Analysis of pore structure of activated carbon fibers using high resolution transmission electron microscopy and image processing

Abstract

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.

Pore Structure and Fractal Characteristics of Activated Carbon Fibers Characterized by Using HRTEM

“…1a and 1c, respectively. The white shapes that look bright are considered to be the pores of the ACF (6) measurements and TEM observation (4,6,7). It is seen from Fig.…”

Image analysis in transmission electron microscope images of amorphous carbon film

“…This shows that the sample has a large area with a morphology that has a 1.9 nm period. Furthermore, if the peak frequency components are extracted from the results of the FFT operation and the IFFT operation is carried out on them, the real space images corresponding to the space frequencies can be obtained and we are able to analyze the TEM image in greater detail [8].…”

“…The optical diffraction patterns of the TEM images [7] were compared with power spectra obtained from the two-dimensional fast Fourier transform (FFT) of the original TEM images. The power spectra were represented by graphs obtained by integration around their central points [8,9].…”

“…From the results of the calculation of the power spectra, the frequency distribution versus Df was analyzed [8,9,12].…”

Morphological effect on the electrochemical behavior of electric double-layer capacitors

“…17,18 Twodimensional fast Fourier transforms (FFTs) were carried out on the TEM (JEM-2010, JEOL, Tokyo, Japan) images (512 × 512 pixels) with our image processing system, and the PSD was obtained by calculation of the power spectrum with a Silicon (Nippon SGI, Tokyo, Japan) graphics system. Figure 1 shows the x-ray diffraction (XRD) profiles of both the AC-series and the MP-series.…”