bluuebunny/crossref_metadata_2025_split huggingface dataset:
A chemical investigation of a chlorite intergrade mineral in the Keuper Marl
Authors: MacNeill S. 
Published: December 2006

AbstractAn extensive X-ray diffraction investigation of Keuper Marl samples from the English Midlands shows the existence of both chloritic and interlayered chloritic clays.Chemical experiments show that the interlayer component of the chloritic phase can be removed. This suggests that the ‘chloritic materials of unusual type’, known since the early 1950s to exist in the Keuper Marl, represent chlorite-montmorillonite intergrades.The mineralogy of any sample identified by an X-ray investigator, is influenced by the completeness of the chlorite interlayer. Since the amount of interlayer material is variable any ‘absolute’ differentiation between species is difficult.
Evolution of surface area in a sepiolite as a function of acid and heat treatments
Authors: Jiménez-López A. , López-González J. de D. , Ramīrez-Sāenz A. , Rodrīguez-Reinoso F. , Valenzuela-Calahorro C. , Zurita-Herrera L. 
Published: December 2006

AbstractThe variations in surface area of a sepiolite (Toledo, Spain) after acid and heat treatments (1 n to 5 n, HNO3, 110°C to 900°C for 100 h) have been studied. Surface areas have been determined from N2 adsorption isotherms at 77 K using B.E.T., Langmuir and Dubinin-Radushkevich equations. SBET values range from 65 up to 391 m2 g−1, the maximum value corresponding to the sample activated with 1 n HNO3 solution and treated at 300°C. SL and SD-R values are similar, but slightly larger than the corresponding SBET values.A correlated study has been carried out with samples activated with 1 n and 2 n HNO3 solutions and heat treated at 110, 200, 300, 400 and 500°C for 10 h. SBET values of these samples are rather similar to those of the corresponding samples treated during 100 h.
The effects of experimental conditions on the 950°C kaolinite exotherm in some tropical soil clays
Authors: Hughes J. C. 
Published: December 2006

AbstractSome predominantly kaolinitic tropical soil clays when examined by DTA in a nitrogen atmosphere gave two exothermic reactions (at ∼880°C and ∼950°C) instead of the usual single exotherm. During heating, iron present in the samples is reduced, possibly by organic carbon, and reacts with the metakaolin phase to form hercynite (FeAl2O4). The presence of Fe2+ also causes mullite to form at a lower temperature than normal. These reactions accompany the lower-temperature exotherm. The higher-temperature exotherm is due to formation of γ-alumina. Although this exothermic doublet is an artifact of the experimental conditions, its occurrence may help to elucidate the sequence of reactions involved in the metakaolinite recrystallization process.
A contribution to the study of the stability of clay minerals from the soil solution composition at different pF values
Authors: Fernandez-Marcos M. L. , Macías F. , Guitián-Ojea F. 
Published: December 2006

AbstractThe composition of the soil solution of various horizons of Galician soils was studied to gain insight into the direction of the processes of weathering and neoformation by means of stability diagrams of the clay minerals. The soil solution was extracted by compression at various pF values.The most significant results are as follows. In all the cases studied the mineral in equilibrium with the soil solution is a 1:1 philosilicate. As the pF at which the soil solution is extracted increases, corresponding to smaller pore size, pH increases and silica concentration falls. The stable mineral does not vary significantly between different horizons of the same profile. Each parent material gives rise to a different zonation in the stability diagrams. The predictions of the stability diagrams are in general agreement with the mineralogical data of the clays of the horizons in question.Finally, weathering processes in Galicia are briefly commented on.
Occurrence of chloritic intergrades in the Recent sediments of the Arno River (Italy)
Authors: Sartori F. , Riffaldi R. , Levi-Minzi R. 
Published: December 2006

AbstractClay mineral assemblages from a Quaternary sequence, sampled near the estuary of the Arno River, commonly contain some intergrade minerals, associated with other 14 Å phases and with illite and subordinate amounts of a kaolin mineral. The X-ray diffraction characteristics of such intergrade phases and their thermal modifications (100–600°C) are analysed and described.The effectiveness of some chemical treatments for removal of interlayer material is investigated and the results discussed on the basis of X-ray diffraction pattern and C.E.C. changes. Finally the properties of these intergrades are compared with those of the 14 Å phases present in the sediments carried by the Arno River and its tributary the Era River as well as with those of a soil from the Era watershed. Hypotheses are expressed about the probable relationships between degree of chloritization and characteristics of the depositional environments.
Origine et signification des zéolites dans les dépôts Cénomaniens de la bordure Sud-Est Du Massif Armoricain
Authors: Louail J. 
Published: December 2006

