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Thermodynamics, structure, and transport properties of the MgO–Al2O3 liquid system

Authors
  • Karki, Bijaya B.1, 2, 3
  • Maharjan, Charitra1
  • Ghosh, Dipta B.1
  • 1 Louisiana State University, School of Electrical Engineering and Computer Science, Baton Rouge, LA, 70803, USA , Baton Rouge (United States)
  • 2 Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, 70803, USA , Baton Rouge (United States)
  • 3 Louisiana State University, Center for Computation and Technology, Baton Rouge, LA, 70803, USA , Baton Rouge (United States)
Type
Published Article
Journal
Physics and Chemistry of Minerals
Publisher
Springer Berlin Heidelberg
Publication Date
Jan 14, 2019
Volume
46
Issue
5
Pages
501–512
Identifiers
DOI: 10.1007/s00269-018-01019-5
Source
Springer Nature
Keywords
License
Yellow

Abstract

Seven liquids along the MgO–Al2O3 join were simulated at zero pressure in temperature (T) range 2000–6000 K using the first-principles molecular dynamics method. The simulation results show continuous changes in various physical properties with composition (molar fraction of alumina, X). They suggest that the binary mixing tends to be nearly ideal with no immiscibility along the entire join. The calculated mean coordination numbers of MgO and AlO polyhedra gradually increase with increasing X, for example, their respective values are 4.6 and 4.3 at/near the MgO end, 5.2 and 4.6 for MgAl2O4 spinel composition, and 5.5 and 4.8 at/near the alumina end. The mean O–O coordination number remains almost unchanged along the join at ≥ 12 implying a closely packed arrangement. In contrast, all other coordination types including O–Mg and O–Al change dramatically along the join. The calculated self-diffusion and viscosity coefficients vary much less with composition (by a factor of 4 or less along the entire join) than with temperature (by two orders of magnitudes over the T range considered). Their T–X variations can be well described by the respective Arrhenius equations with composition-dependent activation energies and pre-exponential parameters. While the alumina and silica components are considered to play a similar role with regard to the structural polymerization of amorphous aluminosilicates, our results show that they influence the melt transport properties very differently. Therefore, the general notion that these two oxide components play an equivalent role in multicomponent magmatic melts is not unambiguous.

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