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 


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 

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 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 

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 


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. 



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