Sciencemadness Discussion Board - Molybdenum from molybdic acid - success!

Molybdenum from molybdic acid - success!

Oscilllator - 17-1-2014 at 21:31

2 weeks ago I obtained ~1kg of Molybdic acid (H2O.MoO3), 500g of sodium molybdate, and ~200g ammonium molybdate.
For lack of anything else to do, I decided to try and extract molybdenum metal from at least one of these compounds. This proved to be quite difficult, partly because I didn't really know what I was doing. I tried reducing it from and aqueous solutions using aluminium powder and a bunch of other stuff but it soon became apparent that my best bet was some kind of thermite.
This patent described using calcium molybdate in an aluminothermic reaction, and they claimed 90+% yield. However they used preheated 500g charges in a special reaction chamber so unsurprisingly my ~60g attempt failed dismally.

I had the idea of using straight molybdic acid. This did work, but the reaction was quite sluggish and not all of the reaction mixture ignited. I then decided to dehydrate the molybdic acd to molybdenum trioxide, however I couldn't find any data on Molybdic acids dehydration temperature. Like a true mad scientist, I proceeded anyway. I filled up a crucible with the stuff and put it in my forge, which should be able to heat it to at least 1000 degrees. This melted the Molybdic acid with no trouble, however it turns out molybdenum trioxide is quite volatile at 1000 degrees, so a significant quantity of black smoke was produced. A lid partially remedied this problem, and some interesting crystals formed in the crucible lid. It is interesting that these crystals are clear, whereas the ones in the bottom are black. Any ideas as to why this is?

When cooled down Molybdenum trioxide (or at least thats what I think it is) is a black, crystalline solid that is reasonably easy to crush up in a mortar and pestle. This is contrary to wikipedias page, which says its yellow or light blue. I did notice a distinct yellow colour while the molybdic acid was melting, but this was only transient.

My total yield of MoO3 was 65.45g, and I mixed this with an excess (30g) of Al, and placed it in a cobbled-together brick enclosure. The reaction was extremely vigorous, and the reaction was over in about a second, producing quite a lot of smoke.
Picture of the partially disassembled reaction chamber, and picture of a strange blue deposit:

The total yield of Molybdenum metal was 30.2g, of which 18.3g was in the biggest chunk, seen glowing red in the above picture. This is a yield of 69%, a surprisingly
high figure for a thermite reaction. A small amount was lost when some of the molybdenum chunks shattered, sending shards of molybdenum metal flying.

Zephyr - 17-1-2014 at 21:46

Good job, just a few questions;
Did you include the white crystals from the roof of the crucible in the thermite?
Where did you purchase your molybdates?
How much molybdic acid was placed in the crucible, and how much did the white crystals weigh?
And what do you plan to do with the molybdenum metal?
Thank you

Oscilllator - 17-1-2014 at 22:26

1: Yes, I did include the white crystals
2: I didn't purchase them, I... inherited them

. If someone wants to buy a small amount I may consider an offer or trade, but I'm not really looking to get rid of it. I also have some potassium iodide.
3: I dont know how much molybdic acid was placed in the crucible, I just kept spooning it in as the melt occupied significantly less volume than the dry powder. I dont know how much the white crystals weighed, but it was likely less than a gram.
4: I plan to put the molybdenum metal in my collection of cool stuff. Perhaps I shall do something else with it, it somebody suggests something interesting that I can do.

UnintentionalChaos - 17-1-2014 at 23:16

Molybdenum readily forms heteropolyacids with things like silicon oxides, arsenic oxides, phosphates, etc. which are typically strongly colored. reduced or partly reduced molybdenum oxides are quite strongly colored. I expect there may have been some decomposition with loss of O2 to lower oxides. The blue is probably the same materials, possibly modified further by the brick composition.

Very nice experiment. I don't think I've ever even heard of a molybdenum thermite and it looks like it worked very nicely. Even more impressive is that molybdenum melts at 2623 °C. You are very lucky that the reaction was powerfully exothermic enough to melt it and didn't just explode like a MnO2 thermite. Things like chromium (III) oxide and titanium thermites require additives to raise the reaction temperature and sometimes fluidize the slag in order to get any metal to coalesce and both melt well below molybdenum.

As for other uses, ammonium molybdate catalyzes the formation of copper phthalocyanine from urea, phthalic anhydride, and anhydrous CuCl2. You could try out some of woelen's experiments here: http://woelen.homescience.net/science/chem/exps/colorfulmoly... You can test for things like phosphate and arsenic in solution using molybdates (formation of strongly colored heteropoly acids). I believe the arsenic test reduces the sample with vitamin C to convert arsenate to arsenite ion and then treats it with an ammonium molybdate- sulfuric acid solution which forms a bright blue color. Phosphate tests yellow, I believe and does not need reduction, but I would double check on those procedures.

