Copper anodic polarization

Most metals entering the cuprate HTSC (with the exception of copper) during anodic polarization in aqueous solutions over a wide pH interval form either soluble products or loose oxide-hydroxide films with a poor adhesion. The passivation of such chemically active metals in electrolyte solutions has been incompletely studied. However, for bismuth, cadmium, antimony, and also for the corresponding chalco-... 

The products of degradation during polarization of HTSC electrodes have not been studied in much detail [44,287,293,476,478], Upon cathodic polarization of cuprates, the reduced forms of copper oxides [44,476], and sometimes metallic copper [293], are formed at considerable rates these processes are photosensitive [453], During anodic polarization, the formation of alkaline-earth compounds on the HTSC surface is accelerated [287,476]. 

Marshakov et al. studied the effect of an ultrasonic field on the anodic dissolution of a variety of metals [120]. Anodic polarization curves were measured in 0.1—0.5 N HC1, NaCl, H2S04, and NajSC solutions in an ultrasonic field of 20 kHz frequency. The effect of ultrasound was different for various metals due to differential effects on the rate-controlling process. Anodic dissolution of Fe was actually slowed down in the presence of ultrasound because the rate-controlling adsorption of anions at the iron surface was inhibited. At a cadmium anode, the energy of metal atoms in a lattice was increased in the presence of ultrasound and, therefore, the ionization of cadmium was accelerated. Anodic dissolution of copper and silver... 

Nogami et al. and Augustynski et al. showed that the activity of copper electrode, deactivated during the CO2 reduction, is recovered by anodic polarization of the electrode. Periodic anodic pulses are effective to maintain the electrocatalytic activity in prolonged electrolysis of CO2 reduction. 

Fie. 5.23 Potentiostatic anodic polarization curve for copper in deaerated 1 N H2S04 at 25 °C. Redrawn from Ref 20... 

The nature of copper dissolution from CuAu alloys has also been studied. CuAu alloys have been shown to have a surface Au enrichment that actually forms a protective Au layer on the surface. The anodic polarization curve for CuAu alloys is characterized by a critical potential, E, above which extensive Cu dissolution is observed [10]. Below E, a smaller dissolution current arises that is approximately potential-independent. This critical potential depends not only on the alloy composition, but also on the solution composition. STM was used to investigate the mechanism by which copper is selectively dissoluted from a CuAu electrode in solution [11], both above and below the critical potential. At potentials below E, it was found that, as copper dissolutes, vacancies agglomerate on the surface to form voids one atom deep. These voids grow two-dimensionally with increasing Cu dissolution while the second atomic layer remains undisturbed. The fact that the second atomic layer is unchanged suggests that Au atoms from the first layer are filling... 

In sulfuric acid, iron could he passivated hy anodic polarization, which leads to low metal dissolution rates without the polarization, active iron corrosion appears. Alloying elements influence the corrosion rate. Copper has a positive effect and normally reduces the corrosion rate, whereas sulfur and phosphorus increase the corrosion rate. In low-suUur-containirig iron, copper can also increase the corrosion rate [16]. 

This is due to (1) a large difference of the standard potentials of the alloy components, (2) a complete miscibility of the alloy components at T > 410 C, and (3) the availability of Iqu from ammeter readings in a potentiostatic circuit using deaerated solutions [94,95]. Typical examples of quasi-stationary partial anodic polarization curves of copper dissolution from various Cu-Au alloys in 1 N Na2S04 + 0.01 N H2SO4 are shown in Fig. 12. Similar polarization curves have been reported for... 

Gordon ef a/. studied adsorption of bacteria on polarized Cu and Pt metal surfaces in seawater, and attributed their adsorption results, in general, to pH changes at the interface. A copper surface was polarized cathodically from —0.12 to —0.24 V (NHE), and anodically from —0.01 to 0.07 V (NHE). Platinum was polarized cathodically from 0.40 to 0.22 V (NHE), and anodically from 0.60 to 1.30 V (NHE). While anodic polarization was seen to decrease bacterial content on both metals, the cathodic polarization produced mixed results for different kinds of bacteria. 

Should the copper electrode be polarized anodically, concentration of copper ion at the surface is larger than that in the body of solution. The ratio (Cu )/ (Cu )j then becomes less than unity and ( 2 - ( )i of (5.3) changes sign. In other words, concentration polarization at an anode polarizes the electrode in the cathodic or noble direction, opposite to the direction of potential change when the electrode is polarized as cathode. For a copper anode, the limiting upper value for concentration polarization corresponds to formation of saturated copper salts at the electrode surface. This limiting value is not as large as for cathodic polarization where the Cu activity approaches zero. 

Figure 6.14. Values of critical and passive current densities obtained from potentiostatic anodic polarization curves for copper-nickel alloys in N H2SO4, 25°C [42]. (Reproduced with permission. Copyright 1961, The Electrochemical Society.)...

Anodic protection is apphcable only to metals and alloys (mostly transition metals) which are readily passivated when anodically polarized and for which /passive is very low. It is not apphcable, for example, to zinc, magnesium, cadmium, silver, copper, or copper-base aUoys. Anodic protection of aluminum exposed to high-temperature water has been shown to be feasible (see Section 21.1.2). 

Figure 14.5 illustrates the component and overall polarization curves when iron is inunersed in acidic solutions with and without Cu " ". The anodic polarization curves in both solutions are almost the same (line A). The counter electrode reaction in pure solution is the hydrogen evolution reaction, whose polarization behavior is shown by line B. These curves cross each other at point P, which is the mixed potential m(H). The anodic and the cathodic overvoltages are jFe(H) and — 7h respectively. The current density corresponding to m(H) is the corrosion current for iron in acid solutions, Jcorr(H)-When iron is placed in a solution containing Cu + ions, copper deposits on the iron substrate at the expense of iron corrosion. Note that the reversible potential of the Fe/Fe + couple of —0.44 V is less noble than that of the reversible potential for Cu/Cu " ... 

Figure 9.35 Anodic polarization curves of copper-plating coatings after different times of friction movement. (1) Normal copperplatingcoating (2) normal copper-plating coating (300 times) (3) composite coating ...

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