bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Solution Conditions on the Proportion and Morphology of Goethite Formed from Ferrihydrite
Authors: Cornell R. M. , Giovanoli R. 
Published: September 2006

AbstractIn alkaline media and at 70°C dilute suspensions of ferrihydrite transformed to goethite between pH 11.2 and 14 and to a mixture of goethite and hematite above and below this pH range. Increasing the temperature of the transformation or the concentration of the suspension reduced the pH range in which goethite alone formed. The morphology of goethite was chiefly a function of the pH of the system. Acicular crystals formed at all pHs and exclusively above pH 12.2. Epitaxial twinned crystals predominated at pHs below 11, and twins free from hematite formed at higher pHs. Increasing the suspension concentration, ionic strength, or temperature extended the pH range over which twinned crystals formed. Electron micrographs showed that twins formed mainly during the initial stage of the transformation, whereas acicular crystals formed over a longer period. Thus, the twins appeared to nucleate in the ferrihydrite; nucleation of acicular particles took place in solution.
Structure and Growth Mechanism of Glauconite as Seen by High-Resolution Transmission Electron Microscopy
Authors: Amouric Marc , Parron Claude 
Published: September 2006

AbstractThe internal fabric of glauconite pellets has been studied by high-resolution transmission electron microscopy (HRTEM) for a better understanding of the glauconitization process. Typical “lamellae” which make up the glauconite pellets showed a spindle-like arrangement of layered crystallite packets. Three main mineral phases were detected: (1) well-ordered glauconite sensu stricto (d(001) = 10 Å) generally in the middle of the spindles; (2) a poorly ordered and undetermined layered-phase “X” with d(001) ~ 12.5 Å, usually sandwiching glauconite such that the interface between the two materials is very sharp; and (3) a noncrystalline or gel-like phase located between the lamellae. A 14-Å smectite-like phase was rarely observed at the periphery of some grains. The glauconite crystallites clearly showed characteristic growth features (e.g., growth steps), whereas the unknown phase X exhibited destabilization characteristics. A structural analysis of the pure glauconite indicates that this dioctahedral mica was present in the IMd (disordered), 1M, and, to a much lesser extent, 2M1 polytypic forms. HRTEM revealed no interlayering of glauconite with the other layered phases. Rather, it appeared to have formed by a layer-growth mechanism at the expense of the unknown phase X which apparently converted into non-crystalline matter before converting to glauconite. The precursor function of the interlamellae “gel” phase during the evolutive process of glauconitization is not understood.
Swelling Pressure Calculated from Mineralogical Properties of a Jurassic Opalinum Shale, Switzerland
Authors: Madsen Fritz T. , Müller-Vonmoos Max 
Published: September 2006

AbstractNineteen drill core samples of lower Dogger opalinum shale from wells drilled in connection with a tunnel project near Brugg, northern Switzerland, were investigated. The shale is a well known swelling rock that has caused problems in underground construction work. Swelling pressures determined under constant volume conditions to obtain maximum values were 0.7 to 2.2 N/mm2. The samples contained 37–59% clay-size material and about 35% quartz, 7–18% carbonate minerals, and about 5% feldspar, pyrite, and organic matter. In addition to kaolinite, illite, and chlorite, the clay-size fraction also contained mixed-layer illite/smectite with about 30% swelling layers. The specific surface area of the clay fraction was 135 m2/g. The specific surface charge of the clay (6.7 × 104 esu/cm2), the ion concentration in the pore fluid of the specimen after the swelling test (10−2 mmole/cm3), the valence of the ions in the double layer of the clay particles (+1), and the half distance between the clay plates in the specimen (8–15 Å) allowed the calculation of the swelling pressure for each sample according to the Gouy double layer theory.The mean value of the calculated swelling pressures was found to be of the same order of magnitude as the measured values, indicating that the technique can be used where cylindrical or rectangular specimens are not available for direct measurement.
Surface Reactions of 3,3′,5,5′-Tetramethyl Benzidine on Hectorite
Authors: McBride M. B. 
Published: September 2006

