Preparation and characterization of magnetite samples having different stoichiometric compositions

Abstract

A novel reaction which produces magnetite particles having reproducibly different stoichio-metries (Fe²⁺/Fe³⁺ ratios) is described. The reaction involves the oxidation at 85 °C of solutions containing ferrous ions and hydroxylamine as the oxidizing agent. Deviations from the ideal Fe₃O₄ stoichiometry have been observed by Mössbauer spectroscopy and are attributed to iron vacancies, thus excluding substitutions by impurity cations in the spinel structure. Scanning electron microscope observations have shown that the magnetite particles have narrow size distributions (ca. 0.3–0.4 µm). The morphology of the oxide is unaffected by the reaction parameters determining the stoichiometric composition of the magnetite. The factors which lead to the variation in stoichiometry are the concentrations of both the hydroxylamine and the electrolyte used as buffer (sodium acetate).