bluuebunny/crossref_metadata_2025_split huggingface dataset:
The 5-M-NaOH Concentration Treatment for Iron Oxides in Soils
Authors: Kämpf Nestor , Schwertmann Udo 
Published: August 2006

AbstractThe boiling 5-M-NaOH treatment was found to aid in the identification and characterization of goethite and hematite by effectively concentrating the two Fe oxides in kaolinitic-gibbsitic soil clays. No transformations of goethite to hematite or hematite to goethite were detected, but poorly crystalline, highly Al-substituted goethite was found to dissolve and recrystallize into a more well-crystalline, less Al-substituted goethite in samples low in Si. The Si released from kaolinite was sufficient to block goethite dissolution and recrystallization in kaolinitic samples, but noncrystalline silica had to be added to samples rich in gibbsite to minimize this effect.
Comparison of Orientations of OH-Bonds in Layer Silicates by Diffraction Methods and Electrostatic Calculations
Authors: Bookin A. S. , Drits V. A. , Rozdestvenskaya I. V. , Semenova T. F. , Tsipursky S. I. 
Published: August 2006

AbstractOrientations of OH-vectors in structural hydroxyl groups of layer silicates were defined both from diffraction data and calculations of electrostatic energy. The comparison of the results showed that for the hydroxyls of the 2:1 layers of chlorites and micas the positions of the hydroxyl protons are mainly determined by electrostatics. For the hydroxyls of dickite, amesite, and the brucitic sheets of chlorite, the results derived by the two methods differed systematically from each other, pointing to a change in the nature of the bond in these OH-groups.
Morphology of Nordstrandite
Authors: Violante P. , Violante A. , Tait J. M. 
Published: August 2006

AbstractNordstrandite was obtained synthetically by precipitation of Al(OH)3 at pH 9.0 to 11.0 in citrate or malate systems with Al: carboxylic acid molar ratios of 10–100 in the absence and in the presence of montmorillonite. Examination by transmission and scanning electron microscopy showed that the nordstrandite had a tabular morphology in the clay-free systems with Al: carboxylic acid ratio >50. Because the inhibiting effect on crystallization of the citrate or malat e anion decreases with increase in pH, the crystal size varied from <2 μm at pH 10 to 5 μm at pH 11. With increasing concentration of citrate or malate, the nordstrandite crystals became more elongated in the c-direction probably due to organic anion occupation of the coordination sites of Al on the edge faces parallel to the c-axis. Irregular growth along the c-axis was probably due to steric hindrance by the organic ligands distorting the arrangement of the unit layers of nordstrandite.The catalytic effect of montmorillonite on the formation of nordstrandite was confirmed. Nordstrandite synthesized in the presence of montmoriUonite at pH 9.0 presented an ill-defined ovoidal outline (0.2–0.5 μm), some showing shafts of bayerite growing from the center. At higher pH, where conditions for crystalline growth were again more favorable, nordstrandite crystals nucleated on the montmorillonite surfaces and condensed in clusters of weak face-to-face associations of plates.
Intercalation of Tetraalkylammonium Cations into Smectites and Its Application to Internal Surface Area Measurements
Authors: Mercier Louis , Detellier Christian 
Published: August 2006

AbstractMonolayer to bilayer (MTB) and bilayer to pseudotrimolecular (BTP) transitions were observed for smectites exchanged with symmetrical tetraalkylammonium cations of increasing sizes: +NR4, where R = (CH2)nCH3, with 0 ≤ n ≤ 7. In the case of SWy-1, SHCa-1 and SWa-1, the variation in layer spacing observed from intercalation of tetramethylammonium up to tetraoctylammonium cations showed a behavior characteristic of smectites with homogeneously distributed interlayer cations. In the case of STx-1, the change in interlayer spacing with the increase of the alkyl chain length was characteristic of a very high charge heterogeneity. Higher charge smectites (SAz-1 and SCa-3, CEC > 1.20 mmol/g) were found to have decreasing cation exchange with increasing cation size, resulting in a "leveling off’ of the interlayer spacing toward larger cations. The MTB and BTP transitions were used to determine the internal surface area of various smectites. The proposed method was found to be a quicker and simpler alternative to the polar liquid sorption method for this measurement, but was ineffective for high-charge smectites (CEC > 1.20 mmol/g).
Hydration Behavior of Na-Smectite Crystals Synthesized at High Pressure and High Temperature
Authors: Yamada Hirohisa , Nakazawa Hiromoto , Hashizume Hideo , Shimomura Shuichi , Watanabe Takashi 
Published: August 2006

