Plasma Spray Physical Vapor Deposition of La1−x Sr x Co y Fe1−y O3−δ Thin-Film Oxygen Transport Membrane on Porous Metallic Supports

Plasma spray physical vapor deposition (PS-PVD) is a very promising route to manufacture ceramic coatings, combining the efficiency of thermal spray processes and characteristic features of thin PVD coatings. Recently, this technique has been investigated to effectively deposit dense thin films of perovskites particularly with the composition of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) for application in gas separation membranes. Furthermore, asymmetric type of membranes with porous metallic supports has also attracted research attention due to the advantage of good mechanical properties suitable for use at high temperatures and high permeation rates. In this work, both approaches are combined to manufacture oxygen transport membranes made of gastight LSCF thin film by PS-PVD on porous NiCoCrAlY metallic supports. The deposition of homogenous dense thin film is challenged by the tendency of LSCF to decompose during thermal spray processes, irregular surface profile of the porous metallic substrate and crack and pore-formation in typical ceramic thermal spray coatings. Microstructure formation and coating build-up during PS-PVD as well as the annealing behavior at different temperatures of LSCF thin films were investigated. Finally, measurements of leak rates and oxygen permeation rates at elevated temperatures show promising results for the optimized membranes.     

Thermal, micro-structural, and electrical properties of a La1−x Sr x Mn0.85Fe0.05Co0.05Ni0.05O3+δ (x = 0–0.4 mole) cathode system

The oxygen stoichiometry, thermal expansion, morphology, and electrical conductivity of a co-doped perovskitetype cathode system, La_1?x Sr _x Mn_0.85Fe_0.05Co_0.05Ni_0.05O_3+ä (x = 0–0.4 mole), are studied for intermediate-temperature solid oxide fuel cell applications. Sr²⁺-doping led to a decrease in the unit cell volume, oxygen stoichiometry, particle size, and activation energy, and an increase in the coefficient of thermal expansion and electrical conductivity. The sample with x = 0.3 mole exhibited four to five fold weight loss with respect to La_0.75Sr_0.25MnO_3+δ at an intermediate temperature range and suggested the availability of a large number of oxygen vacancies due to a co-doping effect. This sample also showed sufficiently high electrical conductivity (～76 S cm^?1) at 650 °C, a low activation energy (～0.15 eV), and a coefficient of thermal expansion (～12.1 × 10^?6 °C^?1) comparable to those of the adjacent components and submicron sized particles. The experimental results are explained using defect models.     

Effect of total dopant concentration and dopant ratio on conductivity of (DyO1.5)x–(WO3)y–(BiO1.5)1−x−y

Dysprosium- and tungsten-stabilized bismuth oxide (DWSB) electrolytes were developed to achieve higher conductivity. With double doping, stabilization of the cubic phase was achieved with as little as 12 mol.% total dopant concentration, resulting in higher conductivity. The conductivity of DWSB electrolytes increased linearly as the total dopant concentrations decreased with fixed dopant ratio. Overall, DWSB has a closer inherent structure to pure δ-Bi₂O₃ than any singly doped compositions. Both lattice parameter and conductivity linearly extrapolate with total dopant concentration to that of pure δ-Bi₂O₃, resulting in the ability to stabilize δ-phase at lower dopant concentration, and thus achieving higher conductivity.     

La(1-x)MgxNi4.25Al0.75(x=0-0.3)合金的结构与储氢性能研究

采用三步感应熔炼法制备了La(1-x)MgxNi4.25Al0.75 (x=0.0,0.1,0.2,0.3) 储氢合金,对该系列合金的晶体结构和储氢性能方面进行了研究。晶体结构和相分析结果表明,当x=0.0和0.1时,合金由单一的LaNi4Al相组成;而x=0.2和0.3时,合金由LaNi4Al相, (La,Mg)Ni3相和AlNi3相构成。随着Mg含量x从0.2增至0.3时,合金的第二相丰度和吸/放氢平衡压明显升高,同时储氢容量减小。研究发现,当Mg添加量x=0.1时,合金除具有良好的储氢容量和低平台压外,其吸氢动力学性能更好。     

Direct production of porous cathode material (La1−x Sr x MnO3) using a reactive DC thermal plasma spray system

The cathode material (La_0.8Sr_0.2MnO₃) in solid oxide fuel cells (SOFCs) was plasma sprayed on mild steel in a reactive DC thermal plasma spray process. This high-speed process of depositing thin films for the components of SOFCs was examined experimentally. The results showed that a coating layer of La_0.8Sr_0.2MnO₃ with a particular porosity could be obtained directly using both prereacted La_0.8Sr_0.2MnO₃ and mixed raw materials (La₂O₃, SrCO₃, and MnO or MnCO₃) as feed materials with or without a pore former. The heat treatment of the plasma coating material at 1073 K (800 °C) for 3 h significantly enhanced the desired crystallization of La_0.8Sr_0.2MnO₃ in the coated material.     

