Alumina electron transport

This category includes a large variety of silica, zirconia, and alumina mesoporous films. Although the inorganic scaffold of such layers does not transport electric current, the pore architecture, which can be also used as a host matrix for incorporation of functional molecules, can alter electron transport to and from the conducting surface, thus influencing electronic properties of the complete system. 

For the screening of herbicides, Rawson et al. [31, 32] used mainly the cyanobacterium Synechococcus (PCC 6301). These bacteria were either immobilized on an alumina membrane or entrapped in alginate. An electrochemical mediator (K3FeCN6) was used to cause an interaction between the electrode and the photosynthetical electron transport system of the cyanobacterium. 

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

The defect concentrations and their dependence on p0l and temperature are derived from the law of mass action by procedures essentially the same as those outlined in Section 2.6.2. In the case of polycrystalline high-purity alumina, the electronic conductivity increases with decreasing grain size and is attributed to hole transport along grain boundaries. 

The jS-aluminas have been extensively used as permeable membranes in sodium-sulfur batteries since they provide the unique properties of allowing sodium transport but neither sulfur nor electron conduction and they are not attacked by molten sodium or sulfur. 

It is commonly accepted that due to the mixing of the electrolyte in industrial cells, the concentration gradients of dissolved metal are present only in the boundary layers at the cathode and the anode, as illustrated in Figure 2.37. Therefore, during electrolysis in cryolite-alumina melts there is a gradient in the transport number of electrons, t, across the cell... 

On the other hand, lead poisoning deactivation curves have non-selective characteristics (Type A). These result when the poison is less strongly chemisorbed, and it tends to suffer many collisions with the alumina washcoat structure before chemisorption. Consequently, lead is found deep inside the washcoat structure, as is demonstrated by electron probe microanalysis, and the more accessible metal sites are left active to gaseous reactants by the faster bulk transport processes. 

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