Structure of liquid tricalcium aluminate

James Drewitt, Adrian Barnes, Sandro Jahn, Simon Kohn, Michael Walter, Alexey Novikov, Daniel R. Neuville, Henry E Fischer, Louis Hennet

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The atomic-scale structure of aerodynamically-levitated and laser-heated liquid tri-calcium aluminate (Ca3Al2O6) was measured at 2073(30)K by using the method of neutron diffraction with Ca isotope substitution (NDIS). The results enable the detailed resolution of the local coordination environment around calcium and aluminum atoms, including the direct determination of the liquid partial structure factor, SCaCa(Q), and partial pair distribution function, gCaCa(r). Molecular dynamics (MD) simulation and reverse Monte Carlo (RMC) refinement methods were employed to obtain a detailed atomistic model of the liquid structure. The composition Ca3Al2O6 lies at the CaO-rich limit of the CaO:Al2O3 glass-forming system. Our results show that, although significantly de-polymerized, liquid Ca3Al2O6 is largely composed of AlO4 tetrahedra forming an infinite network with a slightly higher fraction of bridging oxygen atoms than expected for the composition. Calcium-centered polyhedra exhibit a wide distribution of 4- to 7-fold coordinated sites, with higher coordinated calcium preferentially bonding to bridging oxygens. Analysis of the MD
configuration reveals the presence of ~10% unconnected AlO4 monomers and Al2O7 dimers in the liquid. As the CaO concentration increases, the number of these isolated units increases, such that the upper value for the glass-forming composition of CaO:Al2O3 liquids could be described in terms of a percolation threshold at which the glass can no longer support the formation of an infinitely connected AlO4 network.
Original languageEnglish
Article number064203
Number of pages11
JournalPhysical Review B
Issue number6
Publication statusPublished - 1 Feb 2017


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