SaltyStaves wrote:Skipper1953 wrote:
Would you mind actually explaining what it is you think would be a problem?
You have friction, heat and liquid and two very different metals in contact with each other.
Between two SS ferrules its fine, but I wouldn't want to test it with my one-of-a-kind copper still head.
I have deformation issues with the PTFE gaskets that I have to manage, but at least I know that they are completely inert to my still head.
You've already got a Stainless clamp touching your copper flange. The only difference is that this is outside of the still, so you don't have vapor/liquid in contact. But then, for galvanic reactions, that's pretty important.
Here's a document about the interaction of stainless with other metals. In general, copper and stainless seem to be pretty safe together. They point out that stainless and copper are often used together for potable water, "as both materials have similar corrosion potential in potable water." They also are pretty compatible in seawater. But then what we have in our stills isn't exactly potable water or seawater. And the electrolyte does make a difference. Unfortunately, I'm not finding much info on the corrosion potentials of copper and/or stainless in combinations of water, ethanol, methanol, acetone, fusel oils, and various esters and other congeners. But given that they have a very low difference in potential in all of the electrolytes I've found, I suspect they're also pretty safe together in a still.
In general, copper and stainless are fairly close to each other on the "nobility" scale (both are fairly high), so they won't react much with each other.
Here's a galvanic table. Copper is #33 (of 92), and 304 stainless is #40. So they're pretty close. And closesness is what matters for having minimal reactions.
Also, the relative areas of copper to stainless matters. A small amount of stainless (the cathode) in contact with a large amount of copper (the anode) will result in less corrosion than lots of stainless in contact with little copper. In this case, there would be microscopic stainless particles in contact with macroscopic copper flange, so that would make the potential for corrosion even smaller.
Plus, the steel in the Tuf-Steel gaskets seems to be pretty much encased in the PTFE, so I doubt there is much actual stainless to copper contact.
So it looks to me like this would have very little potentian for galvanic reaction. But no one is forcing anyone to use these things, so make your own decision.
Disclaimer: I'm a software engineer, not a metallurgist. My understanding is based largely on what I've read in the last hour or so.
