, Ag2O, and glass on ceramic substrates at burning temperatures of 878, 1013, and 1113 K. The effect of the burning temperature and Pd content in the initial paste on the phase composition, resistivity, photovoltaic properties of films, free carrier concentration, and mobility was studied. It was found that the films grown at a burning temperature of 878 K have the greatest factor of conversion of the pulsed laser power to the photovoltaic signal, which depends on the direction of the incident radiation wave vector. Using X-ray diffraction, X-ray photoelectron spectroscopy, and thermodynamic modeling, it was shown that the AgPd alloy and PdO oxide are the main components of the Ag/Pd film with photovoltaic properties.     

A survey of surface tension,molar volume and density for Sn–Ag–Cu–Bi–Sb quinary alloys as lead-free solders

ABSTRACT

By applying the geometric models and the theoretical equation, the surface tension, the molar volume and the density were studied. The empirical calculations were carried out in temperature range 623?K?≤?T?≤?1123?K. Only few thermophysical properties were estimated for eight quinary alloys: Sn3.55Ag0.5Cu3Bi3Sb, Sn3.48Ag0.5Cu3Bi5Sb, Sn3.48 Ag0.5Cu5Bi3Sb, Sn3.40 Ag0.5Cu5Bi5Sb, Sn3.53Ag1Cu3Bi3Sb, Sn3.46Ag1Cu3Bi5Sb, Sn3.46Ag1Cu5Bi3Sb, Sn3.38Ag1Cu5Bi5Sb. The results show that surface tension and density have a linear appearance for all temperatures. We have also studied the influence of the composition and temperature in the studied alloys. The obtained theoretical results are compared with the experimental ones and with the conventional Pb–Sn welds.     

Interdiffusion and thermotransport in Ni–Al liquid alloys

In this paper, we present extensive self-consistent results of molecular dynamics (MD) simulations of diffusion and thermotransport properties of Ni–Al liquid alloys. We develop a new formalism that allows easy connection between results of the MD simulations and the real experiments. In addition, this formalism can be extended to the case of ternary and higher component liquid alloys. We focus on the temperature and composition dependence of the self-diffusion coefficients, interdiffusion coefficients, thermodynamic factor, Manning factor and the reduced heat of transport. The two latter quantities both represent measures of the off-diagonal Onsager phenomenological coefficients. The Manning factor and the reduced heat of transport can be related to experimentally obtainable quantities provided the thermodynamic factor is available. The simulation results for the reduced heat of transport show that for all compositions, in the presence of a temperature gradient, Ni tends to migrate to the cold end. This is in agreement with an available experimental study for a Ni_21.5Al_78.5 melt (only qualitative result is available so far).     

First-principles study on the electronic transport properties of M/SiC Schottky junctions (M=Ag,Au and Pd)

In this work, we investigate the electronic transport properties of M/SiC Schottky junctions (M=Ag, Au and Pd). The results show that the band structures of hydrogenated zigzag SiC nanoribbons (ZSiCNRs) and hydrogenated armchair SiC nanoribbons (ASiCNRs) are almost unaffected by their width changes. When the hydrogenated 7-ASiCNR is directly connected to the Ag, Au and Pd electrode, the transmission spectra of three metal-semiconductor junctions show that the Fermi level of metal is pinned to a fixed position in the semiconductor band gap of hydrogenated 7-ASiCNR. The nearly same rectifying current-voltage characteristics are found in three metal-semiconductor junctions. The average rectification ratios of three M/SiC Schottky junctions are all in the neighborhood of 10⁶. In other word, the M/SiC Schottky junction has remarkable application prospect as the candidate for Schottky Diode.     

The thermophysical properties of low‐temperature Pb plasma

The thermophysical properties of low‐temperature Pb plasma are calculated at temperatures 10–100 kK and densities below 0.2 of the solid‐state value. The thermodynamic values (pressure and internal energy) and transport coefficients (electrical conductivity, thermal conductivity, and thermal power) are considered. The plasma composition and thermodynamic parameters are obtained within the chemical approach, namely by means of the solution of the corresponding system of the coupled mass action law equations. Atom ionization up to +4 is taken into consideration. The electronic transport coefficients are calculated within the relaxation time approximation. The results obtained by means of the present model are compared with the available data of other models and experiments.     

