Thesis Abstract

Abstract
Corrosion of metals is a significant issue in various industries, leading to economic losses and safety concerns. The use of corrosion inhibitors is a common method to mitigate corrosion. In this study, the inhibition efficiency of Lasienthera africanum extract as a natural corrosion inhibitor was investigated. Lasienthera africanum is a plant known for its rich phytochemical content, which includes alkaloids, tannins, flavonoids, and saponins, making it a potential candidate for corrosion inhibition. The research involved the extraction of Lasienthera africanum using different solvents to obtain the plant extract, which was then characterized using various analytical techniques. The inhibitory properties of the extract were evaluated using weight loss measurements and electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy. The results indicated that Lasienthera africanum extract exhibited significant corrosion inhibition efficiency for mild steel in a corrosive environment. The inhibition efficiency was found to increase with an increase in the concentration of the plant extract. The plant extract acted as a mixed-type inhibitor, affecting both the anodic and cathodic reactions involved in the corrosion process. The adsorption of the plant extract on the metal surface was found to follow Langmuir adsorption isotherm, indicating a monolayer adsorption process. The thermodynamic parameters calculated from the experimental data suggested that the adsorption of Lasienthera africanum extract on the metal surface was spontaneous and involved physisorption mechanisms. Furthermore, the surface analysis using scanning electron microscopy (SEM) revealed the formation of a protective film on the metal surface in the presence of the plant extract, confirming its role as a corrosion inhibitor. The film formed acted as a barrier, preventing the corrosive species from reaching the metal surface and inhibiting the corrosion process effectively. Overall, the study demonstrated the potential of Lasienthera africanum extract as an effective natural corrosion inhibitor for mild steel. The findings contribute to the development of environmentally friendly corrosion protection methods using plant extracts, which can be further explored for industrial applications to reduce the environmental impact of corrosion inhibitors.

Thesis Overview

1.0 INTRODUCTIONCorrosion is a serious problem in this modern age of technological advancement. This accountsfor a lot of economic losses and irreversible structural damage. The cost of corrosion failuresannually for any nation is difficult to estimate per annum, but it has been stated that the wastageof material resources by corrosion ranks third after war and disease (Olugbenga et al.2011).Efforts have been made to restrain the destructive effects of corrosion using several preventivemeasures (Loto et al. 1989, Popoola et al.2011 and Davis et al. 2001). The effects of corrosion inour daily lives can be direct by affecting the useful service lives of our possessions, and indirect,in that producers and suppliers of goods and services incur corrosion costs, which they pass on toconsumers. At home, corrosion is readily recognized on automobile body panels, charcoal grills,outdoor furniture, and metal tools (Denny et al. 1996). The corrosion of steel reinforcing bars inconcrete usually proceeds out of sight and suddenly results in failure of a section of bridges orbuildings.Virtually all metals will corrode to some extent; the fossil–fuel boilers and fossil-fuel fired powergenerators equipment experience corrosion problems in such component as steam generator andwater walls surrounding the furnace (Natarajanf & Sivan, 2003). Perhaps most dangerous of allis corrosion that occurs in major industrial plants, such as electrical power plants or chemicalHowever, the consequences of corrosion are economic and could lead to:ï‚· Replacement of corroded equipment.ï‚· Overdesign to allow for corrosion.ï‚· Preventive maintenance, for example, painting.ï‚· Shutdown of equipment due to corrosion failure.ï‚· Contamination of a product.ï‚· Loss of efficiency—such as when overdesign and corrosion products decrease the heattransferrate in heat exchangers.ï‚· Loss of valuable product, for example, from a container that has corroded through.ï‚· Inability to use otherwise desirable materials.ï‚· Damage of equipment adjacent to that in which corrosion failure occurs.Corrosion affects most of the industrial sector and may cost billions of dollars each year forprevention and replacement maintenance. Thus, the modern world has made investigations to2overcome this problem by conducting enrichment studies of corrosion inhibitors. Corrosioninhibitors will reduce the rate of either anodic oxidation or cathodic reduction or both. This willgive us anodic, cathodic or a mixed type of inhibition. In an attempt to find corrosion inhibitorsthat are environmentally safe and readily available, there has been a growing trend in the use ofbiological substrate such as leaves or plant extracts as corrosion inhibitors for metals in acidcleaning processes.As a result of increasing awareness on environmentally friendly practices for sustainabledevelopment, the demand for non-toxic inhibitors to replace toxic ones has increasedtremendously. Thus, in recent years, several plant extracts have been investigated for theinhibition of acid corrosion of metals. This is because plants contain naturally synthesizedchemical compounds that are biodegradable, environmentally acceptable, inexpensive, readilyavailable and renewable source of materials.Corrosion is not only dangerous, but also costly, with annual damages in the billions of dollars!If this is difficult to believe, consider some of the direct and indirect effects of corrosion whichcontribute to these costs:Not only that the economic costs are frightening, there is also potential loss of life and damage tothe environment problems, which can have widespread effects upon modern industrialbusinesses. It is essential, therefore, for operators of industrial process plants to have a programfor controlling corrosion.1.1 Literature ReviewCorrosion may be defined as a destructive phenomenon, chemical or electrochemical, which canattack any metal or alloy through reaction by the surrounding environment and in extreme casesmay cause structural failure. The corrosion occurs because of the natural tendency for mostmetals to return to their natural state (reverse of metallurgy); e.g., iron in the presence of moistair will revert to its natural state, iron oxide.Corrosion could be basically carried by water intrusion and some environmental factors.Water intrusion is the principal cause of corrosion problems encountered in the field use ofequipment. Water can enter an enclosure by free entry, capillary action, or condensation. Withthese three modes of water entry acting and with the subsequent confinement of water, it isalmost certain that any enclosure will be susceptible to water intrusion. At normal atmospherictemperatures the moisture in the air is enough to start corrosive action. Oxygen is essential for3corrosion to occur in water at ambient temperatures. Other factors that affect the tendency of ametal to corrode are acidity or alkalinity of the conductive medium (pH factor), stability of thecorrosion products, biological organisms (particularly anaerobic bacteria), Variation incomposition of the corrosive medium and temperature.1.2 Mechanism of CorrosionIn nature, metals are not found in Free State due to their reactivity. Metals are generally in highenergy state because some energy is added during their manufacturing process from the ores.Low energy – state ores are more stable than the high energy – state metals. As a result of thisuphill thermodynamic struggle, the metals have a strong driving force to release energy and goback to their original form. Hence the metals revert to their parent state or ore under a suitablecorrosive environment. The electrochemical process involved in corrosion by nature is oppositeto the extractive metallurgy involved in manufacturing of the metals. Therefore, corrosion issometimes considered as the reverse process of extractive metallurgy as can be seen below: