The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a platinum microelectrode in room temperature ionic liquids

The electrochemical reduction of benzoic acid in the presence and absence of hydrogen (H-2) has been investigated using a 10 mu m diameter platinum microelectrode in four different room temperature ionic liquids (RTILs), namely [C(4)mim][NTf2], [C(4)mpyrr][NTf2], [C(4)mim][OTf] and [C(4)mim][BF4], versus Ag/Ag+. In all cases, reductive voltammetry is observed, and is suggested to occur via a CE mechanism in which dissociation of benzoic acid is followed by electron transfer to H+ ultimately forming adsorbed hydrogen. Furthermore, the adsorbed H atoms, formed from the reduction of benzoic acid, could be used to achieve the rapid hydrogenolysis of the organic compound (bis(benzyloxycarbonyl)-L-lysine) on the timescale of the voltammetric technique under moderate conditions (25 degrees C).

Separate Density and Viscosity Determination of Room Temperature Ionic Liquids using Dual Quartz Crystal Microbalances

The drive towards cleaner industrial processes has led to the development of room temperature ionic liquids (RTIL) as environmentally friendly solvents. They comprise solely of ions which are liquid at room temperature and with over one million simple RTIL alone it is important to characterize their physical properties using minimal sample volumes. Here we present a dual Quartz Crystal Microbalance (QCM) which allows separate determination of viscosity and density using a total sample volume of only 240 mu L. Liquid traps were fabricated on the sensing area of one QCM using SU-8 10 polymer with a second QCM having a flat surface. Changes in the resonant frequencies were used to extract separate values for viscosity and density. Measurements of a range of pure RTIL with minimal water content have been made on five different trap designs. The best agreement with measurements from the larger volume techniques was obtained for trap widths of around 50 pm thus opening up the possibility of integration into lab-on-a-chip systems.

Anisotropy of single crystal 3C-SiC during nanometric cutting

3C–SiC (the only polytype of SiC that resides in a diamond cubic lattice structure) is a relatively new material that exhibits most of the desirable engineering properties required for advanced electronic applications. The anisotropy exhibited by 3C–SiC during its nanometric cutting is significant, and the potential for its exploitation has yet to be fully investigated. This paper aims to understand the influence of crystal anisotropy of 3C–SiC on its cutting behaviour. A molecular dynamics simulation model was developed to simulate the nanometric cutting of single-crystal 3C–SiC in nine (9) distinct combinations of crystal orientations and cutting directions, i.e. (1?1?1) <-1?1?0>, (1?1?1) <-2?1?1>, (1?1?0) <-1?1?0>, (1?1?0) <0?0?1>, (1?1?0) <1?1?-2>, (0?0?1) <-1?1?0>, (0?0?1) <1?0?0>, (1?1?-2) <1?-1?0> and (1?-2?0) <2?1?0>.

In order to ensure the reliability of the simulation results, two separate simulation trials were carried out with different machining parameters. In the first trial, a cutting tool rake angle of -25°, d/r (uncut chip thickness/cutting edge radius) ratio of 0.57 and cutting velocity of 10 m s-1 were used whereas a second trial was done using a cutting tool rake angle of -30°, d/r ratio of 1 and cutting velocity of 4 m s-1. Both the trials showed similar anisotropic variation.

The simulated orthogonal components of thrust force in 3C–SiC showed a variation of up to 45%, while the resultant cutting forces showed a variation of 37%. This suggests that 3C–SiC is highly anisotropic in its ease of deformation. These results corroborate with the experimentally observed anisotropic variation of 43.6% in Young's modulus of 3C–SiC. The recently developed dislocation extraction algorithm (DXA) [1, 2] was employed to detect the nucleation of dislocations in the MD simulations of varying cutting orientations and cutting directions. Based on the overall analysis, it was found that 3C–SiC offers ease of deformation on either (1?1?1) <-1?1?0>, (1?1?0) <0?0?1>, or (1?0?0) <1?0?0> setups.

Shear instability of nanocrystalline silicon carbide during nanometric cutting

The shear instability of the nanoscrystalline 3C-SiC during nanometric cutting at a cutting speed of 100?m/s has been investigated using molecular dynamics simulation. The deviatoric stress in the cutting zone was found to cause sp3-sp2 disorder resulting in the local formation of SiC-graphene and Herzfeld-Mott transitions of 3C-SiC at much lower transition pressures than that required under pure compression. Besides explaining the ductility of SiC at 1500?K, this is a promising phenomenon in general nanoscale engineering of SiC. It shows that modifying the tetrahedral bonding of 3C-SiC, which would otherwise require sophisticated pressure cells, can be achieved more easily by introducing non-hydrostatic stress conditions.

