RésuméLes vermiculites Mg, Ca, Sr et Ba ont été étudiées par diffraction des rayons X et absorption infra-rouge.Pour les vermiculites monocouches, l'espacement interréticulaire est compris entre 12·2 et 11·45 Å.On distingue: (i) les vermiculites Ba; le cation, entouré de 5 à 6 molécules d'eau, est à environ 1Å du plan médian et il intéragit avec un hydroxyle structural du feuillet le plus proche, (ii) les vermiculites Mg, Ca et Sr; le cation, entrouré de 3 ou 4 molécules d'eau,est dans le plan médian ou dans son voisinage (0·3 Å), et il n'interagit pas avec les hydroxyles des feuillets.Pour les vermiculites anhydres, l'espacement interréticulaire est inférieur à 10 Å, le cation est dans le plan médian et il intéragit avec les hydroxyles de 2 feuillets opposés.A partir de ces résultats, complétés par les données de la bibliographie, des modéles sont proposés pour représenter l'organisation de l'espace interlamellaire.
A B S T R A C T:Millimetre-sized flakes of a homogeneous, high layer charge vermiculite from S. Olalla (Spain) saturated with l'ornithine cations were made to swell in l'ornithine hydrochloride solutions of various concentrations, and the gel-like structures formed were subjected to uniaxial loads up to 150 g/cm 2. Small-angle X-ray diffraction measurements from the swollen flakes show well-modulated intensity patterns from which the equilibrium interlayer distances were obtained for the various swelling conditions. The interlayer spacings can be adequately expressed as normal-logarithmic distribution functions of probability density. The gel texture is described in terms of the average number of elementary layers, all in parallel orientation, constituting independent coherent domains within the swollen flake. Changes in structure and in texture taking place as the gel volume increases, or as water is expelled from the interlayer volume under mechanical compression, are followed by the variation of the corresponding parameters of order.In contact with water or with dilute electrolyte solutions, expanding-lattice clay minerals, particularly Na-montmorillonite, take up large amounts of the liquid phase (20 g H20/g clay, or more), forming gel structures in which the elementary silicate layers are separated by water films several hundred A thick (Norrish,
Vermiculite single crystals immersed in aminoacid solutions of varying concentration and pH, form complexes characterized by discrete basal spacings. Organic molecules enter in the interlayer space as cations and as dipolar ions through mechanisms of ion exchange and dipole adsorption.The basal spacings of the complexes were recorded. Based on these results the possible arrangements of the aminoacid molecules have been discussed.The main assumptions used are: (a) the electropositive groups NH3+ penetrate into the holes formed by the basal oxygens of the silicate; (13) the C-N bonds are perpendicular to the silicate sheets; (c) the hydrogen atoms of the —CH2 groups are directed towards the sheet surfaces; (d) the —COO− and —COOH groups are located in the middle plane of the interlayer space, halfway between the negative structural charges; and (e) double hydrogen bonds are formed between —COOH groups belonging to organic cations adsorbed onto opposite surfaces.In solutions of higher concentration the crystals swell to the gel state. This phenomenon is due to: (a) the different nature of interlayer cohesion after substitution of the inorganic cations by the aminoacid cationic form; and (b) the appearance of repulsive forces between —COO− groups of adsorbed dipoles, that overcome cohesive forces.
R]~SUMI~ : Par diffraction des Rayons X sur la vermiculite-Li de Santa-Olalla, il a ~t~ montr~ en fonction de la temp6rature qu'il existait diff~rentes phases homog~nes (dool = 12.17 A, T = 25~ dool = 12.02 A, T --60~ dool = 11.89 A, T = 70~ dool = 10.04 A, T = 100~ Par ailleurs, pendant le processus de d6shydratation entre les phases homog~nes ~ 11.89 A et 10.04 A, il a ~t6 mis en ~vidence l'apparition d'~tats inhomog~nes (interstratifi~s). L'utilisation parall~le des m~thodes directes d'~tude des diagrammes de rayons X par transform6e de Fourier monodimentionnelle pour les phases homog~nes et d'une m~thode indirecte de mod~lisation pour les ~tats interstratifi~s a permis de montrer quele passage de la phase 11.89 A ~ la phase 10.04 A se fair conjointement par une s~gr~gation de ces phases et un interstratifi~ al~atoire (11.89-10.04). Ce travail a en outre montr~ que la caract~risation des &ats interm~diaires entre phases homog~nes ne peut etre faite sans une &ude structurale pr~alable des phases homog~nes.ABSTRACT: It has been shown by X-ray diffraction that there are several homogenous phases of the Santa Ollala Li-vermiculite, depending on the temperature (dool = 12.17 A, T = 25~ dool = 12.02 A, T = 60~ dool --11.89 A, T ~ 70~ dool = 10.04 A, T = 100~ During dehydration of the 11.89 A phase to the i0.04 A phase, it is possible to observe heterogeneous (interstratified) states. By using a direct method involving a one-dimensional electron-density projection on to the Z-axis for the homogeneous phases, and an indirect method in which the observed intensities for the (00/) reflections were compared to the calculated intensities for a model interstratified structure, it has been demonstrated that the transformation of the 11.89 A phase to the 10.04 A phase occurs by a segregation between these phases and a random interstratification (11.89-10.04). It has also been shown that characterization of the intermediate states between the homogeneous phases could not be attained without prior study of the homogeneous phases.En g6n6ral, les phases hydrat6es et anhydres des silicates lamellaires du type de la vermiculite, correspondent ~i des &ats que nous appellerons homog6nes. Ceci signifie que, dans la direction perpendiculaire au plan des feuillets, la structure est ordonn6e au sens de l'alternance r6guli6re des feuillets de silicate avec des couches interfoliaires identiques. Le passage d'un 6tat homog6ne ~ un autre se fait par l'interm6diaire des 6tats que nous appellerons inhomog6nes (ou interm6diaires). Leur structure est alors plus ou moins 9 1989 The Mineralogical Society
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.