bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Cysteine and Manganese on the Crystallization of Noncrystalline Iron(III) Hydroxide at pH 8
Authors: Cornell R. M. , Giovanoli R. , Schneider W. 
Published: August 2006

AbstractTo provide a greater understanding of the crystallization of iron oxides under natural aqueous conditions, the combined effect of an inorganic ion (Mn2+) and a reducing organic ligand (L-cysteine) on the conversion of noncrystalline ferric hydroxide to goethite and/or hematite was investigated at pH 8.At cysteine: Fe ratios ≥ 0.2, L-cysteine caused noncrystalline iron(III) hydroxide to transform rapidly into goethite at pH 8; in the absence of the organic ligand, hematite was the predominant reaction product. The presence of Mn (≥9 mole %) in the cysteine-ferric hydroxide system retarded crystallization and reduced the goethite-promoting effect of cysteine.Polarographic measurements showed that the adsorption of cysteine on noncrystalline iron(III) hydroxide was immediately followed by the oxidation of cysteine to the disulfide with simultaneous reduction of a proportion of the interracial ferric ions. The partly reduced noncrystalline iron(III) hydroxide dissolved at pH 8 more rapidly than the original material, thus facilitating the formation of goethite. In Mn(II)-noncrystalline iron(III) hydroxide coprecipitates, the interfacial oxidation/reduction reaction with cysteine (and hence the partial reduction of the noncrystalline phase) was reduced, due to replacement of some interfacial Fe(III) by non-reducible Mn.At pH 8, uptake of Mn by crystalline iron oxides was low (< 5 mole %). Mn precipitated preferentially as pure Mn phases, either rhodochrosite (in NaHCO3 buffer) or hausmannite (in NH4Cl/NH3 buffer).
Mineral Assemblages of Volcanic and Detrital Partings in Tertiary Coal Beds, Kenai Peninsula, Alaska
Authors: Reinink-Smith Linda M. 
Published: August 2006

AbstractVolcanic and non-volcanic partings are exposed in coal beds of the Tertiary Beluga and Sterling Formations along the shores of the Kenai lowland, Alaska. About two-thirds of the partings originated as air-fall tephra which fell in coal-forming swamps. The tephra partings in the Pliocene strata are unaltered or slightly altered and have a characteristic mineral assemblage of volcanic glass ± montmoriUonite ± kaolinite ± opal-CT. Miocene strata are slightly altered to totally altered, and a typical mineral assemblage consists of feldspar ± kaolinite ± montmorillonite ± quartz ± crandallite ± altered volcanic glass. Crandallite appears to have formed early in diagenesis by the replacement of volcanic glass prior to the formation of montmorillonite and kaolinite.About one-third of the partings originated primarily as detrital sediments derived from surrounding metamorphic and sedimentary terranes and were deposited by periodic floods. Mixtures of tephra and detrital sediments were also noted and were difficult to distinguish from tephra partings in the field. Detrital partings are characterized by detrital chlorite + illite + smectite + quartz ± feldspar ± siderite ± kaolinite. The chlorite in these strata is allogenic. Smectite is less common in the detrital partings.
DLVO and Non-DLVO Interactions in Hectorite
Authors: van Oss C. J. , Giese R. F. , Costanzo P. M. 
Published: August 2006

AbstractThe Derjaguin-Landau-Verwey-Overbeek (DLVO) theory sums the attractive van der Waals and repulsive electrostatic forces as a function of separation distance to predict the interaction between charged particles immersed in a liquid. In aqueous media, however, non-electrostatic polar (electron acceptor/electron donor or Lewis acid/base) forces between particles with high energy surfaces often are comparable to, or greater than, the components of DLVO theory. By means of contact angle measurements on smooth self-supporting clay films, the values of the polar surface forces (AB) and the van der Waals forces (LW) of hectorite were measured. Determinations of ζ were used to derive the electrostatic forces (EL). Calculations based on the values obtained for the EL, LW, and AB forces show that for smooth spheres with a radius of 1 µm in a ≥ 0.1 M NaCl solution a net attraction exists leading to flocculation. At NaCl concentrations of ≤ 0.01 M, a repulsion energy of about +500 to +1300 kT exists at separation distances ≤ 50 Å, preventing contact between particles, thus ensuring stability of the colloidal suspension. At these concentrations, theory predicts that small clay particles or edges of clay crystals having an effective radius of curvature ≤ 10 Å should be energetic enough to overcome the repulsion barrier which prevents flocculation. Experimentally, for NaCl solution concentrations of ≥ 0.1 M, suspensions of hectorite particles flocculated, whereas at concentrations of ≥ 0.01 M, the suspensions remained stable. These experimental results agree with the predictions made by summing all three forces, but contradict the calculations based on classical DLVO theory.
Formation of Trioctahedral Illite from Biotite in a Soil Profile over Granite Gneiss
Authors: Fordham A. W. 
Published: August 2006

