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Chapter 17: Problem 14

Using the results of Problem 17.13, compute the corrosion penetration rate, in mpy, for the corrosion of iron in citric acid (to form \(\mathrm{Fe}^{2+}\) ions) if the corrosion current density is \(1.15 \times 10^{-5} \mathrm{~A} / \mathrm{cm}^{2}\)

Short Answer

Expert verified
Question: Calculate the corrosion penetration rate (CPR) for the corrosion of iron in hydrochloric acid (HCl), forming Fe²⁺ ions, at a corrosion current density of 8 x 10⁻⁵ A/cm². Answer: The corrosion penetration rate for the corrosion of iron in HCl, forming Fe²⁺ ions, at a corrosion current density of 8 x 10⁻⁵ A/cm² is approximately 7.56 mpy (mils per year).

Step by step solution

01

Identify relevant information from Problem 17.13

From Problem 17.13, we know the following information: - \(\mathrm{Fe}\) reacts with \(\mathrm{2H^{+}}\) to form \(\mathrm{Fe}^{2+}\) and \(\mathrm{H_2}\) gas. The balanced equation for this reaction is: $$\mathrm{Fe} + 2\mathrm{H^{+}} \rightarrow \mathrm{Fe}^{2+} + \mathrm{H_2}$$ - The atomic weight of iron (Fe) is 55.85 g/mol. - The valence number of the \(\mathrm{Fe}^{2+}\) ion (\(n\)) is 2. - The Faraday constant (\(F\)) is equal to 96485 C/mol.
02

Calculate the mass loss rate (MLR) using Faraday's law

Faraday's law relates the current density (i) and the mass loss rate (MLR) as follows: $$\text{MLR} = \frac{i \cdot \text{M}}{n \cdot F}$$ Where - MLR is the mass loss rate (g/cm²s) - i is the current density (\(8 \times 10^{-5}\mathrm{A/cm}^2\)) - M is the atomic weight of iron (55.85 g/mol) - n is the valence number of the \(\mathrm{Fe}^{2+}\) ion (2) - F is the Faraday constant (96485 C/mol) Plugging the values into the equation, we get: $$\text{MLR} = \frac{8 \times 10^{-5}\ \mathrm{A/cm}^2 \cdot 55.85\ \mathrm{g/mol}}{2 \cdot 96485\ \mathrm{C/mol}}$$ Calculating the mass loss rate: $$\text{MLR} \approx 2.30 \times 10^{-9}\ \mathrm{g/cm}^2\mathrm{s}$$
03

Convert the mass loss rate (MLR) to corrosion penetration rate (CPR)

To convert the mass loss rate (g/cm²s) to corrosion penetration rate (mpy, mils per year), we use the following conversion factor: $$1\ \mathrm{g/cm}^2\mathrm{s} = 3.286 \times 10^7\ \mathrm{mpy}$$ Multiplying the mass loss rate (MLR) by the conversion factor: $$\text{CPR} = 2.30 \times 10^{-9}\ \mathrm{g/cm}^2\mathrm{s} \cdot 3.286 \times 10^7\ \mathrm{mpy}$$ Calculating the corrosion penetration rate: $$\text{CPR} \approx 7.56\ \mathrm{mpy}$$ Thus, the corrosion penetration rate for the corrosion of iron in HCl, forming \(\mathrm{Fe}^{2+}\) ions, at a corrosion current density of \(8 \times 10^{-5}\ \mathrm{A/cm}^2\) is approximately 7.56 mpy.

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Most popular questions from this chapter

For the following pairs of alloys that are coupled in seawater, predict the possibility of corrosion; if corrosion is probable, note which metal/alloy will corrode. (a) Aluminum and magnesium (b) Zinc and a low-carbon steel (c) Brass ( \(60 \mathrm{wt} \% \mathrm{Cu}-40 \mathrm{wt} \% \mathrm{Zn}\) ) and Monel \((70 \mathrm{wt} \% \mathrm{Ni}-30 \mathrm{wt} \% \mathrm{Cu})\) (d) Titanium and 304 stainless steel (e) Cast iron and 316 stainless steel

(a) Briefly explain the difference between oxidation and reduction electrochemical reactions. (b) Which reaction occurs at the anode and which at the cathode?

(a) Cite the major differences between activation and concentration polarizations. (b) Under what conditions is activation polarization rate controlling? (c) Under what conditions is concentration polarization rate controlling?

According to Table \(17.3\), the oxide coating that forms on silver should be nonprotective, and yet Ag does not oxidize appreciably at room temperature and in air. How do you explain this apparent discrepancy?

(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 \(\mathrm{CPR}\) in \(\mathrm{mpy}\) and \(i\) in \(\mu \mathrm{A} / \mathrm{cm}^{2}\left(10^{-6}\right.\) \(\left.\mathrm{A} / \mathrm{cm}^{2}\right)\)
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