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,
A method of interpretation is presented for the smallangle scattering patterns of vermiculite-ornithine gels. The method has been applied to the results obtained from a vermiculite from Malawi. The distribution of spacings between parallel first-neighbour silicate layers can be described by three order parameters, whose values are found by analysing the experimental modulation functions. The variation of these order parameters with the salt concentration of the suspension should allow one to specify the swelling process as well as the relationship between the crystal chemical properties of the silicate and its behaviour as a colloid.
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