TABLE OF CONTENTS
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND
OF STUDY
1.1.1 CORROSION
1.1.1.2 CORROSION AND ITS MECHANISM
1.1.1.2.1 ELECTROCHEMISTRY OF CORROSION
1.1.1.3 CLASSIFICATION OF CORROSION
1.1.1.4 CORROSION PREVENTION
1.1.1.5 ECONOMIC IMPORTANCE OF CORROSION
1.1.2 ALUMINIUM
1.2 PROBLEM
STATEMENT
1.3 AIM
1.4 SCOPE OF
STUDY
1.5 PROJECT
OUTLINE:
CHAPTER TWO
LITERATURE
REVIEW
CHAPTER THREE
METHODOLOGY
3.1 EXPERIMENTAL
REQUIREMENT/ PROCEDURES
3.1.1 APPARATUS
REQUIRED.
3.1.2 REAGENTS REQUIRED.
3.1.3 PREPARATION OF HCL
SOLUTIONS
3.1.4 STOCK SOLUTION OF
ALANINE
3.2 METHODOLOGY
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 RESULT
4.2 DISCUSSION
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
5.2 RECOMMENDATION
REFERENCES
CHAPTER
ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
1.1.1 CORROSION
Corrosion is defined as a
natural process, which converts refined metal to their more stable oxide. It is
the gradual destruction or degradation of materials (usually metals) by
chemical reaction with their environment which are most likely inevitable. Corrosion
is a natural and costly process of destruction like earthquakes, tornados,
floods and vocanic eruptions, with one major difference. Whereas we can be only
a silent spectator to the above processes of destruction, corrosion can be
prevented or at least be controlled.
Despite different definitions, it can be observed that
corrosion is basically the result of interaction between materials and their
environment. Up to the 1960s, the term corrosion was restricted only to the
metals and their alloys and it did not incorporate ceramics, polymers,
composites and semiconductors in its regime. The term corrosion now encompasses
all types of natural and man – made materials including biomaterials and
nanomaterials, and it is not confined to metals and alloys alone. The scope of
corrosion is consistent with the revolutionary changes in materials development
witnessed in recent years.
1.1.1.2 CORROSION AND ITS MECHANISM
In nature, metals are not found in free state due to their
reactivity. Metals are generally in high energy state because some energy is
added during their manufacturing process from the ores. Low energy - state ores
are more stable than the high energy – state metals. As a result of this uphill
thermodynamic struggle, the metals have a strong driving force to release
energy and go back to their original
form. Hence the metals revert to their parent state or ore under a suitable
corrosive environment. The electrochemical
process involved in corrosion by nature is opposite to the extractive
metallurgy involved in manufacturing of the metals. Therefore, corrosion is
sometimes considered as the reverse process of extractive metallurgy as can be
seen below:
FIGURE 1..2: THE ENERGY CYCLE OF IRON INDICATING ITS
EXTRACTIVE METALLURGY
According to electrochemistry, the corrosion reaction can be
considered as taking place by two simultaneous reactions:
The oxidation of a metal at an anode (a corroded end
releasing electrons) and the reduction of a substance at a cathode (a protected
end receiving electrons). In order for the reaction to occur, the following
conditions must exist:
1. Two
areas on the structure must differ in electrical potential.
2. Those
areas called anodes and cathodes must be electrically interconnected.
3. Those
areas must be exposed to a common electrolyte.
4.
An electric path through the metal or between metals be
available to permit electron flow.
When these conditions exist, a corrosion cell is formed in
which the cathode remains passive while the anode deteriorates by corrosion. As
a result of this process, electric current flows through the interconnection
between cathode and anode. The cathode area is protected from corrosion
damage at the expense of the metal, which is consumed at the anode. The amount
of metal lost is directly proportional direct current flow. Mild steel is lost at approximately 20 pounds for each ampere flowing for a year.
(Thomas, 1994) .
FIGURE 1.3: THE COMPONENT
OF AN ELECTROCHEMICAL CORROSION CELL
At the anode, metals are oxidized and the electrons are
liberated from the metal to form positive
metal ions. The liberated electrons dissolve into the electrolyte, and
deposition is formed on the cathodic metal. Anode corrodes while the
cathode remains intact.
1.1.1.2.1 ELECTROCHEMISTRY OF CORROSION
Corrosion occurs by an electrochemical process. The
phenomenon is similar to that which takes place when a carbon-zinc “dry” cell
generates a direct current. Basically, an anode (negative electrode), a cathode
(positive electrode), an electrolyte (environment), and a circuit connecting
the anode and the cathode are required for corrosion to occur (see Figure 1.3).
Dissolution of metal occurs at
the anode where the corrosion current enters the electrolyte and flows to the
cathode. The general reaction or reactions, if an alloy is involved) that
occurs at the anode is the dissolution of metal as ions:
M
→ Mn+ + en-
Where
M = metal involved n = valence of the corroding metal
species e = electrons
FIGURE 1.4: A
BASIC CORROSION CELL.
The basic corrosion cell consists of an anode, a cathode, an
electrolyte, and a metallic path for electron flow. Note that the corrosion
current (z) enters the electrolyte at the anode and flows to the cathode.
Examination of this basic reaction reveals that a loss of
electrons, or oxidation, occurs at the anode. Electrons lost at the anode flow
through the metallic circuit to the cathode and permit a cathodic reaction (or
reactions) to occur. In alkaline and neutral aerated solutions, the predominant
cathodic reaction is
O2 + 2H2O +
4e- → 4(OH)
(1.1)
The cathodic reaction that
usually occurs in deaerated acids is
2H- + 2e- → H2
(1.2)
In aerated acids, the cathodic
reaction could be
O2 + 4H- +
4e- → 2H2O
(1.3)
All of these reactions involve a gain of electrons and a
reduction process. The number of electrons lost at the anode must equal the
number of electrons gained at the cathode. For example, if iron (Fe) was
exposed to aerated, corrosive water, the anodic reaction would be
Fe → Fe++ + 2e-
(1.4)
At the cathode, reduction of
oxygen would occur
O2 + 2H2O +
4e- → 4(OH-)
(1.5)
Because there can be no net gain or loss of electrons, two
atoms of iron must dissolve to provide the four electrons required at the
cathode. Thus, the anodic and cathodic reactions would be
2 Fe → 2Fe++ + 4e-
(anodic)
(1.6)
O2 + 2H2O +
4e-→ 4(OH-) (cathodic) (1.7)
These can be summed to give the
overall oxidation-reduction reaction
2Fe + O2 + 2H2O
→ 2Fe++ + 4(OH-)
(1.8)
After dissolution, ferrous ions (Fe++) generally
oxidize to ferric ions (Fe+++); these will combine with hydroxide
ions (OH-) formed at the cathode to give a corrosion product called
rust.
(FeOH or Fe2O3.H2O)
(1.9)
Similarly, zinc corroding in
aerated, corrosive water (i.e., Zn → Zn++ + 2e-) will form the corrosion product Zn(OH)2.
The important issue to remember is that anodic dissolution of metal occurs
electrochemically; the insoluble corrosion products are formed by a secondary
chemical reaction.
1.1.1.3 CLASSIFICATION OF CORROSION
Corrosion based on the
appearance of the corroded metal can be classified as uniforrm or localized.
Corrosion is either uniform i.e the
metal corrodes at the same rate over the entire surface,or it is localized, in
which case only small areas are affected.
Classification by appearance, which is particularly useful
in failure analysis, is based on identifying forms of corrosion by visual
observation with either the naked eye or magnification.The morphology of attack
is the basis for classification. Figure 1.5 illustrate some of the most common
forms of corrosion.
FIGURE 1.5 :
MACROSCOPIC VERSUS MICROSCOPIC FORMS OF LOCALIZED CORROSION
There should be vivid
distinction between macroscopically localized corrosion and microscopic local
attack. In the latter case, the amount of metal dissolved is minute (minimal), and
considerable damage can occur before the problem becomes visible to the naked
eye or can be viewed with the aid of a
low – power magnifying device (Schweitzer, 1998).
1.1.1.4 CORROSION PREVENTION
Some corrosion prevention methods include material
selection, conditioning the corrosive environment, electrochemical control,
protective coating and use of corrosion inhibitors. The most common and easiest
way of preventing corrosion is through the judicious selection of material once
the corrosion environment has been characterized. Standard corrosion references
are helpful in this respect. Here, cost may be a significant factor and it is
not always economically feasible to employ the material that provides the
optimum corrosion resistance; sometimes, either another alloy or some other
measure must be used.
Conditioning the corrosive
environment if possible may also significantly influence corrosion. Lowering
the fluid temperature and/or velocity usually produces a reduction in the rate
at which corrosion occurs. Many times increasing or decreasing the
concentration of some species in the solution will have a positive effect; for
example, the metal may experience passivation.
CORROSION INHIBITORS:
Corrosion
inhibitors are chemicals that react with the metal's surface or the
environmental gases causing corrosion, thereby, interrupting the chemical
reaction that causes corrosion. Inhibitors can work by adsorbing themselves on
the metal's surface and forming a protective film. These chemicals can be applied
as a solution or as a protective coating via dispersion techniques.
The inhibitors process of
slowing corrosion depends upon:
•
Changing the anodic or cathodic polarization
behavior
•
Decreasing the diffusion of ions to the metal's
surface
•
Increasing the electrical resistance of the
metal's surface
Major end-use industries for
corrosion inhibitors are petroleum refining, oil and gas exploration, chemical
production and water treatment facilities.
The benefit of corrosion
inhibitors is that they can be applied in-situ to metals as a corrective action
to counter unexpected corrosion.
1.1.1.5 ECONOMIC IMPORTANCE OF CORROSION
The problems of metallic
corrosion is one significant propotion, it has been estimated that appoximatly
5% of an industrial nation’s income is spent on corrosion prevention and its
maintenance or preplacement of products lost or contaminated as a result of
corrosion reaction. The consequences of corrosion are many and the effects of
these on the safe, reliable and efficient operation of equipment or structures
are often more serious than the simple loss of a mass of metal. Failure of
various kinds of equipment and the need for expensive replacement may occur
even though the amount of metal destroyed is quite small. Some of the major
harmful effects of corrosion can be summarized as follows:
•
Perforation of vessels and pipes allowing escape
of their contents and possible harm to the surroundings. For example a leaky
domestic radiator can cause expensive damage to carpets and decorations, while
corrosive sea water may enter the boilers of a power station if the condenser
tubes perforate.
•
Loss of technically important surface properties
of a metallic component. These could include frictional and bearing properties,
ease of fluid flow over a pipe surface, electrical conductivity of contacts,
surface reflectivity or heat transfer across a surface.
•
Mechanical damage to valves, pumps, etc., or
blockage of pipes by solid corrosion products.
•
Added complexity and expense of equipment which
needs to be designed to withstand a certain amount of corrosion, and to allow
corroded components to be conveniently replaced.
•
Reduction of metal thickness leading to loss of
mechanical strength and structural failure or breakdown. When the metal is lost
in localized zones so as to give a crack on the structure, very considerable
weakening may result from quite a small amount of metal loss.
• Hazards
or injuries to people arising from structural failure or breakdown (e.g.
bridges, cars,
aircraft).
• Reduced
value of goods due to deterioration of appearance.
Corrosion processes are
occasionally used to advantage. For example, etching procedures makes use of
the selective chemical reactivity of grain boundaries or various
micro-structural constituent. Also, the current development in dry cell is as a
result of corrosion processes.
1.1.2 ALUMINIUM
Aluminium always finds very regular and diversified uses in
domestic appliances, chemical reactions and storage bottles, vessels and
containers, buildings, bridges, packaging foils, automobiles, aircrafts, ships
and many others. It is used for variety of applications due to its light weight,
very high strength, good thermal and electrical conductivities, good heat and
light reflectivity, its non-rusty
nature, non-toxicity and attractive appearance. It is highly electropositive
and resistant to corrosion because a hard, tough film of oxide is formed on the
surface. The surface film is amphoteric, hence the metal could dissolve readily
in both strong acid and alkaline media. Despite these great properties of
aluminium, it is not a perfect material for engineering applications in all
environments as they suffer corrosion caused by chemical
interactions with their surroundings (Khandelwal et al., 2010). Aluminium is used in industries like shipping,
offshore petroleum exploration, power and coastal industrial plants (for
cooling), fire-fighting, oil fuel water injection and desalination plants.
1.2 PROBLEM STATEMENT
The failure of aluminum equipment and aluminum materials due
to acid corrosion in industries is widely reported (Abiola et al, 2012), as
such there is a need to minimize this common effect. In virtually all
situations, aluminum failure through corrosion can
be managed, slowed or even stopped by using the proper techniques.
The most common and easiest way of preventing corrosion is
through the judicious selection of material once the corrosion environment has
been characterized and by the use of chemical inhibitors is the most practical
and cost effective means of controlling corrosion of metals in acid solutions.
However, a number of inhibitors of acid corrosion of aluminum are toxic,
nonbiodegradable and expensive.
1.3 AIM
The aim of this study is to investigate the inhibitive
effect of alanine on corrosion of aluminium in 0.5 M HCl solution using the
weight loss technique.
1.4 SCOPE OF STUDY
This study is limited to the study of use of organic
inhibitors to reduce the failure of aluminum due to acidic corrosion. This is
achieved by determining the inhibition efficiency of alanine by testing
different concentration of alanine on aluminum in an acidic solution.
1.5 PROJECT OUTLINE:
To ensure clarity as well as understanding, the thesis
consists of five chapters that discusses and describes the detailed operations
carried out on this project.
•
Chapter One introduces a background study on
corrosion, its effects and prevention and also highlights corrosion inhibitors
and aluminium. This chapter also contains the problem statement, aim,
objectives, and the scope of the project.
•
Chapter two discusses the literature review of
corrosion inhibitors and similar researches.
• Chapter
three contains the methodology which describes the experiment performed.
• Chapter
four contains the results of the experiment and also discussion
•
Chapter five contains the conclusion from the
results and observations during the experiment.
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