Surface permeation

Comford, E.M., (1982) Correlation between liquid partition coefficients and surface permeation in Schistosoma iaponicum. J. Membr. Biol. 64, 217-224. 

To test the relative influence of the adsorption and surface permeation of the Pyrex 7740 glass, we sealed the furnace tube off from the system and made a blank run. From the result obtained we must conclude that the surface permeation and adsorption on the Pyrex 7740 glass system is appreciable and has to be considered in the interpretation of the leak rate data. 

Effect of gas pressure on adsorption and surface permeation processes. In order to understand the nature of this gas evolution following a previous charge of the furnace tube with gases, it is necessary to study the extent of adsorption and permeation of the gases into the tube material as a function of the pressure with the intermediate chamber evacuated. The extent of these processes is measured by apparent leak rate measurement 10 minutes after evacuation of the gas. 

An overview of data for different gas-membrane combinations is given by Uhlhorn [21]. It is concluded that in all treatments in the literature the surface flux is taken as an additional contribution to the gas flow and usually the total permeation is obtained as a linear combination of gas and surface permeation. 

Pitting corrosion is initiated by chloride migration from the electrolyte to the metal-passive film interface. Chloride ions adsorb on the outer metal oxide surface, permeate and interact with the underlying metal [9,10]. Redox reaction at the interface increases... 

In order to avoid excessive concentration polarisation at the membrane surface, permeate recovery per membrane element should not exceed 18%. In the case of brackish water RO systems, the average recovery per 100 cm (40-in.) long membrane element is usually about 9%. The overall recovery for a staged system with pressure vessels containing six elements is usually as follows [46] ... 

Finally, the proton-conducting membranes based on perovskites can be used for steam permeation. Such a concept has been demonstrated for fuel cells operating at zero current, but could also be extended to membrane reactor applications [65]. In this concept, water permeates from the feed to the permeate side of the membrane, promoting steam reforming of methane. The generated H2 splits at the permeate/membrane surface, permeating back to the feed side as a Fara-daic flux and reacting with O2. 

Peak or peak ratio Surface Permeate Retentate % Recovery... 

Membranes made by interfacial polymerization have a dense, highly cross-linked interfacial polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less cross-linked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. Because the dense cross-linked polymer layer can only form at the interface, it is extremely thin, on the order of 0.1 p.m or less, and the permeation flux is high. Because the polymer is highly cross-linked, its selectivity is also high. The first reverse osmosis membranes made this way were 5—10 times less salt-permeable than the best membranes with comparable water fluxes made by other techniques. 

A key factor determining the performance of ultrafiltration membranes is concentration polarization due to macromolecules retained at the membrane surface. In ultrafiltration, both solvent and macromolecules are carried to the membrane surface by the solution permeating the membrane. Because only the solvent and small solutes permeate the membrane, macromolecular solutes accumulate at the membrane surface. The rate at which the rejected macromolecules can diffuse away from the membrane surface into the bulk solution is relatively low. This means that the concentration of macromolecules at the surface can increase to the point that a gel layer of rejected macromolecules forms on the membrane surface, becoming a secondary barrier to flow through the membrane. In most ultrafiltration appHcations this secondary barrier is the principal resistance to flow through the membrane and dominates the membrane performance. 

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