Articles de revues : « Allophagy »

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Al Rawi, Sara, Sophie Louvet-Vallée, Abderazak Djeddi, Martin Sachse, Emmanuel Culetto, Connie Hajjar, Lynn Boyd, Renaud Legouis et Vincent Galy. « Allophagy ». Autophagy 8, n^o 3 (19 mars 2012) : 421–23. http://dx.doi.org/10.4161/auto.19242.

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Simamora, Jupri, Purba Marpaung et Alida Lubis. « DETERMINATION TYPE OF ALLOPHANE ON ANDISOL IN DOLAT RAKYAT VILLAGE TIGA PANAH DISTRICT, REGENCY OF KARO ». Jurnal Pertanian Tropik 2, n^o 3 (1 décembre 2015) : 228–38. http://dx.doi.org/10.32734/jpt.v2i3.2916.

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The aim of the research was to determinate the type of Allophane minerals by means of Thermogram and to know the type of Allophane minerals with Allophane–Organic Matter relations. The research was done in Dolat Rakyat villages, District of Tiga Panah Karo Regency, In Soil Fertility Laboratory University of North Sumatera, and College of Chemical Industry (PTKI), Medan in June - October 2014. Soil type is Andisol. The result of the research in Dolat Rakyat Village Tiga Panah District, Regency of Karo Thermogram interpretation showed that type of Allophane minerals Andisol that is Allophane B. Allophane-Organic Matter relations showed that type of Allophane minerals is Allophane B with positive relations between Allophane-Humic Acid; negative relations between Allophane-Fulvic Acid, and Allophane-Humic Acid+Fulvic Acid.

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Airlangga, Tandaditya Ariefandra, Naoto Matsue, Eko Hanudin et Erni Johan. « Phosphate Adsorption Capacity of Allophane from Two Volcanic Mountains in Indonesia ». JOURNAL OF TROPICAL SOILS 25, n^o 1 (2 janvier 2020) : 39. http://dx.doi.org/10.5400/jts.2020.v25i1.39-46.

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Allophane is known as clay mineral with high capacity of phosphate adsorption via ligand-exchange mechanism. This study aims to compare the phosphate adsorption characteristics by allophane from Mt. Merapi and Mt. Lawu in relation to its chemical and mineralogical properties. The results of X-Ray Flourescence analysis shows that both allophane samples from Merapi and Lawu have low Si/Al ratio, i.e. 1.18 and 1.16, respectively. Infrared spectral characteristics of the allophane materials indicated that the main adsorption bands appeared at the range of 2700-3700 cm-1 (due to stretching vibration of all hydroxyl (OH) groups), 1400 – 1800 cm-1 (vibration of HOH deformation), and 650 - 1200 cm-1 (vibration between the Si-O-Al). Adsorption experiment of phosphate on allophane samples were conducted at initial adsorbate concentration of up to 2.0 mM and at pH 4.0 and 8.0. Phosphate adsorption capacity of allophane shows that both allophane from Merapi and Lawu are categorized as very high in adsorbing phosphate and fit well with the Langmuir adsorption equation. Phosphate adsorption increases with decreasing pH due to the positive charge sites such as Al-OH2+ in the allophane structure increase. Another reason is the negative charge of phosphate gradually decreases from -2 to -1 with decreasing pH, and the repulsive force between the negatively charged Si-O- in the allophane structure and phosphate anions decreases.

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Singleton, PL, M. Mcleod et HJ Percival. « Allophane and halloysite content and soil solution silicon in soils from rhyolitic volcanic material, New Zealand ». Soil Research 27, n^o 1 (1989) : 67. http://dx.doi.org/10.1071/sr9890067.

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The relationship between Si in soil solution and allophane and halloysite content was studied by using a drainage sequence of three New Zealand soils from rhyolitic volcanic alluvium. Clay mineralogy was compared with soil colour and drainage. Allophane and halloysite contents of two morphologically similar soils from rhyolitic volcanic ash were also studied and possible reasons for differences in mineralogy were determined. Allophane was estimated by acid oxalate and pyrophosphate dissolution. The Al/Si ratio of the allophane was determined and the allophane content of the soil was estimated from the Si extracted in acid-oxalate. Halloysite was estimated by differential thermal analysis of the whole soil. Soil samples were centrifuged with a dense water-immiscible organic liquid to displace the soil solution from between soil particles. The Si in soil solution was then determined by spectrophotometry. Allophane was predominant when Si in soil solution was <10gm-3, and halloysite was predominant when Si in soil solution was >10gm-3. Low Si in soil solution and the presence of allophane was associated with well drained horizons which could be identified by their ochreous colour. High Si in soil solution, the absence of allophane and predominance of halloysite, was associated with poorly drained horizons. These horizons could be identified by their pale colour (chroma <2). In two morphologically similar soils, the change from allophane dominance in one soil to hahoysite dominance in the other soil also corresponded to an increase in Si in soil solution. This was probably the result of slightly slower horizon permeability which increased Si in soil solution to a level favouring halloysite formation.

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Rois, Ibnu, Pranoto Pranoto et Sunarto Sunarto. « APLIKASI ALOFAN DALAM TANAH ANDISOL SEBAGAI ADSORBEN UNTUK MENURUNKAN BAKTERI Coliform LIMBAH CAIR DOMESTIK ». EnviroScienteae 14, n^o 2 (15 octobre 2018) : 99. http://dx.doi.org/10.20527/es.v14i2.5475.

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Research on allophane has been done as an adsorbent to decrease MPN Coliform in domestic wastewater. The purpose of this study was to look for natural adsorbent materials that can be used to decrease MPN Coliform. Natural allophane was identified from andisol soil by pH analysis of NaF, FTIR, XRD, and SAA. The result of the analysis showed that there was allophane on andisol soil with pH 11,73. The diameter of empty space or alloy pores of 5 nm with a hole/pore size of 0.5 nm. Testing of MPN Coliform is done by method of Most Probable Number (MPN) variety 5: 5: 5. Based on the result of the research, allophane adsorbent can decrease MPN Coliform by 60.9%.

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He, N., T. L. Barr et J. Klinowski. « ESCA and solid-state NMR studies of allophane ». Clay Minerals 30, n^o 3 (septembre 1995) : 201–9. http://dx.doi.org/10.1180/claymin.1995.030.3.04.

