Properties and structure of ultrafine amorphous Fe-Ni-B powder obtained by borohydride reduction

Abstract

Ultrafine amorphous Fe-Ni-B powders were prepared by borohydride reduction, and their properties and structure were investigated by extended x-ray absorption fine structure (EXAFS), x-ray photoelectron spectroscopy (XPS), small-angle x-ray scattering (SAXS), Mossbauer spectra, transmission electron microscopy (TEM), differential scanning calorimetry (DSC), etc. The SAXS results for Fe48Ni21B31 powders reveal the particle size statistic distribution, which is 1.7 nm, 80 % ; 6.4 nm, 8 % ; and 15.3 nm, 12 %. TEM micrographs demonstrate the aggregates with fractal dimension of 1.5. The short-range order parameters of Fe48Ni21B31 powders are obtained from EXAFS measurement. The XPS studies reveal that the higher Hc values of the powder prepared at higher reaction temperature relate to the appearance of the satellite structure at about 715.6 eV, which is characteristic for iron oxides, FeO/FexO. This new interesting finding has been explained by the lattice misfit on the interface between the matrix and oxides, based on EXAFS studies. The crystalline behavior and magnetic properties demonstrate that there is no significant difference in amorphous structure between the chemically synthesized powders and meltspun ribbons. However, the reasonable prediction of difference of amorphous structure and its formation mechanism between them has been proved by the XPS depth profile of Fe48Ni21B31 powders, exhibiting considerable surface enrichment of boron and nickel, and EXAFS studies, showing a stronger interaction between nearer neighbors in the powders.