Project ForgeElectrochemical machining operations are performed with tungsten as the tool, and copper and aluminum as two different workpiece materials. Copper: atomic mass 63 amu, valency 2, density 9 g/cm³. Aluminum: atomic mass 27 amu, valency 3, density 2.7 g/cm³. 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).
Explanation
By Faraday's law, mass MRR = (I×A)/(z×F), depending only on the chemical equivalent A/z (density is a distractor — irrelevant to MASS removal rate). Since current I is identical: MRR_Al/MRR_Cu = (A/z)_Al/(A/z)_Cu = (27/3)/(63/2) = 9/31.5 = 0.2857. MRR_Al = 100×0.2857 ≈ 28.57 mg/s.
Source: GATE ME 2022 Session 1 (ME-1) (2022)
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