Author Topic: Groovy crystallization experience  (Read 495 times)

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Mountain_Girl

  • Guest
Groovy crystallization experience
« on: August 16, 2002, 03:38:00 PM »
Thought I'd share this interesting phenomenon with the bees (undercover DEA agents: you can read to, this was perfectly legal & you might learn something*):

I was boiling off water from a NaOAc soln (from GAA + NaOH) in order to obtain the dry powder for..um..photographic purposes.
I had to stop for a few hours during which the beaker cooled & a bunch of NaOAc crystals were formed. I then heated it up (dissolving the crystals) and resumed the boiling operation but then had to stop again, leaving it overnight.
I expected to find siginficantly more crystallization in the morning but surprisingly the cold soln was clear.. No crystals. I thought: Huh ? But there were crystals before and now there's even less solvent - there must be crystals !
I briefly considered the possibility of meta-stable super saturated equilibrium but then quickly crushed it with the more realistic assumption that I had simply fucked up once again (I have no illusions about by chem skills).
Buuuttt when I picked the beaker up, a small grain of NaOAc was dislodged from the rim and it fell in. The moment it hit the liquid it triggered a nucleation frenzy ! From that point crystal growth rapidly spread in the form of rays so that within about 10 seconds the whole thing (500 ml) became an almost solid mass of crystals. Very entertaining this was !
Also, the process is quite exothermic.
So I guess it was a meta-stable super saturated state after all.  

* On 2nd thoughts, better not read this, you bastards will probably ban home crystallization.

Flip

  • Guest
Beautiful
« Reply #1 on: August 16, 2002, 07:23:00 PM »
It would be soooo worth it just to see that happen.  I can remember getting really pissed scratching on glass plates trying to get other miscellaneous salts to crystalize.  That would be crazy to see 500ml go in 10 sec.  All I have to say is, "Daayumm", and you can quote me on that.

"I like you, but I wouldn't want to see you working with subatomic particles."

Polverone

  • Guest
This exothermic crystallization...
« Reply #2 on: August 18, 2002, 02:22:00 AM »
...is the basis for those reuseable chemical heat packs that camping/hiking suppliers sell. The supersaturated solution is stable until a stainless steel disc in the center of the plastic pouch is flexed, then it crystallizes and provides heat. Microwave heating restores them.

19th century digital boy