Electrode large meshed

Close meshed membrane electrode membrane electrode with large-meshed membrane. The small pores of its membrane allow diffusion of ions and molecules up to a certain size. Its potential is equal to the -> Donnan potential. 

Titanium can be forged, bent, cut, stamped, rolled, extruded and successfully welded under argon, making possible a large variety of electrode shapes, i.e. rod, sheet, tube, wire or mesh. It is a very light yet strong material with a high resistance to abrasion. 

The area of the mercury electrode surface in such a cell is only about 0.45 mm2. Thus only a small amount of radical can be generated. To increase the surface area so that larger quantities can be generated, a foil or wire mesh electrode is used in place of the mercury. However, in this configuration, large potential gradients can promote convection, making the overall electrode behavior impossible to characterize. 

The use of such techniques for radiochemical work has been discussed In detail (203,250,251). In these studies a platinum electrode of large surface area (52 mesh, 30 mm high, 10 mm i.d.) coated with silver chloride is placed in contact with 10 ml of solution containing a very low concentration of radioactive silver. The solution Is stirred magnetically. The electrode is then removed from the solution, washed with nitric acid, rinsed with acetone, and the radioactivity counted. 

Spectroelectrochemistry has become a valued technique coupling spectroscopy and electrochemistry. Spectroelectrochemistry is a bulk electrochemical technique and as such many of the cell requirements discussed above that pertain to BE apply for spectroelectrochemistry. Often concentrations for spectroelectrochemistry are much lower than most electrochemical techniques due to the spectroscopic absorbance requirements. The bulk solution must still be oxi-dized/reduced in spectroelectrochemistry. Large surface area working and auxiliary electrodes are employed as in the bulk methods described above. Cells designed with optically transparent electrodes like thin films of Sn02 or In203 or optically transparent mesh electrodes are employed, otherwise the electrode must be manually removed to record spectra. Optically transparent electrodes can be constructed such that the solution volume to electrode surface area ratio is very small making the BE occm rapidly. 

The form and shape of the electrodes are tailored for the specific reactor configuration. Typical shapes include flat metal sheets, perforated or expanded metal grids, metal foams and meshes, and three-dimensional packed bed electrodes formed by stacking metal meshes, pressing catalyst powders, or by use of microporous carbon felts and cloths (three-dimensional electrodes are particularly attractive for low-current density reactions because the electrode surface per unit reactor volume can be made very large) [28]. 

The different electrode connections are top to bottom (T-B), top to mesh (T-M) and top to mesh + bottom (T-MB). The average ion current values at —400 volts and 2 torr are 2.8, 5.8 and 7.5 /xamp respectively for the different electrode connections. The mesh electrode collects a large fraction of the total current. Ideally the T-B current plus the T-M current should equal the T-MB current. The results show that the T-MB current is a little lower than expected. This is probably because of an artificially high T-M current caused by some transmitted ions being attracted back to the mesh electrode. Thus, in the T-B or T-MB connections 2.8/7.5 = 38% of the ions are transmitted through the mesh electrode. 

The working electrode should have a large surface area. Platinum is used because it is inert Pt gauze or mesh electrodes are used to provide a large surface area. The electrode mesh is like wire window-screening material, with the wire diameter about 0.2 mm. The mesh is welded into an open cylinder to make the electrode. A standard size is a cylinder about 5 mm high and 5 mm in diameter, but Pt mesh electrodes of many sizes are available. 

For electrochemical chloride extraction (abbreviated CE, also called chloride removal, or desalination), a direct current is applied between the reinforcement (cathode) and an anode that is placed temporarily on the outer surface of the concrete. The anode is an activated titanium wire mesh or a reinforcing steel mesh. The anode is surrounded by tap water or saturated calcium hydroxide solution in ponds (upper, horizontal surfaces) or tanks (vertical or overhead surfaces) or as a paste that can be sprayed onto all types of surface. Chloride ions migrate from the reinforcement to the anode. Due to a relatively high current density of 1 to 2 A/m, relatively large amounts of chloride can be removed from the concrete within a relatively short time, usually 6 to 10 weeks. After that, the anode, the electrolyte and the incorporated chloride ions are removed from the stracture. The principle layout and electrode reactions involved are indicated in Figure 20.8. 

Suppose the emulsion consists of a noncontinuous phase and a conducting disperse phases in the form of identical small spherical drops of radius R carrying a constant charge q. The drops move between two parallel flat mesh electrodes. On a large distance from the electrodes, drops move perpendicularly to the mesh plane. Assume that drops acquire the charge as a result of collisions with electrodes. Then, according to [98],... 

The counter electrode was in each case a platinum mesh and mounted downstream within the flat cell at the edge of the cavity. This is a compromise to assure a widespread use of the cell construction. In this way the reaction products at the counter electrode do not interfere the ESR-signal and the reaction at the working electrode (care has to be taken with gas bubbles). On the other hand the contact to the working electrode is also close enough to avoid large cell resistances. 

Magnified image of coimected part between two rectangular units, (d) Photo image of large area (100 mm ) transparent A1 mesh electrode... 

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