The corrosion inhibition of n-hexane extracts of Costus spectabilis leaves in 1M hydrochloric acid solution was studied using weight loss method at 303K and 313K. The result obtained showed that Costus spectabilis leaves extract inhibited the corrosion of aluminum in a solution of HCl and KBr with maximum efficiency of 95.06% in 1.0 g/L at 313K.  The result also reveals increase in temperature increases the corrosion rate and decreases inhibition efficiency, while increase in concentration of the inhibitor decreases corrosion and increases inhibition efficiency.

Keywords: Costus spectabilis leaves, Corrosion, Efficiency, Inhibition, Aluminum, Temperature.


Title page - - - - - - - - - - i

Cover page - - - - - - - - - - ii

Certification - - - - - - - - - - iii

Dedication - - - - - - - - - - iv

Acknowledgements - - - - - - - - - v

Abstract - - - - - - - - - - vi

Table of Contents - - - - - - - - - vii

List of Tables - - - - - - - - - viii

List of Figures - - - - - - - - - ix


1.1.         Types of corrosion - - - - - - - - 1

1.1.1.       Pitting corrosion - - - - - - - - 1

1.1.2.        Auto corrosion - - - - - - - - 2

1.1.3.        Externally induced corrosion - - - - - - 2

1.1.4.        Crevice corrosion - - - - - - - - 2

1.1.5.         High temperature corrosion - - - - - - 2

1.2.             Causes of corrosion - - - - - - - 3

1.3.            Corrosion materials - - - - - - - 3

1.4.              Methods of combating corrosion - - - - - 3

1.4.1.           Corrosion media - - - - - - - - 3

1.5.           Preventive measures - - - - - - - 4

1.6.            Corrosion inhibitors - - - - - - - 4

1.7.             Costus spectabilis - - - - - - - 5

1.8.           Aim and objectives of the project - - - - - - 7



3.1.    Collection of materials - - - - - - - - 13

3.1.1.   Aluminum sheet - - - - - - - - 13

3.1.2.   Reagents - - - - - - - - - 13

3.2.    Equipment - - - - - - - - - 13

3.3.    Preparation of  Costus spectabilis leaves extract. - - - - 14

3.4.     Weight loss method - - - - - - - - 14

3.4.1.    Corrosion rate - - - - - - - - - 15

3.4.2.     Inhibition efficiency - - - - - - - - 15

3.5.        Preparation of 1M HCl solution - - - - - - 15


4.1.    Corrosion of aluminum in 1M HCl solution containing Costus spectabilis 

extract  and KBr at 303K.-------17

4.2.      Corrosion of aluminum in 1M HCl solution containing 

Costus spectabilis extract and KBr at 313K-----18

4.3.     Weight loss measurement, corrosion rates and inhibition efficiency - 21


5.1.        Summary - - - - - - - - - 22

5.2.        Conclusion - - - - - - - - - 22

5.3.         Recommendation - - - - - - - - 22

REFERENCES - - - - - - - - 23

                                               CHAPTER ONE 

1.0.                                       INTRODUCTION 

        Corrosion is one of the major problems in several technical installations involving metals and alloys Hence; prevention mechanism for corrosion of metals is of paramount importance to increase their lifespan especially those in aggressive environments. Corrosion of mild steel is a major problem in some industries with its environment (Rani and Basu, 2012).Corrosion is a natural process, which converts a refined metal to a more stable form such as its oxide, hydroxide or sulfide.  It is the gradual destruction of materials (usually metals)  by chemical and /or electrochemical reactions with their environment ( Breakell et al.,  2005). Corrosion is a natural process that reduces the binding energy in metals with the end result involving a metal being oxidized as the bulk metal loses one or more electrons (Chinwko et al., 2014). Throughout the ages, plants have been used by human beings for their basic needs such as shelters, production of food stuffs, fertilizers, flavors and fragrance, clothing, medicines and last but not the least, as corrosion inhibitors ( Benali et al. 2013).

1.1.      Types of corrosion 

1.1.1.      Pitting corrosion

      This occurs under certain conditions, and leads to accelerated corrosion in certain areas rather than uniform corrosion throughout the piece such conditions include low concentrations of oxygen or high concentration of chlorides (anions)  that interfere with the alloy's ability to reform a passivating film.  In the worst cases, most of the surface remains protected, but tiny fluctuations degrade the film in a few critical areas.  Corrosion at these points is amplified and cause pits. 

1.1.2.      Auto corrosion

            This is that which occurs when a metal is in contact with an electrolyte but is not at the same time in contact with any other electrical conductors, neither metallic or non-metallic. In the classic case of chemically pure iron, corrosion would proceed simply by the exertion of the solution pressure by hydrogen ions and the oxygen dissolved in the electrolyte, which depolarizes the metal surface oxidizes and precipitates the primary products of solution as ferrichydrate or rust.

1.1.3.      Externally induced corrosion

           This is the result of the passage of a current generated from some external source through the metal which the latter is in contact with an electrolyte. If the current flows in that direction which necessitate the metal acting as anode, then corrosion results.If the current flows in the opposite direction ie from the electrolyte into the metal, the latter receive protection from corrosion, which may be complete, provided the electromotive force  of the current is sufficiently high ( Alan and Ernest, 1923).

1.1.4.       Crevice corrosion

              This occurs in confined spaces where access of fluid from the environment is limited such as gaps and contact areas between parts, under gaskets or seals, inside cracks and seams and spaces filled with deposits.

1.1.5.        High temperature corrosion

            This is deterioration of a metal due to heating. This can occur when a metal is subjected to a hot atmosphere in the presence of oxygen, sulfur, or other compound capable of oxidizing the material.

