Porous interfaces

Eig. 2. Microstmctural design approaches for composite interfaces (a) mechanically weak coating (b) porous interface and (c) ductile interface. 

For homogeneously doped silicon samples free of metals the identification of cathodic and anodic sites is difficult. In the frame of the quantum size formation model for micro PS, as discussed in Section 7.1, it can be speculated that hole injection by an oxidizing species, according to Eq. (2.2), predominantly occurs into the bulk silicon, because a quantum-confined feature shows an increased VB energy. As a result, hole injection is expected to occur predominantly at the bulk-porous interface and into the bulk Si. The divalent dissolution reaction according to Eq. (4.4) then consumes these holes under formation of micro PS. In this model the limited thickness of stain films can be explained by a reduced rate of hole injection caused by a diffusional limitation for the oxidizing species with increasing film thickness. 

The compositional and structural complexity of these systems is their principal advantage. It is this feature which allows surface properties to be tuned in order to optimize selectivity and activity with respect to a specific reaction. At the same time, complexity is the reason of the fact that at a molecular level, an understanding of reaction kinetics at heterogeneous and porous interfaces is difficult to achieve. Consequently, the reaction kinetics on their surfaces depend sensitively on a number of structural and chemical factors including the particle size and structure, the support and the presence of poisons and promoters. 

FIGURE 6.10 Different membrane concepts for oxygen-ion conducting membranes, (a) Dense mixed conducting membrane top-layer supported on an asymmetric macroporous support (b) dense self-supported mixed conducting membrane with graded porous interfaces and (c) solid electrolyte cell (oxygen pump). 

Porous interface with large porosity to provide vigorous ingrowth of soft tissue to form an anatomic seal and a barrier to bacteria. 

Sapoval, B, J,-N, Chazalviel, and J. Peyridre, Electrical response of fractal and porous interfaces. Physical Review A, 1988. 38(11) pp. 5867-5887 Reiser, H, K.D, Beccu, and M.A. Gutjahr, Electrochimica Acta, 1976, 21 p. 539 Diard, J.R, B, Le Gorrec, and C. Montella, Linear diffusion impedance. General expression and applications. Journal of Electroanalytical Chemistry, 1999. 471 pp, 126-131 Deslouis, C, C, GabrieUi, M. Keddam, A, Khalil, R. Rosset, B. TriboUet, and M. Zidoune, Impedance techniques at partially blocked electrodes by scale deposition. Electrochimica Acta, 1997, 42(8) pp, 1219-1233... 

Generally, the activation layer is a functionally graded porous structure made of the same composition as the membrane layer. A second case is when the two porous interfaces, acting as mixed ionic/electronic-conducting electrodes, are made of materials different from the membrane (a purely ion-conducting electrolyte), as shown in Figure 9.10c. In this case, the oxygen flux can be precisely controlled by the... 

Dense core membrane with (b) graded porous interfaces... 

To demonstrate the above conclusion, selected results of a numerical study using the so-called one-domain approach to describe the momentum transfer at the fluid/porous interface in a membrane reactor will be presented. 

Goyeau, B., Lhuillier, D., Gobin, D. and Velarde, M.G., 2003. Momentum Transport at a Fluid-Porous Interface. International Journal of Heat and Mass Transfer, 46(21) 4071-4081. 

A. Munoz-Bonilla, Hierarchically structured multifunctional porous interfaces through water templated self-assembly of ternary systems, Langmuir 28 (2012) 9778-9787. 

Ross, S.M. Theoretical model of the boundary condition at a fluid-porous interface. AIChE J. 1983, 29, 840-846. 

Chandesris, M., Jamet, D., 2006. Boundary conditions at a planar fluid-porous interface for a Poiseuille flow. Int J. Heat Mass Transf. 49,2137 2150. 

Kinetics of Dealloying and Structure of the Dealloyed Layer The dealloying kinetics are represented by the time dependence of the flux of creation of vacancies, available from the computer data. The results are compared with the prediction by percolation theory, below and above the percolation threshold p. Below p, nearexponential decay of the current with time is predicted in agreement with experiments. Above / , experiments show a decay much steeper than expected, attributed to ohmic and mass transport effects in the porous interface. No mention is made of the negative power law decay reported in Ref 196 [Eq. (56)]. 

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