Microbial reduction of clay mineral structural Fe(III) decreases the swelling of nontronite gels, most importantly at intermediate oxidation states (40 to 80 cmol Fe(II) kg−1 clay). The purpose of this study was to establish whether microbial reduction of structural Fe(III) decreased the swelling of other Fe-bearing smectites and to discern the influence that organic compounds of microbial origin (bacterial cells, cell fragments and/or exudates) may have on clay swelling and texture. Structural Fe(III) was reduced by incubating smectite suspensions with either a combination of Pseudomonas bacteria or a mixture of anaerobic bacteria. The influence of organics on clay swelling was estimated on smectites suspended in either organic or inorganic media in the absence of bacteria. The gravimetric water content of the reduced clay gels equilibrated at various applied pressures was recorded as a function of Fe oxidation state. Transmission electron microscopy (TEM) was employed to determine the influence of bacteria and type of media on the texture of reduced smectite gels. Reduction of structural Fe(III) by bacteria decreased the swelling pressure of all Fe-bearing smectites. Increased clay swelling, due to the presence of organics (organic medium, exudates or cell fragments), was correlated to the total Fe content, the extent of structural Fe reduction, as well as the initial swelling characteristics of the Fe-bearing smectites. High structural Fe(II) contents (>50 cmol Fe(II) kg−1) resulted in increased attractive forces between clay platelets that decreased clay swelling, even in organic medium suspensions. Microbial reduction resulted in increased face-face association of individual clay layers, forming larger and more distinct crystallite subunits than in nonreduced clay gels. But, perhaps more importantly, microbial reduction of structural Fe(III) resulted in an increased association between crystallite subunits and, thus, an overall larger particle size and pore size distribution, due to the interaction of bacteria ceils, cell fragments and organic exudates.

A sequence of interstratified illite-smectite (I-S) and illite in Paleozoic pelites and metapelites from the Iberian Range, Spain, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The fine-grained matrix of diagenetic pelites is composed of I-S with sequences of illite- and smectite-like layers in a given sample. The Reichweite (R) values as determined by XRD and averaged over heterogenous I-S layer sequences increase with increasing grade, apparently continuously, in sharp contrast with TEM observations of other published sequences. Changes in I-S sequences along layers are rarely observed. In the higher-grade diagenetic pelites, I-S coexists with illite. Each I-S phase has a composition similar to that of illite, implying unique Al-Si distributions in contrast to smectite and muscovite. Selected area electron diffraction (SAED) patterns of I-S and illite are diagnostic of 1Md polytypism. Anchizonal metapelites consist of larger packets of well-crystallized muscovite, with SAED patterns corresponding to a two-layer polytype.

The continuous sequence of changes studied by TEM in I-S sequences and lateral transitions among these units is consistent with illitization by layer-by-layer replacement, although other processes are possible also. Replacement of individual layers probably occurs via fluids at reaction interfaces, in contrast to solid-state reactions, sensu strictu. The transition from the diagenetic to anchizonal rocks (transition in textures and formation of muscovite-2M1) occurred via dissolution/crystallization, however, presumably by tectonic stress. XRD and TEM data imply a consistent prograde trend in the sequence, the XRD data denning the average, long-range Reichweite ordering sequence, whereas the TEM data define the short-range layer sequences.

X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), surface area measurements, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to examine the surface properties of organosilane-modified smectite-type aluminosilicate clays. Organic modified clays derived from the reactions of montmorillonite (containing 93–95% montmorillonite from a bentonite, <1% quartz, and 4–6% opal CT) with octadecyltrichlorosilane (C18H37SiCl3) and octadecyltrimethoxysilane [C18H37Si(OMe)3] are highly hydrophobic. Surface loadings of the modified clays depend on the organosilane and the solvent, and they range from 10 to 25 wt. %. The organic species are probably adsorbed to the outer surfaces and bound to the edges of the clay via condensation with edge-OH groups. Encapsulation of montmorillonite with C18H37SiCl3 and C18H37Si(OMe)3 resulted in a hydrophobic coating that acts like a “cage” around the clay particles to limit diffusion. Basal spacings of the organic modified clays remain at ∼15 Å upon heating to 400°C in N2, whereas those of unmodified clays collapse to ∼10 Å. A considerable reduction in surface area (by 75–90%) for organic modified clays is observed, which is consistent with the existence of a surface coating. The solvent used can affect the amount of organic silane coated on the clay particles, whereas the difference between the products prepared using C18H37SiCl3 and C18H37Si(OMe)3 in the same solvent is relatively small. The carbon and oxygen K-edge NEXAFS spectroscopy of the modified montmorillonite surfaces showed that surface coatings on the outside of the clay particles exist. The encapsulating system may allow for economical remediation and storage of hazardous materials.