AbstractHydration behavior of Na-smectite crystals synthesized at a pressure of 5.5 GPa and temperatures of 1400°–1500°C was examined by X-ray powder diffraction at various relative humidities (RH) in the range of 0–100%. The basal spacing of the Na-smectite crystal increased stepwise with increase in RH. The reflections observed were only normal reflections of a single or dual hydration states of smectite. No irrational, intermediate, or asymmetrical reflections were observed. The simple hydration behavior, not known for natural smectite with fine particle sizes and low crystallinity, indicates that the Na-smectite crystals are as perfect as common inorganic crystals with an ordered structure.
Dioctahedral Tosudite in Hydrothermally Altered Pliocene Rhyolitic Tuff, Neutla, Mexico
Authors: de Pablo-Galan Liberto , Chávez-García M. L. 
Published: August 2006

AbstractDioctahedral tosudite, a regular interstratification of dioctahedral chlorite-dioctahedral smectite, occurs associated with kaolin in the hydrothermal area of Delgado, Neutla, Mexico. Its composition corresponds to the formula:
$$\left( {S{I_{13.77}}A{L_{2.23}}} \right)A{L_8}{O_{40}}{\left( {OH} \right)_8} \cdot C{A_{0.39}}N{A_{0.03}}{K_{1.06}} \cdot \left( {A{L_{3.79}}F{E^{ + 3}}_{0.09}F{E^{ + 2}}_{0.06}M{G_{0.26}}} \right){\left( {OH} \right)_{12}}.$$ It forms as thin irregular flakes up to 5 µm in size. Adsorbed and cation hydration interlayer H2O is lost at 81°C and 184°C, dehydroxylation is intense at 496°C and weak at 656°C, with recrystallization at 970°C and 989°C. Infrared analysis shows OH-stretching at 3605 cm-1 assigned to the Al-OH-Al group and at 3628, 3500, and 3365 cm-1. Also, OH-bending occurs at 822 cm-1, deformation of the H2O molecule at 1630 cm-1, Si-O stretching at 1020 cm-1, and bending at 482 cm-1, displaced by Al substitution and increase of the Si-O distance. The characteristic basal spacing of 29.49 Å for the air-dry mineral is changed to 31.32 Å when solvated and to 23.23 Å upon heating; d060 = 1.496 Å. The interstratification is a regular 1:1 dioctahedral chlorite-dioctahedral smectite, R = 1, with coefficient of variability 0.73% for the air-dried mineral and 0.76% for the solvated one.
The Effect of Surface Modification by an Organosilane on the Electrochemical Properties of Kaolinite
Authors: Braggs Belinda , Fornasiero Daniel , Ralston John , St. Smart Roger 
Published: August 2006

AbstractThe electrochemical properties of kaolinite before and after modification with chlorodimethyl-octadecylsilane have been studied by electrophoretic mobility, surface charge titration, and extrapolated yield stress measurements as a function of pH and ionic strength. A heteropolar model of kaolinite, which views the particles as having a pH-independent permanent negative charge on the basal planes and a pH-dependent charge on the edges, has been used to model the data. The zeta potential and surface charge titration experimental data have been used simultaneously to calculate acid and ion complexation equilibrium constants using a surface complex model of the oxide-solution interface. The experimental data were modeled following subtraction of the basal plane constant negative charge, describing only the edge electrical double layer properties. Extrapolated yield stress measurements along with the electrochemical data were used to determine the edge isoelectric points for both the unmodified and modified kaolinite and were found to occur at pH values of 5.25 and 6.75, respectively. Acidity and ion complexation constants were calculated for both sets of data before and after surface modification. The acidity constants, pKa1 = 5.0 and pKa2 = 6.0, calculated for unmodified kaolinite, correlate closely with acidity constants determined by oxide studies for acidic sites on alumina and silica, respectively, and were, therefore, assigned to pH-dependent specific chemical surface hydroxyl groups on the edges of kaolinite. The parameters calculated for the modified kaolinite indicate that the silane has reacted with these pH-dependent hydroxyl groups causing both a change in their acidity and a concomitant decrease in their ionization capacity. Infrared data show that the long chain hydrocarbon silane is held by strong bonding to the kaolinite surface as it remains attached after washing with cyclohexane, heating, and dispersion in an aqueous environment.
The Effect of Dissolved Ligands on the Sorption of Cu(II) by Ca-Montmorillonite
Authors: Stadler Markus , Schindler Paul W. 
Published: August 2006