AbstractThe adsorption and oxidation of 3,3′,5,5′-tetramethyl benzidine (TMB) on hectorite has been investigated using X-ray powder diffraction, ultraviolet-visible spectroscopy, electron spin resonance, and infrared spectroscopy. The molecule adsorbed by cation exchange at low adsorption levels and oxidized to the monomeric radical cation (yellow). At higher adsorption levels, intercalation of TMB occurred in amounts greater than the cation-exchange capacity of the hectorite, and the π-π charge-transfer complex (blue) became much more evident. The TMB monomers appeared to lie flat in the layer silicate interlayers, whereas the molecules in the charge-transfer complexes assumed a near-vertical orientation relative to the surface. The oxidation of adsorbed TMB was probably due to diffusion of O2 to the surface, because the structural Fe3+ content of the hectorite was too low to facilitate a significant quantity of direct Fe3+-TMB electron transfer.
Kaolinization of Bauxite: A Study in the Vlasenica Bauxite Area, Yugoslavia. I. Alteration of Matrix
Authors: Dangić Adam 
Published: September 2006

AbstractThe kaolinization of bauxite has generally been thought to be a simple process of epigenetic resilification. A study of the karstic boehmitic bauxites in the Vlasenica region of Yugoslavia, however, shows that kaohnization took place in a rather complex manner, in which the alteration was caused by the percolation of siliceous water descending through the deposit by means of cracks, fissures, etc. The matrix of one such Vlasenica deposit was found to be more highly kaolinized than the oolitic fraction. Based on a mineralogical and geochemical examination of matrix material, the following pattern of zoned alteration was identified: kaolinitic zone-boehmite enrichment zone-original bauxite. In the kaolinitic zone, well-crystallized kaolinite, formed by the reaction of dissolved silica with boehmite, has replaced all other minerals in the matrix. This Si metasomatism was accompanied by an outward migration of Al and resulted in the formation of a transition zone in which new boehmite partly replaces both kaolinite and hematite (Al remobilization). A thermodynamic model of the process has been established on the basis of stability diagrams calculated for the mineral assemblages in the alteration zones and in the deposit as a whole.
Role of Structural Hydrogen in the Reduction and Reoxidation of Iron in Nontronite
Authors: Lear Paul R. , Stucki Joseph W. 
Published: September 2006

AbstractThe effects of reduction and reoxidation of octahedral Fe3+ on the exchange of structural hydrogen in nontronite were determined using tritium (3H) as a label element. The uptake of H from the surrounding solution of nontronite suspensions increased as the reduction of structural Fe3+ increased. Similarly, the loss of H from the structure increased as the reduction increased. The results are generally consistent with a reduction mechanism involving the loss of structural OH, leaving the affected Fe sites with less than six-fold coordination. The attenuation of increased negative charge on the clay layer, however, was less than predicted by such a mechanism.During the reoxidation of reduced nontronite in suspension, about one-third of the H remaining as part of the structure following reduction was lost, whereas twice that amount of H was incorporated into the structure from the surrounding solution. A reoxidation mechanism is proposed whereby H2O from the surrounding solution is incorporated into the mineral structure followed by the elimination of a hydrogen ion, returning the Fe to six-fold coordination. This mechanism implies the reversibility of Fe reduction in nontronite.
Influence of Al Substitution and Crystal Size on the Room-Temperature Mössbauer Spectrum of Hematite
Authors: Murad Enver , Schwertmann Udo 
Published: September 2006

AbstractMössbauer spectra of 15 hematites with Al substitutions between 0 and 10 mole % were taken at room temperature. X-ray powder diffraction indicated dimensions of these hematites in the c-direction to range upwards from 27 nm to crystals large enough to show no line broadening. The Mössbauer spectra showed that magnetic hyperfine fields decreased both with increasing Al-for-Fe substitution and with decreasing crystal size. These relationships indicate that hyperfine field variations cannot, as has been done in the past, be unequivocally related to Al substitution alone. Hyperfine field reductions were paralleled by Mössbauer line broadening due to hyperfine field distributions. Only the hematites heated to 1000°C showed a significant variation of quadrupole splittings with Al substitution. No dependence of quadrupole splitting on crystal size was observed, indicating no detectable distortion of coordination polyhedra in the particle size range studied.
Hydrothermal Synthesis and Characterization of Cobalt Clays
Authors: Bruce Linda A. , Sanders John V. , Turney Terence W. 
Published: September 2006

