Oxygen distribution in oxidatively stabilized mesophase pitch fiber

The oxygen profile along the radial direction in mesophase pitch fiber of 10 μm diameter, stabilized by heating at a constant rate of 0.5°C/min in air, was measured with secondary ion mass spectrometry (SIMS), by correcting the atomic OC signal ratio according to that obtained by elemental analysis. The oxygen profile was found to be flat along the radial direction in fibers oxidized to 350°C which showed the maximum weight gain among the stabilized fibers, providing the maximum tensile strength and elongation after the carbonization. When stabilization was stopped at a lower temperature of 250°C, the oxygen profile indicated an unoxidized core, from which volatile components may diffuse to the surface, causing sticking of adjacent filaments together in the successive carbonization. The heating rate during stabilization was also found to influence the oxygen distribution, more rapid heating tending to increase the gradient. Such a situation indicates that a balance of oxygen diffusion and oxidation reactivity governs the oxygen distribution in the stabilized fiber. Hence, SIMS can be an appropriate tool to monitor the stabilization step in carbon fiber manufacture.