Thermodiffusional transport of electrolytes in compact clays (original) (raw)
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Thermal conductivity of unsaturated clay-rocks
Hydrology and Earth System Sciences, 2010
The parameters used to describe the electrical conductivity of a porous material can be used to describe also its thermal conductivity. A new relationship is developed to connect the thermal conductivity of an unsaturated porous material to the thermal conductivity of the different phases of the composite, and two electrical parameters called the first and second Archie's exponents. A good agreement is obtained between the new model and thermal conductivity measurements performed using packs of glass beads and core samples of the Callovo-Oxfordian clay-rocks at different saturations of the water phase. We showed that the three model parameters optimised to fit the new model against experimental data (namely the thermal conductivity of the solid phase and the two Archie's exponents) are consistent with independent estimates. We also observed that the anisotropy of the effective thermal conductivity of the Callovo-Oxfordian clay-rock was mainly due to the anisotropy of the thermal conductivity of the solid phase.
Effect of microstructure on the electrical conductivity of clay-rich systems
Physics and Chemistry of the Earth, Parts A/B/C, 2007
It is well established that the electrical conductivity of clayey materials has two components: (a) a volume conductivity, proportional to the salted water content and (b) a surface conductivity, proportional to the cation exchange capacity. For a good understanding of the surface component associated with the electrical double layer, two fundamental aspects have to be taken into account: (a) the physical and chemical processes in the electrical double layer and (b) the effect of the clay distribution in the material. The present paper proposes a numerical approach to study the impact of clay microstructure on the macroscopic electrical conductivity.
Transport properties of compact clays
Journal of Colloid and Interface Science, 2003
Conductivity and permeability of model and natural clays have been studied experimentally. Local properties such as porosity and zeta potentials were measured as functions of the electrolyte solutions. Whenever possible, experimental data were compared to numerical data obtained for random packings of grains of arbitrary shape, and a good agreement was found between them. Copyright 2001 Academic Press.
Temperature dependence of the AC conductivity of illitic clay
Applied Clay Science, 2018
Electrical conductivity measurement was used to characterize thermophysical processes occurring in illitic clay during firing. In this study, illitic clay was subjected to heating up to 1100°C. The AC conductivity was measured at 10 different frequencies, ranging from 500 Hz up to 2 MHz. In the low-temperature interval (< 250°C) and during dehydroxylation (from 450°C to 750°C), H + and OHions were the dominant charge carriers. Above 600°C, the mobility of alkali ions was high enough to enable them to contribute to conductivity. Formation of glassy phase at high temperature rapidly increases conductivity. The conduction activation energies (E A) were calculated during a second firing. Above 350°C, the values of E A lay in the interval between 0.79 eV (500 Hz) and 0.66 eV (2 MHz), which correspond to the conduction E A of alkali ions in an amorphous matrix. The responsible conduction mechanism was identified to be ion hopping.
Effect of Clay Type on the Diffusional Properties of a Clay-Modified Electrode
Clays and Clay Minerals, 1996
The response of two swelling clays (SWy-1 and SAz-1) and of one non-swelling clay (KGa-1) and of a series of mixtures of these clays to different electrolyte concentrations was examined using clay-modified electrode techniques. A non-interacting probe ion, Fe(CN)6 3-, was monitored via reduction for its arrival at a Pt electrode coated with thin films of the day mixtures. The three clays had both different temporal responses and different equilibrium currents. For SWy-1 the currents were developed over time and were dependent upon the electrolyte of the bathing solution, which was consistent with X-ray diffraction data literature for the interlayer dimension. Similar behavior was found for SAz-1, but for KGa-1, currents were instantaneous and were independent of the bathing electrolyte. This suggests that the pores controlling the probe ion transport were between particle or pinhole in nature. When mixtures of the clays were examined, it was found that KGa-1 caused defects within the structures of the mixed clay films. The SWy-1 mixture was not as affected by these disruptions as was the SAz-1 mixture. Key Words-Clay charge, Clay-modified electrodes, Clay swelling.
Journal of Geophysics and Engineering
The objective of this work was to explore the impact of temperature on shale swelling and explain it in terms of diffuse double layer mechanics: Debye–Hückel length alterations. This was made possible through the use of a newly developed thermal linear swelling test. Moreover, the combined impact of temperature, dielectric constant of water and ionic strength (ionic concentration) of salt solutions on Debye–Hückel length and resultant shale swelling and shrinkage were investigated. For dilute solutions, results showed that the product of temperature and dielectric constant of water (T*εr) remained near constant for a wide range of temperature (25–90°C). Results suggest that the dielectric constant of water may have been reduced by both temperature and ionic strength of solution, all of which caused a greater reduction in Debye–Hückel length and subsequent shale shrinkage. As for saturated NaCl and CaCl2 solutions, shale exhibited swelling behaviour at moderate temperatures followed ...
