bluuebunny/crossref_metadata_2025_split huggingface dataset:
The crystallinity and surface characteristics of synthetic ferrihydrite and its relationship to kaolinite surfaces
Authors: Saleh A. M. , Jones Angela A. 
Published: December 2006

AbstractSynthetic ferrihydrites with Si added at mass ratios of Si/Fe = 0, 10, 20, 40, 80, and 160 × 10−3 have been studied to examine the effect of Si on the properties of ferrihydrite. The Si proportionally reduces the point of zero charge but influences surface area, loss of weight to 800°C and solubility in acid oxalate solution to varying degrees. At a critical concentration of Si (when Si/Fe = 20 × 10−3) these measured properties indicate a greater particle size and a more ordered structure. The relationship between synthetic ferrihydrite and the surface of kaolinite has been studied by a combination of surface area and charge determinations and TEM. An attraction predicted at pH 3 between ferrihydrite particles and the basal surface of kaolinite has been confirmed, and resulted in a stable coating. However, at pH 6 any attraction between the minerals appears to be too weak to produce a coating of the kaolinite surfaces.
Interparticle diffraction: a new concept for interstratification of clay minerals
Authors: Nadeau P. H. , Wilson M. J. , McHardy W. J. , Tait J. M. 
Published: December 2006

AbstractA new conceptual model for interstratified clays is proposed, based on complementary use of the transmission electron microscope (TEM) and X-ray diffraction (XRD). Clays yielding interstratified XRD patterns are shown to be composed of aggregates of fundamental particles (here defined as an individual or free particle which yields a single crystal pattern by electron diffraction) whose interfaces are capable of adsorbing water and organic molecules. In these circumstances, the interstratified XRD character results from an interparticle diffraction phenomenon. Smectites are shown to be primarily composed of particles 10 Å thick corresponding to elementary 2:1 silicate layers. Nearest-neighbour regularly interstratified illitesmectite (K-rectorite) is composed of particles of elementary ‘illite’ 20 Å. thick, corresponding to two silicate layers coordinated by a single plane of potassium ions. Regularly interstratified chlorite-smectite (corrensite) consists of particles 24 Å thick corresponding to two silicate layers coordinated by a single brucitic sheet. The layer sequence examined by XRD is determined by the types and proportions of particles present within the clay material. Thus a sedimented aggregate of 20 Å elementary ‘illite’ particles appears to be a regularly alternating sequence of illite and smectite layers by XRD. Randomly interstratified itlite-smectite and chlorite-smectite can be synthesised by making mixed suspensions of the <0·1µm fractions of smectite with those of K-rectorite and corrensite respectively, providing experimental confirmation of the proposed model. Unusual associations, such as three-component illite-chlorite-smectite interstratified systems can be synthesised by making mixed suspensions of K-rectorite and corrensite. Long range regularly interstratified illite-smectite of the IIS and IIIS types are composed primarily of fundamental ‘illite’ particles 20–50 Å thick. Conventional illite is composed primarily of particles > 50 Å thick. This conceptual model has implications for the chemistry, behaviour and genesis of interstratified clays which are common constituents of soils and sediments.
Thermal analysis in the investigation of zeolitized and altered volcanics of Latium, Italy
Authors: Lombardi G. 
Published: December 2006

AbstractThe data obtained on zeolites, kaolins, alunites, hydrated sulphates and soils by DTA-TG-EGA carried out under various experimental conditions are discussed. Among the main subjects dealt with are chabazite and phillipsite identification and their quantification by TG, clay mineral distribution in size fractions of kaolins, significance and use of thermoanalytical data from alunitic rocks, the influence of calcite and calcined kaolinite on the sulphate DTA curves, rates of decomposition of hydrated sulphates, and thermal analysis of soils in forensic studies.
Thermal reactions of leadhillite Pb4SO4(CO3)2(OH)2
Authors: Milodowski A. E. , Morgan D. J. 
Published: December 2006

