Feat char samples produced by heat treatments under an inert atmosphere of
nitrogen were characterized through C-13 solid-state NMR, allowing the achi
evement of a detailed picture of the mechanism of carbonization. The treatm
ents were realized at temperatures between 200 and 1000 degrees C, with a c
ontrolled heating rate and residence time. NMR spectra were obtained in a h
ome-built spectrometer operating at a field of 2.0 T with the use of high-r
esolution techniques. The results showed the steps followed during the carb
onization process. Initially we observed a degradation of the natural mater
ial, with preferential loss of carbohydrates and carboxylic groups. From a
heat-treatment temperature of about 500 degrees C upward, the spectra were
nearly constituted of only one resonance line with a chemical shift of abou
t 130 ppm (from TMS), typical of aromatic structures. For the most severely
treated samples, a decrease in the chemical shift of the resonance line wa
s observed, indicating a deshielding associated with the increase in the el
ectrical conductivity of the material. The structure of these samples was i
dentified as consisting of planes of sp(2) carbon atoms, with a chemical en
vironment similar to graphitic materials but with no long-range spatial ord
er.