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How to calculate corrosion rate?

  1. Oct 9, 2011 #1
    1. The problem statement, all variables and given/known data

    Iron sample with dimensions 10mm x 20mm x 2mm is exposed to a corrosive environment (neglect thickness for surface area). Both sides of the sample are exposed to corrosive environment. Given Tafel Plot

    (a) Calculate corrosion rate mm/y
    (b) Calculate corrosion rate if one of the sample surfaces is painted (not in contact with corrosive environment)

    2. Relevant equations

    M=56g,
    t=3.1536e7 sec/yr
    number of electrons taking part n=2
    F=96500C
    density=7.87g/cm3
    A=10*20=200mm2

    From Faraday's Law: W=MtI/nF (W=weight loss, I=current in this case corrosion current)

    3. The attempt at a solution

    (a) From Tafel Plot log(Icorr)=0.05mA/cm2 so Icorr=1.12e-3 A/cm2
    I want to convert Icorr to just units of A, but since both surfaces are exposed should I multiply it by double the surface area?

    i.e.: Icorr=1.12e-3*200mm2*2*(1cm/10mm)^2 = 4.48e-3 A

    substituting in W=Mt*Icorr/nF = 40.99 g/yr

    Corrosion Rate CR=W/density*Surface Area

    Again I multiplied the Surface Area by 2 because both sides of the Iron sample is exposed

    CR=(40.99g/yr)/[(7.87g/cm3)*(200mm2*2)*(1cm/10mm)^3)]=13.02mm/yr

    (b) For only one side exposed:
    I'm going to use half of Icorr since only 1 side is exposed so Icorr=2.24e-3 A

    then W=20.49g/yr

    Using only 200mm2 as the surface area

    CR=(20.49g/yr)/[(7.87g/cm3)*(200mm2)*(1cm/10mm)^3)]=13.02mm/yr

    I get the same corrosion rate...is this correct?!
     
  2. jcsd
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