This work presents the different effects of steam and carbon dioxide activation on the microstructure of an oxidized polyacrylonitrile (PAN) fabric. An investigation was conducted on a series of carbonized fabrics and two series of activated carbon fabrics. The fabrics were activated by steam and carbon dioxide using heat‐treatment temperatures of 900–1100°C. Steam and carbon dioxide developed the microstructure initially present in the PAN‐based activated carbon fabrics, but with different effects. These fabrics in the form of fabric and powder were examined by X‐ray diffraction and Raman spectrometry. This study indicated that carbon dioxide only reacted with the crystalline edges or the irregular carbon on the fiber surface and that the inside structure of the fibers was not greatly affected. When the fabrics were activated using steam, water molecules reacted not only on the fiber surface but also with the carbon at the crystal edge and/or the nonregular carbon in the fibers, which led to communicating pore structures on the surface and in the inner portions of the fiber. This activation also promoted the denitrogenation reactions. Because of these structures and reactions, the activated carbon fabrics, which were activated by steam, had the highest stacking height for carbon layer planes (Lc), the highest number of layer planes (Lc/d002), the highest oxygen content, the largest crystal size (La), and the highest density over the other samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1090–1099, 2001

The properties of four kinds of Type II carbon fibers, which had been precarbonized at 300 °C, 400 °C, 500 °C, and 600 °C, respectively, during two-stage continuous carbonization, were measured after being air oxidized for periods of 1 to 6 min at 550 °C. The effects of precarbonization temperature on mechanical properties, density, morphology, elemental composition, and microstructure of the carbon fibers during the air oxidation are discussed in this article. The precarbonization process strongly affected the surface properties and mechanical properties of the final oxidized carbon fibers. The carbon fibers developed from the different precarbonization temperatures all had different structures. The carbon fibers that had been precarbonized at 300 °C had a more ordered structure than other fibers after air oxidation. These carbon fibers also had a higher performance than the other fibers. Carbon fibers also showed different oxidation behaviors caused by differences in surface morphology resulting from each different precarbonization temperature. Optimum conditions not only improved the tensile strength and modulus, but also increased the density and oxygen content. Experimental results showed that the tensile strength of the carbon fibers precarbonized at 300 °C increased from 2.4 GPa to 4.3 GPa (80%) after 6 min oxidation at 550 °C. 1 carbon fibers I Type I carbon fibers FIG. 1. Simplified schematic description of the carbon fiber process.