Originally Posted by
Kontact
Lots of things work - including simple grease. But if you are looking at the chemistry galvanic corrosion, steel, copper, titanium and carbon are all more noble than aluminum. Copper is preferred for higher temperature uses, but if you are concerned about aluminum cups it makes sense to use aluminum paste because it is as anodic as the aluminum. Even better would be magnesium paste would be even better as it would be truly sacrificial compared to aluminum, but that kind of paste is hard to find.
Copper is neither an insulator nor an anode, but it is an excellent conductor.
My experience differs. Greased bolts in aluminium things get stuck after a while, while
"copper pasted" bolts don't.
Of course, copper paste is good for high temperatures (as well). I've been using it for years on bikes and motor bikes. The paste I use is this one (
link) - I'm not selling it, nor advertising, that's just the one that can be bought at a reasonable price locally and for which the tech data is available. The downsides are colour (it looks like rust, copper coloured) and it's hard(er) to wipe off. That is the reason why, in stead of explaining to customers that their bolts are not rusted, I've started using this paste (
link) - it is kaolin and titanium oxide based, white colour, easy to wipe off wherever it's not needed. I still use copper paste on disc brake caliper bolts (and pad slides on motorcycle), because of the high(er) temperatures. The copper paste is noted to have a -30 to +1100 C temperature range, while the "white one" is for -30 to +200 C.
Both prevent galvanic corrosion between two steel parts, two aluminium parts, as well as steel and aluminium combination. That's been my experience for the past 10+ years at least. I'm sure a chemist worth their salt could provide an explanation on why it works better than ("ordinary") grease.
EDIT: for full disclosure - haven't worked with the white paste for more than 3 years, the copper one I've been using for over 10 years and no problems so far. Tech experts from the company that sells the pastes have said that for the intended purposes (preventing bike bolts from galvanic corrosion on steel, alu and steel/alu combination) they should both work equally well. Have consulted one "independent" source before application (a Dr of metallurgical engineering, not a chemist) and they have confirmed the info and recommendations.