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Author: Subject: Hafnium - Plasma Torch Electrode
elementcollector1
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[*] posted on 11-10-2013 at 15:51
Hafnium - Plasma Torch Electrode


Recently got a package of 2 hafnium plasma torch electrodes off of Amazon. Any fun experiments to do with it?



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[*] posted on 11-10-2013 at 16:39


You could shoot some xrays at them and see if it gets your geiger counter ticking :o!
http://en.wikipedia.org/wiki/Hafnium_controversy




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[*] posted on 11-10-2013 at 19:38


Hmm. Everyone on the Internet says hafnium is highly malleable (zirconium was malleable in my experience too), so I'm going to see if I can make a hafnium "plate" of sorts. As it is, the 3/8" diameter electrode doesn't fit in my 1/4" diameter ampoule opening...



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[*] posted on 12-10-2013 at 05:51


Quote: Originally posted by elementcollector1  
Hmm. Everyone on the Internet says hafnium is highly malleable (zirconium was malleable in my experience too), so I'm going to see if I can make a hafnium "plate" of sorts. As it is, the 3/8" diameter electrode doesn't fit in my 1/4" diameter ampoule opening...


Malleability will in all likelihood depend on purity, as small amounts of alloying metals can increase hardness. A harder alloy may also be malleable but requiring higher pressures. In these metals, presence of oxygen leads to loss of ductility.

Hafnium is the 'sister element' to Zirconium and chemically almost indistinguishable from it.

Zirconium is said to dissolve in HCl and H2SO4, so it would be worth testing that with hafnium, at the hobbyist level. With strong HCl (probably refluxed over a considerable time) you'd get hafnyl chloride (HfOCl2.8H2O) which can be crystallised. From hafnyl chloride solutions, with ammonia Hf(OH)4 precipitates, which is fairly soluble in acids and also in NH4HF2, forming (NH4)2HfF6 (ammonium hexafluorohafnate). Historically, M2(Zr,Hf)F6 salts were the basis for the first separations between Hf and Zr.

Good buy!

[Edited on 12-10-2013 by blogfast25]




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[*] posted on 12-10-2013 at 12:58


Hmm. Seems to be somewhat malleable, as it deforms when hit with a hammer. However, upon smashing this sucker into chunks small enough to fit in an ampoule, I discovered a coppery color - this doesn't look like the oxide! I think my torch electrode might just be hafnium-plated copper, or some such mixture...
If hafnium dissolves in HCl (and assuming HfOCl2 isn't an oxidiser), I could separate the two by dissolving the hafnium out and precipitating the metal.




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[*] posted on 12-10-2013 at 14:03


Quote: Originally posted by elementcollector1  
Hmm. I discovered a coppery color - this doesn't look like the oxide! I think my torch electrode might just be hafnium-plated copper, or some such mixture...



What you observe may be a form of iridescence:

http://en.wikipedia.org/wiki/Iridescence

Super-fine layers of oxide on freshly exposed areas can cause this phenomenon.

Hafnium has a much higher density than copper: 13.31 v. 8.96, so a bulk density estimate should tell a lot...




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[*] posted on 14-10-2013 at 16:07


Iridescence in my experience forms all colors of the rainbow - this was just straight copper-colored everywhere.
From a very rudimentary measure, the density was around 3-4 g/mL - nowhere near hafnium or copper. Course, the measurement could very easily have been off...
I still have a torch electrode that is unblemished, I'll try dissolving it and the pieces that were to go in the ampoule in HCl. Even if I can't get a solid lump of hafnium, I can shoot for powder if the impurity is copper.




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[*] posted on 15-10-2013 at 04:56


Quote: Originally posted by elementcollector1  
Iridescence in my experience forms all colors of the rainbow - this was just straight copper-colored everywhere.
From a very rudimentary measure, the density was around 3-4 g/mL - nowhere near hafnium or copper. Course, the measurement could very easily have been off...
I still have a torch electrode that is unblemished, I'll try dissolving it and the pieces that were to go in the ampoule in HCl. Even if I can't get a solid lump of hafnium, I can shoot for powder if the impurity is copper.


Hmmm... Hf will show some reactivity towards HCl, I think.

Density 3 - 4? Have you been sold a lemon, by any chance?




