Sciencemadness Discussion Board - La metal with Bi

La metal with Bi

D4RR3N - 9-10-2008 at 01:04

I have some La metal and also a quantity of the element Bi, I dont have much use for it at the moment and so was thinking of heating a quantity of La and Bi together to make LaBi, I was just wondering firstly if it would need to be done in a vacuum and secondly what would be the correct weight ratios?

Anyone know of any interesting experiments to do with these elements. I was also thinking of growing a Bi crystal, they look amazing.

crystal.jpg - 72kB

not_important - 9-10-2008 at 01:43

Lanthanum is pretty reactive, in vac or under argon.

Weight ration - see your periodic table.

chemrox - 9-10-2008 at 11:24

Are you sharing La?

D4RR3N - 9-10-2008 at 23:59

Hi chemrox, I dont have much La in comparison to Bi, The annoying thing about the La metal is that when it was posted to me Import must have slit open the package to look inside. When they did this they made a small slit in the vacuum sealed bag which I did not notice to later. The result is that the surface of the material is covered in oxide which I will probably have to remove with a wire brush.

D4RR3N - 11-10-2008 at 08:30

In order to make LaBi what temperature would I need to heat the La and Bi to, La melts at 920C whilst Bi melts at 271.5C

12AX7 - 11-10-2008 at 08:31

If they are in perfect contact, you can calculate the diffusion constant at room temperature. Who needs heat?

Tim

D4RR3N - 11-10-2008 at 08:38

"If they are in perfect contact, you can calculate the diffusion constant at room temperature"

I wish I could

I will need to heat it I think because the La is in lump and the Bi is in needle form, If I heat the mixture to the melting point of Bi will it dissolve the La lump?

12AX7 - 11-10-2008 at 14:54

Do you have a phase diagram for the system? Any idea of the heat of formation of LaBi?

The canonical alloying method heats both to the highest melting point, optionally gives a little stir, then the material is cast (in a mold, or cooled in situ if necessary).

Neither will do anything with oxides around, and worse yet, will do a whole lot more than nothing if oxygen is available. I would recommend a vacuum arc furnace or vacuum or inert gas induction furnace. Probably a fused quartz crucible would suffice. A flux would be good too; do you know if La is reactive enough to reduce a silica flux? If not, regular window glass would be a good flux; if so, it would still be a good flux BUT would leave you with an unknown silicon (and probably sodium) impurity.

Tim

not_important - 11-10-2008 at 18:10

Quote:

Originally posted by D4RR3N
In order to make LaBi what temperature would I need to heat the La and Bi to, La melts at 920C whilst Bi melts at 271.5C

Several papers seem to indicate heating the metals in a silica/quartz tube or capsule to roughly 850 C

The rare earth pnictides formation all seem to be exothermic, even for bismuth. I'd be cautious on heating much at once until I'd tried a few small samples.

As a comparison, lithium melts at 180 C, bismuth at 271 C. To make Li3Bi you heat the two metals together in a tantalum crucible in an inert atmosphere; when the react commences the crucible is heated to incandescence as Li3Bi is formed - mp around 1200 C.

D4RR3N - 12-10-2008 at 03:47

Quote:

Originally posted by 12AX7
Do you have a phase diagram for the system? Any idea of the heat of formation of LaBi?

The canonical alloying method heats both to the highest melting point, optionally gives a little stir, then the material is cast (in a mold, or cooled in situ if necessary).

Neither will do anything with oxides around, and worse yet, will do a whole lot more than nothing if oxygen is available. I would recommend a vacuum arc furnace or vacuum or inert gas induction furnace. Probably a fused quartz crucible would suffice. A flux would be good too; do you know if La is reactive enough to reduce a silica flux? If not, regular window glass would be a good flux; if so, it would still be a good flux BUT would leave you with an unknown silicon (and probably sodium) impurity.

Tim

I could not find much info on LaBi at all, I dont know what temperature LaBi is formed but I do know that La is fairly reactive and reacts with many elements directly. I would rather not use a flux.
I was thinking that if I heated the Bi to melting point it would react with the La directly and dissolve it, Im thinking of how gold dissolves in mercury......I have no idea really

D4RR3N - 12-10-2008 at 03:53

Quote:

Originally posted by not_important

Quote:

Originally posted by D4RR3N
In order to make LaBi what temperature would I need to heat the La and Bi to, La melts at 920C whilst Bi melts at 271.5C

Im so glad you told me the reaction may be exothermic as I was going to mix it all in one go

I think La reacts with silicon so I'm wondering what I can heat this mixture in now, this is quickly becoming more complicated then I first thought

not_important - 12-10-2008 at 04:38

Do a search for LaBi lanthanum, even without access to full papers you'll find several references that heat the mixed elements together in a (fused) silica container.

