Preparation and magnetic properties of nano-sized iron powder particles coated with silica film by calcium hydride reduction method

Abstract

Well-defined SiO2-coated Fe nanoparticles with various SiO2 thicknesses from 1.2 to 27.8 nm were successfully prepared by controlling the amount of tetraethyl orthosilicate followed by reduction of the SiO2-coated Fe3O4 nanoparticles with CaH2. The saturation magnetization of the SiO2-coated Fe nanoparticles increased with decreasing SiO2 thickness. The saturation magnetization of the SiO2-coated Fe nanoparticles with a SiO2 thickness of 2.7 nm or more decreased slightly after atmospheric exposure for 192 h, but did not change with longer exposure, whereas that of the nanoparticles with the 1.2 nm SiO2 coating thickness decreased steeply in 24 h, and continued to decrease gradually from 24 h to 1080 h.