Search results for "metals"
showing 10 items of 2013 documents
Metal- and reagent-free highly selective anodic cross-coupling reaction of phenols.
2014
The direct oxidative cross-coupling of phenols is a very challenging transformation, as homo-coupling is usually strongly preferred. Electrochemical methods circumvent the use of oxidizing reagents or metal catalysts and are therefore highly attractive. Employing electrolytes with a high capacity for hydrogen bonding, such as methanol with formic acid or 1,1,1,3,3,3-hexafluoro-2-propanol, a direct electrolysis in an undivided cell provides mixed 2,2′-biphenols with high selectivity. This mild method tolerates a variety of moieties, for example, tert-butyl groups, which are not compatible with other strong electrophilic media but vital for later catalytic applications of the formed products.
The effect of hydration layers on the anodic growth and on the dielectric properties of Al2O3 for electrolytic capacitors
2014
Hydrous films were grown on high purity and cubicity Al foils for electrolytic capacitors in deionized water, ethylene glycol - deionized water and in glycerol - deionized water for different immersion times. According to the X-ray diffraction patterns the hydration treatment allowed to grow a pseudo boehmite layer on Al surface whose morphology is appreciably affected by the bath composition. Capacitance measurements and photoelectrochemical findings suggest that a more compact barrier layer forms during the immersion in alcohol containing solutions. The hydration in water allowed to save energy and to prepare more blocking oxide films. The beneficial effect of hydration in hot water on th…
The resistivity and thermopower of amorphous Mg-Zn alloys
1983
The resistivity and thermopower of amorphous Mg-Zn alloys have been computed as a function of temperature and composition. The diffraction model incorporating the dynamical partial structure factors is applied. The effect of the electron mean free path is investigated. The authors find that the resistivity is well described by the model, and that the inclusion of the mean free path does not change the results considerably. In the case of thermopower the diffraction model turns out to be inadequate: it gives a composition dependence which is against the experimental evidence. This suggests that there exists another scattering mechanism, which is not accounted for by the diffraction model. Th…
Theoretical Study of the 15- and 17-Electron Structures of Cyclopentadienylchromium(III) and Cyclopentadienylmolybdenum(III) Complexes. Dichloride an…
1997
International audience; The structure and the energetics of the model systems CpMX2(PH3) + PH3 ⇄ CpMX2(PH3)2 (Cp = cyclopentadienyl; M = Cr, Mo; X = Cl, CH3) are studied by performing Møller−Plesset second order (MP2) and density functional theory (DFT) calculations. Extended basis sets are employed in the geometry optimizations. The results indicate that the structural preference can be traced back to the competition between electron pairing stabilization and M−P bond dissociation energy along the spin doublet surface. At all levels of calculation, the energy splitting, a measure of the cost of pairing the electron during the promotion process from the quartet ground state to the excited d…
Electric control of the spin Hall effect by intervalley transitions
2013
Controlling spin-related material properties by electronic means is a key step towards future spintronic technologies. The spin Hall effect (SHE) has become increasingly important for generating, detecting and using spin currents, but its strength-quantified in terms of the SHE angle-is ultimately fixed by the magnitude of the spin-orbit coupling (SOC) present for any given material system. However, if the electrons generating the SHE can be controlled by populating different areas (valleys) of the electronic structure with different SOC characteristic the SHE angle can be tuned directly within a single sample. Here we report the manipulation of the SHE in bulk GaAs at room temperature by m…
Biomimetic oxidation of pyrene and related aromatic hydrocarbons. Unexpected electron accepting abilities of pyrenequinones
2014
We present a mild catalytic method to oxidize PAHs and, in particular, pyrene. The pyrenediones are much better electron acceptors than benzoquinone in the gas phase and present similar accepting abilities in solution.
Hydrothermal aging of carbon reinforced epoxy laminates with nanofibrous mats as toughening interlayers
2016
Electrospun mats have been applied as toughening interlayers in high performance carbon fiber epoxy composites. While the toughening mechanism exerted by the mat at the interface is the subject of several recent studies, no investigations are reported on the aging behaviour of laminates comprising these nanostructured elements. This work investigates the influence of the combined effect of water and temperature (90 °C) on laminates with Nylon 6,6 electrospun membranes placed either at the middle plane only or at each interlayer. The water-uptake behaviour is modelled by a two-stage diffusion model and compared with the behaviour of the neat resin and of the laminate without mats. Interestin…
Characterization of the Etna volcanic emissions through an active biomonitoring technique (moss-bags): Part 2 – Morphological and mineralogical featu…
2013
Volcanic emissions were studied at Mount Etna (Italy) by using moss-bags technique. Mosses were exposed around the volcano at different distances from the active vents to evaluate the impact of volcanic emissions in the atmosphere. Morphology and mineralogy of volcanic particulate intercepted by mosses were investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). Particles emitted during passive degassing activity from the two active vents, Bocca Nuova and North East Crater (BNC and NEC), were identified as silicates, sulfates and halide compounds. In addition to volcanic particles, we found evidences also of geogenic, anthropogenic and marin…
Part program automatic check for three axis CNC machines
2001
Abstract The simulation and verification of NC codes for CNC machining is a very important task. The aim of this work is to limit the number of cutting tests needed to verify the right writing of the part program for a CN milling machine in the intent of saving time, human resources and money. This is obtained through the Boolean operation among solids, in AutoCAD environment, of the volume covered by the tool during the operations ruled by the part program.
Finite element modelling of temperature distribution in the cutting zone in turning processes with differently coated tools
2005
Abstract The aim of this study is to check the applicability of various simulation models to obtain finite element solutions of cutting forces, specific cutting energy and adequate temperatures for a range of coated tool materials and defined cutting conditions. Commercial explicit finite element code Thirdwave AdvantEdge has been used in simulations of orthogonal cutting processes performed by means of uncoated carbide and coated tools. The latter were equipped with progressively increasing number of thin layers including TiC, TiN and Al 2 O 3 films deposited onto ISO P20 carbide substrates. Results showing the tool–chip interfacial friction influencing the temperature distribution fields,…