Experimental Investigation on the Corrosion Inhibition Characteristics of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) Using 2 M Oxalic Acid

Experimental Investigation on the Corrosion Inhibition Characteristics of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) Using 2 M Oxalic Acid

Industrial development is vital in the history of any developed country. Various types of metals including their alloys are used in various industries for the fabrication and construction of their plants and other installations (Femi et al., 2015). Solutions commonly used in industrial activities (acidic, basic, or neutral), constitute unfriendly corrosive media for metals (Jonnie et al., 2015). This corrosion causes serious damage to the metal and degrades its properties, thereby limiting its use (Aounitiet al., 2015).

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In view of the above, various industries had adopted several options including oiling, cathodic and anodic protections, painting, etc in order to protect metals used in the industries from corrosive environment. However, one of the best options available for the protection of metals against corrosion has been the use of corrosion inhibitors (Femi etal., 2015). This organic inhibitor reacts with the metal and then is adsorbed on the surface of the metal through electrostatic interaction between the metal and inhibitor (physical adsorption) or through the formation of a coordinate covalent bond (chemical adsorption) (Aounitiet al., 2015). The presence of >C=N- group in the structure of inhibitors enable them to be adsorbed on the metal surface. Due to this adsorption behavior, there is a formation of a thin layer which covers the metal surface, consequently acting as effective corrosion inhibitor by isolating the metal surface from the aggressive medium (Jonnie et al., 2015).
In general, the adsorption of the inhibitor on the metal surface depends on (i) the type of corrosive environment, (ii) the nature and the state of the metal surface and (iii) the chemical structure of the inhibitor. Compounds considered to be effective corrosion inhibitors are organic compounds containing heteroatoms with lone pair of electrons (such as O, S and N) and long carbon chain length, or conjugated bonds or aromatic rings. Also, Schiff bases are used as inhibitors due to the presence of >C=N- group in their structures (Aounitiet al., 2015). The applicability of these compounds as corrosion inhibitors for metals in various media has long been recognized. However, most of these compounds are environmentally hazardous and heavily toxic (Aymanet al., 2015).
This work is in furtherance to the continual search for eco-friendly, easy to synthesize and effective corrosion inhibitors. In this very work, a Schiff base (SB) was synthesized and investigated for its corrosion inhibition potential using immersion and gravimetric methods.

Statement of the Research Problem
Many method have been used to address the problems associated with corrosion of metals in various media but most of these method previously used have a lot of limitations. These limitations include, ineffectiveness of corrosion protective oils, high cost of coating material for the metal, complexity of cathodic and anodic protections, etc. The inability of some these methods to prevent corrosion to a reasonable extent calls for a more efficient and cost effective method for prevention of corrosion of metals.

Objectives of the Study
The general objective of this study is to investigate the corrosion inhibition characteristic of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) (EDDBP) on aluminum in oxalic acid solution by weight loss technique.

The specific objectives of the study include,
To determine the inhibitory effects of different concentrations of EDDBP on aluminum in oxalic acid solution.
To determine the inhibitory effects of EDDBP on aluminum in oxalic acid solution at different temperature conditions and time intervals.
To evaluate the corrosion rate, percentage inhibitory efficiency and surface coverage values from the results obtained.
To evaluate the various rate laws for the corrosion process from the results obtained.
To use various adsorption isotherm models to describe the corrosion inhibition behavior of EDDBP on aluminum.

Scope of the Study
In this work, samples of aluminum will be obtained and the corrosion inhibition potential of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) will be examined on the sheets after immersion in oxalic acid solution. The rate of corrosion of the aluminum sheets in oxalic acid will be quantified by weight loss measurement.

Significance of the Study
It is important to know what corrosion is and how it affects the environment and our daily lives. Corrosion study enables us to know how to prevent the destruction of materials, equipment and structures as well as prevention of home and industrial accidents usually caused by malfunctioning or collapse of corroded materials. Similarly, corrosion of concrete-covered steel and iron can cause the concrete to collapse creating severe structural problems. All these can be avoided by the study of corrosion and its impact on the environment. The study will also provide basis for relevant use of the studied inhibitor for corrosion prevention and/or inhibition in industries, homes or even building construction.

