DETERMINATION OF THE INHIBITION EFFICIENCY OF LASIENTHERA AFRICANUM AS A NATURAL CORROSION INHIBITOR
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
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 heat-
transfer 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
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 iron indicating its extractive metallurgy in reverse
(Kahhaleh et al. 1994)
According to electrochemistry, the corrosion reaction can be considered as taking place by two
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
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
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
The objective of this study is to determine the inhibition efficiency of Lasienthera africanum as a
natural corrosion inhibitor.
· 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..