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Observation of the Hydrated form of Tubular Halloysite by An Electron Microscope Equipped with An Environmental Cell

Published online by Cambridge University Press:  01 July 2024

Norihiko Kohyama
Affiliation:
National Institute of Industrial Health, Ministry of Labor Nagao, Tama-ku, Kawasaki 213, Japan
Kurio Fukushima
Affiliation:
Department of Physics, College of Humanities and Sciences Nihon University, Sakurajosui, Setagaya-ku, Tokyo 156, Japan
Akira Fukami
Affiliation:
Department of Physics, College of Humanities and Sciences Nihon University, Sakurajosui, Setagaya-ku, Tokyo 156, Japan

Abstract

The hydrated form of tubular halloysite [halloysite (10 Å)] was observed by a conventional electron microscope equipped with an environmental cell (E.C.), by which the “natural” form was revealed without dehydration of the interlayer water. This study mainly reports the selected area electron diffraction (SAED) analysis of the halloysite (10 Å) and its morphological changes by dehydration. The SAED pattern showed halloysite (10 Å) has two-layer periodicity in a monoclinic structure with the unit cell parameters of a = 5.14 Å, b = 8.90 Å, c = 20.7 Å, β = 99.7°, in space group Cc, and almost the same structure as the dehydrated form of halloysite [halloysite (7 Å)]. This means that the dehydration of the interlayer water did not greatly change or affect the structure of halloysite (10 Å). Accompanying the dehydration of the interlayer water, there appeared along the halloysite tube axis clear stripes that were about 50–100 Å in width. The diameters of the tubular particles also increased about 10%. From the results of various experiments, such as a focussing series, observation of the surface structure by the replica method, observation of end-views of the tubular particles, and others, these two phenomena were explained as follows: Halloysite crystals have “domains” along the c-axis direction, the thicknesses of the “domains” vary ca. 50–100 Å. They are tightly connected with each other when the halloysite is hydrated, but are separated from each other by the dehydration of the interlayer water, whereupon the stripes come into existence along the tube axis. Taking these considerations into account, a model of dehydration is proposed. Moreover, a new method of calculating the β-angle is proposed in the Appendix.

Резюме

Резюме

Гвдратная форма трубчатого галлуазита /галлуазит (10Å)/ исследовалась под обычном электронным микроскопом,снабженным микросетчатой камерой /М. K./,благодаря чему была выявлена “естественная” форма без дегидратации межслойной воды.Эта статья посвящена анализу методом электронной дифракции избранной зоны /ЭДИЗ/ галлуазита и его морфологических изменений в результате дегидратации.Рисунок ЭДИЗ показал,что галлуазит (10Å) имеет двухслойную периодичность в моноклинальной структуре с параметрами единичной ячейки а=5, 14Å, b=8,90Å, с=20, 7Å, 0=99,7° в пространственной группе Сс и почти такую же структуру,как обезвоженная форма галлуазита /галлуазит [7Å)/.Это означает, что дегидратация межслойной воды не изменяет и не воздействует значительно на структуру галлуазита (10Å).Впроцессе дегидратации межслойной воды вдоль осей трубок появились светлые полосы шириной около 50–100Å.Диаметры трубчатых частиц также увеличились примерно на 10%.В результате различных экспериментов,таких как серии фокусировок,наблюдение поверхностной структкры методом репродукции,наблюдение торцов трубчатых частиц и других, этот феномен объясняется следующим образом.Кристаллы галлуазита имеют “домены”,направленные вдоль о сей с,толщина “доменов” варьирует в педелах 50–100Å.Они тесно связаны друг с другом,когда галлуазит насыщен водой,но разделяются в результате дегидратации межслойной воды,и тогда появляются полосы вдоль осей трубок.Принимая во внимание эти соображения предлагается модель дегидратации.Более того,в приложении предлагается метод вычисления угла ².

Type
Research Article
Copyright
Copyright © 1978, The Clay Minerals Society

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Footnotes

*

Various terms are currently used for the hydrated and the less hydrous forms of halloysite. We use the terms halloysite (10 Å) and halloysite (7 Å) to express the hydrated and the dehydrated forms of haIloysite, respectively, on the basis of the recommendation of the nomenclature committee of A.I.P.B.A. at Mexico City (1975). The term halloysite, however, is occasionaUy used as a group name, i.e. , both forms of halloysite, in this paper.

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