 

CHAPTER TWO
REVIEW OF RELEVANT LITERATURE
Basic concept of Corrosion
Corrosion is one of the natural processes that occur in the environment. This natural process tends to return materials to their lowest possible energy states. Metals have a natural tendency to return to their lowest energy states by combining with other chemical elements. In order to return to their lowest energy states, these metals (especially iron and its ore) frequently combine with oxygen and water, both of which are present in most natural environments, to form hydrated iron oxides known as rust (Payer et al., 2000).
Corrosion is a term that has its origin in Latin. The term “corrodere” means “gnawing to pieces” which describes corrosion. Metallic corrosion has been a problem since common metals were first put to use. Most metals occur in nature as compounds, such as sulphides, oxides or carbonates. This is because of the thermodynamic stability of the compounds as opposed to the metals (Sastrietal., 2007).
The process of extraction of iron from the ore is simply by reduction (Eq. 1). During this extraction, iron oxide is reduced to metallic iron. On the other hand, the oxidation of iron to produce the brown oxide known as rust is the exact opposite reaction to the production of the metal from the oxide (Sastriet al., 2007).
〖2Fe〗_2 O_3 + 3C ⟶ 4Fe + 〖3CO〗_2(1)
Corrosion is said to be a chemical or electrochemical reaction between a material and its environment that produces a deterioration of the material and its properties. The environment consists of the entire surrounding in contact with the material. When corrosion is discussed, it is important to think of a combination of a material and an environment. The corrosion behavior of a material cannot be easily described unless the material which is to be exposed to that environment is identified. In summary, the corrosivity of an environment depends on the material exposed to that environment, and the corrosion behaviour of a material depends on the environment (Payer et al., 2000).
It is important to identify both natural (desirable) combinations and unnatural (undesirable) combinations in corrosion. In desirable corrosion, the interaction between the metal and the environment does not usually result in costly or detrimental corrosion problems. The combination provides good corrosion service. Examples include lead in water, nickel in caustic environment, and aluminum in atmospheric exposure. On the other hand, undesirable corrosion results in severe corrosion damage to the metal because of its exposure to an undesirable environment. Examples include stainless steel in chloride-containing environment, copper in ammonia solution, and lead in wine (Payer etal., 2007).

Chemistry of Corrosion
Almost all corrosion reactions are electrochemical in nature. For example in the corrosion of iron, at an anodic site, iron goes into solution as ferrous ions, and this constitutes the anodic reaction. As iron atoms undergo oxidation to ions they release electrons whose negative charge quickly build up in the metal (Eq. 2).
At the anode: Fe(s) ⟶ Fe^(2+)+ 2e〗^-(2)

At the cathode:〖2H〗^+ + 2e^- ⟶ H_2 (3a)
H_2 O + 1/2O_2 + 〖2e〗^- 〖2OH〗^-(3b)
Reaction 3a is most common in acids while reaction 2b illustrates oxygen reduction. In this oxygen reduction reaction, corrosion is usually accompanied by formation of solid corrosion debris from the reaction between the cathodic and anodic products (Eq. 4).
Fe^(2+) + 〖2OH〗^-⟶Fe〖(OH)〗_2 (4)
Iron(II) hydroxide
Pure Iron(ii) hydroxide is usually white but due to partial oxidation of air, the material initially produced by corrosion is a greenish colour (Eq. 5).
2Fe〖(OH)〗_2 + H_2 O + 1/2O_2 ⟶ Fe_2 O_3.〖3H〗_2 O (5)
Hydrated iron(III) oxide
Continuous oxidation and hydration reaction can occur and the reddish rust will eventually be transformed into a complex mixture whose composition will depend on other minor elements which are present. The rust is porous, tends to be harmful and encourages further corrosion (Ashworth et al., 2010).

Definition of terms
Corrosion
Corrosion can be defined as a chemical reaction between a material and its environment which leads to deterioration of the material and its properties. Corrosion reduces the efficiency of a material and its life span thereby limiting its use. Virtually all materials are susceptible to corrosion (metals, polymers, plastics and so forth) (Payer et al., 2000).

