Structural studies on Ca₃Al₄MgO₁₀ (C₃A₂M)—A ternary phase in the system CaO–Al₂O₃–MgO

Abstract

In a sequence of temperature‐dependent solid‐state reactions in the system CaO–Al2O3–MgO the formation of the ternary phase Ca3Al4MgO10 or C3A2M has been studied. Whereas the compound could not be prepared at 1200°C, a yield of 85 wt.‐% of Ca3Al4MgO10 was obtained at 1320°C (incongruent melting point: 1330°C). Powder diffraction data compare well with results of previous investigations from the 1960s. Single crystals of Ca3Al4MgO10 could be retrieved from the sinter‐pellets. Basic crystallographic data are as follows: orthorhombic symmetry, space group Pbcm, a = 5.14073(8), b = 16.7576(2), c = 10.70977(16) Å, V = 922.61(2) Å3, Z = 4. Using synchrotron diffraction data it was possible to solve the crystal structure. Least‐squares refinements resulted in a residual of R(|F|) = 0.021 for 1000 independent observed reflections with I > 2σ(I) and 97 parameters. The structure contains [TO4]‐tetrahedra (T=Al,Mg) forming a three‐dimensional (3‐D) framework whose topological characteristics have been determined. Al‐Mg distributions on the different T‐sites have been studied. The calcium cations are located in voids of the network. More than 50 years after its first observation our investigation clarifies the crystal structure of a compound belonging to a system that is of relevance for several fields of materials science.

Thermodynamic modelling of cements clinkering process as a tool for optimising the proportioning of raw meals containing alternative materials

“…No previous studies have reported the presence of C 3 A 2 M in experimental clinker samples, and there are some uncertainties about the stability of this phase as a solid in industrial clinker 63 . C 3 A 2 M was verified in the modelling of CaO-Al 2 O 3 -MgO systems 85,86 and synthesised in laboratory scale studies 87,88 , with the hydration rate directly associated with its degree of crystallinity. High levels of SFCC lead to the growth of C 3 A 2 M due to the greater availability of alumina to react with MgO present within CaCO 3 AP (0.29 wt%).…”

Theoretical and computational improvements to the algebraic method for discovering cooperative rigid-unit modes

“…While most of the symmetryunique oxygen atoms are shared between two tetrahedra, two are not: the multiplicity-four O1 site is connected only to a single T site, and the multiplicity-four O3 site is shared between three T sites (Kahlenberg, Hejny & Kru ¨ge, 2019). CAZO has been reported to exhibit tetrahedral tilting under high pressure (Kahlenberg, Hejny & Kru ¨ge, 2019), and the isostructural Ca 3 Al 4 MnO 10 compound might be expected to do the same (Kahlenberg, Albrecht et al, 2019). In order to include contributions from all special k vectors, we consider a P1-symmetry supercell of the Pbcm-symmetry parent cell with relative basis {(2, 0, 0), (0, 2, 0), (0, 0, 2)}, which is eight times larger than the parent, providing N pivot = 160 T-site SUPAs and N shared = 320 oxygen SUSAs (including the O1 sites).…”

Re-investigation and correct symmetry of Ca3CoAl4O10

“…In a recent paper on the phase relationships in the system CaO-MgO-Al 2 O 3 , we reported the existence and the crystal structure of Ca 3 MgAl 4 O 10 (Kahlenberg et al, 2018), a phase of interest for slags occurring in secondary refining processes in metallurgy or refractories, for example. In the course of this study it became obvious that the compound is closely related to the corresponding Zn and Co analogues that have already been reported in the literature (Barbanyagre et al, 1997;Vazquez et al, 2002).…”

“…coordinates were taken from the crystal structure of Ca 3 Al 4 MgO 10 (Kahlenberg et al, 2018). Initially, mixed cobalt-aluminium populations were considered for all four T sites.…”