Biomedical Engineering Reference
In-Depth Information
chemical reaction. The only issue for the in-situ process is to control the
chemical reaction by controlling process parameters. For the ex-situ process,
especially for casting of MMNCs, improving the interface by improving the
poor wettability between ceramic particulates and liquid metal is a
determinant factor for the success of the process. Ibrahim et al. (1991)
summarized three factors that can be improved to increase wettability:
.
increasing the surface energy of the solid
.
decreasing the solid-liquid interfacial energy
.
decreasing the surface tension of the liquid metal.
Cao et al. (2008a) reported that applying ultrasonic vibration to liquid
magnesium can produce a chemically bonded interface between Mg alloy
and SiC. Lan et al. (2004) theorized that ultrasonic vibration breaks the gas
and silica layer and makes a clean SiC surface to accelerate the wetting of
SiC and aluminum. Hashim et al. (2001a, 2001b) summarized the methods
used to improve the wettability between SiC particles and molten aluminum
alloy. These methods include:
.
the addition of alloying elements to the matrix
.
coating the ceramic particles
.
pre-treating the ceramic particles.
The wetting behavior of CNTs and liquid metals has been studied in
detail. It is reported that surface tension, with a cut-off limit between 100
and 200mN/m, is the determining factor for wetting. In this case, aluminum
(surface tension of 865mN/m), copper (1270mN/m), and iron (1700mN/m)
would not be easily wetted on the surface of multi-walled carbon nanotubes
(MWNTs) (Daoush et al., 2009).
The metal-ceramic interface is affected by the process used to fabricate
MMNCs. Nanocomposite particles can be fabricated with mechanical
alloying and sintered later using other methods. This process will be
introduced later in the chapter. Other chemical methods are also used to get
a better metal-ceramic interface. Shehata et al. (2009) used in-situ
technology to produce Al
2
O
3
/Cu nanocomposite powders. He et al. (2008)
discovered a chemical method to co-deposit copper and nanodiamond.
Daoush et al. (2009) reported electroless deposition to form a copper
coating on CNTs and successfully fabricated CNT/Cu nanocomposite
powder. The different chemical methods listed in Table 6.2 can produce
thermal, stable and clean metal-ceramic interfaces.
