Salt precipitation and trapped liquid cavitation in micrometric capillary tubes.

International audienceLaboratory evidence shows that the occurrence of solid salt in soil pores causes drastic changes in the topology of the porous spaces and possibly also in the properties of the occluded liquid. Observations were made on NaCl precipitation in micrometric cylindrical capillary tubes, filled with a 5.5 M NaCl aqueous solution and submitted to drying conditions. Solid plug-shaped NaCl (halite) commonly grows at the two liquid-air interfaces, isolating the inner liquid column. The initially homogeneous porosity of the capillary tube becomes heterogeneous because of these two NaCl plugs, apparently closing the micro-system on itself. After three months, we observed cavitation of a vapor bubble in the liquid behind the NaCl plugs. This event demonstrates that the occluded liquid underwent a metastable superheated state, controlled by the capillary state of thin capillary films persisting around the NaCl precipitates. These observations show, first, that salt precipitation can create a heterogeneous porous medium in an initially regular network, thus changing the transfer properties due to isolating significant micro-volumes of liquid. Second, our experiment illustrates that the secondary salt growth drastically modifies the thermo-chemical properties of the occluded liquid and thus its reactive behavior

In-Pore stress by drying-induced capillary bridges inside porous materials.

International audienceWe present here some evidences that capillary liquid bridges are able to deform micrometric cylindrical pores by tensile stress. Brine-soaked filter membranes are submitted to drying conditions leading to NaCl precipitation inside the 5-10 μm pores. A close examination demonstrated that two forms of NaCl crystallites are successively generated. First, primary cubic crystals grow, driven by the permanent evaporation. When this angular primary solid gets near the pore wall, while the evaporation makes the pore volume to be partly invaded by air, capillary liquid can bridge the nowsmall gap between the halite angles and the pore wall. In a second step, these small capillary bridges are frozen by a secondary precipitation event of concave-shaped NaCl. The proposed interpretation is that the liquid capillary bridges deform the host matrix of the membrane, and the situation is fossilized by the growth of solid capillary bridges. A quantitative interpretation is proposed and the consequences towards the natural media outlined

Experimental solubility of silica in nano-pores

International audienceWe used a pressure membrane extractor (Model 1020, SoilMoisture Equipment Corp.) to study the silica content at equilibriumwith the decreasing pore sizes of amorphous silica. The principle isto extract the aqueous solution through a sequential process fromthe larger (micrometric) pores to the thinner (some nm) pores. Eachextraction step is followed by an equilibration period.The measurements confirmed earlier observations [1,2] that theconcentration in dissolved silica decreases when the extractionpressure increases. The direct conclusion is that the silica solubilityis pore-size dependent. These results are interpreted with the Young-Laplace relationship, at constant silica-solution surface tension,which means to attribute an elasto-capillary pressure to the solid

Experimental solubility of silica in nano-pores

International audienceWe used a pressure membrane extractor (Model 1020, SoilMoisture Equipment Corp.) to study the silica content at equilibriumwith the decreasing pore sizes of amorphous silica. The principle isto extract the aqueous solution through a sequential process fromthe larger (micrometric) pores to the thinner (some nm) pores. Eachextraction step is followed by an equilibration period.The measurements confirmed earlier observations [1,2] that theconcentration in dissolved silica decreases when the extractionpressure increases. The direct conclusion is that the silica solubilityis pore-size dependent. These results are interpreted with the Young-Laplace relationship, at constant silica-solution surface tension,which means to attribute an elasto-capillary pressure to the solid

Mechanical stress due to the capillary bridging in unsaturated zone

International audienc

Metastabilizing aqueous solutions in micrometric cylindrical tubes

International audienceThe occurrence of solid salts in pores has well-known damage effects (e.g. [1]). It is here demonstrated that it also changes drastically the topology of the porous spaces and possibly also the properties of the occluded liquid. We performed a series of observations on NaCl precipitation in 75μm cylindrical tubes, evidencing that the solid forms at the liquid-air interface contributing to isolate the remaining liquid column (Fig. 1a). The homogeneous capillary tube is now heterogeneized by the two NaCl 'corks', apparently closing the micro-system on itself. After 6-months observation of such immobile situation, we observed the cavitation of a vapor bubble in the liquid behind the NaCl cork (Fig. 1b). This event demonstrates that the occluded liquid underwent a metastable superheated state, controlled by the very thin capillary plugs certainly persisting, tough invisible, around the NaCl precipitates

Mechanical stress due to the capillary bridging in unsaturated zone

International audienc

Metastabilizing aqueous solutions in micrometric cylindrical tubes

International audienceThe occurrence of solid salts in pores has well-known damage effects (e.g. [1]). It is here demonstrated that it also changes drastically the topology of the porous spaces and possibly also the properties of the occluded liquid. We performed a series of observations on NaCl precipitation in 75μm cylindrical tubes, evidencing that the solid forms at the liquid-air interface contributing to isolate the remaining liquid column (Fig. 1a). The homogeneous capillary tube is now heterogeneized by the two NaCl 'corks', apparently closing the micro-system on itself. After 6-months observation of such immobile situation, we observed the cavitation of a vapor bubble in the liquid behind the NaCl cork (Fig. 1b). This event demonstrates that the occluded liquid underwent a metastable superheated state, controlled by the very thin capillary plugs certainly persisting, tough invisible, around the NaCl precipitates