Any chemists on here? How do self heating pads work?

Globalti

Legendary Member
These are the clear vinyl pads, which start with a liquid inside. You find a little metal disc, which you squeeze. This sets off a chain reaction, the whole contents becoming crystalline and hot in a few seconds. Having warmed your hands you then have to boil the pad for 15 minutes to re-liquify the contents and start all over again.

I can't find anything on Google or Ask about them - anybody know what is the liquid and how does it work?
 
nuclear fusion
 

BentMikey

Rider of Seolferwulf
Location
South London
Latent heat of liquefaction. The click triggers a change to the solid state, which releases heat. You then "recharge" it by boiling it back to the liquid state.
 

DaveyL

Well-Known Member
I'm a chemist! I'd imagine it's a super-saturated solution, and clicking the metal disc creates a point around which crystallisation can take place. The crystallisation is exothermic (gives out heat) due to the crystal lattice being much lower in energy than the substance in solution. Heating the solid back up causes it to re-dissolve. I'm not 100% sure but I'd guess this is how it works.
 

Fnaar

Smutmaster General
Location
Thumberland
DaveyL said:
I'm a chemist! I'd imagine it's a super-saturated solution, and clicking the metal disc creates a point around which crystallisation can take place. The crystallisation is exothermic (gives out heat) due to the crystal lattice being much lower in energy than the substance in solution. Heating the solid back up causes it to re-dissolve. I'm not 100% sure but I'd guess this is how it works.
Ere we go.
I think there's a mini-hamster on a wheel inside meself. :sad:
 

DaveyL

Well-Known Member
Ah, a quick google reveals the stuff inside is sodium acetate trihydrate and it does indeed work as above

http://en.wikipedia.org/wiki/Sodium_acetate#_note-0
 

Speicher

Vice Admiral
Moderator
This is another question for the chemists, or physicists or biologists.

Some weeks ago I was returning to my car and noticed a white van, nothing unusual about that but the writing on the back and side said some thing very much like

Wankley - thermodynamic ejaculation

its the underlined bit I'm not sure about. Were they extracting the michael, or what? Is there such a process? If it was a joke it was a very good one, as the decals looked very professional.

I wish I had taken a photo, but in my defence I had only recently acquired a camera phone, and did not think quickly enough.
 

DaveyL

Well-Known Member
Googled your phrase and it turned up nothing, so I took out the word thermodynamic and googled it again!

I think it is a play on the Oakley "Thermonuclear Protection" slogan.
 
OP
Globalti

Globalti

Legendary Member
Thanks all! I can sleep at night now!

How come you found all that on Google and Wikipedia? I thought I'd searched thoroughly.
 
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