bluuebunny/crossref_metadata_2025_split huggingface dataset:
Clay-modified electrodes prepared by the Langmuir-Blodgett method
Authors: Hotta Y. , Taniguchi M. , Inukai K. , Yamagishi A. 
Published: December 2006

AbstractAn ion-exchange adduct of saponite with tetra-n-decylammonium cation ((n-decyl)4N+) was prepared and dispersed in chloroform. The material was spread on a water surface to form a thin film at the air-water interface. From the measurements of surface pressure vs. area, it was concluded that the film consisted of the very thin layer which was a mixture of single and double layers of saponite adduct. A clay-modified electrode was prepared by depositing the film on a glassy carbon substrate using the Langmuir-Blodgett method. When the electrode was soaked in an aqueous solution of [Fe(phen)3](ClO4)2 (phen = 1,10-phenanthroline), (n-decyl)4N+ cations were replaced by [Fe(phen)3]2+ ions from solution. This process was followed by measuring the cyclic voltammogram.
Spectroscopic study of the adsorption of rhodamine 6G on clay minerals in aqueous suspensions
Authors: Lopez Arbeloa F. , Tapia Estevez M. J. , Lopez Arbeloa T. , Lopez Arbeloa I. 
Published: December 2006

AbstractAbsorption and fluorescence spectroscopies were applied to study the adsorption of rhodamine 6G on several smectite-type clays in aqueous suspension. The dye can be adsorbed as the monomeric and the dimeric forms on both the external and the interlamellar surfaces of the clay. The presence of these species and their evolution with the stirring time of the sample and the relative dye/clay concentration depend on the nature of the smectite, the clay concentration and the particle size, factors that also affect the dispersion degree of the clay particles in water.
Nature of dioctahedral micas in Spanish red soils
Authors: Martin-Garcia J. M. , Delgado G. , Sanchez-Maranon M. , Parraga J. F. , Delgado R. 
Published: December 2006

AbstractStructural formulae and other crystallochemical parameters were used to study different species of dioctahedral micas in clay and coarse gravel fractions of horizons from a red soil (Ultic Haploxeralf) in southern Spain. Mineralogical analyses using X-ray powder diffraction, and measurements of theb0parameter revealed dioctahedral micas, illite and paragonite. Structural formulae established from electron microprobe analysis and energy dispersive X-ray analysis showed the illites to be K mica related in elemental composition and structure to muscovite and phengite. The paragonites were found to be closer to ideal mica. Structural formulae for Na-K dioctahedral micas were obtained with crystallochemical characteristics intermediate between those of Na micas and K micas. The possibilty of these micas representing individual mineral phases or intergrowths of Na and K micas is discussed. In the soil profile, micas from the Bt horizon showed the largest crystallochemical changes induced by pedogenesis.
Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies
Authors: Drits V. A. , Dainyak L. G. , Muller F. , Besson G. , Manceau A. 
Published: December 2006

AbstractCeladonite, glauconite and Fe-illite samples were studied by XRD, EXAFS, IR and Mössbauer spectroscopy. The samples were monomineralic and corresponded to 1M polytype. In the OH-stretching region of the IR spectra the content of each definite pair of cations bonded to OH groups was determined. The number of heavy (Fe) and light (Al, Mg) octahedral cations nearest to Fe was found by the EXAFS technique. The predicted quadrupole splitting values for each definite arrangement of cations nearest to Fe3+ were used to interpret the Mössbauer spectra. After the fitting procedure, the intensity of each doublet corresponded to a definite set of local cation arrangements around Fe3+ and to a definite occurrence probability of these arrangements. Computer simulation and the experimental data obtained were used to reconstruct the distribution of isomorphous octahedral cations in the 2:1 layers. For all samples, R2+ cations prefer to occupy one of the two symmetrically independent cis-sites and R2+-R2+ and/or Al-Fe3+ were prohibited in the directions forming ± 120° with the b axis. Therefore, octahedral sheets of the samples revealed domain structure, in which domains differ in size, in the nature of predominant cation and/or by cation ordering.
Chlorite crystallinity as an indicator of metamorphic grade of low-temperature meta-igneous rocks: a case study from the Bükk Mountains, Northeast Hungary
Authors: Árkai P. , Sadek Ghabrial D. 
Published: December 2006