1.2.        Causes of corrosion

        Any of or all of these can cause corrosion; Reactivity of metal, presence of impurities, presence of air, moisture gases CO, presence of electrolytes.

1.3.       Corrosion materials.

           They are the materials which are the cause of corrosion, they are toxic in nature, they have very harmful effects as they have a tendency to attack metals and destroy their strength, they also affect the human body, especially tissues, some acids and bases are included in that; example hydrochloric, nitric and sulfuric acid and bases like hydrochloric and ammonia.

1.4.        Methods of combating corrosion

          There are basically two methods of combating corrosion, this include corrosion media and corrosion protection.

1.4.1.          Corrosion media

i.                 Neutral medium

Metal corrodes when exposed to air, the extent of this corrosion depends on the degree of humidity content in the atmosphere. The product usually is a film which covers the metal surface.

2Fe + 3H2O + O2               2Fe (OH) 3

ii.          Acidic medium

       Not all metals corrode in acidic medium e.g Gold does not react at all in an acidic medium, but iron and zinc corrodes easily in an acidic medium with evolution of hydrogen gas.

  Fe + 2HCI           Fecl2 + H2

 Zn + 2HCl             ZnCl2   + H2

 iii.       Alkaline medium

      Corrosion in an alkaline medium results first in the formation of metal hydroxide which dehydrates (possibly) to give an oxide of aluminum.

1.5.       Preventive measures

i.     use of the right metal in the right way in the right place.

ii.     urotective coatings, paints, enamels, other metals, oils, greases etc.

iii.   designs of hydraulic systems to avoid excessive velocities or localized corrosion.

iv.    inhibitors that is, compounds added to the environment in small concentration to form protective films, which increase anodic or cathodic polarization or both or neutralize some corrosion constituents.

v.   removal of dissolved oxygen or other corrosion gases by "deaerators" or the addition of chemicals to react with oxygen (oxygen scavengers).

vi.   neutralizing agents added to adjust acidity or alkalinity to the desired level.

vii.   drying of air or other gases to keep humidity below the  level where corrosion can occur.

viii.   heat- treating metals to leave them in optimum conditions to resist corrosion.

1.6.     Corrosion  inhibitors.

   An inhibitor is a substance which retards or slows down a chemical reaction.  Therefore, a corrosion inhibitor may be defined as a substance which when added in a small concentration to an environment effectively reduces the corrosion rate of metal exposed to that environment. ( Rubin, 1989). 

              Inhibitors can be considered as negative catalyst and their use is a common practice in a number of fields. For an effective inhibition, inhibitors in small amounts can minimize undesirable changes which may become severe if uncontrolled.  They fall in two general classes namely; 

i.     Substances which show a "preferential wetting" effect, that is to say, the inhibitor will wet the surface of the metal easier than the solution therefore, the inhibitor will spread over the surface of the metal effectively to keep the solution from attacking it 

ii.    Substances which either stabilize the natural protective coatings on the metal or  reacts with the metal to form a coating.  For example, if the metal has a tendency to form an oxide film, then a solution which has a small amount of oxidizing materials in it such as a dichromate will allow oxide film to persist, thereby protecting it against corrosive action.  The corrosion of iron and steel is of fundamental industrial and academic concern that has received a considerable amount of attention.  Hence, slowing down or completely inhibiting corrosion has been an intensive field of interest. One of the greatest ways of dealing with this problem is based on the use of chemicals as inhibitors in the media ( Karakus et al., 2005).

              The use of chemical inhibitors to decrease the rate of corrosion processes is quite varied in the oil extraction and processing industries inhibitors have always been considered the first line of defense against corrosion (Koan et al., 2006).

1.7.        Costus spectabilis 

        Costus spectabilis, commonly known as the yellow trumpet, is an African gregarious species of herb; low and perennial. It is found from Sierra Leone to Sudan to as far south as Angola and it is found also in Nigeria. Costus spectabilis is a herbaceous perennial plant. It flowers several weeks before the leaves appear.The plant is sometimes harvested from the wild for local use of its edible leaves. It is often grown as an ornamental in gardens

Figure 1.1    Costus spectabilis leaves

Scientific classification 

Kingdom: Plantae

Clade: Tracheophytes

Clade: Angiosperms

Clade: Monocots

Clade: Commelinids

Order: Zingiberales

Family: Costaceae

Genus: Costus

Species: C. spectabilis

It produces four large (12 x 12 cm), fleshy leaves which lie flat on the ground and form a basal rosette. They are glabrous above and pubescent below, especially along the midrib. The leaf margin is entire, often with an edging of purple-pink. The inflorescence is terminal, growing from the center of the rosette. The flowers are showy, yellow, and open singly and die rapidly, but are immediately followed by another. The species becomes dormant during winter, shrinking to a centipede-like rhizome without roots. In spring it produces paddle-shaped leaves that appress to the soil when fully formed, similar to water-lily pads. The abaxial leaf surface has a spongy white texture. Flowers are bright yellow with a crisped margin, and some 9 cm across, with a large staminodial labellum, and resembling those of a pumpkin. The texture of the flower is soft and thin. Costus spectabilis is a rhizomatous geophyte used by traditional medicine to treat internal and external wounds, coughs, inflammation, arthritis, rheumatism, fever, maternal and neonatal infections. It is also recommended for its laxative, purgative, diuretic and ichthyotoxic properties.

1.8.          Aims and objectives of the project 

1.     To study the corrosion inhibitive effect of Costus spectabilis leaves extract and KBr on aluminum in HCl.

2.       To contribute to the growing chain of inhibitors and monitoring their inhibitory effects on aluminium in HCl using weight loss method. 




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