Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Clay

  • bentonite clay
  • mmt clay
  • modified clay
  • montmorillonite clay
  • natural clay
  • organo-modified clay
  • organophilic clay
  • red clay
  • sandy clay
  • soft clay

  • Terms modified by Clay

  • clay Nanocomposite
  • clay coating
  • clay composite
  • clay concentration
  • clay content
  • clay deposit
  • clay dispersion
  • clay exfoliation
  • clay film
  • clay fraction
  • clay layer
  • clay loading
  • clay loam
  • clay loam soil
  • clay mineral
  • clay mineralogy
  • clay model
  • clay modification
  • clay nanocomposite
  • clay particle
  • clay platelet
  • clay ratio
  • clay sample
  • clay soil
  • clay source
  • clay structure
  • clay surface
  • clay suspension
  • clay system

  • Selected Abstracts

    Poly(vinyl alcohol)/Clay-Based Nanocomposite Hydrogels: Swelling Behavior and Characterization

    Caio M. Paranhos
    Abstract Polymer/clay composite hydrogels were prepared based on PVA hydrogels containing 3,10 wt.-% MOM. Their microstructure and morphology were studied by FT-IR, WAXS and SEM, whereas the interactions between MOM and PVA were evaluated by thermal analyses. The swelling ratios for the PVA/MOM hydrogels decrease with increasing MOM content. WAXS results indicate that MOM was intercalates, and DSC results show a strong interaction between PVA and MOM. This interaction results in a stable network, which is confirmed by the elastic modulus and the thermal decomposition behavior of the hydrogels. Therefore, MOM acts as a co-crosslinker, improving the stability of the network. [source]

    Evaluation of polymethacrylic ionomer as compatibilizers for MCPA6/clay composites

    Tongfei Wu
    Abstract The compatibilization effects provided by polymethacrylic ionomer (PMMA ionomer) on monomer-casting polyamide6 (MCPA6)/clay (pristine sodium montmorillonite) composites were studied in this work. The PMMA ionomer used in this study was sodium polymethacrylate ionomer (PMMA Na+ -ionomer), which is a copolymer of methyl methacrylate and sodium methacrylate, prepared using emulsion polymerization. MCPA6/clay/PMMA Na+ -ionomer composites were prepared by in situ anionic ring-opening polymerization (AROP) of ,-caprolactam (CLA). X-ray diffraction (XRD) and transmission electron microscopy (TEM) plus rheological measurement were used to characterize those composites. The results indicated that PMMA Na+ -ionomer is a good compatibilizer for this system. With increasing PMMA Na+ -ionomer content, a better dispersion of clay layers was successfully achieved in the MCPA6 matrix. Furthermore, differential scanning calorimetry (DSC) and XRD results indicated that well dispersed silicate layers limit the mobility of the MCPA6 molecule chains to crystallize, reduce the degree crystalline, and favor the formation of the ,-crystalline form of the MCPA6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Melt processing of PA-66/clay, HDPE/clay and HDPE/PA-66/clay nanocomposites

    Mahmood Mehrabzadeh
    Polyamide 66/clay, high-density polyethylene (HDPE)/clay and HDPE/PA66/clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), optical microscopy and tensile testing. Effects of processing conditions and clay modifier were evaluated. The results show that exfoliation in the twin-screw extruder is enhanced by the incorporation of mixing and shearing elements and high residence times. Compatibility of the clay modifier with the polymer matrix plays an important role in exfoliation. Clay does not influence the crystal form, melting temperature or crystallinity of PA-66 and HDPE. However, it acts as a nucleation agent, increases marginally the crystallization temperatures, and reduces the crystallite size. Clay in the blend nanocomposites acts as a compatibilizer and changes the morphology of the blend. TEM micrographs suggest the presence of an exfoliated structure in PA-66 and an intercalated structure in HDPE. Polym. Eng. Sci. 44:1152,1161, 2004. © 2004 Society of Plastics Engineers. [source]

    Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocomposites

    Tzong-Ming Wu
    X-ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ,-caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X-ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the , crystalline form. The addition of clay increases the crystallization rate of the , crystalline form at lower saponite content and promotes the heterophase nucleation of , crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed. [source]

    Melt processing of PA-66/clay, HDPE/clay and HDPE/PA-66/clay nanocomposites

    Mahmood Mehrabzadeh
    Polyamide 66/clay, high-density polyethylene (HDPE)/clay and HDPE/PA66/clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), optical microscopy and tensile testing. Effects of processing conditions and clay modifier were evaluated. The results show that exfoliation in the twin-screw extruder is enhanced by the incorporation of mixing and shearing elements and high residence times. Compatibility of the clay modifier with the polymer matrix plays an important role in exfoliation. Clay does not influence the crystal form, melting temperature or crystallinity of PA-66 and HDPE. However, it acts as a nucleation agent, increases marginally the crystallization temperatures, and reduces the crystallite size. Clay in the blend nanocomposites acts as a compatibilizer and changes the morphology of the blend. TEM micrographs suggest the presence of an exfoliated structure in PA-66 and an intercalated structure in HDPE. Polym. Eng. Sci. 44:1152,1161, 2004. © 2004 Society of Plastics Engineers. [source]


    ARCHAEOMETRY, Issue 1 2000
    For several decades, interpreting technical variations in the physical characteristics of pottery has followed two major trends: the ,cultural'approach and the ,behavioural or ,techno-functionalist'approach. Using data collected during extensive ethnographic fieldwork, I will consider the relative importance of social and technical requirements in the field of clay processing techniques in the Faro area (northern Cameroon) 1 will show that environmental and techno-functional constraints cannot explain technical variations, while cultural factors appear determinant. However, faking the discussion one step further, I will show the complexity of the social/cultural mechanism involved in the regional distribution of these techniques. [source]

    Electrogenerated Chemiluminescence Sensor Based on Tris(2,2,-bipyridine)ruthenium(II)-Immobilized Natural Clay and Ionic Liquid

    ELECTROANALYSIS, Issue 2 2010
    Ping Jiang
    Abstract A novel electrogenerated chemiluminescence (ECL) sensor based on natural clay and ionic liquid was fabricated. Tris(2,2,-bipyridine)ruthenium(II) (Ru(bpy)32+) was immobilized on natural clay surface through simple adsorption. An ECL sensor was prepared by mixing Ru(bpy)32+ -incorporated clay, graphite powder and an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) as the binder. The electrochemical behavior and ECL of the immobilized Ru(bpy)32+ was investigated. It was observed that the ECL of immobilized Ru(bpy)32+ was activated by the ionic liquid. The proposed ECL sensor showed high sensitivity to tri- n -propylamine (TPrA) and the detection limit was found to be 20,pM. In addition, the ECL sensor displayed good stability for TPrA detection and long-term storage stability. [source]

    Permselective and Preconcentration Properties of a Surfactant-Intercalated Clay Modified Electrode

    ELECTROANALYSIS, Issue 22 2006
    E. Ngameni
    Abstract This work is focused on the voltammetric examination of the ion exchange properties of a smectite type clay, before and after its modification by the replacement of its native interlamellar cations (Na+, K+, Ca2+) by hexadecyltrimethylammonium cations (HDTMA+). The raw clay and its organically modified form were first characterized by X-ray diffraction (XRD) and N2 adsorption,desorption isotherms (BET method) that confirmed the modification via an intercalation process. These materials were subsequently coated onto glassy carbon surfaces, and the resulting modified electrodes were evaluated for the uptake of [Ru(NH3)6]3+ and [Fe(CN)6]3, ions used as redox probes. Some experimental parameters affecting the incorporation of the probes within the film, including the ionic strength, the surfactant loading and the solution pH are thoroughly examined, in order to highlight the mechanism of the process. The possibility of using the surfactant-intercalated clay modified electrode as an electrochemical sensor for [Fe(CN)6]3, is also evaluated. [source]

