Understanding the structure of the first atomic contact in gold

We have studied experimentally jump-to-contact (JC) and jump-out-of-contact (JOC) phenomena in gold electrodes. JC can be observed at first contact when two metals approach each other, while JOC occurs in the last contact before breaking. When the indentation depth between the electrodes is limited to a certain value of conductance, a highly reproducible behaviour in the evolution of the conductance can be obtained for hundreds of cycles of formation and rupture. Molecular dynamics simulations of this process show how the two metallic electrodes are shaped into tips of a well-defined crystallographic structure formed through a mechanical annealing mechanism. We report a detailed analysis of the atomic configurations obtained before contact and rupture of these stable structures and obtained their conductance using first-principles quantum transport calculations. These results help us understand the values of conductance obtained experimentally in the JC and JOC phenomena and improve our understanding of atomic-sized contacts and the evolution of their structural characteristics.     

Morphology and failure in nanocomposites. Part II: surface investigation

Polymer composites filled with calcium carbonate (CaCO₃) nanofillers (<100 nm), and kaolin filler of layered structure, both well suited to create nanocomposites, were analysed. The aim of this study was to investigate the influence of surface properties of the filler and matrix on the adhesion parameters at the interface in composites. The inverse gas chromatography, contact angle and capillary measurements were used for the surface characterization of filler and matrix. Although these methods are based on different assumptions, we found the same trends in the effects of filler surface treatment and/or matrix chemical structure on the changes in the dispersive and polar components of the surface energy. The energetics of the filler and matrix was varied in order to investigate the work of adhesion, interfacial energy and coefficient of spreading, and their influence on the composite properties. We found that the surface treatment of calcium carbonate filler lowered the filler surface energy and the work of adhesion in the composite with poly (vinyl acetate) matrix. The mechanical, thermal and morphological properties of the composite with treated CaCO₃, measured in the first part of this paper, indicated a weak and thin interphase. In the composite with kaolin filler the higher interaction with the polyacrylate copolymer matrix based on styrene as compared to the one based on methyl methacrylate, was confirmed by the higher work of adhesion in the interphase, resulting in a stronger reinforcing of the composite.     

Microfluidic modeling and simulation of flow in membrane microreactors

We study the development of a mathematical model that describes isothermal microfluidic steady flow in a membrane microreactor, i.e., a silicon microreactor that houses a permeable membrane in one wall. The model employs the Navier-Stokes equation with appropriate boundary conditions for fluid permeation through the membrane and velocity slip at the walls to account for high Knudsen number. The model equations are solved analytically using finite Fourier transforms. The model solution is used to evaluate the effect of fluid permeation through the membrane and the Knudsen number on the velocity profile and pressure drop. For the simplified cases of no permeation and/or no slip, the derived solution is in excellent agreement with published experimental and theoretical results available in the literature. The utility of the model is illustrated by applying the results to a membrane microseparator used to separate hydrogen from the other effluents in a microreformer.     

Wettability and interfacial phenomena in the liquid-phase bonding of refractory diboride ceramics: Recent developments

Joining and integration technologies are integral to manufacturing of components based on ultrahigh-temperature ceramics (UHTCs) such as transition metal diborides. Brazing is a particularly attractive joining technique because of its simplicity and versatility, but its use to join the UHTCs demands knowledge of the complex interplay among high-temperature wettability, interfacial reactions, and chemical and thermoelastic compatibilities. This paper summarizes the research and development activities carried out over the last two decades to characterize the wettability and interfacial phenomena in brazing of refractory diboride ceramics. The contact angle data of various metal alloys on diboride-based ceramics have been collected and critically evaluated in conjunction with an analysis of the chemistry and structure of the interface to understand the underlying mechanisms and phenomena that govern interface formation. It explores how solid–liquid interactions impact and are impacted by physical, chemical, and mechanical properties of joined materials. It also describes how this knowledge has been successfully utilized to create liquid-phase bonded diboride-based joints. The paper concludes with a summary of the current state of the art and highlights integration challenges and future research and technology development needs in the area.     

