MOSSBAUER AND X-RAY-INVESTIGATIONS OF OXIDIZED ULTRAFINE IRON PARTICLES TREATED WITH HIGH-PRESSURE AND ELECTRODISCHARGE PULSES

Ultrafine iron particles with an average size of 30 nm were obtained b y the levitation method in an inert gas flow. Electrodischarge experim ents were carried out under a pressure of 3 GPa. The values of the par ameters of electrodischarge pulses were sufficient to move defects (io ns, atoms, dislocations) by conductivity electrons to destroy the meta stable state of nanocrystals, but not sufficient to generate heat wave . This effect had threshold features. After the first pulse the relati ve resistance drop was more than five times. Next, electrical pulses s lightly reduced resistance up to its saturation. Properties of ultrafi ne iron particles have been studied using Mossbauer absorption spectra and x-ray diffraction for three types of samples: (a) primary powder, (b) powder treated to 3 GPa in a ''toroid'' device, (c) powder treate d by electrical pulses at 3 GPa. An x-ray diffraction pattern revealed seven slightly broadened iron reflexes as well as more broadened oxid e film reflexes. Oxide film reflexes correspond to the most intense re flexes of a spinel structure. The integrated intensities of 220,311 sp inel reflexes divided by integrated intensity of 110 iron reflex are e qual to 0.12, 0.14, and 0.19 for samples (a), (b), and (c) respectivel y. Thus, the relative content of oxide iron phase increases from sampl es (a) to (c). The increase of relative content of the oxide iron phas e was confirmed by a Mossbauer absorption experiment. This effect can be explained by the transformation of the metastable solution of oxyge n in iron lattice to iron oxide with a spinel structure, under the act ion of high-density current pulses.