Microstructure Of Clay Research Articles

Dielectric properties of nylon 6/clay nanocomposites from on-line process monitoring and off-line measurements

Nylon 6/clay nanocomposites were studied by dielectric relaxation spectroscopy (DRS) to correlate morphology and microstructure with relaxation behavior of the polymer matrix at the molecular level. Partially exfoliated clay microstructure was achieved by extruding nylon 6 with surfactant-treated montmorillonite clays. A new on-line dielectric slit die sensor was used to examine the melt state properties during extrusion compounding. Solid state properties were probed by off-line DRS over a temperature range from −50 to 180 °C in a frequency range from 10 −3 to 10 6 Hz. Using non-linear regression methods in conjunction with the temperature–frequency positions of relaxations observed in the dielectric loss data, the experimental data were fit with the Havriliak–Negami and Cole–Cole dielectric relaxation functions corrected for electrode polarization and DC conductivity. Characteristic frequency, relaxation strength, and DC conductivities were extracted from curves with overlapping relaxation modes. Two dielectric relaxations were observed in the composite melt: the α relaxation associated with molecular segmental motion, and a Maxwell–Wagner relaxation (MW) resulting from interfacial polarization at the resin/clay interface. Analysis of the solid-state data yielded a comprehensive master plot of dielectric relaxations attributed to segmental and local molecular dynamics and other relaxations resulting from water and Maxwell–Wagner interfacial polarization. The impact of clay fillers is seen in nearly all relaxation processes changing both characteristic frequency and strength of the relaxation.

Geosynthetic Clay Liner Interaction with Leachate: Correlation between Permeability, Microstructure, and Surface Chemistry

When a geosynthetic clay liner (GCL) containing sodium bentonite is brought into contact with fluids containing other cations, the latter may exchange with the sodium present between clay layers. This modification of clay surface chemistry may change the clay microstructure and hence its hydraulic conductivity. The influence of clay surface chemistry on microstructure and permeability, after prolonged contact between two GCLs (a natural sodium bentonite GCL and a sodium-activated calcium bentonite GCL) and different fluids in oedometer cells, was investigated using exchangeable-cation analysis, small-angle x-ray scattering, and transmission electron microscopy. Results suggest that calcium carbonate in the bentonite, formed during activation of the calcium bentonite, may redissolve during contact with a dilute permeant, releasing calcium ions that exchange with sodium in the clay. This exchange leads to obliteration of a so-called phase (beneficial in terms of low permeability) and to the development of a more permeable hydrated-solid phase. Sodium replacement by calcium during GCL contact with a 0.1 M CaCl2 solution was found to be virtually complete, with or without GCL prehydration with dilute water. No gel phase was observed in these samples. When in contact with real leachate, however, a gel phase appeared, especially when GCL samples were prehydrated. A correlation was observed between the level of hydraulic conductivity and the relative proportions of gel phase and clay interlayer occupation by sodium.

Influence of burial history on microstructure and compaction behaviour of Kimmeridge clay

The paper presents the results of laboratory compaction tests on two samples of the lower Kimmeridge Clay Formation obtained from two different outcrop localities in the UK. The purpose of the testing programme is to study the compaction behaviour of an argillaceous sediment from the same parent material but with different diagenetic histories. Since most available data are for clays subjected to moderate effective stresses (less than 20 MPa), the compaction laboratory tests were carried out to as high as 120 MPa, corresponding to about 9 km burial. The microstructure of the tested materials was studied in a scanning electron microscope before and after compaction testing to evaluate the effects of diagenesis on the microstructure of argillaceous sediments. The two tested materials have, in the past, been subjected to different burial depths and degrees of chemical precipitationand cementation. Several pieces of evidence are shown of the effects of mechanical and chemical processes on the compaction behaviour of argillaceous materials. Mechanical compaction can only account for part of the porosity loss and increase in stiffness of argillaceous materials during burial. Mechanical compaction produces an anisotropic rearrangement of clay particles in uncemented sediments. Once chemical diagenesis has taken place, chemical cementation preserves the microstructure of the sediment and only minor changes in clay particle arrangements take place during further mechanical compaction, even when very high stresses are used. Also, it is seen that chemical processes reduce the permeability more strongly than mechanical compaction.

Physicochemical and Engineering Behavior of Cement Treated Clays

This paper examines the relationship between the microstructure and engineering properties of cement-treated marine clay. The microstructure was investigated using x-ray diffraction, scanning electron microscopy, pH measurement, mercury intrusion porosimetry, and laser diffractometric measurement of the particle size distribution. The engineering properties that were measured include the water content, void ratio, Atterberg limit, permeability, and unconfined compressive strength. The results indicate that the multitude of changes in the properties and behavior of cement-treated marine clay can be explained by interaction of four underlying microstructural mechanisms. These mechanisms are the production of hydrated lime by the hydration reaction which causes flocculation of the illite clay particles, preferential attack of the calcium ions on kaolinite rather than on illite in the pozzolanic reaction, surface deposition and shallow infilling by cementitious products on clay clusters, as well as the presence of water trapped within the clay clusters.

Progressive change of pelagic clay microstructure during burial process: examples from piston cores and ODP cores

Progressive change of microstructure in pelagic clays of different three orders of burial depths, several centimeter, several meters and several hundred meter depths, was observed by measurement of anisotropy of magnetic susceptibility (AMS) and observation by scanning electron microscope (SEM) and thin section. At depths of several centimeters (void ratio >3.0), peds of several 10 μm in diameter are linked by long and narrow connectors in edge-face (EF) contact and pore sizes between the peds are large. At depths of several meters (void ratio 3.0–2.0), the shape of the connectors changes from narrow to broad. The pore size between the peds decreases with burial depth. At depths of several hundred meters (void ratio <2.0), clay flakes are arranged in wavy parallelism in face-to-face (FF) contact. The pores of intra-peds are reduced in volume. The pelagic clays are consolidated due to rotation of clay flakes composed of the connectors and peds. The AMS suggests that parallel coordination is developed strongly at 150 m depth. Below this depth, zeolite occurs around radiolarian tests, and conjugated zeolite veins are observed with a normal fault sense of displacement. Due to cementation, the rotation of clay flakes in pelagic clays ceased and the resulting clay microstructure were further preserved through diagenesis.

Impact of clay microstructure and mass absorption coefficient on the quantitative mineral identification by XRD analysis

Quantitative mineral evaluation of clayey soils is an essential step to provide the reliable soil recognition and behaviour. In this paper the application of the four current XRD methods for mineral quantification purposes is experimentally reviewed for clayey soils. The problems involved in clay mineral evaluation based on the direct use of peak intensity or areas under the peak are addressed. In addition, several mistakes induced by the application of only the major reflection lines of clay minerals for this purposes have been cited. Finally, a method for XRD quantitative mineral evaluation was presented in this paper. By validating the proposed method, a very good agreement was observed between the computed and the real quantity of each mineral present in the series of artificial samples.

Micro-structure of Bentonite Clay and Diffusion Coefficient Given by Multiscale Homogenization Analysis

Bentonite consists of nanometer scale of smectitic clay minerals (mainly montmorillonite) and micrometer scale of macro-grains (mainly quatz). Properties of saturated bentonite are characterized by hydrated clay minerals. For a diffusion problem in bentonite we developed a new multiscale homogenization analysis (HA) procedure which relates microscale characteristics with a macroscopic behavior. We discuss diffusion properties of tritium water (HTO) compared with experimental data. Microscopic properties of the montmorillonite hydrate such as diffusivity of chemical species which are used in HA are determined by a molecular dynamics (MD) simulation method. We show the calculated results are consistent with macroscale experimental data.

THE CHANGE IN MICROSTRUCTURE OF PLEISTOCENE CLAYS DUE TO ONE DIMENSIONAL CONSOLIDATION

大阪湾周辺の2種類の洪積粘土 (大阪湾粘土Ma11層及び京都粘土Ma4層) を用いて, 不攪乱状態及び圧密に伴って変化する微視構造特性を, 水銀圧入型ポロシメータによる間隙径分布の測定と電子顕微鏡による観察から明らかにした. 実験に用いた洪積粘土は, 含まれる粘土鉱物は同一であるが, 京都粘土に比べて大阪湾粘土には多量の珪藻類が混入している. 京都粘土は, 圧密に伴い間隙が顕著に収縮し, 全体的により小さな間隙径分布となっていく. 一方, 大阪湾粘土は, 京都粘土に比較して, 全体的な間隙径の収縮は生じにくい. 最大圧密圧力 (p=10MPa) において比較すると, 京都粘土の間隙径は, 大阪湾粘土のものよりもかなり小さくなる. この違いは, 珪藻類を含めたマクロ的な粘土構成物自体の相違によるものと考えられる.

Stabilization of heavy metals on spent fluid catalytic cracking catalyst using marine clay

Spent fluid catalytic cracking catalyst is a hazardous solid waste generated by petroleum refineries containing vanadium and nickel. The marine clay was used as a matrix to stabilize vanadium and nickel and produce bricks which were then fired at various temperatures. TCLP leaching tests indicated that stabilizing brick had low metal leaching, with a maximum of 6.4 mg/l for vanadium and 19.8 microg/l for nickel. Compressive strength of stabilizing brick was found to range between 20 N/mm2 and 47 N/mm2. It is believed that stabilization and encapsulation mechanisms are responsible for the stabilization of vanadium and nickel. Encapsulation is a process whereby the marine clay matrix forms a physical barrier around the heavy metals which are thus prevented from leaching out into the environment. Incorporation involves the formation of bonds between the marine clay matrix and the heavy metals which thus become incorporated in the clay microstructure.

Influence of swelling on the microstructure of expansive clays

The focus of this work is to elucidate the changes in microstructure during swelling in expansive clays. A new device to enable controlled swelling of clay samples was designed and fabricated. This controlled uniaxial swelling device when integrated with a closed loop mechanical testing load frame allowed for the measurement of swelling pressure at a controlled and predetermined extent of swelling of the expansive clay samples. Further, this cell offered ease of removal of samples for microanalytical testing in a scanning electron microscope. Microstructural analysis was performed on the bentonite samples after the saturated samples were allowed to swell 0, 50, and 75% beyond their original volume. The void and particle gray scales were identified in the images using energy-dispersive X-ray analysis. Digital analysis of the images using custom-developed macros and Scion ImageTM software shows that the increase in swelling and reduction of swelling pressure due to swelling in the clay samples result in appreciable reduction in particle size. Thus, the swelling results in a breakdown of the clay agglomerates into smaller sized particles. These effects of swelling on microstructure of swelling clays could have a significant impact on stress deformation and the hydraulic properties of the clay.Key words: expansive clays, swelling, swelling pressure, microstructure, image analysis, scanning electron microscopy.

Impact of microstructure on the hydraulic conductivity of undisturbed and artificially prepared smectitic clay

The microstructure controls most physical properties of clays. This is obvious when comparing natural smectitic clay and clay prepared by drying, grinding and compression of air-dry powder. The hydraulic conductivity of the artificially prepared clay is higher than that of the undisturbed, natural clay. If the latter clay is percolated with distilled water and Ca-rich water, the difference in conductivity is obvious, while percolation of the natural clay with these solutions does not yield a very dramatic change. This is because the microstructure of the natural clay is very homogeneous, while the artificially prepared clay preserves the high density of the powder grains while the gels in the voids between the grains are soft.

Water permeability, water retention and microstructure of unsaturated compacted Boom clay

Three classes of experiments are considered in this paper to provide information for two artificially prepared Boom clay fabrics: mercury intrusion/extrusion tests; main wetting/drying paths; and water inflow/outflow transient (permeability) tests. These tests, which are usually treated separately, are joined in a common reference frame to provide information about the morphology of the porous medium and factors influencing Boom clay unsaturated hydraulic states with reference to water retention curves and relative water permeability values. The main objective is to interpret mercury intrusion porosimetry results in order to define an entrance pore size region at ca 130 to 180 nm separating intra-aggregate and inter-aggregate zones. This pore size region is further associated to a delimiting zone in the retention curve separating regions of ‘intra-aggregate governing suction’ at gravimetric water contents lower than 13–15% (gravimetric water content is not affected by mechanical effects) and ‘inter-aggregate governing suction’ (gravimetric water content is sensible to mechanical actions). This water content is further used to define a threshold zone around a relative water permeability of k w/ k ws=0.01 delimiting a zone of greater water relative permeability from others that present a restricted flow in a generalised Darcian sense. All these results are consistent with the existence of two main pore size regions: an intra-aggregate porosity with quasi-immobile water that is little affected by loading processes and an inter-aggregate porosity for which the loading mechanism results in a reduction of interconnected macropores affecting free water. Testing results show that intra-aggregate water represents between 54 and 59% of the total volume of water in soil in a low-porosity packing compacted at a dry unit weight of 16.7 kN m −3, whereas it corresponds to ca 28 and 38% in the case of a high-porosity packing compacted at a dry unit weight of 13.7 kN m −3.

The micro-structures of clay given by resistivity measurements

In this study, a structural model consisting of serial and parallel parts with three phase-components, solid, liquid and gas, is developed to give information on soil structures. The structure model is characterized by the ratio of the serial and parallel parts, which have different electrical conductivities at given directions. The ratio is expressed by a structural factor, F. The value of Γ defined by σ w/(1− F) is used and examined to characterize the clay structure, where σ w is the apparent resistivity of pore water. Experimental results showed that the value of Γ is different for undisturbed and remolded clays for a similar void ratio. For unsaturated clays, it is found that the F value depends on the water content and pore distribution. From theoretical and experimental consideration, it is possible to use resistivity to describe the micro-structure of clay with the model developed in this study.

Experience from preparation and investigation of clay microstructure

Clays without expanding minerals can be prepared so that their microstructural constitution is preserved. If expansive clays are treated in the same fashion there is an obvious risk of very significant distortion of the particle arrangement because of drying, expansion and disintegration. It is also a risk that impregnated clay becomes too soft to be cut for microscopy, but experience shows that embedding in a suitable plastic monomer with subsequent polymerization gives sufficiently hard specimens to make ultramicrotomy applicable. Impregnation with this substance requires that the pore water is first removed, which can be done in several ways as described and discussed in this paper. The thickness of the thin section should be as small as possible for transmission electron microscopy, i.e. a few hundred angstroms, but thicker sections can be used for certain microstructural analyses.

Overview of modeling of clay microstructure and interactions for prediction of waste isolation barrier performance

This thematic paper deals with the influence of clay microstructure and internal energy components on transport prediction in partly saturated swelling soils. The need to recognize compatibility between conceptual and numerical models is one of the underlying themes of the paper. The problem of soil swelling and/or swelling forces developed upon water uptake requires careful consideration in the specification of the driving forces responsible for water uptake.

Interaction between clay microstructure, decomposition of plant residues and humification

SummaryWe have studied microstructural changes in montmorillonite and kaolinite, which were amended with organic debris (leaves of chestnut or beech), microbial inoculum and nutrients and subjected, for 30 days at 25°C, to alternate drying and wetting (D–W) or kept continuously moist at water‐holding capacity (WHC). The objective was to evalute the interactions between the decomposition of plant residues and clay microstructural organization in different pore–water regimes. The microstructure was studied by Hg porosimetry, N adsorption at 77 K, and scanning electron microscopy. Decomposition was assessed by measuring residual C and N, the amount of humified material, the relative contents of humic (HA) and fulvic (FA) acids, and their molecular weight distribution. The structural organization at the end of the experiments was different for the two clays, and new classes of pores were found as the result of the microbial metabolism. The decomposition was also significantly affected by clay type. Decomposition of the organic matter (OM) was rapid in the montmorillonite. The humified material occured mainly as low molecular weight FAs. By contrast, transformation was slow in kaolinite, leaving much residual C, and more of the humified material consisted of HAs. Alternate D–W had little effect on microstructure and decomposition. Samples that were kept moist and amended with chestnut leaves produced the greatest amount of humified substances. The dynamics of the decomposition was significantly affected by the nature of the leaves as indicated by the differences in residual C, humified material and C/N ratio. By contrast, changes in pore size distribution (PSD) were litle influenced by the type of organic debris.

