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Abstract

Corrosion, a global phenomenon causing irreversible damage to metals by chemical and electrochemical reactions, underscores their vulnerability to diverse mechanisms and factors. Hence, manufacturers must strike a balance between cost-effective production and ensuring optimal corrosion resistance, considering specific usage environments, and without compromising industry standards. This review briefly explores various factors and types of metallic corrosion. Additionally, it delves into multiple strategies aimed at preventing and mitigating the occurrence of the phenomenon.
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Corrosion of Metals: Factors, Types and Prevention Strategies
Jeffrey Ken B. Balangao1,2
1College of Engineering and Architecture, University of Science and Technology of Southern Philippines, Cagayan de
Oro City, Philippines
2Department of Materials and Resources Engineering & Technology, College of Engineering, Mindanao State
University-Iligan Institute of Technology, Iligan City, Philippines
(Received: 27 October 2023 Revised: 22 November Accepted: 26 December)
KEYWORDS
Metals,
corrosion,
factors,
types,
prevention
ABSTRACT:
Corrosion, a global phenomenon causing irreversible damage to metals by chemical and electrochemical
reactions, underscores their vulnerability to diverse mechanisms and factors. Hence, manufacturers must
strike a balance between cost-effective production and ensuring optimal corrosion resistance, considering
specific usage environments, and without compromising industry standards. This review briefly explores
various factors and types of metallic corrosion. Additionally, it delves into multiple strategies aimed at
preventing and mitigating the occurrence of the phenomenon.
INTRODUCTION
Corrosion is defined as an irreversible damage to a metal
surface that lead to the conversion of a pure metal into
more chemically stable forms like sulphides, oxides,
hydroxides, etc. [1]. Here, chemical and electrochemical
reactions occur on the metal’s surface [2] in a corrosive
environment, which can be solid, liquid, or gas [1]. It is
with this corrosive medium that corrosion can be
classified as dry or wet [3-5].
Metallic corrosion is the inverse of extraction of metals
from their ores [6]. It is a result of materials’ inclination
to transition into their states of least energy. Most metals
occur in nature in ore forms. So to extract metals from
ores, energy is needed. But during metals’ life cycle, they
will tend to be oxidized, going back to their original
states. The greater the energy needed to extract metals,
the greater is their tendencies to corrode [1-2].
In general, metallic corrosion involves an
electrochemical process [1-2]. The process typically
includes an electrolyte that enables the transfer of ions
(cations and anions) within and give rise to anodic and
cathodic reactions. When two different metals are
present in such an electrolyte, the less noble metal
becomes the anode and corrodes, while the more noble
metal becomes the cathode and is protected. The flow of
electrons occurs from the anodic to the cathodic metal.
Among the two metals, the one with a higher reduction
potential, or higher position in the electrochemical series,
is more susceptible to corrosion [1, 6].
Moreover, metallic corrosion occurs in various forms
depending on the morphology of the metal damage [1-2,
6-10]. According to Singh [10], corrosion can take the
form of a general surface attack, gradually diminishing
the metal's thickness. Alternatively, it may occur as
isolated corrosion in specific areas or along vulnerable
lines such as grain boundaries, influenced by variations
in resistance to a corrosive environment.
The diverse nature of metallic corrosion underscores the
susceptibility of metals to various mechanisms and
factors leading to corrosion. Hence, this review
comprehensively discusses the diverse factors and types
involved in metallic corrosion. Moreover, it delves into
the discussion of multiple strategies aimed at preventing
and mitigating corrosion.
FACTORS OF CORROSION
This section places emphasis on various factors
contributing to metallic corrosion. It explores elements
such as metal purity, characteristics of the surface film,
properties of corrosive products, temperature, air
humidity, and pH levels. Understanding these factors is
crucial for a comprehensive examination of the corrosion
process in metals.
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Purity of the Metal
According to Harsimran et al. [6], corrosion rates
typically rise with the increased addition of impurities, as
these impurities create small electrochemical cells where
the anodic part undergoes corrosion. For instance, zinc
with impurities such as iron (Fe) or lead (Pb) experiences
a faster rate of corrosion.
