Chemistry Reference
In-Depth Information
that is inflicted in some of the tests. There are two tests: the continuous salt spray
test and the intermittent test. The continuous salt spray test was used to study the
effect of salts on the properties of coating films. The duration times for the tests were
recorded for cured epoxy systems based on AbA and DAK and are listed in
Tables
2.14
and
2.15
. The test was stopped when a film showed poor adhesion. The results
of salt spray tests indicate that the coatings with higher epoxy functionalities exhibited
strong adhesion. This was shown by the improvement in coating performance from
75 to 95% for AA/DAKAE and MA/DAKAE, and AbA/FA3E, respectively, after 646
h of exposure to the salt spray environment. Coating performance was consistently
improved for each exposure time for both coatings. This can be attributed to the
relationships between the coating properties and performance. The adhesion of the
substrate to the coat is the main reason for coating failure. Cracking, flaking, scaling
or blistering due to rusting underneath the coating (the latter often being accompanied
by brown discolouration of the film) is due to mechanical action by the products of
corrosion.
Table 2.14 Salt spray resistance of cured HAPAE, AA/DAKAE, HMPAE and MA/
DAKAE epoxy resins
Debonded
area AA/
DAKAE
Debonded
area HAbAE
Exposure time
(h)
Theoretical
mixing ratios
ASTM B-117
Polyamide
hardeners
AA/
DAKAE
AA/
DAKAE
AA/
DAKAE
HAPAE
%
mm²
%
mm²
HAPAE
HAPAE
5
5
15.8
18.3
9.7
11.2
646
530
1.6
2
APATA
3
2.5
31
35.9
58.1
67.4
646
530
3
3.1
APAPA
4
4
19.6
22.8
11.6
13.4
646
530
1
1.1
MPATA
2.5
3
58.1
67.4
131
35.9
646
530
2
1.6
MPAPA
AA/
DAKTA
7.2
7.2
4.4
5.2
4.4
5.2
646
530
2.5
2.2
AA/
DAKPA
7
7
6
7.1
6
7.1
646
530
2.8
2.7
MA/
DAKTA
7.1
7.1
4.7
5.5
4.7
5.5
646
530
1.8
1.56
MA/
DAKPA
6
5
11
13
15.8
18.3
646
530
2.3
1.7
