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Water Behavior on Olivine Surfaces

Liu, Tingting
http://rave.ohiolink.edu/etdc/view?acc_num=osu1499990590100178

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Earth Sciences.
Water-rock interaction is one of the most active topics in geochemistry. Olivine group as one of the most important rock-forming minerals extensively occur in the Earth's crust and the upper mantle. The stability and reactivity of olivine minerals in ambient C-H-O fluids has drawn great attention. All the complex surface and bulk reactions occurring between the mineral and surrounding fluids starts with the water on the surface. But how water molecules interact with olivine minerals on the surface on an atomistic/molecular level is still less studied. This work examines the interaction between water and olivine mineral surface, in particular, from the energetics in static state to its structure and dynamics, and vibrational properties of the water molecules on the surface, thus providing a complete picture of molecular behavior of the surface water. This investigation use computational/simulation (first-principles calculations and classical molecular dynamics simulation) tools to calculate the energetics and the dynamic properties. Neutron scattering experimental data are also used to support the dynamic and vibrational property calculations. Water molecule adsorption energy calculations via density functional theory (DFT) calculation is fulfilled by introducing different cation dopants on the forsterite(010) surface as they naturally occur in the crystal structure of olivine minerals as trace elements. It shows that Mg-H2O has the strongest adsorption energy, and the alkaline earth (AE) and transition metal (TM) cations form different types of bonding with H2O, i.e., electrostatic force dominated bonding and covalent bonding, respectively. However, there is no simple trend relating the cation dopant charge or ionic radii to the adsorption energy of water molecule. Instead, it is found that several factors, including surface lattice distortion, ionic size, lattice size (different olivine end members) can together determine the adsorption energy sequence with different metal cations. The structure and dynamics of water molecules on hydroxylated forsterite(010) surface is investigated at 270 K using classical molecular dynamics (MD) simulation. The water structure on the hydroxylated surface is composed of a first weak layer that adsorbs within the trough made by hydroxyl ions and a continuous strong layer on top of the first layer. The dynamic properties pertaining to translation and rotation were investigated separately using intermediate scattering functions (ISF). The translational diffusive motions derived by simulations qualitatively match with the fast and slow motions observed in the experiment. The rotational motion of water molecules and motions of the flexible hydrogen atoms on the surface calculated by simulations is found to be out of the observational energy window of the instrument. MD simulations and inelastic neutron scattering (INS) are used to study the vibrational behavior of water on forsterite surface. Both techniques derived a broad libration band feature by examining the first adsorbed water layer on the surface. MD simulations discover that Ow interacts with the surface Mg atom, and water molecules form an ordered Ih-like ice structure by the network of hydrogen bonding at 10 K. Simulated vibrational data at 150 K was used to compare with INS data at 10 K, avoiding the limitation of classical MD to account for quantum effects that might be significant at 10 K. Confining effect was observed by the simulations, as the molecules near to the surface exhibit smaller bending and stretching magnitude than the free molecule. This works sets up the stage for further investigation on other key geochemical process and could aid in more for water-rock reaction mechanism understanding among C-O-H fluids.
David Cole (Advisor)
Aravind Asthagiri (Committee Member)
David Tomasko (Committee Member)
Wendy Panero (Committee Member)
174 p.
Geochemistry; Geology

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Citations

  • Liu, T. (2017). Water Behavior on Olivine Surfaces [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1499990590100178

    APA Style (7th edition)

  • Liu, Tingting. Water Behavior on Olivine Surfaces. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1499990590100178.

    MLA Style (8th edition)

  • Liu, Tingting. "Water Behavior on Olivine Surfaces." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1499990590100178

    Chicago Manual of Style (17th edition)

osu1499990590100178
365
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This open access ETD is published by The Ohio State University and OhioLINK.