bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural and monoionic aliettite: hydration and dehydration states
Authors: Brigatti M. F. , Poppi L. 
Published: December 2006

AbstractThe dehydration of an interstratified talc-trioctahedral smectite mineral (aliettite) from Monte Chiaro, Taro Valley, Italy, saturated by Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 cations, was studied by X-ray powder diffraction and thermal analysis, under different conditions of temperature and relative humidity. Both in the natural and exchanged states the mineral exhibited several orders of basal reflections and, to varying relative humidity (p/po) and temperature (T) conditions, behaved like a smectite except that: (i) the c-dimension was not very sensitive to relative humidity increase; (ii) the closest packing was for T > 400°C, the collapsed state being reached gradually as T increased and an inverse trend was apparent between 20° and 300°C; (iii) the endothermic reactions at T = 400°C and T = 600°C appeared to be affected by the exchange treatment. The experimental data are consistent with a structural model in which it is possible to distinguish layers containing a patchwork of talc and smectite domains: the patchworks are superposed to make a regular alternation of the two domains.
The reductive dissolution of synthetic goethite and hematite in dithionite
Authors: Torrent J. , Schwertmann U. , Barron V. 
Published: December 2006

AbstractThe reductive dissolution by Na-dithionite of 28 synthetic goethites and 26 hematites having widely different crystal morphologies, specific surfaces and aluminium substitution levels has been investigated. For both minerals the initial dissolution rate per unit of surface area decreased with aluminium substitution. At similar aluminium substitution and specific surface, goethites and hematites showed similar dissolution rates. These results suggest that preferential, reductive dissolution of hematite in some natural environments, such as soils or sediments, might be due to the generally lower aluminium substitution of this mineral compared to goethite.
Volatile products of clay mineral pyrolysis revealed by their effect on calcite
Authors: Heller-Kallai L. , Miloslavski I. , Aizenshtat Z. 
Published: December 2006

AbstractThe volatiles produced when various clay minerals were pyrolysed under a stream of He or in vacuo were condensed and analysed. They contain a wide range of cations and anions in concentrations ranging from ppm to hundreds of ppm. The reactivity of these volatiles was demonstrated by their reaction with calcite. It is suggested that the water liberated on heating acts as a scavenger of various impurities present in the clay.
Cation ordering in lepidolite and biotite studied by X-ray photoelectron diffraction
Authors: Ash L. A. , Evans S. , Hiorns A. G. 
Published: December 2006

AbstractComprehensive X-ray photoelectron diffraction (XPD) studies have revealed octahedral cation ordering in a 1M lepidolite and in a 1M biotite. In the lepidolite (from Høydaler, Telemark, Norway), all three octahedral sites are differentiated, with Li and Mn concentrated in the trans M(1) site and Al in cis M(3); M(2) contains all three cations. In the biotite, the major cations do not order but Ti, present at only 1·2% concentration, preferentially occupies the two cis sites, information which is available uniquely from XPD. Long-range tetrahedral ordering should be detectable by XPD, but was not found in either mica.
Structural studies of montmorillonites by 57Fe Mössbauer spectroscopy
Authors: Cardile C. M. 
Published: December 2006

AbstractFive montmorillonites were analysed by 57Fe Mössbauer spectroscopy and their Fe3+ occupation in tetrahedral and octahedral sites assigned. The montmorillonites, with a range of IVFe3+ contents, were used in an attempt to correlate IVFe3+ content with VIFe3+cis- and trans-OH site occupation to verify the assertion that increasing IVFe3+ content directs VIFe3+ to cis-OH sites. However, VIFe3+ in montmorillonite appears to be located essentially in the trans-OH sites. The two doublets computer-fitted to the VIFe3+ Mössbauer resonance for montmorillonite appear to represent a distribution of a continuum of slightly different Fe3+ resonances, which arise from the variable atomic environment surrounding the VIFe3+ sites, rather than discrete cis- and trans-OH sites. Therefore Mössbauer spectroscopy cannot be used to demonstrate whether an increasing IVFe3+ content directs VIFe3+ substitution into particular sites for montmorillonites.
Mineralogy and genesis of the Pugu Hill kaolin deposit, Tanzania
Authors: Schwaighofer B. , Müller H. W. 
Published: December 2006