Effect of Al content on the phase structure and the hydrogenation characteristic of La(Mg_(1-x)Al_x) alloys

1. Introduction Hydrogen-absorbing materials like sodium alanates, advanced BCC alloys, and Mg-based al- loys have been widely investigated [1]. Mg-based alloys are attractive as potential hydrogen storage materials because of their high storage capacity and low cost [2-3]. The hydrogen desorption kinetics has been improved using various methods [4-6], espe- cially alloying. It was reported that the kinetics of hydriding and dehydriding of Mg-based alloys can be improved by alloying with rar…     

High-temperature deformation and defect chemistry of (La1−xSrx)1−yMnO3+δ

The creep behavior of (La_1−xSr_x)_1−yMnO_3+δ has been studied as a function of oxygen partial pressure (P_O2) and Sr concentration. Polycrystalline samples (x=0.1, 0.2, 0.3) were deformed at 1523 K in constant-crosshead-speed compression tests in various atmospheres (10⁻²≤P_O2≤10⁵ Pa). The material deformed by grain-boundary sliding accommodated by lattice diffusion with some possible cavitation and/or interface reaction control. The defect-chemistry model which is standard in the literature could not explain the dependence of the stress on P_O2 and the Sr concentration. A modified defect-chemistry model shows that cation vacancies controlled the creep rate at P_O2≤10⁵ Pa for x=0.3 and at low P_O2 for x=0.1 and 0.2, and that oxygen vacancies were rate-controlling at high P_O2 for x=0.1 and 0.2.     

Effect of Cr alloying on friction and wear of sputter-deposited nanocrystalline (MoxCr1−x)5Si3 films

In the present work, five kinds of nanocrystalline (Mo_xCr_1?x)₅Si₃(x = 1, 0.78, 0.75, 0.64, 0.57) films with average grain size 8 nm have successfully been prepared on Ti6Al4V alloy by a double cathode glow discharge technique in order to improve its poor tribological properties. The influence of the Cr additions on the mechanical and tribological properties of nanocrystalline (Mo_xCr_1?x)₅Si₃ films have been studied. The microstructure of the films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Nanoindentation was used to measure hardness (H) and elastic modulus (E) of the as-deposited films, and the adhesion strength between the as-deposited films and substrate was evaluated by scratch test. The dry sliding wear properties of the as-deposited films were investigated using against different counterbodies (ZrO₂ ceramic balls and GCr15 rolling bearing steel) in ball-on-disk system at room temperature. The results indicated that alloying additions of Cr affected considerably the wear performance of nanocrystalline (Mo_xCr_1?x)₅Si₃ films. The friction coefficients and specific wear rates of nanocrystalline (Mo_xCr_1?x)₅Si₃ films were significantly reduced by the increasing Cr substitution, and its specific wear rates have been shown to be two orders of magnitude lower than for Ti6Al4V alloy. The dominant wear mechanism of the nanocrystalline (Mo_xCr_1?x)₅Si₃ films experiences a transition from delamination to tribo-oxidation wear, along with the increasing amount of Cr additions.     

Effect of gallium on the crystal structure and magnetic properties of PrFe11 − x Ga x C y compounds

A homogeneity range of the PrFe_{11 ? x} Ga _x C _y phase was determined. As the gallium content increases, the lattice parameters were shown to increase, whereas the Curie temperature decreases; the type of magnetic anisotropy at room temperature is unchanged. In the alloys with x > 3, the transformation of the tetragonal lattice of the compound into an orthorhombic lattice with the axial ratio a/b ≤ 1.006 is observed. This is likely to be caused by the ability of gallium to form covalent bonds. Gallium atoms were found to occupy preferentially 16j ₂ and 4e ₂ sites in the orthorhombic lattice of the FePr_6.5Ga_4.5C compound. The atoms located in the 16j ₂ sites form wavy chains along the [010] direction of the orthorhombic lattice, whereas the iron atoms located in the 16j ₁ sites form analogous chains along the [100] direction. Owing to this fact, one of these directions is likely to become an easy axis. The alloy with x= 4.5 has a low coercive force at room temperature; at 114 K, its coercive force is H _c = 42.4 kA/m.     

