| Pages:
1
2 |
D4RR3N
Hazard to Others
Posts: 271
Registered: 9-1-2007
Member Is Offline
Mood: No Mood
|
|
| 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
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| 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 LaBi<sub>2</sub> 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
LaBi<sub>2</sub> 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 LaBi<sub>2</sub>), and a downward-sloping curved
edge connecting the triple point of Bi-LaBi-LaBi<sub>2</sub> with the melting point of pure Bi. Within this region you have solid
LaBi<sub>2</sub> in equilibrium with liquid Bi and liquid LaBi<sub>2</sub>. 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/LaBi<sub>2</sub> 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 LaBi<sub>2</sub> 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 LaBi<sub>2</sub>, it's much less susceptible to oxidation.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
| 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 LaBi<sub>2</sub>; 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
LaBi<sub>2</sub> 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
Hazard to Others
Posts: 271
Registered: 9-1-2007
Member Is Offline
Mood: No Mood
|
|
| 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. |
Are you set on making LaBi, or will LaBi<sub>2</sub> 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
LaBi<sub>2</sub> 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 LaBi<sub>2</sub> , and a downward-sloping curved edge connecting the triple point of Bi-LaBi-LaBi<sub>2</sub> with the
melting point of pure Bi. Within this region you have solid LaBi<sub>2</sub> in equilibrium with liquid Bi and liquid
LaBi<sub>2</sub>. 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/LaBi<sub>2</sub> 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 LaBi<sub>2</sub> 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 LaBi<sub>2</sub>, 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
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| 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
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| 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 LaBi<sub>2</sub>. 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
Hazard to Others
Posts: 271
Registered: 9-1-2007
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| 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
Hazard to Others
Posts: 271
Registered: 9-1-2007
Member Is Offline
Mood: No Mood
|
|
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
|
|
|
| Pages:
1
2 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
