The physics and the chemistry of the heat pad

B. Sandnes

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Flexing a metallic disk triggers the crystallization of the supercooled sodium acetate solution contained in commercial heat pads. Many mechanisms have been proposed to explain the apparent nucleation of crystalline material. In this paper a simple experiment is described that demonstrates that nucleation is triggered by preserving seed crystals clamped between opposing metal surfaces. An explanation for the retention of the crystalline particles is the elevated melting point caused by very high local pressures. A series of thermophysical properties of the sodium acetate solution is also measured, including the available enthalpy upon crystallization of the supercooled substance, and liquid and solid phase specific heat capacities.

LanguageEnglish
Pages546-550
Number of pages5
JournalAmerican Journal of Physics
Volume76
Issue number6
DOIs
Publication statusPublished - Jun 2008

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acetates
sodium
specific heat
nucleation
chemistry
crystallization
heat
physics
flexing
thermophysical properties
preserving
metal surfaces
melting points
solid phases
seeds
liquid phases
actuators
enthalpy
crystals

Cite this

Sandnes, B. / The physics and the chemistry of the heat pad. In: American Journal of Physics. 2008 ; Vol. 76, No. 6. pp. 546-550.
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The physics and the chemistry of the heat pad. / Sandnes, B.

In: American Journal of Physics, Vol. 76, No. 6, 06.2008, p. 546-550.

Research output: Contribution to journalArticleResearchpeer-review

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