Interstratified XRD characteristics of physical mixtures of elementary clay particles

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Authors:Nadeau, P. H.; Tait, J. M.; McHardy, W. J.; Wilson, M. J.
Author Affiliations:Primary:
Macaulay Inst. Soil Res., Aberdeen, United Kingdom
Volume Title:Clay Minerals
Source:Clay Minerals, 19(1), p.67-76. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1984
Note:In English. 16 refs.; illus
Summary:Transmission electron microscopic (TEM) examination of the <0·1-µm fraction of montmorillonite and regularly interstratified illite-smectite (I-S) shows that these clays, when dried from suspension, consist primarily of particles 10 Å and 20 Å thick respectively. However, X-ray diffraction (XRD) examination of sedimented aggregates of montmorillonite indicate that the effective number of unit cells that are diffracting coherently is ∼9. This discrepancy can be reconciled by postulating an interparticle diffraction effect from the sedimented aggregates of oriented particles. The interfaces of these particles are capable of adsorbing water, ethylene glycol etc. so that on this basis smectite is composed of elementary silicate particles 10 Å thick, and regularly interstratified I-S is primarily composed of elementary 'illite' particles 20 Å thick, values which are in agreement with the TEM observations. This concept is confirmed experimentally by XRD examination of sedimented aggregates from mixed suspensions of both materials; the resulting patterns are identical to those of randomly interstratified illite and smectite layers, which indicates that the layer sequence examined by XRD has been entirely rearranged. It is concluded that the use of XRD peak breadth to determine mean crystal thickness cannot be reliably applied to these systems. Standard XRD data from sedimented aggregates may not be able to distinguish between true interstratification and interparticle diffraction effects of intimate physical mixtures. [D.J.M.]
Subjects:Adsorption; Clay mineralogy; Clay minerals; Experimental studies; Illite; Minerals; Mixed-layer minerals; Montmorillonite; Sheet silicates; Silicates; Smectite; TEM data; Unit cell; X-ray data
Abstract Numbers:84M/2469
Record ID:1984051137
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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