2216.     MAXWELL, L. R., SMART, J. S., AND BRUNAUER, S.  Thermomagnetic Investigations of Promoted and Unpromoted Iron Oxide and Iron Catalysts.  Jour. Chem. Phys., vol. 19, 1951, pp. 303-309.

        The Curie temperature (θ) and intensity of magnetization of certain unreduced and reduced Fe oxide catalysts have been determined.  For the singly promoted unreduced systems of Fe₃O₄, containing small amounts of one of the following, Na₂O, K₂O, Cs₂O, BaO, B₂O₃, Al₂O₃, or SiO₂, θ was found to be virtually the same as for Fe₃O₄, but large reductions in the saturation intensity of magnetization were observed.  The doubly promoted unreduced systems studied contained additions to Fe₃O₄ of Al₂O₃ and one of the following in small amounts:  Na₂O, K₂O, BaO, or SiO₂. θ for these materials varied only slightly and was either equal to or less than that for Fe₃O₄.  Large reductions in magnetization were found.  Magnetic measurements on the reduced materials gave values of θ the same as for pure Fe.  The extent to which the promoters go into solid solution, both for the unreduced and reduced materials, is determined.  Additional unreduced unpromoted Fe oxides were investigated that had variable ratios (γ) of F⁺⁺/Fe⁺⁺⁺.  Starting at γ=0.352, magnetization was found to increase with increasing γ to a maximum at γ=0.50, agreeing with the known value for magnetite, and then to decrease to a small value for large γ.  The value found for magnetization at γ=0.352 is in agreement with Néel’s theory of ferrimagnetism as applied to cubic Fe₂O₃ and Fe₃O₄.  θ was found to be constant at about 583° C for γ from 0.352 to 1.276.