Ultrafine amorphous transition metal-boron (TM-B, TM = Co, Ni, Fe) powders have been prepared, under identical experimental conditions, by chemical reduction of Co2+, Ni2+, and Fe2+ ions with potassium borohydride in aqueous solution. The chemical compositions of the samples are close to TM60B40. The particles have a spheroidal shape with diameters ranging from 10 to 100 nm. X-ray diffraction and transmission electron microscopy investigations show that the Co-B and Ni-B samples are fully amorphous while in a few particles of the Fe-B sample the presence of alpha-iron microcrystallites are observed. Crystallization of the samples has been investigated by differential scanning calorimetry. Under anaerobic conditions the Co-B sample evolves toward t-Co2B accompanied by a minor quantity of o-Co3B; in the Ni-B and Fe-B samples, crystallization gives rise to a metallic component plus boride phases. A significant decrease of the boride phases and a corresponding increase of the metallic component are obtained in all samples when the thermal treatment is performed in the presence of traces of oxygen.
Amorphous transition metal-boron ultrafine particles prepared by chemical methods
CORRIAS, ANNA;ENNAS, GUIDO;MUSINU, ANNA MARIA GIOVANNA;
1993-01-01
Abstract
Ultrafine amorphous transition metal-boron (TM-B, TM = Co, Ni, Fe) powders have been prepared, under identical experimental conditions, by chemical reduction of Co2+, Ni2+, and Fe2+ ions with potassium borohydride in aqueous solution. The chemical compositions of the samples are close to TM60B40. The particles have a spheroidal shape with diameters ranging from 10 to 100 nm. X-ray diffraction and transmission electron microscopy investigations show that the Co-B and Ni-B samples are fully amorphous while in a few particles of the Fe-B sample the presence of alpha-iron microcrystallites are observed. Crystallization of the samples has been investigated by differential scanning calorimetry. Under anaerobic conditions the Co-B sample evolves toward t-Co2B accompanied by a minor quantity of o-Co3B; in the Ni-B and Fe-B samples, crystallization gives rise to a metallic component plus boride phases. A significant decrease of the boride phases and a corresponding increase of the metallic component are obtained in all samples when the thermal treatment is performed in the presence of traces of oxygen.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.