Reference Electrodes position

Reference electrode position from leading edge, cm... 

Figure 9.13 Spectroelectrochemical cell for Raman spectroscopy studies using electrode emersion. (A) Top view of cell, micrometer adjusts cell path length (B) front view with 90° rotation of reference electrode position. [From J.E. Pemberton and R.L. Sobocinski, J. Electroanal. Chern. 575 157 (1991). Copyright 1991 Elsevier Sequoia S.A., Lausanne.]...

F. Variation of Solution Resistance with Reference Electrode Position for Three Geometries... 

Reference electrode position from leoding edge, cm 0 75 6 20 36... 

The anodic polarization curve for a specimen with an active crevice will be in principle as shown in Figure 7.17. In this case a very small free external surface is assumed, and any internal hydrogen reduction is disregarded. is the potential as measured with the reference electrode positioned outside the crevice. As explained above, the real potential in the crevice, Ei , is more negative. The lower limit for corrosion in an active crevice is the protection (or repassivation) potential Epr. However, the critical potential that must be exceeded for initiation of the ereviee corrosion process, the crevice corrosion initiation potential, is higher than the protection potential. 

The system was connected to a gravity-fed flow system, with a silver or platinum pseudo-reference electrode positioned upstream of the mercury electrode and a platinum gauze counterelectrode located downstream of the cell. 

Potentiometric ion-selective electrodes (ISEs) are one of the most important gronps of chemical sensors. The application of ISEs has evolved to a well-established rontine analytical technique in many fields, inclnding clinical and environmental analysis, physiology, and process control. The essential part of ISEs is the ion-selective membrane that is commonly placed between two aqueous phases, i.e the sample and inner solutions that contain an analyte ion. The membrane may be a glass, a crystalline solid, or a liquid (1). The potential difference across the membrane is measured with two reference electrodes positioned in the respective aqueous phases... 

Figure 10.2 (a) Potential through the electrode-supported cell with no current and (h) through a cell with a current load, (c) The potential across the electrolyte at the reference electrode position (thick line) and through the cell part with the current load (thin line). It is. seen that V f 4)/ - RpMnmie + Rp.miiwih + Retm = the total polarisation of the cell apart from concentration polarisation. 

The standard states of Ag and of Ag (aq) have the conventional definitions, but there is an ambiguity in the definition of the standard state of e. Suppose that a reference electrode R is positioned above a solution of AgN03, which in turn is in contact with an Ag electrode. The Ag electrode and R are connected by a wire. Per Faraday, the processes are... 

Fig. V-17. Schematic diagram for the apparatus for measurement of Vobs (see text). The vibrating reference electrode is positioned close to the surface of a AgN03 solution in which there is an Ag electrode, which, in turn, is in electrical contact with the reference electrode. (From Ref. 196.)...

The apparatus consists of a tip-position controller, an electrochemical cell with tip, substrate, counter and reference electrodes, a bipotentiostat and a data-acquisition system. The microelectrode tip is held on a piezoelectric pusher, which is mounted on an inchwomi-translator-driven x-y-z tliree-axis stage. This assembly enables the positioning of the tip electrode above the substrate by movement of the inchwomi translator or by application of a high voltage to the pusher via an amplifier. The substrate is attached to the bottom of the electrochemical cell, which is mounted on a vibration-free table [, and ]. A number... 

The mercurous sulfate [7783-36-OJ, Hg2S04, mercury reference electrode, (Pt)H2 H2S04(y ) Hg2S04(Hg), is used to accurately measure the half-ceU potentials of the lead—acid battery. The standard potential of the mercury reference electrode is 0.6125 V (14). The potentials of the lead dioxide, lead sulfate, and mercurous sulfate, mercury electrodes versus a hydrogen electrode have been measured (24,25). These data may be used to calculate accurate half-ceU potentials for the lead dioxide, lead sulfate positive electrode from temperatures of 0 to 55°C and acid concentrations of from 0.1 to Sm. 

