bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrothermal (200°C) synthesis and crystal chemistry of iron-rich kaolinites
Authors: Petit S. , Decarreau A. 
Published: December 2006

Abstract:In order to study Al-Fe substitution, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content. XRD and IR spectroscopy showed that kaolinites with increasing Fe contents could be synthesized, and Mössbauer spectroscopy indicated that the iron is strictly ferric. Chemical analyses (STEM) of kaolinite particles determined up to almost 7% Fe2O3, which probably does not represent a structural limit. The effect of Fe3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe2O3. However, it is not possible to establish a general correlation between Fe content and percentage of structural defects. Acccording to IR spectroscopy, some synthesized Fe-rich kaolinites can have relatively good crystallinity.
Dissolution kinetics of sepiolite from Eskisehir (Turkey) in hydrochloric and nitric acids
Authors: Cetisli H. , Gedikbey T. 
Published: December 2006

AbstractDissolution kinetics of sepiolite from Eskisehir (Turkey) have been investigated at various temperatures and particle sizes using dilute hydrochloric and nitric acids. Dissolution reaction rate constants were calculated and apparent activation energies were dependent on acid concentration. For both acids, apparent activation energy values reached a minimum of ∼11 kcal/mol at an acid concentration of 0·75 M. For the second-order reaction which is independent of the acid concentration, the activation energy was 14·5 kcal/mol for both acids. The reaction rate constants were proportional to the acid concentrations, and inversely proportional to the square-root of the initial particle radii of the sepiolite.
Etude de la repartition de l'eau dans des argiles saturees Mg2+ aux fortes teneurs en eau
Authors: Touret O. , Pons C. H. , Tessier D. , Tardy Y. 
Published: December 2006

AbstractPowdered 2:1 Mg-clay samples were rehydrated up to the maximum hydration. Both scanning and transmission electron microscopy were used to characterize their structural organization i.e. particle arrangement, texture and crystal structure. Low-angle X-ray scattering experiments were carried out to quantify the microstructure of the system. The results showed that sample water contents reached at saturation are not directly related to changes in layer distance. The hydration mechanism is rather correlated to particle size and particle aggregate size. It is also shown that the a, b plane extension of the layers influences particle size and shape. Finally, it appears that for a better understanding of clay swelling mechanisms, at high water contents, it is necessary to take into account all organization levels and that the contribution of interlayer space to the total water content, for Mg-smectites, is small.
An expert system for the structural characterization of kaolinites
Authors: Plançon A. , Zacharie C. 
Published: December 2006

AbstractUntil recently, the determination of the defect structures (previously referred to incorrectly as “crystallinity”) of kaolinites has been obtained in one of two ways: (1) measurement of the Hinckley index, or (2) by comparing calculated X-ray diffraction patterns based on a model of the defect structure (including types of defects and abundances) with experimental diffraction profiles. The Hinckley method is simple and easy to perform but contains no real information about the defect structure. Calculated XRD patterns are based on real defects but these calculations are time consuming and require some skill in application. Another approach is proposed: an expert system which will accurately describe the defect structure of kaolinites based on a few measurements taken from a normal powder diffraction profile. This system has been verified for nine kaolinite samples for which the defect structure was previously determined by comparison of calculated and observed diffraction profiles. The expert system reproduced the correct defect structure for each of the samples.
Electron paramagnetic resonance study of non-exchangeable vanadium(IV) in rectorites
Authors: Goodman B. A. , Nadeau P. H. 
Published: December 2006

AbstractEPR spectroscopy was used to provide evidence for the existence of vanadium(IV) in two samples of rectorite. Possible sites for the vanadium are the tetrahedral and octahedral sites in the 2:1 layers and the non-exchangeable interlayer sites in the paragonite part of the structure. Consideration is given to each of these possibilities but the experimental evidence is insufficient to identify conclusively the location of the vanadium. Since substantial amounts of vanadium(IV) were present in the only well-defined rectorite samples obtainable, it is possible that the formation of rectorite is facilitated by the presence of vanadium.
A Mössbauer study of green rust precipitates: I. Preparations from sulphate solutions
Authors: Cuttler A. H. , Man V. , Cranshaw T. E. , Longworth G. 
Published: December 2006