Depending on where you live, I may be interested in trading for a small amount of molybdic acid. I have about 10g of ammonium heptamolybdate tetrahydrate but it's not enough to try something like this with.

[Edited on 1-18-14 by UnintentionalChaos]

blogfast25 - 18-1-2014 at 05:59

Quote: Originally posted by UnintentionalChaos

Very nice experiment. I don't think I've ever even heard of a molybdenum thermite and it looks like it worked very nicely. Even more impressive is that molybdenum melts at 2623 °C. You are very lucky that the reaction was powerfully exothermic enough to melt it and didn't just explode like a MnO2 thermite. Things like chromium (III) oxide and titanium thermites require additives to raise the reaction temperature and sometimes fluidize the slag in order to get any metal to coalesce and both melt well below molybdenum.

I’m the resident thermite nut and have known for a while that an MoO3 thermite should be possible. I happen not to have any MoO3 and don’t really want to sacrifice the expensive NH4 molybdate I do have.

Luck doesn’t really come into it: the adiabatic temperature of MoO3 + 2 Al == > Mo + Al2O3 can be calculated and appears to be just right: above the MP of Mo and below the BP of alumina. That MoO3 is a high oxide helps a lot: a dioxide probably wouldn’t generate enough reaction heat.

MnO2 thermites can be semi-explosive because of the low BP of Mn, which literally causes some of the metal to vapourise.

This reaction could be further improved upon by:

1. Not using an excess Al: all that does is cause the excess to end up in the target metal (but I don’t know whether Mo and Al alloy well). Instead use a small excess of the oxide, this way all Al is consumed.

2. Use a slag fluidiser like CaF2 or CaO (about 10 % of total formulation): by reducing the viscosity of the melt, the metal/slag separation is improved and the metal will collect better at the bottom of the crucible, with less voids and such like.

The yield of nearly 70 % is quite good for a first shot but could be higher by further optimising the formulation.

[Edited on 18-1-2014 by blogfast25]

blogfast25 - 18-1-2014 at 06:05

Quote: Originally posted by Oscilllator

No, that is not a 'surprisingly high number'. In fact it's fairly mediocre. Yields of up to 90 % can be obtained with well formulated thermites, preferably large ones.

Still: a very nice experiment, congrats!

Oscilllator - 18-1-2014 at 14:42

Quote: Originally posted by blogfast25

2. Use a slag fluidiser like CaF2 or CaO (about 10 % of total formulation): by reducing the viscosity of the melt, the metal/slag separation is improved and the metal will collect better at the bottom of the crucible, with less voids and such like.

The yield of nearly 70 % is quite good for a first shot but could be higher by further optimising the formulation.

[Edited on 18-1-2014 by blogfast25]

The patent I linked used calcium molybdate because it lowered the melting point of the mixture. They also described using an excess of aluminium to increase yield. They did not post the difference between no stoichiometric excess and 20% stoichiometric excess, however if you look at the article you will see that an increase from 15% excess to 20% excess results in an increase in yield from 93.2% to 98.5%.

blogfast25 - 19-1-2014 at 10:28

I take yield determinations with a pinch of salt, in the case of thermite metal. And the problem remains: where does the excess Al go? There's a 55/45 Mo/Al alloy, so I think I know the answer to that question!

http://www.americanelements.com/moala.html

Using calcium molybdate is equivalent to using CaO: the molybdate is also reduced to Mo, leaving behind CaO. That forms low melting calcium aluminates with the alumina, thus lowering slag viscosity. Or so the theory tells me...

[Edited on 19-1-2014 by blogfast25]

Oscilllator - 20-1-2014 at 02:17

Today I crushed a small amount of the metal, placed it in the bottom of a test tube and then added concentrated sodium hydroxide solution. This did not result in any bubbling, as one would expect if aluminium was present in the alloy. Are there any other convenient tests I could use to determine if there was significant amounts of aluminium present in the molybdenum?

blogfast25 - 20-1-2014 at 05:57

According to this thread Mo dissolves in concentrated nitric acid:

http://www.sciencemadness.org/talk/viewthread.php?tid=10582

Then you can you and look for Al in the solution.

MrHomeScientist - 21-1-2014 at 07:54

Oscilllator:
Damn! I had just received some ammonium molybdate the other day for a different experiment, and had planned to use the excess to try a molybdenum thermite. You beat me to it, though

Nice work! How did you create your molybdic acid? The various wiki pages don't outright say this, but I infer that dissolving a molybdate salt in water and adding acid precipitates MoO₃(H₂O)₂. This is then heated to dehydrate, which is what you showed above. Wiki does claim that both the dihydrate and monohydrate are bright yellow, though, which looks contrary to your experience.

