Page 54 - Handbook of Adhesion Promoters

3.2 Delamination 47

Figure 3.2. Schematic cross-sections of failure process for coatings under high hydrostatic pressure. [Adapted,
by permission, from Liu, Y; Wang, J; Liu, L; Li, Y; Wang, F, Corrosion Sci., 74, 59-70, 2013.]
3.2 DELAMINATION

The delamination is a process of separation into the constituent layers. This definition
shows that cause of the delamination process is not a part of the explanation of the reason
for the delamination. There as several reasons for delamination, such as
• high hydrostatic pressure
• humidity
• internal adhesion
• moisture and thermal expansion
• stress field
• tribocorrosion
• weathering
which are discussed below in the above sequence.
6
Figure 3.2 shows the steps of delamination under a high hydrostatic pressure. In the
epoxy varnish coating, pressure greatly accelerated water diffusion through the coating. 6
Water penetrated the interface between the coating and the steel and it began to accumu-
6
late, resulting in the formation of many small blisters filled with water. Large blisters
6
formed from smaller blisters. Some underfilm corrosion occurred under the blisters. 6
6
Water film formed interface, which separated the coating and substrate. The coating lost
6
adhesion and delaminated.
Delamination of the solar cell cathode upon water ingress leads to a massive active
7
area loss and to a strong decrease in efficiency. The water vapor transmission rates
required to achieve feasible lifetimes (five years and longer) have been estimated to be in
-6
-5
7
2
the range of 10 -10 g/m d. A major reduction of degradation is observed for devices