Nature of Surface Film
In an aerated atmosphere, all metals develop a thin
surface film of metal oxide. The impact of this surface
film is determined by the "specific volume ratio," which
represents the ratio of volumes between the metal oxide
and the metal. A higher specific volume ratio
corresponds to a lower oxidation rate. For instance,
nickel, cobalt, and tungsten have specific volume ratios
of 1.6, 2.0, and 3.6 respectively. Consequently, tungsten
exhibits the least oxidation rate, even at elevated
temperatures [6].
Nature of Corrosive Product
Corrosion advances more rapidly when the formed
product is soluble in the corrosive medium. Additionally,
if the corrosive product is volatile, it evaporates upon
formation, exposing the metal surface for further attack
and exacerbating the corrosion process [6].
Temperature
Corrosion accelerates with higher temperatures, with the
rate expected to nearly double for every 100-degree
increase [11]. Muslim et al. [12] conducted experiments
on aluminum and copper at temperatures of 25°C and
50°C, with pH values of 4.8, 7, and 8.2, respectively, and
found out that their corrosion rates decrease with
increasing pH and increased with higher temperatures.
The temperature-related increase in corrosion is typically
depicted by an exponential curve, but various cases show
a more complex relationship, as temperature changes can
also alter the impact of other factors [13].
Humidity of the Air
Relative humidity significantly influences the rate of
corrosion, rising sharply above a specific point known as
the critical humidity. Beyond this threshold, the
corrosion rate experiences a notable increase. The
heightened corrosion with increased humidity is
attributed to the oxide film's tendency to absorb moisture,
leading to additional electrochemical corrosion.
Moreover, atmospheric moisture provides the necessary
water for the electrolyte, essential for the formation of an
electrochemical cell [6].
pH
The pH level is a crucial determinant of the corrosion
rate, with lower pH values associated with higher
corrosion rates. Acidic environments, characterized by a
pH less than 7, exhibit greater corrosiveness compared to
alkaline or neutral media. For noble metals such as gold
and platinum, the corrosion rate is notably low and
exhibits minimal dependence on the solution's pH [13].
Noble metals, while generally resistant to corrosion, are
often not used for common purposes due to their high
cost [14]. For the other metals such as aluminum, zinc
and lead, there is a significant increase in the corrosion
rate in both acidic and alkaline mediums compared to
neutral solutions. This is explained by the solubility of
the oxides of these metals in both acid and alkaline
environments [13].
TYPES OF CORROSION
This section provides a comprehensive exploration of
diverse types of metallic corrosion. It covers general
corrosion, as well as more specific forms such as
localized corrosion (pitting and crevice), stress corrosion
cracking, intergranular corrosion, galvanic corrosion,
erosion corrosion, waterline, and biological corrosion.
Further, it stipulates thorough grasp of the distinct
mechanisms and challenges associated with different
corrosion processes in metals.
General Corrosion
This type of corrosion is known as uniform corrosion,
characterized by a relatively uniform deterioration of the
metal surface. It progresses at the same rate across the
entire barren area. Oxygen serves as a primary catalyst
for this corrosion, and common materials susceptible to
general corrosion include cast iron and steel [1, 6].
Exposure to a moist atmosphere causes them to develop
a rust-like appearance [6].
Localized Corrosion
Localized corrosion differs significantly from general
corrosion. General corrosion occurs over a relatively
larger area, while localized corrosion is confined to a
comparatively smaller area [15]. This corrosion type
occurs when specific small areas on a metal surface
corrode more easily than the overall surface in a
corrosive environment. These localized areas are
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partially corroded at a faster rate due to the presence of
the corrosive medium. The region with limited oxygen
supply acts as the anode, while the area with a full supply
acts as the cathode. It further manifests in two types,
namely, pitting and crevice corrosion [6].
i. Pitting Corrosion
Pitting corrosion, a significant form of localized
corrosion, starts in a small area on a material and
gradually expands, forming deeper pits on the surface
which may be difficult to detect [1]. Pits or holes, which
can be either hemispherical or cup-shaped [16], are
created in this process, with the area covered by impurity
or water serving as the anode, while the uncovered area
acts as the cathode. The dissolution of the metal is
thought to be governed by an electrochemical
mechanism in this type of corrosion [17]. Stainless steel,
aluminum, and iron are highly prone to pitting corrosion,
making it a particularly dangerous form of corrosion [1].
