10

Pressure of water vapor in mm.

Figure 4-13. Curves showing relation of vapor pressure and cleavage in mont-morillonite. Experiment conducted as 21 °C. (From Ross arid Hendricks.25)

Figure 4-14. Lattice expansion of montmorillonite. X in NaCI solutions; O in Na2S04 solutions. (From Norrish,26 Courtesy of Discussions of the Faraday

Society.)

Figure 4-14. Lattice expansion of montmorillonite. X in NaCI solutions; O in Na2S04 solutions. (From Norrish,26 Courtesy of Discussions of the Faraday

Society.)

because of acid attack on the crystal structure, and because of the consequent release of Al + 3 ions and conversion of the clay to the aluminum form.

Norrish explained the c-spacing changes in terms of repulsive swelling forces arising from hydration of the interlayer cations, and opposing attractive forces arising from electrostatic links between the negatively charged layer surface and the interlayer cations, as shown in Figure 4-15. In the case of the salts shown in Table 4-4, the swelling forces were not strong enough to break the electrostatic links, and only crystalline swelling was observed. On the other hand, the repulsive forces developed in dilute solutions of sodium, lithium, and hydrogen chlorides were strong enough to break the links, thereby permitting osmotic swelling to take place.

Table 4-4

e-Spacing of Mono-ionic Montmorillonite Flakes in Pure Water*

Cation on the Clay

Cs+1

Maximum c-Spacing Angstroms

0 0

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