The effect of hydrogenation/dehydrogenation cycles on palladium physical properties

A series of hydrogenation/dehydrogenation cycles have been performed on palladium wire samples, stressed by a constant mechanical tension, in order to investigate the changes in electrical and mechanical properties. A large increase of palladium electrical resistivity has been reported due to the combined effects of the production of defects linked to hydrogen insertion into the host lattice and the stress applied to the sample. An increase of the palladium sample strain due to hydrogenation/dehydrogenation cycles in α→β→α phase transitions is observed compared to the sample subjected to mechanical tension only. The loss of initial metallurgical properties of the sample occurs already after the first hydrogen cycle, i.e. a displacement from the initial metallic behavior (increase of the resistivity and decrease of thermal coefficient of resistivity) to a worse one occurs already after the first hydrogen cycle. A linear correlation between palladium resistivity and strain, according to Matthiessen's rule, has been found.     

温度场对动涡旋盘应力与应变的影响

针对不同的温度场,运用有限元分析软件ANSYS对汽车空调涡旋压缩机的动涡旋盘进行了应力与应变的模拟和研究。计算结果表明,温度载荷对涡旋盘的应力和应变有着重要影响。其中,非均匀温度场会导致涡旋盘的涡旋齿产生较大应力与应变,涡旋齿断裂故障发生的概率较大。     

The effect of chemical composition of a crystallization medium on the cBN stoichiometry

Abstract

The effect of chemical composition of the crystallization medium in synthesis on and some properties of cubic boron nitride (cBN) has been studied. Cubic BN crystals with the lowest free boron content and a boron-nitrogen ratio close to the stoichiometric one are grown in a multicomponent crystallization medium in a Li₃N-BN system. These crystals are characterized by a higher strength and thermal stability.     

Heats of displacement of hydrogen from palladium by noble gases

It has been observed that noble gases, such as helium, neon and argon produce heat evolution when contacted with Pd powder partially saturated with hydrogen. These phenomena have been studied with flow-through adsorption microcalorimetry. The observed exothermic effects are comparable to those usually associated with the heat of sorption of hydrogen in palladium. It is suggested that the noble gases displace the adsorbed H species from the surface of Pd, causing their reabsorption in the Pd lattice with the exothermic heat of PdH bonds formation, or the formation of H₂, both heat evolutions being observed with a flow-through microcalorimeter.     

Air-exposure effect on the resistivity of thin bismuth films

A survey of previous studies on vacuum deposited metal films shows that in high frequency measurements, explicit reference to the effect of air-exposure is not made. The present work on bismuth films (in-situ and air-exposed) at dc and rf frequencies, carried out mainly to study the air-exposure effect, shows that in-situ dc and rf and exposed rf all show nearly the same resistivity for thick continuous films. But air-exposed dc film resistances, when compared to in-situ dc resistances, show that the grain boundary reflection coefficient, R _gin Mayadas-Shatzkes model changes from 0·2 to 0·6. This is shown to be due to the grain boundary oxidation. The result is substantiated by rf measurements.     

The effect of hydrogen on the magnetic properties of quenched Ti-Zr-Ni rods

Ti-Zr-Ni quenched rods of 3, 2 and 1.5 mm diameter, prepared by vacuum-casting, were analyzed by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) before and after hydrogenation. Samples with two different compositions were prepared, i.e., Ti₄₀Zr₄₀Ni₂₀ and Ti₅₃Zr₂₇Ni₂₀. The as-cast rods were pulverized and hydrogenated from the gas-phase at 45 bar and 300 °C for 1000 min. The mass spectra of the desorbed hydrogen revealed the distribution of the hydrogen desorption temperatures from these alloys, whereas using thermogravimetry we obtained the mass% of desorbed H. We found that the ratio between the i-phase and the C14 Laves phase depends on the master alloy composition and the cooling rate, i.e., the rod diameter. VSM measurements revealed an about 30% decrease in paramagnetic susceptibility upon hydrogenation for all six investigated samples.     

One-step measurements of powder resistivity as a function of relative humidity and its effect on charging

A new one-step technique to measure the effect of ambient humidity on powder resistivity has been previously presented. In this article, we provide more experimental data obtained with five different powders. One-step measurements and traditional multi-step measurements were performed. Also, additional measurements were performed using standard resistivity cell. Results were compared and it could be concluded that the new technique provided meaningful results although significant hysteresis was observed during humidification and drying cycles. Finally, charging of the powder was also measured and it was noticed that it decreases with decreasing resistivity and increasing humidity.     

