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Corrosion- Mixed Potential Theory
We analyzed this
We about these?
Refe
renc
e El
ectr
ode
Voltmeter
0.1M H2SO4Only acid, no dissolved cations
Corrosion- Mixed Potential Theory
We analyzed this
We about these?
Refe
renc
e El
ectr
ode
Voltmeter ?
Only acid, no dissolved cations0.1M H2SO4
Corrosion- Mixed Potential Theory
We about these?
Refe
renc
e El
ectr
ode
Voltmeter
We analyzed this
Zn
0.1M H2SO4Only acid, no dissolved cations
Corrosion- Mixed Potential Theory
This material is taken from Introduction to Corrosion Science, McCafferty
90° CCW Outof
Planeflip Butler-Volmer Equation
Corrosion- Mixed Potential Theory
Refe
renc
e El
ectr
ode
Voltmeter
Zn
0.1M H2SO4Only acid, no dissolved cations
Zn corrodes in the acid according to
Zn→ Zn+2 + 2e−
What’s reduced; what is the cathodic reaction?
2H + + 2e− → H2( g )
Corrosion- Mixed Potential Theory
Refe
renc
e El
ectr
ode
Voltmeter
Cu
0.1M H2SO4Only acid, no dissolved cations
Cu corrodes in the acid according to
What’s reduced; what is the cathodic reaction?
Cu→Cu+2 + 2e−
�
O2 + 4H + + 4e− → 2H2O
Why is H the cathodic Rx for Zn and O the Rx for Cu?
Corrosion- Mixed Potential Theory
2H+ + 2e
− →H 2 ( g
)
2H ++ 2e −
←H2( g )
io on Zn
EoEZn/Zn2+o
ioZn/Zn2+
Butler-Volmer Equation for both Zn and H
Corrosion- Mixed Potential Theory
Butler-Volmer Equation
ηi0
Analogy with
f = FRT
icorr is not easily measured!
2H+ + 2e
− →H 2 ( g
)
Corrosion- Mixed Potential Theory
Corrosion- Mixed Potential Theory
Evan’s diagram for Fe in non-complexing acid
Corrosion- Mixed Potential Theory
Corrosion- Mixed Potential Theory
The work function of a metal is thework required to remove and electronFrom the metal to vacuum level.
Corrosion- Mixed Potential Theory
Corrosion- Mixed Potential TheoryCathodic protection of Fe by Zinc
Lowering of by almost an order ofmagnitude.
Corrosion- Mixed Potential Theory
1.2 0.80 0.40 0.00 -0.400ESHE
Corrosion of Cu in acid
Corrosion- Mixed Potential Theory
The y-axis is done in terms of theCURRENT rather than the current density