CHAPTER ONE
INTRODUCTION
Background to the Study
Corrosion is often referred to as metallic deterioration by chemical attack or reaction of a metal with its environment (Popoola et al., 2013). It is an ever present and unceasing problem, often hard to eradicate totally. Deterrence would be more realistic and attainable rather than absolute elimination. Metallic deterioration progresses very fast after the destruction or penetration of the passive barrier which is followed by a number of reactions that alter the constituents and behaviour of both the superficial metal surface and the immediate environment. This is observed in, for example, oxides formation, metal cation diffusion into the coating matrix, local pH changes, and electrochemical potential. The investigation of metallic corrosion is a subject of immense conceptual and practical concern and has thus received a substantial amount of interest. In industrial acid cleaning, pickling, descaling and oil well acidizing operations, acid solutions are widely employed on metal substrates to achieve the intended purpose (Speller et al., 1927; Ajayi et al., 2011a and Omotosho et al., 2011). These processes however, require the use of corrosion inhibitors in order to reduce acid damage on metallic materials.
Nowadays most important considerations in industry are reduction of overall costs by protection and maintenance of materials used. The protection of corroding metal surface prevents the waste of resources and money during the industrial applications and is vital to extend the equipment’s lifetime; limiting the dissolution into the environment of toxic metals from the components (Ishwara and Vijaya, 2011). Mild steel is extensively used in different industries in the merit of its good structural properties, good mechanical workability and low cost. Corrosion can be minimized using suitable preventive measures, and several techniques have been developed (Yagan et al., 2006; Aramaki, 2001; Battocchi et al., 2006; Hu et al., 2005; AL-Juhni and Newby, 2006) to control corrosion. Corrosion inhibition of mild steel in acid solutions has become one of the most urgent and severe challenges in acid pickling process (Shukla and Qurarishi, 2010; Aljourani et al., 2009; Fouda et al., 2005). Mild steel is exposed to the action of acid in industrial processes in which acids have important functions, for example in oil well acidification, acid pickling, acid cleaning, and acid descaling. Use of inhibitors is one of the best methods of protecting metals against corrosion (Sathiyanarayanan et al., 2005; Ouchrif et al., 2005). Corrosion inhibitors are compounds that are added in small quantities to an environment to prevent corrosion of metals (Sathiyanarayanan et al., 2006). Most of the efficient acid inhibitors are organic compounds containing nitrogen, sulphur and/or oxygen atoms in their molecule (Sudhish and Quraishi, 2010; Eddy and Ebenso, 2008; Sharma et al., 2008).
Thus recent interests for corrosion inhibition focus on non-toxic and environmental-friendly inhibitors due to more stringent environment quality requirements (Eddy and Ebenso, 2008). Obot and Obi-Egbedi (2010) reported that some researchers have worked on some naturally occurring materials such as Gum Arabic, Raphia, hookeri, Ipomoea Invaculcerata, Vigna unguiculata, Pachylobus edulis, Ginseng root, Dacroydes edulis, Zenthoxylum alatum, Hisiscus sabdairffa, Datura stramonium, Limonene, prosopis, to mention but a few; and they were found to be good corrosion inhibitors.
The use of inhibitors has grown in popularity over the years. There exist two major types of inhibitors. These are organic and inorganic/chemical inhibitors. The inorganic inhibitors contaminate the environment after use and cause a lot of problems like disposal and destruction of plant and animal life. Restrictions have been placed on the use of some of these chemical inhibitors because of their toxic nature (CSPC, 1977). The organic inhibitors are further sub-divided into synthetic or artificial organic inhibitors and the green organic inhibitors. Some of the artificial organic inhibitors are harmful to human existence. The focus of this study therefore, is on The Control Of Mild Steel Corrosion In H2so4 Solution With Aqueous Extract Of Chromolaena Odorata As Inhibitor
Aims of the Research
The aim of the present research pertains to the generation of measurable and testable experimental data towards The Control Of Mild Steel Corrosion In H2so4 Solution With Aqueous Extract Of Chromolaena Odorata As Inhibitor.
Specific Objectives of the Study
The objectives of the research are:
- To determine the inhibition mode of the inhibitors using the kinetic parameters;
- To investigate the surface morphology of the metals in the presence and absence of the inhibitors
Justification for the Research
Corrosion is the degradation of the metallic properties of a metal. It progressively expends limited mineral resources and the energy utilized in the mining and processing of metals together with that employed in the production of machinery and infrastructures. Corrosion is known to affect practically all facet of contemporary bdevelopment or advancement, therefore the deterrence of corrosion is of foremost commercial and ecological significance. The world corrosion organization has posited that the annual cost of corrosion globally is approximately 2.2 trillion US dollars. This represents more than 3 % of the World’s Gross Domestic Product (GDP) (Koch et al., 2002). In Nigeria, the cost of corrosion has not yet being surveyed; however the Central Intelligence Agency (CIA) world fact book on Nigeria however puts it at an estimated 3.2 billion USD annually (CIA, 2006). This implies that further increases in corrosion control measures are required in every area of human life and industry. From the power sector where energy is generated and the wastewater treatment plants that purify our water to the pipelines and storage cisterns that transport our much needed petroleum products, corrosion control products are being used extensively.
The addition of an inhibitor to a system is one major technique of controlling corrosion. A study conducted by the National Association of Corrosion Engineers (NACE) in 2002, showed that the total expenditure on corrosion inhibitors in the United States increased by 83.3% from about $600 million in 1982 to almost $1.1 billion in 1998 (NACE, 2002). This shows a fast growing interest in the use of inhibitors as a corrosion protection technique. A passive protective film is formed on the metal when the inhibitor interacts with the metal. Inhibitors that work this way are normally the types added to vehicle cooling units and corrosion retarding extracts in protective coatings for metals. Conversely most of the inhibitors employed presently are harmful with attendant undesirable effect on plant and animal life. At the moment in the industrialized countries like the U.S, there is mounting demands by lawmakers for the eradication of heavy metal mixtures and noxious inorganic and organic
corrosion inhibitors, thus making research efforts geared towards the enhancement and development of efficient and eco-friendly inhibitors crucial. A look at literature shows that there has been some progress made in the emergence of new and efficient inhibitors currently, meanwhile there is an inclination by lawmakers to abolish several of the inhibitors utilized presently.
Consequently heavy metal based inhibitors like potassium, magnesium, lead, chromates and also those comprising of a mixture of lethal anions (molybdates, benzoates, nitrites, phosphates and fluorides) are to any further extent adequate or suitable. Accordingly, a greater part of inhibitors presently utilized in the metal surface engineering and finishing, chemical, coatings and automobile industry need substitution by eco-friendly materials. Unfortunately too, there are insufficient facts on eco-friendly corrosion inhibitors. Therefore, it is an objective of this work to come up with corrosion inhibitor compositions appropriate for use with hydrochloric and sulphuric acid solutions on steel and aluminium alloys.