    Clay Modified Electrodes: Present Applications and Prospects

    ELECTROANALYSIS, Issue 10 2003
    Zuzana Navrátilová
    Abstract This review presents the preparation and use of clay modified electrodes with emphasis on analytical applications. Besides, some investigations on ion-exchange and sorption mechanisms are outlined. Expected prospects of clay modified electrodes in the field of electrochemistry are discussed briefly. [source]

    Zinc ion adsorption on montmorillonite,Al hydroxide polymer systems

    R. P. T. Janssen
    Summary Clay,Al hydroxide polymers (CAlHO) can bind heavy metals effectively and may play an important role in the adsorption behaviour and metal binding capacity of soils. We studied the dependence of Al loading and pH on the adsorption of Zn on Na-saturated montmorillonite,Al hydroxide polymer systems. The available binding sites on Al hydroxide polymers (AlHO) had a very strong affinity for Zn ions. Zinc binding on the clay surface became important when the binding sites on the AlHO were nearly all occupied. The pH had a very strong effect on the Zn binding. At pH 6.6 much more Zn could be adsorbed to the AlHO than at pH 5.0. The effect of the Al:clay ratio on Zn binding was influenced by pH. At pH 6.6, Zn binding to the AlHO, expressed per mole AlHO, was independent of the Al:clay ratio, whereas at pH 5.0 this relation was dependent. This is related to the constant charge of the AlHO at pH 6.6, whereas at pH 5.0 the charge decreases with increasing Al:clay ratio. If clay,Al hydroxide polymers are present in the soil their Zn binding to the AlHO will strongly influence the availability of the Zn. [source]

    Effect of termites on clay minerals in tropical soils: fungus-growing termites as weathering agents

    P. Jouquet
    Summary Termites of the subfamily Macrotermitinae play an important role in tropical ecosystems: they modify the soil's physical properties and thereby make food available for other organisms. Clay is important in the architecture of Macrotermitinae termite nests, and it has been postulated that termites could modify the mineralogical properties of some clays. We have tested this hypothesis of clay transformation by termites in the laboratory under controlled conditions, using Odontotermes nr. pauperans termite species, one of the main fungus-growing species at Lamto Research Station (Côte d'Ivoire). Soil handled by termites in nest building was saturated with SrCl2, glycol or KCl and afterwards heated at 250°C for X-ray diffraction analyses. Termite handling led to an increase in the expandable layers of the component clay minerals. Heating and saturation by potassium of modified clays did not close the newly formed expandable clay layers. However, differences occurred between parts of the constructions built by termites, and the clays can be ranked according to their degree of alteration in the following order: unhandled soils < galleries < chamber walls. Consequently, termites can be seen as weathering agents of clay minerals, as previously shown for micro-organisms and plants. [source]

    Gas breakthrough experiments on fine-grained sedimentary rocks

    GEOFLUIDS (ELECTRONIC), Issue 1 2002
    A. Hildenbrand
    Abstract The capillary sealing efficiency of fine-grained sedimentary rocks has been investigated by gas breakthrough experiments on fully water saturated claystones and siltstones (Boom Clay from Belgium, Opalinus Clay from Switzerland and Tertiary mudstone from offshore Norway) of different lithological compositions. Sand contents of the samples were consistently below 12%, major clay minerals were illite and smectite. Porosities determined by mercury injection lay between 10 and 30% while specific surface areas determined by nitrogen adsorption (BET method) ranged from 20 to 48 m2 g , 1. Total organic carbon contents were below 2%. Prior to the gas breakthrough experiments the absolute (single phase) permeability (kabs) of the samples was determined by steady state flow tests with water or NaCl brine. The kabs values ranged between 3 and 550 nDarcy (3 × 10,21 and 5.5 × 10,19 m2). The maximum effective permeability to the gas-phase (keff) measured after gas breakthrough on initially water-saturated samples extended from 0.01 nDarcy (1 × 10,23 m2) up to 1100 nDarcy (1.1 × 10,18 m2). The residual differential pressures after re-imbibition of the water phase, referred to as the ,minimum capillary displacement pressures' (Pd), ranged from 0.06 to 6.7 MPa. During the re-imbibition process the effective permeability to the gas phase decreases with decreasing differential pressure. The recorded permeability/pressure data were used to derive the pore size distribution (mostly between 8 and 60 nm) and the transport porosity of the conducting pore system (10 -5,10 -2%). Correlations could be established between (i) absolute permeability coefficients and the maximum effective permeability coefficients and (ii) effective or absolute permeability coefficients and capillary sealing efficiency. No correlation was found between the capillary displacement pressures determined from gas breakthrough experiments and those derived theoretically by mercury injection. [source]

    Ground Water Discharge and Nitrate Flux to the Gulf of Mexico

    GROUND WATER, Issue 3 2004
    Carolyn B. Dowling
    Ground water samples (37 to 186 m depth) from Baldwin County, Alabama, are used to define the hydrogeology of Gulf coastal aquifers and calculate the subsurface discharge of nutrients to the Gulf of Mexico. The ground water flow and nitrate flux have been determined by linking ground water concentrations to 3H/3He and 4He age dates. The middle aquifer (A2) is an active flow system characterized by postnuclear tritium levels, moderate vertical velocities, and high nitrate concentrations. Ground water discharge could be an unaccounted source for nutrients in the coastal oceans. The aquifers annually discharge 1.1 ± 0.01 × 108 moles of nitrate to the Gulf of Mexico, or 50% and 0.8% of the annual contributions from the Mobile-Alabama River System and the Mississippi River System, respectively. In southern Baldwin County, south of Loxley, increasing reliance on ground water in the deeper A3 aquifer requires accurate estimates of safe ground water withdrawal. This aquifer, partially confined by Pliocene clay above and Pensacola Clay below, is tritium dead and contains elevated 4He concentrations with no nitrate and estimated ground water ages from 100 to 7000 years. The isotopic composition and concentration of natural gas diffusing from the Pensacola Clay into the A3 aquifer aids in defining the deep ground water discharge. The highest 4He and CH4 concentrations are found only in the deepest sample (Gulf State Park), indicating that ground water flow into the Gulf of Mexico suppresses the natural gas plume. Using the shape of the CH4 -He plume and the accumulation of 4He rate (2.2 ± 0.8 ,cc/kg/1000 years), we estimate the natural submarine discharge and the replenishment rate for the A3 aquifer. [source]

    Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

    Abstract The reactivity of allyl alcohols of the pinane series and of their epoxides in the presence of montmorillonite clay in intra- and intermolecular reactions was studied. Mutual transformations of (+)- trans -pinocarveol ((+)- 2) and (,)-myrtenol ((,)- 3a) were major reactions of these compounds on askanite,bentonite clay (Schemes,1 and 2). However, the two reactions gave different isomerization products, indicating that the reactivity of the starting alcohol (+)- 2 or (,)- 3a was different from that of the same compound (+)- 2 or (,)- 3 formed in the course of the reactions. (,)- cis - and (+)- trans -Verbenol ((,)- 16 and (+)- 12, resp.), as well as (,)- cis -verbenol epoxide ((,)- 20) reacted with both aliphatic and aromatic aldehydes on askanite,bentonite clay giving various heterocyclic compounds (Schemes,4, 5 and 7); the reaction path depended on the structure of both the terpenoid and the aldehyde. [source]

    Modelling the behaviour of an embankment on soft clay with different constitutive models