AbstractReactions undergone by leadhillite from the type locality on heating to 1000°C have been followed by DTA, TG, DSC, evolved gas analysis, continuous-heating XRD and IR, and hot-stage microscopy. Intermediate decomposition products were identified by X-ray powder photography. At 80°C, biaxial leadhillite inverts to a uniaxial phase with properties similar to those of susannite, a naturally occurring polymorph of leadhillite, but this higher-temperature modification only partially reverts to the original structure on cooling (up to 24 hours at room temperature is required for complete reversion). Between 250 and 600°C the mineral undergoes two decomposition reactions: PbO.PbCO3 and PbO.PbSO4 form during the first reaction (PbCO3 may form in the initial stages) and 4PbO.PbSO4 during the second. α-2PbO.PbSO4 appears at 650°C due to solid-state reaction between the other lead oxysulphate products. Melting occurs above 850°C. The reaction products are discussed in relation to the phase diagrams for the systems PbO-CO2 and PbO-PbSO4.
Characterization and reducibility of Itakpe and Agbaja (Nigerian) iron ores
Authors: Adedeji F. A. , Sale F. R. 
Published: December 2006

AbstractTwo iron ore samples from Nigeria have been examined using TG, DTA, EGA, XRD, and optical and electron microscopy. Itakpe iron ore is hematite-rich, this mineral being intergrown with magnetite, and silica is the major impurity. Agbaja ore is an acidic oölite ore consisting of goethite and magnetite, with alumina, silica and phosphorus as major impurities. Itakpe is typical of a rich ore formed by magmatic segregation whilst Agbaja is a lean ore of sedimentary origin. Isothermal mass-change measurements in hydrogen and carbon monoxide in the range 800–1100°C show Agbaja to be less reducible than Itakpe; in particular, Agbaja is very irreducible at 1100°C because of sintering of the ore. Characterization and reducibility experiments were also carried out on Corby (Northamptonshire, UK) iron ore for comparison.
Measurement of high-alumina cement-calcium carbonate reactions using DTA
Authors: Midgley H. G. 
Published: December 2006

AbstractHydrating high-alumina cement will react with calcium carbonate to form the complex mineral calcium carboaluminate hydrate, 3CaO.Al2O3.CaCO3.12H2O. This mineral is reported to be capable of providing strength in concrete and so may provide an alternative to the minerals normally found in the hydration of high-alumina cement, which may under certain conditions convert to other minerals with a loss in strength. Some doubt has been cast on the stability of calcium carboaluminate hydrate and it has been found that in hydrated high-alumina cement, calcium carboaluminate hydrate decomposes at temperatures in excess of 60°C. Cube compressive strength tests on high-alumina cement and high-alumina cement-calcium carbonate pastes have shown that the latter have a lower strength than pastes made with high-alumina cement alone. When cured at 50°C the high-alumina cement-calcium carbonate pastes show a loss in strength with curing time. Cements made with the high-alumina cement-calcium carbonate mixture always have a lower strength than those made with high-alumina cement alone and so no advantage is gained from their use.
Ordered illite-smectite and kaolinite-smectite: pedogenic minerals in a Lower Carboniferous paleosol sequence, South Wales?
Authors: Robinson D. , Wright V. P. 
Published: December 2006

AbstractMixed-layer clay minerals of illite-smectite, having smectite contents ∼25% and IS ordering, kaolinite-smectite, and a three-component variety with kaolinite-smectite-chlorite-like material are described from a Carboniferous paleosol in South Wales. The clays, which are restricted to particular horizons, are unusual occurrences in a pedogenic sediment and pose particular problems as to their genesis. Positive geological evidence, principally in the form of mineralogical and organic thermal maturation data, demonstrates that the rocks of the region cannot have reached diagenetic temperatures > 100°C. This would appear to suggest a pedogenic rather than a diagenetic origin for these clays. In these sediments the only plausible mechanism of illitization to produce the illite-smectite would be by repeated wetting and drying cycles causing irreversible K fixation. Such cycles would be entirely realistic for a vertisol-like paleosol formed on overbank deposits in a floodplain environment subject to strong seasonal moisture contrasts. If this interpretation is correct, this illite-smectite represents the most illitic yet recorded from a non-burial or non-hydrothermal environment.
A contribution to the study of the catalytic action of clays on the polymerization of styrene: I. Characterization of polystyrenes
Authors: Njopwouo D. , Roques G. , Wandji R. 
Published: December 2006

AbstractThree clay samples (a kaolinite, a halloysite and an inseparable mixture of kaolinite-palygorskite-illite-montmorillonite) were, after a mild pretreatment, successfully tested as catalysts in the polymerization of styrene. The catalytic activity of the clay (measured by the conversion rate), the MW and the colour of the polystyrene obtained depended not only on the chemical composition and the structure of the clay catalyst but also on its concentration in the medium. The polystyrenes obtained on the clay catalyst were composed of two groups of macromolecules, one with low MW and the other with high MW.
Structure et proprietes d'hydratation des nontronites
Authors: Suquet H. , Malard C. , Pezerat H. 
Published: December 2006

