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Journal ArticleDOI

Electron Microscopy of Clay Surfaces

01 Feb 1954-Clays and Clay Minerals (Springer Science and Business Media LLC)-Vol. 3, Iss: 1, pp 1-25
TL;DR: The most successful method of sample preparation involves pre-shadowing the specimen with platinum and backing this with a layer of carbon prior to removal of the clay with a suitable solvent.
Abstract: Improvements in replica techniques have made possible the high magnification study of textural characteristics and surface features of clay aggregrates found either in nature or in the laboratory. The most successful method of sample preparation involves pre-shadowing the specimen with platinum and backing this with a layer of carbon prior to removal of the clay with a suitable solvent.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors measured intra-erystalline swelling of Na-montmorillonite and Li-vermiculite using diffraction techniques and showed that the size of the interlayer separation is independent of sheet separation and electrolyte concentration.
Abstract: Various workers have studied the mechanism of swelling of Na-montmorillonite and have demonstrated that its ability to swell is due to water penetrating between the individual silicate sheets. In the present study intraerystalline swelling was followed by diffraction techniques which enabled the movement of the silicate sheets with respect to one another to be measured as a function of electrolyte concentration, with or without an externally applied load. The observations have been made on oriented flakes of Na-montmorillonite and single crystals of Li-vermiculite. Qualitatively the minerals behave similarly when swollen in salt solutions. They both show an initial stage of crystalline swelling, after which there is an explosive increase to the gel state, and then the distance apart of the silicate sheets increases linearly with C-½, where C is electrolyte concentration. Quantitatively, however, their swelling is very different, particularly after the “explosion”, where vermiculite generally gives higher spaeings than montmorillonite. There are two other important differences in the swelling of montmorillonite and vermiculite. Firstly, while the swelling of vermiculite appears to be reversible both with respect to electrolyte concentration and applied pressure, the swelling of montmorillonite shows a marked hysteresis. Secondly, in montmorillonite, swelling depends very strongly on pH or chemical treatment. There is little doubt that the development of diffuse “double layers” gives rise to repulsive forces, which cause the silicate sheets to move apart. Van der Waals’ forces have been regarded as providing attraction, but it is found that, at the observed interlayer separations, the magnitude of these attractive forces is inadequate to balance repulsion, both in montmorillonite and vermiculite. The present results demonstrate that in vermiculite swelling proceeds until the interlayer separation causes the repulsion between sheets to drop to a value of ~ 2.5 × 104 dyn/cm2. This attractive force, which limits swelling, appears to be independent of sheet separation and electrolyte concentration. In montmorillonite swelling is opposed by edge-to-face bonds between sheets, whose number and strength can be controlled by chemical treatment. These bonds act to resist any displacement of the sheets, either swelling or contraction. This mechanism is compatible with the observed swelling behavior of montmorillonite, and explains the differences between the swelling of this mineral and that of vermiculite where, because the sheets are considerably larger, the force arising from edge-to-face bonds is small or absent.

115 citations

Journal ArticleDOI
B. F. Bohor1
TL;DR: Authigenic kaolins make up the bulk of the examples because their larger crystallite size, better crystallinity, and open texture make them more suited to examination by the SEM than most other clay mineral types as discussed by the authors.
Abstract: The scanning electron microscope (SEM) proves to be ideally suited for studying the configuration, texture, and fabric of clay samples. Growth mechanics of crystalline units — interpenetration and interlocking of crystallites, crystal habits, twinning, helical growth, and topotaxis — also are uniquely revealed by the SEM. Authigenic kaolins make up the bulk of the examples because their larger crystallite size, better crystallinity, and open texture make them more suited to examination by the SEM than most other clay mineral types.

