ABSTRACT

Numerous failures and eventual losses in the chemical industry have been traced to corrosion processes. Failures resulting from the inability of metals to support designed load requirements because of losses imposed by corrosion effects can be combated economically through the use of chemical inhibitors. Despite the fact that synthetic inhibitors are effective, nonetheless they are associated with problems of toxicity, disposal, litigation and enormous costs. In order to protect the environment and reduce cost, the use of green inhibitors as substitutes and partial replacement of chemical inhibitors have become a method of choice. However, inhibitors are environment specific, therefore necessitating the need for deeper research into the metal-inhibitor-media combination that would produce the best results. In this study, stand-alone and synergistic inhibitor combinations were employed. In the synergistic combination a fractional substitution model was introduced to tailor the inhibitor to a desired performance. Mild steel and Aluminium samples sourced from the chemical industries were immersed in 0.5 M HCl and 0.5 M H2SO4 solution in the absence and presence of varying inhibitor concentrations of potassium chromate (PC) (K2CrO4), aniline (AN) C6H5NH2, Cassia fistula (CF), Terminalia catappa (TC) and Synergistic Admixtures (SA). Weight Loss (WL) and Tafel Polarization (TP) techniques were adopted. WL data were recorded every 4 days for 60 days, while TP data were obtained instantaneously from the potentiostat after 90 minutes immersion period. Adsorption, Scanning Electron Microscopy (SEM) analysis and Artificial Neural Network (ANN) modelling of the ML data were also conducted. Precisely 1910 WL experiments were performed, out of which the best Inhibitor Efficiency (IE%) was by SA of 2PC+6CF (81.29) for steel in H2SO4 and 4PC+4CF (81.27) for Al in HCl media, while the stand-alone systems of CF (54.5) and TC (78.36) at 10 and 4 g/L concentration performed best for steel immersed in HCl and Al immersed in H2SO4 respectively. TP results showed the SA of 4PC+4AN, 2PC+6AN, 2PC+6TC and 6PC+2AN as having high IE% of 99.99 for steel in HCl, steel in H2SO4, Al in HCl and Al in H2SO4 respectively. Langmuir, Freundlich and Frumkin isotherms best described the 16 stand alone systems used based on R-value. Fourteen of the systems were best described by Langmuir while the remaining two were best explained by Freundlich and Frumkin isotherms respectively. SEM analysis indicated that the introduction of the inhibitors stifled the corrosion reactions for mild steel and aluminium in both acid media, as the micrograph displayed an almost smooth surface, while the frequency of pit occurrence was lowered when compared to the uninhibited samples. ANN model results showed that the trend depicted in the experimental data were captured almost perfectly by the neural network fitting tool. Thus, the control of corrosion induced wastage of infrastructure through novel inhibitor systems and the development of a modelling tool that could be used to mimic the exact corrosion process rather than costly experimentation are major contributions of the work. Fuzzy deduction