HIGH-TEMPERATURE CARBONS FROM KRAFT LIGNIN

High-temperature carbons have been prepared from kraft lignin on therm al treatment up to 3073 K. The structure of these high-temperature car bons has been studied by X-ray diffraction and Raman spectroscopy. The interlayer spacing obtained from XRD approaches the d(002) value of g raphite as the heat treatment temperature is increased. The (002) diff raction peak of the higher temperature carbons shows a modulated profi le, which has been attributed to the presence of both graphitic or hig hly ordered carbon, and turbostratic or less ordered carbon. The avera ge thickness of graphite-like crystallites evaluated from XRD increase s with increasing heat treatment temperature. Raman spectra confirm th e progressive structural ordering as treatment temperature increases. The E(2g) line-width decreases and its frequency shifts to a value clo se to the 1582 cm(-1) of graphite. At the same time a substantial decr ease in the intensity of the band in the 1350 cm(-1) region can be obs erved, indicating a decreasing proportion of imperfect carbon. The evo lution of the 2700 cm(-1) line-width indicates a progressive onset of three-dimensional order as the heat treatment temperature increases. T he O-2-gasification X-T curves of the high-temperature carbons show an increasing oxidation resistance with increasing heat treatment temper ature, in agreement with a higher structural ordering and a lower surf ace area. The inorganic impurities of the precursor (mainly Na) seem t o enhance the onset of structural ordering, and the oxidation resistan ce of the 3073 K carbon prepared from high-ash lignin proved to be sim ilar to that of graphite SP-1.