Preparation and characterization of superparamagnetic α-Fe₂O₃/Fe₃O₄@SiO₂ nanocomposites via a citric-TEOS-ethanol solution combustion process

Superparamagnetic α-Fe₂O₃/Fe₃O₄@SiO₂ nanocomposites were prepared by the citric-TEOS-ethanol solution combustion method. Four key influencing factors, i.e. the calcination temperature, the volume of anhydrous ethanol, the volume of tetraethyl orthosilicate (TEOS), and the molar ratio of iron nitrate and citric acid (IN:CA) were investigated. The calcination temperature and the volume of anhydrous ethanol mainly affected the phase composition of α-Fe₂O₃/Fe₃O₄@SiO₂ nanocomposite, and the volume of TEOS and the ratio of IN:CA had a great influence on the crystallinity of α-Fe₂O₃/Fe₃O₄@SiO₂ nanocomposites. The tendency for the properties of superparamagnetic α-Fe₂O₃/Fe₃O₄@SiO₂ nanocomposites changing with the conditions was explored and the mechanism was analyzed. (paper)