Question

Estimate the MRR (in cc/sec) of an alloy containing 18% cobalt. 62% nickel and 20% chromium during ECM with current of 500 ampere. The density of the alloy is 8.28 g/cc. The following date is available.

Metal	Gram atomic weight	Velency
Cobalt	58.93	2
Nickel	58.71	2
Chromium	51.99	6

Assume Faraday's constant is 96500 coulombs/mole.

• A. 0.0124

Answer 1

The correct option is A 0.0124

$MRR=\frac{AI}{\rho ZF}$
where, A = Atomic weight; I = current
$\rho =\text{Density};Z=\text{Valency}$
F = Faraday's constant

${\left(\frac{Z}{A}\right)}_{\text{equivalent}}=\frac{Z_1{x}_1}{A_1}+\frac{Z_2{x}_2}{A_2}+\frac{Z_3{x}_3}{A_3}$

$=\frac{2\times 0.18}{58.93}+\frac{2\times 0.62}{58.71}+\frac{6\times 0.2}{51.99}$

$=5.03\times {10}^{-2}$

$MRR=\frac{500}{8.28\times 5.03\times {10}^{-2}\times 96500}$

$=1.24\times {10}^{-2}cc/s$