AbstractReaction of mixtures of cobalt nitrate, colloidal silica, and a metal hydroxide (MOH) under hydrothermal conditions produced a range of cobalt hydroxysilicates, the components of which depended upon the identity of M, temperature, and reactant ratios. At 250°C, if M = Na, a smectite of composition Na0.06Co3.07Si3.95O10(OH)2 (I) was produced. If M = K, either a mica, KCo2.5Si4O10(OH)2 (II), intermediate between di- and trioctahedral, or a Si-deficient mica, KCo3Si3.75O10(OH)2 (III), was formed depending upon the reactant ratios. Similarly, if M = Cs, either a vermiculite or a 2:1 layer silicate intermediate between a mica and a brittle mica was produced. If M = Li, only the non-clay mineral Li2CoSiO4 was formed. Tetraalkylammonium hydroxides (NR4OH, R = methyl, ethyl, or propyl) yielded chrysotile. All phases were characterized by elemental analysis, transmission electron microscopy, and X-ray powder diffraction. Further characterization of smectite I was undertaken by diffuse reflectance, infrared, and X-ray photoelectron spectroscopy. The layer charge in these clays appears to stem from cation vacancies within an almost trioctahedral sheet and, possibly, within the tetrahedral sheets. Some of the cobalt present had tetrahedral coordination geometry, but its location was not determined.
Influence of Citric and Tannic Acids on Hydroxy-Al Interlayering in Montmorillonite
Authors: Goh Tee Boon , Huang P. M. 
Published: September 2006

AbstractThe formation of hydroxy-Al-interlayered montmorillonite was affected by complexing organic acids. Montmorillonite (<2.0 μm) was aged for three months at an initial pH of 5.0 or 6.0 in AlCl3 solutions containing citric or tannic acid at organic acid/Al molar ratios from 0 to 1.0. The Al/clay ratio in the system was 900 meq Al3+/100 g of montmorillonite. Ion-exchange experiments revealed that organically complexed Al ions have both positive and negative charges. Evidence from X-ray powder diffraction, electron microscopic examination, measurements of specific surface, cation-exchange capacity, organic carbon, and the nature of sorbed Al indicates that citric and tannic acids influence differently the hydroxy-Al interlayer formation in montmorillonite. Hydroxy-Al-citrate can be adsorbed as interlayers in montmorillonite, but hydroxy-Al-tannate exists principally as a separate phase binding the clay particles. The differences observed between the influence of citric and tannic acids on Al interlayering are probably due to their differences in molecular weight (size) and structure.
Electron Microscopic Investigations of Iron Oxyhydroxides and Accompanying Phases in Lateritic Iron-Crust Pisolites
Authors: Amouric M. , Baronnet A. , Nahon D. , Didier P. 
Published: September 2006

AbstractPisolites from an iron crust in western Senegal were studied by conventional and high-resolution electron microscopy to determine their internal structure and the genetic processes that led to their formation. Each pisolite consisted of a concentric structure of hematite rimmed by goethite. Two types of goethite were distinguished: (1) large (≃ 0.6 μm long and 0.06 μm wide), euhedral laths arranged in fibrous aggregates of slightly misoriented grains devoid of internal defects as shown by their two-dimensional lattice images, and (2) a matrix of smaller (≃400 Å), anhedral grains surrounded by the larger laths. Based upon the crystal habit and the presence or absence of internal alveoles, the large goethite laths probably grew at the expense of the matrix goethite. Poorly crystalline kaolinite, presumably formed from well-crystalline precursor kaolinite, and clusters of partially dissolved quartz grains were also imaged. In addition, two uncommon phases were found—maghemite in topotactic relationship with hematite and a layered, Fe-rich, mica-like mineral with a 2M superstructure. Unlike kaolinite, this latter phase was likely in equilibrium with iron oxyhydroxides. Substituted Al probably was released during goethite recrystallization, and mass transfers probably took place through the heterogeneous porosity (i.e., large voids and cracks coupled with fine pores) revealed by transmission electron microscopy.
Expansion of Smectite by Laurylamine Hydrochloride: Ambiguities in Transmission Electron Microscope Observations
Authors: Lee Jung Hoo , Peacor Donald R. 
Published: September 2006

AbstractTreatment of smectite with laurylamine hydrochloride was verified to cause expansion of d(001) which may be retained and observed in ion-milled samples by transmission electron microscopy. The spacings between layers as observed in lattice fringe images, however, are variable and may be as small as 10 Å. The method therefore produces ambiguities in differentiating between some smectites and illites, similar to those that have been found for untreated samples; e.g., on this basis, expanded layers may be inferred to be smectite, but layers with d-values approaching 10 Å may be either illite or smectite. Expansion also destroys the original rock texture, which, therefore, must be observed using only untreated samples.
Lysis of Erythrocytes by Silicate Minerals
Authors: Oscarson D. W. , Van Scoyoc G. E. , Ahlrichs J. L. 
Published: September 2006