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AbstractThe surface/near-surface chemistry of allophane has been studied by X-ray photoelectron spectroscopy (ESCA) and the bulk material by 27A1 and 29Si solid-state NMR and other techniques. The surface/near-surface Si/Al ratio of allophane is c.1.0, similar to that for kaolinite, zeolite Na-A and sodalite. The core level binding energies for kaolinite and allophane are almost identical, but quite different from those for zeolite Na-A and sodalite, both framework aluminosilicates. The nature and size of these differences is consistent with the differences between the chemistry of sheet and framework silicates. The small variations in the Si(2p) spectra for kaolinite and allophane are discussed in terms of bonding of the tetrahedral units in the two materials.

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Hashizume, H., et B. K. G. Theng. « Adsorption of DL-alanine by allophane : effect of pH and unit particle aggregation ». Clay Minerals 34, n^o 2 (juin 1999) : 233–38. http://dx.doi.org/10.1180/000985599546190.

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AbstractThe adsorption of DL-alanine at pH 4, 6 and 8 by a soil allophane has been determined. Two sets of experiments were carried out: (1) in which the allophane had been kept in a moist state throughout; and (2) in which the mineral had previously been dried at 50°C. In both instances, the adsorption isotherms showed three distinct regions as the concentration of alanine in solution was increased: (1) an initial, nearly linear, rise at low equilibrium concentrations; (2) a levelling off to a plateau at intermediate concentrations; and (3) a steep linear increase at high concentrations. For comparable concentrations of alanine in solution, adsorption decreased in the order pH 6 > pH 8 > pH 4. Irrespective of pH, however, more alanine was adsorbed by the ‘wet’ allophane than by its ‘dry’ counterpart. These observations are interpreted in terms of the morphology and aggregation of allophane unit particles together with the pH-dependent charge characteristics of allophane and alanine. The results are compared with published data on the adsorption of alanine by montmorillonite.

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Cichota, R., I. Vogeler, N. S. Bolan et B. E. Clothier. « Cation influence on sulfate leaching in allophanic soils ». Soil Research 45, n^o 1 (2007) : 49. http://dx.doi.org/10.1071/sr06070.

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We have examined the influence of the ionic composition of the soil solution on the movement of sulfate and calcium in 2 New Zealand soils with differing allophane content. For this study, we have carried out a series of miscible displacement experiments using repacked and intact soil columns, in which sulfate was applied in the presence of either calcium or potassium as the accompanying cation. Our results showed that sulfate leaching was significantly retarded in the soil with higher allophane content when applied with calcium. On the other hand, no effects were observed for all studied soils when potassium was used as the accompanying cation. In addition, in soils with high allophane content, calcium also had its retention increased when sulfate was present. The increase in sulfate adsorption was accompanied by corresponding increase in calcium adsorption. These findings evidenced the presence of co-adsorption, or ion-pair adsorption (IPA), in allophane-containing soils. The extent of this adsorption is dependent on the soil pH, the accompanying cation, and the allophane content of the soil.

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Silva-Yumi, Jorge, Roberto Cazorla Martínez, Carlos Medina Serrano et Gabriela Chango Lescano. « Allophane, a natural nanoparticle present in andisols of equatorial Ecuador, properties and applications ». Characterization and Application of Nanomaterials 5, n^o 1 (17 avril 2022) : 89. http://dx.doi.org/10.24294/can.v5i1.1689.

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Allophane is a natural nanoparticle present in soils of volcanic origin such as andisols, which are distributed around the world in countries with volcanic activity. In Ecuador, andisols constitute 30% of the territory in high and humid areas of the northern highlands. Allophane can be obtained from andisols through physical and chemical processes, or it can be synthesized. This nanomaterial has multiple properties for various applications in different areas. There is a lot of research on these nanoparticles and this type of soils, but they have not been studied yet in Ecuador. In this article, the structural characteristics, properties, formation, isolation, synthesis and uses of allophane are presented, with the ﬁnish of generating knowledge and encouraging research on these soils that are the source of the aforementioned nanoparticle. The literature search was performed in Science Direct and Google Scholar databases, and high impact articles related to natural or synthetic allophane research were used. The particular characteristics that allophane has allows it to be used as an environmental remediator, bactericide, anti-inﬂammatory, flame retardant, enzyme support, but in addition it has been studied in catalysis, photocatalysis and electrocatalysis. Considering the area covered by allophane in the Ecuadorian territory and its availability, it can be used for research based on international studies that have been developed to take advantage of it in the environmental and medical areas.

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Hojamberdiev, Mirabbos, Yuki Makinose, Kenichi Katsumata, Toshihiro Isobe, Nobuhiro Matsushita et Kiyoshi Okada. « Hydrothermal Synthesis and Visible-Light-Driven Photocatalytic Activity of Allophane – Wakefieldite-(Ce) Composite ». Advanced Materials Research 896 (février 2014) : 545–48. http://dx.doi.org/10.4028/www.scientific.net/amr.896.545.

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In this study, highly adsorptive mechanically-mixed and as-synthesized allophane–wakefieldite-(Ce) composites were prepared by mechanical mixing and hydrothermal synthesis, respectively. The results from X-ray diffraction and Raman spectroscopy analyses show that the mechanically-mixed composite has higher crystallinity than the as-synthesized composite. The nanoparticles of wakefieldite-(Ce) were homogenously distributed with allophane in the as-synthesized composite. The specific surface areas of the mechanically-mixed and as-synthesized composites are 164 m2/g and 191 m2/g, respectively. The photocatalytic activity of the samples was evaluated for the degradation of acetaldehyde (AcH) gas under visible light. Both composites demonstrated higher photocatalytic activity than individual wakefieldite-(Ce) and allophane because allophane in the composites played an important role in the adsorption of acetaldehyde gas molecules and the mediation between the gas phase and the wakefieldite-(Ce) surface.

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Parfitt, R. L. « Allophane and imogolite : role in soil biogeochemical processes ». Clay Minerals 44, n^o 1 (mars 2009) : 135–55. http://dx.doi.org/10.1180/claymin.2009.044.1.135.

