Unravelling the iron coordination in the Mössbauer spectra of SFCA

Full text: Much of current ironmaking relies on the use of iron ore sinters to utilize iron ore particles which are otherwise too fine for direct feed into a blast furnace. Iron ore sinter is a complex composite material composed of iron ore fines, calcium silicates and glass, bonded by a matrix made from predominantly SFCA (silico-ferrite of calcium and aluminium) and SFCA-I. A typical SFCA found in iron ore sinter may contain 60-76 wt% Fe₂O₃, 13-16 wt% CaO, 3-10 wt% SiO₂ and 4-10 wt% Al₂O₃. SFCA-I is higher in iron (approximately 84 wt% of Fe₂O₃) at the expense of the silica and alumina. The structure of these SFCA sinter phases is, not surprisingly, very complex. In order to try and shed some light on the iron bonding we have taken room temperature Mössbauer spectra of 12 samples with differing compositions. However, the structure contains 11 distinct Fe or (Fe,Al) sites, and one may expect that many of them will be similar. Since the subspectra of each of the phases will be doublets, one is looking for up to 22 separate lines in spectra with very little resolution. Even when one can distinguish bumps in the spectral envelope, it is not clear how to match them into doublets. We will describe the various approaches, mainly involving spectral subtraction techniques, which we have attempted in trying to analyze these spectra and get an interpretation in terms of the different iron coordinations and how they vary with change in composition. (author)