We study the Diophantine transference principle over function fields. By adapting the approach of Beresnevich and Velani [‘An inhomogeneous transference principle and Diophantine approximation’, Proc. Lond. Math. Soc. (3) 101 (2010), 821–851] to function fields, we extend many results from homogeneous to inhomogeneous Diophantine approximation. This also yields the inhomogeneous Baker–Sprindžuk conjecture over function fields and upper bounds for the general nonextremal scenario.

Nonlinear-optical investigations of new materials are important for 2 complementary reasons. first, the requirements for materials to be used in device applications that utilize nonlinear interactions are very demanding. New approaches to materials research can yield materials with favorable properties compared to traditional nonlinear materials, as shown recently in several supramolecular systems (Cox et a1. 1990; Stucky and MacDougall 1990; Clays et a1. 1993; Kelderman et a1. 1993; Kauranen et a1. 1995; Lehn 1995). This is particularly true for 2nd-order nonlinear optics that require noncentrosymmetric materials (Prasad and Williams 1991). On the other hand. nonlinear-optical processes can provide new techniques to study the properties of new materials. The nonlinear techniques have the potential of being more sensitive than the existing techniques or providing information that is not accessible at all using the existing techniques (Shen 1984). Here again, 2nd-order processes are particularly important because they provide an extremely sensitive tool to study symmetry properties of materials.

Transmission electron microscopy (TEM) including high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM) were used to study the fine clay fraction (<0.1 μm) from the eluvial E horizon of podzols located in central Finland that had developed from till materials. Soils of increasing age (6500-9850 y BP) were selected to represent a chronosequence of soil development. Expandable phyllosilicates (vermiculite, smectites) are formed in the eluvial E horizon of podzols in a short time (6500 y). TEM observations show that dissolution and physical-breakdown processes affect the clay particles. As the age of the soils increases, fragmentation and exfoliation of large precursor minerals lead to thinner clay particles of two to three layers thick. The chemical compositions of individual particles obtained by AEM indicate that expandable phyllosilicates from the E horizon of podzols are heterogeneous, involving a mixture of vermiculite, Mg-bearing smectites, and aluminous beidellite. Results suggest that heterogeneity is related to the nature of their precursors. Vermiculite and Mg-bearing smectites are derived from biotite and chlorite weathering whereas phengitic micas alter to aluminous beidellite. Because the transformation of biotite and chlorite is more rapid than phengitic micas, biotite and chlorite contributes predominantly to smectites in the younger soils, as long as ferromagnesian phyllosilicates are present in the E horizons. If not, a larger proportion of smectites is derived from phengitic micas in the older soils. Direct measurement of d(001 ) values on lattice fringe images from alkylammonium-saturated samples shows that interlayer charge varies from high-charge expandable minerals (0.6–0.75 per half unit cell) in the younger soils to 0.5–0.6 per half unit cell in the oldest soils. Thus, the proportion of the components in the clay assemblage, as well as their chemistry and interlayer charge, change over time with soil evolution.

Bentonite- 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.

The oxidation state of structural Fe greatly alters surface chemistry, which may have a large influence on clay-organic interactions. The effect of structural-iron oxidation state on chlorinated hydrocarbons at the clay-water interface was examined. Pentachloroethane (5CA) was reacted with oxidized, reduced, and reoxidized forms of three different smectites: montmorillonite, ferruginous smectite, and nontronite in aqueous suspension under controlled-atmosphere conditions. Pentachloroethane was found to adsorb at different rates for the three smectites. A series of 5CA-adsorption rate constants in the presence of these clays showed a strong correlation with the Fe(II) content of the clay (r2 = 0.98). The clay surface behaves as a Brønsted base and promotes 5CA dehydrochlorination. The adsorption kinetics at the clay-water interface were described by the formation of a precursor complex prior to 5CA dehydrochlorination.