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AbstractThe literature on the formation, structure and properties of allophane and imogolite is reviewed, with particular emphasis on the seminal contributions by Colin Farmer. Allophane and imogolite occur not only in volcanic-ash soils but also in other environments. The conditions required for the precipitation of allophane and imogolite are discussed. These include pH, availability of Al and Si, rainfall, leaching regime, and reactions with organic matter. Because of their excellent water storage and physical properties, allophanic soils can accumulate large amounts of biomass. In areas of high rainfall, these soils often occur under rain forest, and the soil organic matter derived from the forest biomass is stabilized by allophane and aluminium ions. Thus the turnover of soil organicmatter in allophanicsoils is slower than that in non-allophanicsoils. The organic matter appears to be derived from the microbial by-products of the plant material rather than from the plant material itself. The growth of young forests may be limited by nitrogen supply but growth of older forests tends to be P limited. Phosphorus is recycled through both inorganic and organic pathways, but it is also strongly sorbed by Al compounds including allophane. When crops are grown in allophanic soils, large amounts of labile P are required and, accordingly, these soils have to be managed to counteract the large P sorption capacity of allophane and other Al compounds, and to ensure an adequate supply of labile P. Because of their physical and chemical properties, allophanic soils are excellent filters of heavy metals and pathogens.

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Calabi Floody, M., B. K. G. Theng, P. Reyes et M. L. Mora. « Natural nanoclays : applications and future trends – a Chilean perspective ». Clay Minerals 44, n^o 2 (juin 2009) : 161–76. http://dx.doi.org/10.1180/claymin.2009.044.2.161.

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AbstractBecause of their large potential for agricultural, industrial and medicinal applications, nanomaterials have been the focus of much research during the past few decades. Nanoclays are natural nanomaterials that occur in the clay fraction of soil, among which montmorillonite and allophane are the most important species. Montmorillonite is a crystalline hydrous phyllosilicate (layer silicate). Organically-modified montmorillonites or ‘organoclays’, formed by intercalation of quaternary ammonium cations, have long been used as rheological modifiers and additives in paints, inks, greases and cosmetics and as carriers and delivery systems for the controlled release of drugs. Perhaps the largest single usage of organoclays over recent years has been in the manufacture of polymer-clay nanocomposites. These organic–inorganic hybrid materials show superior mechanical, thermal and gas-barrier properties. Organoclays are also useful in pollution control and water treatment. Allophane is a non-crystalline aluminosilicate derived from the weathering of volcanic ash. A large proportion of the agricultural land in Chile is covered by volcanic soils,the clay fraction of which is dominated by allophane. Consisting of nanosize (3.5–5.0 nm) hollow spherules, allophane is a suitable support material for enzyme immobilization. Allophane is also effective at adsorbing phenolic compounds and colour from kraft mill effluents and phosphate from water and wastewater.

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Nakayama, Chieko, et Yoshinori Tanaka. « Adsorption of nitrate as a groundwater pollutant by soil particles ». Journal of Nepal Geological Society 34 (9 octobre 2006) : 141–46. http://dx.doi.org/10.3126/jngs.v34i0.31890.

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This study discusses nitrogen adsorption in several soil samples of the Kanto loam collected from two locations in the Kanto plain. Their chemical properties were assessed on each of the soil samples as well as on pure allophane clay by instrumental analysis using batch and soil column tests. Nitrogen-nitrate adsorption by soil samples was determined by a 10-hour batch test using a nitric acid solution of 0.14 mmol. A saturation column test was conducted to obtain a breakthrough curve and calculate the coefficients of dispersion and retardation. The extent of nitrate adsorption in soil samples was confirmed by percolation with 0.14 mmol nitric acid through columns packed with the soil sample and silicate sand. In the batch test, it was found that the amount of nitrate adsorption was greater in allophane-rich volcanic ash soils with the amount of nitrate adsorption increasing under conditions of low pH. The breakthrough curve determined by the column test showed that the coefficient of retardation increased in allophane-rich soils. Adsorption of nitrates by Kanto loam soils was thus found to be dependent upon the content of allophane and amorphous material in the soil. Since the positive charge of allophane has the potential to reduce the nitrate content in groundwater, it can be effectively applied to reduce nitrate contamination in groundwater.

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Parfitt, RL. « Allophane in New Zealand - a review ». Soil Research 28, n^o 3 (1990) : 343. http://dx.doi.org/10.1071/sr9900343.

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Studies of allophanes from New Zealand are reviewed, and a definition of the allophane group of minerals is suggested. Three types of allophane are identified, and their structures are discussed under headings Al-rich soil allophanes, Si-rich soil allophanes and stream deposit allophanes. Examples from New Zealand soils and tephras are discussed in relation to properties, identification and weathering processes.

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Childs, C. W., K. Inoue, H. Seyama, M. Soma, B. K. G. Theng et G. Yuan. « X-ray photoelectron spectroscopic characterization of Silica Springs allophane ». Clay Minerals 32, n^o 4 (décembre 1997) : 565–72. http://dx.doi.org/10.1180/claymin.1997.032.4.07.

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AbstractA range of allophane samples (atomic AI/Si bulk ratios 1.1-1.9) from Silica Springs, New Zealand, has been characterized by X-ray photoelectron spectroscopy (XPS). Binding energies of Si 2s, Si 2p, Al 2p, O 1s, C 1s, and N 1s electrons, together with the kinetic energies of Al KL23L23 Auger electrons, at or near the surface of allophane aggregates, have been derived. The values for Al, Si and O electrons are similar to those for kaolinite but also to those for some framework silicates (feldspars) having 4-coordinate Al. Values for N electrons suggest that N occurs in organic structures. Comparison of XPS and bulk Al/Si ratios shows an enrichment of Al at or near the surface of allophane aggregates. The same is true for C and N. Extraction with citrate-dithionite-bicarbonate (CDB) reagent leaves the surfaces depleted in Al. The CDB extracts have higher Al/Si ratios than the bulk allophanes. Similarly, CDB treatment reduces the degree of surface enrichment of C and N. Small increases in the binding energies of Si electrons following CDB treatment suggest partial dissolution of the bulk structure though a concomitant removal of a separate phase or species cannot be ruled out. The results may be accounted for in terms of the structure previously suggested for the primary spherules of Silica Springs allophane (Childs et al., 1990) though the composition of the spherules at or near the surface of the allophane aggregates is different from those of the bulk.

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Ohashi, F., S. I. Wada, M. Suzuki, M. Maeda et S. Tomura. « Synthetic allophane from highconcentration solutions : nanoengineering of the porous solid ». Clay Minerals 37, n^o 3 (septembre 2002) : 451–56. http://dx.doi.org/10.1180/0009855023730052.

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AbstractThe amorphous aluminosilicate allophane was synthesized by rapid mixing of inorganic solutions with high initial concentrations (10 – 100 mmol/l) followed by hydrothermal treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed homogeneous products having a hollow spherical amorphous structure with a particle diameter of 3 – 5 nm. The amorphous products had a high BET specific surface area (490 – 552 m2/g) in comparison with natural allophane and had a narrow pore-size distribution (2 – 5 nm in diameter). The results of water vapour adsorption isotherm studies showed a gradual increase over the range of relative water vapour pressure of 0.6 – 0.9 and reached a maximum of ∼85 wt.%. The synthetic allophane shows promise as an adsorbent material because of its high adsorption-desorption capacity and its unique structure.

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Calderon, Edward H. Jiménez, Marco Rosero et Magdalena Diaz. « Use of Allophane as Face Mask Filter for Coronaviruses (Sars-Cov-2) ». Key Engineering Materials 878 (mars 2021) : 62–72. http://dx.doi.org/10.4028/www.scientific.net/kem.878.62.

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The traditional mouth cover masks can be made by hand. But with the arrival of the Coronavirus pandemic, these masks have special requirements and we will have to use these until at least 2022. Therefore, the current technological problem is what must be the appropriate filter nanomaterial (cuprum, zinc, zeolite or Allophane) to absorb and/or destroy coronaviruses. In addition, the preparation of this specific purpose mask must be certified, easy to manufacture and inexpensive. Taking these requirements into account, there is a suitable nanomaterial called Allophane, which has active centers of silicon and aluminum (Si / Al), which rapidly absorb micro droplets and nanodrops of water [3, 5] nm. Coronaviruses are microscopically embedded in water droplets. To build an absorbent filter that also destroys coronaviruses, we can use some organic surfactant in optimal proportions and that works cooperatively with Allophane. The physicochemical properties of natural Allophane were studied. For the characterization, analytical techniques were used: Fourier transform infrared spectroscopy (FTIR), BET surface area, X-ray diffraction (XRD), Chemisorption and Atomic Force Microscopy (AFM). In addition, the Navier Stokes 3D equations were studied, which allow us studying molecular dynamics contributing substantively to chemical kinetics describing the process of absorption of water and decomposition of water + coronavirus.

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Taylor, T. S., J. C. Hughes et L. W. Titshall. « Mineralogy of volcanically derived alluvial soils at Moshi, Tanzania ». Soil Research 54, n^o 8 (2016) : 926. http://dx.doi.org/10.1071/sr15252.

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Despite intensive commercial agriculture in the rift zone of Tanzania, mineralogical studies on the soils influenced by volcanic parent materials are scarce. A mineralogical investigation of the soils and two buried ash layers from an irrigated sugar estate was undertaken using X-ray diffraction, transmission electron microscopy and measurements of extractable iron, aluminium and silicon and the specific surface area (SSA) of the clay fraction. The dominant mineral in the sand and silt fractions was sanidine. The clay fractions contained mainly high-defect kaolin, illite and K-feldspar, with small amounts of calcite, talc and gibbsite in some samples. Electron microscopy revealed the presence of tubular and spheroidal halloysite and <0.5µm kaolinite crystals, as well as nanocrystalline material, probably allophane, and volcanic glass. The amounts of ferrihydrite (0.34–1.84%) and allophane (0.52–6.84%) were low in the soils but higher in the buried ash layers. The surface areas of the clay fractions were high (up to 145m2g–1) and it was calculated that 5% allophane constituted 22% of the total SSA. Although all soils were dominated by halloysite and small kaolinite particles, it is likely that the small amounts of allophane with high SSA has a strong effect on their physical and chemical properties.

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Perez del Villar, L., M. C. Moro et M. L. Cembranos. « Allophane in weathered zones of barite ore deposits (Vide de Alba and San Blas, Zamora, Spain) : mineralogy and genesis ». Clay Minerals 27, n^o 3 (septembre 1992) : 309–23. http://dx.doi.org/10.1180/claymin.1992.027.3.04.

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AbstractThe allophane studied occurs in the weathered zones of the barite-sulphide-bearing dolomitic levels, interbedded in the barite ore deposits of Vide de Alba and San Bias (Province of Zamora). These ore deposits are interstratified in the Silurian-Devonian sulphide bearing volcano sedimentary materials of the Alcañices Synform. The allophanic samples have been studied by polarizing microscopy, SEM, XRD, DTA, TG, IRS, EMA and chemical analyses, the last after dissolving the samples by acid (HF + HNO3 + 3HCl + H3BO3) and alkaline digestion (0·5 m NaOH). It is suggested that allophane originates from the reaction of acid solutions released during the weathering of sulphides with acid volcanoclastic rocks. Silica-alumina gels were deposited in holes formed during earlier dissolution of the dolomite associated with the barite ores. Later processes of desilication partially transform allophane to gibbsite.

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Moro, M. C., M. L. Cembranos et A. Fernandez. « Allophane-like materials in the weathered zones of Silurian phosphate-rich veins from Santa Creu d'Olorda (Barcelona, Spain) ». Clay Minerals 35, n^o 2 (avril 2000) : 411–21. http://dx.doi.org/10.1180/000985500546873.

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AbstractAllophane-like materials occur in the weathered zones of the phosphate-rich veins hosted in Silurian metasediments of the Catalonian Coastal Ranges. These metasediments also host sulphide and phosphate sedimentary mineralizations. Mineralogical and geochemical investigations of the allophanic samples indicate that they comprise Si-rich allophane, with a molar SiO2/Al2O3 ratio ranging between 1.19 and 2.23, with amorphous Al-(Ca) phosphate and hydroxylapatite as major minerals, and minor goethite and quartz. It is assumed that allophane, amorphous Al-(Ca) phosphate and hydroxylapatite come from the reaction of acid solutions, released during the weathering of sulphide interbedded in black shales, with phosphate-rich veins and volcano- sedimentary host rocks. Silica-alumina gels were deposited in fissures and cavities left by a previous dissolution of the phosphate-rich veins. Later the phosphate minerals filled the conchoidal microfractures and shrinkage microcracks of the allophane.

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Jiménez Calderón, Edward Henry, Ana Emperatriz Paucar Tipantuña, Paulina Fernanda Herrera Mullo, Daniel Alejandro Hidalgo Cháfuel, Washington Ruiz, Ullrich Stahl et José Bermudez. « Natural and Activated Allophane Catalytic Activity Based on the Microactivity Test in Astm Norm 3907/D3907M-2019 ». Applied Sciences 10, n^o 9 (27 avril 2020) : 3035. http://dx.doi.org/10.3390/app10093035.