RésuméLes nontronites ne présentent pas les propriétés caractéristiques des phyllosilicates 2:1 magnésiens ou alumineux à substitutions tétraédriques: domaines d'hydratation homogène, isotherme de désorption d'eau avec paliers, organisation structurale ordonnée ou semi-ordonnée. Or les analyses structurales montrent que ce sont des beidellites ferriffères et l'étude de l'effet Hofmann–Klemen confirme le taux très faible de lacunes et de substitutions octaédriques. Diverses hypothèses justifiant ces propriétés sont présentées et discutées.
The acidity of trivalent cation-exchanged montmorillonite. Temperature-Programmed desorption and infrared studies of pyridine and n-butylamine
Authors: Breen C. , Deane A. T. , Flynn J. J. 
Published: December 2006

AbstractTemperature-programmed desorption (TPD) and IR spectroscopy were used to characterize the number and strength of acid sites in Al3+-, Cr3+- and Fe3+-exchanged montmorillonite. The bases pyridine and n-butylamine occupied three different sites in the interlamellar space: (i) physisorbed base, (ii) base bound to Lewis acid sites, and (iii) protonated base. TPD profiles for pyridine were characterized by maxima at 40°, 150° and 340°C, whilst those for n-butylamine occurred at 30°, 200° and 410°C. The Al3+- and Cr3+-exchanged forms were stable up to pretreatment temperatures of 300°C, but the Fe3+-form required > 3 day exposure to base vapour to re-establish the high-temperature desorption peak. Variable-temperature IR studies showed that the number of Brönsted-bound pyridine molecules increased with increased outgassing temperature.
The adsorption of 1,4-dioxan, tetrahydrofuran and tetrahydropyran from binary solution with methanol on Al3+ and Cr3+-exchanged montmorillonite
Authors: Breen C. , Deane A. 
Published: December 2006

AbstractSurface excess isotherms were determined for the adsorption of 1,4-dioxan (DIOX), tetrahydropyran (THP) and tetrahydrofuran (THF) from binary solution with methanol (MeOH) on Al3+- and Cr3+-exchanged, montmorillonite containing different amounts of pre-adsorbed water. The isotherm type is dominated by the binary mixture whereas the amplitude, which follows the sequence DIOX > THP > THF, is further influenced by the exchange cation, Al3+ > Cr3+, and the water content of the clay. The sorption of DIOX and THP from MeOH exhibit a type IV isotherm in the Schay-Nagy classification on both cation-exchanged forms, whilst that of THF from MeOH is of type I and THF is the preferred adsorbate. The azeotropic point for the type IV isotherms is close to a 1:1 mole ratio for the samples dried at 120°C but when the samples are rehydrated at 12% r.h. following thermal pretreatment at 120°C the azeotropic point shifts in favour of the cyclic ethers DIOX and THP, making them the preferred component over a substantial portion of the composition range.
Synthesis and crystallogenesis of ferric smectite by evolution of Si-Fe coprecipitates in oxidizing conditions
Authors: Decarreau A. , Bonnin D. , Badaut-Trauth D. , Couty R. , Kaiser P. 
Published: December 2006

AbstractSilico-ferric coprecipitates, with chemical formula, were aged in suspension at 75°, 100° and 150°C and the structural evolution of solids with time studied by XRD, TEM, and IR, Mössbauer and EXAFS spectroscopy. The initial Si-Fe coprecipitate was found to be amorphous but showed local order similar to that of a smectite layer. At 75°C only a weak structural evolution of the silico-ferric product towards a smectite-like structure was observed. Experiments performed at 100° and 150°C led to synthesis of a ferric smectite with structural formula. During syntheses a highly soluble silico-ferric complex appeared; the Si/Fe atomic ratio of this complex was 3, and the apparent concentration of Fe3+in solution reached 27 mm/l. These syntheses prove that the crystallization of a dioctahedral smectite, containing only Fe3+atoms in the octahedral sheet, is possible under strictly oxidizing conditions. However, crystal growth of a ferric smectite under these conditions is slow and only syntheses carried out at sufficiently high temperatures give convincing results.
Influence of the chemical composition and textural characteristics of palygorskite on the acid leaching of octahedral cations
Authors: Corma A. , Mifsud A. , Sanz E. 
Published: December 2006