AbstractIn vitro studies of the destruction (lysis) of bovine red blood cells (erythrocytes) by some silicate minerals showed the reaction to be complete in less than 1 hr and very destructive to the cell membrane. The activity as lysing agents was found to be in the order smectites > silica > palygorskite ≃ sepiolite > chrysotile > kaolinite. Different compositions (Fe, Al, Mg, Li, vacancy) of the octahedral sheet of the smectite and fibrous clay minerals did not appreciably alter their hemolytic activity. The most active particle size range for kaolinite and montmorillonite was 0.2-2 μm. Structural folding of palygorskite reduced lysis suggesting that edge surfaces and silanol groups are important in this process. Aluminum oxides and hydroxides caused no lysis, and coatings of positively charged aluminum-hydroxy polymers on montmorillonite, silica, palygorskite, and kaolinite significantly reduced lysis.
Acidic Properties of Montmorillonite in Selected Solvents
Authors: Loeppert R. H. , Zelazny L. W. , Volk B. G. 
Published: September 2006

AbstractMontmorillonites saturated with Al3+, H+-Al3+, and K+ were titrated in H2O, acetonitrile (AN), and dimethylformamide (DMF) to investigate the acidic properties of the clay in these solvents and to evaluate the application of nonaqueous titration procedures for studies of the acidic properties of 2:1 swelling clays. Samples were titrated with tetramethylammonium hydroxide using a combination glass electrode for Potentiometric determination. Titers of base required to reach the final Potentiometric endpoints were greater in AN than in DMF and H2O. The larger titers in AN compared to H2O were attributed to pH-dependent sites for which an inflection was not observed in the latter solvent. Titration curves of Al-saturated montmorillonite in AN showed evidence of a salt-induced hydrolysis which was confirmed by titration curves of salt extracts. The hydrolysis reaction was more evident in AN than in H2O and was probably due to a disruption of the H2O structure by AN and a polarization of the H2O of solvation. The hydrolysis reaction was enhanced in the presence of excess salt due to the ion exchange of H+ from the exchange surface. These studies indicate that acidic properties of clays may be drastically altered in organic solvents. The acidic properties may be used to advantage, for example, in the determination of edge-site acidity. In addition, they have implications concerning possible chemical reactions and/or alterations of clay in organic solvents.
Multiple Cation-Exchange Capacity Measurements on Standard Clays Using a Commercial Mechanical Extractor
Authors: Jaynes W. F. , Bigham J. M. 
Published: September 2006

AbstractSequential cation-exchange capacity (CEC) measurements were obtained from standard clays using a mechanized, variable-rate leaching device. The device consists of a motorized screwjack and as many as 24 leaching tubes coupled to 60-ml plastic syringes. Controlled withdrawal of the syringe plungers produces a vacuum that permits samples in the leaching tubes to be extracted at a uniform rate. A single, 8-hr leaching of clays with 35 ml of salt solution was found to be comparable to multiple saturations or displacements using a centrifuge. CECs consistent with published values were obtained for reference 2:1 clay minerals using both acetate and chloride salts of Na, Ca, and Mg. Potassium-exchange capacities were also successfully measured following in situ thermal treatment of samples in the leaching tubes. Variations in measured CECs for kaolin-group minerals due to salt intercalation were minimized by using chloride rather than acetate salts and by washing with a dilute aqueous solution of the saturating cation following initial saturation. The mechanical extractor significantly reduced the effort required to perform conventional CEC determinations without sacrificing analytical precision.
Mixed-Layer Illite/Smectite Minerals in Tertiary Sandstones and Shales, San Joaquin Basin, California
Authors: Ramseyer Karl , Boles J. R. 
Published: September 2006

