La forme γ du dichlorure de calcium tétrahydraté

Leclaire, Par A.; Borel, M.M.; Monier, J. C.; Crislallographie, Laboraloire tie

doi:10.1107/s0567740880009909

Cited by 15 publications

(10 citation statements)

References 5 publications

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“…The average Ca-O coordination length is 2.26 Å in the g phase optimized structure, which is in agreement with the g phase crystalline structures (2.33 Å). 34 The two H atoms of surrounded H 2 O molecules form a relatively strong H-bonds with the Cl compared to the a and the b phase optimized structures. The H 2 O takes away the Cl atom from the Ca, hence the Ca-Cl distance becomes 4.06 Å.…”

Section: Resultsmentioning

confidence: 96%

“…31 There are two conformers reported for MgCl 2 Á2H 2 O, which differ in energy by 4.53 kcal mol À1 . 15 [32][33][34] We have chosen the initial structure of CaCl 2 Á4H 2 O from these three crystalline phases and observed three stable structures shown in Fig. 4a-c.…”

Section: Resultsmentioning

confidence: 99%

“…CaCl 2 Á4H 2 O also occurs in the g phase. 34 The initial molecular structure is chosen close to the g phase structure. The optimized structure is symmetrical and has almost a planar structure as shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

Pathak¹,

Nedea²,

Rindt³

et al. 2016

Phys. Chem. Chem. Phys.

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Salt hydrates store solar energy in chemical form via a reversible dehydration-hydration reaction. However, as a side reaction to dehydration, hydrolysis (HCl formation) may occur in chloride based salt hydrates (specially in MgCl2 hydrates), affecting the durability of the storage system. The mixture of CaCl2 and MgCl2 hydrates has been shown experimentally to have exceptional cycle stability and improved kinetics. However, the optimal operating conditions for the mixture are unknown. To understand the appropriate balance between dehydration and hydrolysis kinetics in the mixtures, it is essential to gain in-depth insight into the mixture components. We present a GGA-DFT level study to investigate the various gaseous structures of CaCl2 hydrates and to understand the relative stability of their conformers. The hydration strength and relative stability of conformers are dominated by electrostatic interactions. A wide network of intramolecular homonuclear and heteronuclear hydrogen bonds is observed in CaCl2 hydrates. Equilibrium product concentrations are obtained during dehydration and hydrolysis reactions under various temperature and pressure conditions. The trend of the dehydration curve with temperature in CaCl2 hydrates is similar to the experiments. Comparing these results to those of MgCl2 hydrates, we find that CaCl2 hydrates are more resistant towards hydrolysis in the temperature range of 273-800 K. Specifically, the present study reveals that the onset temperatures of HCl formation, a crucial design parameter for MgCl2 hydrates, are lower than for CaCl2 hydrates except for the mono-hydrate.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

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A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

Pathak¹,

Nedea²,

Rindt³

et al. 2016

Phys. Chem. Chem. Phys.

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“…The x and y dimensions of the box are commensurate with the equilibrated hydrate crystal structure at that temperature and pressure, and the pressure is coupled only in the z dimension, the direction perpendicular to the interface. The initial crystal structure was generated from experimental hydrate crystal structures − and then equilibrated in the NPT ensemble for 10 ns. Dihydrate phases were equilibrated with an anisotropic barostat with the angles constrained to keep the simulation box orthorhombic.…”

Section: Methodsmentioning

confidence: 99%

Activity Coefficients and Solubility of CaCl₂ from Molecular Simulations

2019

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We obtain the activity coefficients and lower bounds to the solubility of CaCl2 in aqueous solutions at temperatures between 298.15 and 473.15 K using molecular simulations with three previously developed nonpolarizable force fields. We find that a scaled-charge force field gives incorrect activity coefficients at low concentration and has a different absolute chemical potential than experiments, but still predicts an accurate solubility for the calcium chloride dihydrate. The two full-charge models have chemical potentials and activity coefficients closer to experiments, but there is considerable variation between them, with the chemical potentials differing by over 100 kJ·mol−1. The slow dynamics of the full-charge models at high concentrations are unrealistic and require advanced sampling methods to obtain the activity coefficients. We find that development of polarizable models is likely necessary to accurately represent both thermodynamic and transport properties of divalent electrolyte solutions.

