Hydrogen reduction of fine iron-oxide particles

Crystallographic, magnetic, and morphological changes induced by heating highly acicular -Fe₂O₃ particles (40 nm in diameter and an axial ratio of 8) under hydrogen have been observed. Reduction proceeds via a multi-phase process, and is not complete until 600°C. The -Fe particles produced are cylindrical in shape, 100 nm in diameter, and have an axial ratio of 1.7(3). Fourier analysis of x-ray profiles yielded a mean column length of 105(6) nm perpendicular to (110). Mössbauer spectra show two distinct hyperfine fields; at room temperature the values are 33.1(1) and 30.2(1)T. Evidence for diffusive particle motion is not present in 4.2–300 K spectra.