AbstractLeaching of two palygorskites with different octahedral aluminium contents has been carried out in HCl at 20°–70°C. The acid concentration was varied in the range 0·05–6 mol. 1−1, using 4–500 g.g−1 liquid to solid ratios. Acid leaching of up to 60% of the octahedral cations did not provoke structural changes or amorphization of the samples. On the bases of the selectivity of extraction of Mg2+, Fe3+ and Al3+, it appeared that most of the octahedral edge positions are occupied by Mg2+, some by Fe3+, and practically none by Al3+. Differences in acid-leaching behaviour between the two palygorskites was better related to accessible surface than chemical composition.
Electron spin resonance studies of halloysites
Authors: Chaikum N. , Carr R. M. 
Published: December 2006

AbstractAbsorption lines in the g ∼ 4 region of ESR spectra of three New Zealand halloysites were found to originate from similar paramagnetic centres as in kaolinites. Resonances in the g ∼ 4 region were not common to all the halloysites, although the signal at g = 2·0 for the Matauri Bay halloysite is probably due to a trapped positive hole or trapped ion. A 6-line resonance produced by Te Puke halloysite and removable by Na-saturation is attributed to exchangeable Mn on the clay surface. Low-temperature lines exhibited by all samples are due to V4+ or VO2+ replacing Al3+ in the octahedral sheet.
Caracteristiques structurales d'une smectite dioctaedrique en fonction de l'ordre-desordre dans la distribution des charges electriques: I. Etudes des reflexions 00l
Authors: Ben Hadj-Amara A. , Besson G. , Tchoubar C. 
Published: December 2006

ResumeHofmann & Klemen ont observé qu'en chauffant modérément (200-220°C) une smectite dioctaèdrique à substitutions octaàdriques saturée par du lithium, celle-ci perdait sa capacité d'échange cationique et son pouvoir de solvatation. Les auteurs ont attribué cet effet à la migration des cations Li vers la couche octaèdrique. Nous avons, en utilisant essentiellement la diffraction X aux grands angles et la microscopie électronique, caractérisé de manière quantitative la structure d'une smectite à déficit de charge mixte (c'est-à.-dire ayant 30% de substitutions dans les couches téraèdriques et 70% dans les couches octaèdriques) saturée par du nickel, avant et après chauffage. Nous avons ainsi pu montrer en éudiant les réflexions 00l qu'après un chauffage à 400°C, les cations interfoliaires migrent vers la cavité octaèdrique vacante pour compenser la totalité des charges négatives dues aux substitutions Al → Mg et qu'il existe une distribution inhomogène de la charge entre les couches octaèdriques et tétraèdriques au sein d'un même cristal. Certains feuillets ont des substitutions uniquement dans la couche octaèdrique, d'autres uniquement dans la couche tétraèdrique, et toutes les possibilités peuvent exister entre ces deux pôles extrèmes.
Clay mineral sources of the Grenada Basin, Southeastern Caribbean
Authors: Gandais V. 
Published: December 2006

AbstractThis study of the Quaternary clay sedimentation in the Grenada Basin (Southeastern Caribbean) is based on six cores raised from depths of 1800 to 3000 m. Mineralogical analysis of <2µm and <0·3µm fractions revealed the presence of a four-component association — smectites, illite, kaolinite and chlorite — in which smectites were always dominant. These minerals were derived from two sources: the Lesser Antilles Arc, which contributed only smectites and kaolinite, and the South American continent, where smectites, kaolinite, chlorite and illite coexist. Geochemical data indicate that Ba and Cr are specific indicators of the South American minerals, whereas Cu characterizes the Antillean clays. The South American contribution, now prevailing, was less important during the Sangamon. The Antillean contribution was episodically predominant during the Wisconsin.
Magnetite in soils: I. The synthesis of single-domain and superparamagnetic magnetite
Authors: Taylor R. M. , Maher B. A. , Self P. G. 
Published: December 2006

AbstractA series of experiments has been carried out to investigate the possible formation of magnetite, Fe3O4, under ambient soil-forming conditions. Rapid and easy synthesis of magnetite was achieved through controlled oxidation of Fe2+solutions at room temperatures and near neutral pH values. The synthetic products were found to range in size between 0·01–0·07µm (mean diameter) and hence span the theoretical superparamagnetic-single-domain grain-size boundary.
Magnetic properties and site occupancy of iron in nontronite
Authors: Lear P. R. , Stucki J. W. 
Published: December 2006

