Browsing by Author "White, CE"

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    Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry
    (Royal Society of Chemistry, 2011-02-14) White, CE; Provis, JL; Kearley, GJ; Riley, DP; van Deventer, JSJ
    Common throughout sol–gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments. © 2011, Royal Society of Chemistry
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    Inelastic neutron scattering analysis of the thermal decomposition of kaolinite to metakaolin
    (Elsevier, 2013-12-12) White, CE; Kearley, GJ; Provis, JL; Riley, DP
    Understanding the formation of metakaolin via kaolinite dehydroxylation is extremely important for the optimization of various industrial processes. Recent investigations have reported that the different types of hydrogen atoms in kaolinite are removed concurrently during the dehydroxylation process. Here, inelastic neutron scattering (INS) is used to analyze the location and dynamics of hydrogen atoms in kaolinite, together with the changes induced during dehydroxylation. This is achieved by using prior knowledge of how the inner and inner surface hydrogen atoms contribute to the kaolinite INS spectrum in the 200–1200 cm−1 range, in combination with a semi-quantitative analysis of the experimental INS spectra. Overall, it is seen that there is a distinct preferential loss of inner surface hydrogen-atom types during the dehydroxylation process, as determined from analysis of the Al–O–H vibrational modes (consisting of deformation and torsion) in the INS spectrum. © 2013, Elsevier B.V.
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    Structure of kaolinite and influence of stacking faults: reconciling theory and experiment using inelastic neutron scattering analysis
    (American Institute of Physics, 2013-05-21) White, CE; Kearley, GJ; Provis, JL; Riley, DP
    The structure of kaolinite at the atomic level, including the effect of stacking faults, is investigated using inelastic neutron scattering (INS) spectroscopy and density functional theory (DFT) calculations. The vibrational dynamics of the standard crystal structure of kaolinite, calculated using DFT (VASP) with normal mode analysis, gives good agreement with the experimental INS data except for distinct discrepancies, especially for the low frequency modes (200 - 400 cm(-1)). By generating several types of stacking faults (shifts in the a, b plane for one kaolinite layer relative to the adjacent layer), it is seen that these low frequency modes are affected, specifically through the emergence of longer hydrogen bonds (O-H center dot center dot center dot O) in one of the models corresponding to a stacking fault of -0.3151a - 0.3151b. The small residual disagreement between observed and calculated INS is assigned to quantum effects (which are not taken into account in the DFT calculations), in the form of translational tunneling of the proton in the hydrogen bonds, which lead to a softening of the low frequency modes. DFT-based molecular dynamics simulations show that anharmonicity does not play an important role in the structural dynamics of kaolinite. © 2013, American Institute of Physics.
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    What is the structure of kaolinite? Reconciling theory and experiment
    (American Chemical Society, 2009-05-14) White, CE; Provis, JL; Riley, DP; Kearley, GJ; van Deventer, JSJ
    Density functional modeling of the crystalline layered aluminosilicate mineral kaolinite is conducted, first to reconcile discrepancies in the literature regarding the exact geometry of the inner and inner surface hydroxyl groups, and second to investigate the performance of selected exchange-correlation functionals in providing accurate structural information. A detailed evaluation of published experimental and computational structures is given, highlighting disagreements in space groups, hydroxyl bond lengths, and bond angles. A major aim of this paper is to resolve these discrepancies through computations. Computed structures are compared via total energy calculations and validated against experimental structures by comparing computed neutron diffractograms, and a final assessment is performed using vibrational spectra from inelastic neutron scattering. The density functional modeling is carried out at a sufficiently high level of theory to provide accurate structure predictions while keeping computational requirements low enough to enable the use of the structures in large-scale calculations. It is found that the best functional to use for efficient density functional modeling of kaolinite using the DMol(3) software package is the BLYP functional. The computed structure for kaolinite at 0 K has C-1 symmetry, with the inner hydroxyl group angled slightly above the a,b plane and the inner surface hydroxyls aligned close to perpendicular to that plane. © 2009, American Chemical Society