Gel filled heat pads. How do they work?

[AndyKH]

Ok, i have some of those gel heat pads with the little metal disks. After activating them yesterday i started wondering how they work? Does anyone know as i'm very intrigued.

[knk]

Sodium acetate trihydrate crystals have a melting point of 58 °C. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of supercooling to room temperature 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.

[knk]

http://www.howstuffworks.com/question290.htm

[AndyKH]

Brilliant, thankyou.

[AndyKH]

anonymous said:

[redacted]

[R360]

http://www.heatinaclick.com/Products/PocketsSize/t...

I bought three of these last week for a tenner. I was also wondering how they work, thanks for the info!

[sprinter885]

Now- everybody go & repeat knk's explanation to all your friends--word perfect mind you !!

[Viper_Larry]

AndyKH said:

Ok, i have some of those gel heat pads with the little metal disks. After activating them yesterday i started wondering how they work? Does anyone know as i'm very intrigued.

Let me guess - you were at the Race of Champions yesterday?

[AndyKH]

Erm no, my O/H has a bad back and wanted to place the heat pads on the muscle.

[Mr POD]

knk said:

Sodium acetate trihydrate crystals have a melting point of 58 °C. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of supercooling to room temperature 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.

I asked my son, he said " Exotheric reaction to create the heat, ENDothermic reaction to turn it back to the ready state "

Apparently he's predicted A* in both Physics and Chemistry at GCSE so I left it at that.

[Viper_Larry]

AndyKH said:

Erm no, my O/H has a bad back and wanted to place the heat pads on the muscle.

Oh! We were, it was damn freezing, my wife had her heat pads and we were trying to work out how they worked

[clonmult]

Mr POD said:

knk said:

Sodium acetate trihydrate crystals have a melting point of 58 °C. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of supercooling to room temperature 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.

I asked my son, he said " Exotheric reaction to create the heat, ENDothermic reaction to turn it back to the ready state "

Apparently he's predicted A* in both Physics and Chemistry at GCSE so I left it at that.

I prefer the answer of "its magick!". Much easier to understand ....