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[*] posted on 15-10-2013 at 05:19


If it is a lemon, it's the single most cleverly disguised lemon I've ever seen.



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[*] posted on 15-10-2013 at 12:03


Quote: Originally posted by elementcollector1  
If it is a lemon, it's the single most cleverly disguised lemon I've ever seen.


Possibly but you need to revisit that bulk density measurement. 3 - 4 is less than iron!




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[*] posted on 29-10-2013 at 13:48


So, I put the second torch electrode (untouched, brand new) in a test tube, and filled it with a non-stoichiometric mixture of (read: dumped in some) H2SO4 and H2O2, at 93% and 3% by mass respectively. After about 2 weeks, there is no change - if anything, it seems shinier than before! Wiki states that hafnium 'is resistant to acids (and bases)', and forms a protective oxide layer - but surely even a layer of hafnium dioxide couldn't last this long. If that coppery coating (which is still very present, and in fact has taken over most of the surface of the roughed hafnium) is really an iridescent oxide, then I should see some sort of color change. Failing that... I wouldn't know what to do.



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[*] posted on 30-10-2013 at 03:29


Quote: Originally posted by elementcollector1  
So, I put the second torch electrode (untouched, brand new) in a test tube, and filled it with a non-stoichiometric mixture of (read: dumped in some) H2SO4 and H2O2, at 93% and 3% by mass respectively. After about 2 weeks, there is no change - if anything, it seems shinier than before! Wiki states that hafnium 'is resistant to acids (and bases)', and forms a protective oxide layer - but surely even a layer of hafnium dioxide couldn't last this long. If that coppery coating (which is still very present, and in fact has taken over most of the surface of the roughed hafnium) is really an iridescent oxide, then I should see some sort of color change. Failing that... I wouldn't know what to do.


For Zirconium/Hafnium a mixture of HNO3/HF acid is recommended. A recipe for a Darwin Award, if you're not equipped :o.

But it would be worth trying 35 % HNO3 with some 1 M NaF solution added, on a really small scale, well outside. Zr/Hf like fluorides because they form very stable (Zr,Hf)F62- complex ions with it.

(Hf,Zr)O2 (hafnia or zirconia) is extremely acid insoluble (think TiO2 but much worse). They can be dissolved in strong (or anhydrous) HF or quite easily by alkali fusion (then hafnates/zirconates are formed).


[Edited on 30-10-2013 by blogfast25]




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[*] posted on 30-10-2013 at 04:04


While I agree with blogfast25 that fluorides ought to do the trick, I am also wary of the route and not so sure if the nitric acid will do the oxidation you need at decent rates.

I would suggest electrolysing your rod using it as the anode and doing it in NH4F + 2HF (WARNING Ridiculously toxic!) containing solution using high voltage (12V) if you want to prepare hafnium fluoride salts. That is virtually guaranteed to dissolve it away.

The problem is you will now make (NH4)2HfF6, great, now what? The stuff is freakin stable and useless for converting to other hafnium compounds no?

Ideally you want to make HfCl4 so that you can readily convert it into other hafnium compounds, but the problem is that it behaves a bit like TiCl4, it cannot be allowed to see anything vaguely resembling water or an alcohol etc.

So here's a crazy idea (but safer than working with HF), get a hold of a lipophilic quaternary ammonium chloride salt. In South Africa, you can buy bottles of fairly concentrated didecyldimethylammonium chloride solution as a pool biocide/algaecide... this should work. Get rid of the water and then prepare a solution of it in an inert solvent, e.g. hexane (hopefully enough dissolves otherwise use a more polar a protic solvent but make sure its inert as hell), and then bubble lots of dry HCl through it.

Now electrolyse at 12V using your hafnium as the anode and a carbon cathode. You should form HfCl4 at the anode as a white solid over your rod and lots of chlorine gas as well and H2 at the cathode.

Beware that some chlorine will dissolve in your solvent (would probably stink!) and that your solvent might also chlorinate gradually, though probably slowly.

You might also need to refill your solution with HCl gas if there isn't enough of it there. I would think that most of it would be wasted by forming Cl2 at the anode and only a small amount would actually be used for forming HfCl4?

