Clay-water System Research Articles

Low temperature phase changes in montmorillonite and nontronite at high water contents and high salt contents

Prior work has revealed the existence of one or more low temperature phase changes in clay water systems in the temperature range −20°C to about −50°C. The number and the temperatures at which these phase changes appear seems to be associated with the type of exchangeable ion(s) and the number and nature of individual water domains present. In this paper, we report the results of low temperature differential calorimetry on montmorillonite and nontronite clays at high water and high salt contents. The presence of electrolytes at high concentration is shown to have a very marked effect. The low temperature phase changes are completely absent at high electrolyte concentrations in these clay water systems. The presence of electrolytes also was observed to have a distinctive effect on the shape of the initial freezing peak associated with ice segregation.

A possible role of fluctuating clay-water systems in the production of ordered prebiotic oligomers

A model is proposed for the intermediate stages of prebiotic evolution, based on the characteristics of the adsorption and condensation of amino acids and nucleotides on the surface area of clay minerals in a fluctuating environment. Template replication and translation of adsorbed oligonucleotides and catalytic effects by peptide products on further condensation are proposed, due to specific properties of hypohydrous clay surfaces as well as the biomolecules themselves. Experimental evidence supports some of the proposed interactions, and all of them can be tested experimentally.

Reactivity of Adsorbed and Structural Iron in Hectorite as Indicated by Oxidation of Benzidine

AbstractThe roles of different forms of Fe(III) impurities in a hectorite with respect to the oxidation of benzidine in aqueous suspension have been evaluated using electron spin resonance and UV-visible spectroscopy. Natural surface-adsorbed Fe(III) showed no detectable activity in the oxidation process, while very small quantities of structural octahedral Fe(III) apparently promoted a relatively rapid conversion to the radical cation. However, extremely small quantities of benzidine were oxidized in comparison to the exchange capacity of the clay. Freshly adsorbed Fe3+ cations effectively oxidized benzidine, but lost much of this ability upon aging. The Fe(III)-benzidine electron transfer could be distinguished from an O2-benzidine reaction, since the latter reaction was slow and limited by the rate of O2 diffusion into the clay-water system. The O2-benzidine reaction was also inhibited at high pH. The existence of two reaction mechanisms and the involvement of only a small fraction of the total structural iron, as shown by comparison of the hectorite and a montmorillonite, may explain the conflicting interpretations in the literature. The benzidine blue reaction not only requires an oxidizing agent to form the radical, but also a clay surface to adsorb and stabilize it against further oxidation.

Neutron Diffraction from Clay-Water Systems

AbstractThe use of neutron diffraction to determine some of the structural properties of montmorillonite-water systems at low water concentrations is described. The samples were prepared by compression or suction to give clay samples with between one and three molecular layers of water between the plates.About 10% of the platelets in the clay are randomly oriented. The remainder are partially oriented in the plane of the sample, with an angular spread of 40° about the mean orientation. It is suggested that these oriented domains are formed from the larger platelets present in the system. The Bragg diffraction pattern is better explained by a disordered lattice model rather than by a mixture model with small particles having a well-defined lattice spacing. We have fitted both the intensities of (00l) reflections and the shape of the (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value. The half width of the spread is about 10% of the lattice spacing.No significant structural differences are found between Li, Na, K, and Cs montmorillonites. The method of preparation has no effect on the structural properties of the large platelet particles but does affect the randomly oriented fraction. The lattice spacing of the latter appears to be better defined for samples prepared by compression.Experiments on the variation of lattice spacing with humidity indicate that the structural model we have used is adequate except at humidities where the system is changing over from one to two, or two to three water layers.

