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  Subjects -> EARTH SCIENCES (Total: 598 journals)
    - EARTH SCIENCES (443 journals)
    - GEOLOGY (67 journals)
    - GEOPHYSICS (27 journals)
    - HYDROLOGY (17 journals)
    - OCEANOGRAPHY (44 journals)

EARTH SCIENCES (443 journals)                  1 2 3 4 5 | Last

Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 1)
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Hybrid Journal   (Followers: 7)
Acta Geotechnica     Hybrid Journal   (Followers: 8)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 2)
Advances in High Energy Physics     Open Access   (Followers: 12)
Advances In Physics     Hybrid Journal   (Followers: 7)
Aeolian Research     Hybrid Journal   (Followers: 2)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Algological Studies     Full-text available via subscription   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 4)
AMBIO     Hybrid Journal   (Followers: 12)
Anales del Instituto de la Patagonia     Open Access   (Followers: 2)
Andean geology     Open Access   (Followers: 5)
Annales Henri Poincaré     Hybrid Journal   (Followers: 2)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access   (Followers: 1)
Annals of Geophysics     Full-text available via subscription   (Followers: 9)
Annals of GIS     Hybrid Journal   (Followers: 15)
Annals of Glaciology     Full-text available via subscription  
Annual Review of Marine Science     Full-text available via subscription   (Followers: 9)
Anthropocene Review     Hybrid Journal   (Followers: 1)
Applied Clay Science     Hybrid Journal   (Followers: 2)
Applied Geochemistry     Hybrid Journal   (Followers: 6)
Applied Geomatics     Hybrid Journal   (Followers: 7)
Applied Geophysics     Hybrid Journal   (Followers: 6)
Applied Ocean Research     Hybrid Journal   (Followers: 6)
Applied Petrochemical Research     Open Access   (Followers: 3)
Applied Remote Sensing Journal     Open Access   (Followers: 9)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 21)
Arctic, Antarctic, and Alpine Research     Full-text available via subscription   (Followers: 7)
Artificial Satellites     Open Access   (Followers: 15)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 2)
Asian Journal of Earth Sciences     Open Access   (Followers: 17)
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 3)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 4)
Atmospheric and Climate Sciences     Open Access   (Followers: 14)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 11)
Boletim de Ciências Geodésicas     Open Access  
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 8)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 10)
Bulletin of Geosciences     Open Access   (Followers: 8)
Bulletin of Marine Science     Full-text available via subscription   (Followers: 13)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 17)
Bulletin of Volcanology     Hybrid Journal   (Followers: 13)
Canadian Journal of Plant Science     Full-text available via subscription   (Followers: 12)
Canadian Mineralogist     Full-text available via subscription   (Followers: 1)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Carbonates and Evaporites     Hybrid Journal   (Followers: 4)
CATENA     Hybrid Journal   (Followers: 3)
Central European Journal of Geosciences     Hybrid Journal   (Followers: 5)
Central European Journal of Physics     Hybrid Journal   (Followers: 1)
Chemical Geology     Hybrid Journal   (Followers: 9)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 3)
Chinese Geographical Science     Hybrid Journal   (Followers: 3)
Chinese Journal of Geochemistry     Hybrid Journal   (Followers: 2)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 3)
Ciencia del suelo     Open Access  
Climate and Development     Hybrid Journal   (Followers: 10)
Coastal Management     Hybrid Journal   (Followers: 19)
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 5)
Computational Geosciences     Hybrid Journal   (Followers: 11)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 1)
Computers and Geotechnics     Hybrid Journal   (Followers: 5)
Contemporary Trends in Geoscience     Open Access  
Continental Journal of Earth Sciences     Open Access   (Followers: 2)
Continental Shelf Research     Hybrid Journal   (Followers: 8)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 7)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 2)
Coral Reefs     Hybrid Journal   (Followers: 18)
Cretaceous Research     Hybrid Journal   (Followers: 4)
Cybergeo : European Journal of Geography     Open Access   (Followers: 4)
Developments in Geotectonics     Full-text available via subscription   (Followers: 2)
Developments in Quaternary Science     Full-text available via subscription   (Followers: 3)
Développement durable et territoires     Open Access   (Followers: 2)
Diatom Research     Hybrid Journal  
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 3)
E3S Web of Conferences     Open Access  
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 180)
Earth Interactions     Full-text available via subscription   (Followers: 8)
Earth Science Research     Open Access   (Followers: 6)
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 1)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 11)
Earth System Dynamics     Open Access   (Followers: 4)
Earth System Dynamics Discussions     Open Access   (Followers: 3)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 1)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 7)
Earthquake Science     Hybrid Journal   (Followers: 9)
Earthquake Spectra     Full-text available via subscription   (Followers: 12)
Ecohydrology     Hybrid Journal   (Followers: 11)
Electromagnetics     Hybrid Journal   (Followers: 1)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Exploration & Exploitation     Full-text available via subscription   (Followers: 4)
Environmental Earth Sciences     Hybrid Journal   (Followers: 10)
Environmental Geology     Hybrid Journal   (Followers: 11)
Environmental Geosciences     Full-text available via subscription   (Followers: 4)
Environmental Geotechnics     Open Access  

        1 2 3 4 5 | Last

Journal Cover Applied Clay Science
   [4 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0169-1317
     Published by Elsevier Homepage  [2571 journals]   [SJR: 0.999]   [H-I: 63]
  • Compatibility analysis of municipal solid waste incineration residues and
           clay for producing lightweight aggregates
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Margarida J. Quina , Marisa A. Almeida , Regina Santos , João M. Bordado , Rosa M. Quinta-Ferreira
      This work provides insight into the most important properties of air pollution control (APC) residues from municipal solid waste incineration (MSWI) and clay used at industrial level aiming at producing a ceramic material known as lightweight aggregates (LWA). Both clay and APC residues were characterized to assess the most important chemical, physical, thermal and mineralogical properties to evaluate their compatibility. The maximum percentage of incorporation tested was 10% of APC residues. The results showed that the waste does not own bloating properties and it is not expectable other improvements into the technological properties of LWA, since the fluxing components contribution is high and the amount of silica is low. Although during the thermal analysis of the APC residues the loss on weight is high (about 32% until 1200°C), they seem not to be suitable as a gas-release additive, once for 10% of incorporation the external shell appears to be significantly broken. The environmental impact due to leaching of pollutants from the LWA incorporating less than or equal to 5% of waste appears not to be relevant. In conclusion, the results showed that synthetic LWA may be considered as a possible approach to recycling of APC residues in case of low amount of waste is used or if a pre-treatment is performed.


      PubDate: 2014-11-14T14:15:24Z
       
  • Free swell potential of lime-treated gypseous soil
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Abdulrahman Aldaood , Marwen Bouasker , Muzahim Al-Mukhtar
      Lime treatment generally enhances the geotechnical properties of the soils. However, some studies have reported an adverse effect, especially in the presence of gypsum. To develop an understanding of the underlying mechanisms, a study of fine-grained soil with different amounts of gypsum was carried out. The influence of curing conditions (curing period and curing temperature) and wetting-drying cycles on the swell potential of fine-grained soil with (0, 5, 15 and 25%) gypsum was investigated to assess the long-term behavior of this type of soil (i.e. gypseous soil) when used in the construction of road and pavement structures. Mineralogical and microstructural studies (porosimetry, X-ray diffraction and scanning electron microscopy) were carried out to evaluate the cementitious materials and the presence of ettringite. The results show that increasing the gypsum content decreased the swell potential of the untreated soil samples. On the other hand, the swell potential values of soil samples started decreasing after the first wetting–drying cycle then reached equilibrium. Lime treatment results show that the suppression of swelling in lime-treated soil samples without gypsum was partly lost after the first cycle, especially for short curing periods and for both temperature values (20°C and 40°C), while long-term curing periods (more than 28days) gave good results with respect to the suppression of swell potential values. Lime treatment of gypsum-containing samples showed an adverse effect on swell potential. The swell potential values increased with curing period and curing temperature, due to the formation of ettringite. Lastly, wetting–drying cycles caused an increase in the swell potential values of gypsum-containing samples, cancelling out the beneficial effect of lime treatment to control swell.


