Clays and Clay Minerals

, Volume 37, Issue 5, pp 459–463 | Cite as

Effects of Relative Humidity on the Basal Expansion of Mg-Smectite Equilibrated with Ethylene Glycol at Low Vapor Pressure

  • Y. P. Hsieh


The effects of relative humidity (RH) on the expansion of Mg-smectite, equilibrated with low vapor pressure of ethylene glycol (EG), was studied. Four smectite samples were equilibrated with EG vapor from: (1) saturated vapor of pure EG, (2) an EG-CaCl2 solvate, and (3) 0.05 relative EG vapor pressure at 65°C. X-ray powder diffraction (XRD) analyses of the clays under different RH conditions indicated that without EG, the basal spacing of Mg-smectite samples could only be expanded to 16 Å, even at 0.97 RH. The basal spacing of Mg-smectite samples equilibrated with saturated EG vapor was expanded to 17.1 Å and was not significantly affected by RH in the range 0.1–0.9. The basal spacing of the Mg-smectite samples equilibrated with vapor from the EG-CaCl2 solvate and 0.05 relative EG pressure at 65°C was expanded by an amount that depended on the RH during the XRD analysis. The basal spacing increased from 14.2 to 17.1 Å as the RH increased from 0.6 to 0.75, except for sample API 23, which expanded to 17.1 Å at RH > 0.9. This sample did not expand beyond 16 Å when it was equilibrated with 0.05 EG relative vapor pressure. Sorption of moisture from air caused the one-layer EG-Mg-smectite complex (basal spacing = 14.1 Å) to rearrange itself to a double-layer EG-Mg-smectite complex (basal spacing = 17.1 Å). A small amount of the adsorbed EG in Mg-smectite, much less than was needed to cover a one-layer of the interlayer surfaces, caused an expansion of the basal spacing to 17.1 Å at high RH during the XRD analysis. The minimum amount of adsorbed EG which caused the one-/two-layer EG complex conversion was about 20–30 mg EG/g. The conversion was fast (<5 min) and was relatively reversible.

Key Words

Basal expansion Ethylene glycol Relative humidity Smectite X-ray powder expansion 


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  1. Boublick, T., Fried, V, and Hala, E. (1973) The Vapor Pressure of Pure Substances: Elsevier, New York, p. 98.Google Scholar
  2. Dyal, R. S. and Hendricks, S. B. (1950) Total surface of clays in polar liquids as a characteristic index: Soil Sci. 69, 421–432.CrossRefGoogle Scholar
  3. Hsieh, Y. P., Tsai, P. P., and Hsu, P. H. (1984) Expansion of smectites as a function of vapor pressure of ethylene glycol: Soil Sci. Soc. Amer. J. 48, 935–939.CrossRefGoogle Scholar
  4. Jackson, M. L. (1969) Soil Chemical Analysis–Advanced Course: Published by the author, Department of Soil Science, University of Wisconsin Madison, 127–141.Google Scholar
  5. Keren, R. and Shainberg, I. (1975) Water vapor isotherms and heat of immersion of Na/Ca-montmorillonite systems–I: Homoionic clay: Clays & Clay Minerals 23, 193–200.CrossRefGoogle Scholar
  6. Kunze, G. W. (1955) Anomalies in the ethylene glycol solvation technique used in X-ray diffraction: in Clay and Clay Minerals, Proc. 3rd. Natl. Conf., Houston, Texas, 1954, W. O. Mulligen, ed., Natl. Acad. Sci. Natl. Res. Counc. Publ. 395, 88–93.Google Scholar
  7. Mooney, R. W., Keenan, A. E., and Wood, L. A. (1952) Adsorption of water vapor by montmorillonite–II. Effect of exchangeable ions and lattice swelling as measured by X-ray diffraction: J. Amer. Chem. Soc. 74, 1371–1374.CrossRefGoogle Scholar
  8. Morin, R. E. and Jacobs, H. S. (1964) Surface area determination of soils by adsorption of ethylene glycol vapor: Soil Sci. Soc. Amer. Proc. 38, 190–194.CrossRefGoogle Scholar
  9. Shainberg, I. and Kemper, W. D. (1966) Electrostatic forces between clay and cations as calculated and inferred from electrical conductivity: in Clays and Clay Minerals, Proc. 14th Natl. Conf., Berkeley, California, 1966, S. W. Bailey, ed., Pergamon Press, New York, 117–132.CrossRefGoogle Scholar

Copyright information

© The Clay Minerals Society 1989

Authors and Affiliations

  • Y. P. Hsieh
    • 1
  1. 1.Wetland Ecology ProgramFlorida A&M UniversityTallahasseeUSA

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