Polarisation resistance behaviour of corrosion inhibition of low carbon steel in H_{3PO_{4 acid

The non-linear region of polarisation curve near the corrosion potential can be discussed depending on data of over potential as a function of current densities. These data can be analysed by suggesting a mathematical model taking into account the effect of mass transfer on activation process. This model was used to evaluate the values of polarisation resistance Rp in presence and absence of potassium iodide (KI) as a corrosion inhibitor of low carbon steel in 2.5 M phosphoric acid at different temperatures. The values of polarisation resistance obtained by mathematical model compared with these obtained by Tafel parameters. The suggested ß-model was very useful in evaluating the values of Rp. The maximum value of polarisation resistance was 5049.13 Ωcm² at 30°C in presence of 0.05 M KI, while the minimum value was 1.885 Ωcm² at 60°C in absence of KI. These results indicate that the polarisation resistance values increased with the increase of KI concentration, and decreased with the increase of temperature.