Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

72j 2 Carbon Nanotube–Metal Nanocomposites
and pulse deposition (plating) have been used extensively for the electrodeposition
of metals/alloys. Pulse plating offers more uniform deposition of coating than the
d.c. method. Several parameters such as peak current density, frequency and
duty cycle affect the adsorption and desorption of chemical species in the electrolyte.
The electrodeposition parameters can be tailored to produce deposits of desired grain
size, microstructure and chemistry. Therefore, electrodeposition has emerged
as an economically viable process to produce pore-free nanostructured metals and
nanocomposites in the form of coatings and thick plates [91–96]. Nanocrystalline
coatings can be deposited on the cathode electrode surface by properly monitoring
the electrodeposition conditions such as bath composition, temperature, pH, additive
agent and deposition time.
Very recently, Chai et al. prepared Cu/MWNT nanocomposite by means of
direct current electrochemical co-deposition technique [97]. The MWNTs were
suspended in the copper plating solution initially. Both nanotubes and copper ions
were driven towards the cathode and deposited onto the cathode simultaneously
during the deposition. Homogenous dispersion of MWNTs in copper matrix was
observed.
As CNTs have poor compatibility with copper, special surface treatments are
needed to modify the surfaces of CNTs to enhance interfacial interaction. Lim et al.
used electrodeless plating to deposit a nickel layer on the surface of SWNTs fabricated
by a HiPCo method [98]. They reported that the interfacial bonding was significantly
improved after coating the nanotubes with a layer of nickel by eletrodeless plating.
The coated nanotubes were then blended with copper powders by means of
mechanical mixing process to form the Cu/SWNT nanocomposites.
2.7.5
Patent Process
Copper-based nanocomposites filled with low loading levels of CNTs having
excellent thermal conductivity are potential composite materials for thermal
management applications in electronic industries. As mentioned above, substantial
progress has been made in worldwide research laboratories in the development,
processing and characterization of Cu/CNT nanocomposites. Very recently,
Hong et al. have invented a technical process for possible commercialization of
Cu/MWNT nanocomposite powders [99]. Their invention discloses a process of
producing a metal nanocomposite powder homogeneously reinforced with CNTs.
The invention consists of an initial dispersion of MWNTs in a predetermined
dispersing solvent such as ethanol under sonication followed by the copper salt
(Cu(CH3COO)2) addition. The resulting dispersion solution is again subjected to
sonication for 2 h to ensure even dispersion of the CNT and copper molecules in
the solution and to induce the chemical bond between molecules of the CNT and
copper. This mixed solution is finally heated at 80–100 C to vaporize water, and
calcined at 350 C to form stable CuO/MWNT powders. Such composite powders
are reduced at 200 C under a hydrogen gas atmosphere to form the Cu/MWNT
powders.