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-4x10
7
-3x10
7
-2x10
7
HWS
bis-amino:VTAS
polysulfur silane
bis-amino:polysulfur silane
-1x10
7
0
0,0
2,0x10
7
4,0x10
7
6,0x10
7
8,0x10
7
1,0x10
8
Z
real
[
]
Figure 2.14
Representative Nyquist plots for surface i lms containing dif erent silanes.
2.5.4
Salt Spray Test
h e salt spray test (SST) is one of the most applied corrosion tests in the
aircrat industry. It is used to compare the performances of dif erent coated
substrates, and the specimens are considered to fail if more than 2 pits per
dm
2
are displayed.
Sample surfaces of 1 dm
2
were exposed to a continuous SST for 840 h
and the obtained AA 2024 panels are presented in Figure 2.15.
h e sample which was treated with bis-amino silane:VTAS at er HTS
at 95
C and 30 min showed some signs of corrosion at er 72 h, while the
sample treated with bis-sulfur silane at er HTS at 95
°
C and 30 min had
only one pit that appeared at er 840 h of continuous exposure in SST.
h is is due to the fact that bis-amino:VTAS i lm is hydroi lic and contains
amino groups (positively charged) which attract water and electrolytes to
the siloxane/metal interface. In the case of sample treated with bis-amino
silane:bis-sulfur silane, no signs of corrosion were observed at er 840 h of
exposure in SST. h e results obtained at er 840 h of continuous exposure
from the sealed samples with dif erent silane mixtures are in concordance
with the results obtained from the same samples by EIS.
Alcohol-based silanes of er a higher corrosion resistance compared to
the water-based silane system because the higher alcohol content removes
°
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