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.
Amorphous TM1−xBx alloy particles prepared by chemical reduction (invited)
Amorphous transition‐metal boron (TM‐B) alloy particles can be prepared by chemical reduction of TM ions by borohydride in aqueous solutions. ln the last few years systematic studies of the parameters which control the composition, and, in turn, many of the properties of the alloy particles, have been performed and are reviewed in the present paper. The most important preparation parameters which influence the composition are the concentration of the borohydride solution and the pH of the TM salt solution. By controlling these parameters it is possible to prepare amorphous alloy samples with boron contents from about 9 up to about 40 at. %.
Study of very thin oxide layers by conversion and Auger electrons
Oxidic layers as thin as 20–30 Å on α-Fe and stainless steel are studied by57Fe-DCEMS with K-conversion electrons and ICEMS. No indication of a vanishingf-factor could be found. Mössbauer spectra, recorded by use of LMM-Auger electrons (AEMS) and by electrons emitted with energies below 15 eV (LEEMS), contain information on the surface layer as well as on the bulk material, showing that part of these electrons are due to secondary effects and the high escape depths of K-conversion electrons.