AbstractThe preparation of green rusts from sulphate solutions and representative Mössbauer spectra are described. As the samples oxidized readily, attention focused on the Mössbauer parameters at liquid nitrogen and helium temperatures. The spectra recorded at 77 K could be fitted satisfactorily with one ferrous iron quadrupole doublet with a separation of 2·93 mms−1 and one ferric iron quadrupole doublet with a separation of 0·45 mms−1. In some spectra a ferric iron magnetic hyperfine of strength 49·2 T was also apparent. At 4·2 K, the ferrous iron exhibited a hyperfine splitting with a field of 12·4 T whilst the ferric iron exhibited a hyperfine splitting with a field of strength 50·4 T. The ratio of ferrous to ferric ions was 2·25 ± 0·25 at 77 K and at 4·2 K, and ∼1·6 with a large variation at room temperature. The liquid helium spectra did not always give a good chi-squared fit, the main reason being attributed to relaxation. The line-width of the ferrous iron site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe3+ neighbours at different Fe2+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe2+ and Fe3+ neighbours probably contributed to the increase in line-widths at 4·2 K compared with those at 77 K. The ferrous iron doublet is marginally different to those of chloride and hydroxy-carbonate green rusts and the aluminium analogues.
Les complexes montmorillonite-Cu(III)-benzène: une contribution
Authors: Walter D. , Saehr D. , Wey R. 
Published: December 2006

RésuméDes montmorillonites cuivriques ont été exposées à des vapeurs de benzène, au cours de cycles de déshydratation, adsorption, désorption de l'excès et réhydratation. La fixation du benzène et sa transformation dans les espaces interfoliaires ont été suivies au moyen d'analyses thermogravimétriques, radiocristallographiques et spectrophotométriques infrarouges. Celles-ci ont permis de mettre en évidence deux réactions, correspondant l'une à l'adsorption d'une molécule de benzène par ion Cu2+, l'autre à trois molécules de benzène. Ce dernier se polymérise dans les espaces interfoliaires avec formation tout d'abord de poly (p-phénylène) puis d'un composé qui pourrait s'apparenter à du graphite.
Berthierine from the non-marine Wealden (Early Cretaceous) sediments of south-east England
Authors: Taylor K. G. 
Published: December 2006

AbstractA thin (15–20 cm) Fe-rich intraformational conglomerate in the fresh- to brackish-water Early Cretaceous succession of south-east England contains pisoids and pseudo-ooids of a green clay mineral which has been identified as berthierine. The pisoids (up to 0·5 cm in size) are concentrically laminated, have complex structure, and are frequently nucleated around a sandstone fragment. They show evidence of weathering due to a change in their environment after formation. The ooids have well to moderately well developed concentric lamination, are very often multi-nucleated and do not always completely cover the nucleus. They suggest formation as a result of mineral precipitation as opposed to agitation and accretion. The climate and environment during the Wealden were suited to the formation of Fe-rich soils and it is likely that the pisoids and ooids were originally composed of iron oxyhydroxide and kaolinite, having formed in soil in the Weald Basin. They were then eroded and deposited in the base of a large scour structure as part of the conglomerate. On burial, and the attainment of low Eh conditions, berthierine formed by diagenetic transformation of the pre-existing minerals.
Impact of clay particle orientation on quantitative clay diffractometry
Authors: Zevin L. , Viaene W. 
Published: December 2006

AbstractPreferred orientation of clay particles in various clay mounts was measured with an X-ray texture diffractometer. Pole distributions are approximately symmetrical about the normal to the sample. Particle orientation is characterized by standard deviations ranging from 7° for thin sedimented layers, to 20° and more for dry-pressed samples, the latter showing less dependence on particle size. The orientation of the reflecting particles may span a considerable angular range affecting the intensities of diffraction peaks observed on contemporary powder diffractometers, even those with moderate axial divergence. A theory based on the diffractometer geometry was developed to calculate the effect of particle orientation. Results are presented as modified Lorentz factors for orientations deduced from experimental observations. In qualitative X-ray diffractometry of clays, preference must be given to preparation techniques which ensure a high degree of preferred orientation and therefore strong enhancement of basal reflections. In quantitative X-ray diffractometry, the main factor is the reproducibility of particle orientation, and suction and dry pressing are promising methods of sample preparation.
The I-S contact in 10 Å-17 Å interstratified clay minerals
Authors: Tettenhorst R. T. , Corbató C. E. , Haller R. I. 
Published: December 2006

