Final Report - Strategic Environmental Research and Development ...

Corrosion Volume (mm/yr)
Corrosion Volume (mm 3 )
Corrosion Area (mm 2 )
800
600
Primer Only
Topcoat & Primer
400
200
0
0.0 0.2 0.4 0.6 0.8 1.0
n/(N+1)
Figure 6.61. Corrosion area listed by topcoat in ASTM B117 for 500 h.
For samples exposed in ASTM G85 for 360 h, the corrosion volume of samples with topcoat was
very close to that with primer only (Figure 6.62). What happened upon corrosion rate and area
was identical to corrosion volume (Figure 6.63 and 6.64). Usually topcoat was expected to retard
the corrosion rate. This could be due to barrier property of the topcoat. However, topcoat’s
superior barrier property limits the water diffusion, which results into limited dissolution of
pigments. And most primers require water penetration to dissolve the pigments in order to
release inhibitors. Then the inhibitors reach metal-coating interface to prevent corrosion. In this
experiment, all the coatings were scribed. Since the coatings were scribed which means the
pigments within primers could reach water moisture, the barrier property of topcoat would be
lost. Then the anticorrosive ability would fully reply on the surface pretreatment and primer.
Therefore, there is no obvious increase in corrosion prevention with topcoat.
30
25
20
15
10
5
0
Primer Only
Top Coat & Primer
0.0 0.2 0.4 0.6 0.8 1.0
n/(N+1)
Figure 6.62. Corrosion volume listed by topcoat in ASTM G85 for 360 h
3
2
Primer Only
Top Coat & Primer
1
0
0.0 0.2 0.4 0.6 0.8 1.0
n/(N+1)
Figure 6.63. Corrosion rate listed by topcoat -ASTM G85 for 360 h
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