Influences of stoichiometry on steadily propagating triple flames in counterflows

Most studies of triple flames in counterflowing streams of fuel and oxidizer have been focused on the symmetric problem in which the stoichiometric mixture fraction is 1/2. There then exist lean and rich premixed flames of roughly equal strengths, with a diffusion flame trailing behind from the stoichiometric point at which they meet. In the majority of realistic situations, however, the stoichiometric mixture fraction departs appreciably from unity, typically being quite small. With the objective of clarifying the influences of stoichiometry, attention is focused on one of the simplest possible models, addressed here mainly by numerical integration. When the stoichiometric mixture fraction departs appreciably from 1/2, one of the premixed wings is found to be dominant to such an extent that the diffusion flame and the other premixed flame are very weak by comparison. These curved, partially premixed flames are expected to be relevant in realistic configurations. In addition, a simple kinematic balance is shown to predict the shape of the front and the propagation velocity reasonably well in the limit of low stretch and low curvature.     

Temperature-dependent texture, stress and resistivity in melt spun Cu0.95Co0.05 ribbon

Ribbon samples of Cu_0.95Co_0.05 were prepared by melt spinning method to perform systematic investigations on structure and transport properties as a function of annealing temperature. X-ray diffraction study shows that the ribbon is polycrystalline with a strong 2 0 0 texture along the surface normal of the as-quenched Cu_0.95Co_0.05 ribbon and the degree of texture is enhanced upon annealing. The compressive stress, which relaxes upon annealing, is observed in as-quenched ribbon. The resistivity, which is higher in as-quenched ribbon, decreases toward the bulk value of Cu upon annealing. The compressive stress and higher resistivity in as-quenched ribbon are attributed to the incorporation of Co atoms/particles in Cu matrix. The decrement of the stress and resistivity upon annealing is due to the precipitation of Co atoms from the Cu matrix, segregating as Co or Co-rich Cu grains as observed from the transmission electron microscopy measurements.     

Activating MoS2 basal planes for hydrogen evolution through the As doping and strain

As a non-precious catalyst for the electrochemical hydrogen evolution reaction (HER), the two-dimensional MoS₂ has been widely studied. To activate the MoS₂ inert basal plane to enable optimal activity, high defect concentration of sulfur vacancies is needed. Herein, based on the first-principles calculations we demonstrate that the HER of MoS₂ can be greatly enhanced by As doping and biaxial strain. We show that the As-doping sites are new catalytic sites and the bonding of H can be greatly enhanced. Moreover, the relative hydrogen adsorption free energy ($\mathrm{\Delta }\mathrm{\Delta }{\mathrm{G}}_{\mathrm{H}}$) can be further manipulated by the strain effect, which efficiently adjusts the catalytic activity. With the synergy of the biaxial strain (2%–3%) and the uniform doping of the As atoms (3.125% concentration), the $\mathrm{\Delta }\mathrm{\Delta }{\mathrm{G}}_{\mathrm{H}}$ can be modulated to zero. Our findings provide a way to achieve the high intrinsic HER activity among molybdenum-sulfide-based catalysts.     

The effect of subsurface hydrogen on the adsorption of ethylene on Pd(1 1 1)

The adsorption of ethylene on a hydrogen pre-covered Pd(1 1 1) surface was studied by reflection absorption infrared spectroscopy (RAIRS). The effect of either surface or subsurface hydrogen on the state of ethylene hybridization is explored by making use of the order–disorder transition of hydrogen on Pd(1 1 1) at low temperatures, during which the proportion of surface and subsurface hydrogen varies. The results indicate that the subsurface hydrogen is responsible for the formation of π-bonded ethylene on hydrogen-covered Pd(1 1 1).     

Influence of strain on the Stark effect in InP/GaInP quantum discs

In InP/GaInP quantum discs it is shown that strain induces a type I to type II transition with increasing thickness of the disc. When an external electric field is applied along the cylindrical axis of the disc, the exciton energy exhibits a Stark effect, which for the light hole exciton becomes linear even for a small field value, while for the heavy hole it is more quadratic.     

Effect of pressure on the electrical resistivity and magnetism in updsn

The electrical resistivity of a UPdSn single crystal exerted to various hydrostatic pressures was measured as a function of temperature and magnetic field. Clear anomalies in the temperature dependence of resistivity along the c-axis mark the magnetic phase transitions between paramagnetic and antiferromagnetic (AF) state at T _N and the AF1?AF2 transition at T ₁. Large negative magnetoresistance effects have been observed not only in the AF state as a result of the metamagnetic transition to canted structure at B _c , but also at temperatures far above T _N . The latter result is attributed to the existence of AF correlations or short range AF orderings in the paramagnetic range. The value of T _N increases with increasing applied pressure, whereas T ₁ simultaneously decreases. It is also found that B _c decreases with increasing pressure. As a consequence, the stability range of the AF-1 phase expands with applied pressure partially on account of the ground-state AF-2 phase.     

