Environmental Engineering Reference
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bis-[3-(trimethoxysilyl) propyl] amine (bis-amino silane), bis-[3-(tri-
ethoxysilyl) propyl] tetrasuli de (or bis-sulfur silane) and vinyltriaceth-
oxy silane (VTAS) were provided by ABCR (Germany) and were used as
received without further purii cation (> 95%).
Hot water sealing (HTS) was used as sealing reference method at 95
C
for a period of 30 minutes, whereby mainly the formation of Bayerite and
Boehmite could be observed and the sealed i lms formed provided a good
corrosion resistance proved for 192 h SST. But the energy ei ciency with
respect to the energy costs is too low in order to prolong the corrosion resis-
tance up to 840 h in the SST. h erefore dif erent procedures were applied
such as TSA anodization and conversion with silane and TSA anodization
followed by a HTS sealed by conversion coatings of silane.
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2.3.2
Preparation of Silane Solutions
h e water-based silane mixtures were prepared in a ratio of bis-amino
silane:VTAS = 5:1 (v/v) (pH=4.9) and then diluted with deionized (DI)
water to have a 2% solution, and stirred until the solution became clear.
Bis-sulfur silane solutions (5%  v/v) were prepared by adding silane to a
mixture of DI and ethanol. h e ratio of bis-silane/DI water/ethanol was
5/5/95 (v/v/v) (pH=5-6). h e hydrolysis time is very important, for water-
based silanes this is very short (15-60 min), and in the case of solvent-based
silanes the hydrolysis time is up to 3-4 days. In the case of a silane mixture,
bis-amino silane:bis-sulfur silane, the solution was prepared as follows: a
water/alcohol solution of bis-sulfur silane 5% was prepared by adding i ve
parts of bis-sulfur silane into a mixture of deionized (DI) water and etha-
nol. h e ratio of bis-sulfur silane/DI water/ethanol was 5/5/90 (v/v/v). h e
solution pH was 6.5. h e solution was stirred for 10 min, and then aged in
ambient conditions for at least 2 days to ensure that the silane molecules
were sui ciently hydrolyzed. A 0.5% bis-amino silane water/alcohol solu-
tion was made in a similar way. h e ratio of bis-amino silane/DI water/
methanol was 0.5/4.5/95 (v/v/v). h e solution pH was modii ed from 10.5
to 7.5 by adding acetic acid in order to enhance the solution stability. h e
bis-amino silane solution was used at er one day. h e ratio between bis-
amino silane and bis-sulfur silane was 3/1 and the pH=7.5.
2.3.3 Silane Treatment
At er the anodizing step, the samples were immediately rinsed in deion-
ized water; a part was HTS sealed (95
C, 30 minutes) as reference, the
other part was treated with dif erent silanes at er HTS (mixtures bis-amino
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