Density functional theory study of hydrogen sulfide dissociation on bi-metallic Ni-Mo catalysts

This work presents results on the dissociation of H₂S over Ni-Mo catalysts suggesting that the presence of surface Mo-atom(s) has a significant impact on both the energetics of the process and the reaction mechanism. The presence of one Mo atom provides an additional energetic advantage of 10.2 kcal/mol overall. While increasing the energetic advantage of the process, the presence of Mo atom also increases the activation barriers by at most 3 kcal/mol. The large exothermic nature of this process combined with the comparatively small activation barriers suggests that the H₂S dissociation process is a facile process on all of the surfaces studied here. Additionally, analysis was provided to explain the difference in catalytic behavior between a bi-metallic alloy and a bi-metallic sulfide. It was determined that the bi-metallic alloy binds sulfur strongly (>100 kcal/mol) which can be compared with the results of Sun and co-workers [M. Sun, A.E. Nelson, J. Adjaye, Catal. Today 105 (2005) 36] who predict that S adsorption on the metal sulfide phase is not energetically favorable. It is suggested that the sulfide surface does not bind S in an energetically favorable manner because the sulfide surface structure does not possess a binding site that can emulate the hollow site on a metal surface.     

HCN及其氢加成物分子间氢键问题的量子化学研究

采用量子化学(MNDO、CNDO/2)方法,探讨了HCN、H_2CNH和H_3CNH_2分子间的N…H-C氢键的构成。计算表明:HCN-HCN分子间氢键作用较强,支持了实验结果。HCN及其氢加成物H_2CNH、H_3CNH_2等分子间的氢键作用依次减弱,其随C≡N、C=N、C-N的差异而变化,碳氮链中氮原子的作用是构成N…H-C型氢键的一个决定性因素。     

Immobilized anthraquinone for redox mediation of horseradish peroxidase for hydrogen peroxide sensing

The detection of hydrogen peroxide is detailed using horseradish peroxidase and anthraquinone. Both species are immobilized on a glassy carbon electrode substrate. This dual immobilization gives rise to lower detection limits compared with the situation when either of the species is immobilized. Detection limits of 40 nM are reported within physiologically-relevant media.     

Activation process in hydrogen storage related to oxide layers formed on zirconium alloys

The passive behavior of ZrNi alloys near the rest potential is studied through in situ voltammetry, ellipsometry, and microscopic observation. A significant oxide layer growth is observed in aqueous 1 M KOH during the application of different potential programs currently used in the activation processes of the alloy. Oxide barrier effects and occlusion of hydrogen species within the film take place. The kinetics of the oxide layer formation under potential cycling plays a significant role in the activation process of metal alloys used in metal hydride batteries.Dedicated to Professor Gyorgy Horanyi on the occasion of his 70th birthday.     

Measurement of the effective thermal conductivity of a Mg–MgH2 packed bed with oscillating heating

The magnesium–magnesium hydride–hydrogen-system (Mg–MgH₂–H₂) offers, because of its combined hydrogen and heat storage capacity, the possibility to design hydride heat pumps and heat stores. For such industrial application systems based on cylindrically formed reactors filled with an active magnesium powder, the effective thermal conductivity limits the time in which the metal hydride alloy is charged and discharged with hydrogen. Determination of this transport coefficient is of fundamental importance for the optimum design of magnesium hydride reactors. The complex interrelation of the different transport mechanisms in a metal hydride packed bed and the hitherto undefined rule that the solid effective thermal conductivity behaves as a function of the hydrogen concentration, requires a reliable and simple-to-realize measuring method so as to determine the effective thermal conductivity of a magnesium hydride bed. In the present study, a report is given for the first time on the initiation of a measuring technique with oscillating change of temperature in a non-permeated packed bed of fine-grained material. The measurement of the effective thermal conductivity can ensue by tailoring the problem-specific mathematical result to the experimentally recorded temperature-time function. The effective thermal conductivity of the magnesium hydride bed varies between 2 and 8 W/(m K) in a temperature range of 523–653 K.     

