Effects of boron doping in low- and high-surface-area carbon powders

Two distinctive carbon materials (Saran char and SP-1 graphite) were doped with B at different loading to clarify the intrinsic effect of substitutional B on carbon reactivity. The carbon precursors would be affected in different style by substitutional B due to different important properties (crystallinity and surface area). The B retentivity depended on the nature of B dopant and carbon substrate; a less ordered carbon has higher B loading than its counterpart. Graphitization was enhanced by substitutional B, as expected. Furthermore, the B incorporation was still beneficial for SP-1 although it already had high crystallinity. An interesting behavior was noticed; the increase in L-a was greater than L-c. The intrinsic effect of substitutional B in carbon oxidation was proved to be a catalytic one. Unlike highly ordered SP-1 graphite, Saran char showed both a catalytic effectat low B loading and low conversion, and an inhibiting effect at high B loading and high conversion. The inductive effect was proposed to explain this catalytic effect on different crystallite size. Different sizes of carbon clusters were calculated by Gaussian 98W; the extent of the effect of substitutional B did get smaller to the carbon in bigger size of carbon cluster. (C) 2004 Elsevier Ltd. All rights reserved.