Thermodynamics, structure, and transport properties of the MgO–Al2O3 liquid system
- 78 Downloads
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.
KeywordsMgO–Al2O3 liquid system Melt structure Thermodynamics Diffusivity Viscosity Mixing First-principles molecular dynamics
This work was funded by National Science Foundation (EAR-1426530). High-performance computing resources were provided by Louisiana State University (http://www.hpc.lsu.edu) and Louisiana Optical Network Institute (LONI).
- Bottinga Y, Richet P, Weill DF (1983) Calculation of the density and thermal expansion coefficient of silicate liquids. Bull Mineral 106:129–138Google Scholar
- Fabrichnaya O, Costa e Silva A, Aldinger F (2004) Assessment of thermodynamic functions in the MgO–Al2O3–SiO2 system. Zeitschrift fur Metallkunde 95:793Google Scholar
- Foley SF, Pinter Z (2018) Primary melt compositions in the earth’s mantle. In: Kono Y, Sanloup C (eds) Magmas under pressure: advances in high-pressure experiments on structure and properties of melts, chapter 1, Elsevier, Amsterdam, pp 3–42Google Scholar
- Hageman VBM, Oonk HAJ (1986) Liquid immiscibility in the SiO2 + MgO, SiO2 + SrO, SiO2 + LaO3, and SiO2 + Y2O3 systems. Phys Chem Glasses 27:194–198Google Scholar
- Karki BB, Ghosh DB, Bajgain SK (2018) Simulation of silicate melts under pressure. In: Kono Y, Sanloup C (eds) Magmas under pressure: advances in high‐pressure experiments on structure and properties of melts, chapter 16, Elsevier, Amsterdam, pp. 419–453 Google Scholar
- Levin EM, Robbins CR, McMurdie HF (1964) Phase diagrams for ceramists. America Ceramic Society, ColumbusGoogle Scholar
- Mysen B, Richet P (2005) Silicate glasses and melts, vol 10. Developments in geochemistry. Elsevier, AmsterdamGoogle Scholar