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The optimal conditions of the catalytic activation of allophane were evaluated for possible use as a catalyst within a fluidized bed catalytic cracking unit (FCC). The physicochemical properties of natural allophane and activated allophane were studied by using an alkaline activating agent, followed by a hydrothermal treatment. For the characterization, analytical techniques were used: Fourier transform infrared spectroscopy, particle size, (BET) surface area, thermogravimetry (TGA), X-ray diffraction (XRD), chemisorption, X-ray fluorescence (XRF), atomic force microscopy (AFM), and chromatography. The catalytic evaluation was determined by the (MAT) micro activity test equipment constructed according to ASTM D-3907/D3907M-2019. In addition, the Navier–Stokes 3D equations (nonlinear partial derivatives) were studied, which allow studying molecular dynamics contributing substantively to chemical kinetics describing the process of decomposition of crude oil in thermal cracking, determining the maximum temperature at which it retains its properties through the action of heat.

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Cardinale, Anna Maria, Cristina Carbone, Marco Fortunato, Bruno Fabiano et Andrea Pietro Reverberi. « ZnAl-SO4 Layered Double Hydroxide and Allophane for Cr(VI), Cu(II) and Fe(III) Adsorption in Wastewater : Structure Comparison and Synergistic Effects ». Materials 15, n^o 19 (4 octobre 2022) : 6887. http://dx.doi.org/10.3390/ma15196887.

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Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO4 LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO4 LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.

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Wilson, M. A., S. A. McCarthy et P. M. Fredericks. « Structure of poorly-ordered aluminosilicates ». Clay Minerals 21, n^o 5 (décembre 1986) : 879–97. http://dx.doi.org/10.1180/claymin.1986.021.5.03.

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AbstractThe structure of synthetic aluminosilicates prepared at pH 6 has been investigated by 29Si and 27Al high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Fourier transform infrared (FTIR) spectroscopy and electron microscopy have also been used to characterize the products. The amount of Si and Al in protoimogolite, disordered allophane and other structures has been measured. There is a fair correlation between the intensity of the 349 cm−1 band in the FTIR spectra and the proportion by weight of protoimogolite Si measured by NMR. It is shown that disordered allophanes have similar structures to those proposed by van Reeuwijk and de Villiers (Soil Sci. Soc. Am. Proc. 32 (1968) 238–240), i.e. octahedral Al surrounding a tetrahedral core. Moreover, it is clear that at high Al:Si ratios (⩾1:1), protoimogolite can compete with disordered allophane precursors for aluminum. The driving forces for formation of protoimogolite rather than allophane appear to be long range Al-Al repulsive forces through oxygen.

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Schwertmann, U., J. Friedl, H. Stanjek et D. G. Schulze. « The effect of clay minerals on the formation of goethite and hematite from ferrihydrite after 16 years’ ageing at 25°C and pH 4 – 7 ». Clay Minerals 35, n^o 4 (septembre 2000) : 613–23. http://dx.doi.org/10.1180/000985500547034.

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AbstractIn soils and other weathering environments, hematite and goethite are usually formed in the presence of clay minerals. Two-line ferrihydrite was aged in the presence of six different clay minerals in aqueous suspension at 25°C and pH 4, 5, 6 and 7 for 16 years. The transformation into hematite/goethite mixtures was complete in the systems with gibbsite, kaolinite, illite and smectite, but incomplete in those with soil smectite and allophane. Soil smectite and allophane, as well as increasing pH, favoured hematite over goethite. The grainy and multi-domainic hematite crystals in the allophane system contained Si and Al (EDX) and showed a Si – O vibration at ∼920 cm– 1 (FTIR). The unit-cell contraction due to structural Al was counteracted by structural OH, which was removed at 200°C. Heating also increased the magnetic hyperfine field at RT by 1.2 – 1.6 T. Hematite crystals with irregular shape and grainy interior have also been observed in soils.

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Nishikiori, Hiromasa, Shingo Matsunaga, Naoyuki Furuichi, Hitoshi Takayama, Koji Morita, Katsuya Teshima et Hiromi Yamashita. « Influence of allophane distribution on photocatalytic activity of allophane–titania composite films ». Applied Clay Science 146 (septembre 2017) : 43–49. http://dx.doi.org/10.1016/j.clay.2017.05.026.

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Pranoto, Pranoto, Tri Martini et Deta Agustin Rachmawati. « Karakterisasi dan Uji Efektivitas Allophane-Like untuk Adsorpsi Ion Logam Tembaga (Cu) ». ALCHEMY Jurnal Penelitian Kimia 14, n^o 2 (3 septembre 2018) : 202. http://dx.doi.org/10.20961/alchemy.14.2.18538.202-218.

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Telah dilakukan penelitian karakterisasi dan uji efektivitas allophane-like untuk adsorpsi ion logam tembaga (Cu). Allophane-like dibuat dengan mencampurkan larutan Tetraethyl Orthosilicate (TEOS) dan Aluminum Nitrate Nonahydrate [Al(NO3)3.9H2O] dengan perbandingan 0,5; 0,75; 1; 1,25 dan 1,5. Proses pencampuran dilakukan penambahan NaOH secara bertahap dan dilakukan pengadukan serta pemanasan. Penambahan NaOH dilakukan dengan membuat perbandingan NaOH dan Campuran TEOS dan Al(NO3)3.9H2O 3:1. pH campuran larutan yang diperoleh diukur dan pH larutan dibuat menjadi asam (pH 3-4). Allophane-like dikarakterisasi dengan spektroskopi infra merah (FTIR), XRD, keasaman, dan luas permukaan. Uji adsorpsi terhadap ion logam tembaga (Cu) dilakukan pada variasi perbandingan TEOS dan Al(NO3)3.9H2O 0,5; 0,75; 1; 1,25 dan 1,5, pH larutan tembaga (Cu) 3-7 serta waktu kontak 30-120 menit dengan sistem batch. Hasil penelitian diketahui bahwa allophane-like memiliki gugus fungsi yang sama dengan allophane-alam yang ditunjukkan dengan data FTIR yaitu memiliki puncak yang sama pada 3431-3252; 1631; 1071; 785; dan 562-457 cm-1. Hasil analisa XRD, keasaman dan luas permukaan menunjukkan karakteristik yang berbeda. Kondisi adsorpsi ion logam tembaga (Cu) terjadi pada variasi perbandingan TEOS dan Al(NO3)3.9H2O 1,5, pH 6, waktu kontak 120 menit, persentase penyerapan 41,79% dan kapasitas adsorpsi 0,97865 mg/g.Characterization and Effectivity of Allophane-Like in the Adsorption of Metal Ion of Copper (Cu). The characterization and effectivity testing of allophane-like for adsorption copper (Cu) metal ion has been studied. Allophane-like was prepared by mixing a solution of Tetraethylorthosilicate (TEOS) and Aluminum Nitrate nonahydrate [Al(NO3)3.9H2O] using ratio of 0.5; 0.75; 1; 1.25 and 1.5. The mixing process was done gradually adding NaOH and stirring and heating. The addition of NaOH was done by making a comparison between NaOH and mixture of TEOS dan Al(NO3)3.9H2O in 3:1. The pH of the mixture solution was measured and made acidic solution (pH 3-4). Allophane-like was characterized by infrared spectroscopy (FTIR), XRD, acidity, and surface area. The adsorption evaluation of copper (Cu) metal ion was done on the variation of the composition of TEOS dan Al(NO3)3.9H2O in 0.5; 0.75; 1; 1.25 and 1.5, the pH of a solution of copper (Cu) 3-7 and contact time of 30-120 minutes in batch system. The results revealed that the allophane-like has the same functional group with nature allophane indicated by the FTIR data that has the same peak at 3431-3252; 1631; 1071; 785; and 562-457 cm-1. XRD analysis results, acidity and surface area showed different characteristics. The best conditions adsorption of copper (Cu) metal ion occured at the composition of TEOS dan Al(NO3)3.9H2O in 1.5, pH 6, the contact time of 120 minutes, the absorption percentage of 41.79% and adsorption capacity of 0.97865 mg/g.

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Oh, Young-Mi, Paul V. Nelson et Dean L. Hesterberg. « 256 Evaluation of Phosphate Desorption Characteristics of Clay Minerals for Soilless Root Media ». HortScience 34, n^o 3 (juin 1999) : 486C—486. http://dx.doi.org/10.21273/hortsci.34.3.486c.

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Soilless root media retain very little phosphate. This characteristic necessitates continual application of phosphate, which leads to excessive application and leaching. The phosphate desorption characteristics of synthetic hematite (a-Fe2O3), goethite (a-FeOOH), allophane (Si3Al4O12*nH2O), and a commercial alumina (Al2O3), previously determined for their maximum adsorption capacities, were evaluated to determine their potential for providing a low, constant soil solution phosphate supply with low phosphate leaching from soilless root media. The desorption isotherms of the clay minerals were obtained by introducing 10 mM KCl solution at 0.2 ml/min flow rate into a stirred flow reaction chamber loaded with clay adsorbed with phosphate at maximum adsorption capacity. The suspension in the reaction chamber was held at pH 6.4 during desorption. Effluent solutions were collected for phosphorus analysis until the equilibrium concentration of phosphorus in solution reached 0.05 mg•L-1. Adsorbed phosphorus at 0.05 mg•L-1 equilibrium concentration in solution was in the order allophane (19 mg•g-1) > alumina™ goethite (8 mg•g-1) > hematite (1.3 mg•g-1). The equilibrium concentration of phosphorus in solution over time showed that allophane releases phosphate for a longer time than the other clay minerals at a desirable soil solution concentration for plants, less than 5 mg•L-1. Among the clay minerals tested, allophane showed the most favorable potential to supply phosphate to plants in soilless root media.

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Cipta, Indra, Nur A. Limatahu, N. A. St Hayatun, Indriana Kartini et Yateman Arryanto. « Effect of Allophane from Gamalama Volcanic Soil on Properties of BiOI-Allophane Composite ». Asian Journal of Chemistry 29, n^o 5 (2017) : 1042–44. http://dx.doi.org/10.14233/ajchem.2017.20402.

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Limatahu, Nur A., Indra Cipta, St Hayatun Nur Abu, Indriana Kartini et Yateman Arryanto. « Adsorption and Photodegradation of Methylene Blue by Allophane and Nanocomposite Bismuth Oxyiodide-Allophane ». Asian Journal of Chemistry 30, n^o 1 (2017) : 207–9. http://dx.doi.org/10.14233/ajchem.2018.20990.

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Hodder, A. P. W., B. E. Green et D. J. Lowe. « A two-stage model for the formation of clay minerals from tephra-derived volcanic glass ». Clay Minerals 25, n^o 3 (septembre 1990) : 313–27. http://dx.doi.org/10.1180/claymin.1990.025.3.07.

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AbstractThe kinetics of clay formation in buried paleosols developed from late Quaternary rhyolitic tephra layers near Rotorua, New Zealand, can be described in terms of a combination of parabolic and linear kinetics, reflecting the hydration of glass, and the formation of clay minerals, respectively. Such a model is consistent with the formation of clay minerals showing an Arrhenian temperature dependence and suggests, on the basis of calculated activation energies, that the process of formation of Al-rich allophane (imogolite) is diffusion controlled, whereas the rate of formation of Si-rich allophane is controlled by the chemical processes at the site of reaction.

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Courchesne, F., J. F. Laberge et A. Dufresne. « Influence of soil organic matter on sulfate retention in two Podzols in Quebec, Canada ». Canadian Journal of Soil Science 79, n^o 1 (1 février 1999) : 103–9. http://dx.doi.org/10.4141/s98-024.

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The role of soil organic matter (OM) on SO4 retention was investigated by comparing OM content, SO4 retention, and the distribution of Fe, Al and Si compounds in OM-poor (Grands-Jardins, PGJ) and OM-rich (Hermine, HER) Podzols from Québec, Canada. At both sites, four pedons were sampled by horizon; soil pH in H2O, organic C, phosphate-extractable SO4 and, sodium pyrophosphate, acid ammonium oxalate and dithionite-citrate-bicarbonate (DCB) extractable Fe, Al and Si were measured for each mineral horizon. The mineralogy of the clay (<2 µm) and fine silt (2–20 µm) fractions of selected horizons was determined by X-ray diffraction (XRD) and infrared spectroscopy (IR). Weighted mean organic C and pyrophosphate extractable Fe and Al contents were significantly higher in the HER than in the PGJ sola, while the PGJ soils were richer in amorphous inorganic Al. No trends were observed for inorganic Fe compounds. Chemical dissolution and IR allowed the identification of short-range ordered aluminosilicates, probably allophane, in the OM-poor and slightly acidic to neutral PGJ soils. These materials were absent from the OM-rich and acidic HER soils. Phosphate extractions showed that the weighted mean native SO4 content was five times higher in the PGJ than in the HER soil. Finally, native SO4 was strongly related to inorganic Fe, Al and Si (associated with allophane) at PGJ but only to inorganic Fe at HER. These results indicate that OM indirectly affects SO4 sorption through the influence organic substances exerts on the nature and distribution of pedogenic Fe, Al and Si compounds, such as allophane, in Podzolic profiles. Key words: Organic matter, sulfate, imogolite, allophane, silica, Podzol

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Fauziah, Lilia, Eko Hanudin et Sri Nuryani Hidayah Utami. « Competitive adsorption of phosphate with sulfate, humic acid, and fulvic acid by allophane in different parent materials in Central Java ». Ilmu Pertanian (Agricultural Science) 7, n^o 2 (24 août 2022) : 121. http://dx.doi.org/10.22146/ipas.72050.

