Ultrasonic measurement of the surface area of porous materials

Abstract
We have developed a technique to measure the amount of gas adsorbed on a porous solid using ultrasonic velocity measurements. This allows us to determine both the specific surface area and the porosity of the material. The technique has several advantages over conventional methods of determining absorption isotherms. No calibrated volumes or delicate balances are needed; the only measurements being of gas pressure and sound velocity. There is no need to know the mass of the sample or the dead volume of its container. Continuous and automatic measurements are possible, both during adsorption and desorption. We have demonstrated the usefulness and accuracy of this technique for two samples with very different surface areas (about 100 and 3 m2/g). In both cases, the results agree well with conventional volumetric measurements.

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