The role of copper (II) in the oxidation of ferrous hydroxide colloid with special reference to the corrosion of iron in an SO 2-containing environment

Abstract

The properties of oxidation products of ferrous hydroxide colloid, precipitated with or without the presence of copper (II) ion, have been examined from the viewpoint that the degree of compactness, i.e., the secondary structure, of the products may be affected by copper doped in a certain range of content. The sedimentation volume of the colloid oxidized with a limited amount of air showed particular variations with the Cu Fe ratio; a remarkable minimum exists in the range of approximately 1% to 3% Cu Fe . The dimensions of primary colloidal particles composed of Fe(OH) 2 and Fe 3O 4 minute crystals, revealed by X-ray diffraction and electron-microscopic observations, were apparently larger in the above region of copper content than in other regions where the colloids were more amorphous. The oxidized colloids were then dried to form layers of model corrosion products, and the permeability and diffusion of gases through the oxide layers showed that the oxides are compact in the low range of Cu Fe ratios. The mechanism of the effect of copper on the oxidation of Fe(OH) 2 colloid and on the formation of a particular secondary structure is discussed.