82 citations

Book ChapterDOI
01 Jan 1971

45 citations

Book ChapterDOI
01 Jan 1971

31 citations

Journal ArticleDOI
TL;DR: In this article, it was suggested that a complete morphological series from plates through laths to tubes exists both in platy to fibrous serpentine and in kaolinite to halloysite (4H2O).
Abstract: Electron microscope studies of chrysotile show that tubes are present in bulk specimens and that these tubes commonly have fuzzy, amorphous-looking material on both the inside and outside. Similar material is associated with synthetic chrysotile and has been noted previously in halloysite specimens. The existence of such material between and within the tubes, together with apparent irregularities in size, shape and packing of tubes, explains the apparent discrepancy between the measured density of bulk samples and the calculated density of a hypothetical sample consisting of close-packed, regular, hollow capillaries. Replicas of fractured surfaces of halloysite (2H2O) from various localities reveal that the particles occur as curved to flat laths commonly possessing “hexagonal” terminations and surface features indicative of a higher degree of crystallinity than tubes of halloysite (4H2O). It is suggested that a complete morphological series from plates through laths to tubes exists both in platy to fibrous serpentine and in kaolinite to halloysite (4H2O). In each series a number of structural varieties are to be expected between the morphologically distinct “end members.”

25 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a method for producing carbon films suitable for electron microscope specimen supports was developed, where carbon is evaporated on to an extremely soluble substrate, which is dissolved away leaving very thin films.
Abstract: A method has been developed for producing carbon films suitable for electron microscope specimen supports. Carbon is evaporated on to an extremely soluble substrate, which is dissolved away leaving very thin films.

289 citations

Journal ArticleDOI
TL;DR: In this paper, the authors discussed the factors which determine image contrast in optical and electron micrographs and proposed a shadow casting technique whereby the contrast of images is greatly increased by depositing obliquely a thin film of metal on the microscope preparations.
Abstract: The factors which determine image contrast in optical and electron micrographs are discussed in relation to a new metal shadow‐casting technique whereby the contrast of images is greatly increased by depositing obliquely a thin film of metal on the microscope preparations Further advantages of the use of shadow‐casting are described, and an estimate is made of the lower limit of size of objects which should be observable by shadow‐casting Examples are given and illustrations are shown of the applications of this technique to the electron micrography of particles of macromolecular dimensions, of replicas of such particles, and of surface replicas prepared in several ways

191 citations

Journal ArticleDOI
TL;DR: In this article, a simple method is described for making replicas of surfaces for study in the electron microscope, and the surface to be studied is cleaned and then coated with a very thin slightly wedge-shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm.
Abstract: A simple method is described for making replicas of surfaces for study in the electron microscope. The surface to be studied is cleaned and then coated with a very thin slightly wedge‐shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm. This film is formed by dipping the prepared surface into a 0.5‐percent solution of the resin dissolved in dioxane or ethylene dichloride and permitting the solvent to evaporate while the surface is held in a vertical position. The replica film is removed by placing the coated surface under water and peeling the film from it. A description of this technique is given in detail. A graph is presented which shows the thickness of resin films obtainable from various concentrations of resin in dioxane, and a table gives the interference effects which may be used for determining approximate thicknesses of thin resin films. Several easy procedures are described for checking the thickness of such films. A technique is described for preparing strong films having a thickness of 100A and an area of 3 cm2 when mounted in air. Such films are very useful when working with the electron microscope and several methods are described for mounting specimens on them, including a conditioning treatment—useful in mounting water suspensions—which makes one surface very hydrophilic. Five micrographs show the results obtainable with the techniques described.

83 citations

Journal ArticleDOI
08 Jun 1945-Science
TL;DR: Two improvements are described in the use of shadow electron micrography for the observation of particles of macromolecular dimensions that involve the substitution of gold for chromium as shadowing metal and metal-shadowing small particles deposited on a very smooth surface such as that of polished glass.
Abstract: Two improvements are described in the use of shadow electron micrography for the observation of particles of macromolecular dimensions. One involves the substitution of gold for chromium as shadowing metal. The thinner gold film that can be employed gives a truer representation of the shape of particles so small that shape and size are significantly altered by the thickness of the shadowing metal deposited on them. The other consists in metal-shadowing small particles deposited on a very smooth surface such as that of polished glass and the handling of this metal film as a replica of the glass surface and the particles resting on it. This technique permits the photography of particles whose direct observation is disturbed by the fine structure that is brought out by shadowing a collodion substrate. Application of these methods to the electron micrography of the tobacco mosaic virus protein shows that its fibrils are rods about 125A both in height and breadth. Though the rods appear segmented, these segments have not been found to have a length that is constant or a small integral multiple of an underlying unit.

62 citations