AbstractAccording to field studies of the Pugu Hill kaolin deposit and mineralogical investigations (X-ray, SEM), two main types of Miocene sandstones are distinguished: (i) clayey-silty kaolinitic sandstones with stacks of idiomorphic pseudohexagonal kaolinite crystals; (ii) massive clayey-silty kaolinitic sandstones with irregular fabric of isolated kaolinite plates. The Precambrian metamorphic rocks of the Uluguru Mountains are a probable source for the kaolinitic sediments of the Pugu Hill Formation. Decomposition products of weathering profiles on meta-anorthosites are mainly 7Å- and 10Å-halloysite and gibbsite. It is suggested that the kaolinitic sandstones were deposited in a former delta. The first sandstone type is considered to have developed in situ from weathered arkosic sandstone, and the second represents channel deposits in an old river system (probably a Miocene predecessor of the Ruvu River) with kaolin transported from a hinterland and redeposited. The variable formation and fabric of the kaolinites in the Pugu Hill Formation are due to in situ weathering of transported primary minerals (fedspar), and to transported weathered material (with secondary halloysite).
Catalytic activity of modified silicates: I. Dehydration of ethanol catalysed by acidic sepiolite
Authors: Corma A. , Perez-Pariente J. 
Published: December 2006

AbstractThe kinetics of the dehydration of ethanol on acidic Al3+-exchanged sepiolite has been studied. The product distribution indicates that the formation of diethylether and ethylene takes place by a series of consecutive and parallel reactions. A mechanism for the formation of both products has been derived by studying the influence of different operational variables on the reaction rates.
The kinetics of dehydroxylation of kaolinite
Authors: Redfern S. A. T. 
Published: December 2006

AbstractThe dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the temperature range 734 K to 890 K. An empirical activation energy of 222 kJ mol-1 was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (Ea) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in Ea during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges inwards, parallel to (001).
The rapid estimation of the layer charges of 2:1 expanding clays from a single alkylammonium ion expansion
Authors: Olis A. C. , Malla P. B. , Douglas L. A. 
Published: December 2006

AbstractAn empirical method to estimate rapidly both mean total layer charge and location of charge in smectites and vermiculites is presented, involving exchange with a long-chain alkylammonium ion before and after the Greene-Kelly test. The method utilizes an empirically determined relationship between XRD basal spacings and the mean layer charges calculated from the conventionaln-alkylammonium ion-exchange technique using simple linear regression models to describe the relationships for both monolayer-bilayer and bilayer-pseudotrimolecular layer transitions. The method provides a rapid estimation of these charge parameters and facilitates the proper identification of both smectites and vermiculites consistent with the AIPEA criteria for classification based on total layer charge. It is considered superior to conventional methods of differentiation based mainly on expansion and collapse behaviour.
The effect of CO2 and oxidation rate on the formation of goethite versus lepidocrocite from an Fe(II) system at pH 6 and 7
Authors: Carlson L. , Schwertmann U. 
Published: December 2006

AbstractTo investigate the influence of carbonate on the formation of goethite and lepidocrocite, ∼200 samples were synthesized by oxidizing FeCl2 solutions with air/CO2 gas mixtures at ambient temperature and pH 6 and 7. The proportion of lepidocrocite in the lepidocrocite/goethite mixtures (Lp/(Lp + Gt)) decreased from 100 to 0% with increasing in solution and with decreasing average oxidation rate (AOR). These two parameters explained 81% of the variation of Lp/(Lp + Gt)). At a given , more goethite was formed at pH 6 than at pH 7. The Lp + Gt mixtures contained 0–8 mg g−1 carbon (Ct) which could not be removed by washing. Ct reached apparent saturation at a equilibrium concentration of ∼6–8 and 60–80 mmol l−1 at pH 6 and pH 7, respectively. In a plot of Ct vs. Lp/(Lp + Gt) all data fell on the same line irrespective of oxidation parameters (pH, AOR). IR spectra showed two broad bands at ∼1300 and 1500 cm−1 which can be assigned to distorted carbonate adsorbed at the goethite surface. Identical bands were also found in a young, poorly crystalline goethite formed from coal mine drainage in Ohio. It is suggested that carbonate anions direct the polymerization of the double bands of FeO3(OH)3 octahedra common to both minerals toward a corner sharing arrangement, and thereby to goethite, whereas chloride permits edge-sharing as in lepidocrocite.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: II. The chlorite group
Authors: Wiewióra A. , Weiss Z. 
Published: December 2006

AbstractThe classification and nomenclature of chlorites have been critically reviewed. A new classification based on the unified projection system of chemical composition has been proposed in which for the first time all trioctahedral, di-trioctahedral and dioctahedral species are included. The chemical composition of chlorites is controlled by the general crystallo-chemical formula: This is superior to the known formulae for the trioctahedral and dioctahedral chlorites. It has been shown that the chlorite end-member compositions of Bayliss (1975) project in one point of the projection field leaving many end-member compositions unnamed. As they correspond to the names used previously, a proposal is made to restore these names.
Pore size distribution and adsorption selectivity of sepiolite
Authors: Inagaki S. , Fukushima Y. , Doi H. , Kamigaito O. 
Published: December 2006

