The corrosion rate is to be determined for some divalent metal M in a solution c

Question

The corrosion rate is to be determined for some divalent metal M in a solution containing hydrogen ions. The following corrosion data are known about the metal and solution: For Metal MFor Hydrogen 0.59 V(H+/HZ +0.15 0.17 (a) Assuming that activation polarization controls both oxidation and reduction reactions, determine the rate of corrosion of metal M (in mol/cm2-s) (b) Compute the corrosion potential for this reaction Part 1 The first stepis to establish the potentials of both oxidation and reduction reactions. Next set these expressions equal to one another, and then sove for the value of , which IS really the corrosior current density, What is corrosion current density, ic in A/cm2 the tolerance is +/-2%

Explanation / Answer

Ans)

a)The two potential expressions are as follows

For hydrogen reduction

VH=V (H+/H2) +?Hlog(i/ioH)

And for M oxidation

VM=V (M/M2+)+?Mlog(i/ioM)

Setting VH= VM and solving for logi (logic) leads to

log ic=1/(?M-?H )[ V (H+/H2) –V (M/M2+)-?H log(ioH) + ?Mlog(ioM) ]

logic=1/(0.15-(-0.17))[0-(-0.49)-(-0.17)log(3x10-9)+(0.15)log(1x10-10)]

=3.125x(0.49-1.4488-1.5)

=3.125x(-2.4588)

logic=-7.68375

ic=10(-7.68375)

ic=2.071x10-8 A/cm2

b)corrosion potential

Vc=V(H+/H2)+?Hlog(ic/ioH)

=0+(-0.17)log[(2.071x10-8 )/(3x10-9)]

Vc=-0.14 V

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