AbstractX-ray diffraction chlorite crystallinity (ChC) indices and major element chemical compositions of chlorites and bulk rocks were determined and correlated in meta-igneous rocks from different Mesozoic formations in various tectonic units of the Bükk Mountains, NE Hungary. The rocks, of basic to acidic compositions, range from ocean-floor metamorphic prehnite-pumpellyite facies (diagenetic zone) through regional metamorphic prehnite-pumpellyite facies (anchizone) up to the regional metamorphic pumpellyite-actinolite and greenschist facies (epizone). As in the case of meta-sedimentary rocks, chlorite crystallinity can be applied as an empirical, complementary petrogenetic tool to determine relative differences in grades of low-temperature meta-igneous rocks. Electron microprobe and XRD data show that ChC is controlled mainly by the decreasing amounts of contaminants (mixed-layered components or discrete, intergrown phases of mostly smectitic composition) in chlorite with advancing metamorphic grade, up to the epizone. The apparent increase in calculated Alivcontent of chlorite with increasing temperature is related to the decrease of these contaminants, as stated earlier by Jianget al.(1994). On the basis of the significant correlations found between ChC and temperatures, derived by the chlorite-Alivgeothermometer of Cathelineau (1988), both methods may be used for estimating the approximate temperatures of metamorphism, in spite of the contrasting interpretation of chemical data from chlorites obtained by electron microprobe analyses. After determining the effects of changing bulk chemistry on chlorite composition and ChC, the chlorite crystallinity method may complement the correlation of the illite crystallinity-based zonal classification of meta-sediments and the mineral facies classification of meta-igneous rocks.
An occurrence of stevensite and kerolite in the Devonian Crousa gabbro at Dean Quarry, The Lizard, Cornwall, England
Authors: Elton N. J. , Hooper J. J. , Holyer V. A. D. 
Published: December 2006

AbstractStevensite has been found at Dean Quarry, The Lizard, Cornwall, associated intimately with the disordered, hydrated variety of talc known as kerolite. Both minerals occur as pseudomorphs after pectolite and as microcrystalline anhedral masses filling cavities and veins in gabbro. Associated minerals include calcite and prehnite. The XRD data show that stevensite occurs as a physical mixture with kerolite, rather than as mixed-layer stevensite-kerolite. Kerolite is unaffected by glycerol treatment whilst stevensite readily expands: this test provides the only reliable distinction between the two minerals. Differences in IR and chemical data for stevensite and kerolite are subtle; data are broadly similar to those in the literature. Both minerals are readily decomposed to amorphous silica by hot concentrated HCl. Stevensite dehydroxylated at 400°C for 1.5 h is virtually indistinguishable from kerolite. The Dean Quarry occurrence is similar to many others worldwide. Stevensite and kerolite formed after prehnite, calcite, analcime, pectolite and natrolite during a phase of decomposition and alteration of these earlier minerals. ‘Stevensite’ from the first British occurrence in the Whin Sill, North Tyne, has been re-examined and appears to be kerolite or ‘hydrated-talc’.
A square planar [NiCl4]2− ion in the layered double hydroxide Al2Li(OH)6 [NiCl4]1/2
Authors: Okada K. , Matsushita F. , Hayashi S. 
Published: December 2006

AbstractThe layered double hydroxide (LDH) Al2Li(OH)6[NiCl4]1/2 was synthesized by anion exchange of Al2Li(OH)6(NO3) and the coordination structure of [NiCl4]2− in the interlayers was investigated. The LDH had a hexagonal cell with a = 5.06 and c = 23.06 Å. Since the basal spacing of one layer was 7.7 Å, the interlayer distance was calculated to be 2.9 Å and was too narrow for the usual tetrahedral NiCl4 structure. From extended X-ray absorption fine structure (EXAFS) measurements, the first neighbour Ni-Cl distances in the LDH were 2.10 Å which was compatible with four-fold coordination. Since the electron spin resonance (ESR) spectrum of the LDH showed no absorption, the [NiCl4]2− structure was considered to be square planar, rather than the usual tetrahedral structure in the interlayers of LDH.
Sequential structure transformation of illite-smectite-vermiculite during diagenesis of Upper Jurassic shales from the North Sea and Denmark
Authors: Drits V. A. , Sakharov B. A. , Lindgreen H. , Salyn A. 
Published: December 2006

