bluuebunny/crossref_metadata_2025_split huggingface dataset:
Naturally-Occurring Silicates as Carriers for Copper Catalysts used in Methanol Conversion
Authors: Sun Kou M. R. , Mendioroz S. , Fierro J. L. G. , Rodriguez-Ramos I. , Palacios J. M. , Guerrero-Ruiz A. , De Andres A. M. 
Published: August 2006

AbstractBentonite- and sepiolite-supported copper catalysts have been prepared either by adsorption of Cu(II) from aqueous solutions of copper nitrate at pH ~4.5 or by adsorption of a [Cu(NH3)4]2+ complex from an ammonia solution of CuSO4 at pH ~9.5. The structure and composition of the calcined preparations have been studied by X-ray diffraction, chemical analysis, and energy dispersive X-rays. Textural characteristics have derived from the analysis of the adsorption-desorption isotherms of N2. All catalysts have been tested for the dehydrogenation of methanol to methyl formate. For this reaction, bentonite-based catalysts were found to have very little activity, which indicates that copper located in the inter-lamellar spaces is inaccessible to methanol molecules. On the contrary, copper-sepiolite catalysts showed a very high specific activity even for those catalysts with a very low copper content. The chemical state of copper in the catalysts on-stream has been revealed by X-ray photoelectron spectroscopy and X-ray-induced Auger techniques. In most of the catalysts Cu+ is the dominant copper species.
Iron Oxide-Clay Mineral Association in Brazilian Oxisols: A Magnetic Separation Study
Authors: Fontes Mauricio Paulo Ferreira 
Published: August 2006

AbstractSelected Brazilian Oxisols were sampled and submitted to high-gradient magnetic separation (HGMS) to study the iron oxide-clay mineral associations. The soils, derived from four different parent materials, have mineralogy dominated mostly by hematite, goethite, and kaolinite. Gibbsite appears in most soil samples. The high-gradient magnetic separation showed good separation for some soils, as indicated by color differentiation and iron oxide segregation between magnetic and nonmagnetic fractions. Soils that showed a somewhat low surface area for the iron oxides associated with high phosphate adsorption were poorly separated by HGMS. This suggests a strong interaction between kaolinite and iron oxides, which would indicate a low estimation of their surface areas obtained by the difference method using BET-N2 data. A relative concentration of anatase and rutile in the magnetic portion of some of the samples was attributed to the presence of Fe, either as coatings on the crystals or within the structure of these two minerals.
A New Method of Dehydration for Pure Clay Materials using Peldri II
Authors: Wierzchoś Jacek , Ascaso Carmen , Garcia-Gonzalez Maria Teresa , Kozak Edmund 
Published: August 2006

AbstractA new chemical, Peldri II, is evaluated as a compound for drying soft clay materials. Peldri II, a fluorocarbon (1,1-difluorotetrachloroethane), is a solid at room temperature and is a liquid above 25°C. Clay gels are embedded in Peldri II by immersing them in the liquid and allowing it to solidify. Once solidified, Peldri II will sublime, with or without vacuum, to a dry specimen, probably without introducing surface tension. Wyoming montmorillonite saturated in 10−3 M NaCl and 1 M CaCl2 solutions has been examined to compare preservation of its initial structure after Peldri II, critical point, and freeze drying techniques. Transmission electron microscopy of ultrathin sections, scanning electron microscopy, and mercury intrusion porosimetry techniques were used. No differences were detected between Peldri II and critical point drying methods. Peldri II appears to be a significant improvement as an alternative drying agent for clay materials in studies of their structural properties. It is also very convenient for drying large numbers of samples.
39K Solid-State NMR Studies of Potassium Tecto- and Phyllosilicates: The In Situ Detection of Hydratable K+ in Smectites
Authors: Lambert J.-F. , Prost R. , Smith M. E. 
Published: August 2006

