THE EFFECTS OF SULFUR AND OTHER IMPURITIES ON CARBON-GRAPHITE TRANSITIONS

The transition to graphite of carbons containing sulfur and the effect s of added iron and chromium on this process have been studied using X -ray diffraction analysis and electron microscopy. It was found that a fter heat treatment in the temperature interval 1300-1600 degrees C ca rbons containing at least 1.5 mass% of sulfur, or 0.3 mass% of sulfur and 1.5 mass% of added Cr2O3 become heterogeneous; they consist of an ultradisperse matrix and of large (> 100 nm) and sufficiently perfect (Delta d/d(002) similar to 0.002) regions of coherent scattering with interlayer spacing d(002) that corresponds to the graphite-crystal str ucture. When disperse iron is added, the amount of the graphite phase in this temperature interval decreases by a factor of 2. (C) 1998 Else vier Science Ltd. All rights reserved.