Chemical reduction of hematite by sodium borohydride
Well-crystallized hematite was suspended in water and treated at room-temperature (RT) with sodium borohydride. 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 α-Fe and Fe3O4 and B2O3, respectively. 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 the matrix of α-Fe2O3.
Study on preparation of ultrafine amorphous particles by chemical reduction
Abstract Ultrafine amorphous FeNiB powder was prepared by potassium borohydride reduction by mixing the aqueous solutions in a bath of supersonic oscillator. Different mixing ratios of potassium borohydride to metal salt were applied. Analysis of the composition of the sample and the Fe2+ and Ni2+ remaining in the filtrate after preparation shows that a quantity of KBH4 about 1.5 times the stoichiometrical quantity is enough. Mossbauer measurements were performed at room temperature and it was found that excess KBH4 makes no distinct difference in the spectra of the samples.
Influence of pH on the composition and structure of Fe-Co-B alloy particles prepared by borohydride reduction in aqueous solutions
Fe-Co-B alloys have been prepared by reduction of Fe and Co ions by NaBH4 in aqueous solution. The boron content in the samples was controlled by varying the pH of the reagent solution. For pH above 3.25 the samples were amorphous and contained 20–25 at% B. For lower pH about 12 at% B was present in the samples.