ABSTRACT
The present study examined the adsorption and corrosive inhibitive properties of neem root on mild steel in alkaline and acidic media. The objectives of the study were to extract liquid from Azadirachta indica (neem) root; inhibit the corrosive mild steel in H2SO4 and NaOH solutions and examine the effects of inhibitor and corrodent concentration on inhibitor efficiency. The neem root was obtained from the neem trees in Michael Okpara University of Agriculture, Umudike. The stock solution of the extract obtained was used in preparing 0.5N, 1.0N H2SO4 and NaOH for mass loss method and 3N, 4N, and 5N H2SO4 and NaOH for thermometric analysis, respectively. The weight loss experiment was carried out at 30 and 600C. The result showed that the corrosion rate was found to increase with increase in the corrodent concentration and also with increase in temperature. The extract from the neem root was found to be an inhibitor for mild steel in 0.5 M H2SO4 and NaOH. However, the metal was found to corrode faster in NaOH than in H2SO4 solution. Inhibition efficiency increased with increase in inhibitor concentration. It was therefore recommended that natural plant extracts such as neem root extract can be utilized as a corrosion agent against corrosion in both acidic and alkaline environment.
TABLE OF CONTENTS
Cover page
Declaration i
Certification ii
Dedication iii
Acknowledgment iv
Table of contents v
List of tables vii
List of figures viii
Abstract ix
CHAPTER ONE
INTRODUCTION
1.1 Background of Study 1
1.2 Statement of problem 3
1.3 Aim and Objectives of Study 4
1.4 Justification of Study 4
1.5 Scope of the Study
CHAPTER TWO
LITERATURE REVIEW
2.1 Corrosion 6
2.2 Corrosion Inhibitors 6
2.3 Plant based corrosion inhibitors 8
2.3.1 Solvent effect 10
2.3.2 Temperature and Immersion time effect 11
2.3.3 Adsorption mechanism 12
2.4 Extraction 12
2.4.1 Inhibitors Extraction 16
CHAPTER THREE
MATERIALS AND METHODS
3.1 Materials 19
3.2 Extraction 19
3.3 Gasometric method 19
3.4 Thermometric method 20
3.5 Gravimetric method (weight loss experiment) 21
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1. Effect of corrodent concentration 22
4.2. Effects of inhibitor concentration on inhibition efficiency 24
4.3. Products composition of Pyrolytic oil 33
4.4. Higher Heating value of Char 33
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 Conclusion 29
5.2 Recommendation 29
REFERENCES
LIST OF TABLES
Table 4.1: Values of corrosion rate (mpy), inhibition efficiency (I %) and degree of surface coverage (θ) for mild steel corrosion for neem root in 0.5 M H2SO4 at 30 oC and 60oC 25
Table 4.2: Values of corrosion rate (mpy), inhibition efficiency (I %) and degree of surface coverage (θ) for mild steel corrosion for neem root in 0.5 M NaOH at 30 and 60oC 26
LIST OF FIGURES
Figure 2.1. Basic parts of a plant and their common active compounds 10
Figure 2.2 Diagrams of common extraction methods 14
Figure 3.1a: Mild steel coupons before adsorption 21
Figure 3.1b: Mild steel coupons after adsorption 21
Figure 4.1a: Plot of corrosion rate against corrodent concentration for mild steel corrosion in H2SO4 at 300C and 600C 23
Figure 4.1b: Plot of corrosion rate against corrodent concentration for mild steel corrosion in NaOH at 300C and 600C
Figure 4.2a: Plot of weight loss against time for mild steel corrosion in 0.5 M H2SO4 in the absence and presence of extract at 300C
Figure 4.2b: Plot of weight loss against time for mild steel corrosion in 0.5 M H2SO4 in the absence and presence of extract at 600C
Figure 4.3a: Plot of inhibition efficiency (% I) against extract concentration for mild steel in H2SO4 at 300C and 600C
Figure 4.3b: Plot of inhibition efficiency (% I) against extract concentration for mild steel in H2SO4 at 300C and 600C
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Metals are widely used in human activities due to their excellent mechanical and electrical properties (Parthipan et al., 2018). In order to preserve the desired state of these metals, their preventive maintenance is a priority. Corrosion is probably the most common undesired phenomenon that leads metals to become weaker (Zhu et al. 2020). This natural process originates from the electrochemical interaction of metals with the corrosive environment. Sulfides, oxides, and others are generated through reactions between the metal surface and the corrosive medium (El Ibrahimi et al. 2020).
Among metals, mild steel is the most widely used in the oil, food, energy, chemical, and construction industries due to its different applications, most of which are based on its excellent mechanical properties (Alan and Araceli, 2020). This metal shows high mechanical resistance, durability, and toughness, among others, which makes it a highly available material and at a relatively low cost. The high cost associated with corrosion, due to the replacement of rusted metals, can be reduced by using corrosion inhibitors (Ladan et al. 2017).
