Geoscience Reference
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Fig. 1.6 TEM images of Na-montmorillonite particles: a low-magnification TEM image
showing a typical crystalline aggregate; b the corresponding SAED pattern: note the 001
diffraction spots corresponding to the planes parallel to the e-beam; the calculated spacing is
13.83 Å; c high-resolution TEM image of a particle attached to the edge of the aggregate [white
frame in (a)] exhibiting the layered structure; the measured lattice spacing (13.8 Å) is in
agreement with calculations from the SAED in (b). Reprinted with permission from Yaron-
Marcovich et al. (
2005
)
originates from three different sources: pore water lost below 110 C, adsorbed
water lost below 300 C, and OH water at a temperature above 300 C.
Structural patterns of smectites may be obtained by X-ray diffraction (XRD),
high-resolution transmission electron microscopy (HRTEM), and Fourier trans-
form infrared spectroscopy (FTIR). Borchardt (
1989
) reported on the effect of
saturating cations on the basal spacing of smectites (a mixture of montmorillonite
and beidellite from a Californian soil) using XRD measurements. All magnesium-
saturated smectites give a peak corresponding to a d-spacing of 1.5 nm at 54 %
relative humidity, while potassium-saturated smectites give a peak corresponding
to a d-spacing of 1.25 nm at the same moisture content. These differences are
explained by variations in the hydration status of the saturating ions. When
smectites are kept at 0 % relative humidity after 110 C heating, they yield a peak
corresponding to a d-spacing of 1.0 nm. Simultaneous morphological observation
by HRTEM and chemical analysis by AEM (EDS) techniques provide a com-
prehensive, nanoscale level understanding of smectite interlayer configuration and
composition.
TEM images (Yaron-Marcovich et al.
2005
) show the morphology of a sodium-
montmorillonite along with the corresponding selected area electron diffraction
(SAED) pattern (Fig.
1.6
). At lower magnification, the presence of crystalline
aggregates composed of relatively small, thin, flakelike, and pointed nanoscale
