Can we articulate general correlations between the corrosion rates of iron and the pH in deoxygenated solutions of different chemical compositions?
pH would be more acidic with more H+ ions being available for dissolved salts...Corrosion rates would be higher due to the most common ion (Cl-) being more aggressive towards iron, having a higher electro-negativity, and being destructive of any passive film formation. Have you tried an EIS study?
Thank you Antonio for your response. I am currently performing EIS investigations.
Yes; we can articulate a general correlation between pH and corrosion rate by performing most simple FCT(Ferric Chloride Test) as follows:
Place similar sized, equally weighed and dry 10 pieces of duplex stainless steel immersed in similar sized 10 glass vessels containing same(definite) volume of deoxygenated solution of FeCl3 having 0.01M---0.1 M concentration with known pH values (calculated by pH meter available in all labs.) in an evacuated box for 24hrs at a constant temperature . Dry them all and weigh them all again.Calculate the corrosion rates for all of them as follows:
Corrosion Rate (mm/y) = 87.6 x (W / DAT); where:
W = wt. loss in mg; D = metal density in g /cm3;
A = area of sample in cm2;
T = time of immersion of the steel sample in hours.
Now plot a graph by taking corrosion rate along X-axis and pH along Y-axis to obtain a STANDARD CURVE.
Now perform another experiment with the given iron sample while keeping it immersed in the unknown sample solution of the deoxygenated brine solution under the same conditions and again calculate the corrosition rate. Note this corrosion rate on the X-axis and draw a perpendicular so that it touches the standard curve at apoint. Draw a parallel line from that point so that it touches Y-axis Note the pH on the Y-axis.
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