種々の酸素分圧下で焼成した鉄スピネル(酸化アルミニウム鉄)における鉄イオンの挙動

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Iron Oxide (III) and aluminum oxide (α) were mixed at the molar ratio of 1 to 2, fired for 3hours under various oxygen partial pressure (P_<O2>) ; 3.9 X10^<-7> Pa≦P_<O2>≦2.1 X10^4 Pa at 1300℃, or 4.0X10^<-6> Pa≦P_<O2>≦2.1 X10^4 Pa at 1400℃. The lattice constant of the iron spinel and the valence of iron ions were measured. From the X-ray powder diffraction pat-tern, the distribution of iron ions was obtained by the PFSR method. The lattice constant was almost constant at low P_<O2>, increased gradually with the increase of P_<O_2>, then increased steeply at P_<O2>≈10^<1.5>Pa (1300℃), or P_<O_2> ≈10^0 Pa (1400℃), and finally remained unchanged at high P_<O2>. The valence of iron ions showed the similar change. At, low P_<O2>, the iron ions were all bivalent, and FeAl_2O_4 was produced. About 80% of the tetrahedral sites and 10% of the octahedral sites were occupied by iron ions, because of the tetrahedral site preference of Fe^<2+> ions to Al^<3+> ions. With the increase of P_<O2>, a part of Fe^<2+> ions was oxidized to Fe^<3+> ions, and substituted for Al^<3+> ions with a smaller radius, resulting in an increase in the lattice constant. In iron spinel containing Fe^<3+> ions, the ratio of the tetrahedral sites occupied by iron ions increased because of their tetrahedral site preference over Fe^<2+> ions. In the low P_<O2> region, the oxidation of the iron ions and the substitution of Al^<3+> ions in the tetrahedral sites proceed stepwise with increasing P_<O2>. The steep increase of the lattice constant and the amount of Fe^<3+> ions observed at a certain P_<O2> has been explained as due to the remarkable change in the cation distribution accompanying the promotion of the oxidation of Fe^<2+> ions.
社団法人日本セラミックス協会の論文
1988-12-01

種々の酸素分圧下で焼成した鉄スピネル(酸化アルミニウム鉄)における鉄イオンの挙動

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