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Andisol is a soil that has andic properties and develops from volcanic parent materials, especially ash. Andic soil properties are formed due to weathering of tephra or other parent materials that contain volcanic glass in large quantities. The main components of soil-forming Andisol are amorphous (short-range-order) minerals, such as allophane, imogolite, ferrihydrite, and Al/Fe-humus complexes. The existence of short-range-order minerals causes Andisol to have high P-tapping ability, but efforts to lower the amount of P plunged with organic and inorganic an-ons have not been widely studied. This study aimed to compare the ability of humic acid, fulvic acid, and sulfate in suppressing P adsorption by amorphous minerals from the Andisol of Mount Dieng, Merbabu, and Sumbing. The highest calculation of % ferrihydrite was found at the location of Mount Merbabu with a value of 3.05%, while the % allophane + imogolite was determined by the content of Sio in the ground. The calculation results showed that the highest was found at the location of Mount Sumbing with a value of 7.17%. Based on TEM analysis, Mount Sumbing has allophane diameter of 2.24 – 5.93 nm and the imogolite length of 24 – 187 nm.

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Ding, Yang, Yang Lu, Peng Liao, Shimeng Peng, Yuzhen Liang, Zhang Lin, Zhi Dang et Zhenqing Shi. « Molecular fractionation and sub-nanoscale distribution of dissolved organic matter on allophane ». Environmental Science : Nano 6, n^o 7 (2019) : 2037–48. http://dx.doi.org/10.1039/c9en00335e.

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Wesley, L. D. « Consolidation behaviour of allophane clays ». Géotechnique 51, n^o 10 (décembre 2001) : 901–4. http://dx.doi.org/10.1680/geot.2001.51.10.901.

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Childs, Cyril W. « Five-Coordinate Aluminum in Allophane ». Clays and Clay Minerals 47, n^o 1 (1999) : 64–69. http://dx.doi.org/10.1346/ccmn.1999.0470107.

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Dinkin, Aaron J., et Robin Dodsworth. « Gradience, allophony, and chain shifts ». Language Variation and Change 29, n^o 1 (mars 2017) : 101–27. http://dx.doi.org/10.1017/s0954394517000035.

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ABSTRACTThe monophthongization of /ay/ in the Southern United States is disfavored by following voiceless consonants (price) relative to voiced or word-final environments (prize). If monophthongization is the trigger for the Southern Shift (Labov, 2010) and chain shifts operate as predicted by a modular feedforward phonological theory (cf. Bermúdez-Otero, 2007), this implies price and prize must be two ends of a phonetic continuum, rather than two discrete allophones. We test this hypothesis via distributional analysis of offglide targets and statistical analysis of the effect of vowel duration. As predicted, we find price and prize share a continuous distribution in the Inland South, the region where the Southern Shift probably originated (Labov, Ash, & Boberg, 2006). We use Raleigh, North Carolina, outside the Inland South, as a comparison point; there, the same methodologies indicate price and prize are more discretely separated. Our results thus offer empirical support for the phonological theory that motivated the hypothesis.

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Kaufhold, Stephan, Kristian Ufer, Annette Kaufhold, Joseph W. Stucki, Alexandre S. Anastácio, Reinhold Jahn et Reiner Dohrmann. « Quantification of allophane from Ecuador ». Clays and Clay Minerals 58, n^o 5 (1 octobre 2010) : 707–16. http://dx.doi.org/10.1346/ccmn.2010.0580509.

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Hashizume, H., B. K. G. Theng et A. Yamagishi. « Adsorption and discrimination of alanine and alanyl-alanine enantiomers by allophane ». Clay Minerals 37, n^o 3 (septembre 2002) : 551–57. http://dx.doi.org/10.1180/0009855023730051.

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AbstractWe have investigated the adsorption of D- and L-alanine, and their respective dimers, by three allophanes with different Al/Si ratios. The Kanuma (Al/Si = 1.2) and Kitakami (Al/ Si = 1.5) allophanes were from Japan whereas the Te Kuiti (Al/Si = 1.6) sample came from New Zealand. The three allophanes differed in their capacity for adsorbing alanine but none of the samples showed a clear preference for either the D- or the L-form. In the case of alanyl-alanine both Kanuma and Kitakami allophanes gave a hint of preferring the L- to the D-enantiomer. On the other hand, the allophane sample from Te Kuiti showed a clear preference for L-alanyl-L-alanine. In keeping with this observation, circular dichroic spectrometry indicated that solutions of a racemic mixture of alanyl-alanine, after equilibration with Te Kuiti allophane, became relatively enriched in the Denantiomer. The size, intra-molecular charge separation, and surface orientation, of L-alanyl-Lalanine zwitterions apparently combine to confer ‘structural chirality’ to the complex (adduct) with Te Kuiti allophane. As a result, the mineral-organic complex develops a preference for the L-form of alanyl-alanine. This finding points to a possible role of certain allophanes in the origin of biochirality.

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Iwata, S., F. Izumi et A. Tsukamoto. « Differential heat of water adsorption for montmorillonite, kaolinite and allophane ». Clay Minerals 24, n^o 3 (septembre 1989) : 505–12. http://dx.doi.org/10.1180/claymin.1989.024.3.04.

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AbstractDifferential heat of water vapour adsorption for Cs+-saturated montmorillonite, kaolinite and allophane was measured over a low relative humidity range from 10−4 to 10−1. Two interactions (clay surface atom-water and counterion-water) are mainly involved in the water vapour adsorption process. To assess the affinity of water to the clay surface, the amounts of adsorbed water and the differential heat due to Cs+ were estimated from equilibrium constants in the gas phase reactions. It is tentatively concluded that (i) a dominant role of water adsorption due to the Cs+-water interaction in the adsorption process is evident only for montmorillonite; (ii) the affinity of water to the clay surface is strongest for allophane and weakest for montmorillonite.

