Amorphous Metallic Powder Prepared by Chemical Reduction of Metal Ions with Potassium Borohydride in Aqueous Solution

Amorphous metal-metalloid powders have been prepared by chemical reduction of Fez+, Co2+, and Ni2+ ions with potassium borohydride in aqueous solution. The chemical composition of the samples, TM-B-0, varies with the metal and with the preparation steps. The as-prepared Co-B-0 and Ni-B-0 samples are definitely amorphous, while the FeB-O sample mainly consists of bcc a-Fe. Crystallization of the samples through thermal treatment has been investigated by X-ray diffraction. The Co-B-O sample evolves toward fcc metallic cobalt accompanied first by metastable o-Co3B and, at high temperature, by t-Co,B. The Ni-B-O sample gives rise to fcc metallic Ni and o-Ni3B, which decomposes at higher temperatures. Iron borides are not detected in the thermal treatment of the Fe-B-0 sample. No evidence of metal oxides is present in all the samples, thus suggesting the prevalent bonding of oxygen to boron.