Direct Observation of Raw Coals in Lattice Fringe Mode Using High-Resolution Transmission Electron Microscopy

Abstract

High-resolution transmission electron microscopy (HRTEM) technique has been used to characterize several coals. By careful examination, direct evidence of layered structure in a wide range of coals was for the first time obtained from HRTEM lattice fringes. In general, most of the layers in all coals occur singly or in stacks of 4−5 layers. Quantitative analysis of coal images showed that average number of layers per stack and layer size remain almost the same for lignite and high volatile bituminous and medium volatile bituminous coals, and they are larger for low volatile bituminous coal and anthracite.

Influence of maceral composition on the structure, properties and behaviour of chars derived from South African coals

“…In search mode, the grids were scanned at low magnification (Â6500) to find individual sharp-edged particles, which was situated at least partially across the holes in the carbon film. The particle edge had to be a single layer, to avoid superposition of fringes [1]. Once a thin enough particle edge was identified, the focus mode was activated, focusing on the image from a distance 0.15 lm.…”

“…Various studies found that HRTEM is an effective method to quantitatively study the distribution of the aromatic layers in coal and coal products [1,7,51]. In this investigation, the properties of the aromatic fraction of chars in terms of layer size were used as the core in the initial stages of char model constructions [7].…”

“…However, the relationship of coal structure to its reactivity in gasification, combustion, pyrolysis and liquefaction is of significant interest. With more advanced analytical techniques, such as high resolution transmission electron microscope (HRTEM), Fourier-transform infrared spectroscopy (FTIR), solid-state 13 C nuclear magnetic resonance spectroscopy (NMR), X-ray analysis and pyrolysis gas chromatography mass spectrometry (GCMS), a more detailed picture of coal structure has been obtained [1][2][3][4][5][6]. Larger-scale atomistic representations that incorporate elemental data and structural information from the analytical techniques are emerging and are supported by advanced computer programs that facilitate construction and evaluation [3,[7][8][9].…”

Chemical–structural properties of South African bituminous coals: Insights from wide angle XRD–carbon fraction analysis, ATR–FTIR, solid state 13 C NMR, and HRTEM techniques

“…Hence, when used in combination, these can be more 118 informative and can also be used as a means of checking consistency 119 to some degree. Results from these techniques have shown that the 120 molecular skeleton of bituminous, and higher rank coals consist 121 mainly of aromatic sheets or layers [9][10][11][12][13][14][17][18][19]24,27,30,31]. 122 The improved understanding of the chemical structure of coal 123 at the molecular level that has resulted from these new investiga-124 tions has led to the development of refined coal molecular struc- 125 tures, so that they could be more effectively used in the 126 prediction of coal behaviour (reactivity and reaction mechanisms) 127 in its various utilisation processes [27,[32][33][34][35][36][37][38][39][40].…”

Use of Molecular Modeling to Determine the Interaction and Competition of Gases within Coal for Carbon Dioxide Sequestration

“…This permitted a direct "observation" of the structural diversity to be quantified for the first time on the length basis of the fringe. Lattice stacking [5][6][7] and orientation 8 issues can also be addressed.…”