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“…GIPAW DFT quantum chemical calculations were carried out using the accepted crystal structures of CaCl 2 , 65 CaCl 2 ·2H 2 O, 78 a-CaCl 2 ·4H 2 O, 74 b-CaCl 2 ·4H 2 O, 75 gCaCl 2 ·4H 2 O, 76 and CaCl 2 ·6H 2 O, 66 although for the hydrates (except CaCl 2 ·6H 2 O, whose structure was solved using neutron diffraction data) the H positions were optimized computationally (vide infra). The computed 35 Cl EFG and chlorine CS tensor parameters are presented in Table 1, while more detailed computational results can be found in the Supplementary data, Table S4.…”

Section: Quantum Chemical Computationsmentioning

confidence: 99%

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

Widdifield

Bryce

2011

Can. J. Chem.

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The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a 35/37 Cl and 43 Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl2. The 35 Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl2·2H2O. Chlorine-35 SSNMR spectra are also presented for CaCl2·6H2O, and when taken in concert, the SSNMR observations for CaCl2, CaCl2·2H2O, and CaCl2·6H2O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of diso decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl2·2H2O, and to explore the isostructural relationship between CaCl2 and CaBr2. Finally, the 43 Ca CS tensor span is measured to be 31 (5) ppm for anhydrous CaCl2, which represents only the fifth CS tensor span measurement for calcium. Résumé : Les halogénures des métaux du groupe 2 et les hydrates d'halogénures métalliques sont des systèmes modèles qui permettent comprendre la relation entre le gradient du champ électrique (GCE) et les tenseurs du déplacement chimique (DC) au niveau du noyau d'halogène et la structure électronique et moléculaire locale. Dans ce travail, on présente les résul-tats d'une étude de résonance magnétique nucléaire à l'état solide (RMN-ES) du 35/37 Cl et 43 Ca du CaCl 2 . Les valeurs de la constante de couplage quadripolaire nucléaire du 35 Cl, 8,82(8) MHz, et le DC isotrope du chlore, 105(8) ppm [par rapport au NaCl(aq) dilué], sont différentes de celles rapportées pour ce composé ainsi que les valeurs rapportés pour le CaCl 2 ·2H 2 O. Les spectres RMN-ES du 35 Cl sont aussi presentés pour le CaCl 2 ·6H 2 O et, lorsqu'on les compare, les observations relatives aux spectres RMN-ES du CaCl 2 , du CaCl 2 ·2H 2 O et du CaCl 2 ·6H 2 O démontrent clairement la sensibilité du GCE du chlore et des tenseurs du DC sur la symétrie locale et aux changements dans l'état d'hydratation. Par exemple, les valeurs de d iso diminuent avec une augmentation de l'hydratation. On a fait appel à des calculs selon la théorie de la fonctionnelle de la densité en utilisant une onde améliorée par un opérateur de projection comportant une jauge (« GIPAW-DFT ») pour corroborer les observations faites par RMN-ES, pour éliminer la présence d'autres hydrates dans nos échantil-lons, pour affiner les positions des atomes d'hydrogène dans le CaCl 2 ·2H 2 O et pour explorer la relation isostructurale entre le CaCl 2 et...

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La forme γ du dichlorure de calcium tétrahydraté

Cited by 15 publications

References 5 publications

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

Activity Coefficients and Solubility of CaCl₂ from Molecular Simulations

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

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La forme γ du dichlorure de calcium tétrahydraté

Cited by 15 publications

References 5 publications

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl2 hydrates and MgCl2 hydrates for seasonal heat storage

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl2 hydrates and MgCl2 hydrates for seasonal heat storage

Activity Coefficients and Solubility of CaCl2 from Molecular Simulations

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

Contact Info

Product

Resources

About

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage

Activity Coefficients and Solubility of CaCl₂ from Molecular Simulations