Amorphous metallic powders prepared by chemical reduction of metal ions with potassium borohydride in aqueous solution

Amorphous metal-metalloid powders have been prepared by chemical reduction of Fe2+, Co2+, and Ni2+ ions with potassium borohydride in aqueous solution. The chemical composition of the samples, TM-B-O, varies with the metal and with the preparation steps. The as-prepared Co-B-O and Ni-B-O samples are definitely amorphous, while the Fe-B-O sample mainly consists of bcc α-Fe. Crystallization of the samples through thermal treatment has been investigated by X-ray diffraction. The Co-B-O sample evolves toward fee metallic cobalt accompanied first by metastable o-Co3B and, at high temperature, by t-Co2B. The Ni-B-O sample gives rise to fee metallic Ni and o-Ni3B, which decomposes at higher temperatures. Iron borides are not detected in the thermal treatment of the Fe-B-O sample. No evidence of metal oxides is present in all the samples, thus suggesting the prevalent bonding of oxygen to boron.