Mechanical behaviour of a natural soft clay

The results of an experimental study on the mechanical behaviour of the natural soft clay found at Pisa are discussed. Triaxial and true triaxial stress path—controlled tests were carried out, in which the soil was subjected to a variety of drained stress paths, each starting from the in situ stresses. The stress—strain behaviour was observed to be substantially non—linear from the very beginning of the loading process. The observed results are interpreted using concepts of hardening plasticity. The influence of the damage produced in the clay microstructure during loading is evaluated through a normalization technique. A comparison between the behaviour of the natural and the reconstituted clay is also presented. The results of the true triaxial tests show strength anisotropy. In both the triaxial and the true triaxial tests, the observed stiffness was found to depend strongly on the direction of the stress path. Dans cet exposé, nous présentons les résultats d'une étude expérimentale sur le comportement mécanique de ľargile tendre naturelle trouvée dans la région de Pise. Nous avons effectué des essais de contrainte triaxiale et de contrainte triaxiale réelle á trajectoire conrô1ée, essais au cours desquels le sol a été soumis á une variété de trajectoires de contrainte drainées, chacune commençant á partir des contraintes in situ. Nous avons observé que le comportement contrainte—déformation était substantiellement non linéaire depuis le commencement du processus de charge. Nous appliquons des concepts de plasticité durcissante pour interpréter les résultats observés. Nous évaluons ľinfluence des dé gâts infligés â la microstructure de ľargile pendant la charge grâce á une technique de normalisation. Nous comparons aussi le comportement de ľargile naturelle et de ľargile reconstituée. Les résultats des essais triaxiaux réels ont mis en évidence une anisotropie de résistance. Dans les essais triaxiaux tout comme dans les essais triaxiaux réels, il est apparu que la rigidité observée dépendait fortement de la direction de la trajectoire de la contrainte.

Quantitative Analysis of XRD and SAXS Patterns: Determination of the Mineralogy and Microstructure of Ca-Interstratified Clays

Quantitative Analysis of XRD and SAXS Patterns: Determination of the Mineralogy and Microstructure of Ca-Interstratified Clays

Evolution of the Microstructure of Interstratified Ca-Saturated Clays During Dehydration: SAXS and HRTEM Analysis

This paper aims at characterizing the structural and textural evolution of three mixed-layered clays in Ca-form from Southern and Central Tunisia. These samples contain various amounts of mixed-layer smectite-illite associated with crystallites of kaolinite. The clay fractions were prepared in the Ca-form and submitted to suction pressures increasing from 3.2 up to 1000 kPa. The structural and textural changes of the pastes obtained were studied by TEM and SAXS. The TEM observations and SAXS quantitative analysis on samples at low stress (3.2 kPa) showed that the thickness of the particles (number of layers per particle) and their lateral extension (in the plane of layers) decrease with increasing illite content. The textural evolution during drying, as described by SAXS, is controlled by the geometry of particles which is determined by the mineralogy of the structural units. With incteasing illite content, the particles became shorter, rigid and had flat surfaces. This geometry increases their ability to associate face-to-face during dehydration. When the 2:1 fraction contains a high proportion of smectite, the architecture of the clay-water system at high water content (low stress) seems to be analogous to that of smectites. However, contrary to the behaviour of pure smectites reported in the literature, desiccation led first to a rupture of particles and a reorganization of the geometry of the pore system. This behaviour is due to the rigidity of particles caused by the presence of non-exchangeable K. The structural evolution showed that for an illite-rich sample a transition from the three-water layer to the one-water layer state occurred at 1000 kl'a, whereas for smectite-rich materials, the hydration state of layers, i.e. three water layers, was not affected.

Evolution of the Microstructure of Interstratified Ca-Saturated Clays During Dehydration: SAXS and HRTEM Analysis

Evolution of the Microstructure of Interstratified Ca-Saturated Clays During Dehydration: SAXS and HRTEM Analysis