# PtIr on stainless steel - how to get rid of the stainless ?



## orvi (Oct 30, 2022)

Hi
I recently obtained interesting material - PtIr10 relay contacts welded on stainless steel carriers. It is impossible to mechanically separate the points from carriers, so I thought about some dissolution of the stainless in acid. As I never dissolved stainless in nothing other than AR, I ask here.

It is a classic stainless, around 12-15% Cr and about 10% Ni or so. I do not exactly know how resistant is PtIr10 alloy to AR - so I am concerned some of it will dissolve into the solution during stainless dissolution. Or not, not considerably ? Honestly, I have no clue  But I want to obviate the dissolution and reprecipitation/purification hassle of Pt residues in the waste liquid - because alloy is nicely pure, and refining it in order to separate Ir from Pt has no economical sense for me.

I thought also about using mixture of nitric and sulfuric acid, but I am worried about the speed of the dissolution. Nitrosulfuric mixture should leave PtIr alloy intact, as far as my knowledge goes.

Other types of contacts are on nickel carriers or brass carriers, so no issue there, one bath in nitric does all the job for me.

If nothing pops up here, I will try all of the possibilities anyway (no other option left  ), but I wondered if somebody more experienced will chime in and give me his opinion on this  
Thanks for your replies.


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## Swissgoldrefiner (Oct 30, 2022)

What about this: 





Selection of stainless steels for handling hydrochloric acid (HCl) – British Stainless Steel Association







bssa.org.uk


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## snoman701 (Oct 30, 2022)

That's a pretty darn resistant alloy in AR. 

However, Hot HCl and time work quite well on stainless. 

Be patient though. Patient enough that you'll need to set up a reflux condenser in my experience. I have a graveyard full of broken beakers that took got that last drip from the watchglass.


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## MicheleM (Oct 31, 2022)

Could you show some pictures? Very different "melting points"


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## Yggdrasil (Oct 31, 2022)

orvi said:


> Hi
> I recently obtained interesting material - PtIr10 relay contacts welded on stainless steel carriers. It is impossible to mechanically separate the points from carriers, so I thought about some dissolution of the stainless in acid. As I never dissolved stainless in nothing other than AR, I ask here.
> 
> It is a classic stainless, around 12-15% Cr and about 10% Ni or so. I do not exactly know how resistant is PtIr10 alloy to AR - so I am concerned some of it will dissolve into the solution during stainless dissolution. Or not, not considerably ? Honestly, I have no clue  But I want to obviate the dissolution and reprecipitation/purification hassle of Pt residues in the waste liquid - because alloy is nicely pure, and refining it in order to separate Ir from Pt has no economical sense for me.
> ...


Well it depends completely on which Stainless alloy.
Some dissolves nicely in HCl and others not according to what people say in here.
Its a matter of the concentration of Ni and Cr in the steel, I believe.
I have dissolved a few Stainless items intentionally, and some by accident.
In these cases I had no issues even with cold HCl, except time that is


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## orvi (Oct 31, 2022)

MicheleM said:


> Could you show some pictures? Very different "melting points"


In the evening, I will dissasemble more relays and post some pictures. Practically, it is a miniscule disc of PtIr alloy welded onto the disc of stainless, pressed from the end of stainless wire. Like you will weld precious metal disc onto the top of the nail.


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## orvi (Oct 31, 2022)

Yggdrasil said:


> Well it depends completely on which Stainless alloy.
> Some dissolves nicely in HCl and others not according to what people say in here.
> Its a matter of the concentration of Ni and Cr in the steel, I believe.
> I have dissolved a few Stainless items intentionally, and some by accident.
> In these cases I had no issues even with cold HCl, except time that is


