Structural Characterisation of porous Char Particles by surface Observation Using a field Emission Scanning Electron Microscope

Abstract In this paper, porous char samples were examined using a Field Emission Scanning Electron Microscope (FESEM) at various accelerating voltages. Samples were examined as uncoated, gold coated and chromium coated. For uncoated samples, the images acquired at a low accelerating voltage tended to represent the surface structure and morphology while images obtained at high accelerating voltages typically reflected the internal char structure. Gold coating (∼20 nm) has a significant effect on the images obtained at high accelerating voltages compared to those obtained from uncoated particles. It is found that in the conventional SEM surface observation, which examines gold coated (∼20 nm) char particles at accelerating voltages of 10 kV or above, the images do not represent the surface but start to show the internal structure of the char particle. Chromium coating (∼2 nm) has little effect on the image formation, which could be a good candidate of coating for the surface observation of poorly/non‐conductive char particles. Such observations were determined by the char structure, the coating method, the properties of the coating material, the thickness of the material coated and the operating conditions of SEM surface observation. For porous char particles, a procedure of the structural characterisation for porous char particles using SEM surface observation has been proposed. The interpretations of the SEM images obtained for the porous char particles under various sample preparation and SEM operating conditions are also discussed