Alkaline Blistering

In contrast to thick coatings, thin coatings combined with cathodic protection present certain risks on ships. Blisters filled with highly alkaline liquids resulting... 

After commissioning the protection installation, an on potential of = -0.82 V was imposed. In the course of a few years of operation, the protection current rose from 100 to 130 mA. The mean values were = -0.63 V and the values were t/ = -0.50 V. An inspection carried out after 5 years showed that cathodic blisters, whose contents were alkaline, had developed in the coating. The steel surface at these places was rust free and not attacked. Uncoated steel at the pores was covered with CaC03 deposits as a result of cathodic polarization. 

Hydrochloric acid, thiodiglycol, and chlorovinylarsenious oxide. Alkaline hydrolysis destroys the blistering properties. 

Uses As a mild alkali accelerator in developers of moderate to high alkalinity. Used to avoid the creation of gas when it comes in contact with an acid. For this reason the possibility of blister formation is minimized. 

Hydrolysis products HCl and chlorovinyl arsenous oxide alkaline hydrolysis destroys blister properties... 

A highly alkaline surface (pH > 10) can result in gassing" and subsequent blisters. 

Early blistering due to rain depends on the rain s intensity, duration, and on how long the paints have dried before it rains. The pH of the water may also be an influential variable. The deionized water fog box had a pH of about 8 and the tap water fog box had a pH of 7, whereas the rain had a pH of about 4. The relatively more alkaline deionized water would be ex-... 

The alkaline hydroxide ions disbond the coatings through saponification. Figure 13.7 shows the corrosion mechanisms when the disbondment occurs at the coating pores (microscopic coating defects) producing blisters at the defects of the coating. 

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