SOME SPECIFIC FEATURES OF FINE FE AND FE-NI PARTICLES

By comparing results of Mossbauer spectroscopy and x-ray diffraction i nvestigations of ultrafine Fe and Fe-Ni particles, a formerly stated s upposition on the existence of two spin states of the fee phase in pur e iron and Fe-Ni alloys has been verified. Some structural peculiariti es of particles under study have been observed also. For the pure bcc- Fe particles with an average diameter of 30 and 50 nm the existence of two hyperfine fields (H-1=330 kOe, H-2=360 kOe) at room temperature h as been found. It is supposed that H-2 in the bcc phase could be consi dered as a remnant of a high spin state of the fcc-Fe phase at high te mperature. Particles of Fe-Ni(30.3 wt %), Fe-Ni(35 wt %), and Fe-Ni(52 wt %) alloys with an average diameter ranging from 5 to 15 nm were st udied also. Particles of Fe-Ni (30.3 wt %) and Fe-Ni(35 wt %) alloys w ith diameter of 5-8 nm had the bcc structure. A mixture of the bcc and fee phases appeared with an increase of the particle size. At the sam e time only the fee structure remained for the largest particles. The observed size structural dependences and the existence of the stable b cc phase in small particles can be explained by the martensite fcc-bcc transition.