Well, I conducted some experiments and I am pretty dissapointed. 
I tried to cut a piece of the leading stainless wire - and drop it into the nitric acid. Immediately, it changed colour on top, and evolved small "cloud" of brownish-yellow colour (persumed some top layer dissolved). But no reaction upon heating. So I diluted the nitric with water - and practically immediately very vigorous reaction occured and whole piece dissolved in a minute or so. I was so happy to observe this. 
I dropped the contact cuttings into the small vial, added nitric - and nothin, not even a flinge of colour from them. Then, I diluted the nitric as with previous experiment - nothing.
Addition of sulfuric or sulfuric alone also did nothing. Concentrated HCL managed to slightly colour the solution after like 1 hour of heating... 
So I tried AR - to observe Pt going into the solution relatively comparatively to the carrier stainless... Chemistry is strange


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## kurtak (Oct 31, 2022)

orvi said:


> It is a classic stainless, around 12-15% Cr and about 10% Ni or so.


that is in the 300 series of SS (304 or 316 SS) & HCl should not be a problem to dissolve it

Edit to add; - though slow in doing so


orvi said:


> I thought also about using mixture of nitric and sulfuric acid,


not sure how the combination of nitric/sulfuric would work but for what it's worth - nitric (alone) does not react with 300 series SS - for that reason they use 304 or 316 SS drums for shipping & storing nitric

When I was full time refining all my nitric came in 300 series SS drums

Kurt


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## kurtak (Oct 31, 2022)

orvi said:


> I tried to cut a piece of the leading stainless wire - and drop it into the nitric acid. Immediately, it changed colour on top, and evolved small "cloud" of brownish-yellow colour (persumed some top layer dissolved). But no reaction upon heating. So I diluted the nitric with water - and practically immediately very vigorous reaction occured and whole piece dissolved in a minute or so.


Are you sure it's SS ?

Nitric alone should not react with SS (at least not 300 series SS)

sounds more like a Ni/Cu alloy - which would look like SS & would react with nitric

what color was the solution after metal dissolved ?

Kurt


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## Lou (Oct 31, 2022)

Get an XRF on the "stainless steel" and some pictures of the material.


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## orvi (Oct 31, 2022)

OK, "mystery" solved. And guess what, my fault, didn´t checked the leading wire properly in whole length 
But it was completely counterintuitive (to say for my defense). Contact points are usually welded on top of some BM carrier. This PtIr contact disc is clearly welded on top - of the other PtIr disc    I do not understand USSR technology and meaning of such complicated assembly. The second "disc" is shaped like head of the nail and it is welded right to the stainless steel wire - this time real SS. These are the things you does not think about until you came across something unusual. You see a contact point and intuitively assume base metal carrier, to which it is welded. Now I know I need to check twice 

It is very obvious when I heat the wire with contact discs still in place over a lighter. Stainless steel gets nicely blue, but PtIr is still silver coloured without any oxidation (as expected).

Sorry guys for unnecessary thread. At least, I add the photo of the contact as it is in the relay. Hard to focus with my phone, but I think you will see it 

12 screws to fully dissasemble one piece... 4 very tight, I cracked the tip of my screwdriver half through the lot  No other possibility to get in. Very tiring, but rewarding  Since I am waiting for a lot of similar ones, but this time with PtRh10 contacts.


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## orvi (Oct 31, 2022)

kurtak said:


> Are you sure it's SS ?
> 
> Nitric alone should not react with SS (at least not 300 series SS)
> 
> ...


Yeah, it wasn´t true stainless. I explain. 
I measured wire from one piece, and it clearly shown classic stainless, CrNi and iron, and other minor base metals. But I forgot to be careful with this material - as commies put inside anything they had in hand  All relays are marked with the same numbers, yet material of leading wire to the point differ. The one I dissolved in nitric was some iron alloy with little bit of nickel, and whole wire was nickel plated.
Even the screws and internal parts were clearly different 

Solution was brown.


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## orvi (Oct 31, 2022)

Much more fun with these... 350pcs... Took me good two afternoons to process them  At least these were consistent inside. And leading wires to the contacts are copper, that´s much more nice.


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## snoman701 (Oct 31, 2022)

So is this stuff hard to find over there? 

I save relays out of everything, and I know I don't have anything that "exotic". These are like the needle in the haystack when all the common relays are just silver contacts right?


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## orvi (Oct 31, 2022)

snoman701 said:


> So is this stuff hard to find over there?
> 
> I save relays out of everything, and I know I don't have anything that "exotic". These are like the needle in the haystack when all the common relays are just silver contacts right?


