THE INHIBITORY EFFECT OF ETHANOLIC EXTRACT OF MORINGA OLEIFERA LEAF ON THE CORROSION OF MILD STEEL IN 5 M AND 1 M HYDROCHLORIC ACID
CHAPTER ONE – INTRODUCTION
1.1 Background of study
Corrosion of materials has continued to receive interest in the technological world as its effects on the structural integrity of materials has been a question for some time. Metallic materials are still the most widely used group of materials particularly in mechanical engineering and the transportation industry. In addition, metals are commonly used in electronics and increasingly also in the construction industry (Buchweishaija, 2009a).
However, the usefulness of metals and alloys is constrained by one common problem known as corrosion. Hence, it has been studied comprehensively since the industrial revolution in the late eighteenth century (Sato, 2012). Corrosion is a naturally occurring phenomenon defined as deterioration of metal surfaces caused by the reaction with the surrounding environmental conditions (Buchweishaija, 2009a). Corrosion can cause disastrous damage to metal and alloy structures causing economic consequences in terms of repair, replacement, product losses, safety and environmental pollution. Due to these harmful effects, corrosion is an undesirable phenomenon that ought to be prevented.
Scientists are persistent in seeking better and more efficient ways of combating the corrosion of metals. There are several ways of preventing corrosion and the rates at which it can propagate with a view of improving the lifetime of metallic and alloy materials (Buchweishaija, 2009a). Hunag and Chen (2012) highlighted the measures in preventing and control of corrosion as follows: use of resistant metal alloys, cathodic and anodic protection, use of protective coatings (Stack, 2002) and addition of corrosion inhibitors to the corrosion environment (Papavinasam, 2000).
Among the methods of corrosion control, the use of inhibitors is very popular. It is one of the acceptable practices used to reduce and/or prevent corrosion due to the ease of application. Mostly heterocyclic compounds containing oxygen, sulphur and nitrogen as heteroatoms serve as good inhibitors for corrosion (Kumar et al, 2009). To be effective, an inhibitor must also transfer water from the metal surface, interact with anodic and cathodic reaction sites to retard the oxidation and reduction corrosion reaction, and prevent transportation of water and corrosion-active species on the metal surface (Maqsood, 2011). Despite these promising findings about possible corrosion inhibitors, most of these substances are not only expensive but also toxic and non–biodegradable thus causing corrosion problems (Raja and Sethuraman, 2008).
The known hazardous effects of synthetic organic inhibitors, which have been in use (Popova et al., 2007; Li, et. al., 2009) and the need to develop cheap, non-toxic and ecofriendly processes have now made researchers to focus on the use of natural product (Umoren et al., 2008; Umoren & Ebenso, 2008; El-Etre, 2008). Plants have been recognized as naturally occurring compounds, some with rather complex molecular structures and having varying physical, chemical and biological properties (Buchweishaija, 2009a).
The present work therefore, has been designed to evaluate the effect of the leaf extracts of Moringa oleifera on the corrosion inhibition of mild steel in 5M and 1M hydrochloric acid solution with a view to contributing to the search for further beneficial uses of plant extract. Gravimetric and gasometric methods were used for the investigation.
Corrosion is nature’s method whereby metals and alloys return to their unrefined naturally occurring forms as minerals and ores (Peter Maaß, 2011). Corrosion is the deterioration of metals by chemical attack or interaction with its environment (Acharya et. al., 2013). It can also be defined as the gradual eating away or disintegration or deterioration of materials by chemical or electrochemical reaction with its environment (Dara, 2007).
Corrosion is a constant and continuous problem, often diﬃcult to eliminate completely. Prevention would be more practical and achievable than complete elimination. Corrosion processes develop fast after disruption of the protective barrier and are accompanied by a number of reactions that change the composition and properties of both the metal surface and the local environment, for example, formation of oxides, diﬀusion of metal cations into the coating matrix, local pH changes, and electrochemical potential (Rani and Basu, 2011).