1973 Volume 46 Issue 9 Pages 2665-2668
The relationship between the activity of ferric oxyhydroxides (α-, β-, and γ-FeOOH) and structural changes has been investigated by determining the heat of immersion in H2O and H2O vapor adsorption. For each ferric oxyhydroxide, the monolayer capacity of H2O adsorption and the heat of immersion decreased with the progress of transformation into α-Fe2O3. Above the transformation temperature the heat of immersion increased with the outgassing temperature. The heat of immersion of α-Fe2O3 obtained by outgassing each ferric oxyhydroxide at 400 and 500 °C increased with the accompanying increase in crystallite size. β-FeOOH showed higher heat of immersion and larger monolayer capacity per unit surface area than other ferric oxyhydroxides. It is presumed that the higher heat of immersion and larger monolayer capacity observed for β-FeOOH are ascribed to micropores in β-FeOOH crystals produced by the removal of molecular water originally contained.
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