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Surface Chemistry of Solids
Published in K. S. Birdi, Surface Chemistry of Carbon Capture, 2019
Molecules in the gas phase move much larger distances than when adsorbed on a solid surface. Adsorption takes place spontaneously, which means ΔGad = ΔHad − T ΔSad If ΔGad is negative, this suggests that ΔHad is negative (exothermic). The adsorption of gas can be of different types. The gas molecule may adsorb as a kind of condensation process, it may under other circumstances react with the solid surface (chemical adsorption or chemisorption). In the case of chemo-adsorption, one almost expects a chemical bond formation. On carbon, while oxygen adsorbs (or chemisorb), one can desorb CO or CO2. The experimental data can provide information on the type of adsorption. On porous solid surfaces, the adsorption may give rise to capillary condensation. This indicates that porous solid surfaces will exhibit some specific properties. The most common adsorption process in industry one finds is the case of catalytic reactions (for example, formation of NH3 from N2 and H2). It is thus apparent that in gas recovery from shale the desorption of gas (mainly methane, CH4) will be determined by surface forces (Birdi, 2017).
Particle Adhesion to Surfaces Theory of Cleaning
Published in R. P. Donovan, Particle Control for Semiconductor Manufacturing, 2018
A particle/surface system that is exposed to humid conditions, or immersed and withdrawn from a liquid, can exhibit the presence of a liquid film around the region of contact (see Figure 21-4). The film, or meniscus, draws the bodies together due to surface tension and reduces the pressure of the liquid. Capillary condensation is an attractive force and is a function of the particle radius, the liquid surface tension, and the contact angles of the two materials. For wetting liquids, the contact angle approaches zero, and the capillary force is given by: () Fc=2πdpγ.
Surface Chemistry of Solid Surfaces
Published in K.S. Birdi, Surface Chemistry and Geochemistry of Hydraulic Fracturing, 2016
that ΔGad is negative, which suggests that ΔHad is also negative (exothermic). The gas adsorption on a solid is accompanied by a decrease in entropy (i.e., ΔSad < 0) (Chattoraj and Birdi, 1984; Auroux, 2013; Somorjai, 2000; Somasundaran, 2016). This is related to the fact that the degrees of freedom of the adsorbed molecules are lower than in the gaseous state. The adsorption of gas can be of different types. The gas molecule may adsorb as a kind of condensation process, or it may, under other circumstances, react with the solid surface (chemical adsorption or chemisorption). In the case of chemo-adsorption, one almost expects a chemical bond formation. On carbon, while oxygen adsorbs (or chemisorb), one can desorb CO or CO2. The experimental data can provide information on the type of adsorption. This type of adsorption phenomenon will also be expected in shale (Figure 4.7). On porous solid surfaces, the adsorption may give rise to capillary condensation. This indicates that porous solid surfaces will exhibit some specific properties.
Determination of Water Vapor Transmission Properties of Sandstones in the Yungang Grottoes
Published in International Journal of Architectural Heritage, 2022
Yue Zhang, Yi Zheng, Jizhong Huang
In fact, the dry-cup method gives information about the water vapor transmission properties of porous materials under low humidity conditions, whereas the wet-cup method is concerned with high humidity conditions. Theoretically, the water vapor transport through the rock materials is governed by different processes: gaseous flow, surface flow, and capillary condensate flow depending on the pore structure as well as atmospheric humidity (Franzen and Mirwald 2004; Stuck, Plagge, and Siegesmund 2013). At very low RH, the pore surface is occupied by a single layer of water molecules and vapor diffusion is the only moisture transport mechanism. With the rising air humidity, the number of layers of water molecules increases to induce surface flow, a transport mechanism which is more efficient. Capillary condensation occurs when the adsorption proceeds to the point at which multimolecular layers of water merge to form liquid. At a RH of 35%, water starts to fill in the pores with a maximum radius of about 0.001 μm. When the RH gradually reaches 100%, most pores with a radius smaller than 0.1 μm would be saturated.
Estimation of pore pressure and phase transitions of water confined in nanopores with non-local density functional theory
Published in Molecular Physics, 2020
Christelle Miqueu, David Grégoire
Interesting pore pressure behaviour can also be observed when capillary condensation occurs. As an example, Figure 2 depicts the capillary condensation and evaporation of water in a slit graphitic pore of width L = 0.9 nm at 425 K, and the corresponding pore pressure behaviour. As seen in Figure 2, water average pore density increases with pressure upon adsorption until a capillary condensation due to confinement occurs at nearly half the saturation pressure. After this phase change, density of water saturated inside the pore continues increasing until bulk condensation at the bulk saturation pressure. The average density behaviour is monotonic and in agreement with molecular simulations. It can be well understood by looking at the density profiles plotted in Figure 3 for selected pressures. In all cases, the density profiles reveal the stratification of the confined water perpendicular to the graphitic walls. The stratified structure and the high densities of the water layers are consistent with results obtained with molecular dynamics simulations for water/graphene systems [4,46].
Micropore structure characteristics and water distribution in a coalbed methane reservoir
Published in Australian Journal of Earth Sciences, 2019
F. P. Lai, Z. P. Li, H. K. Dong, Z. Y. Jiang, G. T. Mao
The isotherms are classified as Type II for samples zz-1 and zz-3 according to the classification schemes reported by Sing et al. (1985). Clear differences were observed in the samples used in this study. Sample zz-3 adsorbed the most N2 at the highest pressure, exhibiting the highest adsorption, whereas sample zz-4 absorbed the least N2, indicating slight microporosity. In addition, samples zz-1 and zz-3 showed distinct hysteresis. The presence of hysteresis indicates that the evaporation from pores is a distinctly different process originating from the condensation in the pores and indicates the occurrence of capillary condensation within mesopores (Clarkson & Bustin, 1999; Mastalerz, He, Melnichenko, & Rupp, 2012; Nie, Liu, Yang, Meng, & Li, 2015). According to the Kelvin equation (Gregg & Sing, 1982; Ravikovitch, Haller, & Neimark, 1998), capillary condensation cannot occur when the relative pressure is less than 0.5. Thus, the adsorption hysteresis loop disappears.