    M. Karstunen
    Abstract The paper investigates the effect of constitutive models on the predicted response of a simplified benchmark problem, an embankment on soft soil. The soft soil is assumed to have the properties of POKO clay from Finland and five different constitutive models are used to model the deposit. Two of the models are isotropic models, i.e. the Modified Cam Clay model and the Soft-Soil model. The other models are recently proposed constitutive models that account for plastic anisotropy. The S-CLAY1 and S-CLAY1S models are embedded in a standard elasto-plastic framework and account for anisotropy via a rotational hardening law. In addition, the S-CLAY1S model accounts for bonding and destructuration. In contrast, the Multilaminate Model for Clay (MMC) accounts for plastic anisotropy by utilizing so-called multilaminate framework. The results of numerical simulations show that accounting for anisotropy results in notable differences in the predicted settlements and horizontal movements compared to the predictions using the isotropic models. There are also significant differences in the K0 predictions by the different constitutive models and this has a significant impact on the results. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    An internally consistent integration method for critical state models,

    Randall J. Hickman
    Abstract A new procedure to integrate critical state models including Cam,Clay and modified Cam,Clay is proposed here. The proposed procedure makes use of the linearity of the virgin isotropic compression curve and the parallel anisotropic consolidation lines in e,ln p space which are basic features of the formulation of critical state models. Using this algorithm, a unique final stress state may be found as a function of a single unknown for elastoplastic loading. The key equations are given in this article for the Cam,Clay and modified Cam,Clay models. The use of the Newton,Raphson iterative method to minimize residuals and obtain a converged solution is described here. This new algorithm may be applied using the assumptions of linear elasticity or non-linear elasticity within a given loading step. The new algorithm proposed here is internally consistent and has computational advantages over the current numerical integration procedures. Numerical examples are presented to show the performance of the algorithm as compared to other integration algorithms. Published in 2005 by John Wiley & Sons, Ltd. [source]

    Visual framework for development and use of constitutive models

    Youssef M. A. Hashash
    Abstract Advanced constitutive relations are used in geotechnical engineering to capture measured soil and rock behaviour in the laboratory, and in numerical models to represent the material response. These constitutive relations have traditionally been difficult to use, understand, and develop except by a limited number of specialists. This paper describes a framework for transforming the representation of constitutive relations, as well as stress and strain quantities from a series of mathematical equations and matrix quantities to multidimensional geometric/visual objects in a dynamic interactive colour-rich display environment. The paper proposes a shift in current approaches to the development of constitutive equations and their use in numerical simulations by taking advantage of rapid advancements in information technology and computer graphics. A novel interactive visualization development and learning environment for material constitutive relations referred to as VizCoRe is presented. Visualization examples of two constitutive relations, the linear elastic with von Mises failure criteria and the Modified Cam Clay (MCC) are shown. These include two- and three-dimensional renderings of stress states and paths and yield and failure surfaces. In addition, the environment allows for the visualization of the implicit integration algorithm used for the numerical integration of both constitutive models. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Stabilization of soft clay in irrigation projects,

