Size effects in ultrafine iron. New structures: 2D - 3D

Leonid A Kulikov,Yuriy D Perfiliev,Yuriy V Baldokhin

doi:10.5377/nexo.v34i01.11282

Abstract

This article is devoted to the analysis of the size of iron nanoparticles impact on the structure, to comparison of the results obtained for the nanopowders in the various authors’ researches. The article considers factors that may impact on the form and parameters of the Mössbauer spectra of iron nanopowders obtained by the inert gas condensation technique (Gen-Miller’s method). Possible causes of the new state of the iron are proved with the effective magnetic field at the 57 Fe nucleus (H=365 kOe). But the results related to size effects differ from the researches of other authors. It was revealed that nanoparticles with a mean (X-ray data) particle size of 50 nm have also Angstrem patterns, which can meet the new structure. Presence of small amounts of superparamagnetic oxide could be a catalyst, impetus for the formation of the new structure, and also, at the exchange interactions, could modify the charge of the electron density at the Fe nuclei. Reviewed and other factors can result in appearing of such a high value of the effective magnetic field at the iron nuclei.

Highlights

Ultrafine iron particles with an average size of 10-100 nm are usually in random motion due to their high surface energy, which is a result of uncompensated relationships of atoms at the surface
Mössbauer spectra of the nanoparticles obtained by chemical, electro-explosive or other methods often differ from spectra of nanoparticles prepared by gas evaporation
Based on local interactions of neighbouring atoms and the magnetic state of the sample with 50 nm of pure iron, BCC lattice of iron with H=330 kOe will impact on a flat, single layer formation of iron nanoparticles again, but in new condition, in which there is no three-dimensional crystal lattice (X-ray studies showed the presence of only one BCC structure), i.e. there will be a contribution of the orbital moments of electrons

Summary

INTRODUCTION

Ultrafine iron particles with an average size of 10-100 nm are usually in random motion due to their high surface energy, which is a result of uncompensated relationships of atoms at the surface. Almost the same model is proposed by Pollard & Chadwick (1994) and Campbell et al (1995) for nanopaste obtained by condensation in the gas In these studies, after compaction of the iron particles at room temperature signs of the existence are only weakly expressed in the spectrum of the second sextet in the "sagged wire" form. It’s worth to mention the study by Bianco et al (1997), who, after mechanical alloying of iron powders with an average grain size of 8, 19 and 25 nm in addition to the field strength of the H =330 kOe received fields which are less than 330 kOe. The authors considered these fields as the structure of grain boundaries, the presence of interface areas.This article is devoted to the analysis of the size of iron nanoparticles impact on the structure, to comparison of the results obtained for the nanopowders in the various authors’ researches

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS