Pourbaix diagrams copper

Essentially, the pH is controlled to suppress the hydrogen evolution cathodic reaction- The Pourbaix Diagram for iron indicates that high pH values as well as low values may lead to corrosion. The construction of these diagrams for higher than ambient temperatures - shows how the area of the alkaline zones increases considerably under boiler conditions, so that the risk of corrosion is correspondingly higher. Many feed systems contain copper alloys. 

Potential sweep measurements, with microwave frequency effects, 455 Pourbaix diagrams, applied to adlayers on copper, 93... 

It is important to recognize some of the limitations of the Pourbaix diagrams. One factor which has an important bearing on the thermodynamics of metal ions in aqueous solutions is the presence of complex ions. For example, in ammoniacal solutions, nickel, cobalt, and copper are present as complex ions which are characterized by their different stabilities from hydrated ions. Thus, the potential-pH diagrams for simple metal-water systems are not directly applicable in these cases. The Pourbaix diagrams relate to 25 °C but, as is known, it is often necessary to implement operation at elevated temperatures to improve reaction rates, and at elevated temperatures used in practice the thermodynamic equilibria calculated at 25 °C are no longer valid. 

The behavior of these metals, in fact, must be carefully checked in the actual device configurations on account of the simultaneous presence of two different metals — conductor plus diffusion barrier—which induces different electrochemical potentials. As an example, the difference of behavior of copper in HF-based chemistry (pH = 7) with or without titanium nitride is illustrated in Fig. 4. According to the Pourbaix diagram, at this pH the copper is theoretically passivated by CuO as verified by the slight increase of copper layer thickness. But in presence of titanium nitride copper is severely corroded. 

Porterfield. W. W., 295 Positive oxidation states, halogens in, 837-848 Posttransition metals, 28. 876 Potassium, 309, 582-587 Potentials, electrode, 378-383 Pourbaix diagram, 591-592 Praseo complex, 388,491, 493 Predominance area diagram, 591 Prewitt, C. T., 116-117 Principal axis, 51 Prism, trigonal prism, 489-491 Probability function, 13 Prosthetic group, 919 Proteins, and blue copper proteins, 912-916 Proton... 

Figure 7.19 Simplified Pourbaix diagram for copper/water.

Use of Pourbaix diagrams. Consider copper metal at +0.150V vs SCE in an aqueous solution of pH 2.5 and a cupric ion activity of 0.01 at 25°C. In order to use the Pourbaix diagram, the potential is converted to SHE scale. 

Reference to the Pourbaix diagrams for water and copper shows the stable species to be Cu2+, H+ and H2O. Corrosion is possible under these conditions. Let us consider the case of iron metal at —0.750 V vs SCE in a solution of pH 5.0 and a ferrous ion activity of 10 6 at 25°C. The electrode potential with respect to SHE is 0.509 V and reference to Pourbaix diagrams for water and iron shows the stable species to be Fe2+ and H2, and that corrosion is possible under these conditions. 

FIGURE 7.1 Pourbaix diagram of copper-water system (from Ref. 1). 

Ferric nitrate was among the first oxidizers used in early tungsten and copper CMP processes. As indicated in the Pourbaix diagram [25] for Fe (Fig. 7.8), the reduction potential is 0.77 V for Fe Fe reaction. Considering the fact that the reduction potential for Cu Cu is 0.52 V, ferric nitrate has more than adequate oxidizing power for the Cu CMP process (Eq. 7.7). 

There are several difficulties with using the Pourbaix diagram to predict the stability of copper during polishing, specifically ... 

An example of the use of Pourbaix diagrams and electrochemical potential measurements is the polish performance of copper in three slurries based upon NH3 compounds. These slurries consist of 2.5 wt% AI2O3 abrasive with an average aggregate size of 300 nm, DI water, and either NIf,OH, NH4NO3, or NH4CI. The total concentration of ammonia (as NH3, NH4 or NH4X) in each... 

The Pourbaix diagram for the copper/water system is shown in Fig. 2.15. The more positive standard electrode potential of copper (+337 mV (SHE)) as compared to iron (-440 mV (SHE)) is evident. This greater nobility results in copper being thermodynamically stable in water that is, line 14 (-6) representing aCu2+ = 10-6 lies above line a. 

Analysis of Pitting of Copper with Reference to the Pourbaix Diagram... 

Fig- 7.36 Pourbaix diagram for the system copper-water. Source Ref 7... 

Sketch these onto the stability field of water on the Pourbaix diagram of Figure 9.29 [sketch not shown at the end of this book.]. What copper species will be present in each of these ... 

This means that reducing environments are compatible with relatively noble metals or alloys (copper, lead, niekel and alloys based upon these metals). When metallie materials are to be used in oxidizing environment, on the other hand, their corrosion resistance must be based upon passivity (e.g. titanium and alloys that contain sufiRcient amounts of chromium). These relationships are easy to understand when the Pourbaix diagrams for metals such as Cu and Ti (Figure 10.1) are considered, and it is kept in mind that reducing environments lower the corrosion potential and oxidizing environments lift it. Irrespective of the mentioned rule, a metal is usually most corrosion resistant when it contains the smallest possible amounts of impurities. Some natural combinations of environment and material are listed in Table 10.1. 

Figure 10.1 Pourbaix diagrams of copper (a) and titanium (b) in water. Table 10.1 Some natural combinations of environment and material [10.1].

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