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MEE00139 - STUDY OF CORROSION OF ALUMINUM ALLOY IN DIFFERENT MEDIA


CHAPTER ONE

  • INTRODUCTION
  • BACKGROUND OF STUDY

                  Corrosion can be defined in many ways. Some definitions are very
narrow and deal with a specific form of corrosion, while others are quite broad and cover many forms of deterioration. The word corrode is derived from the Latin corrodere, which means “to gnaw to pieces.” The general definition of corrode is to eat into or wear away gradually, as if by gnawing (Obot et al., 2010). For purposes here, corrosion can be defined as a chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties. Hence, corrosion can otherwise be defined as the destruction or deterioration of material.  In simple terminology, corrosion processes involve reaction of metals with environmental species. Corrosion is an irreversible interfacial reaction of a material (metal, ceramic, polymer) with its environment which results in its consumption or dissolution into the material of a component of the environment (Popova et al., 2003). Often, but not necessarily, corrosion results in effects detrimental to the usage of the material considered.

                  Generally, corrosion is the process whereby the surface of the metal undergoes a slow, relatively uniform; removal of material. This occurs on the surface of a single metal rather than dissimilar metals. In general, corrosion, a nearly infinite of micro-cells is established on the metal surface (Bouklah et al., 2005). Oxidation occurs at anodic areas and reduction at cathode areas. These micro-cells are uniformly distributed over the metallic surface and as the reaction proceeds the cell may migrate or disappear and reform. That is, any particular micro-region may be alternatively anodic and cathodic. The result is a uniform attack on the metal surface. Under some conditions, relatively to migrate and may remain operative for long period of time. In this case, there will be severe attack of the metal at the anodic (oxidation) region (Amin et al., 2009). 

              Corrosion can be fast or slow. Corrosion of metal can be considered as extractive metallurgy. Rusting is a term reserved for steel and iron corrosion, although many other metals form their oxides when corrosion occurs. Practically all environments are corrosive to some degree. Air, moisture, fresh, distilled, salt and mine waters, rural or urban and industrial atmosphere, steam and other gases such as NH3, Cl2, H2S, SO2, fuel gases, inorganic acids, organic acids, solvents, petroleum oils cause corrosion environment. Inorganic materials are more corrosive than the organics (Obot et al., 2010). High temperature and pressure involve more severe corrosion conditions. Anodizing of aluminum is another beneficial corrosion process used to obtain better and uniform appearance in addition to a protective corrosion product on the surface (Badaway et al., 1999).

                  Aluminium and aluminium alloys have emerged as alternate materials in aerospace and in some chemical processing industries. Aluminium and aluminium alloys find vast applications because of the natural tendency of aluminium to form a passivating oxide layer. However, in the aggressive corrosive environment the protective layer breaks down, and the material will undergo corrosion (Nnanna et al., 2011). Aluminum is one of the widely used corrosion- resistant metals. The hard and tough oxide film formed on the surface of the aluminum make it resistant to corrosion. If the protective effect of the oxide film is overcome by scratching or by amalgamation, it is attacked under ordinary conditions by hot alkali hydroxides, halogen, various non-metals and even by water (Umoren et al., 2009).

 

1.2             PROBLEM STATEMENT

                  Corrosion, which is an inevitable problem faced in almost all industries can be considered as one of the worst technical calamity of our time. Corrosion is a serious problem because it definitely contributes to the depletion of our natural resources and if corrective action is not taken, it may lead to failure of equipment or structures. Corrosion studies have also become important due to increasing awareness of the need to conserve the world’s metal resources. Over the year, efforts have been made by many organizations; companies and cooperate bodies to find means of reducing the effect of corrosion especially in industrial environment. Corrosion studies of aluminum being the second to iron in term of production and consumption have received considerable attention by researchers because of their technological importance and industrial applications. Aluminum and aluminum alloys find applications, mainly in automobiles, aviation, household appliances, containers and electronic devices.

 

 

1.3         AIM

        The aim of this project is to investigate the effect of corrosion on aluminum alloy in different media.

   1.4          OBJECTIVES

  • To investigate the rate of corrosion on aluminium in a selected media
  • To develop models in determining the rate of corrosion in the selected media.

 

1.5             JUSTIFICATION

                  Now-a-days more attention has been paid to control the metallic corrosion, due to increasing use of metals in all fields of technology. The first significant area of corrosion studies is economic, which include the objective of reducing enormous material losses resulting from corrosion damages of diverse types. The second area is improved safety and reliability of equipment, which through corrosion, may lead to catastrophic consequences involving both men and money. For example explosion of aircraft in mild air due to corrosion fatigue of parts, or taking off of structure for reinforcement corrosion or breaking down of rusty worn out parts of bridge may sometimes result, in an incalculable loss of human lives. The third area is conversion of limited materials resources and the wastage of these also include corresponding wastages of energy and water resources associated with the production and fabrication of material structures.  No lesser important is the psychological factors at ending imminent failures, and the accompany conservation of human effort entering the design and rebounding of corroded equipment. As a result of these significances, the study of corrosion becomes very necessary in metals and their alloys.

 

1.6             SCOPE OF WORK         

      This project is limited to the study of corrosion of aluminum only in three different selected media. They are;

  • Water
  • Soil
  • Hydrochloric Acid (HCl)