IRON-CATALYZED GRAPHITIZATION IN THE BLAST-FURNACE

The paper describes the study of iron catalysed graphitisation in a se t of coke samples extracted from a blast furnace, by means of optical microscopy, X-ray diffraction (XRD) and Raman microprobe techniques. T he direct link obtained between optical microscopy and Raman spectrosc opy in the Raman microprobe proved useful in linking morphology to mol ecular structure. The results show that catalytic graphitisation takes place at temperatures well below the temperature where graphitisation would normally be expected to occur. The mechanism of graphitisation probably involves dissolution and precipitation processes. The most no ticeable spectral difference between the graphite produced by the cata lytic process and the coke is the resolution of the second order Raman G' band of the former into an overlapping doublet, whereas the latter only has a single symmetric peak. These spectral changes are associat ed with the decrease in the d(002) values and the development of graph itic structure. The results suggest that temperature, amount of iron i n contact with the coke and residence time of the coke in the hottest regions of the furnace are important factors in the catalytic graphiti sation process. The use of XRD and Raman spectroscopy for the characte risation of the thermal history of blast furnace coke samples is discu ssed.