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

Discussion in 'CycleChat Cafe' started by Globalti, 25 Nov 2007.

  1. Globalti

    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?
  2. nuclear fusion
  3. papercorn2000

    papercorn2000 Senior Member

  4. Dayvo

    Dayvo Just passin' through

  5. BentMikey

    BentMikey Rider of Seolferwulf

    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.
  6. palinurus

    palinurus Guru

  7. DaveyL

    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.
  8. Fnaar

    Fnaar Smutmaster General

    Ere we go.
    I think there's a mini-hamster on a wheel inside meself. :sad:
  9. DaveyL

    DaveyL Well-Known Member

    Ah, a quick google reveals the stuff inside is sodium acetate trihydrate and it does indeed work as above
  10. Speicher

    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.
  11. DaveyL

    DaveyL Well-Known Member

  12. Speicher

    Speicher Vice Admiral Moderator

    The mind boggles - how did you know about the existence of these decals?;) and that you could find them on e-bay?

    What does thermonuclear ejaculation mean (if anything) or shouldn't I ask?:sad:
  13. DaveyL

    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.
  14. KitsuneAndy

    KitsuneAndy New Member

    What about self heating cups of coffee?
  15. OP

    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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