Application Note

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Theoretical models of mercury intrusion mechanisms allow information about particle size to be extracted. These models are included in the AutoPore IV Series data reduction package.

In 1965, Mayer and Stowe* published a paper on the mercury breakthrough pressure required to penetrate a bed of packed spheres and the subsequent filling of the interstitial void. This work related particle size to breakthrough pressure and later led to a method for determining the size distribution of particles from the intrusion data in the range of interstitial filling.

This method is based on models of penetration of fluids into the void spaces of a collection of uniform solid spheres packed in a regular manner. The forces resisting penetration of mercury between particles originate from interfacial tensions just as with penetration of mercury into capillaries. The simplest geometry exists when the particles are closely packed monosized spheres in which the shapes of the void necks and void cavities of such a system are calculable.

Regardless of the actual particle shape, the particle size distribution derived from this method is the size distribution of equivalent spheres that, when applied to the mathematical model, most closely reproduces the experimental penetration data. The size unit, then, is ‘equivalent spherical size.' How closely the results compare to that obtained by other methods of particle sizing depends largely on how closely the sample material conforms to the model of closely packed spheres.

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