Production of amorphous Fe–B alloy and a-Fe by chemical reduction of hematite using sodium borohydride

Natural and well-crystallized hematite was suspended in water and treated at room-temperature (RT) with sodium borohydride in acid medium. The product of the reaction is a highly magnetic black powder, which is stable at RT. The NaBH4 treatment converts about half of the hematite to an amorphous Fe–B alloy and to a small fraction of sub-micron sized, amorphous metallic-Fe nodules. Heating at 400 C of this composite has resulted in the crystallization and/or oxidation of more than half of the amorphous Fe–B phase to a-Fe and Fe3O4 and B2O3, respectively. Further, the already present superficial, amorphous metallic Fe is converted to a-Fe and the original, plate like morphology of the hematite has changed to a mix of nodular and acicular particles. After treatment at 800 C, the metallic Fe and the amorphous Fe–B have completely vanished, and the resulting product consists of hematite and FeBO3 embedded in a matrix of a-Fe2O3.