The results of SEM analyses provide information about the
structure and morphological characteristics of RH chars. Fig. 4 displays
the images of the chars obtained at 500 C. These images
show that the globular structure of the raw RH is in general preserved
in the char, although part of the structure is broken due
to the release of volatile matter during the pyrolysis (Fig. 4a). Some
macropores are also formed on the external surface developing
annular spaces in the particle (Fig. 4c). As observed in Fig. 4b, some
small particles with globular shape are deposited on the char. Hu
et al. [67] explained that these particles stem from the dust attached
on the parent RH and from the pyrolytic carbon deposits
due to hydrocarbon cracking. However, Sharma et al. [68] suggested
that the inorganic salts of the raw biomass could also appear
in the carbonaceous matrix.