538
M. Ghasri-Khouzani et al. / Journal of Alloys and Compounds 472 (2009) 535–539
Fig. 6. SEM micrograph of non-activated aluminum sulfate.
Fig. 8. The specific surface area (SSA) of mechanically activated aluminum sulfates
vs. the milling time.
are built of fine particles with sizes well inferior to 0.1 m. The
agglomeration of particles during extended dry milling was also
reported for titanium dioxide [27]. This behavior is common during
dry milling and is usually explained by agglomeration of the struc-
turally modified particles following the initial reduction of particle
size. This occurs because of the tendency of the activated material
to reduce its surface free energy.
surface area increases sharply from 0.3 m2/g for non-activated sam-
ple to 6.8 m2/g for the 3 h activated sample followed by a slight
decrease and then stabilizes for higher milling time due to the for-
mation of dense agglomerates. This trend implies that for tm < 3 h,
the decrease of Ti in the TG curves of activated aluminum sulfates is
caused by increase of the specific surface area as well as the increase
of the structural disorder, but for tm > 3 h, the role of specific surface
area diminishes.
3.4. The specific surface area
The specific surface area of mechanically activated aluminum
sulfates versus the milling time is shown in Fig. 8. The specific
4. Conclusion
Aluminum sulfate does not undergo any reaction or phase
change during high-energy ball milling. The initial temperature
for thermal decomposition of aluminum sulfates in the TG curves
decreases gradually with increased milling time of mechanically
activated aluminum sulfates. This mainly arises from the increases
of the structural disorder and specific surface area. Mechanically
activated aluminum sulfate is more easily subjected to thermal
decomposition than non-activated one.
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