wierd siency stuff
09-20-2007, 10:58 PM
#1
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09-21-2007, 01:53 AM
#3
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Re: wierd siency stuff
Actually I don't believe it has anythign to do with oxygen. I believe its a super cooled liquid. Freezing actually releases heat, since it would be a solid at room temperature, it just requires a shock, or a crystal of the solid form to start a chain reaction. Sodium Acetate is used in those reusable heat packs. They are sealed, with no oxygen and are activated by bending a metallic disc that creates an audible click and shockwave. The solidifying action propagates outward from the disc, and within a couple seconds the whole packet is solid, and very hot.
Edit, I was pretty close. http://en.wikipedia.org/wiki/Sodium_acetate
Edit, I was pretty close. http://en.wikipedia.org/wiki/Sodium_acetate
Sodium acetate is also used in consumer heating pads or hand warmers and is also used in "hot ice". When sodium acetate trihydrate crystals (melting point 58 °C) are heated to around 100 °C, they melt. When this melt cools, it gives a supersaturated solution of sodium acetate in water. This solution is capable of supercooling to room temperature, well below its melting point, without forming crystals. By clicking on a metal disc in the heating pad, a nucleation center is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted.
09-21-2007, 04:45 PM
#6
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Re: wierd siency stuff
Originally Posted by aero
Actually I don't believe it has anythign to do with oxygen. I believe its a super cooled liquid. Freezing actually releases heat, since it would be a solid at room temperature, it just requires a shock, or a crystal of the solid form to start a chain reaction. Sodium Acetate is used in those reusable heat packs. They are sealed, with no oxygen and are activated by bending a metallic disc that creates an audible click and shockwave. The solidifying action propagates outward from the disc, and within a couple seconds the whole packet is solid, and very hot.
Edit, I was pretty close. http://en.wikipedia.org/wiki/Sodium_acetate
Edit, I was pretty close. http://en.wikipedia.org/wiki/Sodium_acetate
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