Preparation and Magnetic Property of Nano-sized Iron Powder Particles Covered with Silica Film by Calcium Hydride Reduction Method

Abstract

Well-defined SiO₂-coated Fe nanoparticles with various SiO₂ thickness from 1.2 to 27.8 nm have been successfully prepared by controlling the amount of tetraethyl orthosilicate and by the subsequent reduction of SiO₂-coated Fe₃O₄ nanoparticles with CaH₂. The saturated magnetization of the SiO₂-coated Fe nanoparticles increased with decreasing SiO₂ thickness. The saturated magnetization of the SiO₂-coated Fe nanoparticles with SiO₂ thickness of 2.7 nm or more have slightly decreased by 192 hr and did not change above 192 hr throughout atmospheric exposure, whereas that with SiO₂ thickness of 1.2 nm steeply decreased in 24 hr and continued to decrease above 24 hr.