Surface oxidation, size and shape of nano-sized magnetite obtained by co-precipitation

The aim of the work was to investigate the influence of the co-precipitation processes on the magnetic properties, the shape and the Surface oxidation of nano-sized magnetite particles. The literature data on the process chemistry are inconsistent. Our task was to clarify the impact of the oxidation on the particles' characteristics when two of the most widely quoted soft-chemistry approaches for preparation of such particles are applied. To this end, we investigated the influence of the Fe2+ oxidizing agent ratio and the Oswalt ripening on the magnetite particle shape and size. The process of oxidation takes place to a depth of approximately 3 nm, following the formula (Fe3+)(A)[Fe5x3+Fe2-6x2.5+ rectangle(x)](B)O-4 with x up to 0.33. SQUID and Moessbauer measurements were carried out to characterize selected samples. The strongly defective surface of the spherical particle can be considered as being a superstructure, or a second magnetic phase, since it affects the particle's magnetic properties. (c) 2005 Elsevier B.V. All rights reserved.