Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

2.8
Transition Metal-Based Nanocomposites
2.8.1
Ni-Based Nanocomposites
Electrodeposited Ni and its nanocomposites reinforced with ceramic nanoparticles
have been studied extensively. Electrodeposited Ni coatings find important application
as bulk nanostructured materials for mechanical characterization [91–93]. This
is because bulk metals and composites prepared by direct hot compaction of
nanopowders undergo excessive grain growth, leading to poor mechanical properties
in tensile measurements. Electrodeposited Ni coatings with nanograins generally
exhibit much higher tensile strength and stiffness but poorer tensile ductility
compared with their micrograin counterparts. It is considered that CNTs with
superior tensile strength, stiffness and fracture strain can further enhance the
mechanical performances of Ni coatings.
In the deposition of Ni coatings, bath composition and plating condition (d.c. or
pulse) play a crucial role on the morphology and dispersion of CNTs in Ni coatings
(Table 2.5). Oh and coworkers prepared Ni/MWNTnanocomposite coatings by using
d.c. plating [100]. The electrolyte used was typical sulfate Watts bath. To assist the
dispersion of CVD grown MWNTs, sodium dodecyl sulfate (SDS) and hydroxypropylcellulose
(HPC) were added into the electrolyte. The total amount of SDS and HPC
was fixed at 10 g L 1 . The length of CVD-grown MWNTs was reduced from 20 mm
to less than 5 mm by milling with zirconia balls for 24 h. The thickness of electrodeposited
coatings was controlled to 50 mm.
Figure 2.26(a)–(e) show field-emission SEM micrographs of Ni/CNT nanocomposite
deposited in a bath containing different additive contents. The MWNT
concentration of the electrolyte is maintained at 10 g L 1 , corresponding to
14.6 vol% CNT. From Figure 2.26(a) and (e), it is evident that SDS is more effective
for CNT dispersion than HPC. Furthermore, the incorporation of MWNTs into Ni
matrix is enhanced by adding SDS-HPC mixture to the electrolyte (Figure 2.26(b) and
(c)). Using the same technique, Oh and coworkers also prepared the Sn/MWNT leadfree
solder for electronic packaging applications [101].
Table 2.5 Bath composition for deposition of Ni/CNT coatings.
2.8 Transition Metal-Based Nanocompositesj73
Bath Composition (g L 1 )
Plating condition NiSO4 NiCl2 H3BO3 Saccharin SDS HPC
Bath
Temperature ( C) pH
d.c. Ref [99] 260 45 15 0.5 2.5–10 2.5–10 40 —
d.c. Ref [102] 315 25 35 0.1 0.1 — 60 3.5
Pulse-reverse Ref [104] 315 25 35 0.1 0.1 — 60 3.5
Pulse-reverse Ref [105] 280 35 45 — — — 54 4