Sciencemadness Discussion Board

Containing iodine as liquid

Steve s - 2-7-2020 at 14:03

As per subject.
I know this is not possible under normal pressure and temperature but i'm thinking it might be if a low enough pressure can be achieved.

I'm thinking thick walled quartz tube containing a sufficient quantity of elemental iodide ''sublimated'' under vacuum and heat before quickly sealing the tube.

Hoping as it cools some might stay as liquid right down to room temp or better still when warmed to just above.

Can't find any info on this so i'm guessing that low of a pressure is not obtainable, don't want to waste my time and iodine on this if it is 'impossible' any thoughts ??

B(a)P - 2-7-2020 at 14:27

Nile Red did a good demo on iodine, busting the myth that it doesn't melt at standard pressure.
https://www.youtube.com/watch?v=dPIaEWd8zf4
Looking at the phase diagram though, I don't see that it is possible to achieve what you are after.

Steve s - 2-7-2020 at 16:29

It was actually that very video that got me thinking about this, yes unless i'm reading it wrong 0.027Kpa at 20c it would be sublimating not melting, then the pressure will rise the more it sublimates.

B(a)P - 2-7-2020 at 17:43

No mater the pressure it can't be a liquid at less than 113.5 C.

DraconicAcid - 2-7-2020 at 17:46

You want a high pressure if you want it to melt rather than sublime.

chornedsnorkack - 3-7-2020 at 03:13

Quote: Originally posted by B(a)P  
No mater the pressure it can't be a liquid at less than 113.5 C.


Oh, it sure can. Liquids commonly undercool in absence of good crystallization nuclei.
But you cannot melt a solid into an undercooled state.
How do you suppress crystallization nuclei in molten iodine to prompt iodine to undercool?

Tsjerk - 3-7-2020 at 04:26

If you ampule iodine under vacuum you can liquify it by heating. Depending on the vacuum it will liquify somewhere above 113 degrees.

october-2015-article-3-graph-sublimation_page_04.jpg - 46kB

unionised - 3-7-2020 at 11:40

Quote: Originally posted by Steve s  
It was actually that very video that got me thinking about this, yes unless i'm reading it wrong 0.027Kpa at 20c it would be sublimating not melting, then the pressure will rise the more it sublimates.


Water at -35C (or thereabouts) has a vapour pressure of 0.027 KPa

Do you think that somehow stops it ever being a liquid?

Steve s - 4-7-2020 at 15:48

Quote: Originally posted by unionised  
Quote: Originally posted by Steve s  
It was actually that very video that got me thinking about this, yes unless i'm reading it wrong 0.027Kpa at 20c it would be sublimating not melting, then the pressure will rise the more it sublimates.


Water at -35C (or thereabouts) has a vapour pressure of 0.027 KPa

Do you think that somehow stops it ever being a liquid?


It would appear that in these conditions it will sublimate before it melts (liquefies) which is still pretty cool but not as cool as being able to warm it enough to melt it with just the heat from ya hand.

Steve s - 4-7-2020 at 15:55

Quote: Originally posted by Tsjerk  
If you ampule iodine under vacuum you can liquify it by heating. Depending on the vacuum it will liquify somewhere above 113 degrees.



Again still pretty cool but important to make sure you've got a decent vacuum in the ampoule before heating it once sealed

Yttrium2 - 4-7-2020 at 21:27

how is it liquid it iodine tincture? alcohol?????????

karlos³ - 4-7-2020 at 21:52

Think of the different physical states.
The question is, how to contain iodine in its molten state, which is obviously a problem.
But that should be apparent when reading the thread.

chornedsnorkack - 4-7-2020 at 22:34

Quote: Originally posted by Yttrium2  
how is it liquid it iodine tincture? alcohol?????????

Yes.

unionised - 5-7-2020 at 01:58

Quote: Originally posted by Steve s  


It would appear that in these conditions it will sublimate before it melts (liquefies) which is still pretty cool but not as cool as being able to warm it enough to melt it with just the heat from ya hand.

As has been pointed out, you can melt it in a test tube; nothing complicated is needed.

But it simply won't melt from the heat of your hand any more than steel would, and for the same reason.


The lowest you can get (pure) iodine to melt is the triple point at 113.5 °C at 12.1 kPa


[Edited on 5-7-20 by unionised]