RésuméDes zéolites de la famille Heulandite-Clinoptilolite se rencontrent dans toute la série cénomanienne littorale péri-armoricaine dans des faciès pétrographiques variés. Souvent présentes à l'étal de traces, leur abondance apparait liée à certaines conditions pétrogénétiques qui peuvent se réaliser localement à diverses périodes mais se généralisent au Cénomanien supérieur provoquant une régionalisation de la ‘paragenèse’: Clinoptilolite, Smectites, Cristobalite.L'étude au microscope pétrographique et au microscope à balayage des échantillons les plus riches montre que la clinoptilolite se présente en cristaux automorphes dans des pores de dissolution intrasédimentaire. Son origine diagénétique est ici évidente; elle est postérieure à la dissolution des spicules de spongiaires et antérieure à la genèse de certaines sphérules de cristobalite. Ces néoformations se réalisent à partir des solutions interstitielles alimentées, au moins en partie, par l'altération de spicules de spongiaires, feldspaths détritiques, paillettes de mica, glauconie ...L'origine détritique de la clinoptilolite des sédiments crétacés de la bordure occidentale du bassin de Paris qui avait été envisagée doit donc être écartée; deplús la paragenèse zéolitesmectites-cristobalite ne peut ici être utilisée comme l'indice d'une activité volcanique en cours de dépôt. Une partie des smectites, qui remplit certains pores de dissolution, prend également naissance par diagenèse précoce.
The role of structural iron(III) in the UV absorption by smectites
Authors: Chen Y. , Shaked D. , Banin A. 
Published: December 2006

AbstractUV-visible light absorption spectra of dilute suspensions of standard and commercial montmorillonites (bentonites) and of nontronite, hectorite and pyrophyllite, were studied.All montmorillonites exhibit either an absorption band or a shoulder at a wavelength of 245 nm. The absorption peak for nontronite is shifted to 260 nm and absorption intensity is very high. Hectorite exhibits a very slight shoulder whereas pyrophyllite shows almost none. Absorption intensity in the UV range was found to be in direct correlation to structural octahedral Fe(III) contents. Direct evidence for the role of Fe(III) in the specific UV absorption of smectites was obtained by the fact that reduction with hydrazine fumes resulted in the disappearance of the peak and reoxidation with H2O2 caused its reappearance with even stronger intensity than originally. Mössbauer spectra showed that the Fe(III) disappeared almost completely in the reduced clay.
The stability, free energy and heat of formation of imogolite
Authors: Farmer V. C. , Smith B. F. L. , Tait J. M. 
Published: December 2006

AbstractFrom equilibrium silica concentrations over imogolite and boehmite at 100–155°C, the heat and free energy of the reaction (HO)3Al2O3SiOH + H2O ⇌ 2AlOOH + Si(OH)4 have been obtained: ΔH°r (298·15 K)=38·6 ± 4·1, ΔG°r (298·15 K) = 26.8 ± 1·1 kJ mol−1, and hence the heat and free energy of formation of imogolite: ΔH°f (298·15 K) = −3189·6 ± 4·1, ΔG°f (298·15 K) = − 2926·7 ± 1·1 kJ mol−1 These results are consistent with observations indicating that imogolite, halloysite and gibbsite can co-exist in soils, but that imogolite is metastable relative to either halloysite or gibbsite in the long term. At temperatures above 25°C there is a widening range of silica concentrations in which imogolite is more stable than halloysite, although both are metastable relative to kaolinite.
Quelques donnees sur la capacite calorifique et les proprietes de l'eau dans divers systemes poreux
Authors: Eger I. , Cruz-Cumplido M. I. , Fripiat J. J. 
Published: December 2006

RésuméL'eau présente dans les divers types de pores que contiennent des solides divisés a été étudiée par calorimétrie à balayage entre 200 et 270° K et sa chaleur spécifique a été mesurée entre 100 et 260° K. Les solides étudiés sont des argiles de la famille des smectites, l'endellite, des zéolites et une opale.Les informations obtenues à l'aide de ces techniques sont comparées à celles dérivées d'autres techniques notamment la résonance magnétique nucléaire et la spectroscopie infra-rouge.Des différences intéressantes sont observées entre des agrégats tri et bidimensionnels de molécules d'eau.
Application de mesures de conductivite hydraulique a l'etude de la structure des gels d'argile
Authors: Prost R. 
Published: December 2006