My tentative plan would be:
1) Dissolve ammonium molybdate in distilled water.
2) Acidify with HCl to precipitate MoO₃(H₂O)₂ and leave NH₄Cl in solution.
3) Filter the oxide, dry, and heat in a crucible to dehydrate as much as possible.
4) Crush the products into a fine powder, mix with a stoichiometric amount of Al powder (and maybe a dash of CaF₂ as blogfast suggested), and ignite thermite-style.

[Edited on 1-21-2014 by MrHomeScientist]

blogfast25 - 21-1-2014 at 12:52

Quote: Originally posted by MrHomeScientist

4) Crush the products into a fine powder, mix with a stoichiometric amount of Al powder (and maybe a dash of CaF as blogfast suggested), and ignite thermite-style.

It would be worth trying CaO instead of CaF<sub>2</sub>. A test with an MnO2 thermite recently showed that CaO works, although it wasn't a neat back-to-back comparison with fluorite.

Lime is easier to get than fluorite and cheaper. It certainly is used on an industrial scale to fluidise alumina, because of that series of low melting calcium aluminates:

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

MrHomeScientist - 21-1-2014 at 13:08

Besides being easier to find and cheaper, is there any other reason to use CaO over CaF₂? (better separation, etc.) If it forms low-melting calcium aluminates, then perhaps it would be preferred in reactions that don't produce a lot of heat on their own. I ask because I already have fluorite powder but would have to make my own quicklime. Not out of the question, but it's an extra step I'd need to take. How's the rest of my scheme sound?

blogfast25 - 21-1-2014 at 14:11

Mr HS:

Unfortunately, I've yet to make a straight back-to-back comparison, so I can't tell yet.

Reactions that don't produce a lot of heat just don't work, period. The adiabatic end temperature (AET) of the reaction must always be (considerably) higher than the highest MP of the post reaction mix (MP of metal or MP of alumina, whichever is the highest), unless you can pre-heat of course. Adding a slag fluidiser actually decreases the AET a little but from my experience much is usually gained in terms of metal/slag separation because the slag/metal mixture is far more fluid. Reducing the slag's melting point also means the slag stays fluid longer, allowing more metal to settle out.

Quicklime here is available from eBay, cheap as chips.

Your plan sounds just fine to me.

Oscilllator - 21-1-2014 at 23:51

Quote: Originally posted by MrHomeScientist

Oscilllator:
Damn! I had just received some ammonium molybdate the other day for a different experiment, and had planned to use the excess to try a molybdenum thermite. You beat me to it, though

I didn't have to make my molybdic acid, as it came as-is in a jar. However I did notice a white precipitate upon the addition of HCl to a concentrated solution of sodium molybdate, so your proposed method sounds like it should work fine. Be sure to use concentrated cold solutions, as I'm pretty sure molybdic acid has a significant solubility in water. Wikipedia says its "1510 mg dm-3" but I have no idea what that means.
Despite what blogfast25 says, I think it would be a good idea to use a stoichometric excess of aluminium powder, as the patent did say it resulted in higher yields. I have yet to do a proper test for aluminium in the molybdenum metal however, so its up to you.

blogfast25 - 22-1-2014 at 06:24

Quote: Originally posted by Oscilllator

Despite what blogfast25 says, I think it would be a good idea to use a stoichometric excess of aluminium powder, as the patent did say it resulted in higher yields. I have yet to do a proper test for aluminium in the molybdenum metal however, so its up to you.

What's the point in having a (reported) higher yield of contaminated metal? You seem to desperately cling to the idea that the excess Al will have somehow vanished into thin air. But that doesn't happen.

You're creating an alloy. Wilfully or not.

[Edited on 22-1-2014 by blogfast25]

blogfast25 - 22-1-2014 at 10:22

Also, what you claim to be a patent appears to be a scientific paper. C.K.Gupta is certainly one of the most prolific writers on the subject of metallothermy.

"This investigation deals with a process for extracting molybdenum metal in well consoli-dated form and in good yield from calcium molybdate, by open aluminothermic reduction. Aluminothermic molybdenum has been further processed both by electron-beam melting and by molten salt electrorefining for the removal of aluminium {my emph.}."

This very different from what you did. Using calcium molybdate as the starting material requires pre-heating because the reaction produces much more slag and this absorbs more heat, leading to lower adiabatic end temperature.

Note also how excess aluminium in the Mo is removed by refining.

[Edited on 22-1-2014 by blogfast25]

vano - 23-6-2022 at 04:28

Can I use sodium fluoride instead of calcium fluoride or sodium hexafluoroaluminate?

bluamine - 6-7-2022 at 16:35

Well done!