A method for determining the maeropore-size distribution in a porous solid, as well as the derived distributions for some typical porous materials, is presented. A glass dilatometer placed in a thermostated high-pressure bomb is used to measure the small changes in volume of a mass of mercury, in which the porous material under investigation is immersed, when the mercury is subjected to varying external pressure.
Since finely divided silver "sorbs" oxygen strongly, but not hydrogen or carbon monoxide, it was considered to provide a particularly suitable substance with which to study the relation of adsorption to the kinetics and absolute rates of catalyzed oxidation reactions.1 More recently it was found2 that such silver is capable of reacting with oxygen to form silver oxide at ordinary pressures and at temperatures as low as 170°, at rates which were slow but still sufficiently great to permit accurate measurement of the equilibrium pressures. This finding indicated the possibility that the catalytic activity of the silver may depend on oxide formation rather than adsorption.
Macropore-size distributions in typical porous substances have been measured, using the pressure porosimeter described in the previous paper. Substances investigated include Fuller's earth, diatomaceous earths, silica-alumina gels, flint quartz, porous iron, activated clay pellets and porous desiccants. POROUS materials are characterized by two related quantities: a particle density which is appreciably lower than the real or true density of the material, and a surface area which is greater than the observable geometric surface area.Porous materials differ widely in each of these characteristics; for example, the particle density of some diatomaceous earths is only 20% of the true density, and some activated carbons have surface areas 500,000 times the external geometric area, while the particle ^Second part of paper on "Pore-Size Distribution in Porous Materials." First part is found on page 782.
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