(April 15, 1993) - The measurement of surface area and the characterization of porous solids are of great technological interest. These material properties are of importance in liquid and gas purification, oil recovery, catalysis and adsorption separation processes. The increasing use of activated carbons and zeolitic materials has especially stimulated interest in that region of the pore size spectrum near a few molecular diameters.
Until now, practical, working methods for obtaining such information from adsorption isotherms have largely been based on methods and technology dating back to the 1930's. For example, fitting data to the BET equation was possible because one could plot the data in a linear form, draw a straight line through visually selected points, read the slope and intercept, and with a slide rule calculate the surface area. Similarly, the BJH method of obtaining a pore volume distribution could be performed manually with little difficulty. More exact formulations were even then available, but unusable for practical purposes.
The computer program supported by this document, called DFT, represents the first practical method of routinely analyzing experimental adsorption isotherms using methods based on modern theoretical physical chemistry. It incorporates the latest developments in the statistical thermodynamics of inhomogenious systems through the use of density functional theory. This program would not have been possible without “supercomputing” resources to construct the underlying models; modern desktop computers, however, are easily able to perform the data reduction.
We expect that DFT, like any pioneering development, will evolve. Additional adsorptives, sample temperatures, pore geometries, and substrate chemistry models will be added to the model library. Future releases of DFT may incorporate new theoretical refinements and will, therefore, not be guaranteed to produce precisely the same answers as this, the first version, when applied to the same data. It is our intention, however, to improve subsequent releases in underlying theoretical structure, in completeness of data analysis and presentation, and in ease of use. We at Micromeritics feel that this release of DFT puts a powerful tool in the hands of those who would use adsorption isotherms to characterize materials. We welcome your comments.
James P. Olivier
William B. Conklin
Michael von Szombathely
Micromeritics Instrument Corporation
One Micromeritics Drive
Norcross, GA 30093
USA April 15, 1993