AbstractThe effects of three organic ligands on the adsorption of copper on Ca-montmorillonite were studied. The results indicate that these effects include three different processes:1)Enhanced uptake of positively charged copper-ligand complexes by ion-exchange.2)Formation of ternary surface complexes involving surface aluminol groups.3)Inhibited uptake due to competition between the surface ligands and the dissolved ligands for dissolved copper.Ethylenediamine promotes copper uptake by ion-exchange at low pH but tends to suppress adsorption at aluminol groups by ligand competition at high pH. The same mechanisms are operative for β-alanine; however, the uptake of Cu(β-ala)+ by ion-exchange is not promoted by the attached ligand. The influence of malonate includes both ligand competition and formation of ternary complexes. A quantitative interpretation based on the surface complexation model using the least-squares programs FITEQL (Westall, 1982) and GRFIT (Ludwig, 1992) is presented. The obtained equilibrium constants are listed in Tables 2b and 3.
Interaction between Organic and Inorganic Pollutants in the Clay Interlayer
Authors: Siantar Darsa P. , Feinberg Benjamin A. , Fripiat José J. 
Published: August 2006

AbstractA synergistic mechanism for the retention of organic and inorganic pollutants in clays is discussed in this paper. The mechanism of adsorption of cis- or trans- 1,2-dichloroethylene vapor (CDE or TDE, respectively) by hydrated smectite clay (hectorite) exchanged with Pb2+, Hg2+, Cd2+, Ca2+, Ag+, or Na+ has been investigated by simultaneously measuring chlorohydrocarbon uptake and water desorption isotherm and by recording the infrared (IR) spectrum of the adsorbed phase. Hydrated hectorite saturated with divalent cations adsorbs about 55% more CDE or 35% more TDE than those saturated with monovalent cations. The quantity of chlorohydrocarbon adsorbed is also a function of the hydration of the clay interlayer space. When dehydrated, hectorite does not adsorb CDE or TDE. Upon long outgassing at room temperature or even at 100°C, the characteristic IR bands of clays with adsorbed chlorohydrocarbon, although much weakened, are still observable. The ratio of the amount of water desorbed to the amount of chlorohydrocarbon adsorbed varied from about 0.22 to 0.34. A shift of the center of gravity of the hydration water OH stretching frequency towards a higher wavenumber and of the asymmetric CC1 stretching vibration toward a lower frequency suggest that the formation of hydrogen bonds between CDE or TDE and water is the driving force for adsorption and that the cation-dipole interaction does not play a major role.
Hysteresis in the Binary Exchange of Cations on 2:1 Clay Minerals: A Critical Review
Authors: Verburg Kirsten , Baveye Philippe 
Published: August 2006

AbstractThe binary exchange of cations on clays and soils is generally regarded as a thermodynamically reversible process. The literature on soil chemistry and geochemistry, however, abounds with reports on cation exchange reactions that appear to have only limited reversibility, i.e., that exhibit hysteresis. A satisfactory explanation of this phenomenon is still lacking, even though a number of mechanisms have been advocated, e.g., charge or site heterogeneity at the surface, differential hydration of cations, dehydration of the exchanger, crystalline swelling hysteresis, and inaccessibility of sites caused by domain or quasi-crystal formation. In the present article, the relevant literature is reviewed and analyzed critically. On the basis of available evidence, it is shown that exchangeable cations can be classified into three groups, defined in such a way that hysteresis has, in the literature, generally not been observed when exchange reactions involved cations belonging to the same group, but has often been found when the reactions involved cations from different groups. Furthermore, it is argued that none of the five mechanisms mentioned can, in and of itself, account fully for the observed exchange hysteresis. A conceptual model is proposed that combines elements of these five mechanisms and is able to describe, at least qualitatively, the effects of factors such as clay type, electrolyte concentration, and extent of dehydration.
Trimethyl Phosphate Induced Decomposition of Kaolinite
Authors: Sánchez-Camazano María , Sánchez-Martín M. Jesús 
Published: August 2006

