The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform

Philip N.h. Nakashima - One of the best experts on this subject based on the ideXlab platform.

  • quantitative convergent beam Electron diffraction and quantum crystallography the metallic bond in aluminium
    Structural Chemistry, 2017
    Co-Authors: Philip N.h. Nakashima
    Abstract:

    The technique of quantitative convergent-beam Electron diffraction (QCBED) is reviewed as a method for making very accurate and precise measurements of low-order Bonding-sensitive structure factors. As such, it is a technique with the potential to make significant contributions to the field of quantum crystallography. To demonstrate this, the application of QCBED in determining the nature of the metallic bond in aluminium is examined in detail. The importance of precision in structure factor measurement when it comes to determining Bonding Electron distributions, especially in metals, becomes obvious from this examination. Uncertainties as low as ±0.1% are routinely attainable by QCBED and are shown to be important in reliably locating Bonding charge. In the case of aluminium, a nearly free Electron gas metal where the Bonding Electron distribution is subtler than in most other materials, the bonds are entirely tetrahedrally centred. This is a conclusion that could not have been reached experimentally without the levels of precision offered by QCBED.

  • Quantitative convergent-beam Electron diffraction and quantum crystallography—the metallic bond in aluminium
    Structural Chemistry, 2017
    Co-Authors: Philip N.h. Nakashima
    Abstract:

    The technique of quantitative convergent-beam Electron diffraction (QCBED) is reviewed as a method for making very accurate and precise measurements of low-order Bonding-sensitive structure factors. As such, it is a technique with the potential to make significant contributions to the field of quantum crystallography. To demonstrate this, the application of QCBED in determining the nature of the metallic bond in aluminium is examined in detail. The importance of precision in structure factor measurement when it comes to determining Bonding Electron distributions, especially in metals, becomes obvious from this examination. Uncertainties as low as ±0.1% are routinely attainable by QCBED and are shown to be important in reliably locating Bonding charge. In the case of aluminium, a nearly free Electron gas metal where the Bonding Electron distribution is subtler than in most other materials, the bonds are entirely tetrahedrally centred. This is a conclusion that could not have been reached experimentally without the levels of precision offered by QCBED.

  • The Bonding Electron density in aluminum
    Science, 2011
    Co-Authors: Philip N.h. Nakashima, Joanne Etheridge, Andrew E Smith, Barrington Charles Muddle
    Abstract:

    Aluminum is considered to approach an "ideal" metal or free Electron gas. The valence Electrons move freely, as if unaffected by the presence of the metal ions. Therefore, the Electron redistribution due to chemical Bonding is subtle and has proven extremely difficult to determine. Experimental measurements and ab initio calculations have yielded substantially different results. We applied quantitative convergent-beam Electron diffraction to aluminum to provide an experimental determination of the Bonding Electron distribution. Calculation of the Electron distribution based on density functional theory is shown to be in close agreement. Our results yield an accurate quantitative correlation between the anisotropic elastic properties of aluminum and the Bonding Electron and electrostatic potential distributions.

Takamitsu Yamanaka - One of the best experts on this subject based on the ideXlab platform.

  • Structural changes induced by lattice-Electron interactions: SiO2 stishovite and FeTiO3 ilmenite.
    Journal of synchrotron radiation, 2005
    Co-Authors: Takamitsu Yamanaka
    Abstract:

    The bright source and highly collimated beam of synchrotron radiation offers many advantages for single-crystal structure analysis under non-ambient conditions. The structure changes induced by the lattice-Electron interaction under high pressure have been investigated using a diamond anvil pressure cell. The pressure dependence of Electron density distributions around atoms is elucidated by a single-crystal diffraction study using deformation Electron density analysis and the maximum entropy method. In order to understand the Bonding Electrons under pressure, diffraction intensity measurements of FeTiO3 ilmenite and gamma-SiO2 stishovite single crystals at high pressures were made using synchrotron radiation. Both diffraction studies describe the Electron density distribution including Bonding Electrons and provide the effective charge of the cations. In both cases the valence Electrons are more localized around the cations with increasing pressure. This is consistent with molecular orbital calculations, proving that the Bonding Electron density becomes smaller with pressure. The thermal displacement parameters of both samples are reduced with increasing pressure.

David L. Davidson - One of the best experts on this subject based on the ideXlab platform.

  • Predicting the mechanical properties of second period refractory transition metal alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003
    Co-Authors: David L. Davidson
    Abstract:

    Abstract Stress–strain data from single crystals of refractory transition metal alloys tested in tension and compression are analyzed to give the parameters describing dislocation motion. The athermal stress and temperature correlates well with the elemental concentration of the alloy, while the Peierls–Nabarro (P–N) stress correlates with the Bonding Electron concentration. An estimate of the magnitude of the P–N stress for mixed dislocations is calculated from the elastic constants and correlates well with the values derived from experiment. These correlations provide the basis for predicting the magnitude of yield stress for transition metal alloys, and two examples are given of how this procedure can be used for alloys of known yield stress.

Thomas F. Fässler - One of the best experts on this subject based on the ideXlab platform.

  • The role of non-Bonding Electron pairs in intermetallic compounds.
    Chemical Society reviews, 2003
    Co-Authors: Thomas F. Fässler
    Abstract:

    The Electron Localisation Function, ELF pictorially visualises chemists' intuitive ideas of single and multiple bonds as well as non-Bonding Electron pairs in molecules. The power of the representation of chemical bonds via ELF is that on the one hand covalent, polar, and ionic bonds are distinguishable, and that on the other hand ELF can be calculated for molecules and solids. This enables us to transfer the ideas of chemical Bonding from molecular to intermetallic compounds. Localised two-Electron-two-centre bonds and lone pairs are present in solid-state valence compounds (Zintl phases) as expected by the 8-N rule. In solids, lone pairs are generally more contracted than in molecules due to 'lone-pair repulsion'. In intermetallic compounds localised Electrons predominantly occur in the form of lone pairs. Lattice vibrations influence the strength of lone pair interactions and non-bonded interactions lead to an exchange of delocalised and localised Electrons. Such a mechanism of local Electron pair formation gives rise to ideas of a chemical view of the phenomenon of superconductivity in intermetallic compounds.

M. Lagrené - One of the best experts on this subject based on the ideXlab platform.

  • Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety: AC impedance and computational studies
    Corrosion Science, 2009
    Co-Authors: F. Bentiss, M. Lebrini, H. Vezin, F. Chai, M. Traisnel, M. Lagrené
    Abstract:

    We report here the use of macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety (n-MCTH) in the corrosion inhibition of C38 carbon steel in 0.5 M H2SO4 acid medium. The aim of this work is devoted to study the inhibition characteristics of these compounds for acid corrosion of C38 steel using electrochemical impedance spectroscopy (EIS). Data obtained from EIS show a frequency distribution and therefore a modeling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution and the protection efficiency increased with increasing inhibitors concentration. The difference in their inhibitive action can be explained on the basis of the number of oxygen atoms present in the polyether ring which contribute to the chemisorption strength through the donor acceptor bond between the non Bonding Electron pair and the vacant orbital of metal surface. Adsorption of n-MCTH was found to follow the Langmuir's adsorption isotherm. The thermodynamic functions of adsorption process were calculated and the interpretation of the results is given. These results are complemented with quantum chemical study in order to provide an explanation of the differences between the probed inhibitors. Correlation between the inhibition efficiency and the structure of these compounds are presented.