Nitrogen incorporation into boron-doped graphite and formation of B-N bonding

Carbon materials having different levels of boron doping were prepared from a mixture of coke and boron carbide at temperatures between 2000 and 2800 degrees C. The XRD measurements showed that crystallites grow with an increase of boron concentration during the preparation and there is a limited concentration of boron in solid solution. Unexpectedly, XPS measurements revealed the increase of N 1s peak intensity with the increase of B 1s peak intensity. The binding energies of these peaks suggested the formation of B-N type bond, though it was not observed by XRD. It implies that the doped boron gives rise to the incorporation of nitrogen in the surface layer of carbon materials. A possible source of nitrogen is air occluded in raw materials during packing into graphite crucibles. Such small amounts of nitrogen must be taken into account with boron-doped carbon materials at high temperatures. (C) 1999 Elsevier Science Ltd. All rights reserved.