J.M. Douillard

Hydration sequence of swelling clays: Evolutions of specific surface area and hydration energy

In order to identify the key steps and the driving force for the hydration process of swelling clays, the water adsorption isotherms and enthalpies were measured on monoionic montmorillonite samples saturated with alkali or calcium ions, and on bi-ionic samples saturated with a sodium-calcium mixture. The specific surface area evolution along the hydration process was determined using a recent interpretation of the experimental adsorption isotherms of swelling solids. Results are interpreted in structural terms. Compared with additional data from sample-controlled thermal analysis (SCTA), the results confirm experimentally that the hydration of Li- and Na-montmorillonite is mainly a cation-controlled process, in contrast with the hydration of Cs samples in which the cation contribution to hydration is negligible, as we have already demonstrated using electrostatic calculations or conductivity measurements.

On the cation dependence of interlamellar and interparticular water and swelling in smectite clays

The osmotic character of long-range interlamellar swelling in smectite clays is widely accepted and has been evidenced in the interlayer space by X-ray diffraction. Such a behavior in mesopores was not experimentally confirmed until the determination of the mesopore size distribution in Na-montmorillonite prepared from MX80 bentonite using thermoporometry experiments. This is confirmed here for other montmorillonite samples where the interlayer cations are alkaline and Ca(2+) cations. The nature of the interlayer cation is found as strongly influencing the behavior of the size and the swelling of mesopores. These results are supported by the BJH (Barrett, Joyner and Halenda) pore radius values issued from the nitrogen adsorption-desorption isotherms at the dry state. Thermoporometry results as a function of relative humidity ranging from 11% to 97% have shown an evolution of the mesopore sizes for a purified Na-montmorillonite. New thermoporometry data are presented in this article and confirm that the interparticle spaces in K-, Cs-, or Ca-montmorillonites are not strongly modified for all the range of relative humidity: the swelling is not observed or is strongly limited. It appears in contrast that only Li- and Na-montmorillonites undergo a mesopore swelling, distinct from the interlayer swelling. More generally, our results confirm the possibility to use thermoporometry or differential scanning calorimetry to study the structure and the evolution of swelling materials in wetting conditions such as natural clays or biological cells. In this paper, we describe the different key steps of the hydration of swelling clays such as montmorillonites saturated with alkaline cations. Using thermoporometry results combined with X-ray diffraction data, we distinguish the evolution of the porosity at the two different scales and propose a sequence of hydration dependent on the interlayer cation. From this study, it is shown that the interlayer spaces are not completely filled when the mesopores start to fill up. This implies that the swelling observed in the mesopores for Li and Na samples is due to an osmotic swelling. For the other samples, it is difficult to conclude definitively. Furthermore, we determine the different proportion of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry, and (3) recent adsorption isotherm results. It is found that the interlayer space is never completely filled by water at the studied relative humidity values for all samples except for the Cs sample.

Surface Gibbs free energy of minerals: some values

In this paper it is demonstrated that it is possible to determine the surface Gibbs free energy of minerals by combining classical measurements of adsorption and van Oss theory. Some practical examples are discussed, using certain approximations. The approximations and questions relevant to different thermodynamic variables and theories of solid surface tensions are also reviewed and discussed.

Thermodynamic investigation of surface of minerals

Abstract In this paper values of surface enthalpies and surface Gibbs free energies are given in order to characterize subsurface minerals. These values are obtained by combining standard measurements of adsorption and the Van Oss–Chaudhury–Good model [Van Oss, C.J., Chaudhury, M.K., Good, R.J., 1987. Monopolar surfaces. Adv. Coll. Interface Sci. 28, 35; Van Oss, C.J., Good, R.J., Chaudhury, M.K., 1988. Additive and nonadditive surface tension components and the interpretation of contact angles. Langmuir 4, 884; Van Oss, C.J., Giese, R.F., Costanzo, P.M., 1990. DLVO and non-DLVO interactions in hectorite. Clays Clay Min. 38, 151; Van Oss, C.J., Giese, R.F., Li, Z., Murphy, K., Norris, J., Chaudhury, M.K., Good, R.J., 1992. Determination of contact angles and pore sizes of porous media by column and thin layer wicking. J. Adhesion Sci. Technol. 6, 413.]. This model is reviewed and modified with a view to identify the types of interactions at solid–fluid interfaces and interpreting experimental results.

