Copper bottom.. real stuff?

[Aeolus]

Hydrozoan's explanation is very clear and interesting. Does the same chemistry affect the copper in anti-foul as much as it would affect sheet copper?

 

[daviddb]

An aluminium hull flame (arc) sprayed with copper as is done with some galvinising processes might make an interesting test bed. Not a diy process though, and would rquire a 'certain amount' of funding..

All agog to see how you get on.

yrs.
D.

 

[Hydrozoan]

Hydrozoan's explanation is very clear and interesting. Does the same chemistry affect the copper in anti-foul as much as it would affect sheet copper?

Thanks. I'm no paint technologist so I cannot say anything very helpful about how other paint components might affect what happens to copper in it – either by intentional design in formulation, or otherwise. Perhaps someone else here can help with that?

PS Can a biologist or antifouling techologist here tell us if initial settlement of, say, barnacle larvae is discouraged by high dissolved copper concentrations in the vicinity of the surface, or does settlement occur before the copper takes effect?

 

[Pasarell]

Thanks. I'm no paint technologist so I cannot say anything very helpful about how other paint components might affect what happens to copper in it – either by intentional design in formulation, or otherwise. Perhaps someone else here can help with that?

PS Can a biologist or antifouling techologist here tell us if initial settlement of, say, barnacle larvae is discouraged by high dissolved copper concentrations in the vicinity of the surface, or does settlement occur before the copper takes effect?

I agree that Hydrazoan's explanation of the behaviour of copper is very accurate except that I think you are assuming metallic copper deters fouling organisms as a consequence of copper ions in the water adjacent to the surface being protected. This is how conventional (painted on) antifoulings work where cuprous oxide is combined with a cocktail of organic biocides applied as part of a resin layer. In these materials the biocide cocktail is designed to leach out of the resin matrix and make the boundary surface layer of water poisonous to fouling organisms. Antifouling makers try to make the cocktail effective against as many fouling types as possible, in other words the more you pay the wider the spectrum it will be effective against.
Metallic copper leaches out of the surface very slowly indeed and losses of metal are more due to mechanical erosion than leaching. In this respect pure copper leaches more quickly and erratically than from a copper nickel alloy where erosion is slower and very predictable. Metallic copper works by a contact mechanism and not by releasing biocide into the water meaning its effect is only where there is actual metal in contact with the water. Even small gaps in the metal will allow fouling organisms to grow healthily. Barnacle larvae immediately start laying down their inert adhesive when they settle on a surface so if they can get even a very small spot down they can exist quite happily on that as they grow to maturity.
We have a Cuprotect installation on equipment in a gas field about 150km off the Canadian coast. The Canadian Government were very nervous about high concentrations of metallic copper in the sea and insisted the owners install sensitive monitoring equipment to measure copper ion concentrations 1 metre up current and 1 metre down current from 5 sites. In nearly 3 years they have not been able to detect any difference in copper concentrations between the fresh water flowing in a steady current, and the water after it has passed over the Cuprotect coating.

 

[Kelpie]

An aluminium hull flame (arc) sprayed with copper as is done with some galvinising processes might make an interesting test bed. Not a diy process though, and would rquire a 'certain amount' of funding..

All agog to see how you get on.

yrs.
D.

Sounds a good way to make a battery...

 

[Hydrozoan]

I agree that Hydrazoan's explanation of the behaviour of copper is very accurate except that I think you are assuming metallic copper deters fouling organisms as a consequence of copper ions in the water adjacent to the surface being protected. ...

Thanks, Pasarell, for your response and the additional information.

I wasn’t assuming that cupric ions in adjacent solution were necessarily deterring settlement – which is why I asked the question about barnacle settlement in my PS, to which you have given a response. I understand that the biochemical interaction of the patina with an organism settled (even briefly) on it will be complex, and different from that of an organism in the water in its immediate vicinity.

I pointed out that water composition can affect (a) the nature of the copper ‘patina’ and (b) the predicted free cupric ion level in equilibrium with it, to amplify your point that the antifouling effect can be impaired by pollution and mud. (In referring to the free ion concentration I am not seeking to make a point about the overall rate of copper loss from the surface, but rather referring to it as a general indicator of the potential bioavailability of the copper in the patina - to organisms near it or on it.)

You specifically mentioned physical ‘blocking’ of the surface by pollution and mud, and I wanted to explain that there are potentially strong chemical factors at work, too. Whether physical or chemical effects matter most I do not know. My guess is that either (or both) may be important in different circumstances, but perhaps your experience points to a greater importance of physical ‘blocking’?