prbset08_key4324 -...

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EMA 4324 Problem Set 8 KEY 4-1. [a] Plot schematically the polarization curve [Evan’s diagram] for the anodic dissolution for the metal M which has the following parameters/features: E corr = -0.500 volt v. SCE [saturated calomel electrode, E SCE = 0.242 volt SHE] , j corr = 10 -4 A/cm 2 , E pp = -0.400 volt [SCE], b a = 0.05 volt, j pass = 10 -5 A/cm 2 , E tr = 1.000 volt SCE. [b] From the plot in [a], determine the critical current density for passivation, j crit . ************************************************** appears to be about 10 -2 A/cm 2 *************************************************** -1.0 -0.5 0.0 0.5 1.0 1.5 potential, volts SCE -10 -8 -6 -4 -2 0 log current density, log[A/cm^2] ~10^-2 A/cm^2
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4-2. [a] Assuming that the measured exchange current density for dissolution of M [j o (M + /M)] is 10 -9 A/cm 2 , determine the reversible [Nernst] potential for this dissolution [E(M + /M)] in this solution. ************************************************** anodic Tafel plot intersects log [j o ] at about -0.75v SCE which is equivalent to -0.51 volts SHE.
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Unformatted text preview: **************************************************** [b] Calculate the activity [concentration] of M + in this solution, assuming that the anodic dissolution reaction is M = M + + e-[E o (M + /M) = - 0.250 volt SHE]. ************************************************* from E nernst = -0.51 = -0.250 + 0.0592log [M + ], [M + ] = 4.06x10-5 mol/liter-1.0-0.5 0.0 0.5 1.0 1.5 potential, volts SCE-10-8-6-4-2 log current density, log[A/cm^2] E eq [M^+/M] = ~-0.75v SCE 4-3. Assuming unit activity of H + ions in the corrosive electrolyte, determine the exchange current density for the reduction of H + on the surface of metal M in problem 4-1. Estimate a value of b C from Table 3.2 for use in your determination [?]. *****************************************************-1.0-0.5 0.0 0.5 1.0 1.5 potential, volts SCE-10-8-6-4-2 log current density, log[A/cm^2] j o [H^+/H2]=10^-4.85 = 1.41x10^-5 A/cm^2 b = ~ 0.3 0.000 V SHE = -0.242 V SCE...
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prbset08_key4324 -...

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