AbstractThe decomposition of kaolinite by treatment with trimethyl phosphate (TMP) and the composition of the new crystalline phase formed were studied. On hot treatment with TMP, kaolinite forms a crystalline white compound that is soluble in hot water. The X-ray diffraction pattern of the kaolinite treated shows both the typical reflections of kaolinite and, furthermore, a very strong reflection at 8.84 Å. After 30 days of treatment with TMP, the silicate structure of kaolinite is completely destroyed and a crystalline phase identical with that resulting from treatment of aluminium oxide (Al2O3) with TMP is formed. The results show that the compound in question is formed by hydrolysis of TMP, catalyzed by the hydration water of exchange cations of kaolinite, followed by removal of Al from the silicate structure by incompletely hydrolyzed TMP. The new crystalline phase thus formed is an aluminium alkyl phosphate of formula Al(CH3)6(PO4)3.
Supergene Vermiculitization of Phlogopite and Biotite in Ultramafic and Mafic Rocks, Central Korea
Authors: Moon Hi-Soo , Song Yungoo , Lee S. Y. 
Published: August 2006

AbstractAn X-ray diffraction study of vermiculitized micas in ultramafic and mafic intrusive rocks from Cheongyang, Korea, shows the following weathering sequence: mica → ordered mica/vermiculite interstratification → vermiculite. Electron microprobe analyses show the general trends of K leaching and Ca enrichment with increased weathering. The vermiculitization of phlogopite from ultramafic rocks proceeds by means of a continuous decrease in Al-for-Si tetrahedral substitutions and a progressive increase in Al-for-(Fe2+ + Mg) octahedral substitutions in the early stage of weathering. These substitutions occur to compensate for the excess of negative charge in the mica-like layer, in agreement with currently accepted vermiculitization mechanisms. They change to a slight increase of Al-for-Si tetrahedral substitutions in the late stage of the vermiculitization of phlogopite, owing to the oxidation of Fe despite its low content. However, the behavior of Fe in the late stage of the transformation of biotite into vermiculite is significantly different; that is, Fe increases substantially. The reason for this Fe increase in the late stage remains unresolved. Recalculations of the structural formulas on the basis of several assumptions indicate that the oxidation of Fe is necessary for the vermiculite derived from biotite to form the reasonable structural formulas.
The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study
Authors: Gehring A. U. , Hofmeister A. M. 
Published: August 2006

AbstractInfrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3). Magnetic analyses showed that the thermal conversion began at about 175°C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic γ-Fe2O3 occurred at 200°C and was complete around 300°C. At higher temperatures, the maghemite converted into hematite (α-Fe2O3). Observation of the transformation from γ-FeOOH to γ-Fe2O3 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145°C and 155°C. The lag time between the onset of the breaking of OH bonds and the release of H2O from lepidocrocite around 175°C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219°C. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.
Solid-State Nuclear Magnetic Resonance Spectroscopy on Synthetic Ammonium/Aluminum-Saponites
Authors: Kloprogge J. T. , Breukelaar J. , Wilson A. E. , Geus J. W. , Jansen J. B. H. 
Published: August 2006

AbstractAmmonium-saponite is hydrothermally grown at temperatures below 300°C from a gel with an overall composition corresponding to (NH4)0.6Mg3Al0.6Si3.4O10(OH)2. Using 27Al and 29Si solid-state Magic Angle Spinning NMR techniques it is demonstrated that synthetic ammonium-saponites have a rather constant Si/AlIV ratio (≈ 5.5) and an AlIV/AlVI ratio that varies between 1.5 and 3.8. The above ratios are independent of the synthesis temperature, although an increasing amount of Si, N, and, to a lesser extent, Al are incorporated in an amorphous phase with increasing temperature. 27Al MAS-NMR is unable to differentiate between Al at octahedral and Al3+ at interlayer sites. CEC, XRD, and the inability to swell prove the AlVI to be mainly on the interlayer sites. Based on the NH4- exchange capacity, X-ray fluorescence, 27Al and 29Si MAS-NMR, it is possible to calculate a relatively accurate structural formula.
Cation Exchange Capacity and Condition of Zero Charge of Hydroxy-Al Montmorillonite
Authors: Helmy A. K. , Ferreiro E. A. , de Bussetti S. G. 
Published: August 2006

