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Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates

Horbach, Jürgen (2008) Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates. In: Lecture Notes in Physics Springer. Seiten 149-171.

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Kurzfassung

Molecular dynamics (MD) simulations of sodium silicate melts, (Na<sub>2</sub>O)x(SiO<sub>2</sub>) with x=2, 3, 20, are presented. In these systems, the mobility of sodium ions is much higher, often by orders of magnitude, than that of the silicon and oxygen atoms forming a tetrahedral network structure. We show that the high mobility of sodium is intimately related to the chemical ordering in sodium silicates. A network of percolating sodium-rich channels is formed in the static structure that serve as diffusion channels for the sodium ions. This channel network is revealed in static structure factors by a prepeak at the wavenumber q=0.95 A<sup>-1</sup>. Inelastic neutron scattering experiments of sodium silicate melts, done at temperatures as high as 1600 K, confirm the existence of the latter prepeak. The channel diffusion of sodium ions yields a peculiar behavior of time-dependent density-density correlation functions, the so-called intermediate scattering functions. Whereas the incoherent scattering function for sodium, F<sup>s, Na</sup>(q,t), detects the fast sodium ion diffusion, the coherent scattering function for Na-Na correlations, F<sub>NaNa</sub>(q,t), decays on the slow time-scale of the Si-O matrix. This reflects the hopping motion of sodium ions between sodium sites, thereby F<sub>NaNa</sub>(q,t) describing site-site correlations. Numerical calculations in the framework of mode coupling theory (MCT) are presented which use the partial static structure factors from the MD simulations as an input. The MCT results are in qualitative agreement with those from MD simulations.

Dokumentart:Beitrag im Sammelband
Titel:Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates
Autoren:
AutorenInstitution oder E-Mail-Adresse der Autoren
Horbach, JürgenNICHT SPEZIFIZIERT
Datum:2008
Erschienen in:Lecture Notes in Physics
Referierte Publikation:Nein
In SCOPUS:Nein
In ISI Web of Science:Nein
Band:736
Seitenbereich:Seiten 149-171
Verlag:Springer
Status:veröffentlicht
Stichwörter:molecular dynamics computer simulation, silicate melts, dynamics, mode coupling theory
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Weltraum (alt)
HGF - Programmthema:W FR - Forschung unter Weltraumbedingungen (alt)
DLR - Schwerpunkt:Weltraum
DLR - Forschungsgebiet:W FR - Forschung unter Weltraumbedingungen
DLR - Teilgebiet (Projekt, Vorhaben):W - Vorhaben Materialwissenschaftliche Forschung (alt)
Standort: Köln-Porz
Institute & Einrichtungen:Institut für Materialphysik im Weltraum
Hinterlegt von: Dr.rer.nat. Jürgen Horbach
Hinterlegt am:16 Mai 2008
Letzte Änderung:27 Apr 2009 14:57

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