AbstractFor mixed-layer clay fractions from the North Sea and Denmark, X-ray diffractograms have been recorded for specimens saturated with Mg, Ca, Na and NH4, both airdry and intercalated with ethylene glycol, and the patterns have been computer-simulated with a multicomponent program. The mixed-layer fractions consist of an illite-smectite-vermiculite (I-S-V) phase constituting ~90% of the fraction and a kaolinite-illite-vermiculite (K-I-V) phase. For each I-S-V, the degree of swelling in swelling interlayers depends on both interlayer cation and glycolation, whereas the amount of non-swelling illite and swelling interlayers and the interstratification parameters are constant. Based on structural characteristics and the degree of diagenetic transformation, the samples investigated can be divided into three groups. The I-S-V of group one is predominantly detrital and has 0.69-0.73 illite, 0.26-0.20 smectite and 0.04-0.07 vermiculite interlayers, the illite, smectite and vermiculite interlayers being segregated. The I-S-V of group two has been diagenetically transformed and has 0.80 illite, 0.12 smectite and 0.08 vermiculite interlayers, the vermiculite interlayers being segregated whereas the illite and smectite have the maximum ordering possible for R = 1. The I-S-V of group three has been further transformed during diagenesis and has 0.84 illite, 0.08 smectite and 0.08 vermiculite interlayers. Statistical calculations demonstrate that the I-S-V transformation can be described as a single interlayer transformation (SIT) within the crystallites.
A rectorite-pyrophyllite-chlorite-illite assemblage in pelitic rocks from Colombia
Authors: Brattli B. 
Published: December 2006

AbstractIn samples of slate from the Fomeque Formation near Bogota, Colombia, pyrophyllite was found to occur together with mixed-layered illite-smectite, chlorite and illite. Other minerals were quartz, K-feldspar, dolomite and pyrite. X-ray diffraction patterns revealed that the mixed-layer represents an R1 ordered rectorite with 80–90% illite layers. The microfabric is developed as a closely spaced cleavage in the phyllosilicate-rich rocks, and grades into a fracture cleavage with coarsening of the grain size. No cleavage was observed in the interbedded siltstones. It is suggested that the microfrabrics developed in these rocks correspond to high diagenetic to anchizonal conditions. The illite crystallinity from the slate has been measured on glycolated samples and ranges from 0.47 to 0.55°Δ2θ with a mean of 0.52°Δ2θ Based on the stability of R1 ordered rectorite, the illite crystallinity and the microfabric development, it is proposed that the rocks have been subjected to a temperature of ∼200°C at low pressure. At this temperature, pyrophyllite can only be stabilized at the expense of kaolinite and quartz if aH2O ≪ 1.
Iron oxides and hydroxides in the weathering interface betweenStereocaulon vesuvianumand volcanic rock
Authors: Adamo P. , Colombo C. , Violante P. 
Published: December 2006

AbstractThe nature and composition of the Fe minerals in the rusty ferruginous material frequently located in the zone of contact between the thallus ofStereocaulon vesuvianumand the leucite bearing rock of Mt. Vesuvius have been studied by microscopic and submicroscopic investigations (SEM, TEM with EDXRA) complemented by X-ray diffraction and chemical analysis. Ferrihydrite is likely to be the main component of the short-range order iron oxyhydroxide pool, although the possibility that significant feroxyhite may be present cannot be completely excluded. Hematite and goethite are the crystalline iron oxides. The organic acids produced by lichens play a key role in the enrichment of poorly-ordered phases at the rock-lichen interface. It is suggested that the peculiar morphology of theStereocaulon vesuvianumthallus and the irregularity of the volcanic rock surface lead to different microsites in the rock-lichen interfaces which have their own conditions of pH, humidity and redox potential, favourable for the neoformation of crystalline phases.
A new, efficient, one-step method for the removal of organic matter from clay-containing sediments
Authors: Meier L. P. , Menegatti A. P. 
Published: December 2006

AbstractFor the purpose of clay examination, a new one-step method for the removal of organic matter was developed using sodium peroxodisulphate combined with different buffers such as sodium hydrogen carbonate, disodium hydrogen phosphate and disodium tetraborate. From an early Cretaceous black shale from the Apennines with a high organic carbon content, the <2 µm clay fraction was separated and contained 10.9 wt% organic carbon. To prevent decomposition of the clay layers, the period of oxidation was short (25-60 min) and the pH was kept between 5 and 9.5. Up to 98% of carbon was removed by this method.
Formation of cubic phases on heating ferrihydrite
Authors: Campbell A. S. , Schwertmann U. , Campbell P. A. 
Published: December 2006