      PubDate: 2014-11-14T14:15:24Z
       
  • Evidence of localised gas propagation pathways in a field-scale bentonite
           engineered barrier system; results from three gas injection tests in the
           large scale gas injection test (Lasgit)
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): R.J.Cuss , J.F. Harrington , D.J. Noy , C.C. Graham , P. Sellin
      Three gas injection tests have been conducted during a large scale gas injection test (Lasgit) performed at the Äspö Hard Rock Laboratory, Sweden. Lasgit is a full-scale experiment based on the Swedish KBS-3 repository concept, examining the processes controlling gas and water flow in highly water-saturated compact buffer bentonite. Three preliminary gas injection tests have been performed. The first two tests were conducted in the lower array of injection filters (FL903). Both of these tests showed similar behaviour that corresponded with laboratory observations. The third gas test was conducted in an upper array filter (FU910), which gave a subtly dissimilar response at major gas entry with an initial pressure drop followed by a secondary gas peak pressure. Lasgit has confirmed the coupling between gas, stress and pore-water pressure for flow before and after major gas entry at the field scale. All observations suggest mechanisms of pathway propagation and dilatancy predominate. In all three gas tests the propagation was through localised features that tended to exploit the interface between the copper canister and the bentonite buffer. Considerable evidence exists for the development of a highly-dynamic, tortuous network of pressure induced pathways which evolves both temporally and geospatially within the clay, opening and closing probably due to local changes in gas pressure and or effective stress.


      PubDate: 2014-11-14T14:15:24Z
       
  • Polypyrrole-coated halloysite nanotube clay nanocomposite: Synthesis,
           characterization and Cr(VI) adsorption behaviour
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Niladri Ballav , Hyoung J. Choi , Shivani B. Mishra , Arjun Maity
      A polypyrrole-coated halloysite nanotube nanocomposite (PPy-HNTs NC) was prepared via in situ polymerization of pyrrole (Py) in the dispersion of HNTs and assessed for the removal of toxic Cr(VI) from aqueous solutions. ATR-FTIR and XRD results confirmed the formation of the nanocomposite. The FE-SEM and TEM images revealed the coating of PPy in the halloysite matrix and the surface morphology of the PPy-HNTs NC. Batch adsorption study showed that the adsorption process was very fast and kinetic data well fitted with pseudo-second-order kinetic model. Adsorption isotherms followed the Langmuir isotherm model and the maximum adsorption capacity was found to be 149.25mg/g at pH2.0 at 25°C. The adsorption process was spontaneous and endothermic in nature. XPS study confirmed the adsorption of Cr(VI) onto the NC where some part of Cr(VI) reduced to Cr(III) by electron-rich PPy moiety. The desorption study suggested that the nanocomposite (NC) can be reused three times without loss of its original removal efficiency. Tests on contaminated groundwater and chrome mine water indicated the potential applicability of the adsorbents for the removal of Cr(VI) for actual field application.
      Graphical abstract image

      PubDate: 2014-11-14T14:15:24Z
       
  • A study on sustained release formulations for oral delivery of
           5-fluorouracil based on alginate–chitosan/montmorillonite
           nanocomposite systems
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Fahimeh Farshi Azhar , Ali Olad
      The objective of this study was to develop a sustained drug release system for 5-fluorouracil (5-FU), an anticancer drug, to improve its half-life. 5-Fluorouracil was loaded on montmorillonite (Mt) layers through the preparation of 5-FU/Mt nanocomposite by an intercalation method. In order to retard the drug release in the gastric environment, the prepared 5-FU/Mt nanocomposite was compounded with alginate (Alg), and further coated with chitosan (CS). This novel drug delivery system was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. By in vitro experiments the effects of Mt contents and pH of the release media on the release rate of the drug were investigated. According to the results, the Alg–CS/5-FU/Mt nanocomposite system containing 30wt.% Mt in the release media with the pH of 7.4 effectively sustained the drug release and the time for 50% release, T50%, is about 8h. The release profile of 5-FU from the Alg–CS/5-FU/Mt nanocomposite system was best fitted by the Korsmeyer–Peppas kinetic model suggesting the diffusion controlled release mechanism. The prepared Alg–CS/5-FU/Mt nanocomposite system is suitable for the delivery of 5-FU in the small intestine with a controlled manner.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Anisotropic thermal conductivity of natural Boom Clay
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Linh-Quyen Dao , Pierre Delage , Anh-Minh Tang , Yu-Jun Cui , Jean-Michel Pereira , Xiang-Ling Li , Xavier Sillen
      The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.


      PubDate: 2014-11-10T13:52:23Z
       
  • Stearic acid hybridizing coal–series kaolin composite phase change
           material for thermal energy storage
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Songyang Liu , Huaming Yang
      This paper aimed at developing a novel form-stable composite phase change material (PCM) by using stearic acid (SA) to hybridize coal–series kaolinite (Kc) via vacuum impregnation method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The thermal properties of the composite were characterized by using differential scanning calorimetry (DSC) and thermal cycling test analysis technique. Natural kaolin (K) was also used as the support to make further investigation on the thermal properties of the kaolinite-based composite PCM. The crystallinity of SA in SA/Kc (90.1%) was higher than that of SA/K (84.9%). The SA/Kc composite showed an enhanced thermal storage capacity compared with the SA/K composite. The latent heats of melting (66.30J/g) and freezing (65.60J/g) for SA/Kc were higher than those of SA/K sample (59.25 and 59.01J/g, respectively). Furthermore, the SA/Kc composite PCM showed an excellent stability after up to 200 thermal cycling. The corresponding mechanism was discussed in detail.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Stabilization of alkali earth metal cations in Na-4-mica
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Jun Hyung Kim , Hong-Jin Kim , Man Park
      Na-4-mica, a highly charged swelling mica, has suffered from insufficient understanding of some fundamental features such as partial layer collapse and rearrangement of interlayered cations and layers during exchange reaction. This study focuses on elucidating the changes in chemical environments of divalent cations and in layered structure during the exchange reaction with divalent cations. Cation exchange reaction with a series of alkali earth cations led to significant changes in both XRD pattern and IR spectra. The extent of cation exchange reaction depended highly and systematically on cation size and hydration energy. Exchange reaction with Mg2+ and Ca2+ led to highly hydrated phases whereas that with Sr2+ to anhydrous phase and that with Ba2+ to remarkable degradation of layered structure. The hydrated divalent cations could be quickly stabilized in interlayer space in spite of localized incompatibility of both lattice and charge through formation of interstratified phases having various ratios of Na+/M2+ and Na+/H3O+. Therefore, divalent cations could be stably accommodated either in hydrated or anhydrous state within the cavities, preferably around crystal edges to obstruct their further uptake.


      PubDate: 2014-11-10T13:52:23Z
       
  • Deformation of “tunable” clay–polymer composites
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Matthew D. Bishop , Sungho Kim , Angelica M. Palomino , Jong-Sub Lee
      Responsive clay–polymer composites are the next step in the development of polymer-modified clay materials. It has been shown at the micro-scale that these materials respond to the surrounding pore fluid environment, resulting in an alteration in fabric. The purpose of this study is to investigate the impact of the responsive nature of these materials on the consolidation properties. Two composite types were selected to highlight the differences based on modified interparticle and interparticle/interlayer spacings: one made from a kaolinite and one from a montmorillonite. Each composite was made with polyacrylamide as the polymer. The clay–polymer composites were subjected to 1-D consolidation tests during which shear wave velocity was also measured. The pH of the saturating fluid was varied to promote composite response. Results show that the compressibility, compression index, and swelling index of the composite materials are greater than the untreated clay materials. Furthermore, these properties are pH-dependent for both types of composite materials and are consistent with the long-term conformational behavior of PAM. This apparent observation confirms that the behavior of the clay–PAM composites is controlled by the behavior of PAM. On the other hand, the shear wave velocities between the control and composite samples were not significantly different.


      PubDate: 2014-11-10T13:52:23Z
       
  • Predicting thermal and thermo-oxidative stability of silane-modified clay
           minerals using thermogravimetry and isoconversional kinetic analysis
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Björn Geyer , Tobias Hundshammer , Stefan Röhner , Günter Lorenz , Andreas Kandelbauer
      Clay minerals play an increasingly important role as functional fillers and reinforcing materials for clay polymer nanocomposites (CPN) in advanced applications. Among the prerequisites necessary for polymer improvement by clay minerals are homogeneous and stable distribution of the clay mineral throughout the CPN, good compatibility of the reinforcement with the matrix component and suitable processability. Typically, clay minerals are surface-modified with organic interface-active compounds like detergents or silanes to obtain favorable properties as filler. They are incorporated into the polymer matrix using manufacturing equipment like extruders, batch reactors or other mixing machines. In order for the surface modification to survive the stresses and strains during incorporation, the modified clay minerals must display sufficient thermal and mechanical stability to retain the compatibilizing effect. In the present study, thermogravimetry was used in combination with isoconversional kinetic analysis to determine the thermal stability of a silane-modified clay mineral based on bentonite. These findings were compared with the stability of the same clay mineral that was only surfactant-modified. It was found that silane modification leads to significantly improved thermal stability, which depends strongly on the type of silane employed.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Synthesis and characterization of soy polyol-based polyurethane
           nanocomposites reinforced with silylated palygorskite
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Chengshuang Wang , Qisheng Wu , Fang Liu , Jing An , Rong Lu , Hongfeng Xie , Rongshi Cheng
      Soy polyol-based polyurethane (PU) nanocomposites were synthesized with 3-glycidoxypropyltrimethoxysilane modified palygorskite (GPTMSPal). The GPTMSPal PU nanocomposites were characterized using XRD, DMA, TGA, SEM, and universal test machine. GPTMSPal increased the glass transition temperature as well as significantly improved tensile strength and Young's modulus of the GPTMSPal PU nanocomposites. Compared to neat PU, GPTMSPal PU nanocomposite with 12mass% GPTMSPal exhibited a 13.1°C increase in the glass transition temperature, a 303% improvement in tensile strength, and a 518% increment in Young's modulus, respectively. TGA results showed that the thermal stability of GPTMSPal PU nanocomposites improved with increased GPTMSPal loading. Furthermore, SEM revealed a uniform dispersion of GPTMSPal in the PU matrix.


