3. Faraday's Laws and Rate of Corrosion

3.2 Example: Calculation of Weight Loss

Steel corrodes in an aqueous solution, the corrosion current is measured as 0.1 mA/cm2. Calculate the rate of weight loss per unit area in unit of mdd.

Solution:

For Fe Fe2+ + 2e, we have
    where
    M = 55.8 g/mol
    i = 0.1 mA/cm2
    n = 2

Substituting these values in the above equation, we get

                     

w/At = 2.897 x 10-8 g/cm2s

Now converting the units g/cm2s to mg/cm2s  (x 103), we get

       = 2.897 x 10-8 g/cm2s x 103 mg/g = 2.897 x 10-5 mg/cm2s

Now converting the units mg/cm2s to mg/dm2s  (x 102), we get

       = 2.897 x 10-5 mg/cm2s x 103 cm2/dm2 = 2.897 x 10-3 mg/dm2s

Now converting the units mg/cm2s to mg/dm2.day  , we get

w/At = 2.897 x 10-3 mg/dm2s x 24 x 3600 = 250.3 mg/dm2.day or mdd