Clay, expansion swelling

The catalytic application of clays is related closely to their swelling properties. Appropriate swelling enables the reactant to enter the interlamellar region. The ion exchange is usually performed in aquatic media because the swelling of clays in organic solvents, and thus the expansion of the interlayer space, is limited and it makes it difficult for a bulky metal complex to penetrate between the layers. Nonaqueous intercalation of montmorillonite with a water-sensitive multinuclear manganese complex was achieved, however, with the use of nitromethane as solvent.139 The complex cation is intercalated parallel to the sheets. 

Slickensides are easily observable shiny planes of weakness along which movement occurs in shrink-swell medium-to-heavy clay soils. These are shearing faults, which exist permanently in wet or dry expansive clays. They take the form of cracked, polished, or grooved surfaces, ranging from 10 mm to 200 mm across. Slickensides often run through the soil mass in many directions and may break the structure up into bowl-shaped blocks. They can move up to 25 mm per year. Hence, the frequency and size of slickensides present can quantify the potential capacity of the soil to shrink and swell (i.e., develop cracks when dry). Soils or soil layers with slickensides are highly impermeable to water movement, especially when they are moist and root growth is restricted. 

Morgenstem, N. R., and Balasubramonian, B. I. (1980). Effects of pore fluid on the swelling of clay shale. In 4th International Conference on Expansive Soils, pp. 190-205. Denver. 

The increase in soil pH could be implicated in increasing soil dispersion as well as in increasing clay-swelling potential. This is likely because of the removal of Al-OH polymers from the interlayer. The presence of Al-OH polymers at the lower pH values may limit interlayer swelling. Clays that have the basic 2 1 mineral structure may exhibit limited expansion because of the presence of Al-hydroxy islands which block their interlayer spaces. It is well known that these Al-hydroxy components are removed at low or high pH through dissolution mechanisms. This interlayer removal... 

There are historic reports of floods in the area (32 J. Rutherford, personal communication) and of an earthquake in 18 B.C. (33). The movement of the expansive Esna shale bed formation that underlies the whole area is also a source of disruption (32). The Esna shale bed formation, which contains montmorillonite clay, swells upon hydration by about 12.5% (32). Therefore, if an adequate amount of water is available, for example from increased irrigation, humidification, or flooding, the movement of this shale formation accelerates. Collectively, these dramatic natural events are the most probable causes of the loss of plaster and painted murals in the lower chamber of the tomb prior to its discovery, and they increasingly (32) threaten tombs in the Thebes area. 

This swelling model does not apply to clays with mostly divalent and polyvalent cations on their exchange sites these clays show the hydration stage of expansion but not the osmotic one. The explanation for their behavior is found in the next section. 

Baveye, P. and M. B. McBride (editors). 1994. Clay Swelling and Expansive Soils. Kluwer, Dordrecht, the Netherlands. 

The results of swelling tests are shown in Figure 7, in which the dispersion of data can be mostly attributed to the variations in dry density caused by the small displacement allowed by the equipment. A clear decrease of swelling pressure as a function of temperature is observed. This behaviour is well-matched with the observed increase in the compressibility of the bentonite in the compression tests and the reduction of swelling strains in the soaking tests. Lingnau et al. (1996) and Romero et al. (2003) found also a reduction in swelling pressure with temperature for a sand/bentonite mixture and for a moderately expansive clay, respectively. 

The infiltration of water into clay-like materials causes changes in the pore structure of the material. Water molecules place in the solid matrix and become immobile. In consequence the effective porosity and the intrinsic permeability decrease. If the volume expansion of the material is restrained, swelling pressure is observed which increases linearly with the degree of water saturation, Studer et al. (1984), and BSrgesson (1984). The correlation between swelling pressure p, and void ratio e can be expressed best with the following empirical relationship, Bdrgesson et al. (1995) ... 

X-ray Data. There is no evidence of lattice expansion (probably no penetration into the lattice) by either ethylene glycol or sorbed 2,4-D when the sorption is done at low temperatures. The X-ray data (Table IV) illustrate that variable swelling is lacking in interlayer spaces with different treatments imposed on the organo-clay. Appreciable penetration by 2,4-D probably does not occur without lattice expansion because the voids are too small. Expansion to accommodate 2,4-D likely requires much activation energy. 

Tovey, N.K., Frydman, S., and Wong, K.Y. 1973. A study of a swelling clay in the scanning electron microscope. Proceedings of the 3rd International Conference on Expansive Sods, Haifa, Israel. 

There are various hypotheses explaining this aggregate expansion mechanism. The most wide spread refer to the swelling of clay minerals and of osmotic pressure formation [141,142]. All these hypotheses agree that this phenomenon relates to the reaction of soluble alkalis from cement with the aggregate leading to the decomposition of dolomite ... 

Intraparticle swelling (i.e. swelling due to the take up of water - not only between particles of clay minerals but also within them - into the weakly bonded layers between molecular units) of clay minerals on saturation can cause mudrocks to break down where the proportion of such minerals constitutes more than 50% of the rock. The expansive clay minerals such as montmorillonite can expand many times their original volume. 

Clay deposits are composed principally of fine quartz and clay minerals. The three major clay minerals are kaolinite, illite and montmorillonite. Both kaolinite and illite have non-expansive lattices, whereas that of montmorillonite is expansive. In other words, montmorillonite is characterized by its ability to swell and by its notable cation exchange properties. 

The maximum movement due to swelling beneath a building founded on expansive clay can be obtained from the following expression ... 

Figure 13. Swelling behavior for a smectite clay derived from molecular dynamics simulations of montmorillonite. The equilibrium d-spacing is presented as a function of water content of the clay. The plateaus in the experimental and simulation results at 12 A and 15 A represe nt the stabiUzation of, respectively, the one-layer (insert stracture) and two-layer hydrates. No further expansion of the smectite is observed in nature beyond the two-layer hydrate. The simulations suggest that further swelling of the clay is possible although not thermodynamically favored.

Figure 5.1 The proposed mechanisms for the formation of polymer/clay nanocomposites by the driving force concept, (a) Sodium-type smectite clays, (b) Intercalation of catalyst/ initiator and modified agent leads to inter-layer spacing expansion, (c) Monomers/ oligomers were driven by the catalyst/initiator to swell into the gallery of clay lamellar.

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