AbstractHeating experiments were carried out with ferrihydrite, in the presence of organics, to gain more insight into the intermediate formation of a ferrimagnetic cubic phase often observed in soils as the result of fire. Without an organic reductant, no intermediate cubic phase was formed when ferrihydrite was transformed into hematite, regardless of whether the ferrihydrite DTA curve showed one or two exothermic peaks. Addition of glucose or charcoal as reductant caused the initial formation of a cubic magnetite and/or magnetite/maghemite phase in samples heated above 300°C in both air and N2 atmospheres. Ferrihydrite reduction, as determined by increasing cubic unit-cell edge lengths between 0.832 and 0.840 nm, increased with reductant concentration and heating time, providing excess reductant remained. Following consumption of the reductant, FeII may be partially or completely reoxidized, forming maghemite and then hematite. The occurrence of maghemite, but not of magnetite, in soils where forest fires have occurred suggests that sufficient oxygen was available, while temperatures remained elevated, to oxidize magnetite to maghemite.
Effect of autotransformation on the layer charge of smectites determined by the alkylammonium method
Authors: Janek M. , Komadel P. , Lagaly G. 
Published: December 2006

AbstractHydrogen-forms of <2 µm fractions of six bentonites of various Fe contents were prepared by H+→OH-→H+ion exchange using resins. Potentiometric titration curves revealed that the number of strong acid sites varied and accounted for 60-95% of the total acidity in the freshly prepared H-forms. The number of strong acid sites decreased and that of the weak acid sites increased on ageing. The process of autotransformation in aqueous dispersion at 90~ was completed within four days. Layer-charge distributions of all samples were inhomogeneous with layer charges from 0.25-0.39 Eq/unit O10(OH)2. Oxalate pretreatment of the samples resulted in changes in the layer-charge distribution due to the removal of readily soluble phases which may have blocked exchange sites. After autotransformation, the alkylammonium exchange method revealed inhomogeneous charge density distributions; the fraction of layers of the highest charge decreased. Comparison of total CEC obtained from potentiometric curves and interlamellar CEC calculated from the mean layer charge confirmed attack of protons from particle edges. However, for several samples the structural attack may also occur from the interlayer space. Autotransformation of the Hsmectites decreased the mean layer charge. Protons probably attack the Mg(O,OH)6octahedra preferentially during the autotransformation.
Polymerization of tetramethylcyclotetrasiloxane monomer by ion-exchanged montmorillonite catalysts
Authors: Nishihama S. , Yamada H. , Nakazawa H. 
Published: December 2006

AbstractMontmorillonites ion-exchanged with Li+, Na+, K+ Ca2+, Mg2+ and Ni2+ and acidic clay were used as catalysts for the polymerization of a cyclic siloxane monomer, 2,4,6,8- tetramethylcyclotetrasiloxane. Montmorillonites with Ni2+ and Mg2+ in the interlayer, and acidic clay exhibit a greater ability for siloxane polymerization in both yield and mean molecular weight of products than those containing Li+, Na+ and K+. The difference in catalytic ability of the ionexchanged montmorillonites is caused by the number of Brmasted acid sites due to the polarization of H2O. This was confirmed experimentally by FTIR analysis of pyridine-treated samples. Therefore, it may be possible to design a catalyst for controlling siloxane polymerization (i.e. mean molecular weight of product) by changing the number of Bronsted acid sites through exchange of the interlayer cations of montmorillonites.
Metachromasy in clay-dye systems: the adsorption of acridine orange by Na-saponite
Authors: Garfinkel-Shweky D. , Yariv S. 
Published: December 2006

AbstractThe adsorption of the cationic dye acridine orange (AO) by Na-saponite and the colloidal properties of the aqueous suspension were investigated by visible spectroscopy and XRD. The organic cation is adsorbed by the mechanism of cation exchange. When small amounts of the dye are adsorbed, the system contains small tactoids and is peptized. At this stage the dye penetrates into the interlayer space and most of it undergoes metaehromasy due to interactions between the aromatic entity and the oxygen plane of the clay. When greater amounts of AO are adsorbed, the clay platelets flocculate to form book-house floes which, with excess AO, are transformed into card-house floes. At this stage metachromasy results from the aggregation of the dye in the interparticle space of the floes, in addition to the π interactions with the oxygen plane. In excess AO, the clay is gradually peptized. At this stage the dispersed clay platelets form small tactoids with monomeric AO in the interlayer space and at the same time adsorb dimerie and polymeric AO cationic species at the solidliquid interface.
An investigation of nephrite jade by electron microscopy
Authors: Dorling M. , Zussman J. 
Published: December 2006