AbstractMicropore distribution and effective size of the channels of natural sepiolite from Turkey were measured by the BET method. Before the BET measurement, the samples were treated under a water vapour atmosphere at various pressures to fill progressively the sepiolite micropores with water. The surface areas measured by means of N2 adsorption decreased with increased vapour pressures of water. The outer surface area was estimated by comparison of the surface area of the vacuum-dried sepiolite with that filled with adsorbed water. The total surface area was ∼290 m2/g, and the outer surface area was 170 m2/g, the difference being attributed to the structural micropores of the sepiolite. The ratio of the surface areas possessed by the channels and that of the outer surface suggest that the mean thickness of the sepiolite fibre was ∼12 nm. The effective size of the channels was estimated from the number of various-sized molecules sorbed by the sepiolite, the results showing that molecules larger than benzene could not migrate into the channels.
Thermal analysis of sepiolite and palygorskite treated with butylamine
Authors: Shuali U. , Steinberg M. , Yariv S. , Muller-Vonmoos M. , Kahr G. , Rub A. 
Published: December 2006

AbstractThe thermal behaviour of sepiolite and palygorskite treated with butylamine was investigated by DTA, TG and EGA-MS under a flow of air and N2. It was shown that the amine was adsorbed by the clays, penetrating into the pores and replacing zeolitic and bound water. The presence of amine in the pores shifted the dehydroxylation peak to temperatures higher than for the untreated clays. Under N2 the thermal desorption of the amine from sepiolite was observed at 175, 275 and 525°C, and from palygorskite at 170 and 270°C. In addition to desorption, reactions of pyrolysis and condensation to charcoal were detected by the evolution of NH3, CH4 or H2, respectively. In air, oxidation of the organic matter led to the appearance of exothermic peaks, the temperatures of the most intense peaks being determined by the rate of C oxidation, but the shape of the DTA curves and the temperatures of exothermic shoulders were determined by the rate at which H from the organic molecules combined with O from the air.
Surface properties and clay mineralogy of hydrated halloysitic soil clays. II: Evidence for the presence of halloysite/smectite (H/Sm) mixed-layer clays
Authors: Delvaux B. , Herbillon A. J. , Vielvoye L. , Mestdagh M. M. 
Published: December 2006

AbstractSix clays from volcanic ash soils at different stages of weathering differ in their relative halloysite content with respect to kaolinite and several surface properties, namely CEC, and exchange selectivity for K+. These three parameters are related to each other in that they all decrease with increasing soil weathering stage. XRD data show that the hydrated 1:1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals. In these mixed-layers, the content and layer charge of smectitic units decrease as the relative halloysite content in the clay decreases. These clays thus depict a weathering sequence that is parallel to the weathering sequence of the soils from which they originate. It is also shown that the smectites in the H/Sm minerals have the distinctive composition and ESR spectrum of Fe-rich 2:1 clay minerals belonging to the beidellite-nontronite series. The information obtained explains why these clays have high CEC and distinct affinities for K+. It is hoped that this study will help to clarify the controversy concerning the CEC and related surface properties attributed to hydrated halloysite.
Kinetics of the acid leaching of palygorskite: Influence of the octahedral sheet composition
Authors: Corma A. , Mifsud A. , Sanz E. 
Published: December 2006

AbstractA study has been carried out on the influence of acid concentration, time and temperature of reaction, liquid to solid ratio and chemical composition of the mineral on the extension and selectivity of the octahedral cations extracted during acid leaching of palygorskite. The mechanism of the extraction of Mg2+, Al3+, and Fe3+ is discussed on the basis of kinetic models fitted for a reacting-shell model, taking into account particle shape and the rate controlling step. A model is given from which kinetics parameters and the activation energy of the process are calculated. The different behaviour observed for the two palygorskites could be explained on the basis of their differences in surface areas.
Effects of tetrahedral isomorphic substitution on the IR spectra of synthetic fluorine micas
Authors: Kitajima K. , Takusagawa N. 
Published: December 2006

AbstractEffects of tetrahedral isomorphic substitution on the IR spectra of fluorine micas were demonstrated by comparing the spectrum of taeniolite KMg2Li(Si4O10)F2 with those of the substituted analogues, in which Ga, Al, B or Ge substituted for Si in tetrahedral sites. The e11 bands move towards lower frequencies as the content of substituted cation in tetrahedral site increases, whereas The a11 and a12 bands moves towards higher frequencies. Linear relationships were found between a12 the band frequency and the extent of tetrahedral substitutions. The magnitude of shifts per molar substitution for the a12 bands is dependent on the species of substituted cation and decreases in the order Ga > Al > Ge > B, showing an intimate correlation with the field strength z1·z2/r2M–O of the substituted cations. This implies that the polarizing power of the substituted cations has a pronounced effect on the Si-O stretching vibrations.
An ESR and calorimetric study of iron oolitic samples from the Northampton ironstone
Authors: Gehring A. U. , Karthein R. 
Published: December 2006