Despite being generally corrosion-resistant, having
chromium and nickel [18-22], materials like stainless
steels can still experience pitting corrosion due to
localized attacks on their protective oxide films [1].
ii. Crevice Corrosion
Crevice corrosion is characterized by corrosion within
restricted spaces, that occurs in stagnant, less oxygenated
areas, like crevices between metal surfaces or beneath
deposits (sand, dirt, mud, etc.). The joint area within the
crevices has a lower oxygen content compared to the
outer area, causing it to act as the anode, while the outer
area serves as the cathode [1, 6]. Crevice corrosion poses
a significant practical challenge, particularly in marine
applications [23-24]. Crevice corrosion also primarily
impacts stainless steels, and the presence of chloride adds
challenges associated with addressing this type of
corrosion [1, 25-27].
Stress Corrosion Cracking
Stress corrosion cracking (SCC) is a type of corrosion
triggered by applied stress on a material, initially present
in an inert environment, leading to the development of
cracks in a corrosive environment. This form of
corrosion can be accelerated by either residual internal
stresses within the metal or externally applied stress [28].
SCC predominantly occurs at high temperatures and is
more prevalent in alloys than in metals. Three essential
factors for SCC to take place are: (i) the presence of a
susceptible material, (ii) exposure to a corrosive
environment, and (iii) the presence of tensile stresses [6].
Intergranular Corrosion
Intergranular corrosion, also known as intergranular
attack, occurs when the edges or margins of a metal
surface are more vulnerable to a corrosive environment
than the core [29]. In this case, corrosion primarily
occurs in a narrow zone at and near the grain boundaries
of a metal alloy, while minimal or no corrosion occurs
within the grains themselves [1]. Further, this type of
corrosion can conceal the material's corrosion resistance
under various conditions and is often assessed through an
IGA Test [29]. It is also not influenced by the addition of
impurities such as carbon, nitrogen, oxygen, manganese,
and sulfur. However, the addition of silicon and
phosphorus does impact the corrosion in this context
[30].
Austenitic stainless steels commonly experience this
type of corrosion, esp. when chromium drops below
10%, the sensitization of austenitic stainless steels
occurs, causing intergranular corrosion. Further, this is
particularly during welding when varying temperatures
lead to chromium combining with carbon, forming
Cr23C6 and depleting chromium around grain boundaries
in areas exposed to 450800 °C. This process leaves
those regions susceptible to corrosion [1]. Stainless
steels, in spite of instigating efforts to manufacture them
innovatively and efficiently [20-22, 31-33], do not resist
corrosion at all times, and are more vulnerable to various
forms of corrosion, including this intergranular
corrosion, even stress corrosion cracking, and pitting
attack, compared to structural steels [34].
Galvanic Corrosion
According to electrochemistry, galvanic corrosion arises
on discrete portions of a metallic surface due to the
presence of an anodic portion and a cathodic portion
[35]. Galvanic corrosion occurs in two dissimilar metals,
when one metal, in the presence of a suitable electrolyte,
preferentially corrodes over another metal with which it
has electrical contact. In this process, the metal acting as
the cathode, the less reactive, is protected, while the
metal serving as the anode, more reactive, undergoes
corrosion [1, 6].
In an example, when zinc (Zn) and copper (Cu) are
electrically connected, the electrochemical series
position of Zn is higher than Cu. As a result, Zn acts as
the anode, and Cu acts as the cathode. This implies that
Zn loses electrons, while Cu accepts electrons. Due to the
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less noble nature of Zn compared to Cu, Zn undergoes
corrosion as a part of the galvanic corrosion process [6].
