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Author: Subject: Dissolving niobium metal
woelen

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Dissolving niobium metal

I purchased some elemental niobium metal of high purity in the form of very thin sheets and I want to do some experiments with salts, containing this metal.
I found, however, that this metal is really inert. Does one of you know a means to dissolve this metal in an aqueous liquid, being acidic, alkaline, oxidizing, whatever? I prefer not to use fused salts or alkalies for dissolving the metal.

[Edited on 22-11-2005 by woelen]

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The_Davster
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I hate it when books do this....
From Patnaik P's Handbook of Inorganic Chemistry
"soluble in HF and fused alkali hydroxides" "insoluble in aquaregia"
From Greemwood Ernshaw's Chemistry of the elements
"vanadium and niobium are attacked by hot concentrated mineral acids, but are resistant to fused alkali"

EDIT: Perhaps an electrolytic dissolution? Or does the form of the metal not allow this?

[Edited on 22-11-2005 by rogue chemist]

chromium
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Connect it as anode in electrolyte cell with acid as electrolyte (as rogue chemist already pointed out). If this does not work try to reflux it with boiling 70% sulfuric acid. If this too does not work then you probably have to find some HF.
IPN
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From "A Treatise on Chemistry by H.E. Roscoe (Vol IIb 1880)" :

 Quote: It is hardly attacked by hydrochloric or nitric acid or aqua-regia even when heated, but dissolves in concentrated sulphuric acid, yeilding a colourless liquid.
BromicAcid
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Electrolysis with a sheet as the anode and another as the cathode using AC in hydrochloric acid. Nothing stands up to that nothing.....

Or as Hawley's says
 Quote: Not attacked by nitric acid up to 100C, but vigorously attacked by a mixture of nitric and hydrofluoric acids. Hot concentrated hydrochloric acid, sulfuric acid, and phosphoric acid attack it, but hot concentrated nitric acid does not. Unaffected at room temperature by most acids and by aqua regia. It is attacked by alkaline soluitons to some extent at all temperatures.

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I am a fish
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Using hydrofluoric acid is a viable and resonably safe option if you generate it in situ.

Place the niobium in dilute hydrochloric acid, and then add a small quantity of sodium fluoride solution. Once the resulting hydrofluoric acid has reacted with the metal, add more sodium fluoride solution, and so on. If done carefully, only a small amount of hydrogen fluoride will be present in the reaction mixture at any one time.

1f /0u (4|\\| |234d 7|-|15, /0u |234||`/ |\\|33d 70 937 0u7 /\\/\\0|23.
hobbylab
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Unless niobium fluoride is insoluble I don't see a need for adding more fluoride?
chloric1
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isn't niobium more closely related to titanium chemically. I have somewhere patent literature which suggest etching titanium in hot oxalic acid before plating. I also have seen compatability tables that suggest titanium is not recommended for working with oxalic acid. Now the attack may be slow and gradual but a pump recirculating system comes to mind. Constant flowing of a hot solution of oxalic acid over the niobium should facilitate faster dissolution. A peristaltic pump would be idea here.

[Edited on 11/29/2005 by chloric1]

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neutrino
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>Unless niobium fluoride is insoluble I don't see a need for adding more fluoride?

It may form a stable fluoride complex when dissolving the metal. The same thing happens when dissolving titanium by this method, so a fluoride must be continuously added.
woelen

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I'm still waiting for my niobium metal to arrive with the post, I expected it quite some days ago already . As soon as it arrives, I'll test all your suggestions and then we will know whether the fluoride method works for niobium as well. It indeed works very well for titanium.

[offtopic]
I have an experiment on that in the riddles section on my website. I do not understand the observations over there, due to very weird results. Any ideas are welcome.
[/offtopic]

@Hobbylab: With adding more and more fluoride, it is meant that fluoride is added in small steps. Each step dissolves just a little of the niobium metal and when all fluoride is used up, a little more is added, until all of the metal is dissolved. That is the idea behind it. The reason for doing it this way is to have as little as necessary of free HF around. That stuff is NASTY.