AbstractClay fractions separated from the A2, B, and C horizons of a soil formed on granite gneiss showed X-ray powder diffraction (XRD) spacings characteristic of trioctahedral illite. The trioctahedral illite was derived from biotite, and its development through various stages of weathering was followed by optical and electron microscopy combined with electron microanalysis. In the initial stages of weathering, Fe2+ within biotite was oxidized, without the loss of much K. During this process, biotite flakes became slightly buckled and fractured. Solutions moved into the damaged flakes leading to chemical weathering and exfoliation along cleavages and angular fractures. Major exfoliation broke up the flakes into segments, which themselves contained minor exfoliations and alterations along cleavage planes. The extent of exfoliation and alteration continued until thinner and shorter segments consisted almost wholly of thin (< 0.25 µm), parallel wafers separated by less compact layers of particles and microaggregates. The segments finally lost their shape and divided into clay-size particles. Parts of the thin wafers had the same chemical composition (and structure) as the original, intact flakes of oxidized biotite. The same parts of wafers retained some of the optical properties of the original biotite, and, when broken down to clay, they produced the XRD spacings of 10 and 1.54 Å, typical of fine-grained, trioctahedral mica (illite).
The Influence of Aluminum on Iron Oxides. XV. Al-for-Fe Substitution in Synthetic Lepidocrocite
Authors: Schwertmann Udo , Wolska Emilia 
Published: August 2006

AbstractLepidocrocite samples, γ-FeOOH, containing 0–10 mole % Al-for-Fe substitution were synthesized at 15°C and pH 8 by oxidizing mixed FeCl2-AlCl3 solutions. The unit-cell parameters a, b, and c were measured from step-counted X-ray powder diffractograms using seven lines and Si as an internal standard. With increasing Al substitution from 0 to 10 mole % the unit-cell edge lengths a, b, and c decreased regularly by 0.3, 0.8, and 0.6%, respectively. Furthermore, the crystals became smaller, but gained in thermal stability. Decrease in crystal size parallel to the y axis led to a significant increase of the OH-stretch vibration and a decrease of the out-of-plane OH-bending vibration due to a weakening of the hydrogen bond between the zig-zag layers in the structure.
Reactivity of Anisoles on Clay and Pillared Clay Surfaces
Authors: Carrado Kathleen A. , Hayatsu Ryoichi , Botto Robert E. , Winans Randall E. 
Published: August 2006

AbstractPillared bentonites were found to be efficient catalysts for the O-methyl bond cleavage of anisoles (e.g., m-methylanisole, guaiacol, and creosol) under very mild, static conditions (150°C, a few hours, inert atmosphere). The O-methyl bond cleavage led to phenolic products. Gas chromatographymass spectrometry and solid-state 13C nuclear magnetic resonance (NMR) techniques used to probe 13C-labeled anisoles revealed that dealkylation and transalkylation reactions occurred to a large extent, and that conversion was efficient at >95% after two days. Ortho- and para-isomers were observed exclusively, without any evidence of meta-substitution. Volatile products were determined by mass spectrometry to be 13CH3OH and (13CH3)2O. Magic-angle spinning 13C NMR experiments showed that the molecules were fairly mobile in the clay micropores prior to catalysis. After catalysis, cross-polarization NMR showed that molecular motion had decreased markedly. Ultraviolet-visible spectroscopy of the colored complexes suggested some quinone formation. The trend of clay reactivity was found to be: pillared bentonite ≫ acid-washed montmorillonite > untreated bentonite > pillared fluorhectorite ≃ untreated fluorhectorite.
Far-Infrared Study of Potassium in Micas
Authors: Prost R. , Laperche V. 
Published: August 2006

