ABSTRACT The effect of exposure time on the surface characterization of galvanized steel corroding in River Niger water has been investigated in the laboratory within an exposure time range: 30-150 days. Results of the corroded surface characterization indicate presence of Lepidocrocite, apart from Fe at exposure time of 30 days. Beyond 30 days up to 150 days, XRD analysis revealed presence of magnetite and unknown element N in addition to Fe. Presence of magnetite indicates increased oxidation (corrosion) of Fe after 30 days of exposure. The low count and high noise of XRD pattern showed that the rusted surfaces mostly are composed of amorphous phase. Discrete point characterization using X-ray mapping revealed presence of encapsulated elements and corrosion enhancing anions which cannot be detected by XRD. These species are Cr such Cl– respectively. This is an indication that corrosion not only took place at the steel surface, but also within the microstructure, since presence of Cl– and Mn bring were as a result of corrosion at the steel surface/ interface and within the microstructure respectively.
TABLE OF CONTENT (EFFECT OF EXPOSURE TIME ON THE SURFACE CHARACTERIZATION OF GALVANIZED STEEL CORRODING IN RIVER NIGER WATER)
Title page – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – -i
Approval page – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – iii
Certification – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – -iv
Dedication- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – -v
Acknowledgement – – – – – – – – – – – – – – – – – – – – – – – – – – – – -vi
Abstract – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – vii
CHAPTER ONE
- INTRODUCTION- – – – – – – – – – – – – – – – – – – – – – – – – – – -1
- SIGNIFICANCE OF THE WORK- – – – – – – – – – – – – – – – – – – – 2
- AIMS OF STUDY- – – – – – – – – – – – – – – – – – – – – – – – – – – -2
- SCOPE OF THE WORK – – – – – – – – – – – – – – – – – – – – – – – – 3
CHAPTER TWO
2.0 LITERATURE REVIEW – – – – – – – – – – – – – – – – – – – – – – – – 4
2.1 GALVANIZING – – – – – – – – – – – – – – – – – – – – – – – – – – – – 4
2.1.1 Uses- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 8
2.1.2 The consequences/economic importance of corrosion- – – – – – – – 12
2.2 GALVANIC CORROSION- – – – – – – – – – – – – – – – – – – – – – – 14
2.2.1Causes of galvanic corrosion- – – – – – – – – – – – – – – – – – – – -17
2.2.2 Conditions necessary for galvanic corrosion- – – – – – – – – – – – -19
2.2.3 Galvanic current- – – – – – – – – – – – – – – – – – – – – – – – – – 20
2.2.3.1 Corrosion current and potential- – – – – – – – – – – – – – – – – – 20
2.2.4 The benefit of galvanic corrosion- – – – – – – – – – – – – – – – – – 21
2.3 CORROSION CONTROL METHODS- – – – – – – – – – – – – – – – – 21
2.4 STEELS- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 23
2.4.1 Steel corrosion- – – – – – – – – – – – – – – – – – – – – – – – – – – 27
2.4.2 White rust- – – – – – – – – – – – – – – – – – – – – – – – – – – – – 29
2.4.3 Methods of corrosion protection of coil coated steel- – – – – – – – -31
2.4.4 Galvanized Steel- – – – – – – – – – – – – – – – – – – – – – – – – -32
2.4.5 Applications- – – – – – – – – – – – – – – – – – – – – – – – – – – – 34
2.4.6 Economics- – – – – – – – – – – – – – – – – – – – – – – – – – – – – 35
2.4.7 Unique combination offers by galvanized steel- – – – – – – – – – – 36
2.5 THE CREATION OF PROTECTIVE COATING- – – – – – – – – – – – 36
2.5.1 Environmental performance of zinc coatings- – – – – – – – – – – – 37
2.5.2 Technical performance of zinc coatings- – – – – – – – – – – – – – -39
2.6 OTHER ZINC COATINGS- – – – – – – – – – – – – – – – – – – – – – – 43
2.7 PREVIOUS WORKS ON GALVANIZED STEEL CORROSION- – – – – 47
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CHAPTER THREE
- EXPERIMENTAL PROCEDURE- – – – – – – – – – – – – – – – – – – – 67
- SPECIMEN- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 67
- SPECIMEN PREPARATION- – – – – – – – – – – – – – – – – – – – – – 67
- METHOD- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 67
CHAPTER FOUR
RESULTS AND DISCUSSIONS- – – – – – – – – – – – – – – – – – – – – – 69
CHAPTER FIVE
5.0 CONCLUSION AND RECOMMENDATION- – – – – – – – – – – – – – 78
5.1 CONCLUSION- – – – – – – – – – – – – – – – – – – – – – – – – – – – – 78
5.2 RECOMMENDATION- – – – – – – – – – – – – – – – – – – – – – – – – 78
REFERENCE- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – -79
CHAPTER ONE
INTRODUCTION
Metals and alloys form the basis for molten technological advancement and no meaningful development can take place without its full understanding and utilization. It has been established that a greater percentage of in service failures of structural parts or elements are caused by corrosion and its attendant consequences.
Galvanized steel which is iron or steel that has been coated with zinc to prevent it from corroding. Galvanized steel has a wide application and as a result come in contact with very aggressive environments which negatively affects its stability, leads to corrosion and may fail as a result of the corrosion
Therefore, the need for an effective and efficient means of protecting these structures from corrosion attack. It is imperative to note that the study of corrosion, its mode of attack, its testing, evaluation and monitoring has become vital in today’s processes so as to achieve a high level of quality and safety assurance in the selections and usage of metals and alloys.
The environment consists of the entire surrounding in contact with the metal and can be described with the following factors:
- Physical state (solid, liquid or gas)
- Chemical composition (the constituents and their concentration)
- Temperature
- Relative velocity of solution
- Mechanical load on the material and
- Residual stress within the material
These factors are of great importance when considering the mechanism of corrosion.
Corrosion therefore could be seen as the combination of a metal with the environment. The corrosion behaviour of a material cannot be described unless the environment in which the material is to be exposed is identified. Similarly, the corrosiveness and aggressiveness of an environment cannot be described unless the material that is to be exposed to such an environment is identified so that the corrosion behaviour of a material depends on the environment to which it is subjected to and the corrosiveness of an environment depends on the material being exposed to that environment.
Since corrosion is an inevitable phenomenon which can only be avoided by vacuum operation which cannot be achieved due to certain conditions, then, there is need to careful study and sufficient control of corrosion.
1.2 Significance of the Work
The research was embarked on in order to ascertain the surface characterization of galvanized steel corroding in River Niger water at different exposure times.
1.3 Aim of the study
The main aim of the research is to examine the effect of different exposure times on the surface characterization of galvanized steel corroding in River Niger water using X-ray mapping Technique.
The specific objective of study was:
- To identify the elemental presence present at the corroded steel surface at each exposure time.
- To determine the effect of different exposure times on the surface characterization of the corroded galvanized steel.
- To identify the elemental phases, present at the corroded steel surface at each exposure time using the XRD component of the X-ray Mapping Technique.
- To reveal encapsulated elements inherent in the galvanized steel.
1.4 Scope of the Work
This project focuses on examine the effect of different exposure times on the surface characterization of galvanized steel corroding in River Niger water using X-ray mapping. Data generated in the course of this work is exclusive and should only be applicable to issues on the work.
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