AbstractCalculated X-ray diffraction profiles of 10 Å-17 Å interstratified clay minerals, which make allowance for fundamental illite particles, confirm many of the inferences made in a previous analysis by Corbató & Tettenhorst (1987). However, some of these profiles do not appear to match well with patterns obtained from real interstratified clay minerals. The lack of agreement is apparently a consequence of the assumption that the interlayer spacing formed at the contact of I and S (illite and smectite) silicate layers is exclusively 17 Å. The results suggest that this interlayer spacing may be either 10 Å or 17 Å.
Sorption of water vapour by M-montmorillonite (M = Na, Li, La)
Authors: Trillo J. M. , Poyato J. , Tobías M. M. , Castro M. A. 
Published: December 2006

AbstractThe effect of heating on the water sorption capacity of a La-saturated montmorillonite, La-Mt, has been investigated. Sodium and Li as exchangeable ions have also been included for comparative purposes. XPS of La-Mt shows no migration of La(III) from interlamellar positions to octahedral sites on heating at 300°C. The water adsorbed as a multilayer on the external surface of the montmorillonite has been subtracted from the total sorbed water. Although the c-spacing of La-Mt corresponds to a two-layer hydrate, in the relative humidity range from 30 to 70%, the interlamellar water amounts to only 70% of the value for a complete monolayer. Heating at 300°C for 24 h has no influence on the uptake of molecular water between the structural layers of the La-Mt. The average numbers of water molecules per exchangeable ion sorbed into the interlamellar spacing up to 50% r.h. are: 5(Na-Mt), 3(Li-Mt) and 13(La-Mt).
Clay mineral distribution and provenance in Mesozoic and Tertiary mudrocks of the Moray Firth and northern North Sea
Authors: Pearson M. J. 
Published: December 2006

AbstractClay mineral abundances in Mesozoic and Tertiary argillaceous strata from 15 exploration wells in the Inner and Outer Moray Firth, Viking Graben and East Shetland Basins of the northern North Sea have been determined in <0·2 µm fractions of cuttings samples. The clay assemblages of more deeply-buried samples cannot be unambiguously related to sedimentary input because of the diagenetic overprint which may account for much of the chlorite and related interstratified minerals. Other sediments, discussed on a regional basis and related to the geological history of the basins, are interpreted in terms of clay mineral provenance and control by climate, tectonic and volcanic activity. The distribution of illite-smectite can often be related to volcanic activity both in the Forties area during the M. Jurassic, and on the NE Atlantic continental margin during the U. Cretaceous-Early Tertiary which affected the North Sea more widely and left a prominent record in the Viking Graben and East Shetland Basin. Kaolinite associated with lignite-bearing sediments in the Outer Moray Firth Basin was probably derived by alteration of volcanic material in lagoonal or deltaic environments. Some U. Jurassic and L. Cretaceous sediments of the Inner Moray Basin are rich in illite-smectite, the origin of which is not clear.
Expert System for Structural Characterization of Phyllosilicates: II. Application to Mixed-Layer Minerals
Authors: Drits V. A. , Plançon A. 
Published: December 2006

AbstractThe expert system described in the first part of this paper has been applied to the identification of mixed-layer phyllosilicates (mica-smectite, mica-vermiculite, chlorite-smectite, chlorite-vermiculite, chlorite-swelling chlorite, chlorite-mica, chlorite-talc, kaolinite-smectite, talc-smectite), and to the determination of their structural parameters (Reichweite, R, and proportions of constituting layers, Wi). The expert system has been run utilizing the data extracted from (1) experimental XRD patterns for which structural parameters had been evaluated by comparison with calculated patterns, or (2) patterns calculated using pre-selected values of the structural parameters. In all cases examined, the expert system provided correct conclusions concerning the identification of a mixed-layer phyllosilicate and the value of the Reichweite, while the abundances of the component layers were evaluated with a margin of error usually <5%.
Saponite, Corrensite and Chlorite-Saponite Mixed-Layers in the Sancerre-Couy Deep Drill-Hole (France)
Authors: Beaufort D. , Meunier A. 
Published: December 2006