      PubDate: 2014-11-10T13:52:23Z
       
  • Acid-treated vermiculites as effective catalysts of high-temperature N2O
           decomposition
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Lucjan Chmielarz , Małgorzata Rutkowska , Magdalena Jabłońska , Agnieszka Węgrzyn , Andrzej Kowalczyk , Paweł Boroń , Zofia Piwowarska , Adam Matusiewicz
      Vermiculites treated with solutions of HNO3, HCl and H2SO4 were tested in the role of catalysts for high-temperature decomposition of N2O to N2 and O2. Acid treatment of clay mineral resulted in a partial leaching of components of its octahedral sheets, which were partially deposited on the surface of vermiculite. Such modification of the clay samples significantly increased their specific surface area and porosity as well as influenced their surface acidity. Acid treatment of vermiculites activated them in the process of high-temperature N2O decomposition, however activation effect depended on type of acid used as well as duration of acid modification.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Study of surface acid–base properties of natural clays and zeolites
           by the conversion of 2-methylbut-3-yn-2-ol
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Lyudmila Novikova , Frank Roessner , Larisa Belchinskaya , Murad AlSawalha , Victoriya Krupskaya
      Surface acid–base properties of natural clays and non-clay minerals from Jordanian (J) and Russian (R) deposits as well as H-ZSM-5 were studied applying catalytic reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. Products of both acidic and basic pathways of the reaction were formed involving surface acid/basic sites of clay minerals. Specific conversions of MBOH decreased in the following order: kaolinite-R>hydromica-R>bentonite-J>red-kaolinite-J=palygorskite-R=H-ZSM-5>zeolite-J>white-kaolinite-J>diatomite-J, which fairly correlated with TPD-NH3 acidity assessment for a majority of samples. However, a contribution of basic sites to the reaction should be taken into account, especially for hydromica-R and kaolinite-R. The strength of acid sites of natural aluminosilicates was compared based on surface acidity and reaction product yields. After 116min of MBOH conversion, the strength of acid sites changed in the following order: kaolinite-R>palygorskite-R>bentonite-J>red- kaolinite-J>white-kaolinite-J>zeolite-J>diatomite-J>H-ZSM-5. At an early (17min) stage of the reaction, the strength of active sites for natural zeolite-J and H-ZSM-5 were comparable, while the latter underwent significant deactivation due to its microporous structure. The rise of activation temperature from 500°C to 700°C for montmorillonite containing sample increased the conversion of MBOH due to the formation of stronger or additional number of basic sites as a result of mineral dehydroxylation. Natural clay samples with a higher content of montmorillonite (30–80%) altered the acid–base properties of the surface and observed higher ability to convert MBOH over acid and basic pathways.


      PubDate: 2014-11-10T13:52:23Z
       
  • The effect of cetyltrimethylammonium ion and type of smectites on the
           luminescence efficiency of bis(8-hydroxyquinoline)zinc(II) complex
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Patcharaporn Pimchan , Nithima Khaorapapong , Makoto Ogawa
      A luminescence metal complex, bis(8-hydroxyquinoline)zinc(II) (Znq2), was incorporated into the interlayer space of smectites (a natural montmorillonite and a synthetic saponite) by two different ways; colloidal processes via the in situ formation of bis(8-hydroxyquinoline)zinc(II) in cetyltrimethylammonium-smectites (CTA-smectites) and the adsorption of cetyltrimethylammonium coated bis(8-hydroxyquinoline)zinc(II) (Znq2CTA) into hydrophilic smectites. The UV–Vis spectra confirmed the formation and the incorporation of bis(8-hydroxyquinoline)zinc(II) in the interlayer space of smectites. The photoluminescence bands of Znq2CTA@montmorillonite and Znq2@CTA-montmorillonite (498nm) were blue shifted in comparison with the weak emission bands of Znq2CTA@saponite and Znq2@CTA-saponite (510nm), indicating the formation of different nanostructures and/or packing of bis(8-hydroxyquinoline)zinc(II) in the two types of smectites. The state of the intercalated cetyltrimethylammonium ions also played a key role to the luminescence intensities of the products due to the concentration quenching and self-absorption.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Morphology and orientation of curling of kaolinite layer in hydrate
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Jinan Niu , Yinghuai Qiang , Xiang Li , Zhangsheng Liu , Shenghui Zhang , Peizhong Feng , Xuemei Ou
      In order to determine if there are curlings along other directions than [100] and [010] in kaolinite (Kaol) layer, 1nm Kaol hydrate with 85% yield was synthesized by the fluorine-free method. Its structure and morphology were investigated by X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM) and selected area electron diffraction (SAED). The results show that: (1) there are not only single curling and two opposite parallel curlings, but also two adjacent curlings with about 120° angle in one single layer; (2) there are four new orientations of curlings [ 1 1 ¯ 0 ], [110], [310] and [ 3 1 ¯ 0 ] in Kaol hydrate. The reasons that Kaol layers can curl along multiple directions may be that: first, two types of incompatible matchings between tetrahedrons and octahedrons; second, the hexagonal distribution and the zigzag distribution of two types of matchings.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Effective stress concept on multi-scale swelling soils
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Hossein Nowamooz
      It is important to predict the behavior of swelling soils during hydro-mechanical solicitations in order to investigate their long-term behavior. The complex hydromechanical behavior of swelling materials is generally connected to their fabric. For swelling soils, the determination of the effective stress parameter (χ) becomes more complicated because of their multiple scales: macro-, meso- and micro-scale. In this work, the χ parameter is related to the degree of saturation of each scale in interaction. Using the effective stress approach, the hydro-mechanical behavior was studied for loosely, intermediately and densely compacted samples. This approach helps us to define the yield surfaces for the compacted samples in the (effective stress–total applied stress) and (suction-effective stress) planes.


      PubDate: 2014-11-10T13:52:23Z
       
  • Synthesis and swelling properties of microcrystal muscovite composite
           superabsorbent
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Tao Wan , Zhiling Zhou , Runqiu Huang , Chuzhang Zou , Min Xu , Wenzhong Cheng , Ruixiang Li
      A new microcrystal muscovite composite superabsorbent (MMCSA) was synthesized by redox copolymerization of acrylic acid (AA), acrylamide (AM) and itaconic acid (IA) with ammonium persulfate (APS) and sodium bisulfite used as redox initiator, N, N-methylene bisacrylamide (MBA) used as crosslinker and microcrystal muscovite used as an inorganic additive. Factors affecting the water absorption and gel strength of the microcrystal muscovite composite superabsorbent, such as crosslinker amount, microcrystal muscovite amount, neutralization degree of AA and IA, IA/AA mass ratio and (AA+IA)/AM mass ratio were systematically studied. Morphology, structure and thermostability of microcrystal muscovite composite superabsorbent were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal gravimertic analysis (TGA), respectively. The results show that swelling kinetics of microcrystal muscovite composite superabsorbent can be expressed by the Voigt-based viscoelastic model. Water absorption of microcrystal muscovite composite superabsorbent is rapid, requiring 24.55min to reach 63% of equilibrium absorbency (1218g/g). Water absorbency, gel strength and thermostability of microcrystal muscovite composite superabsorbent increase with microcrystal muscovite amount increasing from 5% to 15%. Microcrystal muscovite is physically combined into the polymeric network without destroying its polycrystalline structure and the surface of the microcrystal muscovite composite superabsorbent has some deep and small macropores.


