A TECHNIQUE FOR SPATIALLY RESOLVED MOSSBAUER-SPECTROSCOPY APPLIED TO QUENCHED METALLURGICAL SLAGS

We have developed a technique for measuring Mossbauer spectra of metallurgical slags with a spatial resolution of approximately 500-mu-m. Using a Co-57 source with high specific activity, the gamma-ray beam can be collimated from the conventional diameter of approximately 1 cm to a diameter of 500-mu-m. The sample is mounted in an epoxy resin, ground to a thin disc and then mounted on an x-y stage directly behind a lead shield with a 500-mu-m hole. We studied a melt composition in the system Fe(x)O-Al2O3-SiO2 with 62 mol% FeO. Five spectra at 298 K were recorded at increasing depths in the quenched slag, with one additional spectrum taken in a 10-mu-m layer at the surface. The spectra can be fitted to two doublets with different linewidths. The doublet with a narrow linewidth is assigned to crystalline Fe2SiO4 and the doublet with a large linewidth is assigned to an Fe2+- containing glass phase. The isomer shift and quadrupole splitting of crystalline Fe2SiO4 are constant with depth, while the parameters for the glass phase show a consistent variation with depth. The relative areas of the doublets vary dramatically with depth, and indicate that the proportion of the glass phase is highest near the surface and lowest in the centre of the quenched slag. This is consistent with the method of quenching where the cooling rate is higher on the surface of the slag.