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    Structure, Thermodynamics and Kinetics of Chemically Heterogeneous Interfaces

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    Nucleation on the (100) Cu/Pb interface at 450 K (85.56Mb)
    Nucleation on the (111)Cu/Pb at 592 K (104.7Mb)
    Issue Date
    2011-08-31
    Author
    Palafox-Hernandez, J. Pablo
    Publisher
    University of Kansas
    Format
    139 pages
    Type
    Dissertation
    Degree Level
    Ph.D.
    Discipline
    Chemistry
    Rights
    This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.
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    Abstract
    In this work we have used atomistic computer simulations to examine the structure, thermodynamics and transport properties, for two models of chemically heterogeneous interfaces: an ideal model (repulsive soft spheres against a potential wall), and a metal alloy interface (Cu-Pb). In both systems, interfacial prefreezing (crystal formation above the melting point of the fluid) was observed and this prefreezing was seen to promote heterogeneous nucleation, when the systems were cooled below the melting temperature. In our study of inverse-power repulsive soft spheres, we found that the soft-sphere fluid exhibited prefreezing at the wall surface. Similar behavior was previously observed in hard-sphere fluids at hard wall [17, 18, 20], however, to our knowledge, this the first time that prefreezing is reported for soft spheres. The prediction of prefreezing is based on the calculation of interfacial free energies wall-crystal (g_wc) and wall-fluid (g_wf ) using a variant of the cleaving wall method. With the calculated, g_wc and g_wf together with g_cf , previously computed [79], the tendency to prefreeze was quantified by the wetting angle formed between the metastable crystal phase on the wall and the soft-sphere fluid. We found that all the closest packing orientations [(111) FCC and (110) BCC] developed prefreezing (complete wetting). A detailed atomic-level characterization of the structure, energetics and transport properties of the planar Cu/Pb solid-liquid interface in equilibrium was performed at a several temperatures (625K and 750K) above the melting point of Pb and for two Cu crystal orientations [(111) and (100)]. Among the most relevant findings are that the Cu(100)/Pb interfaces presents surfaces alloying and the Cu(111)/Pb exhibits a prefreezing layer of Pb crystal. It was also observed that both interfaces have a nucleation barrier that prevents heterogeneous nucleation and that the mechanisms by which each structure promotes heterogeneous nucleation are different. Both models, the inverse-power soft spheres and the EAM Cu-Pb, showed the connection between atomistic behavior and prefreezing. The crystalline layer formed above the melting point of the fluids showed to be influential in heterogeneous nucleation in both cases. In this way, the study of basic properties shed new light on the atomistic underlying nature of macroscopic events, such as wetting and nucleation
    URI
    http://hdl.handle.net/1808/8179
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    • Dissertations [4321]
    • Chemistry Dissertations and Theses [336]

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    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
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    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

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