      PubDate: 2014-11-10T13:52:23Z
       
  • Effects of pH and temperature on the swelling pressure and hydraulic
           conductivity of compacted GMZ01 bentonite
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): W.M. Ye , Z.J. Zheng , B. Chen , Y.G. Chen , Y.J. Cui , J. Wang
      Gaomiaozi (GMZ) bentonite has been recognized as the first choice for using as buffer/backfill materials in deep geological repository for the disposal of high-level nuclear waste (HLW) in China. Groundwater in Beishan area, which has been considered as a potential site for the construction of Chinese deep geological repository, may reach a high pH value because of its chemical background and possible cement degradation during the operation of the repository. Meanwhile, temperature may increase with decay heat released from the waste in the canister. Investigation of pH value of alkaline-solutions and temperature effects on the behavior of compacted GMZ01 bentonite is of great importance for the Chinese deep geological repository program. For this purpose, a series of swelling pressure and hydraulic conductivity tests with various pHs of NaOH solutions were conducted at different temperatures. The X-ray diffraction (XRD) exploration was performed on the GMZ01 bentonite specimens before and after experiencing the swelling pressure and hydraulic conductivity tests, in order to find out the influences of temperature and pHs on the mineralogy of GMZ01 bentonite. Results show that the swelling pressure of GMZ01 bentonite decreases as the pH value of NaOH solutions increases, while the decreasing rate significantly depends on temperature. The swelling pressure evolution curve was “double-peak” structured, which faded with the increases of pH and temperature. The hydraulic conductivity of GMZ01 bentonite increases with the increase of the pH value of NaOH solutions and the rise of temperature. All these observations were consistent with the XRD test results: the dissolution of montmorillonite in GMZ01 bentonite increases with the pH increases. This process was accelerated by the temperature rise.


      PubDate: 2014-11-10T13:52:23Z
       
  • Magnetically separable Ni/SPL@Carbon nanocomposite for removal of Pb(II)
           from the aqueous solution
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Zhenghui Xiao , Qinqin Cui , Xiangying Chen , Xueliang Li , Fangfang Peng , Rui Zhang , Taofa Zhou
      Magnetically separable nanocomposite adsorbents have been synthesized by a simple hydrothermal/solid-state method, in which sepiolite (abbr. SPL) clay, glucose and nickel nitrate were used as the role of template, carbon and the magnetic medium, respectively. In the present work, carbon firstly was covered onto the surface of rod-like SPL clays by hydrothermal treatment, and further ultrafine nickel particles (0.5–1nm) were loaded into the above carbons, giving rise to unique ternary structures with various kinds of surface areas, pore volumes and pore size distributions. The Ni/SPL@Carbon-1:10 sample possesses the largest surface area (92.0m2 g−1) compared with that of Ni/SPL@Carbon-1:1 (49.6m2 g−1) and Ni/SPL@Carbon-1:5 (51.8m2 g−1). The impact of several key factors, mainly including contact time, initial metal ion concentration and initial pH, upon the adsorptive performance was investigated in depth. The Ni/SPL@Carbon-1:10 sample, as an effective adsorbent, thus exhibits the highest uptake amount (28.04mgg−1) for the removal of Pb(II) ions from an aqueous solution. More importantly, the present adsorbents can be readily separated with an external magnetic field, implying their potential superiority in practical applications.


      PubDate: 2014-11-10T13:52:23Z
       
  • Hydrated burnt clay–lime mixes: Effects of curing time and lime
           addition
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): M. Hajjaji , Y. Mleza
      Effects of hydration time (up to 28days) and lime addition (≤20wt.%) on the changes of the microstructure of a kaolinitic–illitic clay heated at 600°C were investigated using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. Physical properties (strength, density, water absorption) of the cured blends were measured. The relations between properties and the operating factors were formulated using response surface methodology (RSM). Flocculation–agglomeration, carbonation and hydrate (C–S–H and CAH10) formation were the main happening transformations. The pozzolanic reactions involved metakaolin and to a lesser extent illite. Based on RSM results, both factors had positive effects on strength and their interactions were synergistic. However, they manifested opposite effects and significant antagonistic interactions on density and water absorption.


      PubDate: 2014-11-10T13:52:23Z
       
  • Characterization of Fe-smectites and their alteration potential in
           relation to engineered barriers for HLW repositories: The Nui Nua clay,
           Thanh Hoa Province, Vietnam
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Lan Nguyen-Thanh , Thao Hoang-Minh , Jörn Kasbohm , Horst-Jürgen Herbert , Duong Nguyen Thuy , Lai Le Thi
      The stability of smectite-rich clay minerals is of interest because they could be candidates for engineered barriers for high-level radioactive waste repositories. This research characterized the chemical and mineralogical properties of the Nui Nua clay which forms from the weathering of the Nui Nua serpentinized ultramafic–mafic massif (Thanh Hoa Province, Viet Nam) using several methods (including Fourier transform infrared spectrometry and transmission electron microscopy). The Nui Nua clay, taken from Co Dinh and My Cai valleys, is composed of Fe-smectites as the main phase with minor phases of normal smectite, quartz, talc, chlorite, kaolinite, amphibole, antigorite, feldspars and magnetite. The Fe-smectites were characterized as mixed-layer minerals (including Fe-montmorillonitic as an end-member) composed of illitic or dioctahedral vermiculitic layers and Fe-rich smectitic layers. The proportion of the smectitic layer is approximately 80%; the interlayer sheet is dominated by Ca and Mg, while the octahedral sheet is dominated by Fe3+ (not Al). The stability of the Nui Nua smectites was also investigated by a simulation in saturation of 1M NaCl and deionized water under kinetic impaction. The average tetrahedral-Si content of the smectites increased or decreased depending on the “dynamic solution” or hydraulic regime. By chemical identification, the alteration of Fe-smectites is mainly increased by the smectitization process. This research suggests that the Nui Nua clay is a potential candidate for an engineered barrier because during the alteration process, neo-formation of a montmorillonitic layer occurs.


      PubDate: 2014-11-10T13:52:23Z
       
  • Experimental study and analytical model for pore structure of hydrated
           cement paste
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Xudong Chen , Shengxing Wu , Jikai Zhou
      Mercury intrusion porosimetry (MIP) test is one of the techniques that have been widely used for analyzing the pore size distribution of hydrated cement paste and also for determining the pore structure parameters. This study presents the test results of the MIP experiments obtained for different cement paste specimens with the water–cement ratios of 0.3, 0.4, 0.5, 0.6 and 0.7 which had been cured for 1, 3, 7, 14 and 28days. Thus, the effect of water–cement ratio and curing time on the pore structure of cement paste was investigated. The pore structure of samples is characterized by the porosity, pore size distribution as well as characteristic pore sizes. A thermodynamic pore fractal model was also used to calculate the pore fractal dimensions of specimens on the basis of MIP data. A mathematical model was developed to describe the pore size distributions of cement paste and related the pore size distributions with water–cement ratios and curing age. The procedure followed in this paper, i.e., determining the statistical distribution and analyzing the probability, can be used to interpret pore size data in other studies.


      PubDate: 2014-11-10T13:52:23Z
       
  • Composite pigments based on surface coated kaolin and metakaolin
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Václav Štengl , Daniela Popelková , Tomáš Matys Grygar
      Synthesis The method of homogeneous hydrolysis of Fe, Co, Cr, Ni, Mn, Ti, Al, and Zn salts with urea in aqueous solutions in the presence of substrates (kaolin, metakaolin and mullite) was used for the preparation of composite pigments. In these composites individual kaolinite platelets were covered by a thin layer of hydroxide or oxy-hydroxides of selected metals, which were transformed into a metal oxide layer strongly bond to the aluminosilicate surface by heat treatment. An analogous method, homogeneous hydrolysis of thioacetamide in the presence of Cd and Zn salts was used for pigments based on sulphides. Characterization The mineralogical composition of the pigments was identified by X-ray powder diffraction (XRD), the particle morphology was studied by transmission electron microscopy (TEM) and the color was characterized in CIEL*a*b colours coordinates. Results The kaolin and metakaolin coated with layer of metal oxides are interesting new composite materials, obtained by a very simple preparation process at a low cost.


