Activated carbon fibers (ACF's), already used widely as absorbent materials, are now expected to be useful as new electrical and electronic materials, for their very large specific surface areas (SSA). Chemical adsorption as well as x-ray diffraction have been mainly used for characterizing the ACF structure. While TEM observations reveal the texture of ACF's, such observations have not yet yielded quantitative information about the microstructure. To promote the quantitative interpretation of the TEM images, computer image analysis is used in this work to clarify the pore structure of ACF's. The microstructures of three samples, which are all isotropic pitch-based ACF's but with different SSA values, have been investigated. Operations such as noise reduction, low frequency cut-off filtering, and binary image formation are used to clarify the pore images of the ACF's. The distribution of the ACF porosity size is clearly shown by a frequency analysis of the two-dimensional fast Fourier transform (FFT). The results suggest that TEM images include contributions from many different pore sizes. Pores in different size ranges are extracted by the inverse FFT (IFFT) operation by selecting the specific frequency range, and by-this analysis the pore structure is shown to have fractal characteristics.
Recently, the active carbon filter (ACF) has drawn attention because of its usefulness in the electrical and electronics fields. to improve the quality of ACF, the microscopic structure of this material must be analyzed. One method is to observe the structure using a transmission electron microscope (TEM). Recently, the capability of the TEM has been improved drastically. Not only can its molecular structure be observed but also numerous analytical equipment has been attached to it. ACF has been investigated by using a TEM, and it has been found that the ACF structure was so complex that quantitative analysis was impossible. Computer analysis of a TEM image has also been attempted. In this analysis, the TEM image was processed by the two‐dimensional fast Fourier transform and fiequency analysis to investigate the distribution of the pore diameter of ACF. As a result, it was speculated that the pore shape was fractal. Then, it was shown that the contour of the pore cross section was fractal and the fractal dimension was obtained. When the structure was too complex to analyze only by TEM analysis, the introduction of the image processing method was effective.
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