Dehydration of Ca-montmorillonite at the crystal scale. Part 2. Mechanisms and kinetics
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Eric Ferrage
,
Caroline A. Kirk
Abstract
A kinetic study of Ca-montmorillonite dehydration was performed based on information derived from X-ray diffraction (Ferrage et al. 2007, this issue) and, thus, focusing on interlayer water only. The dehydration was quantified following the two processes that were observed in the X-ray pattern modeling: the transitions between the different hydration states and small thickness decrease observed in the bi- and mono-hydrated layers. The thickness decrease of bihydrated layers with dehydration (activation energy Ea = 16 kJ/mol) was found to be controlled by a mechanism of two-dimensional diffusion of water molecules through the interlayer space, whereas for mono-hydrated layers the variation of thickness (Ea = 18 kJ/mol) occurred as a mechanism of slight local layer collapse and collapse propagation, attributed to a rearrangement of the configuration of the interlayer cation hydration shell. For the transition between the bi- and mono-hydrated state (Ea = 84 kJ/mol), the mechanism of reaction was found to evolve gradually with increasing temperature from local layer collapse and collapse propagation to a two-dimensional diffusion mechanism, as the forced diffusion of water molecules produced by the layer collapse transfers the control of the process to diffusion mechanism. This phenomenon causes the coexistence of two hydration states in a given interlayer. Finally, the transition between mono-hydrated and dehydrated layers (Ea = 132 kJ/mol) indicated the concomitance of water diffusion and local layer collapse and propagation mechanisms, although the structures were found to be homogeneous during this transition.
The determination of both mechanisms and the activation energy for these processes were used to establish a model of smectite dehydration at the crystal scale. This model can be used to calculate crystal shrinkage and interlayer water content upon dehydration, and to predict the evolution of the system.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Experimental evidence of sixfold oxygen coordination for phosphorus
- Dehydration of Ca-montmorillonite at the crystal scale. Part I: Structure evolution
- Dehydration of Ca-montmorillonite at the crystal scale. Part 2. Mechanisms and kinetics
- The high-pressure crystal structure of potassium hydrogen carbonate (KHCO3)
- Effect of Al3+ and H+ on the elastic properties of stishovite
- Investigation of synthetic Mg1.3V1.7O4 spinel with MgO inclusions: Case study of a spinel with an apparently occupied interstitial site
- Thermal expansion of deuterated hopeite, Zn3(PO4)2·4D2O
- Compression, thermal expansion, structure, and instability of CaIrO3, the structure model of MgSiO3 post-perovskite
- Crystal chemical relationships in the tourmaline group: Structural constraints on chemical variability
- The energetics of hematite dissolution in iron-oxide-rich melts: In situ high-temperature calorimetric studies
- A simple model of oscillatory zoning in magmatic plagioclase: Development of an isothermal undercooling model
- TEM investigation of Ca-rich plagioclase: Structural β uctuations related to the I1-P1 phase transition
- Crystal-chemistry of Ni in marine ferromanganese crusts and nodules
- Effect of structural transitions on properties of high-pressure silicate melts: 27Al NMR, glass densities, and melt viscosities
- Material conversion from paper-sludge ash in NaOH, KOH, and LiOH solutions
- High-pressure phase relations and crystal chemistry of calcium ferrite-type solid solutions in the system MgAl2O4-Mg2SiO4
- Origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone
- Determination of the refractive index of particles in the clay and sub-micrometer size range
- Crystal chemistry of synthetic Ca2Al3Si3O12OH–Sr2Al3Si3O12OH solid-solution series of zoisite and clinozoisite
- Thermal infrared spectroscopy and modeling of experimentally shocked basalts
- P-V and T-V Equations of State of natural biotite: An in-situ high-pressure and high-temperature powder diffraction study, combined with Mössbauer spectroscopy
- Cation ordering in MgTi2O5 (karrooite): Probing temperature dependent effects with neutrons
- An order-disorder model for omphacitic pyroxenes in the system jadeite-diopsidehedenbergite- acmite, with applications to eclogitic rocks
- The high-pressure structural configurations of Ca0.2Sr0.8Al2Si2O8 feldspar: The I1̅-I2/c and I2/c-P21/c phase transitions
- Mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas
- Brittle fracturing and fracture healing of zircon: An integrated cathodoluminescence, EBSD, U-Th-Pb, and REE study
- Galaxite, MnAl2O4, a spectroscopic standard for tetrahedrally coordinated Mn2+ in oxygen-based mineral structures
- Magmatic paragonite in trondhjemites from the Sierra del Convento mélange, Cuba
- Valence state partitioning of Cr and V between pyroxene-melt: Estimates of oxygen fugacity for martian basalt QUE 94201
- Crystal-structure refinement of Na-bearing clinopyroxenes from mantle-derived eclogite xenoliths
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