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2 Permeation and Separation
Published in Zeinab Abbas Jawad, 2 Sequestration and Separation, 2019
Thiam Leng Chew, Tiffany Yit Siew Ng, Yin Fong Yeong
Surface diffusion is when the specific gas molecules are selectively adsorbed on the pore walls and hence transport through the pore framework in the direction of decreasing surface concentration (Shekhawat et al. 2003). The separation of gas molecules is achieved when the selectively adsorbed and diffusing specific gas molecules hinder the diffusion of the other gas molecule species through the pore framework. Surface diffusion usually occurs at low temperature when the gas molecules could not escape from the surface potential field due to stronger interaction between the inner surface pore wall and gas molecules compared to their kinetic energy (Oyama et al. 2011). Increase in temperature will result in decrease in surface diffusion. Chew and Ahmad (2016) reported higher surface diffusion of CO2, compared to CH4, through Ba-SAPO-34 zeolite membrane owing to stronger adsorption strength of CO2 in Ba-SAPO-34 pore framework. However, the surface coverage of CO2 on Ba-SAPO-34 pore framework decreased, causing decrease of CO2 gas flux from 19.5 to 9.8 × 10−3 mol/m2, when temperature was elevated from 30 to 180°C.
Theory of the Liquid and Solid Films Rupture
Published in Eli Ruckenstein, Gersh Berim, Wetting Theory, 2018
The surface diffusion coefficient, and hence the surface diffusion parameter, can be altered either by affecting the surface properties of the film through the presence of adsorbates and/or impurities or by changing the temperature. Impurities can either inhibit or enhance surface diffusion depending on the properties of the impurity. Experimental evidence suggests that impurities may be divided into two categories: (1) those which decrease the rate of surface diffusion frequently have a higher melting point (cohesive energy) than the film and (2) those which increase the surface diffusion coefficient generally have a lower melting point than the film15. The effect of surface impurities may be quite striking. For example, the surface diffusion coefficient of copper can be enhanced by four orders of magnitude in the presence of chlorine16. Similarly, the surface diffusion coefficient, and therefore βm, can be increased by two orders of magnitude for silver by introducing oxygen into the surroundings17.
Fluid Flow and Pumping Concepts
Published in Marsbed H. Hablanian, High-Vacuum Technology, 2017
There are three more types of gas transfer that do not belong to the category of pneumatic flows: Surface diffusion (see Section 3.9), permeation, and diffusion of one gas through another. Surface diffusion refers to molecules moving from one adsorption site to another without leaving the surface. Permeation is mass transfer of a substance through a solid. It is well known, for example, that helium permeates through glass. The permeation rates depend on the particular gas and the material through which it penetrates. The flow-pressure relationship is based on partial pressure difference or, in other words, on the concentration gradient of the gas (see Section 3.9), () Q∼P11−P21
Numerical modeling of low-temperature and low-pressure sintering of silver microparticles based on surface and grain boundary diffusion mechanisms
Published in Mechanics of Advanced Materials and Structures, 2022
The atoms’ motion along the free surface of particles is controlled by surface diffusion. This type of motion is driven by the negative of the surface Laplacian of the mean curvature [29]. And the velocity which represents the rate of matter accumulation (or removal) on the surface, can be described as:
The role of phosphorus in pore rounding of sintered steels
Published in Cogent Engineering, 2018
Walid Khraisat, Wisam Abu Jadayil, Nathir Rawashdeh, Henrik Borgström
Surface diffusion is attributed to the various lateral interactions developed on the surface. Elastic strains induced in the surface is a kind of the indirect interaction connected within the bulk caused by the adsorbed atoms (Yang, Wang, & Zhao, 2008). Thus the region of the pore surface with high surface strain will have the highest contribution to the chemical potential.
Mass flow rate prediction of shale gas considering gas diffusion and water film evaporation
Published in Numerical Heat Transfer, Part B: Fundamentals, 2019
Feng Gao, Weihong Peng, Xuan Dong, Wei Zhang, Donghui Zhao
The surface diffusion is the phenomenon that the adsorption surface layer can move along the solid surface when the adsorbate is adsorbed on the surface of the solid adsorbent. The diffusion rate is proportional to the concentration gradient of the adsorbent, and it is a unique mass transfer method for adsorbed gas.