Broken reusable supersaturated exothermic hand warmer?

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meatyochre
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Broken reusable supersaturated exothermic hand warmer?

Postby meatyochre » Wed Jul 21, 2010 10:54 pm UTC

My friend loaned me one. You boil it for 10 minutes until all the crystals are gone. Then let it cool to room temp (it's supposed to be a liquid). Crack the metal disc inside and it's supposed to crystallize and heat up.

I think it's broken but I'm not sure how or why something like this can break? After I boil away all the crystals and take it out of the pot and let it cool, it's cooling to a solid. And she said it's supposed to stay liquid until you crack the disc (you can jar it and throw it around and stuff, and the crystals aren't supposed to form). I'd like to know why or how something like this can break? There are no holes in it.
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby Ulc » Wed Jul 21, 2010 11:01 pm UTC

I've had a couple of those, and I don't really think it is broken. But what you need to be aware of, is that if there is even a single crystal left in it when you're done heating it, it will cool to slid.

It takes surprisingly long for them to get fully dissolved, have you tried giving them five minutes more?
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby fooliam » Wed Jul 21, 2010 11:11 pm UTC

If its a supersaturated solution, a lack of 100% complete dissolution will result in full crystallization when cooled, as Ulc stated.

Would some kind of damage to the inside of the container be enough to cause recrystallization, similar to scratching the side of a beaker to induce crystallization?
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meatyochre
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby meatyochre » Wed Jul 21, 2010 11:15 pm UTC

Thanks for the quick replies.

I guess it's possible there were a few crystals left. The packet says to rolling boil for 7-10 minutes and I boiled it for 10, but maybe I need to do it for 15 instead and pay more attention.
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby EricH » Thu Jul 22, 2010 2:23 am UTC

meatyochre wrote:Thanks for the quick replies.

I guess it's possible there were a few crystals left. The packet says to rolling boil for 7-10 minutes and I boiled it for 10, but maybe I need to do it for 15 instead and pay more attention.


Even a tiny crystal will do it, so look carefully when you think you're done. (Pro tip--the crystals sink.) My wife uses them all the time, so I can now recharge two in just over two minutes, using the microwave, but I busted a couple before perfecting the technique, so I have to recommend boiling and patience, if only for safety.
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby sodium » Thu Jul 22, 2010 4:24 am UTC

I bought 3 of those when I moved away to college in a snowy area. Mine say to boil wrapped in cloth for 8-10 minutes, but I usually just throw all of them into the pot and boil for 15 minutes, or whenever I look up from my computer and remember they are on the stove. I tried to do them in the microwave once, but they wouldn't liquefy all the way, and cooled back to a solid.

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Delbin
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby Delbin » Thu Jul 22, 2010 9:14 am UTC

Are you at a higher elevation (3000+ feet,) meatyochre? You'll have to boil it longer if so. It really should crystalize if it gets dropped. I know mine used to.

Hmm. I've been meaning to get some sodium acetate to play with.

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Re: Broken reusable supersaturated exothermic hand warmer?

Postby Waylah » Thu Jul 22, 2010 12:33 pm UTC

apparently if you bump it before it cools you can set it off.

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Re: Broken reusable supersaturated exothermic hand warmer?

Postby uncivlengr » Thu Jul 22, 2010 12:43 pm UTC

If it's been used quite a bit, then the metal disc might have scratched the inside of the packet.
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meatyochre
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby meatyochre » Thu Jul 22, 2010 10:36 pm UTC

I'm not at a high elevation, no. Pretty much sea level (yay Lake Michigan!). It says on the packet not to boil (edit: not to microwave) it though, and it's my friend's so I don't want to test it out. But I would if it was mine because I'm curious like a cat (that's why my friends call me Whiskers).

What exactly does the silver thingy do, just agitates the liquid around it? And there is nothing chemical in the disk, right? Because everywhere I looked just said snapping it starts an AMAZING MYSTICAL CHEMICAL REACTIONTM and not the mechanism behind it.
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby uncivlengr » Thu Jul 22, 2010 11:58 pm UTC

meatyochre wrote:What exactly does the silver thingy do, just agitates the liquid around it? And there is nothing chemical in the disk, right? Because everywhere I looked just said snapping it starts an AMAZING MYSTICAL CHEMICAL REACTIONTM and not the mechanism behind it.
When you snap it, it causes a little bubble in the liquid through cavitation, where the crystals can start to form.
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Re: Broken reusable supersaturated exothermic hand warmer?

Postby RayW » Fri Oct 28, 2011 3:08 am UTC

FYI, this redissolving of the sodium acetate starts its reversal at around 160F, while the crystallization begins around 130-140F (depends on NaAc concentration). If indeed all crystals are not dissolved upon heat-up, the undissolved crystals will act as a seed for crystallization to occur upon cooling. There is actually some controversy and lack of understanding on the way the clicker actually starts the crystallization of our hand warmers. In our literary review of scholarly research in this area (yes, there are a number of published papers on this subject) we believe the most credible theory is small metal clicker actually hides and seals some seed crystals in the crevices of slits that are place in the clicker. Flexing the disc actually exposes and frees some of these crystals, which in turns initiates the crystallization of the supersaturated sodium acetate salt. On occasion, if repeated attempts of lengthening the heating time does not resolve the problem, in very rare instances, can be attributed to a 'bum' clicker. Most likely, an area on the disk that has a minor flaw that may expose crystals as the disc cools, but this is only our hunch, without more investigation being performed. We do find this to be a somewhat rare event with only about one instance per year being recorded. Hope this helps and if there should be any other question about reusable hand warmers based on the sodium acetate and water reaction, please feel free to contact me. Have been working with them for over 8 years now.

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