Electrically controllable metal–insulator-like transition in nanoparticle compacts

We report on the observations of tunneling transport in nanocompacts, where nanoparticles are packed into compact units using selective mass compositions and packing densities. An insulator-like thermal behavior in electron transport is seen in a very loosely packed 6-nm Ag nanocompact, whereas the densely packed 4.5-nm Au nanocompact displays a metal-like thermal behavior. Metal–insulator-like transitions, with the transition temperature can readily be tuned by controlling the bias voltage, are observed in the nanocompact consists of mixtures of 2.4 nm Ag and 4.8 nm core/shell Cu/Cu₂O nanoparticles. The resistivity across the metal–insulator transition is found to change by more than four orders-of-magnitude. At low bias voltages or small excitation currents, the metal–insulator transition occurs at ~190 K. The transition temperature can be tuned to reach the ambient temperature when a higher bias voltage or a larger current is allowed. Possible mechanisms that may produce the observed transport characteristics in the nanocompacts are discussed.     

Thermal desorption spectroscopy of Ni,Cu, Ag and Au from W(110)

Ni, Cu, Ag and Au on W(110) in the submonolayer range are studied by thermal desorption spectroscopy with the goal of obtaining information on lateral interactions and on the phase state of the adsorption layer in the temperature range in which desorption occurs. Ni, Cu and Ag are found to desorb over a wide coverage range from the two-phase (vapor-condensate) region while Au desorbs only from the single-phase vapor region. Segments of the coexistence curve are determined. The desorption energies have the following limiting values: 4.35–4.95. 3.2–3.85, 2.8–3.55 and 3.3–4.1 eV for Ni, Cu, Ag and Au, respectively.     

氙等离子体输运性质计算

采用基于将Chapman-Enskog方法扩展到高阶近似的方法计算获得了温度范围在300—40000 K,不同压力条件下氙等离子体的黏性、热导率和电导率.热力学平衡条件下的计算结果与文献报道的实验和计算结果符合良好,验证了计算方法和结果的合理性与准确性.在此基础上,计算获得了电子温度(T e)不等于重粒子温度(T h)的热力学非平衡和化学平衡条件下氙等离子体的输运性质,并分析了输运性质随压力和热力学非平衡程度变化的原因.     

Combustion mechanism of ultralean rotating counterflow twin premixed flame

In our previous numerical studies [Nishioka Makihito, Zhenyu Shen, and Akane Uemichi. “Ultra-lean combustion through the backflow of burned gas in rotating counterflow twin premixed flames.” Combustion and Flame 158.11 (2011): 2188–2198. Uemichi Akane, and Makihito Nishioka. “Numerical study on ultra-lean rotating counterflow twin premixed flame of hydrogen–air.” Proceedings of the Combustion Institute 34.1 (2013): 1135–1142]. we found that methane– and hydrogen–air rotating counterflow twin flames (RCTF) can achieve ultralean combustion when backward flow of burned gas occurs due to the centrifugal force created by rotation. In this study, we investigated the mechanisms of ultralean combustion in these flames by the detailed numerical analyses of the convective and diffusive transport of the main species. We found that, under ultralean conditions, the diffusive transport of fuel exceeds its backward convective transport in the flame zone, which is located on the burned-gas side of the stagnation point. In contrast, the relative magnitudes of diffusive and convective transport for oxygen are reversed compared to those for the fuel. The resulting flows for fuel and oxygen lead to what we call a ‘net flux imbalance’. This net flux imbalance increases the flame temperature and concentrations of active radicals. For hydrogen–air RCTF, a very large diffusivity of hydrogen enhances the net flux imbalance, significantly increasing the flame temperature. This behaviour is intrinsic to a very lean premixed flame in which the reaction zone is located in the backflow of its own burned gas.     

AES studies of surface composition of AgCu alloys

The influence of pretreatments like sputtering, annealing and cleaving on the surface composition is important in quantitative Auger electron spectroscopy. The present paper deals with this influence for the binary alloy system AgCu with 100, 95, 80, 60, 50, 40, 20, 5, and 0 at% Ag. Sputtering causes an enrichment of Cu on the surface due to the higher sputter coefficient of Ag. In contrast cleaving yields an enrichment of Ag due to the lower tensile strength of Ag. The surface composition obtained by scribing is used as standard for the bulk composition because this technique is independent of parameters like sputter coefficient or tensile strength. The results are compared with previous measurements of homogeneous alloy systems.     

Physical properties of single crystalline BaSn5

We present a comprehensive study of the binary intermetallic superconductor, BaSn₅. High-quality single crystalline BaSn₅ was grown out of a Sn flux. Detailed thermodynamic and transport measurements were performed to study BaSn₅'s normal and superconducting state properties. This material appears to be a strongly coupled, multiband superconductor. H _c2(T) is almost isotropic. De Haas–van Alphen oscillations were observed and two effective masses were estimated from the FFT spectra. Hydrostatic pressure causes a decrease in the superconducting transition temperature at the rate of ≈?0.053?±?0.001?K/kbar.     

