Open circuit potential measurement

The simplest procedure in studying galvanic corrosion is a measurement of the open-circuit potential difference between the metals in a couple in the environment under consideration. This will at least indicate the probable direction of any galvanic effect although no information is provided on the rate. A better procedure is to make similar open-circuit potential measurements between the individual metals and some appropriate reference electrode, which will yield the same information and will also permit obser-... 

Absolute correlations between service performance and electrochemical measurements do not appear frequently in the literature. Based on 300 test systems. Bacon and coworkers (, correlated electrochemical resistance with exposure time. Recently, Mills ( also observed a correlation between salt fog corrosion and electrochemical resistance. We have found open circuit potential measurements to be extremely useful for the routine evaluation of high-nitrile polymer-based photocured coatings. 

The open circuit potential represents the potential of the system taken after approximately a 10 minute equilibration period. In addition to open circuit potential measurements, polarization curves were run for each sample. It was hoped a correlation could be seen between the visual assessment of corrosion and polarization. Unfortunately, only open circuit potentials could be correlated with performance. Therefore, no attempts were made to correlate the corrosion current density or the shapes of the polarization curves with performance. 

Based on the literature, the correlation between open circuit potential rust rating and temperature was unexpected. To rule out the fact that the open circuit potential measurements did not simply represent changes in the phosphated substrate due to temperature,... 

B40 panels were also subjected to heat treatment. As shown in Figure 2, no dependence of the open circuit potential on post-thermal treatment temperature is observed. This suggested that the open circuit potential measurements reflected changes at the coating/B40 panel interface and not in the B40 panel alone. 

Open circuit potential measurements [1,2] were measured with a comparable set-up as used for cyclic voltammetry. Platinized platinum was used as a working electrode. These measurements were performed during reaction i.e. in-situ. 

The direct electrochemical measurement of such low corrosion rates is difficult and limited in accuracy. However, electrochemical techniques can be used to establish a database against which to validate rates determined by more conventional methods (such as weight change measurements) applied after long exposure times. Blackwood et al. (29) used a combination of anodic polarization scans and open circuit potential measurements to determine the dissolution rates of passive films on titanium in acidic and alkaline solutions. An oxide film was first grown by applying an anodic potential scan to a preset anodic limit (generally 3.0 V), Fig. 24, curve 1. Subsequently, the electrode was switched to open-circuit and a portion of the oxide allowed to chemically dissolve. Then a second anodic... 

Investigation of the effect of particulate properties during CMP of W showed a significant increase in the polish rate in the presence of ferric nitrate compared to the polish rate in de-ionized water, at all alumina bulk density values (shown in figure 4). Kaufmann et al. , attributed the increase in the polish rate in the presence of ferric nitrate to the "softness" of the passivating oxide film compared to W. Potentiodynamic experiments and open circuit potential measured as a function of time indicate passivation of W surface. However, the hardness values of tungsten films exposed for 5 min to 0.1 M ferric nitrate, even at the lowest load (300p,N), were the same as those of as-deposited W films within experimental error. Since a 10 nm indentation depth was observed at the lowest load, it is possible that the thickness of the oxide film is smaller and its effect does not manifest itself on the hardness measurement. 

Fig. 4. Changes of properties of LCO with <5 (a) Tc vs. 8 dependence for electrochemically doped LCO [267] (b) anodic charging curves for LCO in 1 m KOH solutions quasi-equilibrium data (open-circuit potentials measured after the interruption of current from [162] (1) and [266] (2) and a common galvanostatic curve [267] (3) (c) comparison of quasi-equilibrium anodic (1) and cathodic (2) charging curves [266].

In general, the open-circuit potential measured between two reversible electrodes, which is also called electromotive force, /f 1, is defined by the Nernst equation. A simplified form of this equation for the electrochemical reaction (3) was given by Eq. (15). In general, the Nernst equation relates the activities (and/or fugacities) of the substances or species, a,-, in the cell s electrochemical reactions and the standard open-circuit potential, E°, of the cell as ... 

Avena, M.J., Camara, O.R., and de Pauh, C.P., Open circuit potential measurements with Ti/TiOj electrodes, Colloids Sutf, 69, 217, 1993. 

Fig. 9 Experimental arrangement for open circuit potential measurements. RE reference electrode.

Figure 7.9 Open-circuit potentials measured when immersing electrochemically reduced PAN layers in Ag ion-containing solutions. The grey reference line shows the OCP of PAN in the absence of metal ions. (Adapted with permission from S. Ivanov and V. Tsakova, Electroless versus electrodriven deposition of silver crystals in polyaniline Role of silver anion complexes, Electrochim. Acta, 50, 5616-5623 (2005). Copyright 2005 Elsevier.)...

OCP Open Circuit Potential Measured potential difference between the... 

Figure 6.6. Schematic instrumentation amplifier set-up for the open circuit potential measurement (RE, reference electrode).

Despite the long history of manufacture, the dry Leclanchd cell dating from the 1880s, its detailed electrochemistry is again far from understood. Indeed the open-circuit potential measured for the completed cell is frequently higher than that estimated on the basis of the equations in Table 10.1 or the more complex equation... 

Preinitialization—An Undisturbed Open Circuit Potential Measurement This step measures, stores, and presents to the screen the interfacial potential of the electroconductive transducer in its electrolyte or test environment. This measurement is made of the complete polymer film relative to a reversible Ag/AgCl, CP electrode that also contacts the electrolyte. The unperturbed open circuit potential is diagnostic of the redox state of the device and conveys information about the integrity of the transducer. 

The four sensor interrogation steps of pulse application, conductivity measurement, float period, and open circuit potential measurement are repeated for a user-defined number of cycles to produce a sensor response curve. Each set of four such steps produces a single-datum point of conductivity and open circuit potential data. Several such points obtained over a period of time produces a response curve. The response curve captures the change in conductivity of the transducer as a function of time following initialization. 

The in-depth interpretation of the polarization curves frequently faces difficulties related to the non-uniform distributions of current and potential on the sample surface. This nonuniformity originates from the intrinsic effect of the sliding that causes an heterogeneity of the electrochemical surface reactivity, combined with the ohmic drop in the electrolyte. A full exploitation of the polarization curves in terms of local behavior is possible only if one can model the current and potential distributions xmder sliding conditions. This brings back to the same approach as in the case of the interpretation of open circuit potential measurements. Note that the effect of non-uniform distributions on the interpretation of polarization curves was already investigated in the absence of any sliding (Law Newman, 1979 Ponthiaux et al., 1995 Tiedemann et al., 1973). 

Open circuit potential measurements are grossly inadequate for predicting the magnitude of galvanic effects since they do not take into account area and polarization effects. They are reliable only for predicting the direction of such effects. 

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