Electrical Properties of Coating Systems 



The results of the electrical measurements are presented in Table 2 

 and in Figures 3 to 20. In the table, average values are shown for the electrical 

 measurements obtained initially and after exposure periods of 6 hours, 10 days, 

 150 days, and 400 days. The 1/4-, 10-, and 400-day exposure durations vary 

 by a factor of 40. When the values for one of the three panels were considerably 

 below the average, these values were disregarded in computing the averages 

 listed in the table. When two panels had considerably inferior electrical prop- 

 erties (lower resistance or higher capacitance), the value obtained for the 

 remaining panel was used. The values shown for each system therefore tend 

 to show the best properties of each coating system and eliminate possible 

 defects in the panels or in the coating application. The deviations of panels 

 not included in the averages shown in Table 2 are, however, shown in Figures 3 

 to 15. 



The criteria for deciding which values should be omitted from the 

 averages were as follows: ( 1 ) for AC resistances, when the deviation of the 

 value from the average was greater than a factor of 1 .5; (2) for capacitances, 

 when the deviation was greater than a factor of 1 .3; and (3) for the DC resis- 

 tances, when the deviation from the average was greater than 0.5 log unit. 



The changes in electrical properties are probably more important than 

 the absolute values. Therefore, the ratios of these measurements as compared 

 to the initial measurements are also shown in Table 2. Thus, R|/R is the ratio 

 of the initial resistance to that at the given exposure time, and log (R|/R) is 

 the corresponding logarithm. For capacitance measurements the ratio, C/Cj, 

 is given so that, again, increasing changes give increasing ratios. 



As shown in Table 2 and in Figures 3 to 15, the initial changes in 

 electrical properties were sometimes quite dramatic. This change presumably 

 is due to water uptake of the coating after it is immersed in seawater.^ Such 

 water uptake will change the capacitance of a coating because of changes 

 produced in the dielectric constant of the coating. For a given amount of 

 water, the change in dielectric constant may vary depending on the method 

 of distribution of the water.^ No attempt was therefore made to relate the 

 change in capacitance to actual water uptake. The changes in AC resistance 

 were found to be even greater than the changes in capacitance. 



For four of the systems (111, 112, 119, and 123) the short-term 

 changes in AC resistance, capacitance, and dissipation factor are shown in 

 graphical form (Figures 16 to 19). The electrical properties of System 1 1 1 

 (Figure 16) change comparatively little during the first 6 hours of exposure, 

 however, there is considerable change during the first 10-day period. System 1 12 

 (Figure 17) shows considerable change during the first 6-hour exposure period 



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