    M. M. Mubeen
    stabilisation de chaux; utilisation d'argile molle; déchet de pierre pulvérisée; ouvrage d'irrigation Abstract Clay,lime improvement is an effective means to improve soft clay soil. Lime stabilization especially improves the strength and the workability of the clay soil. In addition, lime improvement provides more resistance to the soil structure and to the effect of weather on the soil structure. This study has investigated lime stabilization of soft clay and the possibility of utilizing waste rock powder produced in crusher plants as a supplemental material for lime stabilization in order to increase the strength of the soil structure. The purpose of the study was to apply the results especially in irrigation projects in order to avoid the problems of soft clay on irrigation structures in Sri Lanka. However, the results and conclusions can be considered for other regions, where the same type of soft clay problems exists. The Dutch Oostvaardersplassen (OVP) soft clay, which has a high plasticity, low shear strength and high natural water content, was chosen for the investigations. The results of unconfined compressive strength for different water contents of clay and also for different lime and waste rock powder contents show an excellent increase in strength and workability. The waste rock powder proved to increase the effect of lime stabilization. The strength improvement caused by waste rock powder is more significant for those soils which have a low clay content. Since in irrigation projects a wide range of clay soils exist, this investigation may be useful to utilize waste rock powder in order to improve the quality and the durability of the foundation of irrigation structures in the long run. Therefore the application of lime and rock material improvement on soft clay in irrigation projects may be a useful approach to stabilize soft soils and improve medium-scale shallow foundation irrigation structures and road and canal embankments, including repairing canal leaks. It has also been found that by applying this method in irrigation projects in Sri Lanka, the stabilization cost for structures on soft clay can be significantly reduced compared to other methods. Copyright © 2005 John Wiley & Sons, Ltd. L'amélioration de l'argile avec de la chaux est une moyenne effective pour améliorer la terre de l'argile molle. Spécialement la stabilisation de chaux améliore la force et la maniabilité de la terre argileuse. De plus l'amélioration de chaux fournit plus de résistance à la structure de la terre avec l'effet du temps sur la structure de la terre pendant les conditions atmosphériques différentes. Dans cette étude on a examiné la stabilisation de chaux dans l'argile molle et la possibilité de utiliser des déchets de pierre pulvérisée, obtenus par pulvériser des usines, comme une matérielle supplémentaire pour la stabilisation de chaux afin que la force de la structure de la terre s'améliore. L'objective de cette étude était d'appliquer les résultats spécialement dans des projets d'irrigation pour éviter des problèmes de l'argile molle dans des structures d'irrigation en Sri Lanka. Les résultats et les conclusions peuvent être considérés pour d'autres régions, ayant le même problème de l'argile molle. Les Oostvaarderplassen (OVP) en Hollande ont de l'argile molle ayant une plasticité haute, une résistance au cisaillement basse et un haut pourcentage de l'eau naturelle. C'est pour ça les Oostvaardersplassen ont été choisis pour accomplir la recherche. Les résultats de la force de pression indéfinie pour des teneurs en eau différents dans l'argile, aussi pour les teneurs en chaux différents et des déchets de pierres pulvérisées montrent une augmentation excellente de la force et de la maniabilité. Les déchets de pierre pulvérisée se révèlent d'augmenter l'effet de la stabilisation de chaux. L'amélioration de la force, causée par les déchets de pierre pulvérisée, est plus significative pour ces terres ayant un teneur d'argile bas. Parce que les projets d'irrigation ont beaucoup de la terre d'argile cette recherche peut être utile pour user des déchets de pierre pulvérisée pour améliorer la qualité et la durabilité de la fondation des structures d'irrigation à long terme. C'est pourquoi l'application du matériel de chaux et de pierre sur de l'argile molle dans des projets d'irrigation peut être une approche utile pour stabiliser des terres molles et peut améliorer des structures de fondations d'irrigation dans des eaux pas profondes, dans des remblais de chemins et de canaux, inclus dans des réparations des fuites de canaux. Aussi on a révélé qu'en appliquant ce méthode dans des projets d'irrigation en Sri Lanka les coûts de la stabilisation des structures sur de l'argile molle peuvent être réduits d'une manière importante comparée avec d'autres méthodes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Kinetics of styrene emulsion polymerization above the critical micelle concentration: Effect of the initial monomer concentration on the molecular weight

    Jorge Herrera-Ordonez
    Abstract The emulsion polymerization of styrene above the critical micelle concentration has been experimentally studied from a low final polymer content up to a high polymer content (,50%). A maximum in the molecular weight (M) evolution has been observed in all cases. The presence or absence of such a maximum depends on the relative values of the rate of free-radical entry (,) and the rate of chain transfer to the monomer (KtrCMp, where Ktr is the chain transfer to monomer rate coefficient and CMp is the monomer concentration in particles). If , , KtrCMp, M is constant and equal to Kp/Ktr (where Kp is the propagation rate coefficient), except at very low particles sizes typical of the early stages of the reaction, in which the chain length is limited by the particle size. On the other hand, if , , KtrCMp, M is determined by both CMp and ,. It is proposed that , is determined by the sum of the entry of the oligomeric radicals formed in the aqueous phase and those contained in particles that undergo limited coagulation. This coagulative entry can become very significant; therefore, reactor hydrodynamics can play a major role in the kinetic behavior observed. Disagreement between Clay and Gilbert's model and molecular weight distribution data can be ascribed, to a lesser or greater extent, to the degree of correctness of the quasi-steady-state and instantaneous-termination approaches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1963,1972, 2005 [source]

