FORMATION AND ANNEALING OF MICROPORES IN HEMATITE

In iron oxide powders positrons are trapped in the surface layers and the value of the S-parameter is an indicator of the total specific sur face, including external surface and internal surfaces of micropores. The evolution of micropores is followed when alpha-FeOOH is thermally decomposed into alpha-Fe2O3. It is shown that the micropore formation is not linked to the decomposition process, but that they also form in hematite synthesized from a ferrihydrite precursor in aqueous solutio n.