Small-Angle X-Ray Powder Diffraction, Morphology, and Structure of Allophane and Imogolite

S. J. van der Gaast, K. Wada, S.-I. Wada and Y. Kakuto
Netherlands Institute for Sea Research, P.O. Box 59, Texel, The Netherlands
Faculty of Agriculture, Kyushu University 46, Fukuoka 812, Japan

Abstract: Small-angle X-ray powder diffraction analyses and high-resolution electron microscopy of allophane samples (SiO2/Al2O3 ratio, 1.12 to 1.68) showed that allophanes consist of nearly identical spherical particles with diameters of about 40 Å and retain their characteristic “hollow” spherical morphology at different ambient moisture and even after dehydroxylation by heating at 500° to 600°C. Unheated allophane samples gave another X-ray powder diffraction band whose maximum position varied from 12.3 to 14.5 Å depending on their SiO2/Al2O3 ratio. The appearance of this band may denote some long-range ordering in the structure of allophane. Unlike the spherical particles of allophane, the tube unit of imogolite collapsed on dehydroxylation. This observation suggests that imogolite and allophane are different in their framework structures and that a Si- or Si(Al)-tetrahedral sheet rather than an Al-octahedral sheet constitutes the framework structure of allophane, irrespective of its SiO2/Al2O3 ratio.

Key Words: Allophane • Dehydroxylation • Imogolite • Infrared spectroscopy • Morphology • Small angle scattering

Clays and Clay Minerals; June 1985 v. 33; no. 3; p. 237-243; DOI: 10.1346/CCMN.1985.0330310
© 1985, The Clay Minerals Society
Clay Minerals Society (www.clays.org)