AbstractThe effect of interlayering montmorillonite with different amounts of hydroxy aluminum cation on the cation exchange capacity (CEC) and the point of zero charge (PZC) of the clay was studied. The CEC decreased as the Al content of the clay increased. Both the CEC and the loss in the CEC were linearly dependent on the Al content, thus indicating the predominance of a single polynuclear interlayered species. Its composition is [Al6(OH)16.5]1.5+. Acid base titration of the interlayered montmorillonites produced values for the PZC in the range 4.5-5.9, increasing with the Al content of the materials. The values, however, did not represent real conditions of zero charge and some samples were still negatively charged at the determined PZC. The PZC values obtained by acid-base titration are thought to be adversely affected by secondary reactions involving the interlayered material with a concomitant release of soluble Al in amounts dependent on the pH and ionic strength.
Mobility of Small Molecules in Interlayers of Hectorite Gels: ESR Study with an Uncharged Spin Probe
Authors: McBride M. B. 
Published: August 2006

AbstractElectron spin resonance (ESR) spectroscopy was used to measure the rotational mobility of an uncharged nitroxide spin probe (4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy) in hectorite gels of variable water content. Physical adsorption segregated the probe molecules into two populations: probes in the solution or a solution-like phase, and motionally restricted probes in the adsorbed phase. Although the spectra of these two populations were discrete, indicating that exchange between them was slow on the time scale relevant to ESR, their overlap prevented a straightforward determination of mobility of the adsorbed probes. Even though adsorption was weak, effects of the adsorbed population on the spectral lineshape were detectable for suspensions containing as little as 20 grams clay per liter of water. Orientation of the adsorbed probes on the fully hydrated hectorite surfaces was similar to that of a positively charged nitroxide probe, suggesting that steric factors rather than electrostatic forces control short-range organic molecule interaction with the silicate. The possibility of reaching false conclusions about probe mobility and interlamellar water viscosity when using a weakly adsorbing probe is discussed.
A Nexafs Study of the Orientation of Benzoate Intercalated into a Layer Double Hydroxide
Authors: Moggridge G. D. , Parent P. , Tourillon G. 
Published: August 2006

AbstractNEXAFS is shown to be an excellent technique, of potentially widespread application, for the determination of the orientation of organic molecules intercalated in preferentially oriented thin films of polycrystalline, layered minerals. A NEXAFS study of [Mg2Al(OH)6]+C7H5O2 · nH2O, a layered anionic clay, is described. This material shows a transition from a layer spacing of 15.4 Å to only 9 Å at a remarkably low temperature (below 100°C). This is shown to be accompanied by a change in the angle of the plane of the benzoate molecule to the 00ℓ planes from 35° ± 10° to 0° ± 10°. The tilt of the benzoate anion in the room temperature structure demonstrates the presence of an interaction between the phenyl ring and the positively charged, brucite-like layers. Furthermore it is suggestive of the importance of hydrogen bonding in determining the interlayer spacing and stability.
Ba-Bearing Clinoptilolite from ODP Leg 127, Site 795, Japan Sea
Authors: Ogihara Sigenori 
Published: August 2006

AbstractBa-bearing clinoptilolite (with >2 wt. % BaO) occurs in Neogene marine siliceous sediments from ODP Leg 127 Site 795 in the Japan Sea. Ba-bearing clinoptilolite is formed by reaction of volcanic glass and Ba-rich pore water during burial diagenesis.
Refinement of the Crystal Structure of Cronstedtite-3T
Authors: Smrčok Ľubomír , Ďurovič Slavomil , Petříček Václav , Weiss Zdeněk 
Published: August 2006

AbstractThe crystal structure of cronstedtite-3T from Kutná Hora (Bohemia, Czechoslovakia), space group P31, was refined to Rw(all) = 3.1% for 1336 independent diffractions. There are two and three independent tetrahedral and octahedral positions, respectively, in this structure. The tetrahedra are occupied by 0.75 Si and 0.25 Fe while the octahedra are uniformly occupied by Fe. The refinement process was hindered by two problems: a “strong” superposition structure (all atoms of the octahedral sheets, i.e., ÷ 70% of the total diffraction power contribute almost solely to the family diffractions with mod(h–k, 3) = 0), and a slight disorder of the investigated crystal. The first problem was resolved by a preliminary block-diagonal refinement procedure where the atoms coinciding in the superposition structure were separated into individual blocks. The second problem was resolved by including two scale factors into the final full-matrix refinement: one for family diffractions, the other for the remaining ones which are characteristic for this polytype.