Environmental Engineering Reference
In-Depth Information
at which water and electrolyte can reach the interface where these media
would induce corrosion reactions.
Zhu and van Ooij have shown that the i lm deposited from the bis-sulfur
silane solution on aluminium actually is made up of three dif erent regions,
a crosslinked outermost bis-sulfur silane i lm enriched Si-O-Si bond; an
extensively crosslinked or dense bis-sulfur interfacial layer dominant with
Si-O-Si and Al-O-Si bonds; and the inner Al oxide layer on the alloy sub-
strate [28, 31,48]. Nowadays, for a robust coating and for good stability of
the silane solutions some alternative methods were developed, such as the
inclusion of additives in the silane i lm (inhibitors) [31]—rare earth metal
salt, cerium nitrate [49], organic inhibitors, benzotriazole [50] and tolyl-
triazole [51]. Silanes precursors as starting materials are commonly used
in sol-gel processes. h e sol-gel derived coating provides good corrosion
resistance of metals due to chemical inertness, reliable adhesion to metal
substrates and also easiness of application at ambient conditions [52-54].
Our experimental research mainly dealt with a comparative study con-
cerning the performance of BTSE, bis-sulfur silane (PSS), a mixture of bis-
amino silane:VTAS, and a mixture of bis-amino silane:bis-sulfur silane as a
post-treatment for the protection of an anodized AA 2024 T3 alloy against
corrosive attacks induced by moisture and chlorine ions, and the detailed
investigation of the obtained surfaces and interfaces by dif erent surface-
sensitive analytical methods, such as electrochemical impedance spectros-
copy (EIS), contact angle, FTIR, ESEM/FIB and SST.
2.3
Materials, Methods and Experimentals
2.3.1 Materials
Commercially available AA 2024-T3 unclad aluminium alloy metal sheets
(wt%: Cr 0.1; Ti 0.15; Zn 0.25; Fe 0.5; Si 0.5; Mn 0.3-0.9; Mg 1.2-1.8;
Cu 3.8-4.9; others 0.15; Al balance) with the dimensions of 15 cm x 8 cm x
2 cm were used in this study. Before anodizing, the samples were degreased
with acetone, dried in air, and at erwards an alkaline degreasing took place
followed by alkaline etching and acid pickling processes followed by a i nal
washing step with deionized (DI) water. h e anodizing bath contained
40 g L
− 1
(0.41 M) H
2
SO
4
solution, 80 g L
− 1
(0.53 M) of tartaric acid (C
4
H
6
O
6
)
and 4 g L
− 1
Al(III) as Al
2
(SO
4
)
3
. h e anodizing process was carried out at a
constant cell voltage of 14 V for 20 min reached at er a 5 min voltage ramp
and the last step, 1 min ramp from 14 V to 0 V.
h e H
2
SO
4
, tartaric acid (C
4
H
4
O
6
) and Al
2
(SO
4
)
3
were purchased
from Merck and Sigma. Bis 1, 2 [triethoxysilylpropyl] ethane (BTSE),
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