AbstractThe southern San Joaquin Valley contains more than 7 km of sedimentary fill, largely Miocene and younger in age. Ancient depositional environments ranged from alluvial fans at the basin margins to turbidite fans toward the basin center. Mixed-layer illite/smectite (I/S) dominates the <2-μm fraction of Miocene shales, and kaolinite is abundant in Miocene sandstones. I/S from carbonate-cemented sandstones contains 5–20% more smectite layers than I/S from uncemented sandstones. The timing of cementation correlates with the proportion of smectite layers in the I/S, suggesting that cementation slowed the illitization process. Smectite and I/S with > 80% expandable layers occur at present burial temperatures of 120°-l 40°C in Miocene sandstones and shales. This highly expandable I/S is restricted to areas covered by thick deposits (1000-2500 m) of Pleistocene sediments. Rocks of similar age and at equivalent temperatures, but covered by <900 m of Pleistocene sediments, contain I/S having low expandabilities (<30%).Microprobe analyses of 16 discrete smectite and smectite-rich I/S clays indicate an average montmorillonite composition of:
$$\left( {C{a_{0.2}}{K_{0.15}}N{a_{0.1}}} \right)\left( {A{l_{3.0}}F{e^{3 + }}_{0.35}M{g_{0.75}}T{i_{0.03}}} \right)\left( {S{i_{7.7}}A{l_{0.3}}} \right){O_{20}}{\left( {OH} \right)_4} \cdot n{H_2}O.$$ Smectite in I/S-rich clays of Gulf Coast shales has a similar composition except for lower octahedral Al/ Fe ratios (Al/FeVI = 3.1), compared with the San Joaquin samples (Al/FeVI = 8.6).Residence time at different temperatures appears to be an important influence on the percentage of smectite layers in I/S from the San Joaquin basin. Areas containing I/S with high expandabilities (e.g., 95% smectite layers) have a time-temperature index (TTI) of 4.0-4.5 at 120°C, whereas areas containing I/S with low expandabilities (e.g., 30% smectite layers) have a TTI of 5.0. Present data suggest that highly expandable I/S changed to slightly expandable I/S over a narrow temperature interval (10°-20°C). Differences in the potassium availability from detrital components and in the K+/H+ activity ratios of pore water do not appear to be related to the differences in the percentage of smectite layers of these I/S clays.
Pathways of Smectite Illitization
Authors: Bethke Craig M. , Vergo Norma , Altaner Stephen P. 
Published: September 2006

AbstractJunction probability diagrams show variation in both composition and layer arrangement in mixed-layer clay minerals. These diagrams can represent short-range and long-range ordered, random, and segregated interstratifications. Mineralogical analyses of illite/smectite from shale cuttings, bentonites, and hydrothermally altered tuffs define characteristic reaction pathways through these diagrams. Shale and bentonite analyses fall along pathways joining smectite and illite on diagrams showing nearest-neighbor (R1) layer arrangements. Transition from random to R1-ordered interstratifications occurs in shale samples containing 60–70% illite layers, and in bentonites containing 55–67% illite layers. Analyses of alteration products, however, fall near a line connecting rectorite and illite, which represents the maximum degree of R1 layer ordering. No mineralogical evidence is available to suggest that these alteration samples formed from a smectite precursor. All samples develop next-nearest (R2) and thrice-removed (R3) neighbor ordering along similar pathways. Transition to R2 ordering occurs gradually in samples composed of 65–80% illite layers, and samples containing more than 85% illite layers may show strong R3 ordering.
High-Resolution Imaging of Ordered Mixed-Layer Clays
Authors: Klimentidis Robert E. , MacKinnon Ian D. R. 
Published: September 2006

AbstractHigh-resolution transmission electron microscopy (HRTEM) has been used to examine illite/smectite from the Mancos Shale; rectorite from Garland County, Arkansas; illite from Silver Hill, Montana; Na-smectite from Crook County, Wyoming; corrensite from Packwood, Washington; and diagenetic chlorite from the Tuscaloosa Formation. Thin specimens were prepared by ion milling, ultramicrotome sectioning, and/or grain dispersal on a holey carbon substrate. Some smectite-bearing clays were also examined after intercalation with dodecylamine hydrochloride (DH). Intercalation of smectite with DH proved to be a reliable method for HRTEM imaging of expanded smectite (d (001) = 16 Å) which could then be distinguished from unexpanded illite (d (001) = 10 Å). Lattice fringes of basal spacings of DH-intercalated rectorite and illite/smectite showed a 26-Å periodicity. These data support X-ray powder diffraction (XRD) studies which suggest that these samples are ordered, interstratified varieties of illite and smectite. The ion-thinned, unexpanded corrensite sample showed discrete crystallites containing 10-Å and 14-Å basal spacings corresponding to collapsed smectite and chlorite, respectively. Regions containing disordered layers of chlorite and smectite were also noted. Crystallites containing regular alternations of smectite and chlorite layers were not common. These HRTEM observations of corrensite did not corroborate XRD data. Particle sizes parallel to the c axis ranged widely for each sample studied, and many particles showed basal dimensions equivalent to more than five layers. For all illite, smectite, and illite/ smectite particles examined, crystallite sizes of about 20 Å in the basal dimension were not observed.