CORROSION INHIBITION OF ALUMINUM IN ACIDIC MEDIUM BY BAMBOO LEAVES EXTRACT

ABSTRACT

The inhibitive effects of bamboo leaves extracts (BLE) on the corrosion of aluminum in 1M HCl were studied using weight loss, adsorption, thermodynamics  and kinetic  studies. The phytochemical  constituents  of the  BLE  were  tannins,  polyphenols,  flavonols,  terpenoids, sterols and alkaloids.  BLE was noted to contain  more of the  polyphenols  and terpenoids which were largely responsible for the inhibitive action of the extracts. Results obtained from the experiments carried out at 303K and 333K revealed that, the corrosion rate decreased as the concentration of BLE increased. The inhibition efficiency increased as the concentration of BLE increased at 333K. As the temperature increased from 303K to 333K, the corrosion rate increased  significantly.  The adsorption parameters  showed  that the adsorption  of the BLE conformed  perfectly  to the Langmuir,  Temkin and Freundlich  adsorption  isotherms, with the Langmuir isotherm being the best model with R2  = 0.992. The negative values of Gibbs  free  energy  indicated  that  the  reaction  was  spontaneous  and  the  mechanism  of adsorption was electrostatic  (physical) adsorption mechanism since the negative  values of ΔG°ads were lower than -20 kJ/mol. The values of activation energy, Ea, being lower than 80 kJ/mol, also confirmed a physical adsorption mechanism. The values of heat of adsorption being   lower   than   40   kJ/mol,   also   confirmed   that   the   adsorption   mechanism   was physisorption. The positive values of heat of adsorption, Qads indicated that the reaction was endothermic.  The  small  values  of  adsorption  equilibrium  constant,  Kads   indicated  low interaction between the adsorbed molecules and the metal surfaces and thus the extracts were physically adsorbed on the metal surfaces. The reaction showed a first order kinetics, since the plots of log Wf vs Time were linear for all the concentrations of the extracts. The increase in half-life as the  concentration  of the extract  increased  indicated  more protection  of the metals by the BLE.

CHAPTER ONE INTRODUCTION

1.1      BACKGROUND OF THE STUDY

Acid solutions are widely used in various industries for pickling and descaling of metals after most industrial processes involving direct use of metals and processes which are  normally accompanied  by considerable  dissolution of the metal due to the aggressive  nature of the acids solutions. A huge amount of money is spent each year as a result of metallic corrosion, an estimated loss of 276 USD or equivalent to 3.1 percent of the United States GDP.[1]

To protect the metals against acids attack, the use of inhibitors is strongly recommended, as even small concentrations  can decrease the corrosion rate of the metal surface.[2][3][4]  Over time, organic compounds have been employed  as corrosion inhibitors for metals  in acidic

media. These inhibitors are either synthesized from cheap raw materials or from inorganic and  organic  compounds  having  hetero  atoms  in  their  aromatic  or  long  chain  carbon system.[5][6]   A  number  of  organic  compounds  are  known  to  be  applicable  as  corrosion

inhibitors for metals in acidic environments. Such compounds typically contain elements of

high electron density such as nitrogen, oxygen or sulfur, in a conjugated  system.[7]  These compounds function via adsorption of the molecules on the metal surface, creating a barrier to corrodent attack. The adsorption bond strength is dependent on the  composition  of the metal and corrodent, inhibitor structure and concentration as well as temperature.[8]  Despite the broad spectrum of organic compounds, the choice of appropriate inhibitor for a particular application is restricted to several factors. These include increased environmental awareness and the need to promote environmentally friendly processes. Another factor is the vast variety of possible corrosion systems coupled with the specificity of action of most acid inhibitors which often necessitates the use of combinations of additives to provide the multiple services

required for effective corrosion inhibition.[9]  Though many synthetic organic compounds can adsorb on metal sheet and show good anti-corrosive activity, they are highly toxic and cause severe hazards to both human beings and the environment.[5][10]  The toxicity may manifest either during the synthesis of the compound or during its application as these inhibitors may

cause reversible (temporary) or irreversible (permanent) damage to organ system viz, kidney, liver, or disturb a biochemical process and enzyme system at some site in the body.[10]  The safety and environmental issues of corrosion inhibitors arisen in industries have always been

a global concern.

Consequently, there exists the need to develop a new class of corrosion inhibitors with low toxicity  and  good  efficiency.   In  an  attempt  to  find  corrosion   inhibitors   which  are environmentally  safe and readily available,  there has been a growing trend  in the use of natural products such as leaves or plant extracts as corrosion inhibitors for metals in acid cleaning process.[11]

The exploration  of natural products  of plant origin as inexpensive  eco-friendly  corrosion inhibitors is an essential aspect of research. In addition to being environmentally friendly and ecologically acceptable,  plant products are low-cost,  readily available,  biodegradable,  non toxic and renewable sources of materials, and they are widely used as corrosion inhibitors for the protection of metals in acid and alkaline  environment.  The extracts from their leaves, barks,  seeds,  fruits  and  roots  comprise  of  mixtures  of  organic  compounds  containing nitrogen,  sulfur and oxygen atoms  and  some have been reported  to function  as effective

inhibitors of metal and alloy corrosion in different aggressive environments.[12][13][14][15][16][17]

Through these studies, it is agreed that the inhibition performance of plant extract is normally ascribed  to  the  presence  in their  composition,  complex  organic  species  such  as  tannins, alkaloids and nitrogen bases, carbohydrates, amino acids and proteins as well as hydrolysis

products.[18]

Thus,  recently,  researchers  are  focusing  on  natural  products  as  corrosion  inhibitor,  and therefore,  this  research  work  is  in support of the use of extracts  of natural  products  as corrosion inhibitors in industrial processes.

1.2      STATEMENT OF THE PROBLEM

Corrosion of metals and alloys particularly in acidic media is a known industrial problem. Acidic solutions which are widely used for pickling, cleaning, descaling and etching of the metals, also tend to contribute to the corrosion of metal surface. Because of this problem, various organic and inorganic inhibitors have reportedly been used with these acidic solutions to reduce the corrosion effect on these metals and have been effective. But these inhibitors tend to be toxic, expensive and not readily available, hence there is a need for an eco-friendly and inexpensive inhibitors which are readily available; and plant products are preferred for use. Hence, this study seeks to study the effect of bamboo leaves extracts on the corrosion inhibition of aluminum in acidic medium.

1.3      JUSTIFICATION OF THE STUDY

Several studies have been carried out on the corrosion inhibition properties of several plants in various media both acidic and basic. Some of those plants include; red  onion  skin,[19] euphobia  hirta,[20]   fig  leaves,[7]   ficus  abutilifolia,[10]    limonium  thouinii,[21]   chenopodium ambrosioides,[22]  monsoa allicea,[23]  azadirachta indica,[6]  and African bread fruit leaves.[24] Some work have also been carried out on the use of bamboo leaves as corrosion inhibitors, but very few work have clearly stated the factors responsible for the inhibitive action of these extracts. This study therefore supports the use of extracts of natural product (bamboo leaves in this case) as corrosion  inhibitors  and seeks to find out the factors responsible  for the

inhibitive action of the BLE.

1.4      AIMS AND OBJECTIVES OF THE STUDY

The aim of this study is to study the effect of Bamboo Leaves extracts on the  corrosion inhibition of aluminum in the acidic medium.

The objectives of this study include;

1. To study the effect  of the  various concentration  of the bamboo  leaves  extract on  the corrosion inhibition.

2. To study the effect of immersion time on corrosion inhibition.

3. To study the effect of temperature on corrosion inhibition.

4. To study the adsorption of the bamboo leaves extracts on the aluminum through adsorption isotherm.

5. To carry out the thermodynamics and kinetic studies of the extract – aluminum reaction.

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