The molar ratio of the FeCl3:FeCl2 should be about 2:1. Heat the mix to 70 °C, then raise the speed of stirring to about 7500 rpm and quickly add a solution of NH4OH (10 volume %). A dark precipitate  of nanoparticles of magnetite forms immediately.In both methods, the precipitation reaction relies on rapid transformation of acidic iron ions into the spinel iron oxide structure at pH 10 or higher. Controlling the formation of magnetite nanoparticles presents challenges: the reactions and phase transformations necessary for the creation of the magnetite spinel structure are complex. The subject is of practical importance because magnetite particles are of interest in bioscience applications such as magnetic resonance imaging (MRI), in which iron oxide magnetite nanoparticles potentially present a non-toxic alternative to the gadolinium-based contrast agents currently in use. However, difficulties in controlling the formation of the particles, still frustrate the preparation of superparamagnetic magnetite particles, that is to say: magnetite nanoparticles with a coercivity of 0 A/m, meaning that they completely lose their permanent magnetisation in the absence of an external magnetic field. The smallest values currently reported for nanosized magnetite particles is Hc = 8.5 A m−1, whereas the largest reported magnetization value is 87 Am2 kg−1 for synthetic magnetite.Pigment quality Fe3O4, so called synthetic magnetite, can be prepared using processes that use industrial wastes, scrap iron or solutions containing iron salts (e.g.
This is ascribed to electron exchange between the FeII and FeIII centres in Fe3O4. Uses
Fe3O4 is used as a black pigment and is known as C.I pigment black 11 (C.I. No.77499) or Mars Black.Fe3O4 is used as a catalyst in the Haber process and in the water-gas shift reaction. The latter uses an HTS (high temperature shift catalyst) of iron oxide stabilised by chromium oxide. This iron–chrome catalyst is reduced at reactor start up to generate Fe3O4 from α-Fe2O3  and Cr2O3 to CrO3.Bluing is a passivation process that produces a layer of Fe3O4 on the surface of steel to protect it from rust. Along with sulfur and aluminium, it is an ingredient in steel-cutting thermite. Medical uses
Nano particles of Fe3O4 are used as contrast agents in MRI scanning.Ferumoxytol, sold under the brand names Feraheme and Rienso, is an intravenous Fe3O4 preparation for treatment of anemia resulting from chronic kidney disease. Ferumoxytol is manufactured and globally distributed by AMAG Pharmaceuticals. Biological occurrence
Magnetite has been found as nano-crystals in magnetotactic bacteria (42–45 nm) and in the beak tissue of homing pigeons. References
External links
"Ferumoxytol". Drug Information Portal. U.S. National Library of Medicine.