Ammonium-saponite is hydrothermally grown at temperatures below 300°C from a gel with an overall composition corresponding to (NH4)0.6Mg3Si3.4Al0.6O10(OH)2. The synthetic saponite and coexisting fluid have been characterized by means of X-ray powder diffraction, X-ray fluorescence, Induced Coupled Plasma-Atomic Emission Spectroscopy, thermogravimetric analysis, transmission electron microscopy, CEC determination using an ammonia selective electrode, and pH measurement. In the crystallization model developed, crystallization started with the growth of individual tetrahedral layers with an aluminum substitution not controlled by the A1IV/A1VI ratio in the gel and hydrothermal fluid, on which the octahedral Mg layers can grow. During the synthesis, individual sheets stacked to form thicker flakes while lateral growth also took place. The remaining A1VI partly replaced ammonium as the interlayer cation.

The response of two swelling clays (SWy-1 and SAz-1) and of one non-swelling clay (KGa-1) and of a series of mixtures of these clays to different electrolyte concentrations was examined using clay-modified electrode techniques. A non-interacting probe ion, Fe(CN)63−, was monitored via reduction for its arrival at a Pt electrode coated with thin films of the clay mixtures. The three clays had both different temporal responses and different equilibrium currents. For SWy-1 the currents were developed over time and were dependent upon the electrolyte of the bathing solution, which was consistent with X-ray diffraction data literature for the interlayer dimension. Similar behavior was found for SAz-1, but for KGa-1, currents were instantaneous and were independent of the bathing electrolyte. This suggests that the pores controlling the probe ion transport were between particle or pinhole in nature. When mixtures of the clays were examined, it was found that KGa-1 caused defects within the structures of the mixed clay films. The SWy-1 mixture was not as affected by these disruptions as was the SAz-1 mixture.

The structure of the interlayer cation-water system in La-vermiculite with a unit cell of a = 5.33(5), b = 9.18(6), c = 15.13(9) Å and β = 96.82(7)° has been determined in space group C2/m. Under ambient conditions, the interlayer La cations are distributed on a 3a × b superlattice which disappears on dehydration but returns on rehydration. The basal spacing does not change during the dehydration/rehydration process. The character of the superlattice spots indicate that the cation-water system, at ambient conditions, is ordered over relatively large domains. The La cations are surrounded by 8 neighboring water molecules in a distorted cubic arrangement. The spaces between the La-water clusters are occupied by triads of water molecules that are relatively mobile.

Tetramethylphosphonium-smectite (TMP-clay) and tetramethylammonium-smectite (TMA-clay), were prepared and characterized as adsorbents for a series of aromatic and chlorinated hydrocarbons. The sorption of benzene, alkylbenzenes, and carbon tetrachloride as vapors and as solutes from water was studied to evaluate the effect of water on adsorption efficiency. Adsorption of organic vapors depended on the N2 BET surface area. TMA-clay was a slightly better adsorbent than TMP-clay, due to its somewhat higher surface area. The Langumir isotherms obtained indicated that adsorption occurred predominantly in the interlayer micropores, apparently on mineral surfaces between onium ions. Adsorption efficiency of both organo-clays decreased, compared to vapor sorptions, in presence of water. Lower sorption was apparently due to shrinkage of the interlayer pore or cavity sizes by hydration of interlayer TMA and TMP cations. Although sorption efficiencies of both organo-clays was reduced in presence of bulk water, the extent of reduction was much less for TMP-clay. Thus, TMP-clay was a better adsorbent than TMA-clay in presence of water, despite its lower surface area, in direct contrast to vapor sorption. The Langumir isotherms indicated interlayer sorption of benzene, alkylbenzenes and carbon tetrachloride from water by TMP-clay. The absence of Langumir isotherms for toluene, ethylbenzene and p-xylene uptake from water by TMA-clay indicated that these bulkier solutes were not adsorbed in the interlayers. These results indicate that hydration of TMA cations causes shrinkage of the interlayer pores to dimensions that exclude these solutes. The lower degree of hydration of TMP cations enables TMP-clay to maintain interlayer pores large enough to accommodate the bulkier alkylbenzenes.

