Transformation of Nano- to Mesosized Iron Oxide Cores to α-Fe within Organic Shells Preserved Intact

Nanoparticles of α-Fe, an excellent soft magnet, have been successfully made corrosion-resistant and dispersible in polar and nonpolar solvents by coating these with inner and outer layers of amorphous silica and organics like poly(ethylene glycol), respectively. The double coating was facilitated by using stable and easy-to-handle oxide particles as the core to be subsequently metallized at temperatures low enough to keep the organic layer intact. Use of CaH2 as a reductant lowered the working temperature down to 200−300 °C, where thermal particle adhesion did not take place, formation of impurities like iron silicates was suppressed, and the overall morphological features of the starting particles were preserved. The feasibility of organo-functionalization of the surface will open a way for this nanomagnet toward bioscientific and medical applications.