β-alumina-14H and β-alumina-21R : two chromic Na2-δ(Al,Mg,Cr)17O25 polysomes observed in slags from the production of low-carbon ferrochromium

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Authors

Hejny, Clivia
Kahlenberg, Volker
Schmidmair, Daniela
Tribus, Martina
De Villiers, J.P.R. (Johan)

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Elsevier

Abstract

The crystal structures of unknown phases found in slags from the production of low-carbon ferrochromium were studied by powder and single-crystal X-ray diffraction. Two phases of Na2−δ (Al, Mg, Cr)17O25 composition were found to be composed of an alternating stacking of a spinel-type and a Na-hosting block. Similar structures are known for β-alumina and β”- alumina, NaAl11O17. However, the spinel-type block in Na2-δ(Al, Mg, Cr)17O25 is composed of five cation layers in contrast to three cation layers in the β-alumina spinel-block. The two new phases, β-alumina-14H, P63/mmc, a=5.6467(2), c=31.9111(12) Å, and β-alumina-21R, R m, a=5.6515(3), c=48.068(3) Å have a 14-layer and 21-layer stacking with a 2 × (cccccch) and a 3 × (ccccccc) repeat sequence of oxygen layers in cubic and hexagonal close packing, respectively.

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Keywords

β-alumina, Polysome, Crystal structure

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Citation

Hejny, C, Kahlenberg, V, Schmidmair, D, Tribus, M & De Villiers, JPR 2016, 'β-alumina-14H and β-alumina-21R : two chromic Na2-δ(Al,Mg,Cr)17O25 polysomes observed in slags from the production of low-carbon ferrochromium', Journal of Solid State Chemistry, vol. 241, pp. 70-78.