Electrochemical parameters active-passive alloys

Table E4.1 Electrochemical Parameters for Active-Passive Alloys A and B...

E4.3. Construct an anodic polarization curve and calculate the critical passivation current density of an active-passive alloy using mixed potential theory with the following electrochemical parameters Econ = 0-b5V vs. SCE /corr= 10 " A/cm fca = 0.1, Epp= —0.3 V vs. SCE and /pass = 10 A/cm, Etr = + 0.9 V. 

E4.6. Hypothetical active-passive alloys A and B have the electrochemical parameters given in Table E4.4 ... 

Mixed potential theory is used to estimate the galvanic current and the galvanic potential in an active-passive metal that passivates at potentials less noble than the reversible hydrogen potential. A galvanic couple between titanium and platinum of equal area of 1 cm is exposed to 1 M HCl. The electrochemical parameters for the active-passive alloy are eeq xi = —163 V vs. SHE anodic Tafel, b Ti = 0.1 exchange current density, ixi= 10 A/cm passivation potential, pp= —0.73 V passivation current, 7pass= 10 A/cm transpassive potential, = 0.4 V vs. SHE and activity of dissolved species [Ti ] = 1 M. The exchange current densities, i°, on platinum and titanium... 

E4.7. Active-passive alloys A, B, and C have the following electrochemical parameters given in Table E4.5 ... 

The concepts in Chapters 2 and 3 are used in Chapter 4 to discuss the corrosion of so-called active metals. Chapter 5 continues with application to active/passive type alloys. Initial emphasis in Chapter 4 is placed on how the coupling of cathodic and anodic reactions establishes a mixed electrode or surface of corrosion cells. Emphasis is placed on how the corrosion rate is established by the kinetic parameters associated with both the anodic and cathodic reactions and by the physical variables such as anode/cathode area ratios, surface films, and fluid velocity. Polarization curves are used extensively to show how these variables determine the corrosion current density and corrosion potential and, conversely, to show how electrochemical measurements can provide information on the nature of a given corroding system. Polarization curves are also used to illustrate how corrosion rates are influenced by inhibitors, galvanic coupling, and external currents. 

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