The Meaning of Surface Area

It will be seen that each method for surface area determination involves the measurement of some property that is observed qualitatively to depend on the extent of surface development and that can be related by means of theory to the actual surface area. It is important to realize that the results obtained by different methods differ, and that one should in general expect them to differ. The problem is that the concept of surface area turns out to be a rather elusive one as soon as it is examined in detail. 

The difficulty in stating just what is meant by the surface area of a solid, in 

Quite obviously, the geographer solves this logical difficulty by arbitrarily deciding that he will not consider irregularities smaller than some specified size. A similar and equally arbitrary choice is frequently made in the estimation of surface areas. The minimum size of irregularities to be considered may be 

Finally, in the case of solids, there is the difficulty that surface atoms and molecules differ in their properties from one location to another. The discussion in Section VII-4 made clear the variety of surface heterogeneities possible in the case of a solid. Those measurements that depend on the state of surface atoms or molecules will generally be influenced differently by such heterogeneities. Different methods of measuring surface area will thus often not only give different absolute values, but may also give different relative values for a series of solids. 

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K. A. Kini The paper by Bond and Spencer shows the skepticism with which they view the problem of the surface area of coal. More than two decades have passed since the question was first raised, and we are still debating it. I wonder whether this debate needs to continue in view of the work on CO2 adsorption by coals by Kini (3), Walker and Geller (9), Anderson and co-workers (2), and the recent work using krypton and xenon under pressure by Kini (4). Surely, the data in these papers represent reasonably acceptable values of the total surface areas of coals. The meaning of surface area in pores of molecular dimensions is admittedly a difficult question, but I feel that the difficulties are exaggerated by the authors. 

It was about this time that the debate over the meaning of surface area was reaching a climax. It was also the time that several methodologies, for the characterization of porosities. 

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