Kaolinite:NaCl intercalates with basal layer dimensions of 0.95 and 1.25 nm have been prepared by direct reaction of saturated aqueous NaCl solution with well-crystallized source clay KGa-1. The intercalates and their thermal decomposition products have been studied by XRD, solid-state 23Na, 27Al, and 29Si MAS NMR, and FTIR. Intercalate yield is enhanced by dry grinding of kaolinite with NaCl prior to intercalation. The layered structure survives dehydroxylation of the kaolinite at 500°–600°C and persists to above 800°C with a resultant tetrahedral aluminosilicate framework. Excess NaCl can be readily removed by rinsing with water, producing an XRD “amorphous” material. Upon heating at 900°C this material converts to a well-crystallized framework aluminosilicate closely related to low-carnegieite, NaAlSiO4, some 350°C below its stability field. Reaction mechanisms are discussed and structural models proposed for each of these novel materials.

The swelling of some well-defined Mg-, Ca-, Sr- and Ba- homoionic montmorillonites was studied in the domain of water relative pressures lower than 0.95. This involves the expansion of the crystal lattice itself, commonly known as the “interlamellar expansion” or “inner crystalline swelling”. The initial freeze-dried clays were characterized by nitrogen adsorption-desorption volumetry and controlled transformation rate thermal analysis. The evolution of the structural and textural properties of these different clays at different stages of hydration and dehydration was investigated using water adsorption gravimetry, immersion microcalorimetry at different precoverage water vapor relative pressures and X-raydiffraction (XRD) under controlled humidity conditions. Large textural variations are observed in the dry state depending on the exchangeable cations. The 2-layer hydrate exhibits the most ordered layer stacking. Water is mainly adsorbed in the interlamellar space. With increasing water pressure, each homoionic species leads to a 1-layer hydrate and, with the exception of Ba-montmorillonite, to a predominant 2-layer hydrate. The relative pressure corresponding to the formation of the 2-layer hydrate decreases with increasing hydration energy of the interlayer cation. For Ca-, Sr- or Mg-montmoriHonites, simulation of XRD patterns leads to the definition of successive homogeneous states corresponding to the 2-layer hydrate. Furthermore, it yields the water filling ratio corresponding to the different hydration states during adsorption and desorption of water vapor.

Two series of pillared clays were prepared from a purified montmorillonite (95%) from La Serrata of Nijar, Spain, and polycations of Al and Zr using various methods. The effect of both the pillaring cation and the procedure of preparation on the physicochemical characteristics of the resulting materials was studied. Changes in texture were determined by X-ray diffraction (XRD) and N2 adsorption at 76 K and changes in acidity were determined by thermogravimetry following pyridine adsorption at room temperature and further desorption at a constant heating rate of 10 K min−1 in the range of 298–623 K. The relation between the size and charge (n/q) of the pillaring cation, which is dependent on the degree of cation hydrolysis, is the main factor affecting pore size and acidity of the synthesized materials. The pH of the pillaring solution affects the stability of the parent clay and the properties of the pillared clay. Below a pH of 3 and depending on contact time, the montmorillonite may delaminate and partially dissolve to produce products that affect the properties of the resulting materials. Microporosity increases for both Al or Zr-pillared clays. For Zr-pillared clays, microporosity is accompanied by changes in the mesoporosity and macroporosity as a result of clay delamination. Acidity dramatically increases by pillaring, especially strong acidity, and the acid strength distribution depends on starting salt concentration, aging time, and temperature.

The bonding in a cronstedtite layer was studied using a ninefold ordered supercell band structure calculation. The tight-binding scheme based upon the extended Hückel method was used to predict the electronic structure. The size of the problem was 162 atoms with 798 valence orbitals. The calculation showed different orbital interactions of oxygen p-orbitals with neighboring atoms with respect to the position in the layer. Substitution of Fe for Si in the terahedra reduced the role of the valence p-orbitals of the central Fe atoms. The d-orbitals of Fe were split in accordance with the rule of t2g-eg splitting. Although the density of states at the Fermi level was high, the partially filled 3d-bands were too narrow to permit normal metallic conduction.

Complex X-ray diffraction (XRD) profiles are described crystallographically by simulating XRD peaks for each phase, and adding the various elementary patterns to fit the experimental X-ray pattern. X-ray patterns of a ground muscovite and three polyphasic diagenetic I/S samples are fitted with this powerful, but time-consuming, technique. In the 6°–10°2θ CuKα range, the asymmetry of the muscovite peak is related to a very broad coherent scattering domain size (CSDS) distribution; for the I/S samples the even greater asymmetry is due to the presence of several phases with close, but distinct crystallographic characteristics (I/S, illite, and detrital mica).

