Mode d'empilement des feuillets dans la vermiculite sodique hydratee a une couche (phase a 11·85 Å)

Abstract

RESUME: Comme la plupart des vermiculites, l'hydrate ~ une couche de la vermiculite-Na (d00 ~ = 11.85 /~) prbsente une structure semi-ordonn6e, avec des d6fauts d'empilement (glissements selon l'axe b). Le plan (hOl)* du r~seau r6ciproque est enti6rement discret, tandis que les rang~es n'appartenant pas ~t ce plan sont plus ou moins diffuses dans la direction c*. La projection xOz est obtenue par une classique analyse de Fourier bidimensionelle. Darts les plans (Okl)* et (lkl)*, certaines rang~es semblent presque discr~tes: ceci permet d'essayer de d&erminer la translation T'selon l'axe 0y entre deux feuillets adjacents. Le calcul des intensit6s des diffusions le long des rang~es des plans (Okl)* et (lkl)* conduit ~t ne retenir qu'un seul module. Le d6sordre r6sulte d'une distribution al6atoire de trois translations parall~les ~ l'axe Oy: l'une est nulle et les deux autres sont de +0.307b et -0.307b. Le principal int6r& de ce travail est de pr6senter une nouvelle m&hode d'approche pour l'&ude des structures semi-ordonn6es. A B S T R A C T:As in most vermiculites, the 11.85 A Na-vermiculite phase has a semi-random structure with stacking faults along the b axis: the (hOl)* plane presents only discrete reflections while other reciprocal rows are more or less diffuse in the c* direction. The xOz projection is obtained by classical two-dimensional Fourier analysis. In the (Ok/)* and (lkl)* planes, some rows appear almost discrete: this allows determination of the 0y translation T from one layer to the next. Calculation of the diffusion intensities along the rows of the (Ok/)* and (lk/)* planes allows a single model to be derived. The disorder is created by the random distribution of three translations parallel to 0y: one is zero and the two others are +0.307b and -0.307b. This paper illustrates a new approach to the study of semi-random structures.Les vermiculites, scion la nature des cations interfoliaires et l'humidit6 relative, sont susceptibles de pr6senter des modes d'empilement des feuillets tr6s diff6rents. Dans la grande majorit6 des cas, ces modes d'empilement sont semi-ordonn6s, ce qui se traduit par des diagrammes de diffraction pr6sentant selon les rang6es parall61es/t la direction c* du r6seau r6ciproque soit des r6flexions discr6tes, soit des r6flexions plus ou moins diffuses.Les empilements r6guliers de feuillets, conduisant ~ une structure ordonn6e tridimensionnellement, ne se rencontrent que lorsque la configuration de la couche 9 1984 The Mineralogical Society

Monte Carlo Simulation of Interlayer Molecular Structure in Swelling Clay Minerals. 2. Monolayer Hydrates

“…The quantitative agreement is very good between the two profiles and with previous studies based on X-ray diffraction analysis (Bradley et al 1963, Le Renard and Mamy 1971, de la Calle et al 1984.…”

“…This result is expected from the trend observed for the montmorillonites, given the high tetrahedral layer charge in vermiculite. The appearance of a doublet, however seems to be in contradiction with the X-ray diffraction analyses of the monolayer hydrate of Na-vermiculite published by Bradley et al (1963), Le Renard andManny (1971), and de la Calle et al (1984), all of whom placed adsorbed Na + at the interlayer midplane. Skipper et al (1991 a) made the same inference in their neutron diffraction study of I 1.8 A Na-vermiculite.…”

“…The calculated layer spacing of vermiculite in Table 1 can be compared with the d-spacings, 11.78-11.85/k, reported for monolayer hydrates of Na-vermiculite (de la Calle et al 1984, Skipper et al 1991a.…”

“…The trend with increasing tetrahedral charge suggests direct binding between Na § and siloxane surface O atoms, and a corresponding dissimilarity with the coordination structure in bulk solution. Indeed, on the basis of their diffraction experiments with the monolayer hydrate of Na-vermiculite, both de la Calle et al (1984) and Skipper et al (1991 a) have concluded that Na + has significant coordination with surface O and that there are only two water molecules in its first coordination sphere.…”

Stacking Order in a 14.30-Å Mg-Vermiculite

“…The study has confirmed the viability of the methods previously used by de la Calle et al (1984) to examine the one-layer Na-vermiculite structure. These methods relied upon the classical techniques of Fourier projections and also a method in which the observed intensities along each (0,k) and (1,k) reciprocal space rods were compared to the values of calculated intensities given by model defect structure (Plan~on, 1981;de la Calle et al, 1984). 4…”