Gibbs-Thomson effect

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The Gibbs-Thomson effect (not to be confused with the Thomson effect) relates surface curvature to vapor pressure and chemical potential. It is named after Josiah Willard Gibbs and three Thomsons: James Thomson, William Thomson, 1st Baron Kelvin, and Sir J. J. Thomson.

It leads to the fact that small liquid droplets (i.e. particles with a high surface curvature) exhibit a higher effective vapor pressure, since the surface is larger in comparison to the volume. The Gibbs-Thomson effect can cause strong depression of the freezing point of liquids dispersed within fine porous materials.

Another notable example of the Gibbs-Thomson effect is Ostwald ripening, in which concentration gradients cause small precipitates to dissolve and larger ones to grow.

The Gibbs-Thomson equation for a precipitate with radius $R$ is:

$\frac{p}{p_{eq}} = \exp{\left(\frac{R_{critical}}{R}\right)}$

$R_{critical} = \frac{2 \cdot \gamma \cdot V_{Atom}}{k_B \cdot T}$

$V A t o m$ : Atomic volume

$k B$ : Boltzmann constant

$γ$ : Surface tension (J $\cdot$ m

- 2

)

$p e q$ : Equilibrium partial pressure (or chemical potential or concentration)

$p$ : Partial pressure (or chemical potential or concentration)

$T$ : Absolute temperature

Ostwald ripening is thought to occur in the formation of orthoclase megacrysts in granites as a consequence of subsolidus growth. See rock microstructure for more.