A simulation-decomposition approach for modelling XRD patterns is introduced to describe quickly and accurately the various clay minerals (essentially mixed-layer illite/smectite and illite) present in a sedimentary series, and to follow their individual evolution during diagenesis. The theory for these simulations is described briefly. The influence of mixed-layer heterogeneity (the distribution of CSDS, and the distribution of smectite content) on the shape of X-ray peaks is shown theoretically to be minimal. Indeed, for both CSDS and smectite content, the important parameter for peak shape appears to be the mean value of the distribution and not its width and/or its shape. The theoretical limitations of the decomposition method are presented. Minor experimental limitations (reproducibility, experimental peak shape, discrimination) make this method a powerful and reliable tool to describe X-ray patterns. The method is used to show the simultaneous occurrence of three “illitic” phases in a sedimentary series from the Paris Basin. The respective evolution of the three phases is clearly evidenced by using this decomposition method. However, the precise identification of these different phases remains difficult to determine because of the difference in peak width between simulated and experimental X-ray patterns.

Transmission X-ray diffraction (XRD) of C6–16 alkylammonium ion-exchanged montmorillonite SAz-1 with Ag-behenate as an internal standard provided accurate estimates of d(001) values of the alkylammonium ion-exchanged montmorillonite. Inspection of d(001) values were made to assess the possible formation of gauche conformers (alternate arrangements of the molecules) in the interlayer and to determine the critical carbon chain length, nC. Using conventional constraints for nC(I′) and nC(II) equal to 1.36 and 1.77 nm, respectively, provided ambiguous nC(I′) and nC(II) values. The dependence of full-width at half-maximum values on nC allowed better estimates of nC(I′) and nC(II) because “integral” and “non-integral” peak characteristics relating to interstratification could be included in the assessment.

The effect of inaccurate estimates of nC(I′) and nC(II) values on calculated interlayer cation exchange capacity (Ci) using two conventional concepts of calculation were compared. It was found that a procedure based on the summation of fractions of the layer charge gave relative errors of Ci <2%, even where the number of carbon atoms corresponding to both nC(I′) and nC(II) differed by ± 1 nC from the correct values. This method of calculation of Ci is recommended when reliable values of Ci are needed.

Hydroxy-chromium solutions were prepared from chromium nitrate solutions by adding NaOH with OH/Cr = 2.

The solutions were treated at 20°C and 60°C. The hydrolysis times were from 1 to 100 days. Polymeric species in hydrolyzed chromium solutions were followed by visible absorption spectra within the range 325–800 nm and by pH measurement. OH-Cr-smectite with high d(001) spacing (2.07 nm) was obtained when hydroxy-chromium solution was prepared at 60°C and with 1-day hydrolysis. When this sample was heated up to 350°C the basal spacing collapsed at 1.8 nm.

The samples were characterized by X-ray diffraction and N2 adsorption-desorption isotherms.

Experimental alteration of volcanic tuff from Almeria, southeastern Spain, was performed in solutions with different Na/K ratios (0.01, 1, 10, and 100), different total salt concentrations (0.01, 0.1, 0.2, 0.33, and 1 M), and in deionized water, at 60, 80, 120, and 160°C, for periods of 60, 90, 180, and 360 d. Two particle size fractions of volcanic tuff were used: 10–200 and 20–60 μm. Alteration products were examined by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), laser-particle size analysis, scanning electron microscopy equipped with an energy dispersive X-ray spectrometer (SEM-EDS), image computer analysis, and transmission electron microscopy with microanalysis (TEM-AEM). XRD detected neoformed phases only in the products from experiments of 180–360 d at high temperatures (120–160°C), and with Na/K ratios above unity and in deionized water. The synthesized phase is a random mixed-layer illite-smectite (I-S) with 75% smectite. The quantity of newly formed I-S, determined by FTIR, ranged between 3–30%. There was no apparent change in grain size and shape of the grains after the experiments as compared to before.

