Síntesis y caracterización estructural y morfológica de microtubos jerárquicos de óxidos de hierro obtenidos por oxidación térmica

Abstract

The objective of this work was to synthesize and structurally and morphologically characterize hierarchical iron oxide microtubes obtained through thermal oxidation. High-purity iron microwires were used as precursor material and subjected to heat treatment in an air atmosphere under controlled temperature and time conditions. During the oxidation process, an oxide layer initially forms on the metal surface, followed by the simultaneous diffusion of iron ions outwards and oxygen species inwards. The difference in diffusion rates favors the generation and accumulation of vacancies, which can cluster and form pores and cavities associated with the Kirkendall effect. Characterization using scanning electron microscopy revealed the growth of microtubes on the precursor surface and the formation of a hierarchical structure composed of oxide walls, pores, and internal cavities. X-ray diffraction, along with Rietveld refinement, allowed the identification of hematite (α-Fe₂O₃) as the predominant crystalline phase and magnetite (Fe₃O₄) as a minor phase. Complementarily, Raman spectroscopy suggested a radial distribution of these phases, with magnetite mainly in the inner region and hematite in the outer region and within the microtubes. The results obtained showed the formation of an irregular, porous, and hierarchical tubular microstructure, consisting of curved oxide walls, multiple internal cavities of non-uniform shape and distribution and macropores, in addition to microcables developed on the surface.