Corrosive agent
A corrosive agent, also known as a corrosive, is a substance that enhances or promotes the rate of corrosion of a material through a chemical interaction with the material. This substance can dissolve a material uniformly, or non-uniformly depending on its pH. Various corrosives may, in general, be classified as: (i) mineral acids; (ii) organic acids; (iii) alkalies, and (iii) corrosive vapours (Bhatia, 2013).

Corrosioninhibitor

This can be defined as any substance which when added in small quantity to the aqueous corrosive environment, decreases the rate of corrosion of a material. Corrosion inhibitors work through the mechanism of adsorption. The common inhibitors are the silicates and phosphates which are classified as inorganic inhibitors. The inorganic inhibitors possess good inhibition characteristics but are now being replaced by organic inhibitors because oftheir toxicity. A large number of organic compounds have been found to be effective as corrosion inhibitors, but the most effective so far is quinolone (Sharma, 2011).

Kinds of Corrosion

Uniform Attack
This is the most common form of corrosion. Here, chemical reaction (or electrochemical reaction) occurs over entire exposed surface more or less uniformly. It is not usually serious and is predictable from simple test (example coupon or specimen immersion). Uniform attack can be minimized by correctly applying coating, using corrosion inhibitors, and protecting cathodically (Derek, 2010a).

Galvanic Corrosion
This is also known as “two metal corrosion”. Galvanic corrosion occurs when two different electrodes are in electric contact and immersed in the same aqueous electrolyte. In the galvanic series, the metal with the more negative electrode potential will act as anode and the metal with the more positive potential as cathode. The galvanic series allows identifying which material of a given pair will act as cathode and anode when coupled. (McCafferty, 2010).

Pitting
This is highly localized attack at specific areas resulting in small pits that penetrate into the metal and may lead to perforation. Pitting is regarded as one of the most insidious forms of corrosion since it often leads to perforation and to a consequent corrosion failure. In other cases, pitting may result in a loss of appearance of the metal concerned. Example is pitting of passive metals such as the stainless steels, aluminum alloys, etc; in the presence of Cl- ions (Shrier, 2010).
Selective Leaching
This form of corrosion is also known as de-alloying. Here, one component of an alloy (usually the most active) is selectively removed from the alloy. Examples include, de-zincification, de-aluminification, graphitization (Shreir, 2010).

Erosion Corrosion:
This is also known as “fluid assisted corrosion”. Erosion corrosion is an increase in corrosion brought about by a high relative velocity between the corrosion environment and the surface. Removal of metal may be as corrosion product which “spalls off” the surface and bares the metal beneath or as metal ions which are swept away by the fluid before they can deposit as corrosion product (Derek, 2010b).
Other forms of corrosion include: crevice corrosion (Navidet al., 2007), intergranular corrosion (Simon et al., 1999), and stress corrosion cracking (Cottis, 2009).

Methods of Control Corrosion
Since corrosion involves interaction between materials and environment, the approaches to corrosion include the use of the most compatible materials in a given environment and also to reduce the aggressiveness of the environment toward the material. There are five different methods to corrosion control which are: coating, material selection, cathodic protection, design and inhibitors.

Coating
The objective of a coating is to provide a barrier between the metal and the environment. Coatings for corrosion protection can be divided into two broad groups- organic and inorganic. The intent is the same with either type of coating, that is, to isolate the underlying metal from the corrosive medium.

a. Organic coating
The primary function of organic coating in corrosion protection is to isolate the metal from the corrosion environment. In addition to forming a barrier layer to restrain corrosion, the organic coating can contain corrosion inhibitor.

 

b. Inorganic coating
Like organic coatings, inorganic coatings for corrosion protection serve as barrier coatings. Inorganic coatings include porcelain enamels, glass coatings and lining, chemical- setting silicate cement linings, and other corrosion resistance ceramics.

Material selections
Each metal and alloy has unique and inherent corrosion behaviour. The corrosion resistance of a metal strongly depends on the environment to which it is exposed, that is, the chemical composition, velocity, temperature, etc. For a given corrosion resistance of a material, as the corrosivity of the environment increases, the rate of corrosion increases. Often an acceptable rate of corrosion is fixed and the challenge is to match the corrosion resistance of the material and the corrosivity of the environment to be at or below the specified corrosion rate. The material selection process aims at determining which of the candidate materials provides the most economical solution for the particular service. (Payer et al., 2000).

