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The_Davster
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From that site:
Wow, too bad they do not list voltages to make them.
EDIT: not sure if this image stretches anyone's screes resolution, mine is fine, but on high res. Let me know if it does and I'll remove it.
[Edited on 10-6-2007 by The_Davster]
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woelen
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This really is cool. I now have a DC power supply, which can give any voltage between 0 volts and 400 volts and I'll definitely try with that and see
what colors I can get with the different voltages.
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Engager
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Best solvent for niobium and thantalium is HNO3+HF mixture. Blue layer is a film of oxide probably with some oxychloride contamination. Similar things
happen with Ti, Zr, and Ta, after the breach oxide film appears almost momentaly and reduces current density on electrode to hardly measurable level.
This is why Ta and Ti are ofter used as substrates for anodes. Color of oxide film depends from it's thickness and may vary in big interval.
Below is picture of my niobium metall sample, i can post Ta plates picture if requested.
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franklyn
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Hmm I thought that Aqua Regia dissolved everything ( except it's container ) 
Common laundry full strength NaClO solution is an extremely corrosive electrolyte
and is easy enough to try. You don't need to go over 12 volts unless you're
trying for cold fusion
.
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DerAlte
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Slightly OT, but I'm on an elecrolysis kick. Is niobium any good for an anode for anodic oxidation? Seems to resist fairly heroic efforts to oxidize,
in the general sense...
Regards,
DerAlte
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Fleaker
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Actually, I recall Woelen mentioning his electrochem experiments being ruined by its blue oxide layer that just won't dissolve.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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DerAlte
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Sorry. stupid of me. It happens to be a main point of the thread. Must be losing my marbles...
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The_Davster
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Yeah, the oxide layer is completly unconductive. The electrolysis runs for a few seconds colouring the anode, then the current drops to zero.
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Eclectic
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You could try the same sort of surface treatments that work on titanium if you just happen to have niobium but no titanium.
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12AX7
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Incidentially, I have "burned" titanium in ~30% sulfuric acid with more than 20 volts. Up around 100V, it sputters and makes some sort of aerosol,
probably acid.
Might be a little too strong... the same pitted and corroded aluminum as well.
I would be interested to know just how high the voltage can go. Eventually, it's going to tunnel through and erode or dissolve (or at least form a
sol of oxide crud). I'll be damned if it goes beyond, say, 1000V! 
Tim
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not_important
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You can exceed the dielectric strength of the oxide, just as with any film or sheet of insulating material. The breakthrough, in effect discharging a
capacitor, tends to vapourise some of the the underling metal and the electrolyte near the breakthough; the vapourised metal generally is going to
react with the electrolyte as well.
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UnintentionalChaos
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Time for a thread ressurection! I managed to attack some niobium wire to a visual extent. Who knows how long it would take to fully dissolve.
Basically, I plopped the thing in very strong lye with a dash of dilute H2O2 for added flavor. In a few hours, I've gone from polished , shiny metal,
to grainy, etched looking metal, although the extent of the dissolution was not measurable with my calipers. If it sat for a week or two, there might
be some more significant results, so I'll report back.
[Edited on 7-29-07 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Xenoid
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| Quote: | Originally posted by not_important
You can exceed the dielectric strength of the oxide, just as with any film or sheet of insulating material. The breakthrough, in effect discharging a
capacitor, tends to vapourise some of the the underling metal and the electrolyte near the breakthough; the vapourised metal generally is going to
react with the electrolyte as well. |
Actually, an interesting feature of these "valve metal" oxide layers is that they exhibit electroluminescence. I recently stumbled on the following
article "Electroluminescent Rectifiers" by Norman Stanley in his "Chemistry Corner"
http://www.sas.org/E-Bulletin/2001-11-16/chem/column.html
Quote:
"At the outset of the formation process, sparking will occur on the surface of the aluminum due to breakdown of the thin oxide layer; this will
subside as the layer thickens. However a very interesting residual effect remains: If the plates are observed in a darkened room they will be seen to
glow with a uniform soft white luminescence. Presumably this is caused by reverse current leakage, though no individual sparking is seen. Whether it
is due to micro-sparking or some more esoteric effect I don't know. Investigating this by making a cell that can be observed microscopically should
make an excellent amateur project. "
The effect that he describes, refers to Al plates in borax solution, sort of like an early version of an LED 
Lots of scope here for amateur investigation, different metals, electrolytes, voltages, layer thickness etc. etc...
Xenoid
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indigofuzzy
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It doesn't look like anyone else has hit on this yet:
The colors on anodized niobium are caused by interference. (The same was as colors on an oil slick.)
The anodizing voltage affects the thickness of the oxide layer, which is only a few tens of nanometers thick.
An explanation can be found here: http://www.sozra.com/niobium.html
Be forewarned: this was not written for technical folks, and may seem a bit "dumbed down".
I personally own around a dozen pieces of Niobium jewelry. Sadly, this is the only niobium I have on hand, so I'm not too willing to do chemical
experiments on it.
For what it's worth, some beautiful anodized niobium pictures:
http://www.sozra.com/Merchant2/merchant.mvc?Screen=PROD&...
http://www.sozra.com/Merchant2/merchant.mvc?Screen=PROD&...
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UnintentionalChaos
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Long past-due update on that Nb. There never was much dissolution beyond a surface etching.
For anodization, also see this guy: http://www.mrtitanium.com
Jewelry supply places sell variable-voltage sources precisely for anodizing titanium and niobium jewelry, although they are very expensive. I know
some people who do this, so it is definetly possible if you have a precisely controlled voltage source. The typical recommended electrolyte is
trisodium phosphate.
Come to think of it, I never bothered to test HF on the stuff. 1M HF tears titanium a new one in a few minutes, so perhaps Niobium will be similar.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Eclectic
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Mixed concentrated sulfuric and nitric acid is supposed to dissolve Niobium, and well as sulfuric + H2O2.
Also electrolysis in alcohols made conductive with ammonium chloride or NaOR seems to produce distillable alcoholates.
[Edited on 2-17-2010 by Eclectic]
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blogfast25
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Only HF solution or anhydrous, IMHO. Oxidising acids should only yield Nb2O5, I feel.
It does quite readily react with O2 and Cl2 with heat applied.
Fusion with a KOH/KClO3 mixture could yield niobate, which should hydrolyse quickly to Nb2O5 on dilution.
Apart from Nb2O5, NbCl5, NbF5 and the complex fluoroniobates, not much springs to mind in terms of Nb compounds.
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Eclectic
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http://www.4shared.com/file/104119863/7da5825b/Niobium.html
Jeeze, I just did 4 hours of googleing....over 100 pages read....
Niobium sulfates, peroxycomplexes, ammonium niobium oxalate....all water stable... and anodic dissolution in conductive anhydrous alcohols....
"It will never fly"
(Quite possibly dissolution of Nb2O5 needs VERY hot 93+% H2SO4 to proceed at useful rate))
[Edited on 2-17-2010 by Eclectic]
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blogfast25
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But making Niobium metal (from Nb2O5 thermite) is a whole lot more exciting than trying to dissolve it: temperatures in excess of 2,500 Celsius are
needed...
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Eclectic
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I can get the metal, but compounds seem a bit scarce....there are some interesting catalyst applications.
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blogfast25
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That's a very nicely rounded review you're unearthed there nonetheless.
But for backyard scientists it's hard to tell these, say oxychlorides from their chlorides, or oxyfluorides from their fluorides, without precise and
extensive quantitative work... The furthest I might go some day is heat some Nb foil in dry Cl2 to get NbCl5. Woelen bought some of that some time
ago.
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