# Refining silver contacts question



## mike5ive (Feb 25, 2022)

Short and sweet, just did my first batch of contacts, 1 pound, got 6 oz back using the nitric, distilled water and cementing out with copper method. Now then there are a good many contacts left that will not dissolve, not even boiling in 70% nitric acid with no water added they wont dissolve. What gives?


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## nickvc (Feb 25, 2022)

Welcome to the forum Mike.
Many contacts are tungsten sintered, that looks like a waffle pattern to give them strength , they can take some dissolving but should dissolve over time, when done the internal structure looks like wires.


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## kurtak (Feb 25, 2022)

nickvc said:


> Welcome to the forum Mike.
> *Many contacts are tungsten sintered,* that looks like a waffle pattern to give them strength ,



Per the bold print - correct - the W/Ag contacts are a matrix of tungsten sintered with the silver (in other words they are *not an alloy* of W/Ag but rather a combination of W & Ag powder sintered together under heat & pressure --- the silver in them will range from 30 - 40 percent

Tungsten does not solder/braze well so the waffle pattern (rough surface) on the back of them is there to help make a good bond of the point to the bus bar when soldered/brazed 


nickvc said:


> they can take some dissolving but *should dissolve over time,* when done the internal structure looks like wires.



The tungsten does not dissolve --- because the silver is a *fine powder* sintered together in the matrix of tungsten the silver has to be leached out of the tungsten

To leach the silver out you have to* literally boil* them in nitric - that leaching (boiling) process depending on the size of the points &/or the batch size can take a full day *or longer* to leach all the silver out of the tungsten

I will *try* to post more when I get more time 

Kurt


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## mike5ive (Feb 25, 2022)

Well I'm not even going to go through all the trouble of that hell an oz. or so just to get a few grams of silver. I wonder if anyone will want them if i list for sale on ebay


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## nickvc (Feb 26, 2022)

You may get an offer on here if you show pictures and weights.


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## mike5ive (Feb 26, 2022)

Thank you for that and yes I imagine so however after posting that question I googled the price of tungsten and it would seem that a person can purchase a pound of the stuff for the price of a pack of chewing gum and thus a simple postage stamp would be worth more than I have of the stuff LOL


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## nickvc (Feb 27, 2022)

You misunderstood what I meant unless you have hard boiled the tungsten silver contacts there will still be silver to recover, if you just have what looks like a jumble of wires left you have all the silver out, from memory I believe they yield around 40% silver.


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