Mechanism of formation of magnetite from ferrous hydroxide in aqueous corrosion processes
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The stoichiometric conditions for the formation of ferrous hydroxide Fe(OH)2, by mixing Fe2+ ions with caustic soda NaOH, leads by oxidation to magnetite, irrelevant of the foreign anions, e.g. Cl− or SO42−, as demonstrated from Mössbauer spectroscopy. The electrochemical potential Eh and pH value of the initial conditions correspond to the drastic change from basic to acidic medium, observed when varying the initial Fe2+/OH− ratio. Mössbauer analysis of the end products of oxidation at various temperatures shows that magnetite is only obtained at stoichiometry at very low temperature, but extends off stoichiometry at higher temperatures. The mechanism of formation of magnetite through an intermediate compound is discussed.
KeywordsOxidation Thin Film Hydroxide Magnetite SO42
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