Transport of volume in a binary liquid

In this paper, the transport of volume in a binary liquid mixture is theoretically investigated in three steps, with strong implications for the measurement of mutual diffusivities in non-dilute mixtures. In a first step, the velocity of volume transport is determined from the transport velocities of the two components and the thermodynamic relation of state of the liquid mixture in equilibrium. The role played by Galilean invariance and the choice of a rigid frame of reference for reckoning current densities is highlighted. The divergence of the volume-transport velocity field is found to involve the isothermal compressibility and the thermal expansivity of the liquid together with the spatiotemporal variations of pressure and temperature. In a second step, a linear-response relation is introduced between the interdiffusion current density and the gradient of composition; this relation phenomenologically defines the mutual diffusivity of the binary liquid in a manifestly Galilean-invariant way. In a third step, it is examined whether the practical measurement of that diffusivity in a constant-volume container entails a vanishing mass-transport or volume-transport velocity. From a singular-perturbation analysis of the hydrodynamic equations, it is shown that the mass-transport velocity vanishes in the limit of a diffusion of composition that is much slower than the diffusion of momentum. As a consequence, the volume-transport velocity does not vanish during interdiffusion even though the law of additive volumes of the components holds. The physical meaning of the non-vanishing volume velocity is interpreted by means of the thermodynamic results obtained in the second step. Some of the conclusions carry over to multicomponent liquid mixtures.     

Highly Luminescent Material Based on Alq3:Ag Nanoparticles

Tris (8-hydroxyquinoline) aluminum (Alq₃) is an organic semiconductor molecule, widely used as an electron transport layer, light emitting layer in organic light-emitting diodes and a host for fluorescent and phosphorescent dyes. In this work thin films of pure and silver (Ag), cupper (Cu), terbium (Tb) doped Alq₃ nanoparticles were synthesized using the physical vapor condensation method. They were fabricated on glass substrates and characterized by X-ray diffraction, scanning electron microscope (SEM), energy dispersive spectroscopy, atomic force microscope (AFM), UV-visible absorption spectra and studied for their photoluminescence (PL) properties. SEM and AFM results show spherical nanoparticles with size around 70–80 nm. These nanoparticles have almost equal sizes and a homogeneous size distribution. The maximum absorption of Alq₃ nanoparticles is observed at 300 nm, while the surface plasmon resonant band of Ag doped sample appears at 450 nm. The PL emission spectra of Tb, Cu and Ag doped Alq₃ nanoparticles show a single broad band at around 515 nm, which is similar to that of the pure one, but with enhanced PL intensity. The sample doped with Ag at a concentration ratio of Alq₃:Ag?=?1:0.8 is found to have the highest PL intensity, which is around 2 times stronger than that of the pure one. This enhancement could be attributed to the surface plasmon resonance of Ag ions that might have increased the absorption and then the quantum yield. These remarkable result suggest that Alq₃ nanoparticles incorporated with Ag ions might be quite useful for future nano-optoelectronic devices.     

Thermal and structural characterization of Cu–Al–Mn–X (Ti,Ni) shape memory alloys

In this study, the Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys at the range of 10–12 at.% of aluminum and 4–5 at.% manganese were produced by arc melting. We have investigated the effects of the alloying elements on the transformation temperatures, and the structural and the magnetic properties of the quaternary Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys. The evolution of the transformation temperatures was studied by differential scanning calorimetry with different heating and cooling rates. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the aluminum and manganese content, and it was observed that the nickel addition into the Cu–Al–Mn system decreased the transformation temperature although Ti addition caused an increase in the transformation temperatures. The effect of the nickel and the titanium on the thermodynamic parameters such as enthalpy and entropy values was investigated. The structural changes of the samples were studied by X-ray diffraction measurements and by optical microscope observations at room temperature. It is evaluated that the element Ni has been completely soluble in the matrix, and the main phase of the Cu–Al–Mn–Ni sample is martensite, and due to the low solubility of the Ti, the Cu–Al–Mn–Ti sample has precipitates, and a martensite phase at room temperature. The magnetic properties of the Cu–Al–Mn, Cu–Al–Mn–Ni and Cu–Al–Mn–Ti samples were investigated, and the effect of the nickel and the titanium on the magnetic properties was studied.     

Fast joining of melt textured Y–Ba–Cu–O bulks with high quality

Y–Ba–Cu–O bulk superconductors were fast joined using Ag-doped Y–Ba–Cu–O solder (metallic Ag powder additive). The joining process was relatively shorter (around 24 h) comparing with the traditional joining method. The microstructures and the superconducting properties of the joints were evaluated carefully. Microstructure analysis revealed that the crystal pattern in the joint was almost the same as that of the base material. This indicated that the bonding zone grew along the growth direction of the base material. The trapped-field distribution of the joined bulk was almost uniform and only single peak was found. This demonstrated that strong bonding was achieved in the joining process. The ratio of joined bulk’s levitation force to that of original base material was up to 93.5%.