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THE INHIBITION EFFICIENCY OF LASIENTHERA AFRICANUM AS A NATURAL CORROSION INHIBITOR.


Content

TABLE OF CONTENT

CHAPTER ONE

1.0 INTRODUCTION

1.1 Literature Review

1.2 Mechanism of Corrosion

1.3 Forms of corrosion damage

1.3.1 Uniform or thinning corrosion

1.3.2 Fretting corrosion 

1.3.3 Pitting corrosion

1.3.4 Galvanic corrosion

1.3.5 Intergranular corrosion 

1.3.6 Erosion corrosion 

1.4 Methods of Corrosion Protection 

1.4.1 Application of Protective Coatings 

1.4.2 Cathodic Protection 

1.4.3. Corrosion Inhibitors 

1.5 Aluminum as a Structural Metal

1.6 Past work in corrosion inhibition 

1.7 Lasienthera africanum (Editan Leaf)

1.8 Aim and Objectives

Aim

CHAPTER TWO

2.0      MATERIALS AND METHOD

2.1      Experimental Materials 

2.2      Reagents  

2.3      Plant sample 

2.4      Preparation of Aluminum coupons for anti-corrosion study 

2.5      Preparation of plant extract for corrosion inhibition studies

2.6      Weight Loss Measurement

 

CHAPTER THREE

3.0  RESULTS AND DISCUSSION

3.3 Inhibitory action of Lasienthera africanum on the corrosion of Aluminum

3.4 Effect of temperature and time on the inhibition efficiency of Lasienthera

 

CHAPTER FOUR

CONCLUSION AND RECOMMENDATION

 

4.1 Conclusion

4.2  Recommendation

REFERENCE

 

CHAPTER ONE

1.0 INTRODUCTION

Corrosion is a serious problem in this modern age of technological advancement.  This accounts for a lot of economic losses and irreversible structural damage. The cost of corrosion failures annually for any nation is difficult to estimate per annum, but it has been stated that the wastage of material resources by corrosion ranks third after war and disease (Olugbenga et al.2011). Efforts have been made to restrain the destructive effects of corrosion using several preventive measures (Loto et al. 1989, Popoola et al.2011 and Davis et al. 2001). The effects of corrosion in our daily lives can be direct by affecting the useful service lives of our possessions, and indirect, in that producers and suppliers of goods and services incur corrosion costs, which they pass on to consumers. At home, corrosion is readily recognized on automobile body panels, charcoal grills, outdoor furniture, and metal tools (Denny et al. 1996).  The corrosion of steel reinforcing bars in concrete usually proceeds out of sight and suddenly results in failure of a section of bridges or buildings.

Virtually all metals will corrode to some extent; the fossil–fuel boilers and fossil-fuel fired power generators equipment experience corrosion problems in such component as steam generator and water walls surrounding the furnace (Natarajanf & Sivan, 2003). Perhaps most dangerous of all is corrosion that occurs in major industrial plants, such as electrical power plants or chemical However, the consequences of corrosion are economic and could lead to:

      Replacement of corroded equipment.

      Overdesign to allow for corrosion.

      Preventive maintenance, for example, painting.

      Shutdown of equipment due to corrosion failure.

      Contamination of a product.

      Loss of efficiency—such as when overdesign and corrosion products decrease the heattransfer rate in heat exchangers.

      Loss of valuable product, for example, from a container that has corroded through.

      Inability to use otherwise desirable materials.

      Damage of equipment adjacent to that in which corrosion failure occurs.

Corrosion affects most of the industrial sector and may cost billions of dollars each year for prevention and replacement maintenance. Thus, the modern world has made investigations to overcome this problem by conducting enrichment studies of corrosion inhibitors. Corrosion inhibitors will reduce the rate of either anodic oxidation or cathodic reduction or both. This will give us anodic, cathodic or a mixed type of inhibition. In an attempt to find corrosion inhibitors that are environmentally safe and readily available, there has been a growing trend in the use of biological substrate such as leaves or plant extracts as corrosion inhibitors for metals in acid cleaning processes.

As a result of increasing awareness on environmentally friendly practices for sustainable development, the demand for non-toxic inhibitors to replace toxic ones has increased tremendously. Thus, in recent years, several plant extracts have been investigated for the inhibition of acid corrosion of metals. This is because plants contain naturally synthesized chemical compounds that are biodegradable, environmentally acceptable, inexpensive, readily available and renewable source of materials.

Corrosion is not only dangerous, but also costly, with annual damages in the billions of dollars! If this is difficult to believe, consider some of the direct and indirect effects of corrosion which contribute to these costs: 

Not only that the economic costs are frightening, there is also potential loss of life and damage to the environment problems, which can have widespread effects upon modern industrial businesses. It is essential, therefore, for operators of industrial process plants to have a program for controlling corrosion.