Nuclear magnetic relaxation and structure in aqueous heterogenous systems

The relaxation of water in aqueous heterogeneous systems is described in terms of the effects of the substrate structure and order on the motions and arrangements of the water molecules. The general observation that T 1 is long compared to T 2 indicates that at least one of the correlation times (τc) is long. A long τc can result from tight binding of some molecules or from the combination of preferential orientation and substrate order. Since doublet splitting characteristic of preferential orientation has been observed for water on a wide variety of organic and inorganic substrate materials, the latter effect might be of general importance in the relaxation phenomena of heterogeneous systems, including biological tissue. For this effect, the conventional 90°–180° T 2 relaxation curve and the solid-echo curve are calculated for random transitions in a powder sample and for transitions in a gaussian distribution of doublet splitting constants. The results are applied to measurements on clay-water systems to illustrate some effects of structure on transverse relaxation. This application indicates that (a) samples made from oriented clays contain domains characterized by different water contents and different orientations, and (b) the rigidity and domain size and order for powder samples increase with particle size decrease.

Protonation of Organic Bases in Clay—Water Systems

AbstractThe extent of protonation of organic bases in clay—water systems depends upon the adsorptive properties of the organo-clay species involved, and upon the structure and degree of hydration of the clay system. Organic molecules that can disperse cationic charge over two or more condensed aromatic rings give rise to greater surface-induced protonation than do single-ring organic molecules with similar solution pKa. Protonation in clay suspensions is frequently far in excess of that predicted on the basis of electrolytic suspension pH and solution pKa of the organic base. For a given organic base, protonation in a clay film exceeds that in the suspended clay system. Protonation in an organo-clay film increases as the film moisture content decreases. The extent of protonation in organo—clay systems varies with cationic species, cationic saturation, and clay type.

Clay minerals in clay-water system as viewed by freeze etching

Abstract Most electron microscopic studies reported so far are on individual clay particles prepared by drying drops of clay suspensions. The few studies reported about the outer surface structure of clay floccules have been done using scanning electron microscopes on freeze dried samples (1). In the investigation of the internal structure of clay specimens a cross section of clay has to be observed in a solid medium. So far resin media have been used for embedding clay. Using resinous media requires dehydration of the clay prior to embedding. No work has been reported on the internal surface structure of clay arrangements in aqueous media.

Simultaneous existence of different enviroments in aqueous clay systems and its possible role in prebiotic synthesis.

The formation of packets of parallel oriented platelets and separating distances of several angstrom units in montmorillonite-water systems produces an intrinsic inhomogeneity with respect to the proton donating power of internal and external zones. Stable packets can be induced by both inorganic and organic molecules or ions, in suspensions or in drying-out systems. The coexistence of zones with different proton donating power was demonstrated by the pH-sensitive color reaction of benzidine, where stable packets of montmorillonite platelets were formed by the use of either paraquat or diquat. The close proximity of the two types of zones, which can be of the order of several angstroms, produces the conditions which were defined by Katchalsky as essential for the polymerization of amino acids. Since these enviromental conditions are quite common in nature, both at present and in prebiotic times, it is proposed that the inhomogeneity of clay-water systems with respect to proton donating power should be taken into account in both theoretical and experimental efforts to demonstrate the catalytic activity of clays in prebiotic synthesis.

Electrical Conductivity of Na—Montmorillonite Suspensions

AbstractThe electrical conductivity of Na-montmorillonite suspensions in various salt and clay concentrations was measured. The weight conductance of the clay suspension was found to decrease with increase in clay concentration between 0 and approximately 0·5 g clay/100 ml, then rose to a plateau at 6–10 g clay/100 ml. The weight conductance of the clay suspensions also increased with an increase in the salt solution concentration. If the model of two resistors in parallel is used in interpreting the experimental data, these changes can be attributed to an increase in the mobility of the adsorbed Na ions. It is proposed that the two resistors in series model is more realistic in describing the conductivity of the suspensions. This model predicts the observed weight conductance changes of the suspensions, while the mobility of the adsorbed ions remains constant. A constant mobility of the adsorbed Na ions in clay-water systems of low to medium salt and clay concentrations also is predicted by the diffuse double layer.

