Electrode arrangement

We have considered a single length of electrode. If there is more than one length the values can be obtained from BS 74,")0 for different electrode arrangements. 

The most commonly applied indirect method of measuring soil resistivity using the four-electrode arrangement of Fig. 3-14 is described further in Section 24.3.1. The measured quantities are the injected current, /, between the electrodes A and B, and the voltage, t/, between the electrodes C and D. The specific soil resistivity follows from Eq. (24-41). For the usual measuring arrangement with equally spaced electrodes a = b,ii follows from Eq. (24-41) ... 

Since/(a) is a monotonically increasing function, the protection region, a, increases with the polarization parameter, k. As an example, a symmetrical coplanar electrode arrangement with equally large anodic and cathodic polarization resistances is considered. Here/(jc) is defined as [19] ... 

Accurate control of potential, stability, frequency response and uniform current distribution required the following low resistance of the cell and reference electrode small stray capacitances small working electrode area small solution resistance between specimen and point at which potential is measured and a symmetrical electrode arrangement. Their design appears to have eliminated the need for the usual Luggin capillary probe. 

When a pure sinusoidal AC current passes across the electrode/solution interface, the cell voltage (a two electrode arrangement is used) shows a sinusoidal perturbation. It contains multiples of the fundamental frequency of the modulation, the first harmonie dominates. The magnitude of the effect is comparable to Faradaie rectification, but experiments may be easier to perform. Measurement and evaluation have been described in detail [60Old, 72Hil2]. (Data obtained with this method are labelled FD.)... 

Figure 2.48 The top shows the schematic design of a magneto-hydrodynamic mixer with equally spaced electrodes arranged In a micro channel and an external magnetic field oriented along the z-axis. On the bottom theoretical results for the evolution of two parallel liquid lamellae as a function of dimensionless time are shown [146].

Figure 6.6 Electrode arrangement for an electrochemical cell in which both electrodes can function in the same solution. Description The electrochemical cell is found to drive electrons from the hydrogen electrode to the silver electrode with an emf of about 0.2 V. This can be reported by writing the cell as Pt H2 (1 atm) HCI (1.0 M) AgCI Ag and assigning the emf as +0.2 V. If the cell to be written as Ag AgCI HCI (1.0 M) H2 (1 atm) Pt, the emf would be assigned as -0.2 V. In either instance, the emf values show that there is a tendency for electrons to be propelled through the external circuit from the hydrogen to the silver electrode.

For this reason, electrochemical measuring cells are usually based on a three-electrode arrangement. In the Hewlett-Packard HP 1049A Electrochemical Detector it functions as follows (see Figure 2-3). 

Linear dynamic range for different electrode arrangements... 

Figure 10. Electrode arrangement during the electrochemical treatment (ECT) with low-level direct current one platinum electrode is placed at the center of the tumor, four electrodes with opposite polarity are inserted at the border between the tumor and the surrounding liver tissue. Taken from Turler and coworkers. l...

Figure 8 The electrode arrangement in a three-electrode cell WE= working electrode RE = reference electrode AE = auxiliary electrode...

We will discuss, on the one hand, the spaghetti-like CNT electrodes on conductive surfaces or randomly dispersed in a polymer matrix and on the other hand, CNT arrays grown in situ on substrates with large-scale control of location and orientation. Finally, individual CNT electrodes will be briefly discussed. Figure 3.10 illustrates these different CNT electrode arrangements. 

Water electrolyzer units typically consist of several cells or electrodes arranged in two basic configurations, tank type operated in unipolar configuration, or filter press type operated in bipolar configuration. Tbe most common configuration, see Fig. 2.1, is the unipolar tank type where each electrode has only one polarity and all the electrodes of the same polarity are connected in parallel. The anodes and cathodes are alternately connected, with the... 

Steady-state wavelength-specific photocurrents were measured for the Ti-Fe-0 films in a two-electrode arrangement at different applied voltages. Incident photon-to-current efficiencies (IPCE) are calculated using the following equation ... 

There are two electrolytic methods that are of major importance. One involves the electrolysis of fused sodium chloride using the Downs cell. This method currently is most prevalent. The Downs cell consists of a steel cell with brick lining containing the fused bath. The multiple electrode arrangement consists of four cylindrical graphite anodes that project upward from the hase of the cell. Each anode is surrounded hy a diaphragm of iron gauge and a steel cathode. 

Accurate and precise measures of pH can be made with a pH meter. Typical pH meters usually contain a glass electrode and reference electrode arranged similar to an electrochemical cell. We discuss electrochemical cells in Chapter 14. For now, though, consider a pH meter as essentially a modified voltmeter in which the voltage measured is directly proportional to the hydrogen ion concentration of the solution. Simple pH meters are capable of measuring pH within 0.1 pH units, while more sophisticated instruments are precise to within 0.001 pH units. 

To determine an overpotential, however, it is necessary to alter the above two-electrode system by introducing an extra auxiliary electrode, which is termed the auxiliary or counter-electrode. Thus a three-electrode arrangement is set up as shown in Fig. 736. In such a setup, the counter electrode is connected to the test electrode via a polarizing circuit (e.g., a power source) through which a controllable current is made to pass and produce alterations in the potential of the test electrode. Between the nonpolarizable reference electrode and test electrode is connected an instrument that is capable of measuring the potential difference between these electrodes. 

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