High resolution TEM image analysis of coals with different metamorphic degrees

The structural characteristics of 3 coals with different metamorphic degrees were analyzed using high-resolution transmission electron microscopy (HRTEM). Applying FFT-IFFT method, in association with Matlab, Arcgis and AutoCAD softwares, the lattice fringe parameters obtained from HRTEM image were determined using image analysis. The results indicate that the lattice fringes of all the test coal samples exhibit different characteristics. These lattice fringes can be divided into 8 types (1×1-8×8 aromatic fringes) according to the fringe length distribution. Taking the 3×3 aromatic fringe as critical point, the sample ML-8 abundant in 1×1 and 2×2 aromatic fringes while short of 3×3-8×8 aromatic fringes when comparing with sample DP-4 and sample XM-3. The values of d₀₀₂ obtained from both HRTEM and XRD show a decreasing trend with increasing vitrinite reflectance.