I am unsure if your HfCl4 would dissolve in your solvent, TiCl4 certainly does in many organic solvents... but then it's a liquid. HfCl4 has a m.p of 432C, so very little should dissolve in things like hexane. However, in ethers, you may be able to form soluble adducts just like you can with TiCl4, things like HfCl4(THF)2 for example. In fact, this is probably what you would use as solvent to do other reactions with your HfCl4 later on.

[Edited on 30-10-2013 by deltaH]




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[*] posted on 30-10-2013 at 08:01


Quote: Originally posted by deltaH  
While I agree with blogfast25 that fluorides ought to do the trick, I am also wary of the route and not so sure if the nitric acid will do the oxidation you need at decent rates.

I would suggest electrolysing your rod using it as the anode and doing it in NH4F + 2HF (WARNING Ridiculously toxic!) containing solution using high voltage (12V) if you want to prepare hafnium fluoride salts. That is virtually guaranteed to dissolve it away.

The problem is you will now make (NH4)2HfF6, great, now what? The stuff is freakin stable and useless for converting to other hafnium compounds no?



The nitric/HF route is commercially used for dissolving Zr nuclear cladding (or at least was?)

(NH4)2HfF6 is converted to HfF4 by anaerobic or vacuum pyrolysis. I plan to use ZrF4 for reduction with Mg. I've already got some (NH4)2ZrF6 but it's one of those on/off long term projects.

I don't think EC1 really wants to make any Hf compounds, I think just wants to prove the stuff is Hf.




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[*] posted on 30-10-2013 at 08:35


FYI zirconia is dissolvable in very hot, concentrated H2SO4. Sparingly so, but it's do-able.
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[*] posted on 30-10-2013 at 08:43


Quote:
I don't think EC1 really wants to make any Hf compounds, I think just wants to prove the stuff is Hf.


Ah, okay then, point taken :)




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[*] posted on 30-10-2013 at 09:07


Quote: Originally posted by blogfast25  
I don't think EC1 really wants to make any Hf compounds, I think just wants to prove the stuff is Hf.


Very true, although so far it checks out if the only thing that can dissolve it is HF/HNO3.

I think some density measurements are in order again, this time with a much more accurate estimation of volume. I refuse to believe that this is a citric fruit disguised as a torch electrode.


[Edited on 10-30-2013 by elementcollector1]




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[*] posted on 30-10-2013 at 13:20


Quote: Originally posted by elementcollector1  
I think some density measurements are in order again, this time with a much more accurate estimation of volume. I refuse to believe that this is a citric fruit disguised as a torch electrode.


[Edited on 10-30-2013 by elementcollector1]


Use Archimedes:

http://antoine.frostburg.edu/chem/senese/101/measurement/faq...




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[*] posted on 30-10-2013 at 22:56


I'm trying to find the papers I was looking at, but I came across some that said a pure hafnium electrode is used. some newer ones just had an insert at the tip also. but after reading this thread I immediately started searching ebay( I didn't know about this before thanks). I asked one ebay seller(cztools), and he said that the hafnium tips they offered were not pure

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=26130...
..."Sorry we can not tell you exactaly what compand in the hafuim. Only can let you konw it is not purely hafnium. only tiny key woking part is made hafnium. It not collection. only for plasma cutting torch.
- cztools "...

given the nature of foreign sellers on ebay, I have got everything from the honest truth to an out-right lie when inquiring the specifics on items. at least this seller was honest instead of just going for the sale. so one may have to do the home work to avoid getting a generic/impure version. but it seems if you find the right one it will be at least relatively pure.

http://www.messer-cw.co.uk/Products/Consumables/Hypertherm-O...
..."CoolCore™ electrode technology replaces the conventional solid hafnium electrode element in high-current oxygen applications with a hafnium insert that is cored out, permitting heat-extracting copper to be in contact with its inside and outside diameter. Dramatically improved heat transfer from the hafnium results in a significant increase in electrode life."...

but so far in my search, it seems they are largely selling the insert version nowadays. though I'll keep looking as I don't have hafnium in my collection yet. hope to see how your density measurement went soon.

-Violet Sin-
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[*] posted on 31-10-2013 at 04:41


Interesting, Violet Sin, makes sense too...