Driving force for the hydration of the swelling clays: Case of montmorillonites saturated with alkaline-earth cations

Important structural modifications occur in swelling clays upon water adsorption. The multi-scale evolution of the swelling clay structure is usually evidenced by various experimental techniques. However, the driving force behind such phenomena is still not thoroughly understood. It appears strongly dependent on the nature of the interlayer cation. In the case of montmorillonites saturated with alkaline cations, it was inferred that the compensating cation or the layer surface could control the hydration process and thus the opening of the interlayer space, depending on the nature of the interlayer cation. In the present study, emphasis is put on the impact of divalent alkaline-earth cations compensating the layer charge in montmorillonites. Since no experimental technique offers the possibility of directly determining the hydration contributions related to interlayer cations and layer surfaces, an approach based on the combination of electrostatic calculations and immersion data is developed here, as already validated in the case of montmorillonites saturated by alkaline cations. This methodology allows to estimate the hydration energy for divalent interlayer cations and therefore to shed a new light on the driving force for hydration process occurring in montmorillonites saturated with alkaline-earth cations. Firstly, the surface energy values obtained from the electrostatic calculations based on the Electronegativity Equalization Method vary from 450 mJ m(-2) for Mg-montmorillonite to 1100 mJ m(-2) for Ba-montmorillonite. Secondly, considering both the hydration energy for cations and layer surfaces, the driving force for the hydration of alkaline-earth saturated montmorillonites can be attributed to the interlayer cation in the case of Mg-, Ca-, Sr-montmorillonites and to the interlayer surface in the case of Ba-montmorillonites. These results explain the differences in behaviour upon water adsorption as a function of the nature of the interlayer cation, thereby allowing the macroscopic swelling trends to be better understood. The knowledge of hydration processes occurring in homoionic montmorillonites saturated with both the alkaline and the alkaline-earth cations may be of great importance to explain the behaviour of natural clay samples where mixtures of the two types of interlayer cation are present and also provides valuable information on the cation exchange occurring in the swelling clays.

The adsorption of polyoxyethylenated octyl and nonylphenol surfactants on carbon black and sulfur from aqueous solutions

Abstract The adsorption of nonionic surfactants from water solutions on the hydrophobic surfaces of sulfur and carbon black has been investigated. The isotherms and calorimetric experiments were also carried out after characterization of the solid particles. The isotherms of adsorption show the existence of a saturation plateau. The adsorption quantity depends on the length of polar and aliphatic chains. Calorimetric investigations of adsorption on the carbon black indicate the existence of considerable energetic heterogeneity. At low coverage ratios the enthalpy of adsorption is very high and exothermic. Subsequently it becomes progressively weaker and reaches the value of zero at θ = 0.

Surface heterogeneity of passively oxidized silicon carbide particles: vapor adsorption isotherms

The surfaces of silicon carbide particles subjected to two different passive oxidation treatments have been characterized by immersion calorimetry and vapor adsorption techniques. Surface enthalpies and surface free energies have been computed using semiempirical models and are compared to theoretical estimations. The surface entropy term appears higher than in the case of other solids studied with the same analysis. The definition of the surface entropy term is discussed in order to explain the discrepancy between calculation and experiment. An explanation of results is proposed, which is related to the constitution of silicon oxide layers at the surface of silicon carbide, a fact demonstrated by previous XPS measurements.

Assessment of the surface tension of various divided solids

We have attempted to calculate the surface tension of some solids using immersion calorimetry measurements along with the interfacial model of van Oss [1, 2, 3, 4].ZusammenfassungUnter Berücksichtigung des van Ossschen Grenzflächenmodelles [1, 2, 3, 4] wurde mittels Immersionskalorimetriemessungen ein Versuch zur Berechnung der Oberflächenspannung von Feststoffen unternommen.

Study of the influence of location of substitutions on the surface energy of dioctahedral smectites

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.

Adsorption of A Multifunctional Additive (ZnDTC) Onto Iron and Iron(III) Oxide from n-Decane

The adsorption of zinc diisooctylodithiocarbamate (ZnDTC) onto iron and iron(III) oxide from n-decane solution was studied. The adsorption isotherms were determined together with the variation of the apparent differential molar enthalpy of displacement for ZnDTC on both adsorbents at 298 K. The shapes of the iostherms for the adsorption of dithiocarbamate on iron and iron(III) oxide are quite different, especially in the low coverage ratio. The corresponding differential molar enthalpies of displacement for the two studied systems are exothermic. On iron, the very high exothermic values indicate a process of ZnDTC chemisorption, while on iron(III) oxide, the much lower enthalpic effects are characteristic of physisorption.