Conversion of polycyclic aromatic hydrocarbons to graphite and diamond at high pressures

The polycyclic aromatic hydrocarbons (PAH): naphthalene, anthracene, pentacene, perylene, and coronene were submitted to temperatures up to 1500 degreesC at 8 GPa. To avoid catalytic action of metals,on thermal conversion, graphite was used as container material. Moreover, graphite is very permeable to the gaseous products of thermal decomposition of PAH. The resulting thermal transformations and their evolution were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy as a function of temperature for 60-s treatments. The nature of the initial compounds clearly affects the products of the different stages of carbonization and the first steps of graphitization. This becomes hardly discernible in the final stages of graphitization above 1000 degreesC. Above 1200 degreesC, graphite with high crystallinity forms in all cases. The temperature of the beginning of diamond formation does not seem to be influenced by the nature of the initial PAH and is equal to similar to1280 degreesC for all investigated compounds. Diamonds formed from the PAH are high-quality 5-40 mum single crystals. The p(1) T values of diamond formation here obtained are significantly lower than those previously known for direct graphite-diamond transformation. (C) 2003 Elsevier Ltd. All rights reserved.