RésuméL'étude de la conductivité hydraulique sous de faibles charges de pâtes et de gels d'hectorite-Na, montre que:1.La loi de Darcy peut être appliquée,2.Le rayon hydraulique moyen qui est probablement relié à la distance moyenne entre les particules d'hectorite varie linéairement avec la teneur en eau et est très sensible à la présence d'électrolyte dans la suspension.
A soil vermiculite formed from a meta-gabbro, Loire-Atlantique, France
Authors: Ildefonse P. , Copin E. , Velde B. 
Published: December 2006

AbstractMicroprobe and atomic absorption analyses of large vermiculite crystals present in the upper horizon of a weathering profile on gabbro show that they differ appreciably in chemical composition. This together with the lack of any phyllosilicate precursor of comparable grain size, strongly suggests that the vermiculites were formed by precipitation of dissolved silicate matter, higher in the profile the vermiculite becomes unstable and is replaced by an Fe-rich smectite.
Rare earth elements in different size fractions of a marine quick clay from Ullensaker, and a till from Upper Numedal, Norway
Authors: Roaldset Elen 
Published: December 2006

AbstractThe distribution of rare earth elements (REE) in two different sediments, a marine clay and a till, was found to be dependent both on grain size and mineralogical composition. In the marine clay the REE content was highest in the coarsest fraction; in the till REE were markedly enriched in the finest fraction. Detrital and authigenic origins for different size fractions have been attributed on the basis of REE contents.
Natural and synthetic poorly crystallized lepidocrocite
Authors: Schwertmann U. , Taylor R. M. 
Published: December 2006

AbstractPoorly crystallized lepidocrocites precipitated from ferriferous spring waters differ from better crystallized samples by differentially broadened X-ray diffraction lines and higher basal spacings. On the basis of high magnification EM, this was explained as due to the fact that the lath-like crystals consist only of 3–15 unit layers with possibly weakened H-bonding between the layers. These properties are analogous to those of the so called ‘pseudoboehmite’ as compared to boehmite. Poorly crystallized lepidocrocites, exhibiting similar features, were synthesized by oxidation of Fe(II) solutions. From these experiments it was suggested that such lepidocrocite forms in nature by a rapid oxidation of Fe2+ in spring water when it emerges at the surface.
Iron in kaolinite: II. The relationship between kaolinite crystallinity and iron content
Authors: Mestdagh M. M. , Vielvoye L. , Herbillon A. J. 
Published: December 2006

AbstractCalibration of the internal and external signals appearing at geff ∼4 in the electron paramagnetic resonance (EPR) spectra of twenty-four kaolinites, has led to the recognition of two types of kaolinite-iron. The amount of iron associated with the internal signal (I iron) shows good inverse correlations with parameters used to describe the degree of crystalline perfection in kaolinite. Iron associated with the external signal (E iron) is insensitive to crystalline order. By considering both the amount and nature of the iron, the kaolinites investigated are placed in three groups. The first contains well-crystallized varieties characterized by low total iron and EPR spectra consisting mainly of an E signal. Poorly-crystallized kaolinites contain more iron and are characterized by a fifty-fifty partition of this iron into E and I sites. The third group contains samples which are intermediate with respect to both the amount and nature of the iron.
Transient fluorescence studies on sepiolite suspensions
Authors: Ridler P. J. , Jennings B. R. 
Published: December 2006

AbstractMeasurements have been made of the transient changes in the polarized components of fluorescence when aqueous suspensions of dye-tagged sepiolite particles were subjected to pulses of high frequency alternating electric field. The dye was acridine orange, a planar, cationic molecule. From these measurements, the size and electrical prolarizability of the sepiolite particles was evaluated and the directions of the absorption and emission transition moments responsible for the fluorescence of the dye located. The dye molecules were shown to adsorb on the clay surface with their long axes parallel to the sepiolite rods. Adsorption of the dye molecules in the surface channels of the clay was indicated. The electrical polarizability was considered and compared with the cation exchange capacity of the mineral. A novel, rapid means of studying clay minerals is indicated hereby.
Mineralogical composition of the clay fraction of two fluvio-glacial sediments from east Greenland
Authors: Petersen L. , Rasmussen K. 
Published: December 2006