AbstractThe magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K. Results revealed that the magnetic exchange interaction in all samples was antiferromagnetic, except no clear minimum occurred at the Néel temperature. Possible explanations for this phenomenon which are discussed include magnetic dilution due to isomorphous substitution, and antiferromagnetic frustration due to either non-centrosymmetric distribution of octahedral Fe3+or tetrahedral Fe3+substitution. A computer simulation model was developed to demonstrate the effects of these variables on long-range magnetic ordering. Magnetic dilution and tetrahedral Fe3+content could explain the anomalous antiferromagnetic behaviour in some, but not all, samples. The non-centrosymmetric model is the only one which explains the behaviour of all samples. In this model, at least 13% of the octahedral Fe3+would occupytrans-dihydroxide sites, with the balance incissites. Magnetic frustration occurs because two Fe3+neighbours of a third Fe3+ion are also neighbours to each other, making the simultaneous satisfaction of all antiferromagnetic exchange interactions impossible.
EPR of VO2+ ions in Al-pillared montmorillonite
Authors: Braddell O. , Barklie R. C. , Doff D. H. 
Published: December 2006

AbstractA pillared smectite clay has been formed by treating Na-montmorillonite with a hydroxy-aluminium solution with an OH/Al ratio of two. Heating the pillared clay for four h at 500°C reduces the interlayer spacing, measured at ambient humidity, from ∼ 9·4 to 8·0 Å. Hydrated VO2+ (and Mg2+) ions have been introduced into the region between the pillars by immersing the pillared clay in VOSO4-MgCl2 solutions and EPR measurements show that in general both immobile and mobile VO2+ ions are present. The immobile ion is probably VO2+(OH)x(H2O)5·x where x = 2–4, and is adsorbed on the pillars with a concentration that saturates at about 1 per 8 Al13 pillars in the unfired clay, and 1 per 4·3 pillars in the fired clay. The mobile species is VO2+(H2O)5 and for both fired and unfired clay in the wet state at room temperature it has a rotational correlation time of (9 ± 1) × 10−11s rad−1.
Weathering of biotite into dioctahedral clay minerals
Authors: Fordham A. W. 
Published: December 2006

AbstractChanges which occur during the natural weathering of biotite in granite gneiss and associated soils are measured by microanalysis and illustrated by SEM. Biotite weathers through a series of interstratified minerals to vermiculite and/or smectite phases which decompose rapidly to kaolinite. Both vermiculite and smectite phases appear to be dioctahedral, on the basis of chemical compositions derived from microprobe data. Weathering products are first apparent on the edges of laminae, where interstratified minerals are formed at right angles to both the edge face and the cleavage. Weathering soon develops along cleavage planes, initially most strongly near the edges of flakes, but then permeating extensively into the body of flakes and subdivided segments. The orientation of interstratified minerals and kaolinite within cleavages is parallel to the cleavage.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: I. The mica group
Authors: Wiewióra A. 
Published: December 2006

AbstractA unified system of vector representation of chemical composition is proposed for the phyllosilicates based on projection of the composition, as given by crystallochemical formula, onto a field with orthogonal axes chosen for octahedral divalent cations, R2+, and Si (X, Y, respectively), and oblique axes for octahedral trivalent cations, R3+, and vacancies, □, (V, Z, respectively). Point coordinates for each set of axes were used to define the direction and length of the unit vectors for phyllosilicates belonging to different groups. Parallel to these fundamental directions the composition isolines were drawn in the projection fields. Applied to micas, this system enables control of the chemical composition by the general crystallochemical formula covering all varieties of Li-free dioctahedral and trioctahedral micas:where z (number of vacancies) = (y-x+ m)/2; m (layer charge) =1; u+y+z = 3. There is a similar formula for vacancy-free lithian micas:where w = m — x+y;m=1; u+y+w = 3, and for Li-free brittle micas:where z = (y — x+m)/2; m = 2; u+y+z = 3. Projection fields were used to classify micas.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: III. The serpentine-kaolin group
Authors: Wiewióra A. 
Published: December 2006

AbstractA unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group. It has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (Si(2-x)Alx)O5(OH)4, where u+y+z=3, z=y-x. Using projection fields for different chemical systems it has been shown that among the most important end-members are kaolinite minerals, true serpentines, berthierine, brindleyite, amesite, cronstedtite, greenalite, nepouite and their analogues having different substitutions in the octahedral sheets.