Concept explainers
Current density and average current associated with the formation of single pit.
Answer to Problem 57AAP
The average current associated with the formation of single pit is
Explanation of Solution
Write the expression for the mass of the pit.
Here, density of aluminum is
Write the expression for corrosion rate.
Rearrange the equation in terms of I.
Here, the corrosion rate is
The current density is expressed as,
Conclusion:
It is assumed that the pit is in the shape of cylinder.
The density of the aluminum is
The mass of the cylindrical aluminum pit
Substitute
The top surface area of the cylindrical pit is expressed as follows.
Refer Table 13.1, “Standard electrode potentials at 25 °C”.
The anodic reaction of aluminum is as follows:
Here, the number of electrons produced is,
Refer Figure 2.3, “Periodic Table of Elements”.
The atomic mass of aluminum is,
Substitute
Thus, the average current associated with the formation of single pit is
Substitute
Thus, required current density is
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Chapter 13 Solutions
Foundations of Materials Science and Engineering
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