D4RR3N - 12-10-2008 at 11:06

I think I read the same extract, LaBi formed in a sealed tube by heating to 850C.

Im guessing that they put the LaBi mixture in the tube, vacuum sealed it and then put the whole tube into a tube furnace at 850C.

850C is not far-off the melting point of La, I did not think it would need such a high temperature. Bismuth would be a vapour at that temperature, the tube would become highly pressurised and may burst.

JohnWW - 12-10-2008 at 14:44

In makimng such an intermetallic compound, it should be sufficient for only one of the two metals to be melted; the other should then dissolve in it, if any intermetallic compound is going to form..

unionised - 13-10-2008 at 01:24

850C is only about half the boiling point of Bi, though I'm surprised it needs heating that much. The tube would still be under a partial vacuum at that temperature. What's the melting point of the product? Perhaps thay want to be sure that the product all melts to ensure the reaction is complete and the product homogeneous.

D4RR3N - 13-10-2008 at 13:17

I dont know the melting point of LaBi, I am also surprised that a temperature of 850C is needed because I thought LaBi would be formed close to the melting point of Bi which is 272C

Is it possible to calculate what temperature is required?

12AX7 - 13-10-2008 at 16:22

Melt the damn stuff and you'll have no question as to its formation.

Tim

not_important - 13-10-2008 at 17:55

Quote:

Originally posted by D4RR3N
I dont know the melting point of LaBi, I am also surprised that a temperature of 850C is needed because I thought LaBi would be formed close to the melting point of Bi which is 272C

Is it possible to calculate what temperature is required?

I suspect such calculations may be difficult. Repeating:

lithium melts at 180 C, bismuth at 271 C, Li3Bi at around 1200 C. The exothermic nature of the reaction insure complete melting for all but small amounts of starting materials. If that didn't happen, you could see a shell of the pnictide forming around the higher melting element, leading to incomplete reaction.

I suggest that you try to find a phase diagram and other information on this before proceeding. If full papers are behind registration firewalls, but look as if they may have the needed data, perhaps someone could fetch it for you.

This PDF preview looks as it may be helpful.

[Edited on 14-10-2008 by not_important]

Attachment: La-Bi-phase.pdf (73kB)
This file has been downloaded 911 times

D4RR3N - 13-10-2008 at 23:42

Quote:

Originally posted by 12AX7
Melt the damn stuff and you'll have no question as to its formation.

Tim

I would do if I had a vacuum furnace but I dont so I have to adapt the furnace I have which is a muffle furnace with a max temp of 1100C.
I am going to see if I can find a long quartz tube which has a flat bottom, put the mixture in, plug the open end with a rubber stopper and vacuum pump the air out. If the tube is long enough I wont need to worry about pressure causing the tube to burst or thermal reaching the rubber stopper as only one end will be inserted into the furnace.

D4RR3N - 13-10-2008 at 23:50

Quote:

Originally posted by not_important

Quote:

Thanks for the diagram, it mentioned that heating was preformed over several days, also LaBi at 1615C

not_important - 14-10-2008 at 06:21

That extended time could be to allow diffusion to even out the composition. In effect liquid Bi and Bi-rich alloy dissolve La until the alloy freezes, but diffusion allows the remaining La to diffuse into the alloy body. Just guessing on this.

12AX7 - 14-10-2008 at 07:55

Wow, the La end looks exactly like iron!

Sure illustrates the "bismuthide" character of this compound. Should be pretty easy to make then! Combine La and Bi filings (under inert or vacuum), ignite, check that mixture reaches white heat; if not, toss on some arc or induction heat to finish the job. Even if it doesn't melt, the exotherm is a sure sign that something is going on.

Tim

D4RR3N - 14-10-2008 at 08:59

Now that I seen that chart with LaBi formed at 1615C suddenly the other extract which mentioned heating to 850C is more attractive

I have been trying to find a suitable fused quartz tube to heat the mixture but have not been able to find what is essentially a huge test tube. The only thing I can find which looks remotely like what I'm looking for is a 2000ml borosilicate measuring cylinder with removable foot, take the plastic foot off and its basically a large test tube.

I'm thinking of putting the lower end of this tube into my furnace (upright) and plugging the other with a rubber stopper with vacuum tube in centre.

Any better ideas considering I dont have a arc or vacuum furnace, basically got to use what I have.

With Borosilicate glass I will probably only be able to heat to 750C max.

