水溶液中における酸化鉄,オキシ水酸化鉄の生成と物性 Formation of Iron Oxide and Oxyhydroxides in Aqueous Solutions and Their Physical Properties
The oxidation processes of Fe (II) hydroxo-complexes to α-, β-, γ-, andδ-FeOOH and Fe_3O_4 in aqueous solutions were investigated by processing measurements with infrared, far infrared, and Mossbauer spectra and X-ray diffraction of oxidation products. The effect of oxidation rate and addition of Cu^<2+> or PO_4^<3-> ion on the oxidation of Fe (II) hydroxo-complexes were also studied. It has been found that in the present experimental condition the process of oxidation depends on the pH-value of solution as follows : in basic solution (pH12.5〜13.5) Fe(OH)_2⇾α-FeOOH, in the slightly acidic solution (pH6〜6.5) β-Fe_2(OH)_3Cl⇾Green rust I⇾γ-FeOOH, and in neutral or slightly basic solution (pH7〜8) Fe(OH)_2⇾Fe_3O_4 and β-Fe_2(OH)_3Cl⇾Green rust I⇾Fe_3O_4. The infrared spectra of Fe(OH)_2 and Green rust I, an oxidation intermediate, have been obtained. The rapid oxidation of Fe(II) hydroxo-complexes in solutions with the addition of H_2O_2 results in the formation of δ-FeOOH. The oxyhydroxide has also been obtained by removing water from the Fe (II)-complexes, and leaving them in air to be oxidized. The broad absorption band at 450 cm^<-1> has been shifted for 480 cm^<-1> with the increase in size of δ-FeOOH crystallite formed by the oxidation of Fe(OH)_2 with H_2O_2. In the presence of Cu^<2+> or PO_4^<3-> ion, freshly precipitated Fe(II) hydroxo-complexes are oxidized into amorphous δ-FeOOH with air in solutions. This transformation is considered to have been caused by the catalytic effect Cu^<2+> or PO_4^<3-> ion in the oxidation of Fe(II)-complexes.
材料 19(201), 537-542, 1970-06-15