Improvement of the Corrosion Resistance of Aluminium Alloys Applying Diff erent Types of Silanes - Advanced Materials for Agriculture, Food and Environmental Safety - page 45

Figure 2.3 Anodized AA 2024 surface wetting for dif erent silane treatment: (a) bis-
amino silane:VTAS; (b) bis-sulfur silane; (c) bis-amino silane:bis-sulfur silane.

silane:VTAS < bis-sulfur silane < bis-amino silane:bis-sulfur silane.
h erefore it can be stated that the chemical structure of the silane
has a strong inl uence on the hydrophobicity of the layer, and for bis-
sulfur silane and bis-amino silane:bis-sulfur silane, a good hydropho-
bic layer was obtained, increasing the corrosion protection properties
(demonstrated also by SST); but from an economical and environmen-
tal point of view it is better to avoid the use of alcohol-based silanes
or the preparation of the solution in a higher % of water. In addition,
the inl uence of sealing time was studied (2, 5 and 10 minutes), and it
could be observed that the sealing time has nearly no inl uence on the
contact angle value. Comparing the results obtained by us for the con-
tact angle in the case of water-based silane (bis-(trimethoxysilylpropyl)
amine:vinyltriacetoxysilane = 5:1) (the lowest in the range 61.5 ± 5.8
and the highest 75.7 ± 2.8) with those obtained for contact angle in the
case of alcohol-based silane (bis-(3-(triethoxysilyl) ethane (61.0±2.5
and 69.3±1.4), bis-[3- (triethoxysilyl) propyl] tetrasuli de) (87.1±2.9
and 103.8±1.6), one can conclude that chemical structure of silane has
a strong inl uence on the hydrophobicity character of layers. In the case
of the bis-sulfur silane, we observed a good hydrophobicity of the lay-
ers, increasing the corrosion protection properties (demonstrated also
by SST). At the interface, a high density of Al-O-Si bonds are present,
which are formed by the reaction of hydrophilic Al-OH groups, making
the metal surface less favorable for water adsorption and eliminating the
tendency for aqueous corrosion. h e hydrophobicity of the i lm surface
is destroyed in the case of exposure to a considerable amount of water,
due to the fact that Al-O-Si hydrolizes back to re-form hydrophilic
Al-OH and Si-OH groups. A surface i lm with a contact angle value in
the order of magnitude of 90 remains at that order or will even decrease

also in the case of immersion in water or exposure to salt-aerosols for
a few weeks, indicating that Si-O-Si groups are not very stable and it

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