Über die Hydrolyse von Eisen(III)‐perchlorat‐Lösungen

The authors investigate the reaction products formed, when Fe(H 2 O) 3 6 + is deprotonated in perchlorate solutions. When a small amount of base is added, metastable solutions containing the ions Fe(H 2 O) 3+ , Fe(H 2 O) 5 OH 2+ , Fe 2 (H 2 O) 8 (OH) 4+ and Fe(H 2 O) 4 (OH) + are formed, and α‐FeOOH slowly crystallises out. In a narrow intermediate range immediately after adding the base, colloidal amorphous Fe(OH) 3 and crystalline α‐FeOOH are formed. If more base is added a dark brown solution of colloidal amorphous Fe(OH) 3 results, in which the crystallisation of α‐FeOOH, under certain conditions also of γ‐FeOOH, begins after an induction period of several days. Only when a nearly equivalent amount of base is added, Fe(OH) 3 is precipitated. On ageing, this changes partly into α‐Fe 2 O 3 , partly into α‐FeOOH, a rather large amount remaining amorphous. In all the systems, no stable state is reached at room temperature, even after years. If a small amount of Fe 2+ ions is coprecipitated, a complete crystallisation of the amorphous hydroxide to α‐FeOOH takes place. The mechanism of the formation of the crystalline phases is discussed.