      PubDate: 2014-11-10T13:52:23Z
       
  • Study of traditional Tunisian medina clays used in therapeutic and
           cosmetic mud-packs
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Imen Khiari , Samir Mefteh , Rita Sánchez-Espejo , Pilar Cerezo , Carola Aguzzi , Alberto López-Galindo , Fakher Jamoussi , César Viseras Iborra
      The present study was carried out to access the suitability of eleven clay samples (green and brown) from five Tunisian medina markets, traditionally used in home-made mud-packs. The mineralogical composition was determined from X-ray powder diffraction and X-ray fluorescence data. Scanning electron microscopy coupled with energy-dispersive X-ray microanalysis was also carried out, as well as thermogravimetric analysis of raw clay samples. To determine the performance of the samples in mud-pack thermotherapy, cooling kinetics of clay pastes were fitted to obtain the corresponding specific heats. According to their mineralogical composition, the studied medina clay samples were mainly composed by illite and kaolinite, with exception of two Mg smectite-rich samples and other two calcite-rich samples. The presence of relatively high amounts of crystalline silica (quartz) in some of the samples advises against their not controlled manipulation, even if there are no quantitative limits (widely approved) of crystalline silica content above which the usage of commercial clays can be prohibited. The cooling rates and specific heats of the studied pastes were adequate to their use in the preparation of hot mud-packs, able to transfer heat to the skin during a period of at least 15min after application.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Diffusion behavior of Se(IV) and Re(VII) in GMZ bentonite
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Tao Wu , Hai Wang , Qing Zheng , Yao Lin Zhao , Luc R. Van Loon
      The diffusion behavior of HSeO3 − and ReO4 − was investigated in Gaomiaozi (GMZ) bentonite by the through-diffusion method. The effective diffusion coefficient De, porosity ε and rock capacity factor α were measured in order to evaluate the impact of porosity on anion diffusion in compacted bentonite. The De values of HSeO3 − and ReO4 − were (4.5–54)×10−12 and (3.0–53)×10−12 m2/s at dry densities from 1300 to 1800kg/m3, respectively. HSeO3 − sorbed on GMZ bentonite with a distribution coefficient Kd in the range of (1.4–1.8)×10−4 m3/kg, whereas ReO4 − showed little sorption. Moreover, the diffusion behavior of HSeO3 - and ReO4 - was similar to that of SeO3 2-and 99TcO4 -. Since the minimum average pore diameter at a bulk dry density below 1800kg/m3 is much larger than that of anions, the constrictivity δ could be neglected. The De or the apparent diffusion coefficient Da was related to porosity ε by Archie's law and by a pore diffusion model with linear and logarithmic relations between τ and ε. The best fit was obtained by Archie's relation.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Effect of the dispersive method in the preparation of the
           polyurethane/hydrotalcite nanocomposites by in situ polymerization
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Danieli M. Carmo , Marcia G. Oliveira , Bluma G. Soares
      The dispersions were prepared in the proportion of 1g LDH to every 100ml of 1,6-hexamethylenediisocyanate employing four different methodologies. The FTIR results of the dispersions confirmed the presence of monomer in the clay interlayer space, for all methods studied. The XRD analysis showed that the presence of isocyanate contributed to a small structural disorder. Any significant differences between the experimental procedures adopted were observed in TGA results, whereas visual analysis showed that methodology combining ultraturrax and ultrasound bath (TBT) was more effective for dispersion and incorporation of the monomer remaining stable for about a month. The dispersions studied were used in the synthesis of polyurethane nanocomposite. The in situ polymerization step had as objective favor the dispersion of nanofiller during the growth of the polymer chains. The polyurethane obtained was confirmed by the presence of characteristic bands of the urethane group in the FTIR spectrum. The diffraction patterns indicated that in situ polymerization contributed to the structural disorder of the nanocomposites. The strain sweep was carried out by rubber process analyzer (RPA), the lowest values of Payne effect (G0 −G∞) were to TBT and T methodologies suggesting a lower filler-filler interaction. The results of the dynamic mechanical thermal analysis (DMTA) showed significant differences that were associated with the dispersion method adopted and also a stoichiometry imbalance due to the interactions of the isocyanate with the hydroxyl groups of the hydrotalcite and/or water molecules within interlayer space and/or air moisture. SEM micrographs revealed better dispersion in the clay polyurethane nanocomposites, whose nanofiller was previously dispersed in the isocyanate monomer.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Compressibility and hydraulic conductivity of clayey soil mixed with
           calcium bentonite for slurry wall backfill: Initial assessment
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): R.-D. Fan , Y.J. Du , Krishna R. Reddy , S.Y. Liu , Y.L. Yang
      Soil–bentonite vertical cutoff walls, consisting of a sandy soil mixed with Na-bentonite as backfill, are used extensively as engineered barriers for contaminant containment. However, suitable sandy soil and Na-bentonite may not be available at some sites. Consequently, locally available clayey soil and Ca-bentonite may be considered as an alternative backfill. The use of clayey soil/Ca-bentonite backfill may be advantageous to achieve relatively low hydraulic conductivity, which has equivalent performance as that of conventional sandy soil/Na-bentonite backfills. However, studies on the compressibility and hydraulic conductivity of these clayey soil–bentonite backfills are very limited. This paper presents a comprehensive laboratory investigation on the compressibility and hydraulic conductivity of clayey soil/Ca-bentonite backfill through a series of oedometer tests. Kaolin is used as the control clayey soil and it is amended with different contents of Ca-bentonite, 0 (kaolin alone), 5, 10, and 15% (by dry weight basis), to prepare the clayey soil/Ca-bentonite backfills. The initial water contents for the backfills are selected to be 0.75, 1.0, 1.25, and 1.50 times their corresponding liquid limits. The results reveal that the backfills exhibit a noticeable inverse ‘S’ shaped e-log(σ′) compression curves attributed to the existence of the remolded yield stress (σ′yr). The compressibility, in terms of σ′yr and the compression index (C c), is significantly affected by the initial water content and bentonite content. The void ratio at an effective vertical compression stress of 1kPa (denoted as e 1) is a useful characteristic parameter to uniquely correlate with C c for the clayey soil/Ca-bentonite backfills in this study as well as for sandy soil/Na-bentonite and sandy soil–clay backfills that are reported in previous published studies. Unique relationships are also found between the σ′yr, initial void ratio (e 0), e 1, and the void ratio at liquid limit (e L). The hydraulic conductivity of the clayey soil/Ca-bentonite backfills is significantly reduced by the bentonite content; generally to less than 10−9 m/s. An empirical method based on the framework of Kozeny–Carman equation is proposed to predict the hydraulic conductivity of the clayey soil/Ca-bentonite backfills, and the predicted hydraulic conductivity values using these methods are found to fall in the range of 1/3 to 3 times those obtained from the oedometer tests. The proposed method is shown to estimate the hydraulic conductivity for both the clayey soil/Ca-bentonite backfills in this study and the sandy soil–bentonite backfills from published study with reasonable accuracy. Additional research is warranted to prepare the backfills to simulate typical field practice (e.g., use of tap water) and at workable initial water contents (based on the slump testing).


      PubDate: 2014-11-10T13:52:23Z
       
  • Functional organo-Mt/copolymer nanoarchitectures. XXII. Interlamellar
           graft copolymerisation of l-lactic acid onto poly(maleic
           anhydride-alt-1-octadecene) in the presence of different clays as
           catalyst-nanofillers
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Kouroush Salimi , Zakir M.O. Rzayev , Erhan Pişkin
      In this work, novel functional copolymer-g-biopolymer layered silicate nanocomposites were prepared by in situ graft copolymerisation of l-lactic acid (LA) onto poly(maleic anhydride-alt-1-octadecene) in the presence of Na+-montmorillonite (Mt), Ag+-Mt and octadecyl amine-Mt (ODA) nanofillers using a specially constructed vacuum micro-reactor with Dean-Stark unit at 80°C. It was observed that inorganic and organic clays executed the dual functions as catalyst of interlamellar graft copolymerisation and nano-filler in formation of clay polymer nanocomposites (CPNs). This new approach allow us to realise the grafting and graft copolymerisation without use of hazardous tin(oct)2 catalyst. The surfactant matrix copolymer provides the first step of grafting via ring opening monoesterification of anhydride units with LA monomer. The catalytic activity of the positively charged clays and their LA preintercalated complexes as a function of phase separation time, strongly depends on the particle parameters (zeta-size and zeta-potential) of the used clay systems and changed in the following range: organoclay<Na+-Mt<Ag+-Mt. The obtained graft copolymer/clay nanohybrids were characterised by FTIR, 1H and 13C NMR, DSC-TGA-DTG, XRD and SEM-TEM analysis methods. These observed that type of the clays significantly influences the chemical and physical structures, thermal properties, surface and internal core–shell morphology of the copolymer-g-PLA layered silicate nanocomposites. Better results were obtained for the copolymer-g-biopolymer/reactive organoclay nanocomposites. It was concluded that this versatile and green synthetic method can utilise for a wide range of anhydride-containing alternating, random, graft and block functional copolymers as matrix polymers and their silicate layered nanocomposites.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • High temperature phase evolution of Bolivian kaolinitic–illitic
           clays heated to 1250°C
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Edwin Escalera , Ragnar Tegman , Marta-Lena Antti , Magnus Odén
      The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250°C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650°C. During further heating to 1050°C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050–1150°C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2mass %) and Fe (5.6mass%) has an onset temperature for sintering at about 900°C and an onset temperature for liquid formation at 1080°C. This is about 50°C lower onset temperature for sintering and 94°C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3mass %) and Fe (1.6mass %).


