Surface Modification of Graphitic Foam

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This article discusses surface-related issues and possible modification approaches in high-porosity graphitic foam. The microcellular solid is made of graphitic carbon walls, ligaments, and beams supporting a network of interconnected pores. This makes the exposed surface area very high and its understanding a necessity for most applications. Graphitic planes are seen to be stacked at various orientations with respect to exposed surfaces. Therefore, a simplified analytical model that assumes "random" graphitic planes forming a three-dimensional array of tetrahedral cells may be an appropriate approximation. The influence of oxidizing chemicals such as nitric acid and hydrogen peroxide on surface properties has been studied using electron microscopy, photoelectron spectroscopy, and water absorption tests. Bulk properties such as density measurements and mechanical tests have been performed in parallel. It is seen that exposure to nitric acid results in an increase in oxygen-containing functional groups on the surface, which may lead to increased infiltration of polar matrix fluids such as water and epoxy resins. This possibility is further supported by water absorption studies that show increased water infiltration in foam after nitric acid treatment. Electron microscopy and density studies indicate that some surface etching occurs with concentrated nitric acid exposure, but not significant enough to decrease density. Strength of the stand-alone foam is reduced for concentrated nitric acid treatment, but the elastic modulus is unaffected. The scientific significance of these results in terms of future surface modification of microcellular solids has been discussed. (C) 2003 American Institute of Physics.