Formation mechanism of carbon foams derived from mesophase pitch

Carbon foams are comprised of an assembly of pores surrounded by archwise highly aligned graphitic belts. [Display omitted] ► Carbon foams are comprised of pores surrounded by archwise graphite belts. ► The bubble growth generates a shear stress to force aromatic planes to parallel to axis of ligament. ► The viscosity and surface tension of molten pitch are major factors influence the growth of bubbles. ► After graphitization, the well aligned aromatic planes evolve into highly aligned graphite. Carbon foams were prepared from mesophase pitch using foaming, carbonization and graphitization processes. The physical and chemical properties of the mesophase pitch during thermal treatment were studied by Fourier transform infrared spectroscopy, thermogravimetry, mass spectroscopy, rheometry and scanning electron microscopy. The results suggest that gases released from the pitch dissolve, saturate, nucleate and grow in the molten pitch during foaming. Then the resultant bubbles coalesced with the neighboring bubbles driven by the surface tension of the molten pitch. This coalescence generates a shear stress to force aromatic planes of the pitch to arrange regularly and paralleled to the axis of a ligament. The growth of bubbles stopped when the pitch became semi-coke at a temperature above 733 K. The viscosity and surface tension of the molten pitch are major factors that influence the growth of bubbles. After carbonization at 1073 K and graphitization at 2873 K, the well aligned aromatic planes in the foams evolve into highly aligned graphitic structures.