Calciothermic Preparation of Sm-Co From Nanostructured Precursor Oxides

A calciothermic reduction/diffusion process has been developed for the preparation of Sm-Co alloys with good magnetic properties using nanostructured Co- and SmCo-oxide powders as precursors. The precursor oxides were obtained from an aqueous solution of Sm(NO$_{3})_{3}$\textbullet 6H$_{2}$O, Co(NO$_{3})_{2}$\textbullet 6H$_{2}$O, and citric acid which, after the removal of excess water, spontaneously reacts to form a fine mixture of Co$_{3}$O$_{4}$ and SmCoO$_{3}$ nanoparticles. These nanoparticles were then mixed with metallic Ca granules, sealed under inert gas in Nb tubes, and heated to temperatures between 850 and 1000 $^{o}$C for various lengths of time. The products of the reduction/diffusion reaction were studied by scanning electron microscopy with elemental analysis, vibrating sample magnetometry, and x-ray diffraction. These measurements revealed that (in addition to the oxidation product CaO) the products of the reduction/diffusion process were micron-sized particles of essentially single phase SmCo$_{5 }$with a coercivity in excess of 40 kOe and a Curie temperature of about 950 $^{o}$C.