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Mixed potential system systems

The interfacial impedance of mixed potential electrode systems, such as metals undergoing corrosion, was investigated by Haruyama [18] and Epelboin et al. [19]. They showed that the impedance characteristics of such systems can be represented by the equivalent circuit illustrated in Fig. 11, where Q represents the double layer... [Pg.71]

Fig. 11. Schematic representation of an equivalent circuit for a mixed potential system. Q double layer capacitance, R i solution resistance, R anodic charge transfer resistance, R cathodic charge transfer resistance. Fig. 11. Schematic representation of an equivalent circuit for a mixed potential system. Q double layer capacitance, R i solution resistance, R anodic charge transfer resistance, R cathodic charge transfer resistance.
When there are two partial process in a mixed potential system and both are under activation control, the most probable forms of the current densities of the anodic and cathodic partial processes are Equations 33 and 35, respectively. For an isolated metal, the overpotential (since the corrosion potential represents the perturbed electrode potential in this case) is... [Pg.59]

Since Equation 58 is identical in form to Equation 30, the analysis of data for mixed potential systems is the same as that for simple electrode reactions. [Pg.61]

Mixed potential systems with the cathodic partial process under transport control and the anodic partial process under activation control is typical of many corrosion systems. For the cathodic partial process to be under transport control. Equation 44 must be unity or larger. This occurs when the absolute value of the difference between the equilibrium electrode potential of the cathodic partial process and the corrosion is on the order of one volt. This condition prevails for most metals of interest in corrosion studies if oxygen... [Pg.65]

Just as the Butler-Vohner equation was shown to be linear near E " with a slope inversely proportional to j o (low-field approximation. Sect. 1.3.8), the net current in a mixed potential system, represented by Eq. (41), is Knear near corr. with a slope inversely proportional to icorr-Since polarization resistance measurements are made near the corrosion potential, the net currents are often low. Therefore, errors associated with ohmic potential drop are usually small. However, there are cases for which ohmic potential drop creates significant error in the Rp measurement. The measured R is the sum of the trae polarization resistance. [Pg.48]

These equations, therefore, allow the experimentalist to extract fundamental quantities from a mixed potential system in order to understand aspects of the decoupled anodic and cathodic reactions. [Pg.12]

Further interpretation of the polarization curves can be extended using Pour-baix graphical work depicted in Figure 3.5 for pure iron (Fe). The resultant plots represent the functions E = f i) and E va. f [log(i)] for an electrolyte containing CFe+2 — 0.01 g/l = 1.79a 10 mol/l — 1.49a l0 mol/cm at pH = 0. Additionally, the reactions depicted in Figure 3.5 and some related kinetic parameters are listed in Table 3.2 for convenience. One important observation is that both anodic and cathodic Tafel slopes, 0 0ci respectively are equal numerically and consequently. Figure 3.5b has an inflection point at icorr,Ecorr)-This electrochemical situation is mathematically predicted and discussed in the next section using a current density function for a mixed-potential system. [Pg.87]

It was considered that hydrogen peroxide is formed at silver and chalcocite surfaces when oxygen is present as this compound is an intermediate in the cathodic reduction of oxygen. Clearly, then, there is interaction between the two reactions that make up the mixed potential system, namely, xanthate oxidation and oxygen reduction. Thus, care must be taken in considering the individual processes in isolation. [Pg.422]

Electroless plating rates ate affected by the rate of reduction of the dissolved reducing agent and the dissolved metal ion which diffuse to the catalytic surface of the object being plated. When an initial continuous metal film is deposited, the whole surface is at one potential determined by the mixed potential of the system (17). The current density is the same everywhere on the surface as long as flow and diffusion are unrestricted so the metal... [Pg.106]

In a mixed metal system the protection potential to be adopted is that of the least noble metal, i.e. if the heat exchanger channel had been iron and also required protection, the relevant protection potential would have been —0-85 V vs. CU/CUSO4 i.e. the [>otential relating to steel. [Pg.122]

The protection potential refers to the potential at which experience shows corrosion of a metal will cease. Different materials have different protection potentials (Table 10.6). Occasionally a less negative protection potential will be specified because some degree of corrosion is permissible. It should be noted that in a mixed metal system the protection potential for the most base metal is adopted. [Pg.136]

Otherwise it has been shown that the accumulation of electrolytes by many cells runs at the expense of cellular energy and is in no sense an equilibrium condition 113) and that the use of equilibrium thermodynamic equations (e.g., the Nemst-equation) is not allowed in systems with appreciable leaks which indicate a kinetic steady-state 114). In addition, a superposition of partial current-voltage curves was used to explain the excitability of biological membranes112 . In interdisciplinary research the adaptation of a successful theory developed in a neighboring discipline may be beneficial, thus an attempt will be made here, to use the mixed potential model for ion-selective membranes also in the context of biomembrane surfaces. [Pg.237]

