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Picture 1 shows a test cylinder that has been coated with the test product and cured under specified conditions.
Picture 2 shows the conditioning tank. The samples are rotated continuously in sea water maintained at 25oC The water in the tank is filtered through activated carbon and ion exchange resins to prevent the build up of copper in the water.
After set periods of time the samples are removed from the conditioning tank, rinsed and placed in beakers in a second tank (picture 3) and rotated for a measured time. The beakers contain a weighed amount of sea water and are fitted with baffles to prevent the water swirling.
The amount of copper in the sample water is measured using a photometer which is able to measure the amount of more than 40 elements and compounds. It does this by measuring the difference in the amount of light transmitted through a sample before and after the addition of a reagent to a sample of the leachate. The picture shows samples that contain high, medium and low amounts of copper.
The copper leaching rate is then calculated as ug/cm2per day.
LONG TERM COPPER LEACHING RATE TESTING
On completion of the laboratory copper leaching rate testing in the laboratory the test cylinders are being suspended from a pontoon in the tidal stream near the entrance to Fowey harbour.
The cylinders will be returned to the laboratory periodically for testing to provide data on how the copper leaching rate varies over the life of the coating. Test panels coated with the same formulations will be used to compare performance with leaching rate data.
Testing on panels coated with different grades of Synergy have been immersed at selected sites in the UK and abroad.
All of the trial formulations proved to be effective but the decision on which grade to commercialise was made by comparing the results of the current laboratory testing and the results of similar laboratory work conducted at Southampton University in 1993.
One important problem that was revealed was the very short ‘open time’ of the original primer. This resulted in blistering if SYNERGY was applied after more than two or three hours of the primer becoming touch dry. A epoxy primer was decided upon after accelerated ageing tests in water at 40oC proved it to provide far superior adhesion to the finishing coats.
DEVELOPMENT & TESTING
While some of the variations in performance will have been caused by poor application there is obviously a scientific reason for the majoratory.
Another factor that could effect the performance of epoxy bound antifoulings is that epoxy coatings suffer from ‘blooming or blushing’ This occurs when carbon dioxide in the atmosphere reacts with the amine hardener to form a carbamate on the surface of the coating.
The test cylinders shown in this picture are all coated with the same well known copper epoxy product but have been cured under different conditions and immersed for the same length of time. Their colours vary from green to copper red and their copper leaching rates varied by more than 50%
In order to test the theory equipment was set up in our laboratory to test the copper leaching rate of samples cured in different conditions. The method used was a modified version of BS ISO 15181 2007, parts 1 & 2. The main difference in the test proceedure was that we used sea water whereas the BS specifies artificial sea water.
A pack of a popular copper-epoxy product was purchased with which to conduct tests of samples cured under different conditions.
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