A dusky red Oxisol forming on a tholeiitic basalt is found to contain varying proportion of aluminous hematite (Hm) and titanoaluminous maghemite (Mh) in the different size fractions. Maghemite is the main iron oxide in the sand and silt fractions whereas Hm is dominant in the clay fraction, together with gibbsite (Gb), kaolinite (Ka), rutile (Rt) (and probably anatase, An) and Mh. Maghemite is also the major oxide mineral in the magnetic separates of soil fractions (sand, about 65% of the relative Mössbauer spectral area; silt, 60%). Hematite (sand, 30%; silt, 15%) and ilmenite (Im) (sand, 5%; silt, 16%) are also significantly present in the magnetic extract. Accessory minerals are Rt and An. No magnetite (Mt) was detected in any soil fraction. Sand- and silt-size Mh have similar nature (a 0= 0.8319 ± 0.0005 nm; about 8 mol% of Al substitution; saturation magnetization of 49 J T−1 kg−1), and certainly a common origin. Lattice parameters of clay-Mh are more difficult to deduce, as magnetic separation was ineffective in removing nonmagnetic phases. Al content in Hm varies from 14 mol% (clay and silt) to 20 mol% (sand). The proposed cation distribution on the spinel sites of the sand-size Mh is:

$[{\text{Fe}}_{0.92}{\text{Al}}_{0.08}]\hspace{0.17em}\left\{{\text{Fe}}_{1.43}{\text{Ti}}_{0.18}\hspace{0.17em}{\square }_{0.39}\right\}{\text{O}}_4$

(◻ = vacancy, [ ] = tetrahedral sites and { } = octahedral sites), with a corresponding molar mass of 208.8 g mol−1. The predicted magnetization based on this formula is σ ≅ 68 J T−1 kg−1, assuming collinear spin arrangement. The large discrepancy with the experimentally determined magnetization is discussed.

The OH-stretching region in curve-fitted micro-Raman, photoacoustic and transmission IR spectra of St. Claire dickite was investigated. Polarized Raman spectra recorded from th. (001) an. (010) faces of the dickite crystal displayed six prominent OH bands. The relative intensities depend strongly on both the orientation of the crystallographic axes and the direction of the electric vector of the laser beam. Four out-of-plane vibrations, AA, Az, CA and Cz, at ~3710, 3706, 3654 and 3643 cm-1 respectively, predominate when the electric vector is perpendicular to the dickite plates. Two in-plane vibrations, Dz and DA at 3627 and 3623 cm-1, intensify when the electric vector is parallel to the plane. The relationship between band intensity and crystal orientation was interpreted in terms of longitudinal optic (LO) and transverse optic (TO) crystal vibration modes. These LO and TO crystal modes were also observed in curve-fitted photoacoustic and transmission IR spectra of coarse, non-oriented crystals of the dickite.

A stable 8.4 Å hydrate of kaolinite was prepared by exchanging ethylene glycol for water in the 10.8 Å intercalate of ethylene glycol in kaolinite. The hydrate of kaolinite was characterized by XRD, FTIR and TGA/DSC. From the TGA data, one can estimate that there is 0.60 water molecule per Al2Si2O5(OH)4 units. The IR data suggest a similarity of the local environment of the intercalated water in this 8.4 Å hydrate of kaolinite and the 8.4 Å hydrate of nacrite previously described by Wada (1965).

Smectite and fine-grained quartz were separated from 6 volcanic ash samples collected in Japan from Shinmoe-dake Volcano, southern Kyushu, and Mt. Usu Volcano, southern Hokkaido. Oxygen isotope ratios of smectite in the volcanic ash range from +6.9 to +12.9 per mill (‰), which are comparable to the values of smectite (δ18O = +6.5 and +9.4‰) from currently active geothermal fields. Evaluation of the oxygen isotope data from smectite (δ18O = +6.9 and +8.4‰) and quartz (δ18O = +6.6 to +11.2‰) in volcanic ash erupted from Shinmoe-dake in 1959 indicates a hydrothermal origin at elevated temperatures (150 to 270 °C) from waters that have calculated 8180 values (8180 = -3 to +5%o) that are enriched relative to local meteoric water (δ18O = -7 to -8‰). This precludes an authigenic formation of the smectites under ambient temperatures in crater lakes and/or somma-atrios which had been previously proposed as a plausible mechanism. A peculiar clay flow was extruded on the somma-atrio of Mt. Usu Volcano. The isotopic composition of the clay (<0.5 μm, δ18O = + 12.2‰) and evidence from geophysical exploration over volcanic vents of Shinmoe-dake support the concept that extensive hydrothermal alteration is taking place within volcanic vents.

