Structural and phase changes in iron(III)—aluminium(III) mixed hydroxide—oxide system; A thermoanalytical study

Abstract

The structural and phase changes occurring in the ferric hydroxide gel, alumina gel and the coprecipitated ferric—aluminium hydroxide—oxide system are studied by thermoanalytical and X-ray diffraction techniques. The conversion of hydrated ferric oxide to hematite takes place through γ-Fe 2O 3 and alumina gel to oxide occurs through hydrargellite, bohemite as intermediate. The occurrence of solid solutions below 10 mole % of alumina, i.e. interstitial solid solution up to 1.5 mole %, then substitutional solid solution up to 3.43 mole % and thereafter separation of phases is observed. For higher concentrations of alumina, zones enriched in either hydrated iron oxide or aluminum oxyhydroxide are noticed.