Über die Koexistenz der Aluminium- und Eisen(III)-hydroxide und Oxide

Analysis of the IR spectra reveals that traces of aluminium ions reduce the amount of goethite phase in the products of ageing of amorphous ferric hydroxide. X-ray studies showed that the unit-cell parameters of the hematite decrease during ageing, this decrease ceasing at the composition 0,2 Al₂O₃· · 0,8 Fe₂O₃. Electron microscopic examination showed that the hematite grains are always larger in the presence of Al³⁺. Thermal analysis showed the hydrohematite formed in the presence of 0,03 mole of Al₂O₃ to be almost anhydrous.In the concentration range 0,2–0,5 mole Al₂O₃ the processes of ageing show a trend towards the formation of hydrohematite and bayerite, of which the latter could not exist alone at the high ageing temperature. The formation of bayerite is most favoured when the composition is exactly 0,5 Al₂O₃· · 0,5 Fe₂O₃, as is proved by IR spectra, X-ray diffraction patterns, differential thermal analysis and electron microscopy. Study of the products of thermal decomposition of such a sample shows that following the decomposition of bayerite no crystalline hydroxide or oxide of aluminium appears until the temperature reaches 900°.When Al³⁺ predominates in the mixturexAl(OH)_3/y Fe(OH)₃ and boehmite is formed, no ferriboehmite can be detected.

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