AbstractWe report the first application of 39K solid-state NMR to the study of tecto- and phyllosilicates. Under high field (11.7 Tesla) and with the application of a spin-echo sequence, informative 39K spectra can be obtained for several compounds of interest to the geologist and the agronomist. Tectosilicates and phyllosilicates can be distinguished from the uncorrected frequency (δCG) of the observed NMR peak. A series of montmorillonites submitted to increasing numbers of wetting and drying cycles was studied in order to discriminate between mobile and “fixed” forms of K+: when the spectra are run on hydrated samples, two different signals are observed corresponding to K+ in different hydration states, and NMR data can be correlated with the amount of exchangeable K+ measured by ion exchange. Thus, it appears that NMR can provide useful information on K fixation complementary to classical chemical methods.
Randomly Interstratified Serpentine/Chlorite: Its Detection and Quantification by Powder X-ray Diffraction Methods
Authors: Reynolds R. C. , DiStefano M. P. , Lahann R. W. 
Published: August 2006

AbstractX-ray diffraction studies of the pore-lining chloritic mineral from the Tuscaloosa Formation disclose a marked pattern of odd-order line broadening for the 001 to the 00,16 reflections. The odd-order peaks are approximately twice as broad as the even orders after correction for instrumental broadening effects. These results are consistent with a randomly interstratified 7-Å/14-Å structure, which is most likely serpentine/chlorite. Quantitative analysis of line broadening and model calculations indicate that the serpentine/chlorite contains 7% serpentine layers.A simplified method is proposed for quantifying randomly interstratified serpentine/chlorite. Residual line broadening (βr) is obtained from the half-height widths of uncorrected diffraction profiles for the 004 and 005 “chlorite” reflections by means of the following: βr=(β0051.25−β0041.25)11.25.Percent serpentine in the random interstratification is computed from the empirical expression
%S=−0.51+24.27βr, which is valid from about 1 to 20 percent serpentine.
Inverse Gas Chromatography Study of Modified Smectite Surfaces
Authors: Bandosz Teresa J. , Jagiełło Jacek , Andersen Brannon , Schwarz James A. 
Published: August 2006

AbstractInverse gas chromatography at infinite dilution, employing alkanes and alkenes as probes, has been used to characterize the surface properties of a series of smectites of varying chemical composition. The results of this study show that the acidic centers and the interlayer distances have a great influence on the specific interaction of the smectite surface with π-bonds of alkenes. High values of the specific interaction parameter, ɛπ, are caused by the existence of strong acidic centers that are connected with interlayer cations as well as with the chemical structure of the mineral sheets. On the other hand, alkanes, whose interaction with the smectites is predominantly dispersive, are unaffected by changes in the clays’ composition and/or structure.
Structural Characterisation of Kaolinite:NaCl Intercalate and its Derivatives
Authors: Thompson John G. , Uwins Philippa J. R. , Whittaker Andrew K. , Mackinnon Ian D. R. 
Published: August 2006

AbstractKaolinite:NaCl intercalates with basal layer dimensions of 0.95 and 1.25 nm have been prepared by direct reaction of saturated aqueous NaCl solution with well-crystallized source clay KGa-1. The intercalates and their thermal decomposition products have been studied by XRD, solid-state 23Na, 27Al, and 29Si MAS NMR, and FTIR. Intercalate yield is enhanced by dry grinding of kaolinite with NaCl prior to intercalation. The layered structure survives dehydroxylation of the kaolinite at 500°–600°C and persists to above 800°C with a resultant tetrahedral aluminosilicate framework. Excess NaCl can be readily removed by rinsing with water, producing an XRD “amorphous” material. Upon heating at 900°C this material converts to a well-crystallized framework aluminosilicate closely related to low-carnegieite, NaAlSiO4, some 350°C below its stability field. Reaction mechanisms are discussed and structural models proposed for each of these novel materials.
Morphology, Texture, and Microstructure of Halloysitic Soil Clays as Related to Weathering and Exchangeable Cation
Authors: Delvaux B. , Tessier D. , Herbillon A. J. , Burtin G. , Jaunet Anne-Marie , Vielvoye L. 
Published: August 2006

