Sciencemadness Discussion Board - Molybdenum at home

Molybdenum at home

Alzador - 28-1-2015 at 02:16

Hi guys!

Recently I found a can of dry lubricant which - according to the label - contains molybdenum disulfide - MoS₂. My question to all the mad scientists here

would be: what would be the best way to convert it into Mo powder? I know that the MoS₂ is dissolved is some kind of solvent inside the can but getting it out as a powder shouldn't be too hard..

I've read many articles on the Internet from which I've learnt that a viable way would be oxidising it to Mo(VI) - MoO₃ using the O₂ in the air at elevated temperatures and then reduce it back into Mo(0) using either hydrogen as a reductant or using an aluminum thermite reaction to reduce it.

What do you think?

Alzador

woelen - 28-1-2015 at 02:54

MoS2 is exceptionally inert. I have so-called molycote, which is pure MoS2 in the form of a powder, which has a peculiar greasy feeling and is a perfect lubricant on its own (no solvent or oil is needed for that). I tried dissolving this and could not get it dissolved, not even in warm conc. HNO3.
Probably the only way to have it reacted is burning it in air, giving MoO3. I also think that reducing this to the metal will require non-aqueous chemistry at high temperatures. It would be an interesting experiment, but I also want to warn you. MoO3 is quite volatile and a lot of it will evaporate when e.g. mixed in a thermite reaction. You will lose a lot of Mo and you must be very careful not to inhale the metal-containing smoke.

If your goal is to learn something and see whether you can perform this kind of non-aqueous chemistry at high temperatures, then this endeavor certainly is worth the effort. If your goal is to obtain pure molybdenum metal, then I would suggest you to simply buy it. It can be purchased online (e.g. eBay) for reasonable prices.

Alzador - 28-1-2015 at 03:10

Thank you for the fast reply!

My goal with this would absolutely not be to obtain 99.99% pure Mo metal as I don't have the means to produce that, and as you said buying it would be much more reasonable

. I just want to explore the chemistry of producing a not-so-everyday metal from things that can be easily bought in a store. To me Mo is a metal that I don't come by everyday and it would be interesting to make some chemically by myself

.

I've read that MoS2 is really inert that's why I want to try oxidising it up. Then the oxide could be reduced into the metal. The major problem is here. If reduction happens by a thermite reaction then as you said all kinds of evaporations would happen and the yield would be low not to mention it would be mixed with a bit of Al2O3 which also has to be be removed.

Other than that I only know the H₂ reduction method but as of now I can't really produce H₂ gas safely and I don't want to risk an explosion xD. Do you know any other means to reduce the oxide?

woelen - 28-1-2015 at 04:39

For some metals, reduction with carbon can be used, giving CO and the metal. You usually have to assure that excess metal oxide is used, otherwise the excess carbon dissolves in the metal. I can imagine that molybdenum can form very hard and inert carbides. I know of tungsten carbide being formed in this way, and molybdenum is the lighter congener of tungsten, so maybe this metal can also form such carbides.

I, however, expect that VERY high temperatures are needed for carbon-reduction. This may be a serious problem in an amateur/home setting.

Alzador - 28-1-2015 at 05:49

yes :/ i'm aware that carbon reduction is not an option at home. I think I should go with hydrogen reduction but I will have to find or make an apparatus for producing and containing the gas. I have access to Zinc and hydrochloric acid, I only have to find a not so expensive way to get the hydrogen to the molybdenum oxide.

blogfast25 - 28-1-2015 at 11:29

Quote: Originally posted by woelen

MoO3 is quite volatile and a lot of it will evaporate when e.g. mixed in a thermite reaction. You will lose a lot of Mo and you must be very careful not to inhale the metal-containing smoke.

With a BP of 1155 C that's not a real problem.

The real problem is slag/metal separation: the MP of Mo is 2623 C! Is there enough heat in that thermite to reach that temperature, thus allowing slag/metal separation?

[Edited on 28-1-2015 by blogfast25]

woelen - 28-1-2015 at 13:16

In this context, 1155 C is not a high temperature at all. Thermite reactions can become VERY hot, 2000 C are not uncommon and then you will get a lot of evaporation of MoO3.

Even normal iron thermite goes well above the melting point of iron (which is nearly 1600 C) and I believe that it goes over 2000 C, if I look at the low viscosity of the molten iron and the amount of light, emitted by the iron.

blogfast25 - 28-1-2015 at 13:55

woelen:

For aluminothermic reductions to yield any useful metal their end temperature needs to exceed the MP of alumina (2072 C) by at least a couple of hundred C (but higher tends to better). This does not impede the use of relatively volatile heat boosters like KClO<sub>3</sub> (e.g. for Ti, V, Cr and Nb preparations) as very effective heat boosters. The 2000 C you mention is in fact too low.

The aluminothermic reduction reaction proceeds along a reaction front (or zone), it's not as if the mixture is heated to end temperature all at once.

In the aluminothermic reduction of silica, sulphur + extra aluminium is used to boost heat output and reach the required, say 2500 C. Sulphur has a BP of only 445 C but I can assure you no sulphur boils off in that reaction.

On those grounds I don't expect the relative volatility of MoO3 to pose any problems.

[Edited on 28-1-2015 by blogfast25]

Oscilllator - 29-1-2015 at 00:16

Blimey, it looks like somebody else has done a molybdenum thermite, and with some success too!
I wonder if thermites with plain sulfides work? I imagine they do, but there's only one way to find out...

