Отправлено: 18.08.08 03:19. Заголовок: Volume 325, Issue 1, Pages 1-300 (1 September 2008)

Permselectivity and microstructure of anion exchange membranes
Pages 215-222
Xuan Tuan Le

Abstract
The water content, the ion exchange capacity, the transport number of counter-ion of the AMV and AMX anion exchange membranes were determined. The two-phase model (gel phase and interstitial phase) of structure microheterogeneity was validated by means of conductivity measurements. The chronopotentiometric results allowed us to affirm the overall surface homogeneity of the membranes. According to the two-phase model, the influence of the gel phase and the interstitial phase on the membrane permselectivity was discussed in detail. Majorities of co-ions exist in the interstitial phase, thus they have no influence on the transport of counter-ions in the gel phase. The determination of the KCl amount sorbed in the interstitial phase confirmed the existence of partition equilibrium between the interstitial phase and the external solution. Such partition equilibrium can be considered within the microheterogeneous model in order to represent the internal structure of the electromembranes.
Article Outline
1. Introduction
2. Experimental methods
2.1. Anion exchange membranes
2.2. Ion exchange capacity
2.3. Water content
2.4. Membrane density
2.5. Membrane resistance
2.6. Solution conductivity
2.7. Amount of sorbed electrolyte
2.8. Transport number of counter-ion in the membrane
2.9. Chronopotentiometry
3. Results and discussion
3.1. Water content and sorption electrolyte in the membranes
3.2. Membrane microstructure
3.2.1. Two-phase model of structure microheterogeneity
3.2.2. Refinement of the two-phase model
3.3. Membrane surface homogeneity
4. Conclusion
Acknowledgements
Appendix A. Nomenclature
References

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Abstract
The surface energy of some clays belonging to the smectite group has been calculated starting from crystal structures and combining a partial charge model with the computation of the lattice energy. The dioctahedral smectites studied here include montmorillonite; beidellites; and nontronite. One of the differences between these clays is the location of the substitution in the octahedral sheet or in the tetrahedral one. Another is the possibility of vacancies in cis- or trans-octahedral positions. These locations and vacancies have an effect on the distortion of the crystal framework and therefore on the surface energy. Calculated surface energies of the solid samples increase in the order beidellites > montmorillonite > nontronite. The bond energy between the interlayer cation and the layer appears to follow the same order and to depend both on the nature of the most electropositive elements of the layer and on their location. The trends obtained provide elements for an analysis of data related to interlayer enlargement.
Article Outline
1. Introduction
2. Presentation of studied clays
2.1. Montmorillonites
2.2. Beidellites
2.3. Nontronite
3. Computational background
3.1. Lattice energy
3.2. Atomic charges
3.3. Calculations for crystals and layers
4. Results and discussion
4.1. Atomic charges
4.2. Lattice energy
4.3. Surface energy
5. Conclusions
References