Electrode Geometries and Arrangements

For BDD, electrodes in the recognized format, akin to Pt, Au, and glassy carbon, are not currently widely available. For any BDD thin-film electrode, where the 

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In the case of solid electrolytes, such a calibration is usually impossible. The configuration of measuring cells should be selected to provide uniform current distribution or to enable use of a definite solution of differential Ohm s law for the conductivity calculations [ii-iv]. The conductivity values are typically verified comparing the data on samples with different geometry and/or electrode arrangement, or using alternative measurement methods. 

A modification of the arc discharge method is reahzed in the so-called DC-arc jet (plasma jet). In this case, the electrodes are arranged in a way to form a sort of nozzle for the reactant gases. The cathode encloses the anode in a certain distance, and the gas mixture is led through the resultant gap. It partly decomposes between the electrodes before it hits the cooled substrate where the diamond film is deposited then (Figure 6.16). In this manner, an accurate control of the deposition zone is achieved, yet the results are highly dependent on the nozzle geometry and on a very constant reactant flow. 

Figure 11.6.5 Typical cell arrangements and electrode geometries for electrochemical flow cells. Top (A) Thin-layer cell. (B) Wall-jet cell. Bottom Various electrode geometries (a) tubular electrode (b) planar electrode with parallel flow (c) planar electrode with perpendicular flow ...

In photocathodes or photomultipliers the incident photons force electrons to leave the material. This external photoeffect can be calibrated and amplified by acceleration and multiplication of the electrons in multi-electrode arrangements (dynodes). These devices have very short response times and can be successfully used to control the stability of a light source. Therefore such devices are frequently included in commercially available set-ups. An example is given in Fig. 4.32 combining an irradiation source with a measurement set-up. This is commercially available [119] and allows simple control of a photoreaction. However, due to geometry and inhomogeneity of the sensitive layer of the photodiode, non-homogeneous irradiation can cause errors. 

Corrosion rate measurements on-site. The main difference in measuring the polarization resistance Rp on site and not in the laboratory is the geometrical arrangement of the electrodes. In the laboratory a uniform geometry and thus uniform current distribution can be achieved usually with small specimens, whereas on site a there is a non-uniform current distribution between the small counter-electrode (CE) on the concrete surface and the large rebar network (WE). The current fed by the external counter electrode (Figure 16.15) not only polarizes the surface of the reinforcement below the CE itself but also spreads laterally or may reach... 

The ohmic drop in the electrochemical cell is related to the potential field in the electrolyte, which depends on the geometry and the arrangement of electrodes and... 

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