Yes it is.

We had domestic "brand" TESLA back in the days in my country, which manufactured all sorts of components, including relays - but they never used other PGMs than palladium in their goods. Contacts also from that era were mostly silver-cadmium or gold plated silver, for high end precise small relays also gold plated AgPd30 and then in the next category Au70Ag25Ni5 or AuNi5. Also precise switches had contacts from AgPd30 (some).

But it was a different story in soviet Russia. They had plenty of PGMs from mining concentrates of CoNi ores - not that willing to share with their "friendly" eastern countries. Ecology was non-existent, labor force expendable... So they did it differently. Nearly all semiconductors and pins made in soviet Russia were significantly thicker (and many times completely unnecesarilly) plated with gold (famous ceramic SMD chips often running nearly 25-40g/kg etc.) than in other eastern-block countries. In turn, they more often used PGMs (which are harder to plate... lacking technologies  ) for contacts. They overcome lacking technology for thinner and more consistent plating with just more precious metals  Same with MLCCs, some types running nearly 70g Pd/kg - not just ceramic, but whole resin-coated pieces with soldered leads.

But yeah, in terms of level of "exotic", these aren´t common. Never found in usual consumer electronics, but mainly in old military equipment, laboratory measuring machines, computers etc. Still, majority of their relays had silver contacts  But it is hard to find old Soviet household appliances - there weren´t many even in the times they were manufactured  On the other hand, some types of PGM MLCCs are commonly found in old soviet TVs.

This is what happens when you have country insanely rich in natural resources, without functioning and sane government. Completely non-sense things then start to happen.
The above relays with double-disc PtIr contacts weigh around 150g each (and they are rated for like 1 or 2 amps, photo below). Casing is steel, but copper plated on the inside and outside. Inside, there are two coils bolted into the cast aluminium body, apparently to save some weight... But then on the top is like 6mm thick stainless steel plate holding the contacts  screwed with 4 screws, and in between there are two magnets. And these were used in "top" military equipment quite often. Not to mention two heavy steel cylinders inside the coils and upper like 5mm steel plate where they are screwed tight.

Simple switching relay. You need to connect 5 leads from it - 2 for power for the coil, 3 for contacts. Yet the socket has 16 pins  And to kill it straight out - you use PtIr or PtRh contacts for the top reliability, and then plate the socket with silver (...), and insert it into the female socket, which isn´t plated at all  well done

But not to be all negative, some individual components, like small relays in the picture above, they are practically immortal. Same with MLCCs they manufactured.


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## MicheleM (Nov 1, 2022)

Wow , weird stuff, i am really curious to know for which kind of technology they were used for.


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## orvi (Nov 3, 2022)

Some of the small relays have also PtIr contacts... But guess what  maybe folks decided that: "Man, is it enough ? Looks pretty cheap to me, we need it more high-end..." - and gold-plated the PtIr contacts  I am not joking, this is real thing. 2 out of 6 contacts in the relay are gold plated PtIr. There, my mind just doesn´t get what is going on. Does it make better contact ? Why would you do this ?


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## Lou (Nov 4, 2022)

At least they appreciated the aesthetics of it.


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## orvi (Nov 4, 2022)

Lou said:


> At least they appreciated the aesthetics of it.


When you are working with this era material, everytime you came across something completely new to you. Altough I know about these relays some time, I never wondered they contain gold plated PtIr inside. I knew about interesting Pt content, that is why I purchased some for the test of yield.
And I must admit as nice as they look they are PITA to dissassemble. You need to extract them from the boards in the way you do not mangle the steel casing (try to explain that to the guy you are buying from  ). Otherwise you need to peel the case off with pliers. And it is horribly inefficient and slow. Only sane way is to heat the casing with heatgun to melt the solder and pull the casing out of the base. For few dozen mg of Pt inside, I still calculate if it is worth the hassle


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## Lou (Nov 4, 2022)

I often say that most things PM containing weren’t engineered to be easily and efficiently recycled


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