An investigation of vapor-grown carbon fiber behavior towards air oxidation Original Research Article

Thermogravimetric analysis together with scanning electron microscopy observations have been used to study the behavior of vapor-grown carbon fibers towards air oxidation. We show that different peaks are present in the rate of gasification curves and we attribute this result, on the one hand to the presence of traces of iron in the fibers and on the other hand to the triplex structure of these kind of fibers which are composed of a central carbon filament, and of two regions of chemical vapor deposited (CVD) carbon: an inner core, and an outer shell. Oxidation rates have been measured isothermally in the range 500–950 °C. The gasification reaction is free of diffusion limitations below 760 °C, and controlled by mass transfer (film diffusion regime) at higher temperatures. Oxidation experiments performed in a dynamic mode show differences in the gasification rate according to the fiber diameter. X-ray diffraction measurements and temperature programmed desorption experiments supported the fact that this difference in reactivity has not to be interpreted in terms of crystalline perfection but in terms of initial total or active surface area.