1993 Volume 42 Issue 5 Pages 322-330
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.