AbstractThe < 2µm fractions of two fluvio-glacial sediments from East Greenland have been analysed chemically and by XRD and Mössbauer spectroscopy. The bulk of each < 2µm fraction consists of feldspars and micas (biotite) which are important constituents of the Precambrian igneous and metamorphic rocks of the area. Significant amounts of vermiculitic and smectitic minerals are also present. Compared with similar minerals present in Danish soil clays, the Greenland vermiculite and smectite are characterized by a high degree of crystallinity and it is concluded that these minerals have been formed from biotite through K release and lattice expansion. These processes appear to have proceeded at a sufficiently high rate to yield significant amounts of vermiculite and smectite despite the cold climate prevailing in the area.
Facteurs determinant la structure de la couche interlamellaire des vermiculites saturees par des cations divalents
Authors: Alcover J-F. , Gatineau L. 
Published: December 2006

RésuméL'organisation de l'espace interlamellaire des vermiculites a été comparée en fonction: (i) de la nature du cation (Mg, Ni, Ca, Sr et Ba) et de son état d'hydratation (bicouche, monocouche et anhydre), (ii) de la nature du feuillet (charge et localisation des substitutions). Le facteur prépondérant, celui qui confère à l'espace interlamellaire son caractère ordonné ou non, est la nature du cation en particulier sa taille et son degré d'hydratation. La charge du feuillet apparaît comme un facteur complémentaire, elle limite la taille des domaines ordonnés.
Single-crystal X-ray study of mixed structures of vermiculite and biotite (hydrobiotites)
Authors: Weiss Zdeněk 
Published: December 2006

AbstractThe Weissenberg method has been used to study crystalline fragments of hydrobiotites from Stupná near Křemže, Czechoslovakia. The intensity distribution for basal reflections recorded in zero-level photographs indicates that most ‘single crystals’ are nearly regular interstratifications of vermiculite and biotite. Proportions of vermiculite in these interstratifications lie between 12 and 60%.
The application of electron spin resonance spectroscopy to studies of clay minerals: II. Interlamellar complexes—structure, dynamics and reactions
Authors: Hall Peter L. 
Published: December 2006

AbstractA review is given of the application of ESR spectroscopy to the study of hydrated transition metal ions and nitroxide spin probes in the interlamellar region of smectites and vermiculites. These investigations have not only provided information regarding the structure and mobility of the intracrystalline water-cation layers but have also demonstrated the reactivity and catalytic properties of certain transition metal exchange forms of smectites. Several novel coordination complexes and redox reactions between the exchange ions and a variety of simple organic molecules have been characterized.
Influence des proprietes des charges kaoliniques sur les performances des caoutchoucs naturels charges
Authors: Yvon J. , Cases J. M. , Lietard O. , Garin P. , Lhote F. 
Published: December 2006

RésuméAprès avoir défini la notion de charge minérale, on étudie la nature et le nombre des défauts cristallins d'argiles kaoliniques. On montre l'influence des défauts d'empilement (interstratification de feuillets potassiques) et des défauts dans le plan (conséquence des substitutions de l'aluminium) sur les propriétés mécaniques des caoutchoucs chargés. Puis on étudie l'influence de la pureté minéralogique et de certains paramètres superficiels sur les performances des produits chargés. Enfin, on propose des méthodes de traitement qui permettent d'accroître les propriétés renforçatrices de la charge. On présente l'évolution comparée de 64 paramètres descriptifs de la charge et du produit fini en définissant des guides de prospection et de traitement qui permettent l'utilisation optimale des réserves charentaises dans le domaine des caoutchoucs naturels.
Formation and properties of Fe(II)Fe(III) hydroxy-carbonate and its possible significance in soil formation
Authors: Taylor R. M. 
Published: December 2006