Multiscale simulation of nanometric cutting of single crystal copper and its experimental validation

In this paper a multiscale simulation study was carried out in order to gain in-depth understanding of machining mechanism of nanometric cutting of single crystal copper. This study was focused on the effects of crystal orientation and cutting direction on the attainable machined surface quality. The machining mechanics was analyzed through cutting forces, chip formation morphology, generation and evolution of defects and residual stresses on the machined surface. The simulation results showed that the crystal orientation of the copper material and the cutting direction significantly influenced the deformation mechanism of the workpiece materials during the machining process. Relatively lower cutting forces were experienced while selecting crystal orientation family {1 1 1}. Dislocation movements were found to concentrate in front of the cutting chip while cutting on the (1 1 1) surface along the View the MathML source cutting direction thus, resulting in much smaller damaged layer on the machined surface, compared to other orientations. This crystal orientation and cutting direction therefore recommended for nanometric cutting of single crystal copper in practical applications. A nano-scratching experiment was performed to validate the above findings.

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Influence of microstructure on the cutting behaviour of silicon

We use molecular dynamics simulation to study the mechanisms of plasticity during cutting of monocrystalline and polycrystalline silicon. Three scenarios are considered: (i) cutting a single crystal silicon workpiece with a single crystal diamond tool, (ii) cutting a polysilicon workpiece with a single crystal diamond tool, and (iii) cutting a single crystal silicon workpiece with a polycrystalline diamond tool. A long-range analytical bond order potential is used in the simulations, providing a more accurate picture of the atomic-scale mechanisms of brittle fracture, ductile plasticity, and structural changes in silicon. The MD simulation results show a unique phenomenon of brittle cracking typically inclined at an angle of 45° to 55° to the cut surface, leading to the formation of periodic arrays of nanogrooves in monocrystalline silicon, which is a new insight into previously published results. Furthermore, during cutting, silicon is found to undergo solid-state directional amorphisation without prior Si-I to Si-II (beta tin) transformation, which is in direct contrast to many previously published MD studies on this topic. Our simulations also predict that the propensity for amorphisation is significantly higher in single crystal silicon than in polysilicon, signifying that grain boundaries eases the material removal process.

Physical and numerical constraints in source modeling for finite difference simulation of room acoustics

In finite difference time domain simulation of room acoustics, source functions are subject to various constraints. These depend on the way sources are injected into the grid and on the chosen parameters of the numerical scheme being used. This paper addresses the issue of selecting and designing sources for finite difference simulation, by first reviewing associated aims and constraints, and evaluating existing source models against these criteria. The process of exciting a model is generalized by introducing a system of three cascaded filters, respectively, characterizing the driving pulse, the source mechanics, and the injection of the resulting source function into the grid. It is shown that hard, soft, and transparent sources can be seen as special cases within this unified approach. Starting from the mechanics of a small pulsating sphere, a parametric source model is formulated by specifying suitable filters. This physically constrained source model is numerically consistent, does not scatter incoming waves, and is free from zero- and low-frequency artifacts. Simulation results are employed for comparison with existing source formulations in terms of meeting the spectral and temporal requirements on the outward propagating wave.

Studies of the Room-Temperature Multiferroic Pb(Fe0.5Ta0.5)0.4(Zr0.53Ti0.47)0.6O3: Resonant Ultrasound Spectroscopy, Dielectric, and Magnetic Phenomena

Recently, lead iron tantalate/lead zirconium titanate (PZTFT) was demonstrated to possess large, but unreliable, magnetoelectric coupling at room temperature. Such large coupling would be desirable for device applications but reproducibility would also be critical. To better understand the coupling, the properties of all 3 ferroic order parameters, elastic, electric, and magnetic, believed to be present in the material across a range of temperatures, are investigated. In high temperature elastic data, an anomaly is observed at the orthorhombic mm2 to tetragonal 4mm transition, Tot = 475 K, and a softening trend is observed as the temperature is increased toward 1300 K, where the material is known to become cubic. Thermal degradation makes it impos- sible to measure elastic behavior up to this temperature, however. In the low temperature region, there are elastic anomalies near ≈40 K and in the range 160–245 K. The former is interpreted as being due to a magnetic ordering transition and the latter is interpreted as a hysteretic regime of mixed rhom- bohedral and orthorhombic structures. Electrical and magnetic data collected below room temperature show anomalies at remarkably similar temperature ranges to the elastic data. These observations are used to suggest that the three order parameters in PZTFT are strongly coupled.

Simulation of three-dimension cutting force and tool deflection in the end milling operation based on finite element method

This paper presents a 3D simulation system which is employed in order to predict cutting forces and tool deflection during end-milling operation. In order to verify the accuracy of 3D simulation, results (cutting forces and tool deflection) were compared with those based on the theoretical relationships, in terms of agreement with experiments. The results obtained indicate that the simulation is capable of predicting the cutting forces and tool deflection.