Lionel Mercury

Experimental Superheating and Cavitation of Water and Solutions at Spinodal-Like Negative Pressures

The superheated liquids are metastable with respect to their vapour, what means they can exist under arid conditions whatever the temperature: capillary liquid residing in arid soils (desert shrubs, Mars sub-surface, …), solutions in the deep Earth crust, or water involved in rapid disequilibrium events (terrestrial or submarine geysers). The superheating state changes the solvent properties of liquids, and so modifies phase transitions (solid–liquid, liquid–vapor) P-T-X conditions. The synthetic fluid inclusion (SFI) enables to fabricate micro-volumes of hand-made liquid dispersed inside quartz, which readily superheat. Volumes of SFI are intermediate between macro-systems, in which superheating is restricted to around −30–35 MPa with very short lifetime, and nanosystems, wherein confinement effects predominate and in which the host size is similar to the one of the critical nucleus of vapour phase (huge nucleation barrier). This volume-to-metastability relationship is still to be defined quantitatively, and we are targeting to combine thermometric classical measurements with spectrometric characterizations, enabling to establish the threshold between micro- and nano-systems precisely. Meanwhile, the experiments performed so far illustrate the diversity of contexts and situations that could be modelled by superheating issues.

Infrared-Thermodynamics Conversion as a Function of Temperature: Towards Confined Water

An experimental method has been developed to calculate the thermodynamic properties of water from its vibrational properties, relevant to study (in near future) the properties of adsorbed or confined water. The infrared absorption of the intra-molecular OH stretching mode of liquid water has been measured over a wide range of temperature (from−10 to 90 °C). The corresponding large band has been decomposed into three Gaussian components standing for three different water connectivities (percolation model) that feature the liquid state as a function of temperature: network, intermediate, and multimer water. Measurements evidenced that the components are differently shifted with temperature, giving a quantitative insights into the internal energy change of liquid. A vibrational partition function has been used to calculate the corresponding thermodynamic properties, neglecting all energy components except the present intra-molecular vibrational mode. Interestingly, the vibrational free enthalpy thus computed differs of the total free enthalpy only by a multiplicative constant all along the thermal range.

Explosive Properties of Superheated Aqueous Solutions in Volcanic and Hydrothermal Systems

Superheated aqueous solutions in volcanic and hydrothermal environments are known to reequilibrate violently through explosive boilings and gas exsolutions. While these phenomena are purely kinetic problems in essence, the explosivity conditions of these demixion processes can be investigated by following a thermodynamic approach based on spinodal curves. In a first part, we recall briefly the concepts of mechanical and diffusion spinodals. Then, we propose to differentiate superspinodal (explosive) transformations from subspinodal (non-explosive) ones. Finally, a quantitative study of spinodal curves is attempted on the binary systems H2O-CO2 and H2O-NaCl with equations of state with solid theoretical basis. It is shown that dissolved gaseous components and electrolytes have an antagonist effect: dissolved volatiles tend to shift the superspinodal region towards lower temperatures, whereas electrolytes tend to extend the metastable field towards higher temperatures. This study may give some clues to understand the explosive destabilization conditions of aqueous solutions in phreatic, phreato-magmatic and hydrothermal eruptions

Growing Negative Pressure in Dissolved Solutes: Raman Monitoring of Solvent-Pulling Effect

Negative pressure in liquids is both an experimental fact and a usually neglected state of condensed matter. Using synthetic fluid inclusions, namely closed vacuoles fabricated inside one solid host by hydrothermal processes, a Raman study was performed to examine how a superheated solvent (under negative pressure) interacts with its dissolved solutes. As a result, this contribution not only illustrates this well-known tensile state but also displays evidence that a stretched solvent is able to pull on its dissolved solutes and put them also under a stretched state. The dielectric continuum hypothesis may lead to expect a stretching effect in solutes similar to the solvent’s, but our measurements evidence a damping mechanical effect (growing with tension), most probably related to solvation shells. One practical consequence is that the (experimentally known) supersolvent properties of superheated solutions are certainly related to the change of the chemical potential of solutes which results from the damp...