      PubDate: 2014-11-10T13:52:23Z
       
  • Phase transformation of coal gangue by aluminothermic reduction
           nitridation: Influence of sintering temperature and aluminum content
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Haipeng Ji , Minghao Fang , Zhaohui Huang , Kai Chen , Wenjuan Li , Yan-gai Liu
      The effect of sintering temperature and aluminum content on the phase transformation of coal gangue by aluminothermic reduction nitridation (ARN) was investigated. The process was carried out in flowing N2 within the temperature range of 1400–1500°C and holding time of 4h. The results showed that temperature and Al content were two essential factors determining the nitridation of coal gangue and the phase yields of nitrided products. Kaolinite, the main mineralogical phase of coal gangue, was transformed into high-temperature composites containing β-SiAlON, corundum and Al6O3N4 by ARN at 1400–1500°C. The products consisted of globular β-SiAlON/corundum particles and continuous SiAlON fibers. The transformation provided a feasible mean of dealing with coal gangue for high-temperature utilization.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Role of preparation method on the extent of montmorillonite catalysis for
           oligomer formation
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Gözen Ertem , Zhehong Gan
      The extent of catalytic activity of montmorillonites (Mts) 1 1 Bergaya, F., Lagaly,G. (Eds.), 2013. Handbook of Clay Science, Second edition.Developments in Clay Science, vol. 5. Elsevier (ISBN-13: 978-0080993645 ISBN-10: 0080993648, Second Edition: 2013). for RNA-like oligomer synthesis varies considerably depending on the method used to prepare the Mt. Homoionic Mt prepared by titration method produced longer oligomers with higher yields compared with Mt prepared by saturation method. The difference in catalytic activity between these two types of Mts is related to the difference in nature of their edge sites.


      PubDate: 2014-11-10T13:52:23Z
       
  • The specific heat of dry homoionic forms of bentonites SWy-2 and Stx-1b:
           An effect of the fraction of particles less than 2μm
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Tomasz Kozlowski , Anna Rusin , Edyta Nartowska
      The specific heat of Ca2+-, Na+- and K+-forms of SWy-2 and Stx-1b has been determined in the range between −150°C and 100°C by use of Quasi Isothermal Modulated Differential Scanning Calorimetry. According to expectations, a strong temperature dependency is observed, but the results of ANOVA also show high statistical significance of the kind of initial clay and the kind of the exchangeable cation. The effect of the latter proved to be indirect, as the contribution from the heat capacity of the exchangeable cations appeared less significant, although its detailed analysis meets difficulties associated with a lack of data on the specific heat of the cations and its relation to the specific heat of the corresponding metals in bulk. A relatively high and statistically significant correlation of the specific heat at a given temperature and the fraction of particles less than 2μm may indicate a contribution of surface atoms to the specific heat capacity, analogical to that observed and theoretically substantiated in relation to nanoparticles of metals and simple organic compounds. This thesis is supported by the kind of temperature-size dependence, resembling that reported for nanoparticles of cuprum oxide by Wang et al. (2006). However, a proposed simple power function model not taking into account the size effect can predict specific heat of montmorillonites with the standard error of the estimate SEE equal to 0.038Jg−1 K−1.


      PubDate: 2014-11-10T13:52:23Z
       
  • The structure of sepiolite as support of metallocene co-catalyst during in
           situ polymerization of polyolefin (nano)composites
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): K. Núñez , R. Gallego , J.M. Pastor , J.C. Merino
      A study concerning the use of sepiolite (fibrillar clay) as support of the co-catalyst (methylaluminoxane, MAO) for a process of in situ polymerization was performed. The formation of an ether bond on the clay surface was necessary to achieve the heterogenization of MAO over sepiolite's surface. In this sense, the experimental variables used during the process of grafting of MAO onto sepiolite's surface were studied. Therefore, it was demonstrated that the structure of modified clay and the structure of grafted MAO were kept because they were able to form the active species for polymerization in presence of catalyst and monomer. The results show that the grafting process was the simplest one, i.e., it wasn't necessary for any pre-treatments, i.e., calcination or acidification, due to the special structure of sepiolite; an economic process of MAO heterogenization onto sepiolite's surface was established. Moreover, this procedure may be easily transferred to conventional polymerization processes for obtaining polymers in which the chains are synthesized onto the surface of the filler, maximizing the interaction of matrix–nanofiller and leading to (nano)composites with better performance than the ones obtained by melt intercalation.


      PubDate: 2014-11-10T13:52:23Z
       
  • Estimating compaction parameters of clayey soils from sediment volume test
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Ali Hakan Ören
      Predicting the compaction parameters, in terms of maximum dry unit weight and optimum water content, from index properties of fine-grained soils has been of interest for the last few decades. Although various index properties, such as liquid limit, plastic limit and clay contents, have been used for the prediction, it was revealed that plastic limits of fine-grained soils correlate well with the compaction parameters. As an alternative method, this paper proposes sediment volume test to estimate the compaction parameters. In order to show its relevance, compaction and sediment volume tests were performed on nine fine-grained soils. The final sediment volumes (FSVs) of soils were determined from sediment volume tests. Then, the correlations between compaction parameters and FSVs were investigated. It is found from this experimental investigation that there is a good relationship between the compaction characteristics namely maximum dry unit weight (γdmax) and optimum water content (wopt) and the FSV, indicating that this method can be used as an alternate way of predicting the same.


      PubDate: 2014-11-10T13:52:23Z
       
  • Structure and properties of new eco-material obtained by phosphoric acid
           attack of natural Tunisian clay
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): S. Louati , W. Hajjaji , S. Baklouti , B. Samet
      In this work, new three dimensional geopolymer materials based on dehydroxylated natural kaolin and phosphoric acid were synthesized. The effects of Si/P molar ratio and curing time were studied. The structures of raw, calcined kaolin and geopolymers synthesized were investigated using X-ray diffraction analysis, IR spectroscopy, scanning electronic microscope, 31P, 29Si and 27Al MAS-NMR and by mechanical measurements. The mechanical strength of geopolymers is maximum when Si/P molar ratio, equal to 2.25, which corresponds to Al/P ratio=1. The mechanical properties are correlated with the amount of amorphous phase in geopolymer which is determined by the Rietveld method. In addition to metakaolin, illite mineral contributes to geopolymerization.


      PubDate: 2014-11-10T13:52:23Z
       
  • Photoluminescent europium(III) complex intercalated in natural and
           synthetic clay minerals for enhanced latent fingerprint detection
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Seung-Jin Ryu , Aran Kim , Myung Duck Kim , Sung Wook Hong , Seung Sik Min , Jin-Hoon Lee , Jin-Kyu Lee , Hyun Jung
      Fluorescent nanohybrid materials, europium(III) complex intercalated Na+-smectite clay minerals (synthetic hectorite and natural montmorillonite), have been developed to visualize latent fingerprints. The guest europium(III) complex ([EuCl2(Phen)2(H2O)2]Cl·H2O) was obtained by simple complex reaction between europium chloride hexahydrate (EuCl3·6H2O) and 1,10-phenanthroline (Phen) as a 1:2 molar ratio of Eu3+ ion to ligand molecules. The intercalated nanohybrids ([Eu(Phen)2]3+-clay minerals) were obtained through ion exchange reaction of interlayer sodium cation with europium complex ion. Guest europium(III) complex and [Eu(Phen)2]3+-clay mineral hybrids were characterized by powder X-ray diffraction, Fourier transform infrared, thermogravimetry-differential thermal analysis (TG-DTA), elemental analysis, UV–visible and fluorescence spectroscopy. The intercalated complex maintains a characteristic red 5D0–7F2 emission at wavelength 617nm, which is comparable to that of the free complex. The 5D0–7F2 emission intensity of [Eu(Phen)2]3+-laponite was ca. 3.5 times higher than that of [Eu(Phen)2]3+-montmorillonite, due to the presence of quenching impurities in natural montmorillonite itself. Fingerprint residues on glass slides were harvested by using [Eu(Phen)2]3+-clay mineral powders, resulting in good definition for enhanced latent fingerprint detection. Particularly, [Eu(Phen)2]3+-hectorite hybrid powder was more clearly separated from the background compared to the montmorillonite hybrid powder.


