Measurement of the Specific Surface Area of Clays by Internal Reflectance Spectroscopy1

D. J. Mulla2, P. F. Low and C. B. Roth
Department of Agronomy, Purdue University West Lafayette, Indiana 47907
1 Journal paper number 10,117.
2 Present address: Department of Agronomy and Soils, Washington State University, Pullman, Washington 99164.

Abstract: The specific surface area, S, of a clay is commonly measured by the adsorption of ethylene glycol monoethyl ether (EGME); however, this method can be tedious and time consuming, especially if the clay is saturated with a monovalent, highly hydrated cation. An alternative method for measuring S was developed involving infrared internal reflectance spectroscopy. This method is based on the discovery that the ratio of R1, the reflectance of a clay-HOD mixture at the frequency of O-D stretching, to R2, the reflectance of the mixture at the frequency of H-O-D bending, is linearly related to S. The correlation coefficient between R1/R2 and S, as measured by the adsorption of EGME, was 0.995. Consequently, a calibration curve of R1/R2 versus S was constructed, and the measured values of R1/R2 for any clay-HOD mixture were referred to it for the determination of S. Results were obtained in triplicate in about an hour; hence, this method of determining S is more rapid and convenient than that involving the adsorption of EGME. Moreover, it applies to clays in a natural condition, i.e., swollen in water.

Key Words: Ethylene glycol monoethyl ether • Infrared spectroscopy • Internal reflectance spectroscopy • Molar absorptivity • Montmorillonite • Surface area

Clays and Clay Minerals; October 1985 v. 33; no. 5; p. 391-396; DOI: 10.1346/CCMN.1985.0330503
© 1985, The Clay Minerals Society
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