The thermodynamics of electrochemical reactions can be understood by considering the standard electrode potential, the potential of a reaction under standard conditions of temperature and pressure where all reactants and products are at unit activity. Table 1 Hsts a variety of standard electrode potentials. The standard potential is expressed relative to the standard hydrogen reference electrode potential in units of volts. A given reaction tends to proceed in the anodic direction, ie, toward the oxidation reaction, if the potential of the reaction is positive with respect to the standard potential. Conversely, a movement of the potential in the negative direction away from the standard potential encourages a cathodic or reduction reaction. 

The potential dependence of the velocity of an electrochemical phase boundary reaction is represented by a current-potential curve I(U). It is convenient to relate such curves to the geometric electrode surface area S, i.e., to present them as current-density-potential curves J(U). The determination of such curves is represented schematically in Fig. 2-3. A current is conducted to the counterelectrode Ej in the electrolyte by means of an external circuit (voltage source Uq, ammeter, resistances R and R") and via the electrode E, to be measured, back to the external circuit. In the diagram, the current indicated (0) is positive. The potential of E, is measured with a high-resistance voltmeter as the voltage difference of electrodes El and E2. To accomplish this, the reference electrode, E2, must be equipped with a Haber-Luggin capillary whose probe end must be brought as close as possible to... 

The principle of the measurement is described with the help of Fig. 2-7 [50]. Potential measurement is not appropriate in pipelines due to defective connections or too distant connections and low accuracy. Measurements of potential difference are more effective. Figure 3-24 contains information on the details in the neighborhood of a local anode the positions of the cathodes and reference electrodes (Fig. 3-24a), a schematic representation of the potential variation (Fig. 3-24b), and the derived values (Fig. 3-24c). Figure 2-8 should be referred to in case of possible difficulties in interpreting the potential distribution and sign. The electrical potentials of the pipeline and the reference electrodes are designated by... 

According to Fig. 3-24 the reference electrode is remotely positioned, outside the voltage cones of the pipeline holidays. Thus it may also be positioned above a section of the pipeline where there are no defects in the coating, which can be tested by a conventional Cg measurement. If now the electrode Bq lies on such a section (0gQ = 0g ), but electrode B, already lies in the voltage cone of a defect in the pipe coating, Eq. (3-61) applies for the position, a, ... 

Here the voltage is measured directly between reference electrodes at the positions a and a,. 

Even with the superposition of the ac with a cathodic protection current, a large part of the anodic half wave persists for anodic corrosion. This process cannot be detected by the normal method (Section 3.3.2.1) of measuring the pipe/soil potential. The IR-free measurable voltage between an external probe and the reference electrode can be used as evidence of more positive potentials than the protection potential during the anodic phase. Investigations have shown, however, that the corrosion danger is considerably reduced, since only about 0.1 to 0.2% contributes to corrosion. 

Figure 12-9 shows on and off potentials that were measured around the circumference of a flat-bottomed tank 100 m in diameter. These values, however, give no information on the tank/soil potentials at the center of the container or at points away from the edge of the tank. In new tank constructions, long-life reference electrodes are therefore installed in the center of the base where the most positive potentials are found [15]. 

Figure 19-1 shows the experimental setup with the position of the steel test pieces and the anodes. The anodes were oxide-coated titanium wires and polymer cable anodes (see Sections 7.2.3 and 7.2.4). The mixed-metal experimental details are given in Table 19-1. The experiments were carried out galvanostatically with reference electrodes equipped to measure the potential once a day. Thus, contamination of the concrete by the electrolytes of the reference electrodes was excluded. The potentials of the protected steel test pieces are shown in Table 19-1. The potentials of the anodes were between U(2u-cuso4 = -1-15 and -1.35 V. 

Since cathodic protection of concrete structures in the United States has been very much advanced, protection criteria have been developed [46]. They correspond to the pragmatic criteria Nos. 3 and 4 in Table 3-3 (see Section 3.3.3.1). It is assumed that the protective effect is adequate if, upon switching off the protection current, the potential becomes more than 0.1 V more positive within 4 hours. The measurements are carried out in various parts of the protected object with built-in Ag-AgCl reference electrodes or with any electrodes on the external surface. 

Fig. 21-3 Diagram of the protected Kaplan turbine with position of anodes (A1 to A14) and reference electrodes (El to E5).

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