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How to calculate corrosion rate? 
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#1
Oct911, 01:41 AM

P: 92

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=1.12e3 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=1.12e3*200mm2*2*(1cm/10mm)^2 = 4.48e3 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=2.24e3 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?! 


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