Homoionic Ca-saturated clay pastes were prepared and drying curves were obtained by applying suction pressures from 1 kPa to 100 MPa, A transmission device was used to study particle orientation by placing the clay in a cell specially designed to obtain diagrams corresponding to different sample orientations. The 00l and hk0 reflections were compared to determine the best reflections for studying clay-particle orientation. Depending on the clay, 00/ reflections or the 020 reflection and/or hkl bands can be used to analyze orientation. In many cases the 020 reflection is preferred because the intensity of the peak is high and appears to be independent of the H2O content and the degree of stacking order of layers along the [001] direction.

For interstratified clays, the conditions required to obtain 00l reflections depended on several factors, the most important of which is the water content. Also, the intensity relating to particie orientation depends on (1) particle extension (size) in the (001) plane and (2) the crystal structure. Illite crystals of <1000 A gave a poorly oriented clay matrix. In contrast, large aggregates of illite, smectite, and kaolinite particles (>10,000 Å) showed a strongly oriented system. The particles of smectites may be curved and the dry material was poorly oriented owing to weak cohesion forces between the layers in comparison to illite.

The study of the orientation of particles by X-ray diffraction on hydrated samples may be affected by sample mounting techniques. Any change in the content or the way the sample is mounted may modify the microstructure of a material.

Clay containing a high water content affects the disorientation of particles, whereas, for the dry samples, pore size, pore volume, and solid continuity are associated with the geometry and crystal structure of the clay matrix.

In a hitherto unpublished manuscript dated 1794–95, H.-B. de Saussure described three types of rudimentary laboratory experiments on weathering, each one lasting about 4 hours, undertaken on samples of jade, serpentine, feldspar, and mica schist. He submitted these samples to dry heating, heating with continuous addition of water, and heating with periodic addition of water. Experimentation was performed at temperatures of the order of 200–250°C, and Saussure seems to have realized that a reasonable increase of temperature was necessary for laboratory simulation of long-lasting geological processes. No changes were observed during dry heating whereas increasing alteration was noticed in the presence of water, particularly when heating was combined with periodic wetting. He concluded that these tests demonstrated his preconceived idea that weathering of minerals (mostly silicates) resulted from alternating periods of drying and wetting. This concept is basically very close, if not identical, to that underlying modern ideas on seasonal weathering.

There has been much interest in the rare specimen of beidellite from the Black Jack Mine, Florida Mountain, Idaho. A variety of aluminous clays exists along veins such as the Black Jack vein, in rhyolite and latite flows, and in near-surface ash beds, often containing less than 1.0% MgO and 0.5% Na20. Associated clays include beidellite, illite, kaolinite, 10-Å halloysite, dickite, nacrite, rectorite and a tarasovite-like mineral. The predominant clay is mixed-layer illite—beidellite. The beidellites have Al2O3 contents ranging from about 28 to 33%, and predominantly Ca and K as interlayer cations. The typical beidellite dehydroxylation temperatures of about 595 °C readily differentiate the beidellite from montmorillonite, which has a dehydroxylation temperature in the range of 735 °C. A modified differential thermal analysis (DTA) method is given for readily estimating the interlayer cation populations of smectites, including Mg++ and Al+++ cations. Chemical analyses and layer charges of II beidellites from mines around the Black Jack Mine are given. The beidellites have an American Society for Testing and Materials (ASTM) classification of CR, φ value, internal friction angle of about 8° and an expansion pressure of about 9 kgf/cm2 (88.3 kPa), similar to that of nontronite.

