TABLE OF CONTENTS
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:
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).
Fig 1.0: The energy cycle of
iron indicating its extractive metallurgy in reverse (Kahhaleh et al. 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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