Biomedical Engineering Reference
In-Depth Information
12.8
TG-DTA curves of the Cu
2
(OH)
2
CO
3
-Al system after
mechanochemical synthesis for: (a) 0 hours, (b) 20 hours (SDT 2960
TA Instrument) (Wieczorek-Ciurowa and Gamrat, 2006).
CuO is reduced by Al in many steps proceeding locally, in isolated parts of
treated powders. This process of aluminothermic reduction may be
explained by the fact that the occurrence of a highly exothermic reaction
via combustion depends not only on thermodynamics but also on other
factors such as the nature of reactants, their mechanical properties,
crystalline structures and their stability during milling.
The thermoanalytical curves, TG-DTA, presented in Fig. 12.8
(Wieczorek-Ciurowa and Gamrat, 2006) for an untreated mixture of
Cu
2
(OH)
2
CO
3
with Al, and after milling for 20 hours, respectively, indicate
that Cu-hydroxocarbonate completely decomposes during mechanosynth-
esis and aluminium is consumed because of the lack of an endo effect at
640
C. Moreover, any sharp exothermic effect caused by the reaction of
CuO with Al is detected on the DTA curve. This means that the
aluminothermic reaction is completed during that time. It is interesting
that
8
C, which normally
corresponds to the transformation of Cu
9
Al
4
into a CuAl
2
phase. This is
there is no endothermic peak before 450
8