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[*] posted on 31-10-2013 at 06:01


Quote: Originally posted by blogfast25  
Use Archimedes:

http://antoine.frostburg.edu/chem/senese/101/measurement/faq...


Quote: Originally posted by http://antoine.frostburg.edu/chem/senese/101/measurement/faq...  
The density of the bolt must be 8 g / 2 mL or 4 g/mL.

Quote: Originally posted by elementcollector1  
Iridescence in my experience forms all colors of the rainbow - this was just straight copper-colored everywhere.
From a very rudimentary measure, the density was around 3-4 g/mL - nowhere near hafnium or copper. Course, the measurement could very easily have been off...
I still have a torch electrode that is unblemished, I'll try dissolving it and the pieces that were to go in the ampoule in HCl. Even if I can't get a solid lump of hafnium, I can shoot for powder if the impurity is copper.

I think EC1 already used that site... ;)
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[*] posted on 31-10-2013 at 06:09


[offtopic]
Quote: Originally posted by blogfast25  
(NH4)2HfF6 is converted to HfF4 by anaerobic or vacuum pyrolysis. I plan to use ZrF4 for reduction with Mg. I've already got some (NH4)2ZrF6 but it's one of those on/off long term projects.

Did you prepare it out of Zr or out of ZrO2?
Quote: Originally posted by Wizzard  
FYI zirconia is dissolvable in very hot, concentrated H2SO4. Sparingly so, but it's do-able.

Were you able to crystallise the sulfate from the solution? I have been trying to collect articles on this subject, but no ready-to-do procedure for getting ZrO2 into solution has yet come out of this. Apart from dissolving in HF, that is.
[/offtopic]
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[*] posted on 31-10-2013 at 11:51


Quote: Originally posted by Bezaleel  
[offtopic]
Quote: Originally posted by blogfast25  
(NH4)2HfF6 is converted to HfF4 by anaerobic or vacuum pyrolysis. I plan to use ZrF4 for reduction with Mg. I've already got some (NH4)2ZrF6 but it's one of those on/off long term projects.

Did you prepare it out of Zr or out of ZrO2?


Alkali (KOH) fusion of Zircon (ZrSiO4, flour, pottery opacifier), followed by hydrolysis and dissolution in strong HCl leaves behind silica and a solution of ZrOCl2 + KCl.

Precipitate Zr as Zr(OH)4 with strong NH3 and filter and wash. Use a Buchner to suck out most of the water.

Dissolve the fresh, moist Zr(OH)4 in saturated (about 50 %), hot NH4HF2. Filter and cool (ice). (NH4)2ZrF6 crystallises out. Too much NH4HF2 will also yield (NH4)3ZrF7.

Of course you could also dissolve the Zr(OH)4 is strong H2SO4. Zr(SO4)2 is hard to crystallise, from what I've read.



[Edited on 31-10-2013 by blogfast25]




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[*] posted on 10-11-2013 at 12:43


Well, after at least 2 weeks in solution, neither the solution nor any of the hafnium in it (which now includes the iridescent pieces) have done anything. This rules out weaker metals such as iron or copper (there was H2O2 in the mix), leaving only the platinum group metals (given the weight, unlikely at best) and such metals as hafnium that are resistant to acids. On a side note, that means that these plasma torch electrodes might well find a use in electrolysis cells, but I'd have to test them with some electrolytic chlorine from a NaCl cell first.

As for density, I have not been able to make an accurate measurement yet.




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[*] posted on 10-11-2013 at 13:34


Quote: Originally posted by elementcollector1  
Recently got a package of 2 hafnium plasma torch electrodes off of Amazon.
I'm a little dumbfounded that no one else has asked you yet: Who's the manufacturer and what's the model number?

Here's a quotation from a Miller (a welding manufacturer) on consumables in plasma cutters:
Quote:

The second part is the electrode. It is located under and inside the tip. There is a rare piece of metal called Hafnium in the tip of the electrodes that breaks off every time the arc is started. When the Hafnium is depleted there will be a 1/16" deep, and round crater in the tip of the electrode. At this point it is time to change the electrode.
They're talking about their own products, obviously, but is there any indication that there might have been a hafnium insert brazed onto the end of the electrode you have?
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