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 (Fe_1-xAl_x)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.