We are using pure tungsten electrodes in a plasma focus device. While we thought we cleaned them well, with light abrasion, acetone and isopropyl, when we used them with a deuterium fill gas, the production of tungsten bronze and other evidence showed that we still had a lot of oxide left on. We must remove this before our next shots. I would also like to know if there is any way to be sure we have removed the oxide layer.
http://www.eng-tips.com/viewthread.cfm?qid=295311 suggests using a weak acid solution such as vinegar, a highly effective reducing agent. Or http://onlinelibrary.wiley.com/doi/10.1002/sia.3185/abstract suggests that hydrogen plasmas are very effective at removing tungsten oxide layers. :)
So I faced the same problem in my masterthesis. A quit convenient way to do this is to heat up the Electrode to a temperature of about 800 °C and ad low pressure of Hydrogen gas , which leads to WO3 (s) + 3H2 (g) -> W(s) + 3H2O (g). At higher temperatures this works even more effective. If it is not possible to heaht it up to such temperatures, hydrogen plasma should work well to! Better don't use vinegar!!!
In the past, some colleagues of mine used to work with tungsten in a lab. I spoke to them, and their suggestions are as follows: high temperature treatment in-vacuo. The trick is to put a titanium getter near the tungsten specimen. Then, oxygen goes away from tungsten ang goes to titanium.
We are running with deuterium, so we are exposing it to hot hydrogen, chemically. The problem is the formation of tungsten bronze , which as a powder spreads everywhere. I need something we can do before we fire with deuterium to physically remove the oxide layer. Why won't simple abrasion of the outer layer work, since I understand the layer will not re-from at room temperature?
In addition, we want to remove the tungsten bronze itself as well. Any ideas on solvents for this?
A tungsten trioxide (WO3) layer over pure W can be selectively dissolved (etched) by hot NH4OH (aq). Do not add H2O2 to this solution (as it would etch metallic W also).
Thanks!--but what temperature, what strength solution and how long will it take for a 3 micron layer?
You may soak the W/WO3 specimen in 5 wt% NH4OH aqueous solution at 80 ºC. To my best knowledge the etch rate seems not to have been reported.
Hi Eric, are you able to comment on whether dissolving in 5% wt NH4OH at 80°C worked for you? I am in a very similar situation right now and looking for a good way to remove what I think is an oxide from tungsten. Thanks.
- We used rapidly pumped down hydrogen heated with two microwave magnetrons. Seems to have finally worked.
Any reference link for W/WO3 specimen in 5 wt% NH4OH aqueous solution at 80 ºC ?
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