galvanic reactions

[darryl]

Most of us would know that putting differing metals in contact and adding an electrolyte of some kind will cause corrosion. Could be moisture in the air, could be purposely added with different metals in the case of a battery. Because carbon fiber is conductive, this raises the question of what happens when metals are placed in contact with carbon fiber and some means of conduction is provided through exposure to the elements?

[10KPete]

The resistance of carbon fiber is so high that galvanic currents just aren't possible.

Pete

[Arcane]

Most of us would know that putting differing metals in contact and adding an electrolyte of some kind will cause corrosion. Could be moisture in the air, could be purposely added with different metals in the case of a battery. Because carbon fiber is conductive, this raises the question of what happens when metals are placed in contact with carbon fiber and some means of conduction is provided through exposure to the elements?

It's well know that carbon fiber in contact with various metals creates the problem of galvanic corrosion. Google "carbon fiber and galvanic corrosion" for information.

[old mart]

In the aircraft industry, components are assembled with various compounds in the joints and threads to seal against the ingress of water. Grease, special jointing compounds, wet primer paint and silicones, also gasket jointing compounds are used. Many of the sealers are two pack which cure especially if the surface is to be painted later where greasy types would spoil paint adhesion. There are non acidic curing silicone rtv available.

[BCRider]

Consider as well that carbon fiber products are carbon bonded with an epoxy. And that epoxy is an insulator. So in some cases where there is no actual exposed carbon material you would not have the same problem. Just depends on if the carbon product has a final dress coat of resin or not.

[Toby.R]

The reaction between a carbon fibre laminate and aluminium (even anodised aluminium) in a marine environment is explosive!
I have had to deal with three sailing boat spars where aluminium end fittings have been almost entirely converted into white aluminium oxide powder and, in the process, have expanded with enough force to blow the carbon laminate apart.

If you could entirely encapsulate the carbon laminate in epoxy resin then that would insulate the parts and there wold be no corrosion but, in the real world, where anodising gets scratched, the carbon laminate gets trimmed, drilled and sanded and then there are fastenings through the laminate into the aluminium to ensure a good connection then you get this spectacular reaction.

In the cases I have had to deal with the remedy has been either to re-make the aluminium part in carbon fibre or, in repairing the damaged spar, to re-build the damaged end in glass fibre (although component strength has to be considered here) to give some distance between the replacement anodised aluminium part and the carbon laminate.