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Author: Subject: Repair tungsten wedding ring
boringneil
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[*] posted on 19-7-2017 at 05:34
Repair tungsten wedding ring


Hi all this is my first post but this forum looks awesome.

In my foolishness I heated my tungsten wedding ring in a Bunsen flame to show a class of 14 year olds that it wouldn't melt despite glowing bright red.

Well after I did it I dipped it straight into a beaker of cold water so I could put it back on my finger.

The beautiful shiny ring is now the colour of pewter!

I'm led to believe that tungsten wedding rings are ACTUALLY tungsten carbide?

In any event I've tried vigorous rubbing with all types of sandpaper to no avail.

I'm thinking a dip into some kind of acid or maybe aqua regia might take off whatever oxidation I've applied to the surface?

Any help gratefully received!
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woelen
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[*] posted on 19-7-2017 at 06:19


This indeed is not the smartest thing you did.
Probably you have something to explain to your wife ;-)

What happened is formation of a layer of oxide. WO3 is the standard oxide, but in the (very very thin) layer at the interface between the WO3 and the underlying metal, there is a mixed layer, with composition WOx, where x gradually goes from 3 to 0 when going from the oxide layer to the metal. These compounds are dark blue, nearly black and may give your metal a dull appearance.

WO3 does dissolve in acids, like HCl, but the deeper lower oxygen content material will most likely be very hard to remove.

You _may_ have success with very dilute HCl, to which some H2O2 is added. You could take 3% H2O2 (e.g. 10 ml) and add 1 ml of 10% HCl to this. This makes a mildly acidic and mildly oxidizing solution. You could put your ring in this and leave it there for a few tens of minutes.
Such a weak solution is slow-acting, but at least it is safe. It will not eat away your ring in minutes and you can watch what happens.
Do not expect too much of this treatment. It is more of the sort of: if it does not work, it also does no harm. You can give it a try.




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Pok
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[*] posted on 19-7-2017 at 06:26


Try to put the ring in a NaOH solution. If this doesn't work, you could polish it with diamond powder. A high melting point doesn't mean that a material is not attacked if you heat it in oxygen! Tungsten carbide gets oxidized at higher temperatures, probably to WO3 (an maybe additionally to CO2). The dull surface coult either result from this oxide layer (removable with NaOH solution) or from the material loss (the WC got "etched"). The second case seems more probable to me and then you can only get the shiny surface again if you polish it with something equally hard or harder.

The WC could also contain other metals, like Cobalt. Co oxides could be removed with sulfuric acid.
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Sulaiman
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[*] posted on 19-7-2017 at 06:42


I think that you should ask a jeweller or jewellery forum
or give it a strong uniform heating and have a solid black tungsten ring,
but leaving it as is, you have a story to tell to whoever notices,
and your wife will always complain about something anyway,
it may as well be something easy to deal with like a failed science experiment :P




CAUTION : Hobby Chemist, not Professional or even Amateur
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Morgan
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[*] posted on 19-7-2017 at 07:54


Tidbits

Tungsten Ring Tarnish Remover and Polishing Kit
https://www.youtube.com/watch?v=BuZrDjA-lZY

how to polish tungsten carbide ring
https://www.youtube.com/watch?v=LHdSc7-n34k

https://www.youtube.com/watch?v=hsHN2-Xbd1w#t=1m11s

https://www.forevermetals.com/metal-jewelry-quality/

[Edited on 19-7-2017 by Morgan]
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elementcollector1
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[*] posted on 19-7-2017 at 10:22


Have you tried tumbling it in a rock tumbler with fine-grained sand? You can make a makeshift one with a drill, a plastic bottle and some sand, and that should work to polish it if you leave it in there long enough.



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Chemetix
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[*] posted on 19-7-2017 at 14:33


You could try electropolishing. This works for tungsten, not sure your ring is carbide as WC is a sort of hematite looking black material.

If it's a lustrous metallic looking metal ring normally, then attach to a copper wire and dunk into a NaOH solution with another electrode. It can be carbon or even a TIG welding rod of tungsten. Don't worry too much about polarity as reversing the current intermittently cleans off the oxide layer a bit better. You'll see the lustre return more solidly on one electrode and when it's shiny then remove and clean. 12- 20v in a 50ml beaker should work.
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boringneil
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[*] posted on 20-7-2017 at 03:29


Guys thank you so much this is all excellent help and information!

I will give all these methods a try and see if I can jazz this ring up a bit :-)
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NedsHead
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[*] posted on 20-7-2017 at 05:03


Quote: Originally posted by Sulaiman  
your wife will always complain about something anyway


This is why I let my facial hair grow long and shabby, if you give them something obvious to complain about they won't notice all the other things you're doing wrong:D

Leave the ring as is
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zed
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[*] posted on 23-7-2017 at 14:01


Ahhh.

Yes. So true!

They say the prophet Mohammad, was the perfect man. Imbued with every noble quality.

None-the-less; his wife could find things wrong with him.......
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battoussai114
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[*] posted on 23-7-2017 at 17:51


These rings are made of carbide with a filler metal in the pores right? Wouldn't putting the ring in an acid bath dissolve the filler metal before the carbide?



Batoussai.
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24-7-2017 at 10:05

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