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The emergent secondary phases and surface altered layer (SAL) during the aqueous corrosion of borosilicate glass have a great impact on its chemical durability. However, the formation and evolution of these structures are still unclear. Here, by studying the borosilicate glass altered at 90 °C in pore water, the water in pore space between glass powders, the formation of secondary phases could follow two ways: 1. the consumption of aqueous ions forms analcime, zeolite, calcium silicate and barite at the surface of glass; 2. the reorganization of silica aggregates leads to smectite within the SAL. Small-angle X-ray scattering and cross-sectional scanning electron microscopy results show that the release of soluble elements and the formation of smectite within the SAL significantly increase the porosity of SAL. Furthermore, the layer containing smectite reorganizes inwardly and the crystallinity of smectite is gradually increased over time. The observations of transmission electron microscopy reveal that the dissolution of glass potentially goes through an interface-coupled dissolution-reprecipitation process. [ABSTRACT FROM AUTHOR]

The crystal structure and ferroelectric properties of epitaxial ZrO2 films ranging from 7 to 42 nm thickness grown on La0.67Sr0.33MnO3 buffered (110)‐oriented SrTiO3 substrate are reported. By employing X‐ray diffraction, a tetragonal phase (t‐phase) at all investigated thicknesses, with slight in‐plane strain due to the substrate in the thinnest films, is confirmed. Further confirmation of the t‐phase is obtained through infrared absorption spectroscopy with synchrotron light, performed on ZrO2 membrane transferred onto a high resistive silicon substrate. Up to a thickness of 31 nm, the ZrO2 epitaxial films exhibit ferroelectric behavior, at variance with the antiferroelectric behavior reported previously for the t‐phase in polycrystalline films. However, the ferroelectricity is found here to diminish with increasing film thickness, with a polarization of 13 µC cm−2 and down to 1 µC cm−2 for 7 and 31 nm thick ZrO2 films, respectively. Given that the t‐phase is nonpolar, the observations emphasize the influence of external factors, in promoting polarization in t‐ZrO2 thin films. These findings provide new insights into the ferroelectric properties and structure of ZrO2 thin films, and open up new directions to investigate the origin of ferroelectricity in ZrO2 and to optimize this material for future applications. [ABSTRACT FROM AUTHOR]

In this study, various chemical treatments were performed on clay-rich media to investigate their effects on hydrogen adsorption performance. We unequivocally demonstrated that acid-treated samples exhibited significant structural changes compared with those treated with alkali solutions. Gas adsorption isotherms and powder X-ray diffraction analyses clearly revealed that the acid treatment of clayey materials not only increased their surface area, but also enhanced hydrogen sorption uptake, increased interstratification, and reduced particle size. Most importantly, we succeeded in rationalizing the improvement in hydrogen uptake by sequentially applying purification, followed by acid treatment. [ABSTRACT FROM AUTHOR]

In the French north‐western Alps, several lakes of glacial origin, such as Aiguebelette and La Thuile, present some mass‐transport deposits within their sedimentary sequences. These event layers can result from lake sediment destabilization eventually triggered by earthquakes. On Lake Aiguebelette, based on sedimentological, geochemical and magnetic analyses, and high‐resolution seismic and bathymetric surveys a ca 1 m thick event layer was identified in the deepest lake basin and a synchronous ca 2 cm thick deposit in the shallow basin. Age‐depth models based on radiocarbon ages reveal that both mass‐transport deposits in Lake Aiguebelette occurred around the Younger Dryas – Early Holocene climatic transition (i.e. 11 700 cal bp) time range. In Lake La Thuile, located 30 km away, unique mass‐transport deposits (translational slide type) were recorded at the same time range in sedimentary records. Additionally, high‐resolution seismic profiles previously acquired in Lake Annecy and Lake Bourget support the hypothesis of significant mass‐transport deposits occurring at the Younger Dryas – Early Holocene time range. These outcomes on four north‐western peri‐Alpine and Alpine lakes highlight the regional occurrence of mass‐transport deposits in the Younger Dryas – Early Holocene time range. Seismic and rockfall events are discussed as potential sources of these significant and similarly aged mass‐transport deposits. Based on this study and a literature review, the authors suggest that mechanisms induced by rapid climate change and glacial retreat, such as crustal rebound and erosional unloading, could favour the triggering of earthquakes and rockfall events. In the case of mass‐transport deposits archived in north‐western Alpine lakes during this time period, this study favours the hypothesis of increased seismicity as the primary source driving process involved. [ABSTRACT FROM AUTHOR]

Kimberlites carry a dense cargo of olivine. Although normally referred to as macrocrysts, much of this olivine is present as multigrain xenoliths of dunite. Because of their well-rounded outlines, we refer to these objects as 'nodules' and apply the term to both multigranular and monogranular varieties. Although compositions within each nodule are very uniform, the entire population displays an enormous variation in Fo content (100*Mg/(Mg + Fe), cation proportions), from close to Fo95 to about Fo82. The change is continuous, and there is no indication of separate Fo-rich and Fo-poor populations. Likewise, the sizes, internal textures and habits of Fo-rich and Fo-poor olivines are indistinguishable. Fo-poor nodules have compositions like those of olivines of the megacryst suite, and they share similar sizes and internal structures. We propose that the dunite nodules in kimberlites and olivines of the megacryst suite have a common origin. In our interpretation, almost all olivines in kimberlites, except for the marginal rims and rinds, are fragments of dunite that was produced during interaction between mantle peridotite and CO2-rich fluid. Analogues of this process can be found in ophiolites where dunite is the product of reaction between basaltic magma and peridotite. In situ reactive crystallization eliminated pyroxene, leaving only olivine with Fo contents ranging from higher to lower Fo than in the host peridotite. This interaction occurred near the base of the lithosphere and not during transit of kimberlite towards the surface. [ABSTRACT FROM AUTHOR]

