Structural elucidation of triclinic and monoclinic SFCA-III – killing two birds with one stone

Kahlenberg, Volker; Krüger, Hannes; Goettgens, Valerie Sue

doi:10.1107/s2052520619014380

Cited by 16 publications

(19 citation statements)

References 42 publications

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“…X 21,22) and SFCA-II [23][24][25] are crystallographically closely related. It has also been shown that the alumina-free silico ferrite of calcium (SFC) phase has a crystal structure identical to the SFCA phase.…”

Section: Sfca Nucleationmentioning

confidence: 99%

Mechanisms of Phase and Microstructure Formation during the Cooling of “Fe2O3”–CaO–SiO2–Al2O3 Melts in Air and Implications for Iron Ore Sintering

et al. 2020

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Section: Sfca Nucleationmentioning

confidence: 99%

Mechanisms of Phase and Microstructure Formation during the Cooling of “Fe2O3”–CaO–SiO2–Al2O3 Melts in Air and Implications for Iron Ore Sintering

et al. 2020

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“…2a). This modular approach has been already outlined in detail using concepts of ODtheory in several previous publications for the different members of the SFCA family (Merlino & Zvyagin, 1998;Zvyagin & Merlino 2003;Kahlenberg et al 2019). As can be seen from Fig.…”

Section: Crystal Structurementioning

confidence: 99%

“…Their complex crystal structures exhibit low triclinic symmetry, comparatively large unit-cell volumes, and there is a clear structural relationship between them. Indeed, SFCA and SFCA-I belong to a so-called polysomatic series with general composition A 14+6n O 20+8n (A: Ca, Al, Mg, Si, Fe 3+ , Fe 2+ ) where they represent the members with n = 0 and 1, respectively (see Kahlenberg et al 2019 and references cited therein). The crystal structures of the series allow for a couple of cation substitution mechanisms, which can be summarized according to the following exchange reaction: 2(Fe 3+ ,Al 3+ ) = (Ca 2+ ,Fe 2+ ) + Si 4+ (Patrick and Lovel 2001;Patrick and Pownceby 2002).…”

Section: Introductionmentioning

confidence: 99%

Structural systematics of SFCA-I type solid-solutions in the system CaO–Fe2O3–FeO–Al2O3

2021

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Effects of Fe ↔ Al substitution on triclinic SFCA-I-type compounds with general formula A40O56 (A: Ca, Al, Fe3+, Fe2+) have been studied using single-crystal X-ray diffraction. Crystals of sufficient quality and size were synthesized in the temperature range between 1200 and 1300 °C. Six samples with Al/FeTot ratios of 0.127, 0.173, 0.216, 0.310, 0.349 and 0.459 have been structurally characterized. SFCA-I can be described with a modular approach involving the stacking sequence < PSS > of “P” and “S” modules that can be imagined as being cut from the well-known pyroxene (P) and spinel (S) structure types. Furthermore, SFCA-I is related to the sapphirine supergroup of minerals. Within the present solid-solution series, the contents in calcium show only minor variations (≈ 6.7 a.p.f.u.). The twenty crystallographically independent tetrahedrally (T) and octahedrally (M) coordinated cation sites exhibit considerable differences concerning the Al uptake. Indeed, Al is preferentially incorporated into the tetrahedra belonging to the single-chains located in the pyroxene modules. Ferrous iron, on the other hand, is restricted to one of the T-positions within the spinel blocks. Most structural aspects from unit-cell parameters and cell volumes to site occupancies, tetrahedral chain kinking as well as polyhedral distortions are defined by linear or nearly linear trends when plotted against the Al/FeTot ratio. Analysis of the < T–O > and < M–O > distances showed a complex interplay between the different coordination polyhedra resulting in a contrasting behavior of these values with positive or negative change rates as a function of composition. Evaluation of the average chemical strain tensor derived from the sets of lattice parameters for the two samples of the abovementioned series showing the highest and lowest Al/FeTot ratios indicated, that the major contraction with increasing Al content is perpendicular to the pyroxene- and spinel modules. Furthermore, the pyroxene module seems to be more affected when compared with the spinel block. There is evidence that the SFCA-I-type solid-solution series is limited on both the Al- and Fe-rich sides. The present investigation provides—for the first time—a detailed crystallographic analysis on the impact of chemical variations on a compound that is of relevance to the field of applied mineralogy related to the technologically important process of iron-ore sintering.

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“…3). This modular approach has been already outlined in detail in several previous publications for other members of the SFCA-family (see Kahlenberg et al 2019 and references cited therein). Therefore, we will restrict our description to the key point of this concept.…”

Section: Crystal Structurementioning

confidence: 99%

SFCA-II type Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 – an improved structural model for an iron-ore sinter phase

et al. 2021

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Single crystals of SFCA-II with composition Ca2.46Fe3+8.57Fe2+0.52Al5.45O24 have been obtained from synthesis experiments in the temperature range between 1300 and 1200 °C. Diffraction experiments at ambient conditions yielded the following basic crystallographic data: space group P$$ \overline{1} $$ 1 ¯ , a = 10.3016(4) Å, b = 10.4656(4) Å, c = 17.9553(6) Å, α = 90.062(3), β = 89.977(3)°, γ = 109.510(3)°, V = 1824.66(12) Å3, Z = 4. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 0.0349 for 7406 independent reflections and 773 parameters. Site occupancy refinements on the 35 octahedral (M) and tetrahedral (T) positions in the asymmetric unit were aided by crystallochemical considerations and the assumption of charge balance between the cations and anions. The derived formula compares well with the outcome of electron microprobe studies. The crystal structure of SFCA-II shows the typical features of the SFCA-family. It can be built from an alternating sequence of two different types of fundamental layers. For SFCA-II, they are oriented parallel to (100). Layer-type I is solely based on [MO6]-octahedra (M: Ca, Fe3+, Al) forming individual five polyhedra wide bands. Within a single band, the octahedra share common edges. Layer-type II, on the other hand, contains [MO6]-octahedra as well as [TO4]-tetrahedra (T: Al, Fe3+, Fe2+). By corner sharing each [MO6]-group is linked to two adjacent tetrahedra into [MT2O12]-clusters or “winged octahedra”. Linkage between neighboring strips of these moieties is provided by additional [TO4]-tetrahedra arranged in vierer single-chains. Our investigation rectifies previous studies on SFCA-II where wrong atomic coordinates have been published.

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Structural elucidation of triclinic and monoclinic SFCA-III – killing two birds with one stone

Cited by 16 publications

References 42 publications

Mechanisms of Phase and Microstructure Formation during the Cooling of “Fe<sub>2</sub>O<sub>3</sub>”–CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Melts in Air and Implications for Iron Ore Sintering

Mechanisms of Phase and Microstructure Formation during the Cooling of “Fe<sub>2</sub>O<sub>3</sub>”–CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Melts in Air and Implications for Iron Ore Sintering

Structural systematics of SFCA-I type solid-solutions in the system CaO–Fe2O3–FeO–Al2O3

SFCA-II type Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 – an improved structural model for an iron-ore sinter phase

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