Thermal Analysis of Hydrous Iron Oxides as the Corrosion Products of Steels

Abstract

Applications of thermoanalytical techniques of DTA, TG and DSC were described to show inhibitory effects of the added foreign metal ions on α-FeOOH formation during aging of amorphous ferric hydroxide precipitates and α-Fe₂O₃ formation by heating of the hydroxides. The metals used were Cu, Co, Mg, Ni, Zn, Cr, and Al, which were added to the hydrous oxides by co-precipitation method. Gel-mixing and mortar-mixing of Cu(OH)₂ and CuO were tried and showed that the former resulted in a similar inhibitory effect to the co-precipitation method and the latter was less inhibitory. Oxidation temperature for Fe₃O₄→γ-Fe₂O₃ and transition temperature for γ-Fe₂O₃→α-Fe₂O₃ were also observed to change with the foreign metals added to Fe₃O₄ precipitates.