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woelen

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Finally I received my niobium metal . I did some experiments with it, trying to dissolve it.

I took a small piece and put this in 10% HCl. That does not do anything, as expected. Next I added a pinch of NaF, which dissolves quickly. Still, this does not do anything at all, while such a solution really works nice for dissolving titanium.

Next, I took a larger part of niobium and did electrolysis, with a carbon cathode and a niobium anode. As electrolyte I used a 10% HCl solution, reagent grade.

At 3V no reaction occurs at all. I raised the voltage to 4 V. Some H2 bubbles from the cathode, no gas is formed at the anode. This lasts for a few seconds, the reaction comes to a halt within a second or three. Next, I pumped up the voltage again, this gives some H2 but only for a few seconds. Finally, I raised the voltage to 30 V (yes, 30 V!!). This results in formation of some H2 at the cathode, but again, the reaction comes to a halt after a few seconds. The anode becomes passivated and non-conductive. It is covered by a beautiful blue, non-conductive layer, which protects the underlying metal REALLY good. This result is so amazing, that I want to share it with you. I made pictures of the piece of niobium, which served as anode. The blue part was under the HCl, the metallic part was above the liquid and there, the copper wire was connected by means of a small clamp. The blue layer is VERY inert. It cannot be removed by applying concentrated HCl and also rubbing it does not remove it.

Here follow two pictures of the piece of niobium metal. This is a piece of 2.7 grams and the size of the piece is approximately 3.5 cm at its longest edge.

http://woelen.scheikunde.net/science/chem/pics/niobium1.jpg
http://woelen.scheikunde.net/science/chem/pics/niobium2.jpg

Does anyone of you have a nice explanation for these observations?

I hoped a little that I would have an anode, which would be very inert, allowing me to do electrolysis without pulverization, such as with graphite anodes. Indeed, it does not pulverize, nor does it dissolve , but is becomes totally non-conductive due to the blue layer .

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chloric1
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I like it!

Woeler you are becoming one of my favorite members here! You always provide stunning visuals, especially on your website. Niobium is a valve metal like titanium and tantalum. That means a very inert oxide layer is deposited on the metals surface. The color is a result of the thickness of the oxide and how it bends light. This anodizing process is very popular with metallurgist and jewlers because there is no need for expensive dies and the color is voltage controlled. What you need is a 3 amp variac transformer and a rectifing diode set rated over 100 V. you can create many colors at voltages between 0 up to I think 80 or 90 volts DC.

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12AX7
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Ah, looks like the colors I've seen on pieces of titanium I've induction-heated to yellow incandescence. Those reactive/refractory metals have wonderful colors, don't they?

I guess you should try AC then, that was suggested. Might have to start with a lot of negative voltage though, depending on the rectification effect of the oxide, its thickness, and if it reduces very well at all...

Could you do an alkali fusion with it?

Tim

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IrC
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Just for fun I started googling niobium and niobium chloride, as I have several sheets of the stuff and was going one day to play with this neat element. In most of the information they state that the chloride is yellow. Finally I found mention of niobium IV chloride as being violet-black:

http://www.webelements.com/webelements/compounds/text/Nb/Cl4...

Below are a few links that are interesting.

https://fscimage.fishersci.com/msds/58773.htm This page shows the chloride as a yellow solid with real unfriendly toxicology.

[Edited on 14-12-2005 by IrC]
12AX7
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Hum, suprised it's that nasty. I'd think it would be relatively harmless besides hydrolysis (as with TiCl4). Isn't Nb inert in the body, or is that just the oxide on the metal?

Tim

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Fleaker
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12AX7, the metal may be inert, but the ion could be a different story. Platinum salts are a good example, you can swallow a nugget of elemental Pt and come to no harm, but look at all of those chemotherapy drugs (cisplatin and the like), they aren't exactly the best for you.

