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.
Mossbauer studies of small amorphous particles in granular films
Granular films consisting of finely dispersed Fe 82 B 18 amorphous grains in a Al 2 O 3 matrix are studied by Mossbauer spectroscopy and electron microscopy. The samples are prepared by cosputtering with rotating target. The particle diameters vary between the limits 40 and 70 A depending on the samples. The hyperfine field distribution becomes wider as the particle diameters decrease. The superparamagnetic properties are studied. It is shown that the value of anisotropy energy is high and is principally due to magnetoelastic energy.