      PubDate: 2014-11-10T13:52:23Z
       
  • Preparation of granulated LTA and SOD zeolites from mechanically activated
           mixtures of metakaolin and sodium hydroxide
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): V.Yu. Prokof'ev , N.E. Gordina
      The LTA and SOD zeolites were synthesized from the mechanically activated solid mixtures of metakaolin, NaOH and γ-Al2O3. The process of synthesis is controlled by X-ray diffraction, IR-spectroscopy, and scanning electron microscopy. The stages of both thermal treatment and hydrothermal crystallization were investigated and optimized. The size of LTA particle was directly measured by scanning electron microscopy as well as calculated using the X-ray diffraction spectroscopy data. It was shown that the maximum content of LTA can be achieved with an γ-Al2O3 excess over the stoichiometry of the synthesis reaction in an amount of 30–50mol%. The absence of aluminum oxide in the reaction mixture leads to the formation of SOD. It was found that the optimal temperature of the thermal treatment is 600°C. An increase of the temperature leads to a decrease in the amount of the zeolite crystalline phase as well as in the formation of nepheline. The optimum concentration of the NaOH solution at the hydrothermal crystallization stage was defined to form both LTA and SOD. They are 2–4mol/l for the LTA and more than 8mol/l for the SOD. Under these conditions, the amount of the zeolites is more than 90 wt.%.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Excellent adsorption of Acid Flavine 2G by MgAl-mixed metal oxides with
           magnetic iron oxide
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Feipeng Jiao , Jingang Yu , Hailei Song , Xinyu Jiang , Hua Yang , Shuyun Shi , Xiaoqing Chen , Weijie Yang
      Background Most of synthetic dyes that appear in wastewaters may pose aesthetic problem even at a very low concentration. Adsorption is an important method for dye removal. Layered double hydroxides (LDHs) and calcined layer double hydroxide (CLDH) as adsorbents have received wide attention, which combined with magnetic iron oxide, would be better for LDHs/CLDH separation and recycle. Methods Co-precipitation method was used to prepare the composites of LDHs and magnetic iron oxide (Fe/LDHs). Then Fe/LDHs were calcined at 450°C for 4h to obtain Fe/CLDH. The prepared materials were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption measurements, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Batch adsorption experiments were carried out to investigate the removal of Acid Flavine 2G (AF 2G) from aqueous solution by using Fe/CLDH as the adsorbent. Results Fe/LDHs and Fe/CLDH were successfully prepared. The adsorption process could be well described by the pseudo-second order kinetic model and fitted well with the Langmuir isotherm model. The values of thermodynamic parameters (ΔH, ΔS and ΔG) indicated that the adsorption process was endothermic and spontaneous. Competitive adsorption experiments showed that competing anions strongly affected the adsorption process. The adsorption of AF 2G occurred only on external surface of the LDH. After 5 cycles of magnetic separation, regeneration and calcination, the removal efficiency of AF 2G was still above 85%. Conclusions Fe/CLDH could be used as a low-cost and alternative sorbent for the removal of dyes from wastewaters.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Editorial Board
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101




      PubDate: 2014-11-10T13:52:23Z
       
  • Adsorption characteristics of Cs+ on biogenic birnessite
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Keiko Sasaki , Qianqian Yu , Taichi Momoki , Takuya Kaseyama
      Adsorption of Cs+ on biogenic birnessite was investigated and compared with (ad)sorption of other heavy metals and also with (ad)sorption on chemically synthesized birnessite. The adsorption density of Cs+ on biogenic birnessite was smaller than that on chemically synthesized birnessite; however, the (ad)sorption densities of Co2+ and Ni2+ on biogenic birnessite were larger than on chemically synthesized birnessite. These phenomena can be interpreted by considering the distinctive nano-structure of biogenic birnessite, which is not only poorly crystalline and includes organic matter but also according to EXAFS contains a greater proportion of vacant central metal sites than is found in synthetic birnessite. Adsorbed Cs+ ions on both birnessites were mainly in the form of outer sphere complexes, which cannot easily occupy vacant central metal sites in biogenic birnessite. Biogenic birnessite has a greater specific surface area and more fine pores than synthetic birnessite, but these factors do not necessarily lead to more adsorption sites for Cs+ ions.


      PubDate: 2014-11-10T13:52:23Z
       
  • Preparation of CoAl layered double hydroxide nanoflake arrays and their
           high supercapacitance performance
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Pan Guoxiang , Xia Xinhui , Luo Jingshan , Cao Feng , Yang Zhihong , Fan Hongjin
      Porous cobalt aluminum layered double hydroxide (CoAl-LDH) nanoflake arrays on nickel foam were synthesized by a facile hydrothermal synthesis method. The obtained CoAl-LDH film consisted of interconnected nanoflakes with the thicknesses of ~20nm and showed an extended net-like structure. The electrochemical performance of CoAl-LDH nanoflake arrays was tested by cyclic voltammetry and galvanostatic charge/discharge test. The porous CoAl-LDH nanoflake arrays showed good pseudocapacitive performances with high capacitance and good cycle stability. At room temperature, the porous CoAl-LDH nanoflake arrays exhibited a high specific capacitance of 930F/g at 2A/g and their specific capacitances were still up to 669F/g at 16A/g. A good cycling stability was also observed for the CoAl-LDH nanoflake arrays with a capacitance retention of 88.9% of the highest value after 2000cycles at 2A/g.


      PubDate: 2014-11-10T13:52:23Z
       
  • Fundamental basis of single-point liquid limit measurement approaches
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Stuart K. Haigh , Paul J. Vardanega
      The liquid limit is defined as the point at which a clay's behaviour changes from liquid to plastic. This transition is in reality gradual, rather than sudden. The definition of when this transition has been crossed must therefore be determined based on some arbitrary criterion. The percussion cup method of determining liquid limit in the manner suggested by Atterberg and subsequently standardised by Casagrande determines liquid limit as the water content at which 25 standard blows are required to cause closure of a standard groove. In order to speed up the determination of the liquid limit, a single-point method is defined in ASTM D4318, and in many other codes, to interpret liquid limit from groove closure at a different number of blows by assuming a relationship between water content and the number of blows required for groove closure. These methods differ considerably between different codes of practice currently in use worldwide. This paper examines the procedures for single-point determination of the liquid limit and offers some fundamental explanations that underpin the applicability of these procedures. This paper demonstrates that the variation in single-point liquid limit procedures suggested by various codes of practice can be attributed to the variability of liquid limit devices, rather than to variation in the soils being tested.


      PubDate: 2014-11-10T13:52:23Z
       
  • Stability of lanthanum-saturated montmorillonite under high pressure and
           high temperature conditions
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Vicente Fiorini Stefani , Rommulo Vieira Conceição , Larissa Colombo Carniel , Naira Maria Balzaretti
      Smectite has been used to capture radioactive cations through adsorption in deep radioactive waste repositories in various parts of the world. Smectite is also important in the transport of water and some trace element cations such as rare earth elements (REE), which are captured in its structure, back to the mantle in subduction environments. Such captures are based on the ionic strength of the surrounding solution and the adsorption coefficient of smectite. However, captured cations can be released from the smectite structure once the ionic strength of the solution changes. In this work, the stability of a particular smectite (montmorillonite) structure saturated with lanthanum was verified at high pressures (up to 12GPa) and room temperature and at high pressure and high temperature (HPHT) concomitantly. La3+-montmorillonite remains stable up to 12GPa at room temperature with a small variance in its vibrational mode. At HPHT, however, the structure becomes muscovite-like and rich in La3+. When in contact with a Ca2+-enriched solution, La3+ is partially replaced by Ca2+ in the new phase, returning to its original Ca2+-montmorillonite phase, whereas another part remains La-muscovite-like. These results were confirmed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy.