Effect of the Rare-Earth Addition (R = Ce,Sm) on the Phase Equilibria and Microstructure of Ni-Al Alloys

The peculiarities in the phase formation in the Al-rich region of the Ce-Ni-Al and Sm-Ni-Al ternary systems have been investigated by means of optical and scanning electron microscopy, electron probe microanalysis and x-ray powder diffraction (XRD) study. The following ternary phases have been identified: Ce₄Ni₆Al₂₃ (τ₁, mS66-Y₄Ni₆Al₂₃), CeNiAl₄ (τ₃, oS24-YNiAl₄), Sm₃Ni₅Al₁₉ (τ₂, oS108-Gd₃Ni₅Al₁₉), Sm₄Ni₆Al₂₃ (τ₁, mS66-Y₄Ni₆Al₂₃) and SmNiAl₄ (τ₃, oS24-YNiAl₄). Moreover, a temperature of 622 °C ± 1 has been established for the ternary eutectic reaction L ? (Al) + NiAl₃ + αCe₃Al₁₁ using a differential scanning calorimeter (DSC). The general characteristics of the sections are discussed in comparison with those of other R-Ni-Al systems (R = rare earths).     

Dislocation interaction of layers in the Ge/Ge-seed/GexSi1−x/Si(0 0 1) (x ∼ 0.3–0.5) system: Trapping of misfit dislocations on the Ge-seed/GeSi interface

High-resolution electron microscopy has been applied to study the dislocation redistribution between Ge and GeSi layers at the atomic scale. Ge_0.3Si_0.7 (30 nm in thickness) and Ge_0.5Si_0.5 (10 nm) buffer layers buried between the Si(0 0 1) substrate and the plastically relaxed Ge layer 0.5 μm thick remain in a metastable (stressed) state during the growth of Ge/Ge-seed/Ge_xSi_1?x/Si(0 0 1) (x ～ 0.3–0.5) heterostructures, though the buffer layer thickness is several times greater than the critical value for insertion of misfit dislocations (MDs). An ordered grid of edge MDs is observed only on the Ge/GeSi interface; the mean distance between the MDs is ～10 nm (which is close to the equilibrium value for the non-stressed Ge/Si system). After 30 min of annealing at 700 °С, the Ge_0.3Si_0.7 buffer layer still remains in a metastable state, and the edge MDs are located only on the Ge/GeSi interface with the same dislocation spacing of ～10 nm. At the same time, approximately one-half of MDs in the structure with the Ge_0.5Si_0.5 buffer layer passes through the Ge/GeSi interface to the GeSi/Si(0 0 1) interface, and the buffer layer plastically relaxes by almost 100%. An assumption is put forward that there exists a barrier for the MD transition from the Ge layer to the GeSi layer, which results in MD trapping on this interface. The magnitude of this barrier depends on the difference in the compositions of the main Ge (x = 1) film and the Ge_xSi_1?x buffer layer, and increases with increasing this difference.     

TEM analysis of Gd5(SixGel−x)4, where x=1/2

The material Gd₅(Si_xGe_l−x)4, with x=1/2 was investigated using transmission electron microscopy. The material possesses a complex crystallographic structure and undergoes a unique, reversible, transformation at low temperatures and an irreversible high temperature transformation. The high, room and low temperature microstructures of arc-melted and heat treated samples are reported. Direct observation of the transformation with a discussion on the mechanism of the reversible, low temperature, phase transformation is detailed.     

The hydriding behaviour of U(Fe1−xNix)Al system (0≤x≤0.75) and magnetic studies on U(Fe1−xNix)AlH0.8

