2270. ---------------. [MICHEL, A.] [Substitutions in Magnetite and Preparation of New Cubic Sesquioxides of Iron.] Bull. Soc. chim. France, 1949, D128-D131; Chem. Abs., vol. 44, 1950, p. 17.
Preparation of magnetite is described in which a bivalent Fe ion is replaced by K, Na, Mn, or Mg, and a trivalent Fe ion is replaced by Al or Cr. Variation of parameters and of the Curie point is given for these substituted magnetites and for the cubic sesquioxides obtained by heating. Temperatures of transformation for cubic (Fe1-xAlx)2O3 are: for x=O~450°; for x=0.03 610°-615°; for x=0.09~650°. Thermomagnetic analysis revealed significant differences between the heating and cooling period. These differences increase, but Curie point for both periods decrease, at higher Al2O3 contents. Al2O3 stabilizes the cubic form of the sesquioxides. The cubic structure of (Fe,Al)2O3 is obtained also by calcination of the nitrates and to some extent by calcination of the sulfates.