## How to Calculate and Solve for Concentration Polarization | Corrosion

The image of concentration polarization is shown below.

To compute for concentration polarization, six essential parameters are needed and these parameters are Gas Constant (R), Temperature (T), Number of Electrons (n), Faraday’s Constant (F), Current Density (i) and Limiting Diffusion Current Density (iL).

The formula for calculating concentration polarization:

ηc = 2.3RT/nF log(1 – i/iL)

Where:

ηc = Concentration Polarization
R = Gas Constant
T = Temperature
n = Number of Electrons
i = Current Density
iL = Limiting Diffusion Current Density

Let’s solve an example;
Find the concentration Polarization when the gas constant is 14, the temperature is 7, the number of electrons is 8, the faraday’s constant is 4, the current density is 1 and the limiting diffusion current density is 2.

This implies that;

R = Gas Constant = 14
T = Temperature = 7
n = Number of Electrons = 8
F = Faraday’s Constant = 4
i = Current Density = 1
iL = Limiting Diffusion Current Density = 2

ηc = 2.3RT/nF log(1 – i/iL)
ηc = 2.3(14)(7)/(8)(4) log(1 – (1/2))
ηc = 225.39/32 log(1 – 0.5)
ηc = 7.043749 log(0.5)
ηc = 7.043749 (-0.301029)
ηc = -2.120

Therefore, the concentration polarization is -2.120.

## How to Calculate and Solve for Exchange Current Density | Corrosion

The exchange current density is illustrated by the image below.

To compute for exchange current density, three essential parameters are needed and these parameters are Current Density (io), Number of Electrons (n) and Faraday’s Constant (F).

The formula for calculating exchange current density:

γredoxid) = io/nF

Where:

γredoxid) = Exhange Current Density
io = Current Density
n = Number of Electrons

Given an example;
Find the exchange current density when the current density is 8, the number of electrons is 4 and the faraday’s constant is 2.

This implies that;

io = Current Density = 8
n = Number of Electrons = 4
F = Faraday’s Constant = 2

γredoxid) = io/nF
γredoxid) = 8/(4)(2)
γredoxid) = 8/(8)
γredoxid) = 1

Therefore, the exchange current density is 1.

## How to Calculate and Solve for Corrosion Rate | Corrosion

The corrosion rate is illustrated by the image below.

To compute for corrosion rate, three essential parameters are needed and these parameters are Current per Unit Time (i), Number of Electrons (n) and Faraday’s Constant (F).

The formula for calculating corrosion rate:

r = i/nF

Where:

r = Corrosion Rate
i = Current per Unit Time (Current Density)
n = Number of Electrons

Given an example;
Find the corrosion rate when the current per unit time is 15, the number of electrons is 5 and the faraday’s constant is 3.

This implies that;

i = Current per Unit Time (Current Density) = 15
n = Number of Electrons = 5
F = Faraday’s Constant = 3

r = i/nF
r = 15/(5)(3)
r = 15/15
r = 1

Therefore, the corrosion rate is 1.

Calculating the Current per Unit Time when the Corrosion Rate, the Number of Electrons and the Faraday’s Constant is Given.

i = r (nF)

Where:

i = Current per Unit Time (Current Density)
r = Corrosion Rate
n = Number of Electrons

Let’s solve an example;
Find the current per unit time when the corrosion rate is 10, the number of electrons is 8 and the faraday’s constant is 3.

This implies that;

r = Corrosion Rate = 10
n = Number of Electrons = 8
F = Faraday’s Constant = 3

i = r (nF)
i = 10 (8)(3)
i = 10 (24)
i = 240

Therefore, the current per unit time is 240.

## How to Calculate and Solve for Nernst Equation | Corrosion

The nernst equation is illustrated by the image below.

To compute for nernst equation, seven essential parameters are needed and these parameters are Electrochemical Cell Potential (ΔV°), Gas Constant (R), Temperature (T), Number of Electrons (n), Faraday’s Constant (F), Molar Concentration [M1n+] and Molar Concentration [M2n+].

The formula for caluclating nernst equation:

ΔV = ΔV° – RT/nF In(M1n+/M2n+)

Where:

ΔV = Nernst Equation | Potential
ΔV° = Electrochemical Cell Potential
R = Gas Constant
T = Temperature
n = Number of Electrons
M1n+ = Molar Concentration
M2n+ = Molar Concentration

Let’s solve an example;
Find the nernst equation when the electrochemical cell potential is 8, the gas constant is 2, the temperature is 5, the number of electrons is 3, the faraday’s constant is 9, the molar concentration is 10 and the molar concentration is 4.

This implies that;

ΔV° = Electrochemical Cell Potential = 8
R = Gas Constant = 2
T = Temperature = 5
n = Number of Electrons = 3
F = Faraday’s Constant = 9
M1n+ = Molar Concentration = 10
M2n+ = Molar Concentration = 4

ΔV = ΔV° – RT/nF In(M1n+/M2n+)
ΔV = 8 – ((2)(5)/(3)(9)) In(10/4)
ΔV = 8 – (10/27) In (2.5)
ΔV = 8 – 0.37 (0.91)
ΔV = 8 – (0.339)
ΔV = 7.66

Therefore, the nernest equation is 7.66 V.