GATE 2022 ME (ME1) – Question 33
Electrochemical machining operations are performed with tungsten as the tool, and copper and aluminum as two different workpiece materials. Properties of copper and aluminum are given in the table below.
| Material | Atomic mass (amu) | Valency | Density (g/cm$^3$) |
|---|---|---|---|
| Copper | 63 | 2 | 9 |
| Aluminum | 27 | 3 | 2.7 |
Ignore overpotentials, and assume that current efficiency is 100% for both the workpiece materials. Under identical conditions, if the material removal rate (MRR) of copper is 100 mg/s, the MRR of aluminum will be ________________ mg/s (round-off to two decimal places).
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Correct answer: 28.43 to 28.71
Explanation
By Faraday's law the mass removal rate for the same current is proportional to the equivalent weight $\frac{A}{z}$. For copper it is $\frac{63}{2} = 31.5$ and for aluminium $\frac{27}{3} = 9$. So the MRR of aluminium is $100 \times \frac{9}{31.5} = 28.57$ mg/s (the densities are not needed for a mass rate).