Cathodic protection
Cathodic protection tends to suppress the corrosive current that causes damage in the corrosion cell and limits the flow of current to the metal. In the overall context, the corrosion or metal dissolution is prevented. In practice, cathodic protection can be achieved by two application methods, which differ based on the source of the protective current. In a sacrificial- anode system method, an active metal anode is connected to the structure to provide the cathodic-protection current while in an impressed-current method uses a power to force current from inert anodes to the structure to be protected.

Design
The application of the design principles may reduce the corrosion problems and reduce the time and cost involved in corrosion repair as well as maintenance. Corrosion often occurs in dead spaces or crevices where the corrosive medium becomes more corrosive. These areas can be eliminated or minimized in the design process (Patilet al., 2013).

Inhibitors
Just as some chemical species promote corrosion, other chemical species inhibit corrosion. The mechanisms of inhibition can be quite complex. In the case of organic amines, the inhibitor is adsorbed on anodic and cathodic site and stifles the corrosion current. Other inhibitors specifically affect either the anodic or cathodic process. Still others promote the formation of protective films on the metal surface. Inhibitors can be incorporated in a protective coating or in a primer for the coating. At a defect in the coating, inhibitor leaches from the coating and controls the corrosion (Payer et al., 2000).

Mechanism of Inhibitor Action
The mechanism of inhibitory action of most organic inhibitors occurs through adsorption process. Existing data has shown that compounds that act as inhibitors act by the mechanism of adsorption on the metal surface. This phenomenon is strongly dependent on the nature and surface charge of the metal, the chemical structure of the inhibitor, and the type of aggressive environment (Thomas, 1980).

It is generally accepted that the first step in the adsorption of organic inhibitors on a metal surface usually involves the replacement of one or more water molecules adsorbed at the surface (Oguzieet al., 2007). The inhibitor may then combine with freshly generated Fe2+ ions on the metal surface, forming metal-inhibitor complexes represented by Eq. 6a and 6b:
Industrial development is vital in the history of any developed country. Various types of metals including their alloys are used in various industries for the fabrication and construction of their plants and other installations (Femi et al., 2015). Solutions commonly used in industrial activities (acidic, basic, or neutral), constitute unfriendly corrosive media for metals (Jonnie et al., 2015). This corrosion causes serious damage to the metal and degrades its properties, thereby limiting its use (Aounitiet al., 2015). In view of the above, various industries had adopted several options including oiling, cathodic and anodic protections, painting, etc in order to protect metals used in the industries from corrosive environment. However, one of the best options available for the protection of metals against corrosion has been the use of corrosion inhibitors (Femi etal., 2015). This organic inhibitor reacts with the metal and then is adsorbed on the surface of the metal through electrostatic interaction between the metal and inhibitor (physical adsorption) or through the formation of a coordinate covalent bond (chemical adsorption) (Aounitiet al., 2015). The presence of >C=N- group in the structure of inhibitors enable them to be adsorbed on the metal surface. Due to this adsorption behavior, there is a formation of a thin layer which covers the metal surface, consequently acting as effective corrosion inhibitor by isolating the metal surface from the aggressive medium (Jonnie et al., 2015).

In general, the adsorption of the inhibitor on the metal surface depends on (i) the type of corrosive environment, (ii) the nature and the state of the metal surface and (iii) the chemical structure of the inhibitor. Compounds considered to be effective corrosion inhibitors are organic compounds containing heteroatoms with lone pair of electrons (such as O, S and N) and long carbon chain length, or conjugated bonds or aromatic rings. Also, Schiff bases are used as inhibitors due to the presence of >C=N- group in their structures (Aounitiet al., 2015). The applicability of these compounds as corrosion inhibitors for metals in various media has long been recognized. However, most of these compounds are environmentally hazardous and heavily toxic (Aymanet al., 2015).
This work is in furtherance to the continual search for eco-friendly, easy to synthesize and effective corrosion inhibitors. In this very work, a Schiff base (SB) was synthesized and investigated for its corrosion inhibition potential using immersion and gravimetric methods.

Statement of the Research Problem
Many method have been used to address the problems associated with corrosion of metals in various media but most of these method previously used have a lot of limitations. These limitations include, ineffectiveness of corrosion protective oils, high cost of coating material for the metal, complexity of cathodic and anodic protections, etc. The inability of some these methods to prevent corrosion to a reasonable extent calls for a more efficient and cost effective method for prevention of corrosion of metals.