If a system is not at equilibrium, which is common for natural systems, each reaction has its own Eh value and the observed electrode potential is a mixed potential depending on the kinetics of several reactions. A redox pair with relatively high ion activity and whose electron exchange process is fast tends to dominate the registered Eh. Thus, measurements in a natural environment may not reveal information about all redox reactions but only from those reactions that are active enough to create a measurable potential difference on the electrode surface. [Pg.188]

By enhancing the metabolism of trichloroethylene to its cytotoxic metabolites, compounds that induce the hepatic mixed-function oxidase system can potentiate the hepatotoxicity of trichloroethylene. [Pg.172]

An electrode in a system containing two couples automatically adopts a mixed potential (or more correctly, a mbcture potential) At this... [Pg.1]

Use of zileuton is uncommon due to the need for dosing four times a day, potential drug interactions, and the potential for hepatotoxicity with the resulting need for frequent monitoring of liver enzymes. In patients started on zileuton, serum alanine aminotransferase concentrations should be monitored before treatment begins, monthly for the first 3 months, every 2 to 3 months for the remainder of the first year, and then periodically thereafter for as long as the patient continues to receive the medication. Zileuton also inhibits the cytochrome P-450 (CYP) mixed function enzyme system and has been shown to decrease the clearance of theophylline, R-warfarin and propranolol.34... [Pg.222]

In contrast to the equilibrium electrode potential, the mixed potential is given by a non-equilibrium state of two different electrode processes and is accompanied by a spontaneous change in the system. Besides an electrode reaction, the rate-controlling step of one of these processes can be a transport process. For example, in the dissolution of mercury in nitric acid, the cathodic process is the reduction of nitric acid to nitrous acid and the anodic process is the ionization of mercury. The anodic process is controlled by the transport of mercuric ions from the electrode this process is accelerated, for example, by stirring (see Fig. 5.54B), resulting in a shift of the mixed potential to a more negative value, E mix. [Pg.392]

The dissolution of zinc in a mineral acid is much faster when the zinc contains an admixture of copper. This is because the surface of the metal contains copper crystallites at which hydrogen evolution occurs with a much lower overpotential than at zinc (see Fig. 5.54C). The mixed potential is shifted to a more positive value, E mix, and the corrosion current increases. In this case the cathodic and anodic processes occur on separate surfaces. This phenomenon is termed corrosion of a chemically heterogeneous surface. In the solution an electric current flows between the cathodic and anodic domains which represent short-circuited electrodes of a galvanic cell. A. de la Rive assumed this to be the only kind of corrosion, calling these systems local cells. [Pg.394]

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. [Pg.9]

NB. Mixed solvent systems are shown as e.g. acn-aq (0.01 M) where the number in parentheses indicates the concentration of the lesser constituent ITO-Indium/tin oxide-coated glass, Ar- Solutions purged with argon, Ar atm - Experiment performed under an argon atmosphere, N2 atm - Experiment performed under a nitrogen atmosphere b All potentials are measured vs. SCE unless otherwise stated ... [Pg.13]

In the mixed potential theory (MPT) model, both partial reactions occur randomly on the surface, both with respect to time and space. However, given the catalytic nature of the reductant oxidation reaction, it may be contended that such a reaction would tend to favor active sites on the surface, especially at the onset of deposition, and especially on an insulator surface catalyzed with Pd nuclei. Since each reaction strives to reach its own equilibrium potential and impose this on the surface, a situation is achieved in which a compromise potential, known as the mixed potential (.Emp), is assumed by the surface. Spiro [27] has argued the mixed potential should more correctly be termed the mixture potential , since it is the potential adopted by the complete electroless solution which comprises a mixture of reducing agent and metal ions, along with other constituents. However, the term mixed potential is deeply entrenched in the literature relating to several systems, not just electroless deposition. [Pg.229]


See other pages where Mixed potential system systems is mentioned: [Pg.30]    [Pg.44]    [Pg.54]    [Pg.72]    [Pg.26]    [Pg.347]    [Pg.2131]    [Pg.229]    [Pg.142]    [Pg.144]    [Pg.39]    [Pg.202]    [Pg.120]    [Pg.29]    [Pg.31]    [Pg.123]    [Pg.256]    [Pg.150]    [Pg.9]    [Pg.137]    [Pg.163]    [Pg.588]    [Pg.322]   
See also in sourсe #XX -- [ Pg.26 ]




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