AbstractThis paper aims at characterizing the morphology, texture, and microstructure of three hydrated kaolin rich clays (f < 0.2 μm) from volcanic soils. These clays represent a weathering sequence in which CEC, halloysite content with respect to kaolinite, as well as smectite content in the halloysite-smectite mixed-layer clays decrease with increased weathering. The clay samples were made homoionic (K+ or Mg2+) and hydrated under a low suction pressure (3.2 kPa). After replacing water by a resin, ultrathin sections were cut and examined by TEM. Particle shape varies with increased weathering, as follows: spheroids → tubes → platelets. Higher aggregation and dispersion are observed by TEM after Mg2+ and K+ saturation, respectively, at two levels of the clay-water system organization: intraparticle and interparticle. The microstructure variations induced by the nature of the exchangeable cation become less pronounced with decreasing layer charge of the 2:1 layers. They are thus related here to the presence of smectite layers localized in the halloysite habitus, mostly at the particle periphery. These results show that small amounts of smectite largely affect the organization of clays rich in kaolins at a high water content, and that K+ behaves here as a dispersing ion.
Effect of Tartaric Acid and Ph on the Nature and Physicochemical Properties of Short-Range Ordered Aluminum Precipitation Products
Authors: Violante A. , Huang P. M. 
Published: August 2006

AbstractThe influence of tartaric acid and pH on chemical composition, morphology, surface area, and porosity of short-range ordered Al precipitation products was studied. Samples were prepared (1) at pH 8.0 and at the tartaric acid/Al molar ratios (R) ranging from 0 to 0.25 and (2) at R = 0.1 and in the pH range of 4.7 to 10.0. In Al precipitation products formed at pH 8.0, the organic C content increased from 8 g/kg (R = 0.01) to 93 g/kg (R = 0.25), whereas the Al content decreased from 363 g/kg (R = 0.01) to 271 g/kg (R = 0.25). The specific surface of the materials was particularly high (>400 m2/g) when samples were prepared at R < 0.1, but drastically decreased when samples were prepared at R > 0.1 (e.g., 78.6 m2/g at R = 0.25). When the C content was relatively high (>45 g/kg), aggregation between the particles was promoted, and the specific surface, thus, decreased. Electron optical observations showed that such samples were strongly aggregated. In the materials prepared at R = 0.1, but at different initial pH values, the C content decreased from 90 g/kg (pH = 4.7) to 25 g/kg (pH = 10.0). As a consequence, the lower the initial pH, the lower was the specific surface of the Al precipitation products. Tartaric acid plays an important role in both Pertubation of crystallization of Al hydroxides and promotion of aggregation of the reaction products. The two processes counteract in influencing the specific surface and pore volume of Al hydroxides.Heating treatments greatly affected the specific surface and porosity of Al precipitation products. The specific surface and porosity of the samples generally increased by increasing the temperature up to 400°C and then decreased. Small amounts of C still remained after heating some samples for 12 hr at 600°C.
Computer Simulation of Cation Distribution in Dioctahedral 2:1 Layer Silicates Using IR-Data: Application to Mössbauer Spectroscopy of a Glauconite Sample
Authors: Dainyak Lydia G. , Drits V. A. , Heifits L. M. 
Published: August 2006

AbstractA new approach is described to computer simulate cation distribution in octahedral sheets of dioctahedral 2:1 layer silicates with vacant trans-octahedra. This approach makes use of the information on cation distribution at the one-dimensional level provided by integrated IR optical densities for the region of OH-stretching frequencies. By using this program it is possible to show that (1) the Mössbauer spectrum of glauconite B. Patom conforms to the structural model composed of celandonite-like and illite-like domains whose dimensions are limited by approximately 2 or 4 unit cells; (2) non-equivalency of “left” and “right” cis-positions (with fixed b-direction) with respect to R2+ and R3+ occupancy is a characteristic feature of a celadonite-like domain.
Diagenetic Illite-Chlorite Assemblages in Arenites. I. Chemical Evolution
Authors: Jahren J. S. , Aagaard P. 
Published: August 2006

AbstractAuthigenic chlorites and illites coexisting in clastic reservoir sandstones have been studied by energy dispersive X-ray spectroscopy (EDS) in the transmission electron microscope (TEM). All 16 samples studied are drill or sidewall cores from sandstones of relatively uniform age situated offshore Norway with burial depths ranging between 2400 m and 5000 m and representing temperatures between 90°C and 180°C. Chlorites and illites with authigenic equilibrium type texture and morphology were analyzed by EDS. Tetrahedral Al and octahedral Fe+Mg in chlorite increases with burial at the expense of Si and vacant octahedral positions in the chlorite structure. Illites show a clear increase in K. These factors indicate that a continuous chemical modification of these minerals takes place in the diagenetic interval studied through continuous dissolution and precipitation reactions.
Diagenetic Illite-Chlorite Assemblages in Arenites. II. Thermodynamic Relations
Authors: Aagaard P. , Jahren J. S. 
Published: August 2006