Objectives of the Study
The general objective of this study is to investigate the corrosion inhibition characteristic of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) (EDDBP) on aluminum in oxalic acid solution by weight loss technique.

The specific objectives of the study include,
To determine the inhibitory effects of different concentrations of EDDBP on aluminum in oxalic acid solution.
To determine the inhibitory effects of EDDBP on aluminum in oxalic acid solution at different temperature conditions and time intervals.
To evaluate the corrosion rate, percentage inhibitory efficiency and surface coverage values from the results obtained.
To evaluate the various rate laws for the corrosion process from the results obtained.
To use various adsorption isotherm models to describe the corrosion inhibition behavior of EDDBP on aluminum.

Scope of the Study
In this work, samples of aluminum will be obtained and the corrosion inhibition potential of 4,4ʹ-(1,2-ethanediyldinitrilo)bis-(2-pentanone) will be examined on the sheets after immersion in oxalic acid solution. The rate of corrosion of the aluminum sheets in oxalic acid will be quantified by weight loss measurement.

Significance of the Study
It is important to know what corrosion is and how it affects the environment and our daily lives. Corrosion study enables us to know how to prevent the destruction of materials, equipment and structures as well as prevention of home and industrial accidents usually caused by malfunctioning or collapse of corroded materials. Similarly, corrosion of concrete-covered steel and iron can cause the concrete to collapse creating severe structural problems. All these can be avoided by the study of corrosion and its impact on the environment. The study will also provide basis for relevant use of the studied inhibitor for corrosion prevention and/or inhibition in industries, homes or even building construction.

CHAPTER TWO
REVIEW OF RELEVANT LITERATURE

Basic concept of Corrosion
Corrosion is one of the natural processes that occur in the environment. This natural process tends to return materials to their lowest possible energy states. Metals have a natural tendency to return to their lowest energy states by combining with other chemical elements. In order to return to their lowest energy states, these metals (especially iron and its ore) frequently combine with oxygen and water, both of which are present in most natural environments, to form hydrated iron oxides known as rust (Payer et al., 2000).
Corrosion is a term that has its origin in Latin. The term “corrodere” means “gnawing to pieces” which describes corrosion. Metallic corrosion has been a problem since common metals were first put to use. Most metals occur in nature as compounds, such as sulphides, oxides or carbonates. This is because of the thermodynamic stability of the compounds as opposed to the metals (Sastrietal., 2007).
The process of extraction of iron from the ore is simply by reduction (Eq. 1). During this extraction, iron oxide is reduced to metallic iron. On the other hand, the oxidation of iron to produce the brown oxide known as rust is the exact opposite reaction to the production of the metal from the oxide (Sastriet al., 2007).
〖2Fe〗_2 O_3 + 3C ⟶ 4Fe + 〖3CO〗_2(1)
Corrosion is said to be a chemical or electrochemical reaction between a material and its environment that produces a deterioration of the material and its properties. The environment consists of the entire surrounding in contact with the material. When corrosion is discussed, it is important to think of a combination of a material and an environment. The corrosion behavior of a material cannot be easily described unless the material which is to be exposed to that environment is identified. In summary, the corrosivity of an environment depends on the material exposed to that environment, and the corrosion behaviour of a material depends on the environment (Payer et al., 2000).
It is important to identify both natural (desirable) combinations and unnatural (undesirable) combinations in corrosion. In desirable corrosion, the interaction between the metal and the environment does not usually result in costly or detrimental corrosion problems. The combination provides good corrosion service. Examples include lead in water, nickel in caustic environment, and aluminum in atmospheric exposure. On the other hand, undesirable corrosion results in severe corrosion damage to the metal because of its exposure to an undesirable environment. Examples include stainless steel in chloride-containing environment, copper in ammonia solution, and lead in wine (Payer etal., 2007).