Dynamics Response and Non-linear Characteristics Analysis of Complex Planar 2-DOF Mechanism with Revolute Clearances

二自由度含回转间隙九杆机构的动力学响应及非线性特性分析

陈修龙 潘鹏

（山东科技大学 机械电子工程学院,山东 青岛,266590）

创新点说明：

现有研究主要集中在单间隙的单自由度机构上,而考虑多间隙多自由度的机构研究较少,本文以含双间隙具有两个自由度的新型九杆机构为对象,该机构中的三角板处于摆杆位置,其承载能力较大,可作为多连杆压力机的主体机构,对此机构进行了系统的动态响应研究,分析了机构在不同间隙位置、间隙值和间隙数下的动态响应;当前针对机构混沌现象的研究较少,本文也着重研究了转动副间隙处的混沌现象,分析了其非线性特性,并利用相图和庞加莱映射图对其混沌现象进行了识别,给出了不同间隙值和驱动速度下的分岔图。

研究目的：

由于制造、装配误差和磨损等原因,机构中必然存在间隙,降低了机构的使用寿命和工作精度,对平面机构的动态响应有很大影响。通过本文研究可较准确地预测含间隙九杆机构的动力学特性,为机构的间隙设计、混沌控制和可靠性设计奠定基础。

研究方法：

首先,采用L-N模型建立了机构的法向接触力模型,利用改进的库仑摩擦模型建立了机构的切向摩擦模型,利用拉格朗日方程建立了多间隙平面机构的动力学方程。然后,利用MATLAB软件分析了含多间隙九杆机构在不同间隙数、不同间隙值和不同位置下的动力学特性。最后,利用庞加莱映射和分岔图研究了机构在不同间隙值和不同驱动速度下的非线性动力学特性。

研究结果：

随着间隙值的增大,含多间隙九杆机构的动态响应峰值和振动频率增大,间隙处的轴心轨迹变得更加混乱,机构的输出精度降低。随着间隙数的增加,机构的动态响应峰值和振动频率增大,输出精度降低。随着间隙值的增大,机构的运动由周期状态变为混沌状态。随着驱动速度的增大,机构的混沌现象更加明显。

结论：

1）采用L-N模型建立机构的法向接触力模型,利用改进的库仑摩擦模型建立机构的切向摩擦模型。通过拉格朗日乘子法,建立了改进的动力学模型。

2）分析不同间隙位置、间隙值和间隙数对机构动态响应的影响。不同位置间隙对机构动态响应的影响不同。随着间隙值的增大,机构的动态响应峰值和振动频率增大,间隙处的轴轨迹变得更加混乱,机构的输出精度降低。随着间隙数的增加,机构的动态响应峰值和振动频率增大,输出精度降低。其为机构间隙的选择和设计提供了可靠的依据。

3） 研究不同间隙和驱动速度对间隙接头处非线性特性的影响。利用相图和庞加莱映射图分析机构中的混沌现象,得到不同间隙值和不同驱动速度下的分岔图。结果表明,随着间隙值的增大,机构的运动由周期状态变为混沌状态。合理的间隙值有利于机构的稳定。随着驱动速度的提高,机构的混沌现象更加明显。因此,适当降低驱动速度也有利于提高机构的稳定性。

关键词：平面连杆机构;转动间隙;动态响应;非线性特性;混沌现象

     

Theoretical challenges in understanding the inhibition mechanism of aluminum corrosion in basic media in the presence of some p-phenol derivatives

Using quantum electrochemical/thermodynamical approaches based on coupled cluster/polarized continuum models and density functional theory (CM/PCM–DFT), we investigated the corrosion inhibition mechanism of Al/NaOH system in the presence of some p-phenol derivatives. The influencing parameters on inhibitory action, i.e. charges on oxygen and hydrogen atoms of hydroxyl group, charge transfer, interaction energy, molecular activity and softness, electric dipole moment and de-solvation free energy, were determined for both neutral and deprotonated species at metal|solution interface. A good correlation was observed between these parameters and inhibition efficiency data reported in the literature. By introducing an appropriate thermodynamic procedure, we also determined the proton-loss tendency of the molecules nearby interface. The results were amazing and revealed a complicated protonation/deprotonation cycle for inhibitor species inside electrical double layer; the corrosive agents in the vicinity of metal surface become locally neutralized and pushed away.     