AbstractThe characterization of cations associated with clay materials has generally been approached by the sequential use of specific chemical reagents. To avoid the disturbing effect of the chemical reagents on the state and location of compensating cations of clays and to get information in situ, far-infrared spectroscopy was used. The far-infrared vibrational spectra of the potassium cation in muscovite, phlogopite, and biotite were recorded before and after heating at the dehydroxylation temperature. The vibrational frequency of K in micas before dehydroxylation was found to be a function of the di- or trioctahedral character and of the Fe content. After dehydroxylation or deprotonation, shifts of the K absorption band to lower frequencies were observed for the heated muscovite, in which K exchangeability increased, and to higher frequencies for the heated biotite, in which K exchangeability decreased. These results suggest that the vibrational frequency of potassium is characteristic of the state of K in these minerals and of its ability to be exchanged.
Characterization of Synthetic Na-Beidellite
Authors: Kloprogge J. Theo , Jansen J. Ben H. , Geus John W. 
Published: August 2006

AbstractNa-beidellite, a member of the smectite group, was grown hydrothermally from a gel of composition 0.35Na2O·2.35Al2O3·7.3SiO2 in NaOH solutions at a pH between 7.5 and 13.5, a pressure of 1 kbar, and a temperature of 350°C. The synthetic Na-beidellite was characterized by means of scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, electron microprobe, inductively coupled plasma-atomic emission spectroscopy, and thermogravimetric analysis. The unit-cell parameters of the orthorhombic cell are: a = 5.18, b = 8.96, and c = 12.54 Å. The cation-exchange capacity was determined to be 70 meq/100 g. A maximum of 40 wt. % water was present and reversibly lost by heating to about 55°C. The loss of water caused a decrease of the basal spacing to 9.98 Å. At temperatures ≥600°C, the Na-beidellite started to dehydroxylate, reaching its maximum in the range 600°–630°C. At 1100°C the remaining solid recrystallized to Al6Si2O13 (mullite) and SiO2 (cristobalite).
Hydrothermal Reactivity of Mixed-Layer Kaolinite/Smectite: Experimental Transformation of High-Charge to Low-Charge Smectite
Authors: Proust D. , Lechelle J. , Lajudie A. , Meunier A. 
Published: August 2006

AbstractA mixed-layer kaolinite/smectite (K/S) containing trace amounts of quartz, discrete kaolinite, goethite-hematite, and calcite was hydrothermally reacted with deionized water at 150°, 200°, and 250°C for 1 to 12 months. The starting K/S contained 50% smectite consisting of 15% low-charge and 35% high-charge layers. The X-ray powder diffraction and chemical analyses of the reacted products indicated a progressive reaction from high-charge to low-charge smectite as a function of time and temperature. The reaction reached completion after 4 months at 250°C, at which point high-charge smectite layers entirely reacted to low-charge smectite layers, the latter maintaining a constant proportion of about 90% for longer run durations. For long reaction times, discrete kaolinite totally reacted, whereas quartz showed only partial dissolution and iron oxides remained stable. Thus, the reaction of high-charge to low-charge smectite layers may be expressed as: high-charge smectite + kaolinite (both interstratified and discrete component) + quartz → low-charge smectite.
Thermal Stability of Halloysite by High-Pressure Differential Thermal Analysis
Authors: Johnson Sheryl L. , Guggenheim Stephen , Koster van Groos A. F. 
Published: August 2006

AbstractPlaty (Te Puke, New Zealand), cylindrical (Spruce Pine, North Carolina), and spherical (North Gardiner mine, Huron, Lawrence County, Indiana) halloysite samples were analyzed by high-pressure differential thermal analysis (HP-DTA) to determine the effect of morphological and chemical differences on their respective thermal stability. In halloysite, these morphological differences imply structural features. The metastable phase relations of each are analogous to those of kaolinite. At 1 bar, the platy, cylindrical, and spherical samples showed peak temperatures (maximum deflection in the dehydroxylation endotherm) of 560°, 578°, and 575°C, respectively, whereas at about 600 bars the peak temperatures were 622°, 655°, and 647°C. At low pressures the observed reaction is related to dehydroxylation: halloysite (H) metahalloysite (MH) + vapor (V), whereas higher pressures produce melting reactions, either H + V = metaliquid (ML) for conditions of P(H2O) = P(total), or H + MH = ML for P(H2O) < P(total). The PT conditions of the invariant point, H + MH + ML + V, for each system are: Te Puke, 612° ± 4°C, 25 ± 7 bars; Spruce Pine, 657 ± 2°C, 30 ± 7 bars; North Gardiner, 652° ± 2°C, 34 ± 7 bars. The lower thermal stability of the Te Puke sample may be related to its higher iron content, although additional data are necessary to confirm that it is not related also to the platy structure. Furthermore, morphological differences between the cylindrical and spherical varieties appear to have had little effect on the energy required to dehydroxylate these halloysite structures. Exceptionally high values obtained for the dehydroxylation enthalpies using the van't Hoff equation, compared with values derived using other methods, may be explained by a 10–15-bar excess in the intracrystalline H2O fugacity during dehydroxylation. Intracrystalline fugacity is defined here as the H2O fugacity within crystallites and is not related to the partial pressure of H2O around individual particles.
Electrostatic Potential at the Basal (001) Surface of Talc and Pyrophyllite as Related to Tetrahedral Sheet Distortions
Authors: Bleam William F. 
Published: August 2006

