Civil Engineering Reference
In-Depth Information
Platinum
Silica
40%nickel-60%alumina
80%nickel-20%alumina
Interlayer
50 nm
Aluminium
8.9
Scanning electron micrograph of the cross section of a sol-gel-
produced multilayer coating of Ni-Al
2
O
3
and SiO
2
deposited onto an Al
substrate (with an interlayer to boost the adhesion to the substrate).
The top layer of platinum was applied by sputter deposition in order
to allow the imaging. From Boström
et al.
(2011).
aluminium (Wernick
et al.
, 2001), but other metals - such as titanium (Dia-
manti and Pedeferri, 2007) and tantalum (El-Sayed and Birss, 2011) - can
be used too. Numerous alternative techniques exist as well. The anodization
of aluminium can be carried out following several different strategies. Thus
'mild' anodization can lead to a self-ordered pore structure at the nanoscale,
but this technique is slow and confi ned to a limited set of process param-
eters; 'hard' anodization, on the other hand, is a fast and industrially viable
process leading to thick layers with a disordered pore arrangement. The
latter technique is applied routinely for aluminium surfaces exposed to air.
It was recently realized that a combination of 'mild' and 'hard' anodization
in what is known as 'pulse' anodization can yield particularly interesting
nano-features, such as those depicted in Fig. 8.10 (Lee
et al.
, 2008), which
shows alternate layers with well developed nanostructures.
8.2.4 Nano-particle-based coatings
Vacuum-based coating methods, as discussed extensively above, had an
important historical role for making fi lms based on nanoparticles. In fact,
vacuum-based techniques provided some of the fi rst insights into approaches
Search WWH ::
Custom Search