Erosion
Erosion occurs when the metal surface undergoes
corrosion due to relative movement between the metal
and a corrosive fluid [9, 36-37]. In cases where the fluid
contains solid particles harder than the metal surface,
erosion results from the combined action of corrosion
and abrasion. Conversely, when the fluid contains softer
particles than the metal, erosion occurs through corrosion
and attrition [36-37]. The rate of relative flow provides
insights into abrasion, while the mechanism of chipping
and cracking determines the cause of erosion. Erosion
occurs due to the simultaneous formation and removal of
scale from the surface of the material [38].
Waterline Corrosion
Waterline corrosion occurs in metallic tanks when they
are partially filled with water. The area below the water
surface, which is poorly oxygenated, acts as the anode,
while the area above the water line, with a significant
amount of oxygen, acts as the cathode. As a result, the
area just below the water level undergoes corrosion,
while the area above the water level remains protected
from this specific type of corrosion. This type of
corrosion is commonly encountered by marine engineers.
The impact of this corrosion can be mitigated to some
extent by using anti-fouling paints [6].
Biological Corrosion
Biological corrosion is influenced by the activities of
living organisms, including microorganisms (e.g.,
bacteria) and macroorganisms (e.g., algae, fungi,
barnacles) [1]. Other terms used for this type include,
microbial, microbiologically influenced corrosion (MIC)
or microbially induced corrosion (MIC) [39]. Thriving in
diverse pH, temperature, and pressure conditions, this
type of corrosion manifests in various environments. The
involvement of living organisms in metabolic reactions
directly impacts anodic and cathodic reactions, disrupts
protective films, and creates corrosive conditions or
deposits, making biological corrosion distinct due to the
role of organisms in facilitating or accelerating specific
corrosion types [1].
PREVENTION OF CORROSION
Various methods to prevent corrosion have already been
reported in the literature. Some of these methods include
pre-treatment, proper design and material selection,
sacrificial protection, cathodic protection, barrier
protection, electroplating, zinc galvanizing, and use of
laser technology. Each method aims to mitigate or resist
the corrosive effects on metal surfaces in different ways.
Pre-treatment of Metals
Prior to implementing any protective measures, it is
essential to thoroughly clean the metal surface.
Degreasing, commonly accomplished using a volatile
organic solvent like trichloroethylene, effectively
dissolves oily and greasy surface films. Additionally,
acid pickling serves as an alternative method to remove
scale, complementing mechanical cleaning. Adequate
preparation of the metal surface, including the removal
of oils and grease, is necessary before applying any
coating and can be achieved through washing with an
alkali solution [40].
Proper Design
In designing materials to minimize corrosion, key
principles include ensuring that when two different
metals make contact, the metal designated as the anode
should have a larger area, while the other metal should
have a smaller area. Additionally, if dissimilar metals are
in contact, they should be positioned as close as possible
in the electrochemical series. When direct contact is
unavoidable, the use of insulating materials is
recommended to prevent direct metal-to-metal electrical
contact. Sharp corners should be avoided to discourage
solid accumulation, and caution is advised against
painting or coating metals to prevent rapid localized
corrosion in the event of coating breaks [41].
Right Material Selection
The selection of the right material must be based on their
intended use in the working environment to ensure
optimal resistance [1]. This is instigated by considering
properties such as tensile strength, corrosion resistance,
and cost-effectiveness. The process includes prior
selection based on experience and safety, followed by
laboratory testing to re-evaluate the material under
specific conditions, and an analysis of the results to
assess factors like impurities, temperature, and pressure
[41].
Sacrificial Method
Sacrificial protection involves safeguarding a metal by
applying a layer of another metal that is more active or
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electropositive, providing protection through the
sacrificial corrosion of the outer layer rather than the
primary metal [42]. In sacrificial protection, the more
active metal surface loses electrons, entering an ionic
state by releasing electrons. Over time, the more active
metal gets depleted, but only as long as it is present. For
example, coating iron (Fe) with zinc (Zn) in
galvanization serves as sacrificial protection, where Zn,
being more electropositive, acts as the anode and
corrodes, protecting the underlying Fe until the zinc layer
is exhausted [6].