IrC, would you care to trade a few grams of that niobium for some titanium alloy pieces?

Nice job Woelen! That is an interesting blue coating. Have you tried hot aqua regia (won't dissolve titanium, but still worth a try) or other concentrated mineral acids? If they do not work, perhaps an alkali fusion would be in order :-/ Although, (purely speculation here) you could heat some of the plate in a sealed container with bromine or chlorine gas to oxidize the metal.

[Edited on 14-12-2005 by Fleaker]
IrC
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[Edited on 15-12-2005 by IrC]
woelen

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I've read the rembar link and I tried some of the combinations from that site. It allows me to dissolve some niobium, but at a VERY low rate. Practically, it still is insoluble.

I did some further experimenting with the electrolysis (not yet AC, I need to make a safe provision for that, I don't want to do that directly off the wall-outlet anymore, after I had a shortcircuit because the electrodes touched each other under water with a few drops of acid in it).

The blue color is not due to niobium (IV) chloride. Exactly the same blue color is obtained with lab grade nitric acid as electrolyte.
The color indeed depends on the voltage applied. I can get light yellow, bronze, shades of brown/green and blue.

In order to keep this post short, I want to refer to the page I added to my website. I contains all things I did with the niobium metal and its solutions. This is really interesting stuff and I certainly will delve deeper into this. The URL is

http://woelen.scheikunde.net/science/chem/exps/niobium/index...

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IrC
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Cool. You should go to the hardware store and buy one of those light bulb sockets that mounts flat onto wood or a box or whatever. Put the socket in series with your wall current (line side not neutral, thats the smaller blade, the wider blade is the neutral) to your electrodes. Then you have no short circuit worries, and can get an idea of current flow by watching the brightness of the light. You can even control things by choosing the wattage of the bulb, and colored lights such as red ones look neat and are easier on the eyes. Kind of a poor mans current meter and short circuit protection combo. I have used a setup like this for years to test high power audio amps, so that when the biasing is optimal the lamp filament dims down to a null, and of course full brightness equals a bad transistor in the output stage (or in your case shorted electrodes in the cell).

Transformer? Then he would not have the cool light and raw AC on the bench. Where is the danger in this I ask. There must be at least some danger or it is not mad science.

[Edited on 17-12-2005 by IrC]
12AX7
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...Or get a fricking transformer...YIKES!

They have those things at RadioShack you know.

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The_Davster
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Finally found my niobium in the lab! I have been wanting to try this for a while, I really wish I had a 30V source, All I got was the brown/bronze colour at 12V

The_Davster
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Heh, forgot about the -12V line on the PSU, instant 24V

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Niobium is one of the coolest transition metals in the periodic table. The sheer number of colors you can get through anodization is remarkable. The best part is that the coloring is consistent and looks almost like paint as opposed to some other anodization where it seems more like tarnish than coloring. (Though I will say that potassium has one of the most beautiful oxidation colors on it when it is JUST starting to oxidize. I almost wish I could ampoule a sample of it right when that faint purple/blue hue first hits).

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The_Davster
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Hmm I wonder if tantalum does anything similar?
I have some tantalum in the same form as the niobium, 1/4" tubes. I will have to try this again with it.

UnintentionalChaos
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Anyone wanting to play with niobium should check out this source:
http://theringlord.com/cart/shopdisplayproducts.asp?id=126&a...
It helps to have diverse and bizarre hobbies
I'm sure its nowhere near the cheapest out there, but the supply is consistent, the source is well respected within the chainmaille community (shipping is not too fast if you're in the US though), and they sell small quantities to anyone. They also have 99.9% fine silver wire and titanium wire.

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 Sciencemadness Discussion Board » Fundamentals » Chemistry in General » Dissolving niobium metal Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues   » Detritus   » Test Forum