Regular Article
Phase Equilibrium of the La–Ca–Mn–O System

https://doi.org/10.1006/jssc.2000.8994Get rights and content

Abstract

Phase equilibrium of the La–Ca–Mn–O system at 900°C in atmosphere was examined and illustrated in the form of a phase diagram. La1−xCaxMnO3 forms a solid solution with two distinct perovskite structures (R3c and Pnma). A new compound La2Ca2MnO7, identified in the phase diagram, crystallizes in a rhombohedral structure (R3) with the lattice constants of a=5.62176(4), c=17.3161(2) Å. The phase regions in the La–Ca–Mn–O system were clarified based on the X-ray diffraction analysis of the samples.

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      2016, International Journal of Refractory Metals and Hard Materials
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      In our recent work [12], we have proposed a novel technique for converting the unleachable CaWO4 to the readily soluble Ca3WO6 in aqueous ammonium carbonate solution even at 323 K. The same route is unsuitable for tungsten-containing concentrates with high iron or manganese content because both iron and manganese can react with calcium carbonate and oxygen to generate many calcium compounds such as Ca2Fe2O5 [13], Ca3Fe2WO9 [14], Ca2MnO4 [15], and Ca3Mn2WO9 [16], which require a large amount of calcium carbonate to completely convert tungsten-containing minerals to Ca3WO6. We have noted that Ca2FeWO6 [17] and Ca2MnWO6 [18] are similar to Ca3WO6 in composition and may show the same leaching performance in aqueous ammonium carbonate solution.

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