Chapter 17: Problem 26
(a) What are inhibitors? (b) What possible mechanisms account for their effectiveness?
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Chapter 17: Problem 26
(a) What are inhibitors? (b) What possible mechanisms account for their effectiveness?
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Briefly explain why, for a small anode-to-cathode area ratio, the corrosion rate will be higher than for a large ratio.
A piece of corroded metal alloy plate was found in a submerged ocean vessel. It was estimated that the original area of the plate was \(800 \mathrm{~cm}^{2}\) and that approximately \(7.6 \mathrm{~kg}\) had corroded away during the submersion. Assuming a corrosion penetration rate of \(4 \mathrm{~mm} / \mathrm{yr}\) for this alloy in seawater, estimate the time of submersion in years. The density of the alloy is \(4.5 \mathrm{~g} / \mathrm{cm}^{3}\).
An electrochemical cell is composed of pure copper and pure cadmium electrodes immersed in solutions of their respective divalent ions. For a \(6.5 \times 10^{-2} M\) concentration of \(\mathrm{Cd}^{2+}\), the cadmium electrode is oxidized, yielding a cell potential of \(0.775 \mathrm{~V}\). Calculate the concentration of \(\mathrm{Cu}^{2+}\) ions if the temperature is \(25^{\circ} \mathrm{C}\).
(a) Demonstrate that the CPR is related to the corrosion current density \(i\left(\mathrm{~A} / \mathrm{cm}^{2}\right)\) through the expression $$ \mathrm{CPR}=\frac{K A i}{n \rho} $$ where \(K\) is a constant, \(A\) is the atomic weight of the metal experiencing corrosion, \(n\) is the number of electrons associated with the ionization of each metal atom, and \(\rho\) is the density of the metal. (b) Calculate the value of the constant \(K\) for the CPR in mpy and \(i\) in \(\mu \mathrm{A} / \mathrm{cm}^{2}\left(10^{-6} \mathrm{~A} / \mathrm{cm}^{2}\right)\).
Briefly describe the two techniques that are used for galvanic protection.
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