Interactive comment on “Thermal conductivity of unsaturated clay-rocks” by D. Jougnot and
2009
This paper extends the thermal conductivity model of Revil (2000) to account for variable saturation. The new model is unique in that its functional form allows for a connection between thermal conductivity and electrical conductivity. Effective thermal conductivity is modeled using the same Archie exponents used to model electrical conductivity. The proposed approach is rather clever and appears to be a new and original contribution. Tests are conducted using published data, and it is shown that the new model adequately describes the dependence of thermal conductivity on the degree of saturation. Thus, the approach appears to have merit. The paper is well written, it is organized in a logical manner, and the derivation of the new model is presented in sufficient detail.
Electrical conductivity of 1 : 1 and 2 : 1 clay minerals
Surface Engineering and Applied Electrochemistry, 2014
The A.C. impedance plots were used as tools to analyze the electrical response of two varieties of Tunisian halloysite 1:1 and illitic samples 2:1 as a function of frequency at different temperatures (80-800°C). The real and imaginary parts of the complex impedance trace semicircles in the complex plane. Except for the illite, It-1, the second sample analyzed in this study, these plots give evidence for the presence of both bulk and grain boundary effect, above 600°C onwards. The bulk resistance of the materials decreases with the rise in temperature. Impedance Spectroscopy data reveal a non-Debye type of dielectric relaxation. The Nyquist plots show the negative temperature coefficient of resistance of both pure Tunisian illite and halloysite samples. The results of bulk electrical conductivity and its activation energy are presented for the two mineral clay samples. For illite It-1, the activation energy values estimated from the AC conductivity pattern and modulus pattern are very similar and suggest a possibility of a long-range mobility of charge carriers (ions) via hopping mechanism of electrical transport processes at higher temperature. On the other hand, for the halloysite sample provided from kasserine, (Ha-Kass), the modulus analysis admit that the electrical transport processes of the material are very likely of electronic nature. Relaxation frequencies follow an Arrhenius behavior with the activation energy values not comparable to those found for the electrical conductivity.
Analytical Expressions for Thermo-Osmotic Permeability of Clays
Geophysical Research Letters
• Thermo-osmotic permeability for for clay-rocks with monovalent-divalent solutions is ascertained • Based on limiting case analysis, analytical expressions for thermo-osmotic coefficients are proposed • Introducing divalent cations only slightly weakens thermo-osmosis contrarily to chemo-osmosis
Journal of Colloid and Interface Science, 1999
Ionic diffusivity, electrical conductivity, membrane and thermoelectric potentials in isotropic and homogeneous colloidal suspensions, and granular porous media saturated by a binary symmetric 1:1 electrolyte are four interrelated phenomena. The microstructure and the surface properties of the solid grains-water interface influence directly these properties. The ionic diffusivities (and the electrical conductivity, respectively) in colloids and porous media have contributions from diffusion (and electromigration, respectively) through the bulk solution occupying the pores, together with electromigration occurring at the grains-water interface in the electrical double layer. Surface diffusion in porous materials has no contribution from concentration gradients along the grains-water interface. Instead, surface diffusion is envisioned as a purely electromigration process due to the membrane potential. The tortuosities of the transport of anions and cations are equal to the bulk tortuosity of the pore space only at high ionic strength. As the ionic strength decreases, the dominant paths for transport of the ion corresponding to the counterion of the electrical double layer shift from the pore space to the solid grains-water interface. Because anions and cations do not move independently, the membrane potential created by the charge polarization alters the velocity of the anions and influences the mutual diffusivity coefficient of the salt in the porous material. An electric potential of thermal origin is also produced in nonisothermal conditions. The ionic contributions to the electrical conductivity are based on a differential effective medium approach. These ionic contributions to the electrical conductivity are used to derive the ionic diffusivities and the membrane and thermoelectric potentials. The influence of the temperature and the presence, in the pore space, of a second immiscible and nonwetting phase is also considered in this model. Porosity is shown to affect the membrane potential. Several predictions of the model are checked with success by comparing the model to a set of experimental data previously published.