The main objective of the present work was to functionalize nanoclays with organosilanes and surfactant in order to facilitate the dispersion of the nanofillers in the host fluoroelastomer (FKM) polymer matrix. Better dispersion was achieved by improving interaction between the clay polymer nanocomposite (CPN) constituents. The first part of this study investigated modification of montmorillonite (Mnt) using different saturated and unsaturated alkyl silanes and an alkyl hydrocarbon ammonium quaternary surfactant. Silicon magic angle spinning nuclear magnetic resonance spectroscopy, thermal gravimetric analysis (TGA), elemental analysis, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy were used to characterize the silane-grafted clays. Results indicated that the amount of silane grafted depended on the specific structure of the silane. Silane-grafted Mnt was also modified with ionic surfactants intercalated between the clay layers. A 169% increase in the clay basal spacing (from initial spacing of 10.0 Å to 26.9 Å) was achieved. The second part of the study successfully synthesized FKM nanocomposites containing custom-functionalized Mnt, with the aim of producing reinforced high-performance materials. The effects of clay modification on the morphology and thermal properties of the CPN were studied using XRD, TGA, scanning electron microscopy, and transmission electron microscopy. The CPN made with the modified clay exhibited greater thermal stability than the CPN of the commercially available modified Mnt, with a degradation onset point ~ 40°C higher.

An overlap of bands produced by the O−H stretching vibrations of H2O (O–Hw) and structural OH (O−Hs) in smectite hampers the study by infrared spectroscopy (IR) of both their layer and interlayer structure. The present study re-evaluated the D2O saturation of smectite as a tool to enable separation of the overlapping bands at ambient conditions. Real-time monitoring by Attenuated Total Reflectance infrared spectroscopy (ATR-IR) was employed during in situ sample drying and H2O or D2O saturation at ambient temperature. Six dioctahedral and one trioctahedral pure smectites in Ca2+-, Na+-, and Cs+-cationic forms were studied to explore variability in total layer charge, charge location, and interlayer cation. The IR data showed the interlayer O−Dw signature at 2700–2200 cm−1 as a proxy for the O−Hw signature in the 3700–3000 cm−1 region. In addition to the expected liquid-like bands of D2O in the interlayer, these O−Dw spectra exhibited an additional sharp stretching feature in the 2695–2680 cm−1 range. No significant cation dependence of the sharp band position was observed between pairs of Ca- and Na-smectites for relative humidity (RH) between 60 and 80%, despite the large difference in the ionic potential between these interlayer cations. The intensity of the sharp band was found to be almost insensitive to changes in water content within the range 60–80% RH. The sharp band frequency decreased linearly with increasing total charge of the 2:1 layer (and can be used as a proxy for it), but no effect of charge location could be discerned. In agreement with early studies, this band was attributed to D2O located on the surface of the interlayer, pointing one O−D group toward the siloxane surface. Based on its high frequency, this band was indicative of free O−D oscillators, with very little or no involvement in hydrogen bonding (“dangling OD”). By analogy to the spectra of D2O-smectites, the spectrum of H2O-smectites also involves a sharp O−Hw analog at ~3630 cm−1 overlapping with typical OHs bands (e.g. Al2OH). As a result of this overlap, the sharp 3630 cm−1 O−Hw contribution was often missed or attributed solely to O−Hs.

Montmorillonite-rich clays are important in many engineering applications. The compressibility of such plastic clays at high consolidation pressures is important for predicting routine settlement and for applications in nuclear-waste repositories. Laboratory measurement of compressibility data at high consolidation pressures is not only time consuming but very expensive also. Theoretical predictions can help to determine the compressibility of plastic clays at high consolidation pressures. A linear relationship between e/eNvs. 1/√P (eN is the normalization void ratio at normalization pressure N and P is the consolidation pressure) was derived using diffuse double-layer theory. The compressibility data of several plastic clays in published studies were found to support the derived relationship. A generalized theoretical equation was proposed to predict the compressibility data over a wide range of consolidation pressures using an experimentally measured void ratio at low consolidation pressure. The compressibility data for different plastic clays were predicted accurately up to maximum consolidation pressures that ranged from 0.7 to 30 MPa using an experimentally measured void ratio near the pre-consolidation pressure. The preconsolidation pressures for different clays considered here ranged from 25 to 133 kPa. The proposed predictive model is supported by experimental data, is simple, and does not require knowledge of clay-surface and pore-fluid parameters.

The equivalent diffuse double layer (DDL) thickness in clay-electrolyte systems is a very useful parameter for analyzing the engineering behavior of clays under different environmental conditions. The equivalent DDL thickness is generally assumed to be equal to the characteristic (Debye) length. The present work examined critically the applicability of characteristic length to define equivalent DDL thickness under various clay-surface and pore-fluid conditions. A critical analysis is presented of the changes in the equivalent DDL thickness and characteristic length under the influence of different clay-surface and electrolyte properties. The equivalent DDL thickness was found to be smaller than the characteristic length for a wide range of surface and pore-fluid parameters normally encountered in engineering practice. An accurate and simple power relationship was developed to predict the equivalent DDL thickness from the characteristic length, which is applicable to a wide range of clay-electrolyte systems.

Bentonite and iron metals are common materials proposed for use in deep-seated geological repositories for radioactive waste. The inevitable corrosion of iron leads to interaction processes with the clay which may affect the sealing properties of the bentonite backfill. The objective of the present study was to improve our understanding of this process by studying the interface between iron and compacted bentonite in a geological repository-type setting. Samples of MX-80 bentonite samples which had been exposed to an iron source and elevated temperatures (up to 115°C) for 2.5 y in an in situ experiment (termed ABM1) at the Äspö Hard Rock Laboratory, Sweden, were investigated by microscopic means, including scanning electron microscopy, μ-Raman spectroscopy, spatially resolved X-ray diffraction, and X-ray fluorescence.

The corrosion process led to the formation of a ~100 μm thick corrosion layer containing siderite, magnetite, some goethite, and lepidocrocite mixed with the montmorillonitic clay. Most of the corroded Fe occurred within a 10 mm-thick clay layer adjacent to the corrosion layer. An average corrosion depth of the steel of 22–35 μm and an average Fe2+ diffusivity of 1–2 × 10−13 m2/s were estimated based on the properties of the Fe-enriched clay layer. In that layer, the corrosion-derived Fe occurred predominantly in the clay matrix. The nature of this Fe could not be identified. No indications of clay transformation or newly formed clay phases were found. A slight enrichment of Mg close to the Fe—clay contact was observed. The formation of anhydrite and gypsum, and the dissolution of some SiO2 resulting from the temperature gradient in the in situ test, were also identified.

Page 276: Change the average value of Cr in the ophiolitic rocks from 1850 ppm to 2530 ppm.