AbstractMaps of the electrostatic potentials at the basal plane of talc and pyrophyllite, computed using a two-dimensional Ewald lattice-sum, reveal the effects caused by structural distortion of the phyllosilicate layer. Rotation and tilting of basal tetrahedra in phyllosilicates dramatically perturb the electrostatic potential near the (001) surface. A potential high exists at the center of each six-fold ring of the talc (001) surface. Concerted counter-rotations of basal tetrahedra by 10°, as are typical in pyrophyllite, cause the potential lows above basal oxygens rotated into the ring to overlap, eliminating the ring-centered potential highs. Expansion of the vacant site in dioctahedral minerals tilts the basal tetrahedra by 4° and moves one-third of the basal oxygens about 0.2 Å toward the center of each phyllosilicate layer and away from the (001) surface, thereby producing corrugations of the basal surface. This shift dramatically reduces the contribution of these displaced basal oxygens to the (001) surface potential. Rotation and tilting of basal tetrahedra may influence the arrangement of interlayer water molecules on smectites and other swelling phyllosilicates by the effect that these distortions have on the (001) surface potential.
Relevance of Different Intercalation Tests for Distinguishing Halloysite from Kaolinite in Soils
Authors: Churchman G. J. 
Published: August 2006

AbstractThe expandabilities of kaolin-group minerals in different horizons in 10 soils from New Zealand and Fiji were measured immediately after the application of formamide and after the sequential application of hydrazine, water, and glycerol (HWG treatment). The expandabilities of these minerals in some of the soil samples with dimethylsulphoxide (DMSO) and after long-term (4-day) formamide treatments were also measured. The abundance of characteristic halloysite shapes was determined from electron micrographs of selected samples. The expandabilities of several non-soil kaolinite samples with the DMSO and HWG treatments were also measured.The expansion of kaolin-group minerals showed the same trends within almost all profiles, whether determined using formamide (by the immediate-formamide treatment) or glycerol (by the HWG treatment). Except where both treatments led to complete intercalation, the HWG treatment always caused more expansion of kaolin-group minerals than obtained immediately after formamide application. The HWG treatment expanded some non-soil kaolinite samples, but well-crystallized kaolinite was not affected by this treatment. The DMSO treatment expanded kaolin-group minerals in the soils to a similar extent as the HWG treatment and also expanded well-crystallized kaolinite. The degree of expansion resulting from the immediate-formamide treatment matched abundance of typical halloysite particle shapes more closely than the degree of expansion given by the other intercalation treatments. The degree of expansion immediately following formamide application could be diminished, if the samples were heated at 40 ± 5°C.
Preparation and Properties of Pillared Interstratified Illite/Smectite
Authors: Sterte Johan 
Published: August 2006

AbstractPillared, regularly and randomly interstratified illite/smectite (I/S) was prepared by interacting aluminum chlorohydrate with I/S in aqueous dispersion. I/S samples from Kinnekulle, Sweden, ranging in composition from 30–60% smectite layers, were used as starting clays. The pillaring resulted in a separation of the smectite layers in the I/S of about 9 Å, as estimated by X-ray powder diffraction and by nitrogen adsorption studies. Only the smectite layers of the clay were modified by the pillaring procedure. The pillared products had surface areas of 200–260 m2/g and pore volumes of about 0.18 cm3/g. The uptake of Al by the clay and the micropore surface area of the pillared products were proportional to the fraction of smectite layers in the I/S. The thermal and hydrothermal stability of the pillared I/S was similar to that of pillared montmorillonite prepared using the same procedure.
K-Rich Mordenite from Late Miocene Rhyolitic Tuffs, Island of Samos, Greece
Authors: Pe-Piper G. , Tsolis-Katagas P. 
Published: August 2006

