EFFECT OF COCONUT SHELL ON THE ELECTROCHEMICAL BEHAVIOR OF AUSTENITIC STAINLESS STEEL AISI 316 IN ACID SOLUTION: CHEMICAL, ELECTROCHEMICAL AND SURFACE CHARACTERIZATION STUDIES

In recent times, efforts have been made widely to replace toxic inhibitors with eco-friendly materials. Agricultural waste with their inimitable features has been identified as a high potential material in achieving high demanding goals. In this study, the electrochemical performance of AISI 316 austenitic stainless steel was studied in 0.5 M H SO 2 4 medium at various inhibitorconcentrations in the absence and presence of coconut shell (CS). Gravimetric and electrochemical procedures were used in investigating the electrochemical behavior of stainless steel. Adsorption of the CS at the steel surface was further supported by scanning electron spectroscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results obtained showed that the inhibitor retards both active and pitting attack to an extent depending on the time of exposure and inhibitor concentration. Potentiodynamic results show that CS slows down the rate of cathodic and anodic corrosion reactions by forming a protective layer on the surface of the stainless steel and its adsorption fits the Langmuir adsorption isotherm model. It was also concluded that the CS performed as mixed type inhibitor by decreasing cathodic and anodic corrosion densities. This was concluded by comparison of the changes in the value of the cathodic and anodic Tafel slope. The inhibition efficiency of 88.45% was achieved using this inhibitor in 0.5M H SO solution. An increase in the CS concentration leads to a decrease in the corrosion rate values. This 2 4 signifies an excellentadsorb-ability of coconut shell on the stainless steel surface. Reasonable consistency was found between the methods used.