My apologies.As an aquatic chemist by education, having at one time research interests in heavy metals in both fresh and saline waters, I found myself somewhat puzzled over 10 years ago (when there was a lot of discussion in the magazines and forums of various ‘copper-in-epoxy’ products) by the descriptions of the products of chemical copper corrosion in seawater, and set myself to sorting it out to my own satisfaction.
I do sympathize with those writing for a non-chemical readership – and with those who find my posts on the subject difficult. Unfortunately there is danger of confusion unless likely substances are correctly identified – not so much with the mineral names, which typically refer to naturally-occurring crystalline forms and ores, but with modern chemical nomenclature and formulae. And it is difficult to write with accuracy and concision without using the appropriate chemical terms like ‘thermodynamic equilibrium' or ‘thermodynamic stability’.
Put simply, and as far as I can see, in normal aerated seawater there is evidence of a chemical ‘progression’ from metallic copper, to an oxide (cuprous and/or cupric) to a green basic chloride (or perhaps, especially at lower salinity and therefore lower chloride concentration, to a green basic carbonate like the verdigris we see on copper roofs and bronze statuary).
I talk about the relative thermodynamic stabilities of different solid corrosion products, and thermodynamic equilibrium may take a long time to establish because of slow kinetics. Less thermodynamically stable products may persist alongside those that are more thermodynamically stable, which are the ‘ultimate’ chemical corrosion products over time.
I am not an expert on copper toxicity or antifouling, but do know that in terms of copper in solution (which includes many different dissolved copper complexes, with hydroxyl and chloride ions for example) there is much accumulated evidence that the free cupric ion (Cu2+) concentration is often the best predictor of toxicity to many aquatic organisms. As the ‘earlier’, less thermodynamically stable solids will typically maintain a higher Cu2+ concentration in the boundary seawater, to the extent that antifouling properties are a function of the dissolved copper in the boundary layer they will I presume be at least as effective as the ultimately thermodynamically stable forms.
I’ve perhaps made things worse for you – if so, I'm sorry but I have tried!
See my previous posts ^^^^
It’s not a puzzle to me btw .Its related to the differing anodic potentials of all the metals in the salt solution we call seawater .
Oh one more thing did some say “ coated in epoxy “ then in the next breath “water soluble “ - to continue to re- expose ?
All very kings new suit and clique
I just read your post 44. Is that really true? Quite extraordinary science is behind it if so. It is clear, something is going on between the keel cooler and hull and I don't know what.
Good post :encouragement: from what we know
