Geoscience Reference
In-Depth Information
Fig. 18.22 Schematic diagram depicting the breakup and formation of quasicrystals. On the left,
the layers are grouped together in a single quasi-crystal; in the middle the same layers are split
into four quasi-crystals; on the right, the layers are completely delaminated (Laird
2006
)
Reprinted from Laird (
2006
). Copyright 2006 with permission from Elsevier
attraction (e.g., Wada et al.
1990
) and to the rigidity of the unit layer (e.g., Norrish
1954
) or to the clay-water system (e.g., Fu et al.
1990
). Evidence of swelling
hysteresis was observed in various experiments using gravimetric measurements
and basal spacing determination, as well as various relative humidity and salt
concentrations (Laird et al.
1995
, and references therein). In general, swelling was
explained in terms of restructured arrangements of the clay and changes in
interactions between layers upon expansion or contraction. It was also considered
that swelling and shrinking of clay minerals is a cause of hysteresis.
Correlation coefficients relating hysteresis magnitude to surface charge density,
percentage of tetrahedral charge, and surface area are not significant, indicating
that the magnitude of hysteresis is independent of the surface charge properties of
the smectites. Based on these results, Laird et al. (
1995
) considered that crystalline
swelling is an ''irreversible thermodynamic process.'' In support of irreversibility,
free energy changes occurring during swelling and collapse can be classified as
free energy of expansion, free energy of attraction, and free energy of transition.
Free energy of expansion is due to changes in the hydration states of the interlayer
cations and negative charge sites, free energy of attraction is due to changes in the
net electrostatic attraction between layers, and free energy of transition is due to
the irreversible work needed to affect transfer of heat and mass during swelling and
collapse. As a consequence, the cause of hysteresis in crystalline swelling is
attributed to both intrinsic and extrinsic processes. Intrinsic hysteresis is a con-
sequence of changes in expansion and attraction energy levels during swelling
caused by the rigidity of the clay-water system. Extrinsic hysteresis is caused by
factors that contribute to additional rigidity of smectite quasicrystals.
