An investigation on the inhibitory effect of Allopurinol on mild steel st 37corrosion in hydrochloric acid solution

Steel corrosion is a costly problem and is one of the most important issues in materials science.The corrosion of mild steel is the most common form of corrosion, especially in acid solution.Inhibitors are commonly used to reduce the corrosion attack on metallic materials. Most of thecommercial inhibitors are toxic in nature and therefore it is necessary to replace them byenvironmentally benign inhibitors. The use of pharmaceutical compounds offers interestingpossibilities for corrosion inhibition due to the presence of hetero atoms like nitrogen, sulphurand oxygen in their structure, and they are of particular interest because of their safe use, highsolubility in water and high molecular size [1].In the present work, the inhibition effect of allopurinol drug on the mild steel in 1 M hydrochloricacid solution is studied using the potentiodynamic polarization, the electrochemical impedancespectroscopy (EIS), the infrared spectroscopy (FT-IR) and the scanning electron microscopy(SEM) methods [2]. The experiments have been performed for various inhibitor concentrationsusing these methods and the optimum concentration of the inhibitor has been determined.Furthermore, the influence of the temperature on the corrosion inhibition of the allopurinol at theoptimum concentration has been investigated. Results show that the addition of the allopurinol tothe hydrochloric acid solution reduces the corrosion of the mild steel. It has also been shown thatthe corrosion inhibition efficiency increases by increasing the concentration of allopurinol to acertain value and increasing temperature. Potentiodynamic polarization measurements show thatallopurinol acts as mixed-type inhibitor. Electrochemical impedance measurements show thatincreasing the inhibitor concentration to a certain value increases the charge transfer resistanceand decreases the capacity of the double layer ( Cdl ). The results obtained using thepotentiodynamic polarization and electrochemical impedance techniques are in good agreement. Furthermore, the adsorption of the allopurinol inhibitor on the alloy surface obeys the Langmuiradsorption isotherm model. The absorption process is a combination of the physical and thechemical adsorption and it is spontaneous. In the hydrochloric acid solution, the adsorptionprocess is endothermic with an increase in the entropy. The results obtained from infrared spectraconfirmed the formation of a protective layer on the alloy surface after immersion in hydrochloricacid solution containing allopurinol. SEM investigations also validate the adsorption of inhibitor.

Keywords:

Natural corrosion inhibitor , Allopurinol , Potentiodynamic polarization , Electrochemical impedance spectroscopy , Adsorption isotherms , Mild steel