Alzador - 29-1-2015 at 00:17

Well thank you for your thoughts

I'm going to try the aluminothermic way in the next few days and I will certainly keep you up to date

Peace

Alzador

blogfast25 - 29-1-2015 at 07:52

Quote: Originally posted by Oscilllator

Blimey, it looks like somebody else has done a molybdenum thermite, and with some success too!
I wonder if thermites with plain sulfides work? I imagine they do, but there's only one way to find out...

Blimey, I'm the thermite nut here, how could I forget that post!! Well f*cking done!

Oscillator, slag/metal separation (yield!) would almost certainly benefit from adding a slag fluidiser like CaO or CaF2 (fluorite).

Sulphides thermites would not work so well because the Heat of Formation of Al2S3 is much, much lower than that of Al2O3.

St HoF Al2O3 = - 1676 kJ/mol
St HoF Al2S3 = - 651 kJ/mol (less than half)

For a general sulphurous aluminothermic reduction:

MSx + 2x/3 Al === > M + x/3 Al2S3

... the heat of reaction would be much smaller, all other things being equal. The end temperature would be much lower. It could work in some specific cases, maybe CuS, PbS, CdS and such like.

[Edited on 29-1-2015 by blogfast25]

Alzador - 29-1-2015 at 08:14

Could you explain how slag fluidisers work?

blogfast25 - 29-1-2015 at 08:43

Quote: Originally posted by Alzador

Could you explain how slag fluidisers work?

When the thermite reaction is over (and assuming the mixture was well designed) the metal and slag (alumina) are both present in the liquid state. That mixture is comparable to an oil/water mixture because the molten metal isn't soluble in the molten alumina.

As the mixture cools down rapidly, gravitational separation takes place, with the denser metal sinking to the bottom. This process is greatly sped up if the viscosity of the molten slag is lower.

CaF2 is an inert material (in this context) with a relatively low MP (1418 C) and a high BP (2533 C). It reduces the viscosity of molten alumina significantly, depending of course on dosage.

CaO works slightly differently. It too is inert (in this context: is not reduced by aluminium) but with alumina it forms a series of low melting calcium aluminates, which also reduce the viscosity of the alumina slag:

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

And slag fluidisers have another advantage: the cooled slag (essentially annealed alumina) is somewhat softer, making metal recovery easier.

No industrial aluminothermic reductions are performed w/o slag fluidisers, better known as fluxes.

[Edited on 30-1-2015 by blogfast25]

Alzador - 31-1-2015 at 22:51

Thank you very much for the thorough explanation

I will post pics when I will obtain results.

Alz

blogfast25 - 1-2-2015 at 06:24

Quote: Originally posted by Alzador

Thank you very much for the thorough explanation

I will post pics when I will obtain results.

Alz

Yes, you MUST.

Alzador - 2-2-2015 at 13:37

Well.. here you can see my source of MoS₂: a red can of rust dissolver/lubricant. Sadly It doesn't write the exact compunds of which the stuff is made of but MoS₂ is surely there. I sprayed out quite a bit of the stuff in a plastic cap and saw that the dark greenish black molybdenum sulfide is in some kind of carrier fluid in a very small particle size.

Currently I am waiting for the fluid to evaporate, only then will I be able to do anything to it. Also the small particle size worries me a bit too... :/ What do you think?

Alz

blogfast25 - 2-2-2015 at 14:11

The liquid is a light oil of course, it will take till Kingdom come to evaporate that.

Dilute your product with white spirits (or similar), allow to stand (or filter, if granulometry allows), decant off liquid. Repeat a few times. Then wash with hexane or cyclohexane a few times, then dry.

That should mostly MoS2.

[Edit: reference to oxidation with peroxide removed. Probably not practical/feasible]

Oxidise to MoO3 by roasting: heat very strongly with plenty air oxygen present:

MoS2 + 7/2 O2 === > MoO3 + 2 SO2

[Edited on 3-2-2015 by blogfast25]

Alzador - 4-2-2015 at 01:17

Could other solvents be used to wash the solid from? Pentane or Heptane? Or something more polar like ether? Hexane and other alkane solvents are a bit expensive for me at this time ^^".

Oscilllator - 4-2-2015 at 01:39

Quote: Originally posted by Alzador

Could other solvents be used to wash the solid from? Pentane or Heptane? Or something more polar like ether? Hexane and other alkane solvents are a bit expensive for me at this time ^^".

Anything nonpolar with a low boiling point will work. In the past I have just skimmed a low boiling fraction (<80°) off some of the petrol that goes in my lawnmower. Works fine.

Alzador - 4-2-2015 at 05:27

That sounds really nice but I don't know how to catch the low boiling vapours for separation from the rest. :/ I only have a few beakers and things a normal person would have at home.

EDIT: I managed to find 30-40°C petroleum ether cheap

I think that could be used for washing..

[Edited on 4-2-2015 by Alzador]

blogfast25 - 4-2-2015 at 06:05

Quote: Originally posted by Alzador

EDIT: I managed to find 30-40°C petroleum ether cheap

I think that could be used for washing..

Totally. See if it filters OK.

Alzador - 4-2-2015 at 06:17

Will do but I highly doubt it that I could filter it off..it's particle size is extremely fine.. I think that I would be needing filter paper that is used for BaSO₄ :/

blogfast25 - 4-2-2015 at 08:22

There's nothing like trying it though.

If it fails, a series of decantations will work: MoS2 is pretty dense. Then dry.

Alzador - 4-2-2015 at 10:18

Well since I only have coffee filter atm at home I highly doubt it will filter

but once I get my hands on petroleum ether I will post again.

Until then farewell Gentlemen..