Cathodic Protection
In the process of sacrificial protection, a material, say
iron, which is to be protected is connected to a more
active metal, designating the iron as the cathode and the
protective metal as the anode. The anode, being more
active, undergoes oxidation and gradually depletes into
ions through the loss of electrons [43-44]. Cathodic
protection is done in two ways, namely, sacrificial anode
and impressed current methods [1, 6].
The sacrificial anode method involves sacrificial
corrosion of the anode to protect the material, which is
why it is referred to as the sacrificial anode method [6].
The commonly used metals for anodes are magnesium,
zinc, and aluminum, having qualities such as efficient
current yield in both theory and practice and sustained
current without diminishing over time, avoiding issues
like passive film formation [1].
On the other hand, impressed current method employs
non-corroding inert anodes to generate a current flow
through an external source, and the degree of protection
is determined by the applied potential. To facilitate
protection, the potential should be sufficiently reduced to
eliminate the anodic reaction of metal dissolution,
reaching a value equal to or below the equilibrium
potential of its oxidation reaction [1]. Specifically, in this
method, an insulated wire internally connects the anode
and the material to be protected, establishing a current
path through the electrolyte. Unlike the galvanic system,
which relies on the difference in oxidation potential, the
impressed current method uses an external power supply
to drive the current flow [6].
Barrier Protection
Coating the metal surface is a protective measure against
corrosion, and many of these coatings act as barriers
between the metallic surface and the corrosive
environment. This method is referred to as barrier
protection [45]. Coatings can be metallic or nonmetallic
[1, 46], and their effectiveness are significantly
influenced by the preparation of the surface, emphasizing
the importance of thorough cleaning and preparation
processes to achieve adherent and uniform coatings [1].
Coating is one of the simplest methods to prevent
corrosion by placing a suitable barrier between the metal
surface and the atmosphere, shielding it from the action
of air, water, and carbon dioxide. This protection can be
achieved by coating the metal surface with paints, oils,
or grease, using non-corroding metals, or applying
certain chemicals [6].
According to Armijo [47], graphene is extensively
employed in the barrier protection method due to its inert
nature, unique structure, and electrical properties.
Comprising carbon atoms strongly bonded in a
hexagonal structure, graphene remains inert under
conditions where other materials might undergo
chemical reactions.
Electroplating
The Italian chemist Luigi Brugnatelli is credited with
inventing electroplating in 1805. After several attempts
and failures, he achieved success by successfully plating
a thin layer of gold onto silver [48]. Electroplating is a
method of coating one metal over another by passing an
electrical current through a solution. It serves various
purposes, including decoration, enhancing appearance,
and providing protection. For instance, chromium plating
is employed to coat vehicle wheel rims and gas burners
for corrosion resistance, while nickel plating is used for
both decorative purposes and various machinery parts.
The electroplating process involves a specific procedure
[6].
Zinc Galvanizing by Hot Dipping Method
The process involves immersing cleaned steel in molten
zinc at a temperature of approximately 445-450°C, hence
it is termed the hot-dipping method. This method is
commonly used for applying a zinc coating to steel
surfaces. Compared to electroplating, the hot-dipping
method is often preferred because it offers superior
corrosion protection to the metal. The coating applied
through hot dipping is more effective in preventing
corrosion [49].
In the process of hot dip galvanization, steel is immersed
in a container filled with a minimum of 98% pure molten
zinc [50]. The zinc metal reacts with the iron on the steel
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surface, forming a zinc/iron intermetallic alloy. Any
excess zinc is then removed through the process of
centrifuging [6].