The hydriding behaviour of the solid-solution series of compounds, U(Fe_1−xNi_x)Al, has been investigated. In the parent pseudoternary compounds, as Ni is gradually substituted for Fe, the magnetic correlations grow. As a result, the magnetic properties change from exchange enhanced Pauli-paramagnetic and spin fluctuating (x=0), via weakly magnetic with no long range magnetic ordering down to 4 K (0<x≤0.3) to ferromagnetic (0.35≤x≤0.75) and eventually to antiferromagnetic for x≥0.9. The present hydriding report covers compositions up to the ferromagnetic regime. It is found that hydrogen absorption does not take place for x below ≅0.7. The lowest nickel containing composition, which forms a well defined hydride phase, viz., U(Fe_0.3Ni_0.7)Al, absorbs y=0.8 H atoms per formula unit. This matches exactly with the lower hydride phase of pure UNiAl. No other hydride phase is formed either above or below y=0.8. The magnetization studies show that U(Fe_0.3Ni_0.7)AlH_0.8 has much higher values of the magnetic ordering temperature (T_C), paramagnetic Curie temperature (θ_P) and the uranium magnetic moment, relative to the unhydrided composition. These findings are in consonance with the large increase in the ⁵⁷Fe Mössbauer isomer-shift value, on hydriding. It is suggested that the electron charge transfer from H to the Fe 3d band (inferred from the Mössbauer studies) weakens the 5f–3d hybridization, thus enhancing the ferromagnetic correlations. The observed large increase in the a-axis cell parameter also implies a reduction in U–U hybridization, further justifying the observed increase in T_C, θ_P and U moment values.     

A microscopic study of the effect of γ-radiation on Pb1 − x Mn x Se epitaxial films

The surface morphology of n- and p-type epitaxial films of lead manganese selenide (Pb_1?x Mn _x Se (x = 0.01)) on barium fluoride substrates of the (111) orientation in the initial state and after exposure to gamma-radiation is studied by atomic force microscopy. It is shown that the surface relief undergoes modification in the absorbed dose region of 5 ≤ D _γ ≤ 35 kGy. The p?n conductivity inversion at 10 ≤ D _γ ≤ 25 kGy is found from the characteristics of the surface structures and confirmed by the electrophysical measurements. It is revealed that the radiation resistance of these films is violated at a dose above 35 kGy.     

Effect of Si on the Formation and Growth of Intermetallic Compounds at Roll-Bonded Aluminum–Steel (Al-St) Interface

The formation and growth of intermetallic compounds (IMC) were investigated using the Al-St clad materials with additional different Si content to aluminum and steel substrate by differential scanning calorimetry, scanning electron microscopy and energy-dispersive x-ray spectroscopy, x-ray diffraction and transmission electron microscopy. The addition of Si to Al (Al-0.8Si/St) can drastically delay the formation of IMC and accelerate the growth of IMC layer. The Si (Al-0.8Si/St) segregates at the interface and inhibits the diffusion of Al atom to steel before the IMC forms, which further decreases the diffusion depth of Al in the steel layer. By contrast, the addition of Si to St (Al/St-0.8Si) has limited impact on delaying the formation and decelerating the growth of IMC layer. The Si (Al/St-0.8Si) hardly affects the diffusion of Fe atom to the aluminum layer. Among the four clad materials, the major IMC layer (η-Fe₂Al₅) always exhibits the parabolic growth phenomenon. The addition of Si cannot influence the phase compositions of IMC at the interface between the η-Fe₂Al₅ layer and the aluminum. However, we observe an extra Fe-rich phase β₁-Fe₃Al at the interface between the Fe₂Al₅ layer and steel substrate in the Al-0.8Si/St clad material.     

Optical and photocatalytic properties of nanoparticulate (TiO2)x(ZnO)1−x powders

In this study, we have investigated the optical and photocatalytic properties of nanoparticulate (TiO₂)_x(ZnO)_1?x powders that were synthesised by mechanochemical processing. The objective was to establish the suitability of these powders for use as optically transparent ultraviolet light screening agents. It was found that the photocatalytic activity of single phase ZnO can be substantially reduced through the incorporation of TiO₂ at the cost of a comparatively minor decrease in optical transparency. The composition given by (TiO₂)_0.10(ZnO)_0.90 was characterised by a photocatalytic activity that was approximately 20% of that exhibited by the ZnO powder synthesised using similar processing conditions. These results demonstrate that (TiO₂)_x(ZnO)_1?x powders synthesised by mechanochemical processing are potentially useful as optically transparent ultraviolet light screening agents.     

Effect of annealing atmosphere on the kinetics and mechanism of low-temperature decomposition of the nonstoichiometric Ba2YCu3O7−δ ceramics

The effect of heat treatments in helium, nitrogen, and vacuum (P = 10^?2, 20, and 100 mmHg) on the kinetics of low-temperature decomposition (T < 400°C) of the nonstoichiometric Ba₂YCu₃O_7?δ ceramics has been studied. The decomposition in the vacuum was found to be very slow; the rate of the decomposition in both helium and nitrogen is substantially higher. The results obtained indicate the strong effect of the nature of gas absorbed on the grain surface. Possible mechanisms of the effect of absorption on the kinetics of low-temperature decomposition are considered.