Chemical reduction synthesis of fine particle FeZrB alloys under aerobic and anaerobic conditions

Fine particle FexZryB alloys have been prepared by chemical reduction of an aqueous solution of iron (II) sulphate and zirconium (IV) sulphate by sodium borohydride, under both aerobic (1) and anaerobic (2) conditions. Spherical particles of 120-150 nm diameter were obtained, with compositions Fe59Zr6B35 (1) and Fe63Zr7B29 (2) respectively. The aerobic sample was found by electron microprobe analysis to be more homogeneous than the anaerobic sample. Approximately 90% of each sample constituted an amorphous phase as revealed by Fe-57 Mossbauer spectroscopy, which gave a broad sextet with mean hyperfine field 20.8 T (1) and 23.5 T (2) and rms deviation 10.0 T (1) and 8.9 T (2) respectively, with the remainder of the samples existing as fine particle Fe(II) complex, Fe(III) oxide and, in the aerobic sample only, Fe metal phases. The presence of a dominant amorphous phase was confirmed by X-ray diffraction and by differential scanning calorimetry. On exposure to air the anaerobic sample reacted violently, whereas the aerobic sample, which is intrinsically passivated with a surface oxide layer, reacted much more slowly. Preliminary Zr edge EXAFS data were consistent with the Zr atoms being incorporated into an amorphous FeZrB alloy. ZFC/FC magnetisation data showed typical fine particle effects for both samples. The anaerobic sample had almost double the maximum magnetisation of the aerobic sample. (C) 1999 Elsevier Science B.V. All rights reserved.