Properties of "coin silver"?

I thought 'coin silver' had a lot of nickel in it.

You might want to talk to a low-temperature engineer who's had experiences with non-magnetic materials. If you need something structural a common alloy is cupronickel, the nickel does not form a local moment below about 20 percent or so.

What's your specific application, and how low do you need the moment to be?

Jim

The country of the coins will be central to getting a good answer. If it's USA'n, then I'm sure there are FAQs out there which google could scare up for him. Other large countries as well, I would think.

Nope------it's 10% copper, 90% silver, at least here in the US. It was the standard for striking silver coins, likely the reason it's called *coin silver*. Canada uses a lower silver content, I think 80%. Other countries use varying percentages.

There is no nickel in coin silver, never has been, although nickels, during the war years, were made from silver and manganese, with no nickel content. It's easy to distinguish the war years nickels (aside from looking at the dates) because the mint marks are very large. Likely none left in circulation now, though. They were probably all taken out of circulation when the silver content exceeded their face value, in the same manner the rest of our silver coinage experienced.

Harold

I find one every 5 years or so in circulation. Instantly recognizable due to the green-ish coloration.

The term "coin silver" has a specific meaning when used in the electrical contact industry - and that is quite different than the term when used in numismatic terms.

I seem to recall that somebody on RCM a long time ago researched this, and found there was an appreciable amount of Ni in electrical contacts that were called 'coin silver' and the term had its roots in germany from long ago.

I suspect the original poster was not refering to silver gotten from coins for his apparatus. The term seems to be a bit vague, but the

90/10 cu/ag number you cite seems pretty much the standard. If that meets his needs, it will of course be non-magnetic - but there may be other more mechanically desirable materials out there.

I still seem to remember somebody here posted historic details on that alloy that included Ni though.

Jim

Are you shure that you don't confuse this with "new silveer" (Neusilber) that has no silver at all. It is als called Alpaka:

77-30% copper 11-26% nickel 12-44% Zinc

and is used for contacts.

just guessing. If I'm off, ignore me.

Nick

On Mon, 11 Jul 2005 18:44:01 -0500, snipped-for-privacy@ameritech.net wrote in Msg.

Mechanical as regards strength, hardness, and machineability.

Thanks, robert

Hardness Rockwell 15T, annealed 70, cold worked 83 Electrical conductivity %IACS 85 Ultimate tensile strength (psi), annealed 40000, cold worked, 75000 Elongation % in 2in , annealed 32, cold worked, 4

As to machinability, they do not list it, so this info is anecdotal based on my own limited experience.

Fine silver maccines about like copper. Sterling silver machines about like 260 brass Coin silver machines slightly better.

Paul K. Dickman

Use aluminum, it will be better than Cu/Ag 90/10 alloy in all of those catagories.

Jim

They're right tough on contact burnishers!

LLoyd

But probably horrible in the way of contact value, however. Aluminum enjoys forming aluminum oxide rapidly---which is not known for its good electrical properties.

Heavy duty silver contacts are made from tungsten powder and silver------which yield the best of all worlds. Don't have a clue how they'd machine, but I can't help but believe they'd be tough on tools.

Harold

I can well imagine, having machined tungsten on more than one occasion. It's not for the feint of heart.

Refining the tungsten contacts was interesting. A prolonged boil in nitric acid and water to remove the silver was required. Interestingly, some of the contacts maintained their form, while others disintegrated. You could tell when the silver had been totally removed by breaking a contact. Those that broke easily were free of silver, while the others would have a distinct line in the center, where silver was still present.

Harold

Umm, Harold, that wasn't one of the properties he listed.

Aluminum

They also use to be made from sintered silver, Wo, and Cd. I knew a group at GTE labs that were trying to eliminate the Cd from those.

Jim

Chuckle!

Just thought the information might be useful. I can see it all now. An aluminum oxide grinding wheel used as a contact. Somehow, it sort of loses something along the way. On the positive side, it doesn't arc much!

I encountered the cad filled ones occasionally. It blended so well with the silver that you weren't aware of its presence, yet there was a loss in weight when the overall mass was processed. Had to be Cd. I can't help but think that they were in better quality house switches and other light duty devices. It's been too long to remember.

Harold

These were contacts for circuit breakers for GTE's product line.

Back in the early 80s there was a realization that putting a lot of cadmium in products like that was a bad idea, even if it made the breakers (contacts) work really well.

When breakers close they don't dry switch, there's a period when they have to arc a bit to make good contact for passing high current. My understanding is that somehow the Cd would flash on opening, and make it easier to close for the next cycle.

They were trying to replace them with the above-mentioned Ag/Wo sintered contacts I think. The shop was very good at pressing and sintering stuff.

The guy doing the research ironically lived in Woburn, Mass, which was the town that had its wells all contaminated by WR Grace, et al. He used to bring his drinking water home from the lab in a gallon jug every night. I thought it was ironic anyway, here was a guy working to eliminate a toxic metal from a product, but at the same time he had to deal with corporate irresponsibility in a very concrete fashion.

Jim