The formation of urchinlike nanostructures under thermal oxidation and depassivation of iron particles

Abstract

Methods of scanning electron microscopy with an X-ray probe, Raman spectroscopy, and thermogravimetry are used to study the morphology and composition of metal–oxide nanostructures obtained by thermal oxidation of spherical microparticles of iron powder with a diameter of 1–3 μm. It is shown that unidimensional hematite nanoflakes and fibers grow under atmospheric annealing at 300°C and above in the radial direction from powder microparticles, which is accompanied by depassivation and acceleration of corrosion layer growth. An increase in temperature and oxidation time results in transformation of microparticles into urchinlike multilayer nanoparticles consisting of elongated crystalline α-Fe₂O₃ nanowhiskers growing normally to the surface of the particle consisting of an iron core and shells of the magnetite and hematite phases. Growth of hematite nanowhiskers continues until the metallic core is completely oxidized.