Abstract:Synthèse par voie sèche d'un plagioclase potassique à partir du labrador. Formation, en présence de l'eau sous pression, de l'orthose et de l'anorthite en arrangement épitaxique à partir du labrador. Action de l'eau sur la mobilité des ions Si et Al dans les feldspaths.
“…It emerges that it is possible to have an equiprobable distribution of Si*−O* ionic and Al−O* ionic configurations. These partially ionic structures can explain the chemistry of zeolites (as well as of other silicates) upon acid conditions, since they can be thought as “precursors” to many solid state reactions, like dealumination, hydrolysis, , or Si/Al mobility in minerals. , 8 Plots of the calculated Al−O* and Si*−O* distances (in angstroms) vs time in sodium sodalite and in hydrogen sodalite. Labels are defined in the text and Figure .…”
Section: Resultsmentioning
confidence: 99%
“…Figures 6 and 7 These partially ionic structures can explain the chemistry of zeolites (as well as of other silicates) upon acid conditions, since they can be thought as "precursors" to many solid state reactions, like dealumination, 3 hydrolysis, 30,31 or Si/Al mobility in minerals. 32,33 3.3. Vibrational Spectra.…”
We present the results of ab initio molecular dynamics simulations on the structural and dynamical properties of the Brønsted acid site in a zeolitic cage. The protonated sodalite H[AlSi 11 O 24 ] is the case studied, and the sodium sodalite is the reference unprotonated zeolite. The comparison between the geometrical parameters calculated for these two sodalites shows that the formation of an O-H bond gives rise to a significant local distortion of the framework geometry. Moreover, an equilibrium between partially ionic and covalent structures in the T-O bonds of the acid site is deduced from our calculations. We have found that the OH bond oscillates in and out of the plane of the 6-T-ring. The analysis of the simulated vibrational spectra has allowed us to assign the bands relative to the O-H in-plane and out-of-plane bending modes and confirms that these bands overlap with the framework modes.
“…It emerges that it is possible to have an equiprobable distribution of Si*−O* ionic and Al−O* ionic configurations. These partially ionic structures can explain the chemistry of zeolites (as well as of other silicates) upon acid conditions, since they can be thought as “precursors” to many solid state reactions, like dealumination, hydrolysis, , or Si/Al mobility in minerals. , 8 Plots of the calculated Al−O* and Si*−O* distances (in angstroms) vs time in sodium sodalite and in hydrogen sodalite. Labels are defined in the text and Figure .…”
Section: Resultsmentioning
confidence: 99%
“…Figures 6 and 7 These partially ionic structures can explain the chemistry of zeolites (as well as of other silicates) upon acid conditions, since they can be thought as "precursors" to many solid state reactions, like dealumination, 3 hydrolysis, 30,31 or Si/Al mobility in minerals. 32,33 3.3. Vibrational Spectra.…”
We present the results of ab initio molecular dynamics simulations on the structural and dynamical properties of the Brønsted acid site in a zeolitic cage. The protonated sodalite H[AlSi 11 O 24 ] is the case studied, and the sodium sodalite is the reference unprotonated zeolite. The comparison between the geometrical parameters calculated for these two sodalites shows that the formation of an O-H bond gives rise to a significant local distortion of the framework geometry. Moreover, an equilibrium between partially ionic and covalent structures in the T-O bonds of the acid site is deduced from our calculations. We have found that the OH bond oscillates in and out of the plane of the 6-T-ring. The analysis of the simulated vibrational spectra has allowed us to assign the bands relative to the O-H in-plane and out-of-plane bending modes and confirms that these bands overlap with the framework modes.
“…It was concluded that the large cations could migrate under anhydrous conditions, but that water was essential for migration of silicon and aluminium. 71 The action of water was explained by a mechanism involving diffusion into the structure of both H+ and OH-ions; experiments with oxygen-18 showed that considerable exchange of oxygen between crystal and solution had Catalysis of silicon migration by water was also postulated in the reactions of olivine and of calcium silicates previously discussed, but a different mechanism involving only protons was assumed. From the study of rhodonite,, also previously discussed, it was concluded that migration of silicon can probably also occur under anhydrous conditions.…”
in particular the leached layer theory. Most importantly, our data provide critical evidence for 51 a single mechanism based on interfacial dissolution-reprecipitation. This concept not only 52 unifies weathering processes for the first time, but we also suggest that nanoscale-surface 53 processes can have a potentially negative impact on CO 2 uptake associated with chemical 54 weathering. The results in this study, when combined with recently published research on 55 fluid-assisted mineral replacement reactions, supports the idea that dissolution-reprecipitation 56 is a universal mechanism controlling fluid-mineral interactions . 57Based on this we propose the existence of a chemical weathering continuum based solely on 58 the interfacial dissolution-reprecipitation mechanism. 59 3
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