Preparation and identification of clay samples with controlled fabric

Techniques have been developed to prepare reasonably homogeneous, reproducible bulk samples of a kaolinite clay (Hydrite 10) with predetermined microfabrics and to reliably identify these microfabrics both quantitatively and qualitatively. Eight samples with quite diverse histories were produced in the laboratory by controlling the chemistry of the clay-water system, the consolidation stress path (either isotropic or anisotropic), and the magnitude of the consolidation stresses. The fabrics of these samples are identified and quantified by the combined use of scanning electron microscopy, optical microscopy, and X-ray diffractometry, and reasonably comprehensive appraisals of particle associations and orientation are obtained. Anisotropic consolidation was found to induce a preferred particle orientation, whereas isotropic consolidation tended to provide basically random samples. The anisotropically consolidated samples from dispersed slurries exhibited somewhat greater particle orientation than those from flocculated slurries, and, although considerable particle orientation occurred at low values of the consolidation stress, increases in the major principal consolidation stress did accentuate the particle orientation. The presence of domains or small groups of particles is suggested in certain samples, especially in those consolidated isotropically.

Thermodynamics of Clay-Water System

Specific energy designating the partial specific Gibbs free energy of water in a clay-water system is a fundamental parameter that can be used by ceramists to study the mechanical properties of this and other similar systems as well as the moisture mobility in them. Various methods available to measure this thermodynamic quantity including a new method based on mercury penetration measurements have been discussed. Variation of coefficient of internal friction with the specific energy has been studied and the results interpreted in the light of the available data on the relationships of specific energy with drying rate, Young's modulus and slip casting rate in plaster moulds.

The role of water in the origin of life and its function in the primitive gene

A brief outline is presented of the structure of clays and of modern views on the structure of water. The interactions between clays and water are discussed, together with the effect of hydration on the adsorption and catalytic properties of clays. From these considerations an attempt is made to show that the hydrated silica surfaces of clay-water systems could have provided the necessary environment for the abiogenesis of primitive macromolecules. The transfer of catalytic functions to abiopolymers is outlined, and a possible route to growing, dividing coacervate droplets is described. Finally, attention is drawn to analogies between the clay-water system and living matter, and the suggestion is made that the structural properties of water could be the basis for the cellular communication network on which life depends.

Pressure-induced changes in the thermal and electrical properties of clay—water systems

Na-saturated clays were prepared from Wyoming bentonite by three different methods which allowed progressively greater contamination with hydrous aluminum oxide. These clays are referred to as Na-clay, Na/Al-clay and Na/Al ∗-clay, respectively. Water or dilute NaCl was added to them to form clay-water mixtures having different clay contents. The heat of compression of each mixture was determined at several pressures in a Calvet microcalorimeter. The emf between reversible electrodes in and the electrical resistance of each mixture were also determined at several pressures. When plots were made of the heat of compression, change in emf and change in electrical resistance against pressure, breaks were observed in the curves for the Na/Al-clay at concentrations greater than ∼ 3.0% by volume in the pressure range 20–30 psi. Similar breaks were not detected in the curves for the other clays. It was concluded that the water in the Na/Al-clay mixtures underwent a pressure-induced phase transition in the specified pressure range. However, sensitive differential thermal analyses revealed that a phase transition was not induced in this water by raising its temperature to 70°C.

On the modification of Darcy's law for the flow of water in clay-water systems

It has been shown that the modification of Darcys law as suggested by Srivastava and Abrol (1969) may not be generally valid. Instead, it is suggested that the flow of water through the clay-water system may be more properly described by an extension of the Onsager reciprocal relation involving non-linear phenomenological coefficients.

Sequential Active Alteration of Rhyolitic Volcanic Rock to Endellite and a Precursor Phase of it at a Spring in Michoacan, Mexico

