Iron catalysed graphitisation in the blast furnace

The paper describes the study of iron catalysed graphitisation in a set of coke samples extracted from a blast furnace, by means of optical microscopy, X-ray diffraction (XRD) and Raman microprobe techniques. The direct link obtained between optical microscopy and Raman spectroscopy in the Raman microprobe proved useful in linking morphology to molecular 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 noticeable spectral difference between the graphite produced by the catalytic 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 associated with the decrease in the d002 values and the development of graphitic structure. The results suggest that temperature, amount of iron in contact with the coke and residence time of the coke in the hottest regions of the furnace are important factors in the catalytic graphitisation process. The use of XRD and Raman spectroscopy for the characterisation of the thermal history of blast furnace coke samples is discussed.