AbstractTwo specimens of tremolite and one of richterite, all with nephrite jade texture, have been examined by transmission electron microscopy using ion-thinning for specimen preparation. The specimens contain clusters of very small lath-like crystallites with z-axes approximately parallel but in a range of azimuthal orientations. It is suggested that these clusters which are themselves in varied orientations are the result of post-tectonic recrystallization of strained amphibole crystals, the new crystals inheriting the z-axis orientations of the old. The extreme toughness of nephrite jade is attributed to a number of the sub-microscopic features observed, including the sizes, habits, and orientations of its crystallites, and the nature of its grain boundaries.
Schultenite from King County, Washington, USA; a second occurrence, and review
Authors: Falls R. , Cannon B. , Mandarino J. A. 
Published: December 2006

AbstractSchultenite, PbHAsO4, known only from Tsumeb, Namibia, has been identified from a second occurrence: near North Bend, King County, Washington, USA. It occurs as euhedral crystals in a quartz-arsenopyrite-galena vein. It has a measured density of 6.07(3) g/cm3 and a calculated density of 6.079(4) g/cm3. The white to colourless crystals have a white streak, adamantine lustre, and fluoresce dull yellow under long wave ultraviolet light. Schultenite is monoclinic. Pa or P2/a; the unit cell parameters refined from the X-ray powder diffraction data are: a 5.827(3), b 6.743(3), c 4.847(3) Å, β 95.34(5)°; V 189.6(1) Å3; Z = 2; a:b:c = 0.8642:1:0.7188. The forms {010}, {001}, and {3̄22} were observed on the Washington schultenite crystals.
The occurrence of coarse-grained massive tilleyite in the Redcap Creek magmatic skarn, North Queensland
Authors: Rubenach M. J. , Cuff C. 
Published: December 2006

AbstractEndoskarns formed where a swarm of diorite dykes have intruded calcite marble at Redcap Creek include an inner melilite-dominated, a wollastonite-dominated, and an outer massive tilleyite zone in contact with marble. The massive tilleyite is unusual in that it is coarse-grained (prisms 2–15 cm in length) and its deep grey colour contrasts with the lighter coloured varieties described elsewhere. A chemical analysis gives a formula close to ideal, with only minor substitution of Al, Ti, and Mg. Refined unit cell parameters are in close agreement with those quoted in the literature. The skarns have clearly formed by transport of Si, Mg, Fe, Al, and Ti from the igneous rocks, and Ca in the reverse direction from the marble. Activity diagrams derived from experimental data are most useful in interpreting the zonal sequence of endoskarns, and preliminary results suggest mass transfer at low Xco2 and temperature of the order of 800°C or higher for the formation of the massive tilleyite.
Experimental investigation of clogging of fissures and pores in granite
Authors: Bourg A. C. M. , Oustrière P. , Sureau J. F. 
Published: December 2006

AbstractFluid flow through a fractured granite core and leaching experiments on granite powder (at constant temperatures of 50 and 100°C and during cooling from 100 to 50°C) indicate that the dissolved silica content of the fluids originates from the dissolution of feldspars and phyllosilicates. The dissolution of quartz is not ruled out but it should be a minor phenomenon. The precipitation of quartz may control the dissolved Si content during constant temperature leaching. During cooling from 100 to 50°C chalcedony, alumino-silicates, and chlorite are all capable of precipitation, possibly leading to some clogging or sealing of fissures.
The NAGRA investigation project for the assessment of repositories for high-level radioactive waste in geological formations
Authors: Balderer Werner 
Published: December 2006

AbstractThe first results of isotopic investigations as a part of the hydrogeological study of northern Switzerland are presented. This study is part of the global geological research project of the NAGRA (National Co-operative for the Storage of Radioactive Waste) which is intended to provide the scientific knowledge required for the assessment of the feasibility of safe disposal of highly radioactive waste in the geological formations of the area. The aim of the hydrogeological research programme is to assess the natural conditions in the sedimentary sequence and the underlying granite basement, by regional investigation of hydraulic parameters, isotopic composition, and hydrogeochemistry at all existing wells (boreholes and natural thermal springs) and in 11 to 12 deep-drilled boreholes (to final depth of 1500–2500 m).