X-Ray Study of Interactions between Montmorillonite Platelets

Abstract

SMALL angle X-ray scattering curves have been obtained for a series of Na Wyoming Bentonite clay samples containing 10~o clay by weight and NaPOa in concentrations ranging from 0 to 100 meq/1. From the scattering data, the relative probability of spacings between parallel clay platelets was computed. For the sample containing no NaPOs, the probability distribution showed a relatively broad maximum at an interparticle spacing of about 180 ~. As the concentration of NaP O3 increased, the maximum became sharper and occurred for smaller interpartiele distances. At NaPOa concentrations between 25 and 100 meqfl, the position d of the maximum was given approximately by the equation d=21-b 18.4c-1/~, where d is in angstroms, and v is the NaPO3 concentration in eqfl. The similarity of this relation to the dependence of d on the concentration of NaC1 (Norrish and Rausell-Colom, 1963; Norrish, 1954) suggests that the interparticle spacing depends primarily on the sodium ion concentration and not on the concentration of the anion. The value of d appears to be independent of whether the gel was prepared by the method of lgorrish and Rausell-Colom, in which a dried flake was allowed to come to equilibrium with an electrolyte solution, or whether, as in this investigation, the gel was obtained by centrifuging a dilute suspension. Since the Na ions act to reduce the double-layer repulsion between platelets, while the anions tend to be adsorbed on the platele} edges and thus reduce the edge-to-face linkages (H. van Olphen, 1962), the value of the most probable interpartiele distance appears to be determined primarily by the magnitude of the double-layer repulsion, even though other properties of the clay gels, such as the rheological behavior, are governed mainly by edge-to-face attractions.

Relation Between Crystal-Lattice Configuration and Swelling of Montmorillonites

“…Observe that p is much greater than f. The same observation has been made by others (Norrish, 1954;van Olphen, 1962;Norrish and Rausell-Colom, 1963;Andrews, Schmidt and van Olphen, 1967) who have explained the discrepancy by assuming that an additional attractive force exists because of positive-edge to negativesurface association. However, it has been shown that the edges of the 1 : 1 minerals, kaolinite and dickite, are positively charged only under acidic conditions (Schofield and Samson, 1953;Sumner, 1963;Okuda and Williamson, 1964;Follett, 1965) and that the edges of the 2:1 minerals, pyrophyllite and talc, are negatively charged even under these conditions (Okuda, Inoue and Williamson, 1969).…”

“…These expectations are consistent with Foster's (1953Foster's ( , 1955 observations. Conceivably, free swelling is linearly related to the b-dimension because the b-dimension is proportional to the attraction between negative surfaces and intermediate cations which prevents layer expansion (Norrish, 1954) or, alternatively, to the attraction between negative surfaces and positive edges which causes cross-linking (Norrish and Rausell-Colom, 1963;Andrews, Schmidt and van Olphen, 1967). However, both kinds of attraction, being electrostatic, depend primarily on lattice substitutions that alter electrical charge (Low,t968), whereas, the b-dimension depends on all lattice substitutions (equation 8).…”

Vermiculite gelation: structural and textural evolution

“…Small angle X-ray diffraction (SAXRD) techniques have provided a useful means for measuring preferred equilibrium distances between parallel clay platelets as constrictions of various kinds are imposed on the gel. These measurements have lead to the understanding of the major factors affecting the forces originating at the clay-water interfaces (Norrish, 1954;Norrish & Rausell-Colom, 1963;Andrews et al, 1967). Recently developed methods of interpretations of SAXRD diagrams from disordered layer structures together with experimental improvements involving the use of very strong X-ray sources (synchrotron radiation) have made possible significant advancements in the study of the microstructure of montmorillonite clay gels, enabling quantitative determinations of interlayer distance distributions, order-disorder relationships, pore size distribution and particle geometry analysis under controlled swelling conditions (Pons, 1980;Pons et al, 1981 ;Ben Rhaiem et al, 1987).…”

Interparticle Potential Energies in Na-Montmorillonite Clay Suspensions

“…IN A RECENT investigation of interparticle interactions in Na-montmorillonite clay suspensions to which sodium metaphosphate had been added (Andrews, Schmidt and van Olphen, 1967), small angle X-ray scattering data were used to calculate the pair correlation function g(x) which described the probability$ that, in an aggregate of parallel platelets, the centers of two platelets would be separated by a distance x.…”

“…The pair correlation function g(x) can be obtained from the scattering data by numerical evaluation of the equation (Andrews, Schmidt and van Olphen, 1967) g…”