AbstractSmall amounts of Fe(III) induce precipitation of Fe(II) from carbonate solutions around neutral pH values. The reaction involves the formation of Fe(II)Fe(III) hydroxycarbonate, a green, layer-structured compound of the pyroaurite group of minerals. Variations in the concentration of Fe(II) in the solution phase, and in the form and amounts of the total Fe(III) in the system, may cause other phases such as magnetite and siderite to form also. Freeze-dried Fe(II)Fe(III) hydroxy-carbonate undergoes topotactic alteration to a magnetic phase, presumably maghemite, when stored under vacuum. The compound is readily oxidized in air in either the moist or dry state, rapidly becoming yellow or yellow-brown in colour. Oxidation leads to the formation of either goethite, lepidocrocite, ferrihydrite or mixtures of these phases, depending on the mode of oxidation and the impurities present. The similarity between the rapid colour changes and the oxidation products of the blue-green precipitates in gleyed soil horizons and this Fe(II)Fe(III) hydroxy-carbonate leads to the speculation that this and related compounds may be the meta-stable precipitates in such soils, rather than a previously postulated hydro-magnetite phase. Eh and pH conditions for the formation of Fe(II)Fe(III) hydroxy-carbonate are given, and are in the range encountered in the soil environment.
Characterization of clays by organic compounds
Authors: Lagaly G. 
Published: December 2006

AbstractMany problems—from soil research to ceramics—require a reliable characterization of the clay minerals involved. This can be done using four clay-organic reactions: (i) staining tests and dye adsorption; (ii) glycerol and glycol adsorption; (iii) intercalation; (iv) alkylammonium ion exchange. Dye adsorption (staining tests) and glycerol adsorption allow a preliminary identification of the clay mineral groups. Intercalation reactions indicate minute differences between kaolins which cannot be detected by XRD and DTA. Alkylammonium ion exchange provides the best method for characterizing smectites and is sensitive to changes in the layer charge.
Utilisation du rayonnement synchrotron en diffusion aux petits angles pour l'étude du gonflement des smectites: I. Etude du systeme eau-montmorillonite-Na en fonction de la temperature
Authors: Pons C. H. , Rousseaux F. , Tchoubar D. 
Published: December 2006

ResumeNous proposons l'étude du mècanisme de gonflement d'une smectite, basée sur l'exploitation des diagrammes de diffusion aux petits angles obtenus avec la source de rayons X synchrotron de Lure (Orsay). Cette technique a permis d'étudier le gonflement, en fonction de la température, d'une montmorillonite Na, en suspension dans l'eau et concentrée à 20%.L'analyse des diagrammes est éffectuée par une méhode basée sur la comparaison des courbes expérimentales à des courbes théoriques. Les modèles de structure permettant le calcul des diagrammes théoriques fait appel à la notion de particule (définie comme un empilement de feuillets parallèles) et de structure interne de la particule (définie par un ensemble de translationsdiaffectées des probabilitéspiqui déterminent la position mutuelle des feuillets).Les résultats montrent qu'à basse température, les particules de très grande taille sont constituées par la superposition de sous empilements, comportant 4 à 5 feuillets, hydratés d'une manière homogène et se désorientant mutuellement pour former la structure du gel. On explique ainsi que la structure du gel formé est correlée avec celle du solide initial et que le phénomène de gonflement est quasi réversible.
Formation of gibbsite in soils and saprolites of temperate-humid zones
Authors: Macías Vazquez F. 
Published: December 2006

AbstractAnalysis of the distribution of gibbsite in soils and saprolites of Galicia, NW Spain, leads to the conclusion that this mineral is mostly formed by inorganic mechanisms in open, well-drained and desaturated systems in the initial stages of weathering of various aluminosilicates, especially plagioclases. No evidence has been found to support the hypothesis that it is a feature inherited from hotter climates, as it has not been identified to date either in ancient sediments or in the most evolved and weathered soils. The role of organic matter and the possibility ofa biogeochemical origin is also discussed: it is considered that this mechanism is only important during podsolic soil development.
Variation du parametrebet de la distance basale d001dans une serie de saponites a charge croissante: I. Etats hydrates
Authors: Suquet H. , Malard C. , Copin E. , Pezerat H. 
Published: December 2006

RésuméNeuf saponites synthétiques ont été utilisées pour étudier l'influence des substitutions Si-Al sur le paramètrebet la distance basale d001des phyllosilicates 2/1 trioctaèdriques. Dans les saponites hydratées à deux couches, le paramètre best le résultat des interactions entre couches octaèdrique et tétraèdriques. Dans les saponites hydratées à une couche, il dépend non seulement des paramètres des couches octaèdrique et tétraèdriques mais encore de la nature de la couche interfoliaire. L'effet du cation interfoliaire varie avec sa taille et sa localisation dans l'espace interfoliaire.