    Henry Clay and the Supreme Court


    "A More Perfect Union": Ableman v. Booth and the Culmination of Federal Sovereignty

    Michael J. C. Taylor
    The discourse over federal versus state jurisdiction was ingrained into American politics at the nation's inception. It has been the premise of our most historically significant rivalries,between Thomas Jefferson and Alexander Hamilton, Andrew Jackson and Henry Clay, and Daniel Webster and Robert Hayne. Though this debate remains a contentious topic in contemporary political discourse, the U.S. Supreme Court settled the legal controversy on the eve of America's bloodiest conflagration. Unanimously, the Court ruled that the federal union was of greater importance than the authority of the individual states. The 1859 Ableman v. Booth1 decision was wrought from moral controversy, legal precedent, and political necessity, coupled with the full force of law, and has endured as a compelling pronouncement on the need for continuity and stability in uncertain times. [source]

    Effect of Varying Quartz Particle Size and Firing Atmosphere on Densification of Brazilian Clay-Based Stoneware

    G. P. Souza
    Body mixes for stoneware containing a Brazilian red clay, nepheline syenite, and quartz with two different median particle sizes (,2 and 18 ,m) were fired under oxidizing and reducing atmospheres. The densification behavior was followed by dilatometry simulating the firing schedule, as well as by water absorption, linear shrinkage, and bulk density measurements on as-fired specimens. It was revealed that finer quartz led to interconnected pore closure at 1125°C when fired under an oxidizing atmosphere. Densification was systematically related to the uniformity of the compacts in the unfired state. Phase and microstructural examination by X-ray diffractometry, scanning electron microscopy/energy-dispersive spectroscopy (EDS), and transmission electron microscopy/EDS showed that mullite developed more extensively in the stonewares fired in an oxidizing atmosphere, along with cristobalite and haematite, whereas metallic iron was found in stonewares fired under a reducing atmosphere. [source]

    Molecular Characteristics of Poly(N -isopropylacrylamide) Separated from Nanocomposite Gels by Removal of Clay from the Polymer/Clay Network

    Kazutoshi Haraguchi
    Abstract The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N -isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2,wt.-%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high (=5.5,×,106 g,·,mol,1). Also, was almost constant regardless of the clay concentration (Cclay,=,1,25,×,10,2 mol,·,l,1), even though the properties of the NC gel varied widely over this Cclay range. Comparisons of NC gels, PNIPA, and SiO2 -NC gels indicated that the clay platelets specifically play an important role in NC gels. [source]

    pH Tailoring Electrical and Mechanical Behavior of Polymer,Clay,Nanotube Aerogels

    Matthew D. Gawryla
    Abstract Aerogels are low density (<0.1,g,·,cm,3), highly porous materials that are especially interesting for insulating applications. Combinations of clay and water-soluble polymers are commonly used to produce aerogels, but these materials are often mechanically weak. Single-walled carbon nanotubes (SWNT) were combined with clay and found to significantly improve mechanical behavior and impart electrical conductivity to these aerogels. Poly(acrylic acid) (PAA) as the matrix polymer provides a means of tailoring the electrical conductivity and mechanical behavior by altering the pH of the aqueous aerogel precursor suspensions prior to freeze drying. An aerogel, made from a pH 9 aqueous suspension containing 0.5,wt.-% PAA, 5,wt.-% clay, and 0.05,wt.-% SWNT, has a compressive modulus of 373,kPa. In the absence of nanotubes, this modulus is reduced to 43,kPa. Reducing suspension pH to 3, prior to freeze drying, also reduces modulus for these aerogels, but electrical conductivity is increased when nanotubes are present. It was found that bundled nanotubes provide better reinforcement for these low-density composites, which may provide some new insight into the use of nanotubes in materials that will be exposed to compressive loading. [source]

