CORROSION INHIBITION OF MILD STEEL IN ACIDIC MEDIUM BY CHINESE BURR (Triunfetta rhomboidea J.) SIAM WEED (Chromolaena odorata L.) EXTRACTS AND THEIR TITANIUM NANOCOMPOSITES.

Abstract

The use of corrosion inhibitors is one of the effective methods employed in mitigating corrosion of mild steel in process, oil and gas industries. However, the toxicity of the majority of the inhibitors commonly used poses a threat to the environment and life and this have led to the search for less toxic and eco-friendly corrosion inhibitors. Hence, titanium nanocomposites from the extracts of Triumfetta rhomboidea and Chromolaena odorata leaves were synthesised, characterised and the inhibitory effect on the corrosion of mild steel in 1 M HCl was explored as possible alternative green corrosion inhibitors using weight loss and electrochemical methods. FTIR analysis revealed that the nanocomposites contain organic functional groups identical to those of the extracts they were synthesised from while XRD identified the crystallinity of the nanocomposites correspond to anatase phase of TiO2 with average crystallite size of 25.95 nm, 11.74 nm and 10.22 nm for TiO2, Ti-TR and Ti-CO respectively. SEM and HRTEM microscopy revealed the aggregate natures of the nanocomposites while BET and BJH isotherms from nitrogen-adsorption analysis identified the nanocomposites to be mesopores with large surface areas (162.52 m2/g for Ti-TR and 172.82 m2/g for Ti-CO) greater than for TiO2 (74.53 m2/g). Experimental results from weight loss corrosion study revealed that the synthesised titanium-plant extract nanocomposites have higher inhibition efficiencies (84.26% for Ti-TR and 91.39% for Ti- CO) than the corresponding crude extracts (79.19% for TR and 84.77% for CO) at 1.0 g/L concentration of each sample. The efficiency of the inhibitors increases with increasing concentration but decreases with temperature increase. Thermodynamics parameters suggest that the dissolution of the mild steel proceeds is orderly and endothermic. The addition of the inhibitors to the corrosive medium increased the shelf-life of the mild steel substrate with a first-order kinetics. The corrosion inhibition mechanisms of the nanocomposites and corresponding crude extracts were observed to follow physisorption process on the surface of the metal in conformity with Langmuir isotherm. Negative Δ􀀂􀀃􀀆􀀄􀀅 suggests that the adsorption is spontaneous. Surface morphology study using SEM-EDX confirmed the formation of protective layers on the surface viii of the mild steel, shielding it against the corrosive environment. Electrochemical measurements identified the nanocomposites and crude extract inhibitors to be mixed-type, inhibiting both that anodic and cathodic corrosion processes. Quantum chemical studies of the compounds identified by GC-MS technique suggest that the adsorption mechanisms of the molecules on the mild steel substrate is by electron transfer from heteroatoms in the compounds. The present work has successfully demonstrated that titanium nanocomposites of T. rhomboidea and C. odorata have better corrosion inhibitory potential than their corresponding crude extracts due to their smaller particle size and large surface-to-volume property.