Biomedical Engineering Reference
In-Depth Information
12.10
SEM microphotograph (BSE image) illustrating that Al
2
O
3
particles (ranging from 100 nm to 500 nm) are embedded in the
Cu-Al matrix formed during reactive milling of the CuO-Al system.
The dark spots correspond to Al
2
O
3
, the brighter grey ones to Cu(Al)
(SEM Hitachi S-4700 with EDX Noran Vantage) (Wieczorek-Ciurowa
et al., 2007a).
matrix. They are resistant to very high temperature, corrosion, mechanical
and abrasive actions and they have a relatively low density. However, their
low intergranular cohesion is responsible for their great brittleness. For this
reason, a ceramic component is often present in the composite.
In Sections 12.6.1 and 12.6.2, in situ mechanochemical syntheses of Ni-
Al/Al
2
O
3
are described, starting from two different mixtures, Ni
2
(OH)
2
CO
3
.
xH
2
O or NiO with Al, respectively (Wieczorek-Ciurowa and Oleszak, 2008).
The milling procedure was similar to the one described in Section 12.5. The
component systems were prepared as physical mixtures in which the amount
of Al was calculated assuming that NiAl with Al
2
O
3
or Ni
3
Al with Al
2
O
3
formed as final products of the synthesis. Among the intermetallics in the
binary Ni-Al phase diagram (Hansen, 1958), the main ones are Ni
3
Al, NiAl,
Ni
2
Al
3
, NiAl
3
and solid solutions. It was found that if Ni
3
Al was the
expected phase, mechanosynthesis brings about the formation of composite
powder particles consisting of Ni
3
Al matrix and Al
2
O
3
.
In mechanochemical syntheses in the NiO-Al system where reagent
proportions were calculated for the NiAl phase, the expected NiAl and
additionally the Ni
3
Al intermetallic phase were formed as well as Al
2
O
3
.
However during the mechanical treatment of Ni
2
(OH)
2
CO
3
·xH
2
Owith
