TEM bright-field image of carbonaceous
matrix), especially in relatively thin areas. Due to the fact that
most of these spherules have a size less than 40 nm, the thick carbonaceous
matrix produces a low signal-to-background ratio hampering
identification. The results described above about the CFAs samples composition
are consistent with the assemblage identified in the mineralogical
composition of coal from Douro Coalfield and with the combustion
conditions in the thermal power plant