SEM-EDS and TEM-AEM revealed the following alteration sequence: 1) intense etching on glass-grain surfaces; 2) formation of hemispherical morphologies on grain surfaces; 3) precipitation of very thin, individual flakes of illite-smectite on glass-grain surfaces; 4) development of I-S at the edges of glass grains; and 5) development of I-S honeycomb structures either covering large areas of the glass grains or resulting from the complete alteration of glass grains. A direct transformation of glass to I-S seems to be the major reaction mechanism, although there also is evidence of glass dissolution and subsequent I-S precipitation.

Fundamental particle thickness measurements of Dolná Ves hydrothermal illite/smectite (I/S) samples confirmed earlier findings regarding the content of fixed cations in illite interlayers (ca. 0.9/O10(OH)2). The distributions of fundamental particles and mixed-layer crystals of a given sample are internally consistent. In samples dominated by bilayer fundamental particles, mixed-layer crystals most often contain even numbers of layers. The expandabilities measured by XRD are much higher than so-called minimum expandabilities obtained from HRTEM measurements. This discrepancy is explained by assuming that the coherent scattering domains of Dolná Ves clays do not correspond to natural mixedlayer crystals but are thicker, probably due to parallel association of crystals on the oriented XRD slide. This tendency to produce intercrystal contacts is probably related to the unusually large ab dimensions of crystals of Dolná Ves clays.

The smectite-to-illite diagenetic transformation has been documented in 5 different sedimentary basins using X-ray diffraction (XRD). Intermediate reaction products coexisting because of the effect of kinetics on this reaction have been characterized using decomposition of XRD patterns and comparison with calculated patterns. The nature and relative abundances of the various subpopulations of particles are shown to vary as a function of the geothermal gradient and of the age of the sediment. In all sedimentary basins that experienced a low steady geothermal gradient the physico-chemical characteristics (coherent scattering domain size [CSDS], junction probabilities) of intermediate mixed-layered illite-smectites (I-S) are similar. However, both the relative abundance and the crystallinity of the end-member illite increase as a function of the age of the sediment.

In basins that have experienced a higher geothermal gradient, the CSDS of the I-S subpopulation is higher for a given illite content, indicating a slightly different reaction pathway. This difference in the characteristics (peak position and width) of elementary peaks may be used to infer the presence of such a high geothermal gradient when no other data are conclusive. In this case the growth of the illite end-member is favored over the growth of intermediate I-S phases even in young basins. Illitic phases formed from the alteration of kaolin minerals exhibit characteristics similar to the reaction products of the smectite-to-illite diagenetic transformation in the case of a high geothermal gradient. In contrast with what is observed in shale diagenesis, the characteristics of the illitic subpopulations describe a continuum with absolutely no gap in between subpopulations. In sandstone reservoirs, the various subpopulations crystallize simultaneously from a kaolin precursor. As a consequence, no kinship is expected between the various subpopulations.

The cation exchange capacity (CEC) of fine-grained materials, and especially clay minerals, is a fundamental property of these materials, and can be determined routinely. A search of the recent literature illustrates the great interest of this property to researchers. For example, a search of the GeoRef database for references to “cation exchange capacity” for the years 1980 to 1999 yields 2559 citations.

Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(TV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.

Iron-manganese concretions are common in upper sola of Alfisols in the Inner Bluegrass Region of Kentucky. Their nature and quantities appear to be related to the fluctuation of seasonal perched water tables above clayey argillic horizons. This study was conducted to examine changes in the macro-and micromorphology, chemistry and mineralogy of concretions as a function of size, color and soil depth. Total Mn and Fe contents increased, while SiO2 decreased with concretion size. Black concretions contained higher Mn, while brown concretions were higher in Fe. Crystalline Mn- and Fe-oxides fractionated with a sequential extraction procedure increased, but amorphous Mn and Fe decreased with concretion size. Goethite was the only crystalline Fe oxide mineral identified by X-ray diffraction (XRD) analysis. Manganese oxide minerals were very difficult to detect due to the diffuse nature of their XRD peaks and poor crystallinity. Examination of soil thin sections showed concretions of soil horizons overlying restrictive clayey layers to exhibit differentiated fabrics, sharp external boundaries and generally spherical shapes. Concretions found within clayey restrictive layers or above lithic interfaces usually had less structural organization, softer matrices and diffuse external boundaries due to longer term saturated conditions. Scanning electron microscopy (SEM) examinations suggested that the concretionary matrix, in spite of its density, has numerous cavities and an extensive micropore system within which dissolved plasmic Fe and Mn can diffuse and precipitate.