Corrosion is a natural process in which metals and alloys attempt to return to their more stable thermodynamic state as a result of chemical attack or reactivity with their surroundings. In other words, metals, with the exception of platinum and gold, are found in nature in impure forms, mainly as oxides or sulfides, which are stable. In most processing techniques, energy is consumed to obtain pure metals, causing the pure metals to be in a higher energy state compared to their ore (Zakeri et al. 2022). As a result, metals corrosion is the simplest and fastest way to reach their most stable state. Corrosion can also be triggered by natural or man-made causes. In general, metals corrosion is described as the natural and inevitable loss of desired metal characteristics due to interaction with particular elements present in the environment. Corrosion is proven to be hazardous to both the environment and human health (Salleh et al. 2021).
Corrosion reactions are frequently electrochemical in nature. The hydrogen evolution and the oxygen reduction are the two most prevalent reactions that keep a corrosion process progressing in acidic media and neutral/alkaline environments, respectively (Zakeri et al. 2022). The use of corrosion inhibitors (CIs) is one of the most economical and convenient of these approaches to implement. The CIs are substances that, when added in small concentrations in a corrosive media, can reduce the rate of metal degradation (Verma et al. 2021).
In many industrial operations, the addition of inhibitors to process fluids to minimize the rate of metal corrosion is very common. Chemicals are usually applied on metal surfaces as part of the final finishing procedures prior to plating, painting, or storage (Bentiss et al., 1999). According to Patricia et al. (2017), the chemicals are capable of removing scales, soil and light rust from the metal surfaces. Apart from this, they often contained about 1 % organic corrosion inhibitors by volume of the acid such as hydrochloric acid. Synthetic inhibitors have been widely applied to protect metal surfaces against corrosion (Markhali et al., 2013). However, these inhibitors are toxic, expensive with environmental and safety issues. Alternative sources including natural products, extracts from plants, and other environmental benign organic sources have been widely reported (Sharma et al., 2015).
Many organic compounds have been tested for corrosion inhibition. The functionality of these compounds has been attributed to their electronegative functional groups and presence of π electrons in triple or conjugated double bonds. They also contain nitrogen, sulphur or oxygen atoms in their structures. Their mode of operation is by physical or chemical interactions between their molecules and the metal surfaces (Patricia et al., 2017). Several plant extracts including an extract from Carica papaya, Rosmarinus Officinalis, Damsissa, Murrayakoenigii, cashew, mango, Uncaria gambir and Fiscusycomorus had been investigated (Hussain and Kassim, 2011; Ogwo et al., 2017; Ogunleye et al., 2018).
According to Helen et al. (2014), these plants possess adequate cyclic organic phytochemicals, nitrogen, sulphur and oxygen atoms that are responsible for their inhibition properties. The large scale synthesis of various natural plant extract is faced with many challenges. The chief of which is the isolation of specific components of the plant extract with inhibitory characteristics. Nevertheless, many natural plant extracts have proven efficient as corrosion inhibitors (Kamal and Sethuraman, 2012; Yaro et al., 2013). Therefore, this present study seeks to evaluate the adsorption and corrosive inhibitive properties of some naturally occurring plant extracts in alkaline and acidic media
1.2 Statement of Problem
Industries depend heavily on the use of metals and alloys. One of the most challenging and difficult tasks for industries are the protection of metals from corrosion. Corrosion control of metals and alloys is an expensive process and industries spend huge amounts to control this problem. Corrosion damage can be prevented by the use of corrosion inhibitors (De Souza and Spinelli, 2009), which is the best to prevent destruction or degradation of metal surfaces in corrosive media. The use of corrosion inhibitors is the most economical and practical method in reducing corrosive attack on metals. A number of synthetic compounds are known to be applicable as good corrosion inhibitors for metals. Nevertheless, the popularity and use of synthetic compounds as a corrosion inhibitor is diminishing due to the strict environmental regulations and toxic effects of synthetic compounds on human and animal life.
Consequently, there exists the need to develop a new class of corrosion inhibitors with low toxicity, eco-friendliness and good efficiency. The study of plant extracts as low cost, eco-friendly corrosion inhibitors is of interest from an environmental perspective and is attracting a significant level of attention as various researchers have reported on the successful application of extracts from plant as corrosion inhibitors for mild steel in highly acidic solutions and the possible mechanisms of the process. The present investigation continues to focus on the broadening application of plant extracts for metallic corrosion control and describes the inhibiting effect of root extracts of Azadirachta indica (neem) on mild steel corrosion in acidic and alkaline media.
1.3 Aim and Objectives of the Study
The aim of this study is to examine the adsorption and corrosive inhibitive properties of some naturally occurring substance in alkaline and acidic media.
The objectives of the study were to;
i. extract liquid from Azadirachta indica (neem) root
ii. inhibit the corrosive mild steel in H2SO4 and NaOH solutions
iii. examine the effects of inhibitor and corrodent concentration on inhibitor efficiency
1.4 Justification of the study
This study has dual purpose; first to further establish the effectiveness of plant extracts as corrosion inhibitors and next to attempt deduction of the inhibition mechanism. Such methods have traditionally been used as the starting point for investigating the mechanisms of inhibiting additives for paints and surface coatings.
1.5 Scope of the Study
To gain insight on the working and applicability of natural extracts for commercial purposes, inhibition mechanism and adsorption process were investigated on a pilot scale. The extract, after careful extraction under controlled temperature, were utilized for corrosion inhibition in both acidic and alkaline media.
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