Sciencemadness Discussion Board

Problem in making tungsten compounds

LHcheM - 10-11-2011 at 01:22

I have 11g of 99% tungsten wire, which is obtained from an old electronic store. For a long time I have been trying to convert the tungsten into its compounds (WO3, WOCl4, WO2Cl2 or whatsoever), but have been unsuccessful.

I tried with direct burning it with a butane torch, the wire glows white upon heating, but it just became thinner as the atoms evaporate.
I have also tried to dissolve the metal by using aqua regia, conc hot HNO3, conc Sulphuric acid, but all these has no effect on the metal. I don't have HF and don't want to buy it, but the metal also remains inert towards NH4HF2

So what should I do with the metal in order to obtain its compounds?

strontiumred - 10-11-2011 at 02:18

I think you need alkali and an oxidizing agent to make tungstate. Perhaps try adding dry sodium hydroxide with a nitrate or persulfate salt. Cover the wire with this mixture then melt. I've not tried it with wire though, perhaps the surface area will not be enough?

Something like:
W + 3NaNO3 + 2NaOH --> Na2WO4 + 3NaNO2 + H2O



[Edited on 10-11-2011 by strontiumred]

IrC - 10-11-2011 at 03:49

"Tungsten is a relatively inactive metal. It does not combine with oxygen at room temperatures. It does corrode (rust) at temperatures above 400°C (700°F). It does not react very readily with acids, although it does dissolve in nitric acid or aqua regia."

From:

http://www.chemistryexplained.com/elements/T-Z/Tungsten.html

One would think you could take advantage of this rusting reaction, not to mention maybe your acid mix should be above room temperature if you use that route. You might also search for making tungstic acid.

http://books.google.com/books/about/Experimenting_with_chemi...

To save you searching for the book Entropy51 mentions below. Also I did not know acids will not work, good to know but depressing to think you just cannot trust anything on the web anymore. I liked that electrolysis idea. Can anyone provide more info such as chemicals used, as well as a good idea of the proper voltages/currents, should the other electrode be carbon or Pt, etc., or another one of W?


[Edited on 11-11-2011 by IrC]

Endo - 10-11-2011 at 06:35

Acidified peroxide works, although it is slow it will chew up your tungsten over time. I dissolved several 1/4" round tungsten rod ends and discussed the WO3 formation/ complex peroxytungstate ion formation in this post. Thanks to Not Important for his help on this.

http://www.sciencemadness.org/talk/viewthread.php?tid=6862#p...

blogfast25 - 10-11-2011 at 06:47

Quote: Originally posted by Nick F  
Tungsten is easy to dissolve by electrolysis. I did this once to get the thoria out of some 2% thoriated electrodes. A search should bring up the thread if you're interested.


(from that thread)

entropy51 - 10-11-2011 at 06:50

Tungsten is not attacked by acids. Tungsten powder will dissolve in boiling KOH solution to form the tungstate. The wire will not dissolve in boiling KOH, rather it requires fusion with KOH or NaOH.

See page 55 of Experimenting with Chemistry: Experiments for the Home Lab By Burton L. Hawk which is available for free download on Google Books.

blogfast25 - 11-11-2011 at 05:00

Quote: Originally posted by entropy51  
Tungsten is not attacked by acids. Tungsten powder will dissolve in boiling KOH solution to form the tungstate. The wire will not dissolve in boiling KOH, rather it requires fusion with KOH or NaOH.

See page 55 of Experimenting with Chemistry: Experiments for the Home Lab By Burton L. Hawk which is available for free download on Google Books.


I found the book but not as a free download?

entropy51 - 11-11-2011 at 11:08

Quote: Originally posted by blogfast25  

I found the book but not as a free download?
On my screen there is a "PDF" button on the top right. I think Google Books may limit downloads geographically so if your IP is not in the US it may not show for you.

blogfast25 - 11-11-2011 at 14:16

Yes, that may explain it. No free book for me then...:(

entropy51 - 11-11-2011 at 15:47

Quote: Originally posted by blogfast25  
Yes, that may explain it. No free book for me then...:(
Maybe Polverone would be kind enough to post this book in the forum library. It is one of the few available books on home chemistry. I am only aware of five such books above the elementary school level. It would be nice if they were all in the library given the focus of this forum.

