TEM micrographs of magnetite are presented in Fig. 3, from (a)
to (f). The magnetite crystals appeared as quasi-spherical
nanoparticles, property which is related to the high nucleation
speed during the precipitation. At higher iron concentrations,
magnetite nanocrystals also appear better crystallized in accordance
with some reported crystalline habits [32], as can be seen in
Fig. 3(b and c). The mean particle diameters (MPD) of the
magnetite precipitate, as well as other characteristics are shown in
Table 1. In the studied total iron concentration range, there is a
linear correspondence between the mean particle diameter and
the total iron concentration, represented as follows: