Silver Tantalum Capacitors - problem with plastic coating

[snoman701]

I am in what feels like a no-win situation. I've got a number of silver tantalum capacitors.

I have the choice of going direct to nitric acid. This works, but it makes a huge mess between the rubber o ring that's in there as well as the plastic overcoat.

I figured out that if I tumble the tantalum anodes after the fact with a little excess of water, the thin plastic overcoat sort of floats to the top...but then I'll also find the occasonal capacitor that didn't get touched by the nitric because the plastic coating was so tight.

The other option is a light burn. This makes these little guys pop like angry sulfuric acid spitting popcorn. I did this once and only once.

Final option and one I really don't want to do is mechanically cut the plastic overcoat. I really really don't want to do this.

Just curious if someone has a shortcut on these. I've done a lot of them already, but I've been putting off the rest of them for a while.

Any suggestions?

 

[slsmp40]

Can you post a pic of your caps? You are not working with the yellow or black smc type are you? If so a mini jaw crusher works great.

 

[macfixer01]

It sounds like Jacob is probably talking about these type? For me, I’d probably bite the bullet and just cut them with an X-Acto knife. Maybe you could rig up some kind of jig, slide them through a trough or tube with a blade attached and push a line of them through with a rod? That would require the blade position being adjustable and sorting them by diameter though. What about one of those hot wire strippers for removing insulation? I’ve never actually seen one demonstrated, so I don’t know if that’s applicable. Seems like just pressing a hot piece of nichrome against it might work if the case doesn’t draw too much heat away? Something like the way a bag sealer is arranged with a non-flammable backing to hold pressure against the wire. Last thought was maybe you could pass them through one of those mechanized wire strippers? But the short lengths could be a problem as well as the kind of cases which have a groove.

 

[anachronism]

I slice them with a stanley knife which allows the Nitric to get in. They'll then denude themselves during the Nitric dissolve quite happily.

 

[snoman701]

Sounds like my current method is actually more efficient.

 

[Yggdrasil]

Sounds like my current method is actually more efficient.

Can you tumble them with some abrasive elements so the coating become scratched enough for the Nitric to get an attack vector?

 

[snoman701]

I could, but I'd still have the thin plastic to deal with. I was hoping for someone to say "hey, that plastic is soluble in beer". No such luck.

 

[Yggdrasil]

I could, but I'd still have the thin plastic to deal with. I was hoping for someone to say "hey, that plastic is soluble in beer". No such luck.

Hmm, I can see better use of beer

 

[snoman701]

Can you post a pic of your caps? You are not working with the yellow or black smc type are you? If so a mini jaw crusher works great.

Are you actually doing these in quantity? Seems like a tiny amount of silver to make it worthwhile.

 

[orvi]

I could, but I'd still have the thin plastic to deal with. I was hoping for someone to say "hey, that plastic is soluble in beer". No such luck.

Test that plastic with various solvents. There is low chance it is some soluble plastic. Also, if it is soft PVC (which is my bet), it will swell in solvents like DCM or maybe also others like toluene or acetone. Then, it will be easy to just "pop" them out of the plastic sleeve like pits from cherries.

I never had such problem since local AgTa caps aren´t coated in the plastic shrink tube. But once the acid find the way to it, it will penetrate. I will mangle them in the cement mixer with something sharp and heavy, like rough sharp cut steel pieces. This will maybe make the access for the nitric. And then you will be left with plastic/Ta mix, which can also be run through some kind of tumbler/mill with sharper material to liberate it some more.

I do not know at what temp Ta start to burn, but another option will be just pyrolyze without access of oxygen. Ta won´t burn without oxygen and if you can cook it nice and crispy black, that will tumble away easily. But if you will have PVC coatings, I do not know how it would behave since copious HCl is liberated when PVC burn - and Ta will certainly react with HCl.

 

[adam mizer]

Like orvi states maybe pyrolyze.
180°F to 500°F

---

Compared to other thermoplastics like polyethylene and polypropylene, PVC plastic exhibits a comparatively lower melting point. Its melting point typically ranges from 82°C to 260°C (180°F to 500°F) and may vary based on the specific grade and formulation used.

Also theres that little rubber cap.
I thought the body is made from aluminum.
Aluminium / Melting point
1220.6 °F

And tantalum is super high to melt.
5462f degrees.

 

[snoman701]

Tantalum won't burn or dissolve in AR, but it will oxidize and I'd rather not if I can avoid it. There is a small premium for colored tantalum anode over blacks.

 

[macfixer01]

Like orvi states maybe pyrolyze.
180°F to 500°F

---

Compared to other thermoplastics like polyethylene and polypropylene, PVC plastic exhibits a comparatively lower melting point. Its melting point typically ranges from 82°C to 260°C (180°F to 500°F) and may vary based on the specific grade and formulation used.

Also theres that little rubber cap.
I thought the body is made from aluminum.
Aluminium / Melting point
1220.6 °F

And tantalum is super high to melt.
5462f degrees.

They use aluminum cans for ordinary electrolytic capacitors. The cans on tantalum caps are always made from either tantalum or silver aren’t they?

 

[adam mizer]

They use aluminum cans for ordinary electrolytic capacitors. The cans on tantalum caps are always made from either tantalum or silver aren’t they?

Attachments​

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Wow I did'nt know that, great information.
Years ago I tossed one 3" long one away after tearing it apart didn't know any better.
Then tried to burn up the internal stuff, and threw away the can.
Thank you for showing this macfixer.

Is this picture below a tantalum capacitor?

 

[eaglekeeper]

I could, but I'd still have the thin plastic to deal with. I was hoping for someone to say "hey, that plastic is soluble in beer". No such luck.

Maybe Everclear instead.

Everclear (151 proof), and I have a long-standing agreement to stay away from each other.

 

[macfixer01]

Is this picture below a tantalum capacitor?

That’s a good question and sometimes tantalums can be really confusing. As many times as I’ve looked through the Google photos of them before, I’m thinking now I’ve probably thrown away some tantalums that I didn’t think were? For the heavier metal-cased types a lot of times you just know on sight that it’s a tantalum for sure. Of these lightweight ones that I’m unsure of, I would have normally said that only the ones with the very thick red plastic end section are tantalum, but that the type you have was not?

When I was looking for the attached photo though, I Googled red tantalum capacitor. If you do that and click on images, it does show some tantalums that look pretty much just like your capacitor! According to Google, both of these photos show tantalum capacitors.

For the heavier metal-cased ones I normally expect to see either a short straight tantalum lead coming out the + side with a copper lead attached to that, or a larger weld bead right next to the seal with a copper lead attached. Not in these types though, which always seems odd. So in any case, I can’t definitely say yes or no for your cap. You should try to look up the part numbers that are on the one you have to see if you can find them listed anywhere? Or try to match up the brand and markings to one of the photos on Google, since often the capacitors don’t even have actual part numbers on them.

 

[anachronism]

Mac it's the neck and the weight that make the difference in terms of separating the solid silver cased ones. They feel really heavy and have that deeper neck.

 

[Alondro]

That’s a good question and sometimes tantalums can be really confusing. As many times as I’ve looked through the Google photos of them before, I’m thinking now I’ve probably thrown away some tantalums that I didn’t think were? For the heavier metal-cased types a lot of times you just know on sight that it’s a tantalum for sure. Of these lightweight ones that I’m unsure of, I would have normally said that only the ones with the very thick red plastic end section are tantalum, but that the type you have was not?

When I was looking for the attached photo though, I Googled red tantalum capacitor. If you do that and click on images, it does show some tantalums that look pretty much just like your capacitor! According to Google, both of these photos show tantalum capacitors.

For the heavier metal-cased ones I normally expect to see either a short straight tantalum lead coming out the + side with a copper lead attached to that, or a larger weld bead right next to the seal with a copper lead attached. Not in these types though, which always seems odd. So in any case, I can’t definitely say yes or no for your cap. You should try to look up the part numbers that are on the one you have to see if you can find them listed anywhere? Or try to match up the brand and markings to one of the photos on Google, since often the capacitors don’t even have actual part numbers on them.

I've found some that were tantalum FOIL that had aluminum cases. They looked similar to the aluminum foil ones, but had that red band around the positive terminal. But once cut open, the dark, brittle foil spool was clearly NOT aluminum. It was also rather small and the rest of the space in the case was taken up by electrolyte-soaked paper.

 

[anachronism]

I've found some that were tantalum FOIL that had aluminum cases. They looked similar to the aluminum foil ones, but had that red band around the positive terminal. But once cut open, the dark, brittle foil spool was clearly NOT aluminum. It was also rather small and the rest of the space in the case was taken up by electrolyte-soaked paper.

Agreed- the weight is the key to telling the difference.

 

[snoman701]

no, there are brass cased ones as well

Is this picture below a tantalum capacitor?

Not a tantalum capacitor.