Physicochemical Investigation of Biocompatible Mixed Surfactant Reverse Micelles: III. Aqueous NaCl Solubilization, Thermodynamic Parameters of Desolubilization Process and Conductometric Studies

Solubilization of water and aqueous NaCl in mixed reverse micelles (RMs) comprising sodium bis(2‐ethylhexyl) sulfosuccinate (AOT), and polyoxyethylene (20) sorbitan trioleate or polyoxyethylene (20) sorbitan monooleate has been studied at different compositions (X_nonionic = 0–1.0) at a total surfactant concentration, S_T = 0.10 × 10³ mol m^?3 in biocompatible oils of different chemical structures; viz., ethyl oleate (EO), isopropyl myristate (IPM) and isopropyl palmitate (IPP) at 303 K. The enhancement in water solubilization (i.e., synergism) has been evidenced by the addition of nonionic surfactant to dioctyl sulfosuccinate/oil(s)/water systems. Addition of NaCl in these systems at different X_nonionic enhances their solubilization capacities further until a maximum, ω_NaCl,max is reached. ω_NaCl,max and [NaCl]_max (concentration at which maximization of NaCl solubilization occurs) depend on type of nonionic surfactant, its content (X_nonionic) and oil. A new solubilization efficiency parameter (SP*_water or SP*_NaCl) has been proposed to compare solubilization phenomena in these oils. The energetic parameters of the desolubilization process of water or aqueous NaCl in single and mixed RMs have been estimated. Energetically, the water dissolution process in oil has been found to be more exothermic as well as more organized in IPP. Overall, the dissolution of water and aqueous NaCl in mixed RMs is entropically driven process. Conductance behavior of these systems in the presence of NaCl has been investigated under different [NaCl] at 303 K. An attempt has been made to give an insight to the mechanism of solubilization phenomena, percolation in conductance and microstructures vis‐à‐vis role of biocompatible oils in these systems.     

Evaluation of Transport Phenomena for Removing Vanadium from Petrochemical Industry Solid Waste

Transport phenomena are investigated which are involved in the electrokinetic remediation process used for removing vanadium from deactivated catalysts from oil catalytic cracking that are currently allotted to cement plants and class-I landfills. Variables such as the concentration of electrolyte, electric potential, and applied electric current were evaluated in order to determine the effects produced by electroosmosis, diffusion, hydraulic gradient, and electromigration on the removal of vanadium from the catalyst. It was observed that migration is the most relevant phenomenon in the remediation tests, and for the best remediation condition, the migratory flow accounted for about 87 % of the vanadium removal.     

Local analysis of Marangoni effects during and after droplet formation

The influence on the mass transfer in liquid-liquid extraction was investigated during droplet formation in a quiescent aqueous continuous phase for the two transition components, acetone and acetonitrile, in toluene. Both transition components have similar characteristics. However, an approximately eight times slower mass transfer of a droplet hanging on a capillary in relation to a rising droplet could be observed. The droplet formation time and the initial solute concentration are decisive for the mass transfer behaviour. A lower volumetric flow leads to slower droplet formation and a higher specific mass transfer area enhancing mass transfer, which is visualized via laser induced fluorescence (LIF). Additionally, as expected, higher initial solute concentrations promote Marangoni turbulences and thus mass transfer, which is measured via confocal Raman spectroscopy inside a fixed hanging droplet.     

Fabrication of porous (Ba,Sr)(Co,Fe)O3-δ (BSCF) ceramics using gelatinization and retrogradation phenomena of starch as pore-forming agent

Porous (Ba,Sr)(Co,Fe)O_3-δ (BSCF) ceramics with high open porosity and good electrical conductivity was fabricated using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which shows a high mixed ionic-electronic conductivity. In general, during the fabrication of porous ceramics by the sacrificial template method using pore former particles, closed pores are easily formed unless sufficient pore former particles are added. In this study, we have devised a method using the gelatinization-retrogradation phenomena of starch for producing a porous body with an excellent percolated pore network structure. By dispersing BSCF and starch in an aqueous slurry (0–50% by weight) and heating, gelatinization of the starch occurred and the starch particles adhered to each other. Furthermore, in order to retain the percolated structure, the water solvent was removed by freeze-drying without heating to obtain a dried green body. The sintering behavior of the porous BSCF bodies prepared under various conditions was characterized by microstructural observations and relative density measurements. By optimizing the process conditions of the gelatinization and retrogradation, a porous body having an open porosity of 48.3%, and with 99% of the total pores open, was obtained. The matrix was also well connected and showed a sufficiently high conductivity which was similar to the porous bodies made by the traditional sacrificial template method.