1.1 Literature Review

Corrosion may be defined as a destructive phenomenon, chemical or electrochemical, which can attack any metal or alloy through reaction by the surrounding environment and in extreme cases may cause structural failure. The corrosion occurs because of the natural tendency for most metals to return to their natural state (reverse of metallurgy); e.g., iron in the presence of moist air will revert to its natural state, iron oxide.

Corrosion could be basically carried by water intrusion and some environmental factors. Water intrusion is the principal cause of corrosion problems encountered in the field use of equipment. Water can enter an enclosure by free entry, capillary action, or condensation. With these three modes of water entry acting and with the subsequent confinement of water, it is almost certain that any enclosure will be susceptible to water intrusion. At normal atmospheric temperatures the moisture in the air is enough to start corrosive action. Oxygen is essential for corrosion to occur in water at ambient temperatures. Other factors that affect the tendency of a metal to corrode are acidity or alkalinity of the conductive medium (pH factor), stability of the corrosion products, biological organisms (particularly anaerobic bacteria), Variation in composition of the corrosive medium and temperature. 

1.2 Mechanism of Corrosion

In nature, metals are not found in Free State due to their reactivity. Metals are generally in high energy state because some energy is added during their manufacturing process from the ores. Low energy - state ores are more stable than the high energy – state metals. As a result of this uphill thermodynamic struggle, the metals have a strong driving force to release energy and  go back to their original form. Hence the metals revert to their parent state or ore under a suitable corrosive environment. The electrochemical process involved in corrosion by nature is opposite to the extractive metallurgy involved in manufacturing of the metals. Therefore, corrosion is sometimes considered as the reverse process of extractive metallurgy as can be seen below:

                                                                                                                            

         

                                         

Fig

 

1.0

:

 

The energy cycle of ir

on indicating its extractive metallurgy in reverse

 

                                                     

(

Kahhaleh

et al.

 

1994)

          

 

 


 

            

                                                           

According to electrochemistry, the corrosion reaction can be considered as taking place by two simultaneous reactions:

The oxidation of a metal at an anode (a corroded end releasing electrons) and the reduction of a substance at a cathode (a protected end receiving electrons). In order for the reaction to occur, the following conditions must exist:

          Two areas on the structure must differ in electrical potential.

          Those areas called anodes and cathodes must be electrically interconnected.

          Those areas must be exposed to a common electrolyte.

          An electric path through the metal or between metals be available to permit electron flow. When these conditions exist, a corrosion cell is formed in which the cathode remains passive while the anode deteriorates by corrosion. As a result of this process, electric current flows through the interconnection between cathode and anode. The cathode area is protected from corrosion damage at the expense of the metal, which is consumed at the anode. The amount of metal lost is directly proportional to the flow of direct current.  Mild steel is lost at approximately 20  pounds for each ampere flowing for a year. (Thomas, 1994).

 

                                 

         Figure 1.1:   The Component of an Electrochemical Corrosion Cell

 

 At the anode, metals are oxidized and the electrons are liberated from the metal to form positive     metal ions. The liberated electrons dissolve into the electrolyte, and deposition is formed on the cathodic metal. Anode corrodes while the cathode remains intact.

 

1.3 Forms of corrosion damage

1.3.1 Uniform or thinning corrosion

In this form of corrosion attack, the entire surface of the metal is corroded, and the metal thickness reduced by a uniform amount. This would occur with a homogenous metal when no difference in potential existed between any points on the surface.

1.3.2 Fretting corrosion  

Fretting corrosion occurs when two or more parts rub against each other. The rubbing action removes the corrosion products and exposes new metal to the electrolyte.

1.3.3 Pitting corrosion

This is the most common type of attack that occurs with heterogeneous metals such as steels and other alloys. It is a localized attack, where the rate of corrosion is greater at some areas than at others. This is caused by differences in potential between different points on the metal surface

1.3.4 Galvanic corrosion

Galvanic corrosion occurs where two different metals or alloys come in contact. The severity of galvanic corrosion depends upon the difference in potential between the two metals, and the relative size of the cathode and anode areas

1.3.5 Intergranular corrosion  

Corrosion occurs at the grain boundaries due to a difference in potential between the anodic grain boundaries and the cathodic grains. "Sensitized" stainless steels, where carbides have been precipitated in the grain boundaries during improper heat treatment or in the heat-affected zone of a weld, are particularly susceptible to intergranular corrosion.

1.3.6 Erosion corrosion  

Erosion is the removal of metal by the movement of fluids against the surface. The combination of erosion and corrosion can provide a severe rate of corrosion.

1.3.7 Crevice corrosion  

Crevice corrosion occurs when there is a difference in ion, or oxygen, concentration between the metal and its surroundings. Oxygen starvation in an electrolyte at the bottom of a sharp V-section will set up an anodic site in the metal that then corrodes rapidly.

 

 

 

1.4 Methods of Corrosion Protection  

1.4.1 Application of Protective Coatings  

Metallic structures can be protected from corrosion in many ways. A common method involves the application of protective coatings made from paints, plastics or films of noble metals on the structure itself (e.g., the coating on tin cans). These coatings form an impervious barrier between the metal and the oxidant but are only effective when the coating completely covers the structure.

Flaws in the coating have been found to produce accelerated corrosion of the metal. 

1.4.2 Cathodic Protection  

Cathodic protection using an impressed current derived from an external power supply is a related form of protection in which the metal is forced to be the cathode in an electrochemical cell. For example, most cars now use the negative terminal on their batteries as the ground. Besides being a convenient way to carry electricity, this process shifts the electrical potential of the chassis of the car, thereby reducing (somewhat) its tendency to rust.

1.4.3. Corrosion Inhibitors  

Corrosion inhibitors can be added to solutions in contact with metals (e.g. inhibitors are required in the antifreeze solution in automobile cooling systems). These compounds can prevent either the anode or the cathode reaction of corrosion cells; one way that they can do this is by forming insoluble films over the anode or cathode sites of the cell. Examples of anodic inhibitors are sodium phosphate or sodium carbonate while zinc sulfate and calcium or magnesium salts act as cathodic inhibitors. New forms of paints are being developed which take advantage of similar properties. These paints promise to nearly eliminate corrosion in applications like painted car fenders, etc. 

1.5 Aluminum as a Structural Metal

Aluminum is a silvery white material and a member of boron group. It is the most abundant metal in the Earth's crust, and the third most abundant element therein, after oxygen and silicon. It is soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull grey, depending on the surface roughness. Aluminum is nonmagnetic and non-sparking. It is also insoluble in alcohol, though it can be soluble in water in certain forms. The yield strength of  pure aluminum is 7–11 MPa, while aluminum alloys have yield strengths ranging from 200 MPa to 600 MPa (Toralf, 1999). Aluminum has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, drawn and extruded. Corrosion resistance can be excellent due to a thin surface layer of aluminum oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminum alloys are less corrosion resistant due to galvanic reactions with alloyed copper (Das et al. 2004).  

This corrosion resistance is also often greatly reduced when many aqueous salts are present, particularly in the presence of dissimilar metals.  Aluminum is the most widely used non-ferrous metal (Cock et al, 1999). Having its global production in 2005 as 31.9 million tonnes, It exceeded that of any other metal except iron which was (837.5 million tonnes) (Hethorington et al, 2007). Relatively pure aluminum is encountered only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminum can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrors. When so deposited, a fresh, pure aluminum film serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation. Pure aluminum has a low tensile strength, but when combined with thermo-mechanical processing, aluminum alloys display a marked improvement in mechanical properties, especially when tempered. Aluminum alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio. Aluminum readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to as "aluminum", are actually alloys. For example, the common aluminum foils are alloys of 92% to 99% aluminum. (Millberg, 2010). Aluminum metal and alloys are used in Transportation

(automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.) as sheet, tube, castings etc.  Packaging (cans, foil, etc.), Construction (windows, doors, siding, building wire, etc.) other uses include household items, from cooking utensils to baseball bats, watches. Street lighting poles, sailing ship masts, walking poles etc.  Outer shells of consumer electronics, and also cases for equipment such as photographic equipment.  Electrical transmission lines for power distribution MKM steel and Alnico magnets are all components made from aluminum metal.  Super purity aluminum (SPA, 99.980% to 99.999% Al), are used in electronics and CDs.   Heat sinks for electronic appliances such as transistors and CPUs.  Substrate material of metal-core copper clad laminates used in high brightness LED lighting.  Powdered aluminum is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.

 

1.6 Past work in corrosion inhibition 

The consequences of corrosion are many and the effect of these on the safe, reliable and efficient operation of equipment are often more serious than simple loss mass of a metal. Corrosion can be minimized by employing suitable strategies which retard the corrosion reaction. It is widely accepted that inhibitors especially the organic compounds can effectively protect the metal from corrosion. Several works have been done with compounds containing polar functions on the corrosion inhibition of metals in various aqueous media. Polymer functions as corrosion inhibitor because of their ability to form complexes through their functional group, with metal ions which occupy large area and by so doing blanket the metal surface from aggressive environment.  The practice of corrosion inhibition in recent years has become oriented towards health and safety considerations. Consequently greater research efforts have been directed towards formulating environmentally acceptable organic compounds and polymers as corrosion inhibitors for metals is reviewed.

The use of inhibitor is one of the most dogmatic method employed to tackle corrosion especially in acidic media (Touir et al., 2008). Inhibitors naturally react  physically or chemically with metals by adsorbing on its surface. The adsorption may form a layer on the metal and function as a barrier protecting the metal. The adsorption process, as reported by Emregul and Hayvali (2006), depends on the nature and surface charge of the metal, the chemical structure of the organic molecule, distribution of the charge in the molecule and the aggressive medium. The efficiency of inhibitor may depend on the nature of environment, nature of metal surface, electrochemical potential at the interface and the structural feature of inhibitor, which include number of adsorption centres in the molecule, their charge density, the molecular size and mode of adsorption (Ahamed et al., 2009). The adsorption phenomenon could take place via electrostatic attraction between the charged metal and charged inhibitors molecules and Pi ( ) – electron interaction with the metals (Abdel – Gaber et al., 2009).  A good inhibitor should be easily prepared from low cost raw materials and the organic compound has to contain electronegative atoms such as O, N, P, and S.  Inhibition increases in the sequence:  O < N < S < P. (Musa et al . 2009). These organic compounds function by forming a protective adsorption layer on aluminum surface which isolates the corroding metal from action of corrodent. Organic compounds have been widely used as corrosion inhibitor for aluminum in acid media. Several inhibitors in use is either synthesized from cheap raw materials or chosen from compounds having heteroatoms in their aromatic or long chain carbon system. The influence of such organic compounds on the corrosion of aluminum in acidic solution has been investigated by several researchers (Ebenso,2004; Khandelwal, 2010; Oguzie, 2004). The inhibition property of these compounds is attributed to their molecular structure (Mora-Mendoza et al., 2002). The organic inhibitors decrease corrosion rate by adsorbing on the metal surface and blocking the active sites by displacing water molecules and form a compact barrier film on the metal surface. 

In recent years, natural products such as plant extracts have become important as an environmentally acceptable, readily available and renewable source of materials for wide range of corrosion control. Attention has been focused on the corrosion inhibiting properties of plant extracts because plant extracts serve as incredibly rich sources of naturally synthesized chemical compounds that are environmentally benign, inexpensive, readily available and renewable sources of materials and can be extracted by simple procedures. A lot of works have been reported on the inhibition of acid corrosion of metals using economic plants such as Vernonia  Amydalina (bitter leaf) extracts (Loto, 1998), Zenthoxylum  alatum  plant (Chauhara and Gunasekara, 2006), the juice of Cocos nucifera (Abiola et al., 2002), Fenugreek (Ehteram, 2007), seeds extract of Strychnos nuxvomica (Ambrish Singh et al, 2010), Gossipium hirsutum Liquid extract (Abiola et al., 2009),  Areca catechu (Vinod Kumar et al, 2011). 

 

1.7 Lasienthera africanum (Editan Leaf)

Lasienthera africanum is a low erect or subscandent, vigorous shrub with stout recurved prickles and a strong odour of black currents; Lasienthera africanum has several uses, mainly as an herbal medicine and Plant extracts are used in folk medicine for the treatment of cancers, chicken pox, measles, asthma, ulcers, swellings, eczema, tumours, high blood pressure, bilious fevers, catarrhal infections, tetanus, rheumatism and malaria of abdominal viscera (Mahathi S. 2012).  Lasienthera africanum is found mainly in the humid tropical forest regions of Central African Republic, Cameroon, Gabon, Democratic Republic of the Congo and Angola. In Nigeria, it is mostly found in the southern part of the country (Calabar and Akwa Ibom) and used in preparing special delicacies (editan soup). In this research, there is a shift from the normal medicinal activities of Lasienthera africanum to other function like corrosion inhibitor.

 

 

 

1.8 Aim and Objectives

Aim

The objective of this study is to determine the inhibition efficiency of Lasienthera africanum as a natural corrosion inhibitor.

 

 

Objectives: 

      Investigate the inhibiting effect of lasienthera Africanum towards the corrosion of aluminum sheet in 0.5M and 1.0M HCl solution.

      Determine the rate of corrosion of the aluminum sheet in the presence and absence of these derivatives by weight- loss method (chemical method),  Study the effect of the temperature on the corrosion rate  Determine percentage inhibition.

 

 

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