Biomedical Engineering Reference
In-Depth Information
Solid phase characterization is realized ex situ when a sample of milled
powder is picked up from the vial after a defined milling period. Thus, in the
case of a material in crystalline form, the X-ray diffraction (XRD) method is
advantageous; it is fast and allows the progress of the syntheses to be
followed. However, this is not convenient after some stages of milling where
the mechanical treatment caused comminution and prolonged activation
destroyed the crystallinity of the solid powder particles leading to their
complete or partial amorphization and simultaneously to consumption of
the initial mixture components, making them undetectable by XRD because
the amounts were too small.
Thermal analysis (TA) with registration of thermogravimetric (TG/
DTG) and differential thermal analysis (DTA) curves facilitates the
determination of an amount of undecomposed and/or unreacted reagents,
oxidation/reduction processes and mechanically induced physical transfor-
mations in/or between the reagents. The example shown in Fig. 12.5 allows
us readily to see that the analysed sample consists of mechanically unde-
composed salt, that is Cu-hydroxocarbonate with the remaining amount
being aluminium. The endothermic effect at 350
8
C reveals that the
Cu
2
(OH)
2
CO
3
-Al mixture decomposed into CuO, which was then reduced
by Al to metallic Cu, generating a large amount of heat at about 600
8
C. This
heat may accelerate the alloying of Cu with Al,
for example into
intermetallic phases. The effect at 520
8
C can be related to the eutectoid
transition of CuAl
2
with Al
!
L at 528
C, according to the phase diagram
of the binary Cu-Al system (Massalski, 1992), because the sample used in
this thermo-analytical experiment was a product of the early stage of salt-
metal mixture milling.
In addition to the above-mentioned analytical techniques for solids,
versatile scanning and transmission electron microscopy (SEM and TEM)
with backscattered electron imaging and quantitative energy dispersive
X-ray elemental microanalysis (EDS) are very helpful in estimating the
microstructure of synthesized composite particles for a relatively coarse
powder and for fine powders. By combining the grey tone levels with the
results of EDS some compounds can be identified and localized (Yakowitz,
1975; Wieczorek-Ciurowa et al., 2003c). To illustrate the utility of
transmission electron microscopy in estimating the microstructures of
mechanochemically synthesized composite powders, Fig. 12.6 shows a set of
TEM microphotographs of Cu
2
(OH)
2
CO
3
-Al powder after mechanochem-
ical synthesis showing nanocrystalline copper. Electron diffraction patterns
unquestionably confirm that the detected Cu, CuAl
2
phases are in the
nanocrystalline form.
Moreover, it is worthwhile adding methods such as neutron diffraction,
magic angle spinning solid-state nuclear magnetic resonance (MAS NMR),
Fourier transform infrared (FT-IR), ultraviolet (UV) or X-ray photo-
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