水酸化鉄 (II) ゲルの酸化におけるα-FeOOHの溶解析出過程

概要

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Coarse crystals of Fe(OH)2 were prepared by adding iron (II) sulfate solutions to concentrated sodium hydroxide solutions at around 80°C. The Fe(OH)2 gel was oxidized at 7°C by air bubbling. The oxidation of Fe(OH)2 proceeded by the zeroorder reaction with its rate independent of the size of hexagonal Fe(OH)2 crystals which turned into acicular α-FeOOH crystals. The rate-determining step of the oxidation may be the dissolution of oxygen into the solution. In the oxidation process of the coarse Fe(OH)2 gels, star-shaped aggregates composed of six α-FeOOH crystals were formed Electron-diffraction analysis of the star-shaped aggregates indicated that the six equivalent [100] directions in the hexagonal crystal of Fe(OH)2 coincide with the [010] direction in each of six crystals of orthorhombic α-FeOOH. The oxygen arrangement on the (100)hex planes of Fe(OH)2 is equivalent to that on the (010)orth planes of α-FeOOH. It is concluded that Fe(OH)2 crystals in the solution are oxidized selectively on their (100) planes, followed by epitaxial growth of α-FeOOH.
社団法人日本セラミックス協会の論文
1986-12-01