Die Bedeutung von Aluminiumspuren im Alterungsvorgang von amorphem Eisen(III)-hydroxid für die Eliminierung der Goethitphase

Abstract

The hydrothermal method may lead to “structurally pure” hydrohematite when traces of aluminium ions are added during the precipitation of iron(III)-hydroxide.

The concentration needed to eliminate the goethite phase increases with increasing alkalinity of the solution. The best results, preserving hydrohematite in an excellent crystalline state without any contamination by another phase are obtained at pH 9 in the presence of 0.01 mole Al³⁺ pro one mole Fe³⁺.

Due to complete elimination of the goethite phase from hydrohematite, it was possible to study the IR spectrum of the latter, and to prove its individual character by absorption bands at 960 cm⁻¹ and 660 cm⁻¹. In this way may be distinguished the roentgenographically indistinguishable hydrohematite from hematite. The molecules of water responsible for these two bands confer high resistance on the hematite lattice.