Potentials of Extracts of African Star Apple and Cock’s Comb Leaves as Corrosion Inhibitors for Medium Carbon Low Alloy Steel in Acidic Media

Potentials of Extracts of African Star Apple and Cock’s Comb Leaves as Corrosion Inhibitors for Medium Carbon Low Alloy Steel in Acidic Media

CHAPTER ONE

Aim and Objectives of the Research

The aim of this research is to assess the suitability of utilizing extracts of Chrysophyllum albidium and Heliotropium indicum leaves as corrosion inhibitors of medium carbon low alloy steel in 1M HCl and 1M H₂SO₄environments.

While the specific objectives of the research are to:

Assess the biodegradability limits of formulated and standard Shell Ensis SX inhibitors using OECD Marine BOD
Carry out corrosion tests on medium carbonlow alloy steel using gravimetric basedmass loss and linear resistance polarization techniques in the presence and absence of the formulated and standard
Carry out mechanical tests and microstructural examination on the low alloy steel before and after corrosion test.

CHAPTER TWO

LITERATURE REVIEW

CORROSION

Corrosion is the degradation of a material caused by environmental interaction (Revie and Uhlig 2008). It is a continuous and costly problem that encompasses both naturally occurring and man- made materials such as metals, plastics, rubber, and aggregates such as concrete, composites materials; and woods.

The Nature of Metallic Corrosion

Corrosion is an electrochemical reaction which is caused by the flow of direct electrical current (d.c.). The electrochemical reaction is destructive in nature caused by the flow of direct electrical current (d.c.), and involves anodic and cathodic reaction. The anode is the part of the metal surface that corrodes – that is, the metal that dissolves in the electrolyte with loss of electrons which is called oxidation (2.1). The oxidation causes the actual metal loss but the reaction, maintaining charge neutrality. Otherwise, a large negative charge would rapidly develop between the metal and the electrolyte and the corrosion process would cease.

Fe → Fe²⁺ + 2e^– (2.1)

Where 2.1 is the anodic reaction for corrosion of iron in water (Fig. 2.1), Iron ion goes into solution and the two electrons are left behind in the metal.

The cathode is that portion of the metal surface that does not dissolve. It is the site where electrons generated as the iron dissolves at the anode travel through the metal to the cathodic surface area. There are two primary reactions possible at the cathode, the “hydrogen evolution reaction” and the “oxygen absorption reaction.” Other reactions are possible but are encountered less often. In the hydrogen evolution reaction, the electrons combine on the surface of the metals with hydrogen ions in the electrolyte to form hydrogen molecules, which escape as gas bubbles (2.1 and 2.3). If, as is usually the case, dissolved oxygen is present in the water, another cathodic reaction can occur, the reduction of oxygen: This consumption of electrons is called a reduction reaction and is as follows:

2H⁺+ 2e^– → H₂ (2.2)

¹⁄₂ O₂ + H₂O + 2e→2OH- (2.3)

As would be expected, increasing the amount of dissolved oxygen increases the corrosion rate of iron. However, at very high dissolved oxygen concentrations, the corrosion rate drops to a very low value. This surprising drop is the advent of the phenomenon called “passivity”, a specific form of “polarization”.

Passivity is as a result of a thin invisible protective film formed on metal surface either metal oxide, insoluble salt or chemisorbed oxygen, preventing further contact with the electrolyte. In the case of iron, when more oxygen reaches the metal surface than can be used in the cathodic reaction, a protective passive film will be form. A temporary passive iron oxide film is also formed when iron is immersed in concentrated nitric acid. More permanent films are formed on aluminum, titanium and stainless steels and chromium bearing nickel alloys.

In practice, a metal often shows a high initial rate of corrosion. However, in general, the rate often diminishes with time. This effect, known as polarization, might be defined as the change from open-circuit electrode potential as the result of the passage of current. Polarization may result from reactions at either the anode or the cathode. Polarization may result from reactions at either the anode or the cathode.

Anodic polarization – In some corrosion reactions (e.g. iron in aerated water) the corrosion rate diminishes due to an accumulation of insoluble corrosion products which become somewhat protective of the iron anode. This phenomenon, anodic polarization, is defined as the change of the electrode potential in the noble (positive) direction due to current flow. Other examples of anodic polarization are iron or non-alloyed steel exposed to concentrated nitric, sulfuric and phosphoric acids.