[Edited on 14-10-2008 by D4RR3N]

unionised - 14-10-2008 at 09:18

I don't think borosilcate glass will stand the temperature- particulalry not under the strees of being evacuated.
http://www.glassonweb.com/articles/article/376/
Even fused quartz might be pushing it slightly.

watson.fawkes - 14-10-2008 at 09:57

@not_important: Great phase diagram! One of the more interesting I've seen, with both positive and negative azeotropic aspects. (Not the best word, since properly "zeotrope" refers to liquid-gas transitions, but I digress.)

@D4RR3N: The horizontal line at 932° C is the melting point of LaBi2; above this line this compound is liquid. Now look at the rectangular region from 50%-75% Bi and 932° - 1615° C. Below the curved line is a mixture of liquid LaBi2 and solid LaBi. This is the crystal-pulling range of this mixture.

Part of this region is within the stated 1100° range of your furnace. You might be able to pull solid crystals out of the melt. It will take a bit of equipment construction, to be sure, not the least because you'll likely need an argon shield. Sorry, am I making a big project for you?

D4RR3N - 14-10-2008 at 11:42

Quote:

Originally posted by watson.fawkes

It will take a bit of equipment construction, to be sure, not the least because you'll likely need an argon shield. Sorry, am I making a big project for you?

Please dont, your going to make me cry

The thing is what kind of tube am I going to find which is suitable to melt this stuff in, its fairly easy to obtain fused quartz tubes but not capped ended ones.

watson.fawkes - 14-10-2008 at 13:17

Quote:

Originally posted by D4RR3N
The thing is what kind of tube am I going to find which is suitable to melt this stuff in, its fairly easy to obtain fused quartz tubes but not capped ended ones.

Are you set on making LaBi, or will LaBi2 do? You can get that by dissolving some La in liquid bismuth and crystallizing out. This is "just like" precipitating out insolubles in water, except for "water" read "bismuth" and for "room temperature" (implicit) read "low-melting alloy temperature", say 500° C. Melt some bismuth, toss in a limiting amount of La, stir, cool it off to, say, 300° C, so your solvent remains liquid, pour it over a filter, say, brass mesh, and collect LaBi2 crystals.

So why will this work? Look at the phase diagram. There's a quadrilateral with a vertical edge at 2/3 Bi, a horizontal edge at 271° C (the melting point of Bi), another horizontal edge at 932° C (the melting point of LaBi2), and a downward-sloping curved edge connecting the triple point of Bi-LaBi-LaBi2 with the melting point of pure Bi. Within this region you have solid LaBi2 in equilibrium with liquid Bi and liquid LaBi2. Hence simple physical phase separation is feasible.

The phase diagram does not directly address solubility. This is relevant to how much La you'll tie up in your Bi/LaBi2 mother liquor after it solidifies. A priori, there's no universal principle to predict this. It depends on whether the compounds can form a single crystal lattice (think "water of crystallization"), whether they act like a non-interacting alloy mixture, whether there is a solid-solid solution phase, or any number of odd things the solid state can do.

I might also point out that LaBi2 is a good candidate for a precursor to practical LaBi synthesis, since you're rejecting some of the exothermic heat of formation in the precursor step. Check the heats of formation of these compounds to see just how advantageous that might be. I would also expect that once the La has formed LaBi2, it's much less susceptible to oxidation.

12AX7 - 14-10-2008 at 14:56

Quote:

Originally posted by watson.fawkes
@not_important: Great phase diagram! One of the more interesting I've seen, with both positive and negative azeotropic aspects. (Not the best word, since properly "zeotrope" refers to liquid-gas transitions, but I digress.)

The minima are eutectic points and the "incongruent melting" (like LaBi2 decomposing into LaBi and melt at 932°C) are peritectics. Regions between straight lines are completely solid phase (but note that there may be solid state reactions taking place, which can look very similar to eutectics (= eutectoid) and such; this diagram however is quite straightforward over 5% Bi), while regions bounded by a curve are "mushy" (liquid + solid). The region above the curves is liquid.

Quote:

@D4RR3N: The horizontal line at 932° C is the melting point of LaBi2; above this line this compound is liquid. Now look at the rectangular region from 50%-75% Bi and 932° - 1615° C. Below the curved line is a mixture of liquid LaBi2 and solid LaBi. This is the crystal-pulling range of this mixture.

Part of this region is within the stated 1100° range of your furnace. You might be able to pull solid crystals out of the melt. It will take a bit of equipment construction, to be sure, not the least because you'll likely need an argon shield. Sorry, am I making a big project for you?