LanthanumK - 14-11-2011 at 08:05

To make WO3 just pass a large amount of current through the filament. Anhydrous WO3 is formed, which undergoes hardly any reactions.

barley81 - 14-11-2011 at 14:04

In a previous thread, Woelen suggested electrolysis in alkaline peroxide to dissolve bulk tungsten. Here is the thread.
http://www.sciencemadness.org/talk/viewthread.php?tid=11962#...

LHcheM - 15-11-2011 at 00:42

Well a long time since I logged on to this forum! I did put a wire into an acidified solution of hydrogen peroxide, I use quite a strong solution: 75% H2SO4 with ~10% hydrogen peroxide, and the wire has become thinner since then...then problem is I didn't obtain a yellow precipitate of WO3, but instead I got some light grey-black flakes in the solution? What's the possible reaction occurred?

I will try on the electrolysis later ;)

nezza - 15-11-2011 at 00:49

Tungsten can be oxidised, but needs rather severe conditions. I have made WO3 by adding tungsten as small pieces or powder to molten potassium and sodium chlorate. It reacts fairly readily and burns red to white hot so a CLEAN pyrex tube can be used. The WO3 produced is insoluble in water or acids, but can be dissolved in aqueous alkali. Be aware that molten chlorates are vigorous oxidising agents and will react violently with any traces of organic material, hence the need for clean apparatus and pure salts.

careysub - 9-8-2014 at 14:05

A bit of an old thread (2 years, 8 months since the last post) but I ran across an interesting ACS article about dissolving tungsten in 30% H2O2 and nothing else:
http://pubs.acs.org/doi/abs/10.1021/ac60176a021

You can only read the first page without having an ACS login, but it pretty much covers the subject. They dissolved tungsten rod of various thicknesses (fastest rate was at 60 C), time to complete dissolution:
5 mils, 1.5 hr
10 mils, 2.5 hr
15 mil, 2.75 hr
25 mil, 3 hr

If you plot this you see the time curve flattening out at 25 mil, so that the time for 60 mils (a 1/16" TIG electrode) would be a good bit less than double the 25 mil time.

This would look like the method of choice for dissolving tungsten metal.

Polverone - 9-8-2014 at 20:37

Quote: Originally posted by careysub  
A bit of an old thread (2 years, 8 months since the last post) but I ran across an interesting ACS article about dissolving tungsten in 30% H2O2 and nothing else:
http://pubs.acs.org/doi/abs/10.1021/ac60176a021

You can only read the first page without having an ACS login, but it pretty much covers the subject. They dissolved tungsten rod of various thicknesses (fastest rate was at 60 C), time to complete dissolution:
5 mils, 1.5 hr
10 mils, 2.5 hr
15 mil, 2.75 hr
25 mil, 3 hr

If you plot this you see the time curve flattening out at 25 mil, so that the time for 60 mils (a 1/16" TIG electrode) would be a good bit less than double the 25 mil time.

This would look like the method of choice for dissolving tungsten metal.



Indeed. That's how I dissolved TIG rods.

jock88 - 10-8-2014 at 02:22

De page for posterity

W.GIF - 117kB

careysub - 10-8-2014 at 06:38

And it looks like a good way to separate the tungsten trioxide and thorium dioxide is to treat with NaOH and form the soluble sodium tungstate.

nezza - 10-8-2014 at 10:11

Molten Potassium chlorate dissolves finely divided tungsten. I have tried it with crushed tungsten as smalll lumps/powder. The reaction is exothermic so a pyrex tube is advisable and will need to be smashed to get at the mass of tungsten oxide once the reaction has stopped. It may work on tungsten wire.