Silver contacts question

[Ianf82]

Hi, new here. I gathered some silver contacts a while back. Trimmed them as close as possible and used an ap solution to dissolve base metals. After staying in the solution for quite some time, and even trying with a new solution, I am still left with quite a bit of non silver attached. It is copper in color. Also, some pieces are magnetic. What could these remaining metals be, and what is a way to get rid of them? I havent been able to find hydrochloric acid anywhere, so only tried muriatic acid/hydrogen peroxide so far.

 

[FrugalRefiner]

I havent been able to find hydrochloric acid anywhere, so only tried muriatic acid/hydrogen peroxide so far.

They are the same thing. Muriatic acid is an older name for hydrochloric acid. Some may argue that muriatic acid is less concentrated than hydrochloric acid, but the acid is the same HCl.

Dave

 

[Ianf82]

Should A/P not remove all metals except the silver from these contacts? The reddish colored parts of my mix appear to be copper, but I may be wrong. I want to be able to melt these down into a button, but do not want it to be contaminated. Any tips on how to proceed?

 

[FrugalRefiner]

Silver contacts are rarely pure silver. They are almost always an alloy of silver with any number of other metals. To end up with a pure silver button, you will need to refine the contacts.

Dave

 

[sena]

Mostly tungsten ,melt the lot and pour in shots .. you will be left over with w (tungsten)
Use dilute nitric with mild heat under fume hood to dissolve the shots

 

[Ianf82]

Mostly tungsten ,melt the lot and pour in shots .. you will be left over with w (tungsten)
Use dilute nitric with mild heat under fume hood to dissolve the shots

Is there a way to do it without nitric acid?

 

[kurtak]

Mostly tungsten ,melt the lot and pour in shots .. you will be left over with w (tungsten)
Use dilute nitric with mild heat under fume hood to dissolve the shots

Although there "may be" some tungsten points in that mix (its hard to tell from the pic) MOST of what I see are NOT the tungsten/silver type point --- I say that because from what I see most of them show the rivet that riveted the point to the bus bar

I have done hundreds of pounds of contact points over the years & I have never seen the tungsten/silver type contact points that were riveted to the the bus bar - they are always brazed to the bus bar

Although I can not really see it in the pic - IF - some of them are the tungsten/silver type points they can/will be identified by a "waffle" like pattern on the back side of the point where the point is brazed to the bus bar

those "need" to be sorted out & separated from the non tungsten/silver ones because they "need" to be processed different

tungsten/silver type contacts run between 60 - 70 % tungsten & 30 - 40 silver & are made in a process where the silver is sintered into a matrix of the tungsten with the silver --- in other words they are not a true alloy but rather the silver is tied up in a matrix of tungsten sintered together (with the silver) under high temp & high pressure

tungsten has a melting point of 6,192 degrees F (or 3,422 C) so unless you have away to reach those kinds of temps you certainly are not going to be able to simply melt them & pour them to shot

The only way I know of processing the tungsten/silver type points is to literally BOIL them in nitric acid to "leach" the silver out of the tungsten matrix

Depending on the batch size & the size of the contacts it can take 12 to 24 hours of literally BOILING the contacts in nitric acid to get all of the silver leached out of the tungsten

The tungsten/silver type points are most commonly found in circuit breaker "switches" (like the switches found in your house electrical switch panel) but will also be found in LARGE industrial switch panels --- in other words "hand" thrown switches rather then electric coil operated switches/disconnects

electric coil operated switches/disconnects are normally a true silver alloy & can be processed as any other silver alloy

the point being the tungsten/silver points are not an alloy so the process to get the silver "out of them" is different then the process for true silver alloy points

Kurt

 

[kurtak]

Is there a way to do it without nitric acid?

if you want to end up with "pure" silver you NEED nitric acid - that's because the "points" them selves are not a pure silver but some kind of an alloy (& there are "many" point alloys) - "normally" they run 80 - 90 % silver

so even if you can get rid of all the base metals (with the AP process) & you then just melt the points they wont be pure silver

you can get them cleaner by continuing to run them in the AP process until more of the base metal is removed but that's all you will do is get them cleaner

Kurt

 

[Ianf82]

Thanks for the reply. Some are riveted and some were brazed. Haven't noticed waffle pattern on any. Almost all were from modern appliances such as stoves, washers, dryers, etc.

 

[Kubik_Rubik]

Hello, I need advice.
I have a large number of silver contacts from the relay on a copper base. I would like to first remove the copper base with AP solution first, before treating the contact in nitric acid. Some of these contacts also contain palladium, it is safe to use AP solution. Or can palladium be dissolved? I would use little H2O2 and a bubbler. I only have limited sources of HNO3, but I would not like to lose palladium.
Thank you for answer.