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Handy, thanks!
Yeah, I’m filing that away…
Thanks Harvey!
This conversation came up in my build article thread. And What I suspected was right is proven by your chart. Brass rail clamps on aluminum rail is a bad idea. Your chart shows that aluminum is markedly eroded when in contact with brass fasteners.
This confirms that I will want split jaw aluminum clamps on my aluminum rail.
Thanks Harvey.
Devon, yes dissimilar metals don’t play well together when they get wet. The 2 different metals actually form a very weak battery, and one metal starts to try and plate itself onto the other metal. The metal that is trying to plate itself onto the other metal ends up just being eaten away. That was/is a known problem with people who work on aircraft, when they don’t use the approved fasteners for whatever they are fastening.
I learned all about galvanic reactions from sailing. Lots of Stainless, aluminum, and brass. Having owned several sailboats now I have learned the hard way at times. Then in the water business we are seeing the effects of galvanic reactions with brass/copper to galvanized steel connections in a particularly “hot” area of our district. The zinc in the galvanizing is definitely the sacrificial metal. These galvanized pipes are less than 20 years old and they are completely rotten and can be crumbled with the hand. It would be very interesting if it didn’t require me to get all muddy fixing them. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)
Now if someone were hell bent on using dissimilar metals for some reason I would think one could attach a sacrificial zinc anode and save their aluminum. stainless and brass should be pretty safe for a long time they almost never are the sacrificial metal. But aluminum on the other hand almost always is. (the chart plays that out). So I would think if someone just had to have brass or stainless clamps on aluminum track, I would think they could go to a local marine supply store and get some zinc anodes and attach them every so often. But they would need to be replaced. Not sure why anyone would do this but I am just throwing it out in case.
David Maynard said:
Devon, yes dissimilar metals don’t play well together when they get wet. The 2 different metals actually form a very weak battery, and one metal starts to try and plate itself onto the other metal. The metal that is trying to plate itself onto the other metal ends up just being eaten away. That was/is a known problem with people who work on aircraft, when they don’t use the approved fasteners for whatever they are fastening.
What a lot of people do not know is that this is exactly the principle by which electroplating works, well with a lot of extra help. One of the most interesting things I got to see was a process used to extract silver from Galena ore. Galena, at least the Galena in my neck of the woods, is a very pure mineral made up of mostly lead, zinc, and silver. There are a few other trace elements but very little. It is a high yield ore. Anyway, some very clever folks came up with a way to take the finely pulverized ore (concentrated) and electro-chemically separate it. By using chemistry and elctro-physics they would take various chemicals and separate the elemental metals from each other and them by using their natural charges apply electricity and have them come out of solution and stick to big copper plates acting as cathodes (electroplating). The silver in particular formed very cool crystals that looked a lot like snow flakes. Unfortunately, while a very clean technology it was a n expensive technology and it required very high silver prices. The company is out of business. But it was a great science field trip learning about chemistry.
Probably way more than anyone cared to know