Crystal pulling? Mmmmm lovely...a bit ambitious though I think? Pulling crystals from a peritectic, hmm... as you remove LaBi from solution, melting point drops, so not only do you need careful temperature control, you need it to track concentration! I suppose if you made a device which, like, tracks the width of the boule and regulated the temperature (over the long term) based on that, it would work for any method...hmm... that sounds like fun!

Tim

D4RR3N - 15-10-2008 at 05:46

Quote:

Originally posted by watson.fawkes

Quote:

Originally posted by D4RR3N
The thing is what kind of tube am I going to find which is suitable to melt this stuff in, its fairly easy to obtain fused quartz tubes but not capped ended ones.

, and a downward-sloping curved edge connecting the triple point of Bi-LaBi-LaBi2 with the melting point of pure Bi. Within this region you have solid LaBi2 in equilibrium with liquid Bi and liquid LaBi2. Hence simple physical phase separation is feasible.

The phase diagram does not directly address solubility. This is relevant to how much La you'll tie up in your Bi/LaBi2 mother liquor after it solidifies. A priori, there's no universal principle to predict this. It depends on whether the compounds can form a single crystal lattice (think "water of crystallization"), whether they act like a non-interacting alloy mixture, whether there is a solid-solid solution phase, or any number of odd things the solid state can do.

I might also point out that LaBi2 is a good candidate for a precursor to practical LaBi synthesis, since you're rejecting some of the exothermic heat of formation in the precursor step. Check the heats of formation of these compounds to see just how advantageous that might be. I would also expect that once the La has formed LaBi2, it's much less susceptible to oxidation.

Well when I started out I did not know that LaBi2 existed so I assumed you mix La with Bi and get LaBi. I think it would be interesting to make some of each. I was going to weigh out 40% La and 60% Bi and heat the mixture in a sealed evacuated tube. The Borosilicate tube would be ok for making LaBi2 but looking at the diagram its not going to be useful for making LaBi.

Will LaBi be prone to rapid oxidation or will the Bi prevent this?

watson.fawkes - 15-10-2008 at 11:56

Quote:

Originally posted by 12AX7
Crystal pulling? Mmmmm lovely...a bit ambitious though I think? Pulling crystals from a peritectic, hmm...

Well, yeah, ambitious. Probably not recommended for the original poster.

Quote:

as you remove LaBi from solution, melting point drops, so not only do you need careful temperature control, you need it to track concentration! I suppose if you made a device which, like, tracks the width of the boule and regulated the temperature (over the long term) based on that, it would work for any method...hmm... that sounds like fun!

Yeah, it's an interesting technology problem. I'd imagine the easiest way to solve it is to make a powder dispenser that put the same amount into the melt that the pulling was taking out.

watson.fawkes - 15-10-2008 at 13:07

Quote:

Originally posted by D4RR3N
Well when I started out I did not know that LaBi2 existed so I assumed you mix La with Bi and get LaBi. I think it would be interesting to make some of each.

Well, start with LaBi2. Without new equipment, it's unlikely you'll reach LaBi.

Quote:

I was going to weigh out 40% La and 60% Bi and heat the mixture in a sealed evacuated tube.

Look at the phase diagram closely before you do. You're likely to get unreacted La at the temperatures you can reach.

Quote:

Will LaBi be prone to rapid oxidation or will the Bi prevent this?

Figure out the La oxidation state. Compute the energy of formation.

D4RR3N - 16-10-2008 at 02:15

The mass percent composition of LaBi is 39.9285% La and 60.0715% Bi

The mass percent composition for LaBi2 is 24.9441% La and 75.0559% Bi

If my target is LaBi2 I will heat 25% La with 75% Bi in a Sealed tube at 500C
If my target is LaBi I will heat 40% La with 60% Bi in a sealed tube at 1100C

If the reaction is exothermic then there should be some self heating effect which will raise the temp of the mixture above the maximum temp of my furnace?

watson.fawkes - 16-10-2008 at 09:33

Quote:

Originally posted by D4RR3N
The mass percent composition of LaBi is 39.9285% La and 60.0715% Bi

Ah. Since we had been talking about the phase diagram, I had assumed you were still talking molar percentages.

Quote:

If the reaction is exothermic then there should be some self heating effect which will raise the temp of the mixture above the maximum temp of my furnace?

The maximum temperature of your furnace refers to its ability to heat, not its ability to withstand heat. What you might well worry about is the capacity of your various refractories. If you're using borosilicate as a refractory (which it is compared to flint glass), then it would be useful to estimate the temperature rise before you do anything above microscale. You'll need to know the heats of formation and the heat capacities.

D4RR3N - 16-10-2008 at 13:10

I dont know how exothermic the reaction is going to be, I would actually have to heat a small quantity to see how violent the reaction is, I hope its nothing like a thermite reaction