Laser Technology
The use of laser technology can also be used to protect
metals from corrosion [51-55]. For instance, laser shock
peening (LSP), a recent surface treatment, aims to
minimize metal corrosion by inducing deep residual
mechanical stress through shock waves generated by
high-energy density laser pulses onto the target surface
[54]. The growing use of lasers is attributed to their high
productivity, automation capabilities, non-contact
processing, elimination of finishing operations, reduced
processing costs, improved product quality, maximum
material utilization, and minimal heat-affected zone
(HAZ) [55-56].
CONCLUSION
Corrosion, a global phenomenon affecting materials,
particularly metals and alloys, requires effective
mitigation to prevent its adverse effects. The various
forms of corrosion result from the inherent nature of the
metal and the corrosive environment. These forms
encompass general or uniform corrosion, localized
corrosion, stress corrosion, intergranular corrosion,
galvanic corrosion, erosion, waterline and biological
corrosion. Multiple methods have been implemented and
documented to combat or resist corrosion in metals.
Manufacturers must find a balance between cost-
effective material production and ensuring optimal
corrosion resistance, considering the specific
environments in which the materials will be employed.
Simultaneously, meeting industry standards and
regulations while optimizing material performance
against corrosion remains an ongoing challenge.
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... Corrosion refers to the degradation of mechanical properties induced by chemical or electrochemical reactions between a material and its environment (Li et al. 2015;Jeffrey et al. 2024). Corrosion is a global problem impacting materials, especially metals and alloys, which need efficient mitigation to prevent the negative impacts. ...
... Since most metals reside in the form of oxides, they require a significant amount of energy to be extracted into their free state. When exposed to an external environment such as, moisture or oxygen, they may return to their combined state using the energy provided (Jeffrey et al. 2024). Electrochemical corrosion causes metals to revert to their original state and lose their properties, compromising their performance and durability (Fernandes et al. 2015). ...
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... Lebih lanjut dijelaskan bahwa Korosi, sebuah fenomena global yang memengaruhi material, khususnya logam dan paduannya, memerlukan mitigasi yang efektif untuk mencegah dampak buruknya. Berbagai bentuk korosi terjadi akibat sifat alami logam dan lingkungan korosif (Balangao, Jeffrey Ken 2024). ...
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...  Water Treatment: wastewater treatment to neutralize and antagonize acids and reduce corrosive causes can help mitigate corrosion. (Balangao, 2024)  Frequent Maintenance: Using routine inspections, cleaning and maintenance, corrosion-related problems and severe and serious damage can be detected and repaired.  Metal corrosion in acidic environments is a well-known phenomenon, particularly in wastewater treatment applications. ...
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... The other type is concrete corrosion, as it is possible for steel reinforcement in reinforced concrete structures to corrode if it is exposed to corrosive chemicals, chloride ions, and carbonation over time. Due to this, the concrete may crack and crumble as a result [1][2][3][4][5][6][7][8][9][10][11][12][13]. As mentioned above, the corrosion of metal occurs as a result of chemical reactions between the metal and the environment around it, which causes the metal to slowly disintegrate over time as the environment around it changes [14,18]. ...
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Conference Paper
Laser is becoming an important surface treatment to induce a compressive residual stress field, which improves micro-hardness, wear resistance and fracture properties of components via laser shock processing (LSP) technique. This work investigates the effect of LSP technique to enhance wear resistance of 6009 Al and 70275 Cu-Ni alloys by using Nd: YAG laser (λ = 1064 nm, t = 10 ns). Four different pulse repetition rates have been used to perform hardening (2, 3, 4 and 5 Hz). A pin-on-disc technique has been used to evaluate wear rate of the specimens as-received and specimens treated by Nd: YAG laser at different applied loads with 750 rpm and 60.8 HRC of rotating disc. It is observed that LSP treatment can improve the wear resistance of both alloys, where the wear rate is reduced by 69.23% for 6009 Al and 69.11% for 70275 Cu-Ni compare to untreated LSP samples due to work hardening and compressive residual stress of LSP impact. SEM micrograph analysis of worn surface showed that the grooves and compacted debris of LSP treated sample are smaller and less than these untreated LSP samples.