THE INHIBITORY EFFECT OF ETHANOLIC EXTRACT OF MORINGA OLEIFERA LEAF ON THE CORROSION OF MILD STEEL IN 5 M AND 1 M HYDROCHLORIC ACID (HC)
CHAPTER ONE – INTRODUCTION
1.1 Background of study
Corrosion of materials has continued to receive interest in the technological world as its elects 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
elects, corrosion is an undesirable phenomenon that ought to be prevented.
Scientists are persistent in seeking better and more eicient
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 eective,
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 erects of synthetic organic inhibitors, which have been in use (Popova et al., 2007; Li, et. al., 2009) and the need to develop cheap, nontoxic
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 elect 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 gasometer methods were used for the investigation.