Chemistry of Corrosion
Almost all corrosion reactions are electrochemical in nature. For example in the corrosion of iron, at an anodic site, iron goes into solution as ferrous ions, and this constitutes the anodic reaction. As iron atoms undergo oxidation to ions they release electrons whose negative charge quickly build up in the metal (Eq. 2).
At the anode: Fe(s) ⟶ Fe^(2+)+ 2e〗^-(2)

At the cathode: 〖2H〗^+ + 2e^- ⟶ H_2 (3a)
H_2 O + 1/2O_2 + 〖2e〗^- 〖2OH〗^-(3b)
Reaction 3a is most common in acids while reaction 2b illustrates oxygen reduction. In this oxygen reduction reaction, corrosion is usually accompanied by formation of solid corrosion debris from the reaction between the cathodic and anodic products (Eq. 4).
Fe^(2+) + 〖2OH〗^-⟶Fe〖(OH)〗_2 (4)
Iron(II) hydroxide

Pure Iron(ii) hydroxide is usually white but due to partial oxidation of air, the material initially produced by corrosion is a greenish colour (Eq. 5).
2Fe〖(OH)〗_2 + H_2 O + 1/2O_2 ⟶ Fe_2 O_3.〖3H〗_2 O (5)
Hydrated iron(III) oxide
Continuous oxidation and hydration reaction can occur and the reddish rust will eventually be transformed into a complex mixture whose composition will depend on other minor elements which are present. The rust is porous, tends to be harmful and encourages further corrosion (Ashworth et al., 2010).

Definition of terms
Corrosion
Corrosion can be defined as a chemical reaction between a material and its environment which leads to deterioration of the material and its properties. Corrosion reduces the efficiency of a material and its life span thereby limiting its use. Virtually all materials are susceptible to corrosion (metals, polymers, plastics and so forth) (Payer et al., 2000).

Corrosive agent
A corrosive agent, also known as a corrosive, is a substance that enhances or promotes the rate of corrosion of a material through a chemical interaction with the material. This substance can dissolve a material uniformly, or non-uniformly depending on its pH. Various corrosives may, in general, be classified as: (i) mineral acids; (ii) organic acids; (iii) alkalies, and (iii) corrosive vapours (Bhatia, 2013).

Corrosioninhibitor
This can be defined as any substance which when added in small quantity to the aqueous corrosive environment, decreases the rate of corrosion of a material. Corrosion inhibitors work through the mechanism of adsorption. The common inhibitors are the silicates and phosphates which are classified as inorganic inhibitors. The inorganic inhibitors possess good inhibition characteristics but are now being replaced by organic inhibitors because oftheir toxicity. A large number of organic compounds have been found to be effective as corrosion inhibitors, but the most effective so far is quinolone (Sharma, 2011).

Kinds of Corrosion

Uniform Attack
This is the most common form of corrosion. Here, chemical reaction (or electrochemical reaction) occurs over entire exposed surface more or less uniformly. It is not usually serious and is predictable from simple test (example coupon or specimen immersion). Uniform attack can be minimized by correctly applying coating, using corrosion inhibitors, and protecting cathodically (Derek, 2010a).

Galvanic Corrosion
This is also known as “two metal corrosion”. Galvanic corrosion occurs when two different electrodes are in electric contact and immersed in the same aqueous electrolyte. In the galvanic series, the metal with the more negative electrode potential will act as anode and the metal with the more positive potential as cathode. The galvanic series allows identifying which material of a given pair will act as cathode and anode when coupled. (McCafferty, 2010).

Pitting
This is highly localized attack at specific areas resulting in small pits that penetrate into the metal and may lead to perforation. Pitting is regarded as one of the most insidious forms of corrosion since it often leads to perforation and to a consequent corrosion failure. In other cases, pitting may result in a loss of appearance of the metal concerned. Example is pitting of passive metals such as the stainless steels, aluminum alloys, etc; in the presence of Cl- ions (Shrier, 2010).

Selective Leaching
This form of corrosion is also known as de-alloying. Here, one component of an alloy (usually the most active) is selectively removed from the alloy. Examples include, de-zincification, de-aluminification, graphitization (Shreir, 2010).

Erosion Corrosion:
This is also known as “fluid assisted corrosion”. Erosion corrosion is an increase in corrosion brought about by a high relative velocity between the corrosion environment and the surface. Removal of metal may be as corrosion product which “spalls off” the surface and bares the metal beneath or as metal ions which are swept away by the fluid before they can deposit as corrosion product (Derek, 2010b).
Other forms of corrosion include: crevice corrosion (Navidet al., 2007), intergranular corrosion (Simon et al., 1999), and stress corrosion cracking (Cottis, 2009).

Methods of Control Corrosion
Since corrosion involves interaction between materials and environment, the approaches to corrosion include the use of the most compatible materials in a given environment and also to reduce the aggressiveness of the environment toward the material. There are five different methods to corrosion control which are: coating, material selection, cathodic protection, design and inhibitors.

Coating
The objective of a coating is to provide a barrier between the metal and the environment. Coatings for corrosion protection can be divided into two broad groups- organic and inorganic. The intent is the same with either type of coating, that is, to isolate the underlying metal from the corrosive medium.

Organic coating
The primary function of organic coating in corrosion protection is to isolate the metal from the corrosion environment. In addition to forming a barrier layer to restrain corrosion, the organic coating can contain corrosion inhibitor.

 

b. Inorganic coating
Like organic coatings, inorganic coatings for corrosion protection serve as barrier coatings. Inorganic coatings include porcelain enamels, glass coatings and lining, chemical- setting silicate cement linings, and other corrosion resistance ceramics.

Material selections
Each metal and alloy has unique and inherent corrosion behaviour. The corrosion resistance of a metal strongly depends on the environment to which it is exposed, that is, the chemical composition, velocity, temperature, etc. For a given corrosion resistance of a material, as the corrosivity of the environment increases, the rate of corrosion increases. Often an acceptable rate of corrosion is fixed and the challenge is to match the corrosion resistance of the material and the corrosivity of the environment to be at or below the specified corrosion rate. The material selection process aims at determining which of the candidate materials provides the most economical solution for the particular service. (Payer et al., 2000).

Cathodic protection
Cathodic protection tends to suppress the corrosive current that causes damage in the corrosion cell and limits the flow of current to the metal. In the overall context, the corrosion or metal dissolution is prevented. In practice, cathodic protection can be achieved by two application methods, which differ based on the source of the protective current. In a sacrificial- anode system method, an active metal anode is connected to the structure to provide the cathodic-protection current while in an impressed-current method uses a power to force current from inert anodes to the structure to be protected.

Design
The application of the design principles may reduce the corrosion problems and reduce the time and cost involved in corrosion repair as well as maintenance. Corrosion often occurs in dead spaces or crevices where the corrosive medium becomes more corrosive. These areas can be eliminated or minimized in the design process (Patilet al., 2013).

Inhibitors
Just as some chemical species promote corrosion, other chemical species inhibit corrosion. The mechanisms of inhibition can be quite complex. In the case of organic amines, the inhibitor is adsorbed on anodic and cathodic site and stifles the corrosion current. Other inhibitors specifically affect either the anodic or cathodic process. Still others promote the formation of protective films on the metal surface. Inhibitors can be incorporated in a protective coating or in a primer for the coating. At a defect in the coating, inhibitor leaches from the coating and controls the corrosion (Payer et al., 2000).

Mechanism of Inhibitor Action
The mechanism of inhibitory action of most organic inhibitors occurs through adsorption process. Existing data has shown that compounds that act as inhibitors act by the mechanism of adsorption on the metal surface. This phenomenon is strongly dependent on the nature and surface charge of the metal, the chemical structure of the inhibitor, and the type of aggressive environment (Thomas, 1980).
It is generally accepted that the first step in the adsorption of organic inhibitors on a metal surface usually involves the replacement of one or more water molecules adsorbed at the surface (Oguzieet al., 2007). The inhibitor may then combine with freshly generated Fe2+ ions on the metal surface, forming metal-inhibitor complexes represented by Eq. 6a and 6b:

To Place An Order For The Complete Project Material Pay N,5000 To

Guaranty Trust Bank (GTBank)
Acct. Name - Uwadia Eyemeka
Acct. No. - 0127561472

Then Send a text of your names, the topic you paid for, a valid email address to 07036785443
To Place An Order For The Complete Project Material Pay N,5000 To

Guaranty Trust Bank (GTBank)
Acct. Name - Uwadia Eyemeka
Acct. No. - 0127561472

Then Send a text of your names, the topic you paid for, a valid email address to 07036785443

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