AbstractThe internal equilibrium status among chlorite-illite pairs has been evaluated through coupled substitution reactions. Compositional data of chlorites and illites from arenites at present burial temperatures between 90° and 180°C have been used to calculate end member activities and reaction quotients of the combined Tschermak reaction:
Muscovite+Clinochlore=MgAl−celadonite+Amesite.The reaction quotient data in the 90° to 180°C temperature range have then been compared with the equilibrium curve for the same reaction, and found to be in reasonable agreement. This indicates that chlorites and illites in these arenites grow at near equilibrium conditions.The data set has also been compared with chlorite-illite pairs from hydrothermally altered arenites of the Salton Sea area. For chlorite-illite containing assemblages, these data agree well with the diagenetic ones. The introduction of biotite at higher temperatures alters with the iron-magnesium distribution and breaks down the substitution relationship between chlorite and illite.The model predicts an increasing stability of muscovite and clinochlore components with increasing temperature, while celadonite and amesite would be stabilized with increasing pressure. This is consistent with high pressure occurrences of phengite. However, at the low pressure region of diagenesis and hydrothermal alteration, the temperature effect is dominant.
Sedimentary Structure in Gray Kaolins of Georgia
Authors: White G. Norman , Dixon J. B. , Weaver R. M. , Kunkle A. C. 
Published: August 2006

AbstractOne Tertiary and two Cretaceous gray kaolin sites in Georgia were examined using X-ray radiography of core sections to determine the processes of formation of the deposits. The Tertiary kaolin was oxidized in the upper 3 m of the deposit and reduced below that point. The two Cretaceous kaolins were reduced from the top of the deposit to an abrupt boundary with oxidized red kaolin below. Radiography of the first Cretaceous core revealed thin laminar bedding in the gray kaolin and in the underlying red kaolin. The laminae continue without interruption across the gray kaolin/red kaolin boundary. The laminae were not visible in the gray kaolin except in radiographs. Sedimentary bedding was not observed visually or radiographically at the Tertiary site nor in sections of the core from the second Cretaceous site where kaolinite was recrystallized to large vermiforms. The original sedimentary structure in the first Cretaceous kaolin was preserved possibly due to the inhibition of kaolinite recrystallization by a higher organic matter content. Recrystallization of kaolinite and iron compounds may have destroyed sedimentary structures in part or all of the other two kaolin cores. It is hypothesized that the first Cretaceous physical and biological mixing. The same hypothesis may apply to the other two kaolins but recrystallization after deposition has destroyed sedimentary structures.
Sedimentation Behavior of a Fine Kaolinite in the Presence of Fresh Fe Electrolyte
Authors: Ma Kunsong , Pierre Alain C. 
Published: August 2006

AbstractThe sedimentation behavior of a fine kaolinite, comprising a substantial proportion of colloidal particles as well as non-colloidal ones, has been studied when fresh FeCl3 or F2(SO4)3 electrolytes are added. The sedimentation behavior depends on the pH and the nature of electrolytes and can be explained qualitatively, in our study, by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO theory). Fe helps also to aggregate the kaolinite particles in flocs. Two extreme kinds of qualitative sedimentation have been observed: flocculation-sedimentation and accumulation-sedimentation. However, the transition between the two kinds of sedimentation is quite progressive. The present results are discussed in reference to the DLVO theory and the hydrolysis behavior of Fe electrolytes.
Color Variations Associated with Rapid Formation of Goethite from Proto-Ferrihydrite at pH 13 and 40°C
Authors: Nagano T. , Nakashima S. , Nakayama S. , Osada K. , Senoo M. 
Published: August 2006

