Metal Compatibility

[Archena]

Okay, I know certain metals do not get along - brass and steel really don't like each other (stupid el cheapo handyman repairs ) but I don't know which ones are safe to use together. I couldn't find anything when I searched - probably not familiar enough to narrow down the search (well, that and I'm about to drop from exhaustion). I've got to attach copper to wood (it's a craft thingie so I'm using screws on flattened tubing). I'm thinking brass will work with copper (did I mention brass hates steel? Killed the water heater here... Stupid tightwad 'repairs'...) but I'm not sure. Any idea where I can find out?

Thanks!

[edschmidt]

Re: Metal Compatibility

Search for nobility chart, or galvinization chart, the metals which are closest together do not react, the ones that are farther apart do. Suprisingly steel and stainless steel are quite a bit apart, but aluminum and steel are close.
Good luck

[Archena]

Re: Metal Compatibility

Thanks! I really appreciate it!

[gjbingham]

Re: Metal Compatibility

Gold won't react with anything. How about a gold door?

You'd think that brass and copper would get along pretty well, but probably over time, there'd be some corrosion. I wonder if you can get copper screws?

Edschmidt correct in his post above. Metals close together on the chart do not react as much (but do react) as those farther apart. Keeping them dry, or "out of solution" will extend their life.

[Archena]

Re: Metal Compatibility

Gold is a bit much.

I've never seen copper screws - wouldn't copper be way too soft for that?

It's a votive wall display/mirror made out of an old window with the copper used for votive holders. I'm seriously thinking about sealing the copper (wonder if polyacrylic would work?) but that wouldn't help since the screw will strip that off as it goes in.

Is this what you mean? Galvanic and Corrosion Capatability Chart - Engineers Edge

Thanks for the help guys - I really appreciate it.

[dmun]

Re: Metal Compatibility

Brass and steel don't get along together? This is going to be news to about three centuries of clockmakers who attach brass parts with steel fasteners, and alternate brass and steel gears to take advantage of natural dry lubricity of the sliding surfaces. This is true even in clocks working in "chalenging" environments like church towers and parking meters.

I've only seen "galvinization" happen once, when a client had me make a part from a zinc alloy - It grew hair like a bad battery in contact with another metal.

[Archena]

Re: Metal Compatibility

:shrug: The steel nut turned to powder on the brass drain - I'd say something didn't get along.

I'm not sure what the connector to the water heater was (I'm thinking brass) but it also disintegrated and took out the water heater while it was at it.

[edschmidt]

Re: Metal Compatibility

When I first learned about this process in an wiring class it was in refereance to the debacle that occured when there was a copper price spike in the 1970's. They decided to go with aluminum wiring which was substantially cheaper. This would be fine if not for the fact that almost all appliances have copper cords, the aluminum would corrode, and soon heat up and cause fire. Another example is in ships which have steel hulls and brass propellers. The salt water actually accelerated the process, but the props kept getting smaller, and the ship would have a lovely brass coating, I believe they fixed this by applying an electrical charge to the ships hull. Also freeze plugs in automobiles. They are brass attached to an iron block. Ive replaced a few of these which disintigrate if you dont change your antifreeze often which has an anticorrosion agent.

The other way this works is when you take a metal which is high on the chart and attach a metal which is lower. The lower nobility metal is called sacrificial. In other words if there is to be corrosion the lower metal will take the hit and desintigrate long before the higher metal begins to degrade. Thats why zinc is attached to steel to prevent corrosion. In buried water tanks they often attach a zinc bar and every few years replace the bar to stop corrosion of the steel. Youll find one of these in your water heater.

[Archena]

Re: Metal Compatibility

I've heard about that. They do it in sluss gates and on caskets as well.

Weird. My drain appears to be fine but the nut literally fell apart in my hands when I removed it. I know it was steel - I'd put it on 7 years ago.

[cvdukes]

Re: Metal Compatibility

You'll want to use "silicone bronze" fasteners for your craftie thing with the copper tubing. Silicone Bronze is an alloy of copper,tin, and steel. Widely used in classic boat re-building as it doesn't react with other metals (another hobby). Some of the better hardware suppliers carry them... if not check with Jamestown Distributors (where you can also get copper nails and tacks).

[Archena]

Re: Metal Compatibility



Thanks!!!! I really appreciate it!

[christo]

Re: Metal Compatibility

Could there be any chance the nut was pot metal or zinc?

- that would explain a lot to me - I've seen a lot of cast metal nuts as well as sheet metal

[Archena]

Re: Metal Compatibility

I don't know what pot metal is. I've never seen zinc take a polish (dunno if it can) so I really doubt zinc. I wouldn't have thought it was sheet metal - it had an interior concave which I wouldn't expect from a punch. I remember it being steel. I'll check when I go back to the hardware store - they still carry that brand...

Or, I might still have the 2 inch nut I bought in the package. I'll check.

[fortran]

Re: Metal Compatibility

If you connect dissimilar materials in the presence of an electrolyte, corrosion can always happen. Pure water at pH 7 isn't a very good electrolyte, but most water has dissolved salts in it of some kind. Even heat treating a metal can cause it to become different enough from an un-heat treated version of the same metal, to make it look different. What is happening is an electric circuit is being set up, with some of the current traveling through the electrolyte and then returning through the dissimilar metals. Brass gets used in many kinds of plumbing, because it is lousy at conducting electricity. However, it is still better than things like plastic at conducting electricity.

The best thing to do, is use the same material. Next best, is if you have to use different materials, separate them with something like plastic which doesn't conduct electricity (is a dielectric).

[Xabia Jim]

Re: Metal Compatibility

This is a huge issue in the boating industry where you have salt water and metal thru-hulls, steel shafts, brass props, etc. If stuff corrodes, boat can sink... They attach the sacrificial zincs at various places around the boat to protect (slow down) this corrosion. These often need to be changed out more than once a year.

Years ago I worked for an acid distributor. They had one truck go out with a load of nitric acid, I think in a stainless steel tank truck but someone had put a brass plug somewhere....made quite a mess.