The kinetics of the irreversible reaction Ca(OH)2+MgCO3 → CaCO3+Mg(OH)2 were investigated at high pressures and temperatures relevant to metamorphic petrology, using both in situ synchrotron X-ray diffraction and post-mortem analysis of reaction rim growth on recovered samples. Reaction kinetics are found to strongly depend on water content; comparable bulk-reaction kinetics are obtained under water-saturated (excess water, c. 10 wt %) and under intermediate (0.1-1 wt % water) conditions when temperature is increased by c. 300 K. In contrast, similar reaction kinetics were observed at ~673 K and 823 K between intermediate and dry experiments, respectively, where dry refers to a set of experiments with water activity below 1.0 (no free water), as buffered by the CaO-Ca(OH)2 assemblage. Given the activation energies at play, this gap-- corresponding to the loss of no more than 1 wt % of water by the assemblage--leads to a difference of several orders of magnitude in reaction kinetics at a given temperature. Further analysis, at the microscopic scale, of the intermediate and dry condition samples, shows that intergranular transport of calcium controls the reaction progress. Grain boundary diffusivities could be retrieved from the classic treatment of reaction rim growth rate. In turn, once modeled, this rate was used to fit the bulk kinetic data derived from X-ray powder diffraction, offering an alternative means to derive calcium diffusivity data. Based on a comparison with effective grain boundary data for Ca and Mg from the literature, it is inferred that both dry and intermediate datasets are consistent with a water-saturated intergranular medium with different levels of connectivity. The very high diffusivity of Ca in the CaCO3+Mg(OH)2 rims, in comparison with that of Mg in enstatite rims found by earlier workers, emphasizes the prominent role of the interactions between diffusing species and mineral surfaces in diffusion kinetics. Furthermore, we show that the addition of water is likely to change the relative diffusivity of Mg and Ca in carbonate aggregates. From a qualitative point of view, we confirm, in a carbonate-bearing system, that small water content variations within the 0-1wt % range have tremendous effects on both intergranular transport mechanisms and kinetics. We also propose that the water content dependent diffusivity of major species (Mg, Ca) in low-porosity metamorphic rocks is strongly dependent on the interaction between diffusing species and mineral surfaces. This parameter, which will vary from one rock-type to another, needs also to considered when extrapolating (P, T, t, xH2O) laboratory diffusion data to metamorphic processes. [ABSTRACT FROM AUTHOR]

Herein, we report new insights into the nucleation and growth processes of chrysotile nanotubes by using batch and semi-continuous experiments. For the synthesis of this highly carcinogenic material, the influences of temperature (90, 200, and 300 °C), Si/Mg molar ratio, and reaction time were investigated. From the semi-continuous experiments (i.e., sampling of the reacting suspension over time) and solid-state characterization of the collected samples by XRPD, TGA, FTIR spectroscopy, and FESEM, three main reaction steps were identified for chrysotile nucleation and growth at 300 °C: 1) formation of the proto-serpentine precursor within the first 2 h of the reaction, accompanied by the formation of brucite and residual silica gel; 2) spontaneous nucleation and growth of chrysotile between about 3 and 8 h reaction time, through a progressive dissolution of the proto-serpentine, brucite, and residual silica gel; and 3) Ostwald ripening growth of chrysotile from 8 to 30 h reaction time, as attested to by BET and FESEM measurements. Complementary results from batch experiments confirmed a significant influence of the reaction temperature on the kinetics of chrysotile formation. However, FESEM observations revealed some formation of chrysotile nanotubes at low temperatures (90 °C) after 14 days of reaction. Finally, doubling the Si/Mg molar ratio promoted the precipitation of pure smectite (stevensite-type) under the same P (8.2 MPa)/ T (300 °C)/pH (13.5) conditions. [ABSTRACT FROM AUTHOR]

This paper revisits the clay mineralogy of the "smectite" alteration zone in the Krafla geo-thermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, corrensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resident and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity. [ABSTRACT FROM AUTHOR]

The microstructural evolution of CaSiO3 wollastonite subjected to carbonation reactions at T = 90 °C and pCO2 = 25 MPa was studied at three different starting conditions: (1) pure water; (2) aqueous alkaline solution (0.44 M NaOH); and (3) supercritical CO2. Scanning and transmission electron microscopy on reacted grains prepared in cross-section always revealed unaltered wollastonite cores surrounded by micrometer-thick pseudomorphic silica rims that were amorphous, highly porous, and fractured. The fractures were occasionally filled with nanometer-sized crystals of calcite and Ca-phyllosilicates. Nanoscale chemical profiles measured across the wollastonite-silica interfacial region always revealed sharp, step-like decreases in Ca concentration. Comparison of the Ca profiles with diffusion modeling suggests that the silica rims were not formed by preferential cation leaching (leached layer), but rather by interfacial dissolution-precipitation. Extents of carbonation as a function of time were determined by quantitative Rietveld refinement of X-ray diffractograms performed on the reacted powders. Comparing the measured extents of carbonation in water (condition 1) with kinetic modeling suggests that carbonation was rate-controlled by chemical reactions at the wollastonite interface, and not by transport limitations within the silica layers. However, at conditions 2 and 3, calcite crystals occurred as a uniform surface coating covering the silica layers, and also within pores and cracks, thereby blocking the connectivity of the originally open nanoscale porosity. These crystals ultimately may have been responsible for controlling transport of solutes through the silica layers. Therefore, this study suggests that pure silica layers were intrinsically non-passivating, whereas silica layers became partially passivating due to the presence of calcite crystallites. [ABSTRACT FROM AUTHOR]