Adsorption of cetylpyridinium chloride (CPC) onto kaolinite can be followed using the electroacoustic effect. The dynamic mobility, measured at a frequency of 1 MHz, varies from about −2 to +1 × 10−8 m2 V−1 s−1 in a number of steps, reflecting the adsorption of two separate layers, with the bilayer being more obvious, especially at pH 5–8. The behaviour at different pHs reflects the different charge characteristics of the basal cleavage planes and the crystal edges. When the amount of added CPC is equal to the cation exchange capacity of the clay, the kinetic charge changes from negative to positive and there is a pronounced break in the conductivity curve. It is also possible to estimate the edge to face area from such measurements and so obtain a measure of the aspect ratio of the clay crystallites. The (minimum) value for this clay is about 5:1.

The fine clay (<0.1 μm) fraction of a clayey soil (Vertisol) from Sardinia (Italy) was studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, cation exchange capacity (CEC) and surface area measurements. Smectites were the dominant clay minerals both in the parent material and the soil horizons. The magnitude and location of the smectites’ layer-charges were analyzed using the Hofmann & Kiemen effect (suppression of the octahedral charge following lithium-saturation and heating). The amount of montmorillonite layers was evaluated by measuring the reduction of total surface area and CEC after suppression of octahedral charges and subsequent collapse of montmorillonite interlayers. Reduction of total surface area and CEC after fixation of K and irreversible collapse of interlayers were used to quantify high-charge layers before and after the suppression of octahedral charges. This allowed us to evaluate the amount of tetrahedral high-charge layers. The smectites in the parent material were montmorillonitic-beidellitic mixed layers and exhibited a small proportion of high-charge layers; in particular, layers with a high tetrahedral charge were a very minor component. In the upper soil horizons, the amount of montmorillonitic layers decreased whereas the amount of smectite layers with a high tetrahedral charge increased. FTIR spectroscopy indicated more Fe for Al substitution in the smectites of the soil horizons than in the smectites of the parent material. The results suggested that octahedral charged smectite layers (montmorillonitic) were altered, whereas high-charge beidellitic layers were formed in this soil environment characterized by rather high pH (>8.0).

Reported in this paper is a study of the influence of pore fluid composition on sediment volume of kaolinite suspensions. Laboratory tests have been conducted with kaolinite in water with NaCl, CaCl2 and A1C13 of different concentrations and in 10 types of organic liquids of varying values of static dielectric constant. The types of tests performed include regular suspension tests and leaching and cyclic leaching tests on kaolinite sediments. In the leaching tests, sediments formed during the regular suspension tests in water of low salt concentration were subsequently leached with water of high salt concentration. In the cyclic leaching tests, the salt concentration was increased and then decreased. The purpose of the leaching and cyclic leaching tests was to study the change in existing equilibrium fabric caused by subsequent changes in the concentration of salt in pore fluid. Results of the suspension tests indicate that sediment volume of a water suspension decreases with increase in ion concentration and increase in valence of cation. Leaching and cyclic leaching tests indicate that substantial change in salt concentration is required to change the existing fabric. The effect of dielectric constant of pore fluid on sediment volume is somewhat complex. As the dielectric constant increases from 1.9 for heptane to 110 for formamide, sediment volume first decreases, assuming a minimum at 24 for ethanol, increases with a maximum at 80 for water, and decreases again until 110 for formamide. An approximate physico-chemical analysis model is used to interpret some of the data in a quantitative manner. In the analysis model, recently developed theories of double-layer repulsive and van der Waals attractive forces are combined to simulate the behavior of suspensions.

A glass in the intermediate composition of montmorillonite and beidellite, 50/50 in mole ratio, was treated under a hydrothermal pressure of 100 MPa, in the temperature range from 250 to 500°C and durations from 2 to 129 days. The phases identified in the products were plotted in a time-temperature-transformation (TTT) diagram. The TTT diagram showed that the regularly interstratified montmorillonite-beidellite (r.i.M-B) was a metastable phase above the temperature of 350°C and changed to the assemblage of Na-rectorite + saponite + quartz, through the intermediate assemblage of beidellite + saponite + quartz. The TTT diagram suggested also that the r.i.M-B might be a stable clay mineral below the temperature of 300°C in the middle region of montmorillonite-beidellite pseudo-binary system, although the laboratory confirmation of the mineral stability was not easy for the sluggish reaction.