Chemical synthesis of magnetic Fe-B and Fe-Co-B particles and chains

With an objective to develop magnetic materials with high saturation magnetization for the Magnetically Assisted Chemical Separation (MACS) process the chemical synthesis of Fe-B and Fe-Co-B alloys by reducing iron and cobalt chloride solutions with potassium borohydride has been investigated systematically. The influence of the concentration of the reactants, applied magnetic field, reaction atmosphere, and method of mixing the reactants on the microstructure, particle size, composition and magnetic properties has been studied. Both M-B (M = Fe and Co) particles and elongated chains composed of nanometer size M-B particles have been obtained depending on the reaction conditions. The Fe-B samples exhibit saturation magnetization of M{sub S} of 120--190 emu/g, remanent magnetization M{sub r} of 10--22 emu/g, and coercive field H{sub c} of 400--900 Oe. A high M{sub S} value of 190 emu/g, which is close to the theoretical value of 218 emu/g for pure Fe, has been achieved particularly for samples with well-defined chain structures. Increasing the Co content in the Fe-Co-B alloys increases the boron content and thereby decreases the crystallinity and M{sub S} values although marginal increase in H{sub c} (1,250 Oe) and M{sub r} (36 emu/g) values could be made in some Fe-Co-B compositions. The chain structure with high M{sub S} may be attractive for other magnetic separation processes as well