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Jeong-Im Han. « Allophony and Contrast in Speech Perception ». Korean Journal of Linguistics 34, n^o 1 (mars 2009) : 155–79. http://dx.doi.org/10.18855/lisoko.2009.34.1.008.

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Su, Chunming, et Donald L. Suarez. « Boron Sorption and Release by Allophane ». Soil Science Society of America Journal 61, n^o 1 (janvier 1997) : 69–77. http://dx.doi.org/10.2136/sssaj1997.03615995006100010012x.

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Hagiwara, Mamoru, et Hajime Takenaka. « Shrinkage and Structure of Allophane Soil ». Soils and Foundations 25, n^o 2 (juin 1985) : 1–13. http://dx.doi.org/10.3208/sandf1972.25.2_1.

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Childs, C. W., R. L. Parfitt et R. H. Newman. « Structural studies of Silica Springs allophane ». Clay Minerals 25, n^o 3 (septembre 1990) : 329–41. http://dx.doi.org/10.1180/claymin.1990.025.3.08.

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AbstractThe structure of Silica Springs allophane from New Zealand has been studied by high-resolution 27A1 and 29Si NMR spectroscopy, IR spectroscopy and electron microscopy. Experimental NMR conditions were chosen to give a quantitative relationship between signal strength and Al content. Aluminium is present in both octahedral (Alvi) and tetrahedral (Aliv) coordination, and the ratio Alvi:Aliv was obtained for three samples with different total Al:Si ratios. In all cases the Aliv:Si ratio was 1 : 3, consistent with the ratio in ideal muscovite. The negative charge arising from Aliv was apparently balanced by positive charge at adjacent Alvi sites. Both NMR and IR spectra indicate that Si exists in a condensed network, probably a sheet, with Si atoms linked (through oxygen) to one, two and, possibly, three other Si atoms, but not four. The spectra are consistent with a mixture of Si-O-Si, Si-O-Al, and Si-OH linkages. A structure based on fragments of single curved 1 : 1 aluminosilicate layers, with the tetrahedral sheet on the outer surfaces, is suggested, the diameter of curvature being 2–3 nm. The tetrahedral sheet is more or less complete and has a Aliv : Si ratio of 1 : 3; the octahedral Alvi sheet is incomplete. Electron micrographs suggest that, at least in some cases, the fragments form more or less complete spherules. This proposal seems to accord with Farmer's concept of “aluminous hydrous feldspathoids”. The minimum pH at which Silica Springs allophane has precipitated corresponds to the initial presence of tetrahedrally coordinated Al species in solution.

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Scarpace, Daniel, David Beery et José Ignacio Hualde. « Allophony of /ʝ/ in Peninsular Spanish ». Phonetica 72, n^o 2-3 (2015) : 76–97. http://dx.doi.org/10.1159/000381067.

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Montarges-Pelletier, Emmanuelle, Sandrine Bogenez, Manuel Pelletier, Angelina Razafitianamaharavo, Jaafar Ghanbaja, Bruno Lartiges et Laurent Michot. « Synthetic allophane-like particles : textural properties ». Colloids and Surfaces A : Physicochemical and Engineering Aspects 255, n^o 1-3 (mars 2005) : 1–10. http://dx.doi.org/10.1016/j.colsurfa.2004.11.036.

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NISHIKIORI, H., J. SHINDOH, N. TAKAHASHI, T. TAKAGI, N. TANAKA et T. FUJII. « Adsorption of benzene derivatives on allophane ». Applied Clay Science 43, n^o 2 (février 2009) : 160–63. http://dx.doi.org/10.1016/j.clay.2008.07.024.

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Nishikiori, Hiromasa, Masaaki Ito, Rudi Agus Setiawan, Ayaka Kikuchi, Tomohiko Yamakami et Tsuneo Fujii. « Photofuel Cells Using Allophane–Titania Nanocomposites ». Chemistry Letters 41, n^o 7 (5 juillet 2012) : 725–27. http://dx.doi.org/10.1246/cl.2012.725.

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Yariv, S., L. Heller-Kallai et Y. Deutsch. « Adsorption of stearic acid by allophane ». Chemical Geology 68, n^o 3-4 (mai 1988) : 199–206. http://dx.doi.org/10.1016/0009-2541(88)90020-4.

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de Roy, G., I. Verhaert et E. F. Vansant. « Allophane and halloysite minerals. Structural considerations ». Recueil des Travaux Chimiques des Pays-Bas 100, n^o 3 (2 septembre 2010) : 102–6. http://dx.doi.org/10.1002/recl.19811000306.

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DAZA, R., et M. A. BUSTILLO. « Allophanic and ferric root-associated stalactites : biomineralization induced by microbial activity (Galeria da Queimada lava tube, Terceira, Azores) ». Geological Magazine 152, n^o 3 (29 septembre 2014) : 504–20. http://dx.doi.org/10.1017/s0016756814000491.

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AbstractRoot-associated stalactites (rootsicles) in Galeria da Queimada lava tube have a mineralogical composition and developmental association with microbes that render them unique. Samples were examined by X-ray diffraction, micro-Raman spectrometry and scanning electron microscopy/X-ray energy-dispersive spectroscopy. Three types of rootsicle were defined: incipient; hard (white and red); and black spongy. The incipient rootsicles still contained rotten organic material and showed the beginning of mineralization by allophane. The white hard and black spongy types were also composed of allophane, while the red hard type was composed of hydrous ferric oxi-hydroxide minerals (HFO). The allophane and HFO in the andisol covering the cave roof precipitated out of the dripwater running along the roots to form the studied rootsicles. All three types of rootsicle showed black layers, coatings, spots or patches composed of manganese oxide minerals and, occasionally, hisingerite (iron (III) phyllosilicate). An alternation of organic precipitation caused by filamentous bacteria and inorganic precipitation (the latter facilitated by pH changes in the dripwater and the cave's temperature) built up both the porous and compact rings observed in the white and red hard rootsicles. The largely straight filaments seen in the porous rings of the white hard rootsicles may be indicative of the previous presence ofLeptothrixspp., while the helical morphologies seen in the red hard rootsicles may be indicative of that ofGallionellaspp. The manganese oxide minerals detected probably formed via microbial activity. This study reflects the important role of filamentous bacteria in rootsicle formation, independent of their mineralogy.

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