Civil Engineering Reference
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enhanced corrosion and oxidation resistance. The disclosed method relates
to such nanoparticles as CeO
2
, nanoceria, or an oxide of an element selected
from the group consisting of Al, Si, Ti, Y, Nb, Zr, and other rare earth ele-
ments. One possible mechanism is that these elements exhibit a reactive
element effect that decreases the oxide scale growth rate and reduces scale
spallation by improving the scale-alloy adhesion. The invention suggests
exemplary applications of this technology in protecting SS and Ni or Al
alloys at high temperatures and in steam environments. The effectiveness
of nanoparticle surface treatments in managing metallic oxidation and cor-
rosion was demonstrated. For instance, the steel samples were dip-coated
with nanoparticles in their respective solutions once or several times with
intermediate drying at 200°C. After heating to 1000°C for 34 h, the 316 SS
treated with nanoceria had a self-protective, thin, and adherent oxide fi lm
formed on its surface, whereas the sample without the nanoparticle treat-
ment had thick, spalled oxide scale on its surface. Similarly, benefi cial effects
of nanoceria surface treatment for 430 and 410 SS were observed after
heating to 800°C in air for some time. Tests of nanocrystalline-coated and
uncoated SS confi rmed the corrosion resistance of the self-protective sur-
faces to humid air, to direct contact with liquid in the temperature range of
150°C to 350°C, to submerged service in high salinity solutions, and to the
vapor phase above these solutions.
Another invention in this category (Sugama, 2009) presents methods of
endowing the alloy surfaces with outstanding corrosion resistance by
forming an ultrathin (preferably less than 10 nm), Cr-free fi lm comprising
an at least partially crosslinked amido-functionalized silanol component
and nanoparticles of rare-earth metal oxide. The formed coatings were
reported to provide better coverage of the substrate metal and similar or
superior corrosion resistance than Cr-based coatings. For instance, one such
coating demonstrated to extend the lifetime of the steel substrate under
salt-fog test at 35°C from approximately 10 h to approximately 768 h.
Third, nanotechnology has been utilized in decorative and protective
coatings that provide the steel substrate with superior abrasion resistance
and good corrosion resistance. Chen (2008) discloses the use of cathodic
arc evaporation (CAE) for physical vapor deposition (PVD). For Zr, the
resulting strike layer exists either as amorphous to nano-size crystals up to
50 nm or as preferentially-oriented crystals up to 80 nm in size, with a small
percentage of amorphous refractory oxide acting as precipitation hardening
particles. By maintaining the fl ow ratio of oxygen to argon into the vacuum
chamber during CAE, a stoichiometric ZrO
2
layer (preferably between 10
and 30 nm thick) is then deposited on the strike layer, which provides
another non-conductive barrier layer to improve resistance to corrosion
and pitting.
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