Year: 1986
Type: article
Abstract: 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.
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W22696381