The System CaO–"CaCr2O4"–CaAl2O4 in Air and under Mildly Reducing Conditions |
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Authors: | Arno Kaiser Burkhard Sommer Eduard Woermann |
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Affiliation: | Institut für Kristallographie, Rheinisch Westfälische Technische Hochschule Aachen, W-5100 Aachen, Germany |
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Abstract: | The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca5Cr3O12, Ca3(CrO4)2, and Ca5(CrO4)3) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ -CaCr2O4, is observed. In the CaO-rich section of the CaO–Al2O3–Cr2O3 system a ternary intermediate phase, chrome-haüyne, Ca4(Al,Cr3+)6O12](Cr6+O4), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6Al4Cr2O15, coexists with CaO, CaCr2O4, chrome-haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2O3 system is insignificant. |
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Keywords: | calcium aluminum chromium oxides chromates |
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