      PubDate: 2014-11-10T13:52:23Z
       
  • The effect of organoclay addition on the properties of an acrylate based,
           thermally activated shape memory polymer
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Michael J. Barwood , Chris Breen , Francis Clegg , Carol L. Hammond
      Shape Memory Polymers (SMPs) exhibit the intriguing ability to change back from an intermediate, deformed shape back to their original, permanent shape. In this contribution a systematic series of t-butylacrylate-co-poly(ethyleneglycol) dimethacrylate (tBA-co-PEGDMA) polymers have been synthesised and characterised prior to incorporation of organoclay. Increasing the poly(ethyleneglycol) dimethacrylate (PEGDMA) content in increments of 10% increased the storage modulus from 2005 to 2250MPa, reduced the glass transition temperature from +41 to −26°C and reduced the intensity of the associated tan δ peak. The tBA-co-PEGDMA crosslinked networks displayed useful shape memory properties up to PEGDMA contents of 40%. Above this PEGDMA percentage the materials were prone to fracture and too brittle for a realistic assessment of their shape memory capability. The system containing 90% t-butylacrylate (tBA) and 10% PEGDMA was selected as the host matrix to investigate how the incorporation of 1 to 5mass% of a benzyl tallow dimethylammonium-exchanged bentonite (BTDB) influenced the shape memory properties. X-ray diffraction data confirmed that BTDB formed a microcomposite in the selected matrix and exerted no influence on the storage modulus, rubbery modulus, glass transition temperature, Tg , or the shape or intensity of the tan δ peak of the host matrix. Therefore, it was anticipated that the presence of BTDB would have no effect, positive or negative, nor on the shape memory properties of the host matrix. However, it was found that the incorporation of clay, especially at the 1mass% level, significantly accelerated the speed, compared with the clay-free SMP, at which the microcomposite returned to the original, permanent shape. This accelerated return to the permanent shape was also observed when the microcomposite was coated onto a 100μm PET film.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Template-free preparation of mesoporous silica and alumina from natural
           kaolinite and their application in methylene blue adsorption
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): Zhu Shu , Tiantian Li , Jun Zhou , Yun Chen , Dongxue Yu , Yanxin Wang
      A facile top-down strategy of preparing mesoporous materials directly from natural minerals by selective-etching was proposed. Kaolinite (Al2O3·2SiO2·2H2O), a cheap and abundant clay mineral, was chosen and processed into mesoporous materials with well-defined mesopores (2–6nm) and high specific surface areas (170–430m2/g). In the process, kaolinite was activated by heat-treatment, and then etched by an acid or alkali solution according to its chemical and crystalline features. The activated amorphous alumina or silica component was selectively etched by acid or alkali, respectively, and nanopores were generated in-situ as a result. The pore sizes and specific surface areas can be controlled by the calcination and etching conditions. The as-prepared mesoporous silica and alumina materials showed favorable adsorption abilities towards methylene blue with the monolayer adsorption capacity up to 362mg/g. The template-free preparation of mesoporous materials directly from natural clay minerals may help to promote not only the development of clay products but also the wide application of mesoporous materials with encouraging economic and environmental benefits.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Microwave assisted acid treatment of sepiolite: The role of composition
           and “crystallinity”
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): F. Franco , M. Pozo , J.A. Cecilia , M. Benítez-Guerrero , E. Pozo , J.A. Martín Rubí
      Three sepiolites with differences in composition and structural ordering were treated with 0.2N HCl and 0.2N HNO3 solutions assisted with microwave radiation. This treatment caused in the firsts 16min the progressive Mg2+ depletion of the octahedral sheet, the gradual degradation of the sepiolite structure and the formation of an amorphous silica phase which contributes to a noticeable increase of the BET specific surface area. The assistance of microwaves during the acid treatment allows us to get specific surface areas equivalent to those obtained after 48h with conventional heating methods. The influence of mineralogical impurities, “crystallinity” and chemical composition on the reactivity of sepiolite were also studied.


      PubDate: 2014-11-10T13:52:23Z
       
  • Effects of humic acid release from sepiolite on the interfacial and
           rheological properties of alkaline dispersions
    • Abstract: Publication date: December 2014
      Source:Applied Clay Science, Volume 102
      Author(s): B. Benli
      Humic acid (HA) is a major extractable and soluble component of soil organic matter that can play an important role in the stability of environmental colloidal dispersions. This study suggests that HA content of sepiolite is one of the essential reasons for non-Newtonian behaviour of sepiolite dispersions in alkaline media. Releases of HA from sepiolite matrix dramatically changed their rheological properties (thixotropy, apparent viscosity and yield stress), and interestingly, the level of sepiolite surface hydrophobicity. Alkaline environments also increased the release of Mg2+ ions from the sepiolite matrix and, thus, caused to a stable complex formation with HA macromolecules. This colloidal solid phase was directly observed and imaged by atomic force microscopy (AFM) which revealed a spherical shape of complexes between Mg2+ ions and HA in the size range of 18–63±8nm at pH11.5. Alkaline environments also led to significant changes in the surface properties of sepiolite; after HA release, acid/base components of the surface free energy of sepiolite were determined as γ S −/γ S + =1.49 and defined as having a highly hydrophobic character like natural hydrophobic minerals, e.g. talc. The major soil organic matter component, HA, was also found to be responsible for the changes in the sepiolite surface hydrophilicity.
      Graphical abstract image

      PubDate: 2014-11-10T13:52:23Z
       
  • Quantification and comparison of the reaction properties of FEBEX and
           MX-80 clays with saponite: Europium immobilisers under subcritical
           conditions
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): María Villa-Alfageme , Santiago Hurtado , Miguel A. Castro , Said El Mrabet , M. Mar Orta , M. Carolina Pazos , María D. Alba
      The evaluation of the retention mechanisms in FEBEX and MX-80 bentonites, selected as reference materials to construct engineered barriers, carries major implications in the safe storage of immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with Eu(NO3)3 (151Eu and 153Eu, with 52.2% 153Eu) and spiked with radioactive 152Eu for the quantification of the reactions. Results were compared with saponite as the reference smectite. The strong dependence of the reaction parameters with temperature and time was quantified and the reaction velocity was evaluated. The velocity follows these trends: 240days are needed for the total retention of europium for temperatures over 200°C; below 150°C, significantly longer reaction times, on the order of three years, are required to complete the reaction. Clays do not influence velocity rates, but the retention capacity of bentonites remains lower than for saponite. At 300°C, the milliequivalents retained by the three clays are consistently over CEC. The structural analyses reveal not only adsorption of europium but also the presence of Eu(OH)3 precipitation and Eu2SiO3 confirming the existence of a chemical reaction.
      Graphical abstract image

      PubDate: 2014-09-18T03:20:16Z
       
  • High morphological stability and structural transition of halloysite
           (Hunan, China) in heat treatment
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Jing Ouyang , Zheng Zhou , Yi Zhang , Huaming Yang
      Halloysite is one of the nanoscale tubular minerals in nature. This article reports the mineralogical character, dispersion treatment, structural, and morphological stabilities of a 10Å-type halloysite mineral from Hunan, China. X-ray diffraction (XRD), transmission electron microscopy (TEM), particle-size distribution and N2 adsorption–desorption isotherms were adopted to characterize the raw and calcined minerals. Ammonium lauryl sulfate was used as the surfactant to obtain mono-dispersed halloysite nanotubes. The raw mineral is a kind of tubular nanotube with a hollow interior channel, the specific surface area is 56.7m2/g. Alunitization occurred in the impure mineral. Thermal treatment to the mineral induced shrinkage of the c-axis and yielded a 7Å-type structure. The tube wall was transformed to an amorphous structure in the dehydration process at 450°C. Phase segregation occurred to yield amorphous SiO2 and γ-Al2O3 at around 1000°C. The tubular morphology can be maintained even after it is calcined at 1100°C for 6h, and the specific surface area is enlarged slightly to 65.7m2/g. While after being calcined to 1300°C, the mineral will generate mullite and silica, accompanied with collapse of the tubular walls. A schematic diagram is proposed to illustrate the structural transformation procedure. The results provide assurance to the use of halloysite in high temperature circumstances, such as three-way catalysts.


      PubDate: 2014-09-18T03:20:16Z
       
  • The effect of magnesium chloride solution on the engineering properties of
           clay soil with expansive and dispersive characteristics
    • Abstract: Publication date: November 2014
      Source:Applied Clay Science, Volume 101
      Author(s): Murat Turkoz , Hasan Savas , Aykut Acaz , Hasan Tosun
      Because expansive and dispersive soils damage engineering structures, extensive studies on using additives to ameliorate the effects of these soils have been conducted. In this study, the effect of magnesium chloride (MgCl2) solution on the engineering properties of clay soils was evaluated. Previous studies on this subject have shown that MgCl2 is more commonly used as an anti-icing agent on roads than as a soil stabilizer. MgCl2 is also used to control dust and humidity on roads and to reduce the scattering of coarse particles from road surfaces. However, as the use of MgCl2 becomes more common, its potential to improve the geotechnical properties of problematic soils will receive increasing attention. To this end, the variation in the engineering properties of expansive and dispersive clay soil samples as functions of the added MgCl2 content was investigated. First, the physical and chemical properties of the soil sample were determined. Next, the swell percentage, swell pressure, crumb, pinhole and unconsolidated undrained (UU) triaxial compression tests were performed at different curing times on samples with and without the additive by compressing the sample to achieve particular compaction characteristics. Scanning electron microscopy (SEM) analyses were performed to observe the microstructures in the sample without the additive and with the amount of additive that most strongly improved the expansive and dispersive qualities of the clay. The results show that dispersive and expansive clay soils can be effectively improved using an additive MgCl2 solution.


      PubDate: 2014-09-10T02:21:04Z
       
 
 
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