AbstractSequential alteration of volcanic rock of rhyolitic composition to a precursor of endellite, and thence to tubular endellite, may be observed at a hot spring about 27 km north of Ciudad Hidalgo, Michoacan, Mexico. Ojo Caliente de Laguna Larga (or Verde) yields H2S-SO2-containing water, temperature about 45°C pH 3·5–3·7, from multiple orifices in vesicular and slabby rock with which the water reacts.First-stage alteration of the rock consisted of permeation and dissolution, accompanied by deposition of clay substance in vesicle walls. The clay substance, although “amorphous” to X-rays, yields a weak DTA of endellite, and kaolinite. It is interpreted as a precursor of endellite. Further reaction included continued filling of vesicles and spreading argillation which coalesced between vesicles and other rock pores. Ultimately, the rock was completely “digested” to well-defined endellites.Strong desilication and depotassication of the rock is indicated by the dissolved substances in the spring water: Si 59·1 (equivalent to 127 SiO2) ug/ml: Al, 1·63; Fe, 0·65: Mg, 0·21: Ca, 178: Na, 0·73: K, 13·7. Despite high K+, predominantly high H+ and Al3+ induce formation of endellite. The clay-water system accords well with stability diagrams.Allophane-endellite in Indiana and endellite at Stanford, Kentucky, are formed from cold, strongly acid, meteoric-water solutions high in Si and Al relative to kaolinite dissolved in water. Factors of genesis common to both hot- and cold-water endellite are cited, suggesting that they are premissively critical, but not necessarily restrictive, to the origin of endellite.

Aging Effects on Swell Potential of Compacted Clay

The swelling potential of compacted clay, which develops upon inundation, is first defined in terms of the parameters affected by aging. These parameters include swell pressure, volume change and suction. Because in nature the clay is exposed to water some time after compaction, the aging effects on the swelling potential are rather important. Compacted clay samples were aged for up to 90 days and then tested for swelling pressure and free swell, using triaxial technique. It was found that the swell pressure, particularly at high initial densities, tends to increase with aging and then gradually to decrease to the initial value of zero aging. The amount of swell (under practically zero load) was not markedly affected by aging. The peak values of the swelling potential amounted to two to three times the initial value, and they were found to be dependent on the initial placement conditions of the clay. The results are explained by energy concepts, as well as by concepts mainly used in soil science, such as thixotropy and entropy of clay-water systems.

Low-Temperature Phases of Interfacial Water in Clay-Water Systems

LOW TEMPERATURE DIFFERENTIAL THERMAL ANALYSES OF SELECTED CLAY-WATER SYSTEMS WERE MADE TO LOCATE IMPORTANT PHASE CHANGE TEMPERATURES AND TO DEFINE FRUITFUL TEMPERATURE-PRESSURE FIELDS FOR PRECISE CALORIMETRIC INVESTIGATION. IN ADDITION TO AN EXOTHERM CORRESPONDING TO INITIAL FREEZING, ONE, TWO OR THREE EXOTHERMS WERE OBSERVED BETWEEN -35C AND -60C. THE LOW TEMPERATURE EXOTHERMS DO NOT DEPEND CRITICALLY UPON WATER CONTENT, BUT CLEARLY THEY ARE RELATED TO CLAY MINERAL AND EXCHANGEABLE CATION TYPE. THE EVOLUTION OF HEAT IN THIS TEMPERATURE RANGE PROBABLY CORRESPONDS TO A PHASE CHANGE IN THE INTERFACIAL WATER. /AUTHOR/

A tetrahedral model for pulsed nuclear magnetic resonance transverse relaxation: Application to the clay-water system

A calcuation of the pulsed nmr signals resulting from slow random reorientation of the nuclear interaction vector among the four orientations described by the four vectors joining the center and each of the four vertices of a regular tetrahedron is described. This tetrahedral model is useful in describing two different phenomena observed in clay-water systems. The first of these is the existence of a doublet splitting in the pulsed nmr spectra of clay-water systems of low water content. The second is the shape of the pulsed nmr signals for clay-water systems in which translational diffusion is important. The latter systems usually have a high water content. The doublet splitting and the correlation time, which is related to the translational path of the water molecule, are used to describe the orientation effects of water molecules in clay-water systems.

Hydrogen bonding and polywater in clay-water systems

Hydrogen bonding and polywater in clay-water systems

Dynamic properties of materials

Bentonite and stockalite clay-water systems were strained sinusoidally in shear over a wide strain range. The hysteresis loops were shown to vary from an almost straight line (elastic system) to a ferromagnetic type loop (plastic system) as the energy of oscillation was increased. The normalised dynamic modulus-strainwork plots were shown to be very similar to those observed in carbon black-elastomer and carbon black-paraffin systems.