AbstractMordenite occurs in hydrothermally altered rhyolitic volcanic rocks at the margin of a Late Miocene lake basin on the island of Samos, Greece. The mordenite was identified by its X-ray powder diffraction pattern and appearance in scanning electron micrographs. Electron microprobe analyses show high Si, Ca, and K, low Na, and high balance errors. The b cell dimension is consistent with a high Si/(Al + Si) ratio, and the balance errors are apparently due to Na deficiency. The missing Na was estimated from the amount required to give (Si + Al) = 48 and yielded analyses comparable with X-ray fluorescence analyses of samples predominantly of mordenite. Even after this correction, the mordenite had a low Na:K ratio compared with most analyses reported in the literature. The peculiar chemistry of the mordenite may have resulted from a high-temperature metasomatic origin as a result of basaltic volcanism at the basin margin and characterized by hydrothermal circulation of alkaline lake water rich in K.
X-Ray Powder Diffraction Rietveld Characterization of Synthetic Aluminum-Substituted Goethite
Authors: Fazey P. G. , O'Connor B. H. , Hammond L. C. 
Published: August 2006

AbstractRiet veld X-ray powder diffraction (XRD) analysis has been evaluated as a procedure for characterizing Al-substituted goethite according to the Rietveld scale factor, unit-cell parameters, and atom positional parameters. The study was conducted with three synthetic goethite samples for which the degree of Al substitution for Fe determined by chemical analysis was 8.0 ± 0.4, 12.0 ± 0.4, and 20.1 ± 0.4 mole %. The weight fractions of crystalline material (WFCM) in the specimens, determined from the Rietveld scale factors after correcting for adsorbed water and impurities, were 0.878 (esd = 0.014), 0.919 (0.014), and 0.965 (0.015), respectively. The Al mole % substitutions, inferred from the Rietveld cell parameters according to the method of Schulze (1984), were 10.4 ± 2.5, 16.5 ± 2.6, and 17.1 ± 2.6, respectively. The cause of the significant difference between the second value and the chemical analysis result is not known. The atom positional parameters did not differ significantly within the sample suite and agreed satisfactorily with literature values. The results have demonstrated the value of using Rietveld XRD analysis to determine simultaneously the WFCM and Al mole % substitutions, as well as to confirm the non-hydrogen atom positions.
Characteristics of Products from the Acid Ammonium Oxalate Treatment of Manganese Minerals
Authors: Mendelovici Efraím , Sagarzazu Amaya 
Published: August 2006

AbstractTo determine the parameters that control the attack of Mn minerals by acid ammonium oxalate in darkness (AAOD), rhodochrosite, pyrolusite, manganosite, hausmannite, and bixbyite were shaken with AAOD for 2 hr. These treatments were followed systematically by X-ray powder diffraction (XRD) and AAOD-extractable Mn analyses. About 5% of original hausmannite (surface area = 6 m2/g) remained in the solid residue of the AAOD treatment; however, if the hausmannite surface area was increased to 8 m2/g, by grinding, it completely dissolved in oxalate. Synthetic hausmannite of high surface area (37 m2/g) and rhodochrosite were completely dissolved by oxalate. Manganosite (1.5 m2/g) and especially pyrolusite (~ 1 m2/g) were more resistant to AAOD attack. Ground manganosite (4.2 m2/g) dissolved completely, but ground pyrolusite (7.2 m2/g) was only partially attacked by AAOD, inasmuch as about 25% of pyrolusite was found in the residue. An increase of the extraction time to 4 hr did not completely dissolve the ground pyrolusite.As a result of the AAOD treatment, MnC2O4 · 3H2O and MnC2O4 · 2H2O precipitated from the oxalate solutions with all starting minerals, except pyrolusite (~ 1 m2/g), which only slightly dissolved. The seldom reported MnC2O4 · 3H2O phase was identified in residues of freshly extracted samples by its strong characteristic peak at 6.5.-6.6 Å, the intensity of which gradually decreased and disappeared over several days when the sample was exposed to ambient conditions (22°C and 70% relative humidity). The trihydrate phase also collapsed after heating AAOD-treated rhodochrosite at 50°C; α-MnC2O4 · 2H2O was identified as the main crystalline product. Heating the α-MnC2O4 · 2H2O product at 115°C overnight transformed most of it to MnC2O4. The color of the oxalate-treated samples ranged from pinkish-gray to black (7.5 YR); their surface area ranged from about 20 to 30 m2/g. The degree of transformation of Mn minerals by oxalate depended on the surface area and structural characteristics of the starting materials.