Cathodic polarization – Conversely, polarization can result from reactions at the cathode. For example, when iron is immersed in non-aerated neutral water, the absence of dissolved oxygen permits development of an adsorbed film of hydrogen which likewise reduces the corrosion current. This is known as cathodic polarization and is defined as the change in the electrode potential in the active (negative) direction due to current flow.

CHAPTER THREE

MATERIALS AND METHODS

Materials: The materials used for this research work are listedbelow:
19mm medium carbon low alloy steel rod
Aerial parts of Chrysophyllum albidium and Heliotropium indicumplants
5 litres each of Fishers certified (UK) Hydrochloric and sulphuric acids
60cl Shell Ensis Fluid SX and 85 litres Distilled water
5 litres of Acetone and 7.5 litres of Ethanol (BDHgrade)
Equipment: The equipment used for this research work includes:
Emission Optical Spectrometer
Nikkon Metallurgical Microscope (Model: NJF-20A)
Soxhlet Apparatus
Scanning Electron Microscope
Ultraviolent-visible Spectrometer (Model: HitachiF-4500)
Shimadu Fourier Transform Infrared Spectrophotometer (Model: 8400S)
Digital pH meter (Model:pHS-25)
Brooks Universal Hardness Tester (Model: CRBD)
Izod Impact tester (120 Foot pound)
Hounsfield Tensometer (20KN)
Automated Digital Viscometer (Model: KV DV-1)
Potentio stat equipped with platinum electrode (Model:P-50)
Polishing Machine
Incubator and Muffle Furnace
Digital top loading Balance (MettlerP-160N)
Vacuum Rotary Evaporator

METHODS

Design of Experiment

Experimental design for plants and number of specimen used in the research work is as follows: Table 3.1: Summary of the notations adopted for experimental design.

CHAPTHER FOUR

RESULTS AND DISSCUSION

Chemical analysis of As-received Low Alloy Steel

CHAPTER FIVE

CONCLUSION ANDRECCOMENDATION

Conclusion

This work encompasses biochemical extraction and characterization of two plant extracts, formulation of the produced extracts into inhibitors and testing the formulated inhibitors for the protection of low alloy steel in H₂SO₄ and HCl media. Based on the results obtained the following conclusions could be drawn:

Phytochemical screeningof the plant leavesshow presence ofphytochemical constituents such as saponins, tannins, alkaloids and flavonoids, in these orderupto percent values for Chrysophyllum albidium (CA) as 16.65%, 1.65%, 0.62% and 86.44% while Heliotropium indicum (HI) has 24.90%, 2.05%, 1.04% and 96.25% respectively, which are a good indicator that they can be used as corrosion
Physico-chemical properties of the two plant extracts showed that they are slight acidic, non-toxic, biodegradable hence environmental friendly. The formulated plant extracts attained upto 95 percent biodegradation while standard Shell Ensis SX (SE) gives 62 percent extent of biodegradation as established in the OECD marine BOD
The gravimetric basedmass loss experiments showed decreased corrosion rates with increase in inhibitors concentration and exposure time. Potentiodynamic studies showed higher value of inhibition efficiencies percent of 98.2% (CA), 96.0% (HI) and 96.2% (SE)obtained informulated inhibitors at ambient temperature; however this could not be reproduced during gravimetric based mass loss experimentdue its environment dependent nature of this
The inhibition efficiencies were observed to increase with increase in concentration of inhibitors for both gravimetric basedmass loss experiments and electrochemical measurements.
Potentiodynamic polarization curves reveal that the two plant extracts affected both anodic and cathodic processes, i.e., these are mixed-type
The adsorption of the inhibitors onto the steel surfaces is an endothermic process, and in the process both physical and chemical adsorption takes place and are best described by Langmuir absorption isotherms obtained from the kinectic

Recommendations

Potentio dynamic polarization studies of the action of the inhibitors invaryingH₂SO₄and HCl acid concentrations at elevated temperature is recommended so as to verify the kinetic and thermodynamic models arrived at in this work.
The extracts of Chrysophyllum albidium and Heliotropium indicum will serve as effective and eco-friendly inhibitors, therefore could be used as corrosion inhibitors in the processes of oil well acidizing, chemical cleaning, acid pickling and descaling of medium carbon
Acute toxicity (LC₅₀) and OECD 501tests so as to further verify the biodegradability limits established at in this

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