Passive Film on Copper

The metal may corrode by formation of both monovalent and divalent cations, the latter case occurring most readily in corrosion [24]. The passive film on copper is poor and may be broken down by atmospheric pollutants. 

TYPES OF PASSIVATING FILMS ON COPPER SURFACE UNDER OXDIZING CONDITIONS... 

As shown in Fig. 8.4, to form an effective passivating film on copper, a corrosion inhibitor must adsorb onto the surface. The adhesion to the copper surface must be strong enough to protect against the shear force impinged by slurry flow. The coordinate bond found in a typical copper(I) or copper(II) complex is usually sufficient to serve as an anchor. The static charge attraction between a surfactant and a charged surface may be too weak to perform such... 

A modified point defect model for the formation of the bi-layer Cu/Cu2S/CuS passive films on copper in the sulfide-containing solutions is proposed. The physico-chemical basis of the modified PDM is shown in Figure 19.3. In all previous systems this model was applied to the formation and dissolution of the passive oxide films on different metals, but... 

Some inhibitors produce films on the anode and hence stifle the corrosion reaction (iron in chromate or nitrite solutions). Several authors consider the presence of a thick barrier of corrosion products, relatively protective, on the metallic surface as passivation. Inhibitors may enhance the formation of passive films on top of the substrate, such as benzotriazole on copper or benzoate on iron, or they may form monomolecular... 

The catalytic effect of copper-nickel alloys as a function of composition for the reaction 2H H2 is shown in Fig. 6.17 [53]. Above 60 at.% Cu, the filled d-band is less favorable to hydrogen adsorption hence, favorable collisions of gaseous H with adsorbed H are less probable, and the reaction rate decreases. The similarity to passive behavior of copper-nickel alloys, which also decreases above 60 at.% Cu, can be noted. The parallel conditions affecting passivity and catalytic activity support the viewpoint that the passive films on transition metals and their alloys are chemisorbed. 

FIGURE 7.11 Implementation of a defect exposing Cu atoms on the O-enriched passive film for copper in interaction with a 20M CF aqueous solution (pH 7). Left schematic top view of the unit cell at the passive film surface. The circular defect (radius of 0.8 nm) is configured using periodic boundary conditions. Middle side view of the unit cell for the complete system. Right side view after 300 ps relaxation showing Cl adsorption and pit nucleation at the implemented defect and defects generated in the bulk substrate around the defects site. Adapted from Jeon et al. [135], 1229, with permission from the American Chemical Society. 

Figures 19.4 and 19.5 show typical experimental electrochemical impedance spectra for the passive sulfide film on copper in a deaerated 0.1 M NaCl + 2 x 10 " M Na2S-9H20 solution at 25 °C. The best fit results, calculated from the parameters obtained from optimization of the proposed mechanism based on the modified PDM (Figure 19.3), as listed in Tables 19.2 and 19.3, are also included in these figures as solid lines. It can be seen that the correlation between the experiment and the model is fairly good, indicating that the proposed model can provide a reasonable account of the observed experimental data. It should be noted that the obtained parameters should not only reproduce the experimental impedance spectra but also deliver values that are physically reasonable. The obtained kinetic parameters, such as the standard rate constants, transfer coefficients and defect diffusivities listed in Tables 19.2 and 19.3, show no systematic dependency on the applied...

A metal resists corrosion by forming a passive film on the surface. This film is naturally formed when the metal is exposed to the air for a period of time. It can also be formed more quickly by chemical treatment. For example, nitric acid, if applied to austenitic stainless steel, will form this protective film. Such a film is actually a form of corrosion, but once formed it prevents further degradation of the metal, provided that the film remains intact. It does not provide an overall resistance to corrosion because it may be subject to chemical attack. The immunity of the film to attack is a fimction of the film composition, temperature, and the aggressiveness of the chemical. Examples of such films are the patina formed on copper, the rusting of iron, the tarnishing of silver, the fogging of nickel, and the high-temperature oxidation of metals. 

A galvanic cell is formed when two metals differing in potential are joined together. For instance, if copper is joined to aluminum, aluminum would corrode because it has a more negative potential (—1.66 V) than copper (-f0.521 V). Copper being less active becomes the cathode and aluminum becomes the anode. But if iron is joined to aluminum, the iron corrodes (in seawater), due to the passive film on aluminum which causes it to behave like a nobler metal than iron (but not nobler than copper). The formation of such galvanic cells often leads to the corrosion of underground buried structures. A steel plate with copper rivets... 

All metals (M) react with atmospheric oxygen ( 02-) to form surface films of metal oxides (MOx). When this film is formed under controlled conditions, it produces an inert (passivated) surface that precludes further reaction and corrosion. However, the oxide films on copper alloys and structural steel undergo dissolution when exposed to aqueous media that contain 02- and salts, acids, or bases, and the surface no longer is protected and corrodes (dissolves). 

However the formation of thin polymer film on the electrode, i.e. passivation of the electrode, resulted in cessation of the polymerization, which restricted the electro-oxidation as a polymerization procedure. The electro-oxidative polymerization as a method of producing poly(phenyleneoxide)s had not been reported except in one old patent, in which a copper-amine complex was added as an electron-mediator during the electrolysis (4). The authors recently found that phenols are electro-oxidatively polymerized to yield poly-(2,6-disubstituted phenyleneoxide)s, by selecting the electrolysis conditions This electro-oxidative polymerization is described in the present paper. 

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