微重时卧圆柱内静液面方程与数值计算

由力学平衡方程导出了微重时卧圆柱内静液面方程,推出了边界接触角条件,使用Ｒｕｎｇｅ Ｋｕｔａ法在计算机上得出了数值结果,绘出了静液面形状,并对结果进行了分析．     

Mechanics of rubber shear springs

FEA calculations have been carried out for a model rubber shear spring, consisting of a block of a highly elastic material, bonded between two rigid parallel plates and sheared by displacing one of the plates parallel to the other in its own plane. The block was prevented from deforming in the perpendicular direction, and thus was deformed in plane strain. Stress distributions along the bond-line and the center-line are reported and compared with those expected from the theory of large elastic deformations. Unexpected tensile stresses were found to develop in the interior of the sheared block. They are attributed to the absence on the end surfaces of the stresses needed to maintain a simple shear, causing a pronounced change in the reference pressure—a consequence that is usually overlooked. Because the internal stresses are governed by the boundary conditions, they were strongly affected by the shape of the end surfaces. In addition, they were reduced markedly by assigning values to Poisson's ratio slightly lower than 0.5, thus allowing some volume expansion of the rubber. Strain energy release rates were also evaluated for growth of a crack along the bond-line, starting at the edges, and compared with those reported previously by Lindley and Teo [Energy for crack growth at the bonds of rubber springs, Plast. Rubber Mat. Appl. 4 (1979) 29-37], Muhr et al. [A fracture mechanics study of natural rubber-to-metal bond failure, J. Adhes. Sci. Technol. 10 (1996) 593-616], Gregory and Muhr [Stiffness and fracture analysis of bonded rubber blocks in simple shear, in: D. Boast, V.A. Coveny (Eds.), Finite Element Analysis of Elastomers, Professional Engineering Publications, Bury St. Edmunds, UK, 1999, pp. 265-274] and Gough and Muhr [Initiation of failure of rubber close to bondlines, in: Proceedings of the International Rubber Conference, Maastricht, Netherlands, June 2005, IOM Communications Ltd., London, 2005, pp. 165-174]. They confirm that a long crack at the compression edge will grow faster than one at the tension edge, but the results for short cracks were inconclusive.     

Prediction of bond failure and deflection of carbon fiber-reinforced plastic reinforced concrete beams

Carbon fiber-reinforced plastic (CFRP) reinforced concrete beams can fail due to interface debonding, due to the high tensile strength of such rebars. A set of 16 concrete beams reinforced with different amounts of CFRP reinforcement was subject to static three-point bending. The beam dimensions and CFRP reinforcements used were selected to demonstrate a transition from compression failure to bond failure with decreasing reinforcement ratio. It is shown that accurate bond strength data to predict such failures can be obtained from a “hinged-beam” test configuration, rather than the conventional direct “pull-out” tests. Deflection under service loads can also be predicted more accurately using a proposed equation that includes the reinforcement ratio and the elastic modulus of the reinforcement.     

Modal part analysis of slosh of the liquid in a cylindrical container in the case of small bond number

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丝网印刷普鲁士蓝修饰电极催化还原测定过氧化氢

制备了普鲁士蓝修饰的丝网印刷过氧化氢传感器,研究了过氧化氢在该修饰电极上的电催化还原特性,考察了有关修饰膜制备和试验条件对传感器性能的影响。结果表明,pH4.0的0.2mol·L-1KH2PO4 K2HPO4缓冲溶液(PBS)中,修饰电极对过氧化氢显示出快速的电化学响应,较高的稳定性、重现性和催化活性,测定的线性范围为1.0×10-5～1.0×10-3mol·L-1,相关系数为0.999,检出限为6.0×10-6mol·L-1(3σ)。电极制作方法简便,可用于实际样品的测定。