AbstractThe clay deposits in fractures of the metamorphic basement under the Paris Basin sedimentary formations at Sancerre-Couy (France) are composed of trioctahedral species which are exceptionally well crystallized. Three samples were chosen in order to study the chemical composition of 100% expandable saponite, 50% expandable corrensite and 10% expandable chlorite-saponite mixed-layer mineral C90–S10 Two sets of microchemical analyses were performed in order to determine the variations of the composition on large and small numbers of particles. X-ray diffraction (XRD) and Mössbauer spectrometry were performed on purified samples.The mathematical decomposition of Si, Al and Mg histograms established from microanalyses of a large number of crystals of saponite, corrensite and C90–S10 evidences bimodal populations. The total Fe content of the three species is unimodal whatever the chemical composition of the surrounding rock and the Fe2+/Fe3+ ratio. The structural formulae established from a large number of microanalyses of a few particles show that there are no parental relationships between saponite, corrensite and C90–S10. The expandable layer of corrensite is characterized by a high charge. It is proposed that the tetrahedral sheets adjacent to the brucitic sheet and the exchangeable interlayer in a 2 : 1 unit are identical in corrensite.
The Formation of Green Rust and Its Transformation to Lepidocrocite
Authors: Schwertmann U. , Fechter H. 
Published: December 2006

AbstractThe formation of FeII,III hydoxy salts (green rusts) from FeII sulphate and chloride solutions and their transformation to lepidocrocite, γ-FeOOH, was studied at ambient temperature, constant pH of ∼7.0 and under controlled air flow. The formation of green rust and its subsequent transformation to lepidocrocite could be distinguished by the reaction rate and solution chemistry. The SO42− and Cl− concentrations in solution attain a minimum at the break between the two reaction steps and are completely restored to their initial values after complete transformation to lepidocrocite. While the green rust is being formed, its FeII/FeIII ratio shows a minor decrease and its FeIII/anion ratio a minor increase. These ratios, however, deviate from the ideal pyroaurite-type structure (M2+/M3+ = 3; M3+/A− = 1; M: metal; A−: anion) and possibilities to accommodate this deviation are discussed. A period during which no protons were produced (i.e. no base consumed) was found to separate the two reactions in the chloride, but not in the sulphate system. During this period a partial solid state oxidation of the green rust took place, leading to its destabilization and eventual decomposition.
Diagenetic Development of Clay and Related Minerals in Deep Water Sandstones (S. Spain): Evidence of Lithological Control
Authors: Ruiz Cruz M. D. 
Published: December 2006

AbstractThe turbiditic facies of the Aquitanian-Oligocene of the Algeciras and Bolonia Units consist of lutitic-marly beds alternating with varied sandstones. Early diagenetic processes and the development of secondary porosity in sandstones were controlled largely by sedimentary facies. Mineral dissolution processes were important in rocks with high primary porosity (quartzose sandstones) and led to the development of allophane and kaolinite/dickite in later diagenetic stages. In rocks with high contents of biotitic matrix, chlorites and iron oxides were produced, together with the development of secondary porosity. In feldspathic sandstones, the early diagenetic processes produced chlorite, illite, illite-smectite mixed-layers and smaller amounts of kaolinite. In calcareous sandstones, the presence of an early cement prevented, to a certain extent, the dissolution of unstable fragments and restricted the development of clay minerals. The movement of fluids was not important during this early diagenetic stage in controlling the variety or abundance of mineral cements; the controlling factors were the different chemical conditions developed in the pore-solution of the various sandstone types. In spite of similar sandstone burial conditions, the different sandstone lithologies continued to determine the diagenetic processes, especially the degrees of compaction and dissolution. Certain burial processes are common to all levels: the development of reducing conditions is indicated by the development of Fe and Mn carbonates, Fe-dolomites and Fe-chlorites. A later alkaline diagenetic phase was responsible for the development of calcite, feldspar and illite. The circulation of fluids in these stages remained limited, although there was probably some movement from the lutitic-level fluids to the overlying sandstones.
Spectroscopic Study of the Adsorption of Rhodamine 6G on Laponite B for Low Loadings
Authors: Tapia Estévez M. J. , López Arbeloa F. , López Arbeloa T. , López Arbeloa I. , Schoonheydt R. A. 
Published: December 2006