The effect of prior tensile strain on resistivity of torsionally deformed aluminium at room temperature

This work deals with the effect of tensile pre-strain on the electrical resistivity changes of high purity aluminium samples during torsional deformation at room temperature. It was found that as the amount of tensile pre-strain was increased, the percent rise in resistivity decreases. This behaviour was explained in terms of the formation of jogged dislocations, and decreased density of lattice vacancies.     

Effects of Ag addition on phase transformation and resistivity of TiSi2 thin films

In this study, the effects of adding Ag to TiSi₂ thin films are examined. It is demonstrated that both the C49 → C54 transformation temperature and the electric resistivity are appreciably lowered with Ag addition. Due to the presence of Ag nanocrystals precipitated at the C49 grain boundaries, the overall grain boundary density would increase to result in the higher nucleation rate of C54 and the lower transformation temperature. The precipitation of pure Ag network can provide another electric current conductive path except for the TiSi₂ grains. Due to the lower vacuum condition and the higher oxygen content in the current sputtered and annealed films, the C49 → C54 transformation temperature and the resistivity of the TiSi₂-20 at%Ag films can only be reduced by ∼100 °C and 10 μΩ cm, as compared with the non-Ag additive films. With better fabrication vacuum, the transformation temperature and resistivity might be lowered to a level below 700 °C and 15 μΩ cm, which are highly applausive for engineering applications.     

The effect of the strain amplitude changes on the stress amplitude and resistivity of torsionally fatigued copper

Polycrystalline copper wires were cyclically strained in torsion in liquid nitrogen and the effect of the strain amplitude changes on the stress amplitude and resistivity was followed. It was found that both stress amplitude and resistivity are able to increase or decrease in dependence on the applied plastic strain amplitude. When the strain amplitude was decreased, the reversibility was not complete. By means of intermediate annealing it was found that both the dislocation density and the point-defect concentration follow the changes of the plastic strain amplitude.     

Critical size and surface effect of the hydrogen interaction of palladium clusters

Metal hydrides are used for electrochemical or gaseous storage of hydrogen because considerable amounts of hydrogen are reversibly absorbed and desorbed at interstitial sites. Palladium is often used as a model system. Nanophase material is of interest because properties related to the hydrogen absorption are size dependent. In this study, clusters from the size of 55 to 1415 atoms are investigated and compared with bulk Pd. It turns out that not only the amount of hydrogen per palladium that can be intercalated changes but also kinetics and chemical potentials are dependent on the cluster size. The clusters used for this study were chemically synthesised and stabilised by a ligand shell. Received 9 October 1998 and Received in final form 10 May 1999     

超细钨丝的电解腐蚀制备及其性能表征

 直径小于7 μm的超细钨丝是制备Z-pinch丝阵负载的主要原料,为了满足Z-pinch物理实验需要,利用电解腐蚀法原理,制备出了直径最小为3.0 μm的超细钨丝。研究了电解液温度、电解液质量分数、电解电压和收丝速度等工艺条件对钨丝的影响,并用扫描电镜、原子力显微镜和万能测力计测试了所制备钨丝的直径、形貌及抗拉强度。实验表明,电解电压和收丝速度是影响钨丝腐蚀速度的主要因素,所制备的钨丝表面光滑,均方根粗糙度为2.42 nm,直径为3.5 μm的钨丝其抗拉强度为2.32 g。利用这种方法所制备的超细钨丝已用作Z-pinch丝阵负载的靶材料,取得了很好的物理实验结果,X光能量已达到36.58 kJ。     

Quantitative evaluation of process induced strain in MOS transistors by Convergent Beam Electron Diffraction

Convergent Beam Electron Diffraction (CBED) experiments and simulations associated with Finite Element calculations were performed in order to measure strain and stress in a complex device such as periodic MOS transistors with a spatial resolution of about 2 nm and a sensitivity that could reach 50 MPa. A lamella of a thickness of about 475 nm was extracted from the wafer with the transistors by Focus Ion Beam (FIB) and was observed in cross-section in a Transmission Electron Microscope (TEM). When approaching the transistors, the HOLZ lines of the CBED patterns acquired in the silicon substrate, become broader and broader. This HOLZ line broadening, which is due to the stress relaxation in the thin foil, was used to determine quantitatively the strain and stress in the lamella and then in the bulk device. We showed that this procedure could be applied to a complex device. Two parameters, the intrinsic material strains – or equivalently the intrinsic material stresses – in the nickel silicide (NiSi) and nitride (Si₃N₄) layers on the top of the transistors gate, were successfully fitted by trial and error, in the procedure.     

管内电缆导体应变对稳定性影响模拟研究

提出了应变对CICC导体稳定性作用的仿真设计思想,研究了应变对临界电流密度的影响,量化了应变作用,推导了导体设计的数学公式,建立了数值仿真设计模型,并进行了导体结构的模拟设计。将数值仿真设计与工程设计进行了比较,结果显示,采用数值仿真设计模型能有效减轻工程设计工作量,缩短设计周期。