Geochemistry of Capillary Hydrogeochemical Systems in Arid Environments

In arid environments, porous media are unsaturated with water which is submitted to capillary constraints. The present chapter focuses on the geochemical impacts of such physical constraints and how theoretical analysis can help interpreting field or laboratory observations. The basic principles of capillary geochemistry suggest that the fate of contaminants, either organic or inorganic, can be significantly impacted in terms of reactive mass transfer in addition to flow and transport processes. All these mechanisms are closely interconnected, what makes the description of the behavior of such systems very complicated. An important work still has to be done in order to achieve such a goal: a number of mechanisms are not taken into account in the current state of development of the capillary geochemistry, namely mechanisms that occur in the thinnest confining geometries, like disjoining pressures, surface forces, etc.

Size effect in metastable water

We experimentally determined the maximum tension in synthetic fluid inclusions from the difference between the temperatures of homogenization (Th) and spontaneous vapor nucleation (Tn). At temperatures of 100–200°C, liquid water may exist at negative pressures of up to 100–150 MPa. Owing to an increase in surface tension, the effect is even more significant in salt solutions and occurs at higher temperatures. A decrease in the linear dimension of fluid phase by an order of magnitude and, correspondingly, a three orders of magnitude decrease in volume (which is proportional to R3) increase the maximum tension by ∼25MPa. Tension in the liquid phase of water-salt systems may be higher than ~200 MPa without cavitation. Metastability of water and salt solutions in small-sized vacuoles generates stresses in the fluid-mineral system resulting in high solubilities of solid phases. An increase in volume due to coalescence of small inclusions or vanishing of metastability results in an abrupt decrease in supersaturation.

Lifetime of Superheated Water in a Micrometric Synthetic Fluid Inclusion

A synthetic pure water fluid inclusion showing a wide temperature range of metastability (Th − Tn 50°C; temperature of homogenization Th = 144°C and nucleation temperature of Tn = 89°C) was selected to make a kinetic study of the lifetime of an isolated microvolume of superheated water. The occluded liquid was placed in the metastable field by isochoric cooling and the duration of the metastable state was measured repetitively for 7 fixed temperatures above Tn. Statistically, metastability lifetimes for the 7 data sets follow the exponential reliability distribution, i.e., the probability of non nucleation within time t equals e −λt . This enabled us to calculate the half-life periods of metastability ρ for each of the selected temperature, and then to predict ρ at any temperature T>Tn for the considered inclusion, according to the equation ρ(s) = 22. l × e1.046×ΔT, (ΔT = T − Tn). Hence we conclude that liquid water in water-filled reservoirs with an average pore size 10 4μm3 can remain superheated over geological timelengths (1013 s), when placed in the metastable field at 24°C above the average nucleation temperature, which often corresponds to high liquid tensions ( −50 MPa).

Pore scale modelling of DNAPL migration in a water–saturated porous medium

A numerical simulator based on the discrete network model approach has been developed to simulate drainage processes in a water-saturated porous medium. To verify the predictive potential of the approach to simulate the unstable migration of a dense nonaqueous phase liquid (DNAPL) at the pore scale, the numerical model was applied to laboratory experiments conducted on a sand-filled column. The parameters relative to pore body size and pore throat size used in the construction of the equivalent network were derived from discrete grain-size distribution of the real porous medium. The observed water retention curve (WRC) was first simulated by desaturation of the network model. The good agreement of the modelled WRC with the experimental one highlights that the applied approach reproduces the main characteristics of the real pore space. The numerical model was then applied to rate controlled experiments performed on a homogenous sand-filled column to study the gravity-driven fingering phenomenon of immiscible two-phase flow of water and a DNAPL. The numerical results match within 10% based on the standard deviation with the experiments. They correctly reproduce the effect of several system parameters, such as flow mode (upward flow and downward flow) and the flow rate, on the stability of the water/DNAPL front in a saturated porous medium.

Vapour Nucleation in Metastable Water and Solutions by Synthetic Fluid Inclusion Method

Experimental data for temperatures of homogenization (Th, L+V→L) and vapour phase nucleation (Tn, L→L+V) presented after recalculation to P-T parameters with equation of state for water (Wagner, Pruss, 2002) or Duans equations for salt solutions. Samples were prepared by method of synthetic fluid inclusions in quartz with densities > 0.8 g/cm3. The spontaneous nucleation begin at pressure −20 MPa and in the same sample some inclusions keep homogeneous state up to — 150 MPa. Increasing of quartz solubility in trapped liquids lead to decreasing of quantity of high temperature boiling inclusions.