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Capillary Condensation (capillary + condensation)
Selected AbstractsStress Development Due to Capillary Condensation in Powder Compacts: A Two-Dimensional Model StudyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Stefan Lampenscherf A model experiment is presented to investigate the relationship between the humidity-dependent liquid distribution and the macroscopic stress in a partially wet powder compact. Therefore, films of monosized spherical particles were cast on silicon substrates. Using environmental SEM the geometry of the liquid necks trapped between particles was imaged as a function of relative humidity. Simultaneously the macroscopic stress in the substrate adhered particle film was measured by capacitive deflection measurement. The experimentally found humidity dependence of the liquid neck size and the macroscopic film stress are compared with model predictions. The circle,circle approximation is used to predict the size of the liquid necks between touching particles as a function of the capillary pressure. Using the modified Kelvin relation between capillary pressure and relative humidity, we consider the effect of an additional solute which may be present in the capillary liquid. The results of the stress measurement are compared with the model predictions for a film of touching particles in hexagonal symmetry. The contribution of the capillary interaction to the adhesion force between neighboring particles is calculated using the integrated Laplace equation. The resulting film stress can be approximated relating this capillary force to an effective cross section per particle. The experimentally found humidity dependence of the liquid neck size is in good agreement with the model predictions for finite solute concentration. The film stress corresponds to the model predictions only for large relative humidities and shows an unexpected increase at small values. As is shown with an atomic force microscope, the real structure of the particle,particle contact area changes during the wet/dry cycle. A solution/reprecipitation process causes surface heterogeneities and solid bridging between the particles. It is claimed that the existence of a finite contact zone between the particles gives rise to the unexpected increase of the stress at small relative humidities. [source] On the Thermodynamic Stability of Liquid Capillary BridgesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007Janet Aw Elliott Abstract Capillary condensation is important in the behaviour of various materials encountered in nature and in industrial processes. The behaviour of liquid capillary bridges has mostly been investigated from a mechanical perspective, with an emphasis on computing the relevant adhesion forces. In the present paper, a thermodynamic approach is used, computing the free energy of such systems (based on numerically constructed shapes of liquid bridges) in order to determine the nature and properties of their equilibrium states. The dependence of the thermodynamic equilibrium configurations on the geometry of the system is investigated, and comparisons are made with experimental findings reported in the literature. La condensation capillaire est importante dans le comportement de divers matériaux rencontrés dans la nature et dans les procédés industriels. Le comportement des ponts capillaires liquides a surtout été étudié d'un point de vue mécanique, l'accent étant mis sur le calcul par ordinateur des forces d'adhésion pertinentes. Dans le présent article, on utilise une approche thermodynamique utilisant le calcul par ordinateur de l'énergie libre de tels systèmes (d'après les formes numériquement construites des ponts liquides), dans le but de déterminer la nature et les propriétés de leurs états d'équilibre. La dépendance des configurations d'équilibre thermodynamique sur la géométrie du système est étudiée, et des comparaisons sont faites avec les résultats expérimentaux présentés dans la littérature scientifique. [source] Macroscopic Single-Walled-Carbon-Nanotube Fiber Self-Assembled by Dip-Coating MethodADVANCED MATERIALS, Issue 43 2009Eui Yun Jang Pure macroscopic single-walled-carbon-nanotube (SWNT) fibers are fabricated by using a dip-coating method without any additive or additional electrical equipment or complex apparatus. The present method only utilizes microfluidics, which includes capillary condensation, capillary flow, and surface tension, and results in the self-assembly and self-alignment of SWNT colloids. [source] In-situ small-angle neutron scattering study of pore filling and pore emptying in ordered mesoporous silicaJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2010M. Erko The capillary condensation and capillary emptying of water and perfluoropentane in ordered mesoporous SBA-15 silica is studied by in-situ small-angle neutron scattering (SANS). The SANS data can be perfectly described by a simple analytical model for spatially random pore filling (Laue scattering) for the entire range of pore-filling fractions. From this it is concluded that recently proposed pore correlations due to elastic interactions between neighbouring pores upon capillary condensation do not play a role in this system. The pores fill randomly according to their size distribution, in perfect agreement with the classical Kelvin equation. The relation between the overall pore-filling fraction as determined from the volumetric sorption isotherm, and the fraction of completely filled pores as obtained from the fit of the SANS data, allows conclusions to be drawn about the thermodynamic metastability of the adsorption process. [source] Prediction of gas sorption kinetics for porous media using MRIAICHE JOURNAL, Issue 9 2006Matthew J. Watt-Smith Abstract Diffusion and reaction within porous media involving condensable vapors are important processes in catalysis, fuel cells, and membrane separations. In this work, 3-D maps of the spatial variation of porosity, pore size and network tortuosity within a porous solid, derived from magnetic resonance images, have been used to construct a structural model for a mesoporous catalyst pellet. Simulations of the kinetic uptake, adsorption and capillary condensation of butane vapor within the porous solid, conducted on the structural model, have successfully predicted experimental measurements of the effects of the onset of capillary condensation on mass transfer rates without the need of the various adjustable parameters prevalent in other models. These findings suggest that accurate mathematical models for both the complex void space of the porous medium, and the mass transport processes taking place within it, have been successfully developed. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] | |||||||||||||