AbstractColor variations from brown to yellow of synthesized goethite have been studied colorimetrically and spectroscopically. Goethite with various colors was synthesized at pH 13 and 40°C by varying the incubation time. Colorimetry revealed that the b* value (yellowish chroma) in L*a*b* color space was a quantitative indicator of color variations of the diluted samples. From UV-VIS-NIR spectra, the increase in the b* value was found to be caused by the increase in crystal field absorptions due to goethite formation around 500 nm. The b* value was a good indicator of the relative proportion of goethite in the precipitates including ferrihydrite. X-ray diffraction patterns and infrared spectra revealed that crystallization of goethite was associated with loss of water from the proto-ferrihydrite.
Charge Reversal of Kaolinite by Hydrolyzable Metal Ions: An Electroacoustic Study
Authors: Hunter Robert J. , James Michael 
Published: August 2006

AbstractElectroacoustic measurements at 1 MHz, using the Electro-Sonic Amplitude (ESA), on a kaolinite suspension provide a ready method for following the adsorption of hydrolyzable metal ions onto the clay surface. Co2+, Cd2+ and Cu2+ ions show similar behavior: The initially negative surface becomes less negative, approaches zero, and may become positive at pH values around neutral, depending on the initial metal concentration. At higher pH, electrokinetic potential goes through a maximum. If the surface has become positive, it becomes less so; and at still higher pH values it may become negative again, depending on the metal ion concentration. The behavior can be interpreted using the model proposed by James and Healy.
Shale Diagenesis: A Case Study from the Albian Harmon Member (Peace River Formation), Western Canada
Authors: Bloch J. , Hutcheon I. E. 
Published: August 2006

AbstractShales have often been cited as the source of authigenic material that occurs in coarser grained sediments, but there are few comprehensive studies of diagenesis in shales that rigorously attempt to determine if they are sources for potentially mobile constituents or if they retain those constituents within the shale body. The silicate diagenesis of a Lower Cretaceous marine mudstone, the Harmon Member, was investigated by determining the bulk chemistry, clay mineral compositions and mineral modes using standard analytical techniques and linear programming. Changes in mineralogy are observed in hemipelagic laminated mudstones (LM) that are attributable to diagenesis despite relatively constant bulk compositions. These include authigenic kaolinite formation and illitization of detrital muscovite, K-feld-spar and authigenic kaolinite. No diagenetic trends in mineralogy are observed in rapid and episodically deposited transition zone (TZ) sediments because of primary (depositional) mineralogical variability. Diagenetic changes in mineral modes for shales of the Harmon Member are small, suggesting that silicate diagenesis proceeds under relatively “closed system” conditions. The occurrence of authigenic quartz suggests that much of the Si released from the dissolution of quartz and chert is precipitated within the Harmon Member. Al, Ti, and K apparently are conserved. Burial induced increase in temperature is inferred to be the primary control on silicate diagenesis within the Harmon Member.
Effects of Acidification on the Chemical Composition and Layer Charge of Smectite from Calcareous Till
Authors: Warren C. James , Dudas Marvin J. , Abboud Salim A. 
Published: August 2006

AbstractThe objectives of the study were to determine the chemical composition and layer charge of smectite found in calcareous till of the Interior Plains region of western Canada and to examine the effects of acidification on alteration of the smectite. Samples of acidified and non-acidified (calcareous) late-Wisconsin till were obtained from four soil pits located immediately adjacent to an elemental sulfur block located in southern Alberta. Samples of the surface material (0–10 cm depth) had been subjected to extreme acidity for 25 years due to the oxidation of elemental sulfur and displayed pH values of about 2.0. Samples of the till obtained at depth (65–75 cm) remained calcareous with pH values between 7.3 and 7.6. A combination of analytical methods was used to determine the chemical composition of the smectite found in the samples. The layer charge of the smectite was determined independently using X-ray diffraction data for n-alkylammoniurn saturated specimens. Smectite found in the non-acidified calcareous material was characteristic of montmorillonite with a low content of Fe and very little substitution of Al for Si in the tetrahedral sheet. The smectite had a structural formula of M+0.40(Si3.96Al0.04)(Al1.56Fe3+0.10Mg0.33)O10(OH)2, which compared well with a mean value for layer charge of 0.399 mol(−)/O10(OH)2 determined using X-ray diffraction data for n-alkylammonium treated specimens. Smectite remaining in the till material subjected to extreme acidity underwent incongruent dissolution with a net loss of layer charge and preferential loss of octahedral Mg.