    Effect of Organic Modification on the Compatibilization Efficiency of Clay in an Immiscible Polymer Blend

    Suprakas Sinha Ray
    Abstract Summary: This communication describes the effect of organic modifier miscibility with the matrices, and the effect of the initial interlayer spacing of the organoclay, on the overall morphology and properties of an immiscible polycarbonate/poly(methyl methacrylate) blend. By varying the organic-modifier-specific interactions with the blend matrices at the same time as changing the initial interlayer spacing of the organoclay, different levels of compatibilization were revealed. The evidence for the interfacial compatibilization of the organoclay was assessed by scanning electron microscopy observations and was supported by differential scanning calorimetry analyses. The effect on the level of clay exfoliation was also examined. Differential scanning calorimetry scans of virgin, montmorillonite, and various organically modified montmorillonite-compatibilized 40PC/60PMMA blends [source]

    The Role of Functional Group on the Exfoliation of Clay in Poly(L -lactide)

    Guang-Xin Chen
    Abstract Summary: A new method was attempted to improve the interaction between poly(L -lactide) (PLLA) with a commercially available organoclay, Cloisite 25A (C25A), which was functionalized with (glycidoxypropyl)trimethoxysilane to introduce epoxy groups, and is referred to as twice-functionalized organoclay (TFC). Tethering PLLA molecules to the epoxy groups on the surface of the TFC was attempted by melt compounding. X-Ray diffraction and transmission electron microscopy images showed that fully exfoliated PLLA/TFC nanocomposites were prepared successfully. Transmission electron micrographs of the PLLA composites of the three clays used here. [source]

    Compatibilization of Immiscible Poly(propylene)/Polystyrene Blends Using Clay

    Yong Wang
    Abstract Inorganic clay was investigated as a compatibilizer for immiscible poly(propylene)/polystyrene blends. A substantial decrease in the number of polystyrene particles was seen after adding small amounts of an organically treated clay (2,5 wt.-%) to the blends. A possible mechanism for this kind of compatibilization is discussed, but these unique and completely new findings need further verification. Schematic representation of the intercalated structure in PP/PS/OMMT blends: (a) PP and PS confined in the same gallery of OMMT, and (b) parts of PP and PS molecules located outside the gallery serving as a compatibilizer. [source]

    Book Reviews: Symbols in Clay: Seeking Artists' Identities in Hopi Yellow Ware Bowls by Steven LeBlanc and Lucia Henderson

    E. Charles Adams
    No abstract is available for this article. [source]

    Corn in Clay: Maize Paleoethnobotany in Pre-Columbian Art

    Frances B. King
    Corn in Clay: Maize Paleoethnobotany in Pre-Columbian Art. Mary W. Eubanks. Gainesville: University Press of Florida, 1999. 249 pp. [source]

    A new psittaciform bird from the London Clay (Lower Eocene) of England

    PALAEONTOLOGY, Issue 2 2000
    Gareth J. Dyke
    A new psittaciform bird from the Lower Eocene (Ypresian) London Clay of England is described. This taxon, Pulchrapollia gracilis gen. et sp. nov., is assigned to the order Psittaciformes (parrots) on the basis of several distinctive structures of the tarsometatarsus, namely the trochlea for metatarsal III (trochlea metatarsi III) bearing a tubercle on its lateral side and the trochlea for metatarsal IV (trochlea metatarsi IV) completely retroverted (fully zygodactyl foot). Comparisons with other fossil and Recent taxa further support this conclusion. Cladistic analysis shows that Pulchrapollia is the sister-taxon of the single extant family within Psittaciformes, the Psittacidae. Palaeopsittacus georgei, a taxon previously described from the London Clay, is most likely based on some unassociated material and is regarded here as incertae sedis. [source]