AbstractElectron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.
Structural studies of Silica Springs allophane
Authors: Childs C.W. , Parfitt R.L. , Newman R.H. 
Published: December 2006

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.
Thermogravimetric analysis of the iso-butene oligomerization activity of various forms of synthetic mica-montmorillonite
Authors: Vogel A. P. , O'Connor C. T. , Kojima M. 
Published: December 2006

AbstractThe iso-butene oligomerization activity of pure and metal-substituted synthetic mica-montmorillonite (SMM) was studied by simultaneous thermogravimetric-differential thermal analysis (TG-DTA). The incorporation of matrix Ni and ion-exchanged Co, Ni and Zn into SMM increased its iso-butene oligomerization activity while the presence of water in the olefinic feed reduced activity. These findings corresponded to trends found in previous work on high pressure (50 MPa) propene oligomerization over SMM and metal-substituted SMM.
Quantification des teneurs en opale biogene des sediments de l'Ocean Austral par diffractometrie X
Authors: Bareille G. , Labracherie M. , Maillet N. , Latouche C. 
Published: December 2006

RésuméLe dosage de l'opale biogène dans les sédiments marins peut être effectué par diffractométrie X par la mesure des surfaces des bandes de diffusion et par la mesure des surfaces des pics de cristobalite. La surface de la bande de diffusion, observée sur les diagrammes X de sédiments non chauffés, caractérise la concentration en composés amorphes (organiques et inorganiques). Elle permet de quantifier l'opale biogène de sédiments ne contenant que peu ou pas d'amorphes non biogènes. La surface du pic de cristobalite, obtenu par transformation de l'opale biogène par chauffage à 1050–1100°C pendant 12 h, permet de doser la silice biogène de divers sédiments. Ces deux approches méthodologiques ont été appliquées aux sédiments d'une carotte (MD 84–527) prélevée dans le secteur ouest-Indien de l'Océan Austral. Ce matériel, qui a enregistré la sédimentation des 40,000 dernières années, ne renferme qu'accessoirement des constituants amorphes volcaniques. Les concentrations en silice biogène sont obtenues avec une précision de ±10%. Le comptage des diatomées par observation au microscope a été également réalisé sur les mêmes sédiments. Les courbes des teneurs en opale biogène obtenues par les deux méthodes sont comparables et se corrèlent bien à l'abondance totale des diatomées.
X-ray study of the nature of stacking faults in the structure of glauconites
Authors: Sakharov B. A. , Besson G. , Drits V. A. , Kameneva M. Yu. , Salyn A. L. , Smoliar B. B. 
Published: December 2006

AbstractGlauconites are dioctahedral, microdivided, Fe-containing silicates whose idealized structure may be described as a stacking of 2 : 1 layers with the same azimuthal orientation. The diffractometric and crystallochemical data do not coincide with this idealized structural model. For each glauconite studied the best fit between experimental and theoretical XRD patterns was obtained using the same model. It was possible to describe the stacking by an equally probable occurrence of layers rotated by multiples of 60°. The layer types alternate with a definite tendency to segregation. The model is characteristic for all glauconites, irrespective of composition, age and type of host rock. The alternation of layers rotated by 60° in the structure leads to both octahedral and prismatic coordination for the interlayer K+ cation.
Nature and origin of an aluminous vermiculitic weathering product in acid soils from upland catchments in Scotland
Authors: Bain D. C. , Mellor A. , Wilson M. J. 
Published: December 2006

AbstractVermiculitization of mica is one of the main weathering processes in soils from three upland catchments receiving various levels of acid deposition. Usually this process is manifested by the presence of interstratified mica-vermiculite with the interlayer space in the vermiculite often partially filled with polymeric hydroxyaluminium species. In one peaty podzol, regularly interstratified mica-vermiculite clearly develops at the expense of mica and is the dominant mineral in the Eh horizon. It was concentrated by chemical treatments to remove organic matter, free iron oxides, and any Al species in the interlayer, and the structural formula calculated from chemical analysis confirmed the dioctahedral character of both vermiculite and mica components, and indicated that the vermiculitic weathering product was formed from a dioctahedral mica. The degree of interlayering in the interstratified phases seemed to be pH-dependent with resultant implications for soil and freshwater acidification.