8 9 The euhedral shapes of pyrite FeS2 are usually exposing three main surfaces: striated (001), smooth 10 (111) and striated (210) leading to the cubical, octahedral and pyritohedral morphology respectively. 11 The macroscopic... more
8 9 The euhedral shapes of pyrite FeS2 are usually exposing three main surfaces: striated (001), smooth 10 (111) and striated (210) leading to the cubical, octahedral and pyritohedral morphology respectively. 11 The macroscopic striations, sometimes called triglyphs on cubic crystals, are parallel on specific 12 surfaces and aligned to the <100> directions. Other types of striated and unstriated (hkl) surfaces 13 can be observed on pyrite crystals from Peru, a country offering a rich diversity of shapes. A rare 14 specimen from Elba island (Italy) is a pyritohedron with uncommon directions of striations (so15 called negative striations, firstly described in Japanese minerals). The Wulff kinetic growth and the 16 periodic bond chain (PBC) theories were not relevant enough to explain crystal shapes, the texture 17 of the surfaces and twinning. To bring some new insights on crystal growth, twinning and 18 anisotropy, pyrite samples are analyzed using XRD, SEM and EDS techniques c...
Marcasite mineral is a metastable iron sulphide, α-FeS2, less known and less abundant than pyrite β-FeS2. Their chemical compositions are similar, formed by S2 2dimers and Fe2+ species, but the marcasite crystal structure is orthorhombic... more
Marcasite mineral is a metastable iron sulphide, α-FeS2, less known and less abundant than pyrite β-FeS2. Their chemical compositions are similar, formed by S2 2dimers and Fe2+ species, but the marcasite crystal structure is orthorhombic while pyrite is cubic. The thermodynamic stability of a range of selected surfaces and their kinetic growth are analysed with molecular mechanics simulations implemented in METADISE code. The most stable surface of marcasite corresponds to the (101) surface having the lowest surface energy (marcasite 101 γ = 1.06 Jm-2) and the most favoured kinetic growth rate is expected for the [010] direction (the attachment energy of (010) surface is 0.20 |eV|/at). Mirror twinning is another characteristic of the mineral contributing to a distinctive crystal growth forming different shapes such as striated needles or pseudo-pentagonal flowers. Similarities, differences and overgrowth between the two dimorphs are highlighted.
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Molecular Simulation of Mineral Surfaces and the Role of Impurities on Surface Stability. [AIP Conference Proceedings 916, 268 (2007)]. SC Parker, JP Allen, C. Arrouvel, D. Spagnoli, S. Kerisit, DC Sayle. Abstract. Molecular simulation ...
Research Interests: Materials Science, Surfaces and Interfaces, Crystal Growth, Molecular modeling, Structural Stability, and 11 moreCrystal structure, Molecular Simulation, Impurity, Simulation Methods, Electronic Structure, Surface Properties, Microstructures, MINERAL WATER, Molecular Dynamic Simulation, Electronic Structure Calculation, and Molecular dynamic
ABSTRACT The properties of hydroxyl groups on γ-Al2O3, TiO2-anatase and MgO are rationalized by Density Functional Theory calculations. Oxide ionicity is found to be determinant in the water/oxide interaction strength when dissociation of... more
ABSTRACT The properties of hydroxyl groups on γ-Al2O3, TiO2-anatase and MgO are rationalized by Density Functional Theory calculations. Oxide ionicity is found to be determinant in the water/oxide interaction strength when dissociation of H2O occurs, and in the bridging ability of monocoordinated surface OH groups. For a hydroxyl, being the hydrogen bond donor, acceptor or having an isolated nature is found to be the most important parameter governing the O–H stretching frequency.
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ABSTRACT The adsorption of glycine (G) on the (0001) surfaces of α-alumina with terminations modeling increasing water activity, O3Al (anhydrous) and (Al3O−H, O3Al−OH) (oxy-hydroxide-like) were investigated at low coverage. Different... more
ABSTRACT The adsorption of glycine (G) on the (0001) surfaces of α-alumina with terminations modeling increasing water activity, O3Al (anhydrous) and (Al3O−H, O3Al−OH) (oxy-hydroxide-like) were investigated at low coverage. Different possible glycine conformers have been considered (neutral (NG), zwitterion (ZG), anion (AG)), as well as different binding modes and orientations toward the surface. In all cases, glycine interacts preferentially with the surface through the carboxylic group. The binding with the O3Al termination of the anhydrous oxide surface may be unidentate Al−O(C) or bridging Al−OCO−Al. The anion perpendicular unidentate form is the most stable one with an energy of adsorption of ΔEads = −214 kJ/mol. The nature of the Al−O(C) bond is found to be iono-covalent. On the hydroxylated surface with (Al3O−H, O3Al−OH) terminations, two types of adsorption may occur: forming only H bonds with the surface (ΔEads = −70 kJ/mol) or by the combination of Al−OC and H bonds (ΔEads = −159 kJ/mol). An additional scenario was considered, where glycine substitutes a surface OH group and forms an Al−O−C bond, whereas the OH group combines with a proton from the surface to form a water molecule that coadsorbs with gycine. This reaction is thermodynamically favored (ΔE = −213 kJ/mol). The ZG and AG forms are isoenergetic in a unidentate parallel mode of adsorption. It is shown that coadsorbed water has a stabilizing effect and has an influence on the nature of the most stable G conformer.
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Research Interests: Physics, Materials Science, Polymorphism, Nuclear Magnetic Resonance, Physical sciences, and 10 moreCHEMICAL SCIENCES, Granular Material, Porous Material, Photoemission, Chemical Shift, Coordination number, Radial Distribution Function, Molecular Dynamic Simulation, Generic model, and Distribution Function
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ABSTRACT BaAl2O4 nanoparticles samples were prepared by sol–gel proteic route. The preparation of the precursor mixture and the formation of the ceramic product were monitored using TG/DTA, X-ray diffraction (XRD), electron microscopy... more
ABSTRACT BaAl2O4 nanoparticles samples were prepared by sol–gel proteic route. The preparation of the precursor mixture and the formation of the ceramic product were monitored using TG/DTA, X-ray diffraction (XRD), electron microscopy (SEM, TEM). The results show that sol–gel proteic route is a reliable method for the synthesis of pure BaAl2O4 powders and that irregular hexagonal facetted nanoparticles are observed. Atomistic modeling was used to calculate the structures and energies of 24 (hkl) surfaces and to evaluate morphologies of BaAl2O4 at the thermodynamic and pseudo-kinetic equilibrium. The calculations show that the two most stable surfaces are the (001) and (011) with a surface energy of 1.33 J m−2 and 1.36 J m−2 respectively and that the predicted morphologies are in accord with experiment.
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ABSTRACT A comparative investigation of surface hydroxylation states for anatase–TiO2 and γ-alumina is crucial for a better understanding of how these materials behave as catalytic supports under working conditions. Our approach combines... more
ABSTRACT A comparative investigation of surface hydroxylation states for anatase–TiO2 and γ-alumina is crucial for a better understanding of how these materials behave as catalytic supports under working conditions. Our approach combines density functional simulations and thermodynamic analysis, to determine the types of hydroxyls existing on the (100), (101), (001), and (110) surfaces of anatase–TiO2, as a function of temperature and water pressure. The vibrational analysis of surface OH groups allows for the assignment of experimental infrared bands as a function of the surface orientation. A consistent and quantitative comparison with recent DFT simulations on γ-alumina highlights the different acidic–basic properties of the two supports. Finally, we suggest directions for increasing the density of basic and exchangeable hydroxyls which is governed by morphology effects.