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Structure analysis of montmorillonite crystallites by convergent-beam electron diffraction

T. Beermann and O. Brockamp
Structure analysis of montmorillonite crystallites by convergent-beam electron diffraction
Clay Minerals (March 2005) 40 (1): 1-13

Abstract

The small particle size and the random stacking of layers has previously hindered systematic structure investigations of montmorillonite. By applying the convergent-beam electron diffraction mode (CBED) of a transmission electron microscope (TEM) with a beam spot of approximately 800 Aa we were able to examine undisturbed areas of montmorillonite crystallites. Because montmorillonite crystallites are mostly thin particles, kinematic theory can be applied and the CBED patterns can be interpreted directly, provided that the particle thickness remains below the critical value of 350 Aa. An average thickness of approximately 90 Aa was calculated here for montmorillonite of bulk samples from X-ray diffraction analysis and lattice-fringe images. However, satisfactory diffraction intensity patterns for quantitative evaluation were obtained only from crystallites with a thickness above the average, which yielded a sufficient scattering volume. These patterns could be described in terms of the kinematic theory and therefore these crystallites were <350 Aa thick. Yet, crystallites of adequate thickness were extremely rare in the three samples investigated (Clay Spur, Rock River and Upton, all in Wyoming, USA). The diffraction intensities from the ab plane of single montmorillonite crystallites of the various origins fit the three structural models for a trans-vacancy distribution, a cis-vacancy distribution or a random-cation distribution within the octahedral sheets. The configuration of the diffraction patterns also shows a 1M symmetry of the layer. Due to the limited data set of CBED patterns, a refinement of the structure could not be achieved. However, energy dispersive X-ray spectroscopy data and computation of the cation-anion distances and valences using the "distance valence least square" program permitted a refinement of the models.


ISSN: 0009-8558
EISSN: 1471-8030
Coden: CLMIAF
Serial Title: Clay Minerals
Serial Volume: 40
Serial Issue: 1
Title: Structure analysis of montmorillonite crystallites by convergent-beam electron diffraction
Affiliation: Universitaet Bremen, Fachgebiet Mineralogie, Bremen, Federal Republic of Germany
Pages: 1-13
Published: 20050301
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 32
Accession Number: 2005-027058
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
N43°30'00" - N44°10'00", W105°04'60" - W104°04'60"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200515
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