Structure of liquid tricalcium aluminate

Abstract

This is the final published version of the article (version of record). It first appeared online via APS at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.064203. Please refer to any applicable terms of use of the publisher. University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. The atomic-scale structure of aerodynamically levitated and laser-heated liquid tricalcium aluminate (Ca 3 Al 2 O 6 ) 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, S CaCa (Q), and partial pair distribution function, g CaCa (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 Ca 3 Al 2 O 6 lies at the CaO-rich limit of the CaO:Al 2 O 3 glass-forming system. Our results show that, although significantly depolymerized, liquid Ca 3 Al 2 O 6 is largely composed of AlO 4 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 four-to sevenfold coordinated sites, with higher coordinated calcium preferentially bonding to bridging oxygens. Analysis of the MD configuration reveals the presence of ∼10 % unconnected AlO 4 monomers and Al 2 O 7 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:Al 2 O 3 liquids could be described in terms of a percolation threshold at which the glass can no longer support the formation of an infinitely connected AlO 4 network.

Structure, properties, and fabrication of calcium aluminate‐based glasses

“…The net charge of +2 for an alkaline earth ion, for example, a calcium cation, can either promote a clustering effect between two AlO 4 tetrahedra, and consequently, balance a −1 charge on each, or possibly stabilize one AlO 4 and create one NBO. Extensive studies of the structure of calcium aluminate liquids and glasses have been performed by Drewitt and coworkers …”

Neutron diffraction of calcium aluminosilicate glasses and melts

“…This shows that the use of more selective techniques than conventional ND are important in order to more precisely determine the atomic arrangement around Ca atoms. Recently, NDIS experiments have been made to investigate the structure of liquid Ca0.25 [31]. …”

From Molten Calcium Aluminates through Phase Transitions to Cement Phases

“…The principal cement phases nucleate eutectically during melting and quenching, ranging from CaAl 2 O 4 (CA) and CaAl 4 O 7 (CA2) in calcium‐aluminate cements to Ca 3 Al 2 O 6 (C3A) in Portland cement (PC), with Ca 12 Al 14 O 33 (C12A7) effectively acting as a systemic flux. Individual crystalline structures are well established and corresponding melt and glass structures have been modeled from diffraction and spectroscopy …”

“…The calcium‐aluminate glass‐forming system is very extensive compared, for instance, to binary silicates, incorporating additional oxygen sites to the well‐known bridging O 2 and nonbridging O 1 varieties. These include O 3 triclusters as well as isolated O 0 species . Moreover, not all aluminum polyhedra are tetrahedral Al IV , wherein Al V and some more constrained Al VI sites occur; with occurrent calcium octahedra rarely undistorted .…”

“…These include O 3 triclusters as well as isolated O 0 species . Moreover, not all aluminum polyhedra are tetrahedral Al IV , wherein Al V and some more constrained Al VI sites occur; with occurrent calcium octahedra rarely undistorted . O, Al, and Ca speciation evolves similarly with the composition across calcium‐aluminate liquids and crystalline phases.…”