AbstractThe adsorption of Rhodamine 6G in aqueous suspension on Laponite B was investigated by electronic absorption and emission spectroscopies. Fluorescence spectra suggest that the monomer is adsorbed at two different surfaces, the external and the internal. A monomer is intercalated in the interlamellar space at low loading of dye (<3% CEC), whereas the monomeric state of the dye seems to be at the solid-aqueous interface in suspensions with high loading (>12% CEC). The metachromatic effect observed in the absorption spectra, for the loading interval between 1% and 15% CEC of Laponite B, is attributed to the dimerization of the dye, which seems, from X-ray diffraction measurements, to be formed at the clay interlayer. The formation constant and the absorption spectrum of the aggregate were obtained and the dimer was structurally characterized by applying the Exciton Theory. The observed fluorescence quenching for loadings lower than 15% CEC is attributed to energy transfer from monomer to the dimer, which obeys the Perrin model.
Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite
Authors: Arcoya A. , González J. A. , Travieso N. , Seoane X. L. 
Published: December 2006

AbstractSamples of natural clinoptilolite modified by treatment with NH4Cl or HCl solutions, followed by thermal treatments, have been characterized, and their catalytic activity evaluated, in o-xylene isomerization and ethanol dehydration reactions. The substitution of the compensating cations by NH4+ does not produce structural changes in the original material, but it opens the channels and increases its acidity and thermal stability. The treatment with HCl increases both the acidity and the effective diameter of the channels and pores but it produces an important loss of zeolite phase. Calcination of the acidic forms above 973 K leads to the breakdown of the zeolite structure. Catalytic activity of the samples is related to the surface acidity. For the original and NH4Cl-treated samples, however, the conversion of o-xylene is limited by the access of the reactant inside the channels of the zeolite. A comparative study with modified sepiolite in dehydration of ethanol has also been performed.
The Progression from Optical Light Microscopy to Transmission Electron Microscopy in the Study of Soils
Authors: Van Oort F. , Jongmans A. G. , Jaunet A. M. 
Published: December 2006

AbstractThe use of electron microscopy to study clay microfabrics in thin-sections is discussed. A technique is described to isolate undisturbed microparts of pedofeatures from thin-sections, which are subsequently used for TEM analysis. Re-embedding with a polyester resin of undisturbed, in situ, neoformed clay microfabrics, obtained by microdrilling and preparation of ultrathin sections by microtoming with a diamond knife are emphasized; these steps enable micromorphology, clay mineralogy, microchemical and HRTEM analysis to be performed on one unique microsample of clay fabrics, with conserved micro-organization. Two examples on clay neoformation are presented to demonstrate that this technique can successfully be applied to unravel the impact of mineral alteration and clay neoformation in undisturbed soil samples on a micro- and a nanometer scale.
Aluminium coordination and structural disorder in halloysite and kaolinite by 27Al NMR spectroscopy
Authors: Newman R.H. , Childs C.W. , Churchman G.J. 
Published: December 2006

AbstractIt has been suggested that interlayer water in halloysite is due to the presence of hydrated cations that balance the negative layer charge produced by Al for Si substitution. To find evidence of 4-coordinate Al (Al(IV)), we investigated six halloysites and two kaolinites using ‘high-field’ and ‘medium-field’ solid-state 27Al MAS NMR spectroscopy. We found Al(IV) in both kaolinite and five halloysite samples, but the contents are all <1% and provide no basis for distinguishing between kaolinite and halloysite. Therefore, the presence of interlayer water in halloysite cannot be attributed to Al for Si substitution. There are, however, signals, tentatively assigned to A1(V), present in the kaolinite spectra but not in the halloysite spectra. The shapes of the low-frequency ‘tails’ of Al(VI) signals in medium-field NMR vary from sample to sample. We interpret this variation in terms of a ‘crystallinity index’. Disorder in kaolinite appears to be primarily the result of Al-vacancy displacements in the octahedral sheet. The NMR crystallinity indices correlate with those from IRS and DTA but not with those from XRD.