Energy & Fuels, Vol.18, No.2, 365-370, 2004
Structural characterization of graphite materials prepared from anthracites of different characteristics: A comparative analysis
Graphite materials were prepared from two Spanish anthracites, AF and ATO, by heating at different temperatures within the range 2000-2800 degreesC. XRD and Raman spectroscopy were employed to characterize the degrees of crystallinity and crystal orientation of the materials. In addition to studying the evolution of typical crystal parameters such as interlayer spacing, d(002), and crystallite sizes, L-alpha and L-c, with temperature, this work aimed to evaluate the influence of elemental composition, texture (as measured by optical microscopy), and mineral matter of the raw anthracites on their ability to graphitize. Two temperature segments were discerned during the development of crystallinity. The first segment exhibited major improvements in crystal parameters, which afterward reached a plateau value. Raman parameters indicated that further improvement in crystal orientation could be obtained after heating at the highest temperature (2800 degreesC). The limiting temperature at which the materials showed their highest degree of structural order, i.e., the temperature at which the plateau was reached, was lower for the most graphitizable anthracite (AF). This anthracite was found to have higher hydrogen and mineral matter (specifically Al, Fe, K, and Si) contents. However, the textural anisotropy of this most graphitizable anthracite was lower than that of the other anthracite under study (ATO). Optical microscopy characterization of the carbonized materials showed that this trend changed after heating the anthracites at 1000 degreesC, i.e., the anisotropy of the texture in the carbonized AF was higher than that of the corresponding carbonized material prepared from ATO. It was concluded that the structural and textural changes of the anthracites during carbonization, which are related with both their microtexture and hydrogen content, influence the graphitization process.