Flavonoids as Anticorrosion Agents for Building Materials: A Review

Corros Rev 2025; 43(1): 1–22
Review
Nishant Verma, Tarun Kumar, Vinod Kumar Vashistha*, Dipak Kumar Das, Suman Yadav,
Rajasekhar VSR Pullabhotla and Gaurav Sharma
Anticorrosion properties of flavonoids for
rust-free building materials: a review
https://doi.org/10.1515/corrrev-2024-0024
Received February 18, 2024; accepted May 14, 2024;
published online August 23, 2024
aims to stimulate further research endeavors, fostering the
development of effective and eco-friendly corrosion protection
strategies for the construction industry.
Abstract: Rust-free building materials are crucial for
ensuring the durability and structural stability of constructions. Corrosion, a widespread issue affecting metals like
steel, copper, and concrete, can be effectively managed with
the help of corrosion inhibitors. One effective method for
corrosion inhibition involves the application of corrosioninhibiting coatings, which form resilient and tightly
adherent films on metal surfaces. Flavonoids, renowned for
their diverse biological activities, demonstrate significant
anticorrosive properties. They contain beneficial compounds such as antioxidants and chelating agents. The efficacy of plant extracts as corrosion inhibitors is influenced by
their organic constituents, particularly phenols and flavonoids.
Flavonoids act by creating a protective film that serves as a
barrier, shielding the metal surface from corrosive agents and
limiting their access to the metal. This contributes to the
prevention of corrosion. The integration of flavonoids into
building materials has the potential to transform corrosion
prevention practices, leading to improved durability, reduced
maintenance costs, and a more environmentally friendly built
environment. This article explores the promising prospects of
flavonoids as an innovative and sustainable approach to
corrosion prevention in building materials. Additionally, it
Keywords: flavonoids; flavone; chalcone; anticorrosion;
corrosion inhibitors
*Corresponding author: Vinod Kumar Vashistha, Department of
Chemistry, University of Lucknow, Lucknow, UP-226007, India,
E-mail: vkviitr@gmail.com
Nishant Verma and Suman Yadav, Department of Chemistry, Swami
Shraddhanand College, University of Delhi, Delhi-110036, India
Tarun Kumar, Department of Applied Sciences, MIET Kumaon Haldwani
Nainital, Uttarakhand-263139, India
Dipak Kumar Das, Department of Chemistry, GLA University, Mathura,
UP-281406, India
Rajasekhar VSR Pullabhotla, Department of Chemistry, Faculty of Science,
Agriculture and Engineering, University of Zululand, P/Bag X1001,
KwaDlangezwa, 3886, South Africa
Gaurav Sharma, Department of Chemistry, BSA College, Mathura, UP281001, India
Open Access. © 2024 the author(s), published by De Gruyter.
1 Introduction
1.1 Corrosion and its implications
Corrosion is a natural process that occurs when metals are
exposed to environmental factors like oxygen, water, and
certain chemicals. The process of corrosion can be accelerated in harsh environments like marine environments due
to the presence of saltwater and other corrosive substances.
The combination of high salt concentrations, humidity, and
temperature variations can cause corrosion to occur more
quickly and severely, leading to the deterioration of metal
structures and components. Additionally, radiation exposure can also cause corrosion in certain materials. Effective
corrosion prevention and control measures are essential to
prolonging the lifespan of metal structures and components,
especially in harsh environments (Harsimran et al. 2021).
Corrosion is a significant problem for industrial economies,
and its direct costs can be substantial (Figure 1). According to
various studies conducted over the past 30 years, the annual
direct cost of corrosion to an industrial economy is
approximately 3.1 % of the country’s gross domestic product
(GDP). In the case of the United States, this translates to over
$276 billion per year (Koch 2017).
Corrosion of building materials is caused by the reaction
of the material with its environment, such as air, water, or
chemicals), which can lead to the degradation of the material
over time. Steel is particularly susceptible to corrosion due to
its iron content, which can react with oxygen and water to
form iron oxide, or rust (Roberge 2019). The presence of salts
or acids can accelerate the corrosion process, leading to
structural damage and potentially compromising the safety
and integrity of steel structures (Chen et al. 2017). Copper,
This work is licensed under the Creative Commons Attribution 4.0 International License.
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N. Verma et al.: Flavonoids as anticorrosive materials
Figure 1: Total percentage cost of corrosion in
USD billion (a); total GDP percentage of
economic regions in USD billion (b).
while more resistant to corrosion than steel, can still be
affected by environmental factors such as air pollutants,
moisture, and acids. Over time, copper can develop a patina
or greenish coating, which can protect the underlying metal
from further corrosion, but this protection can be compromised if the patina is damaged or worn away (Prosek et al.
2014). Concrete, while not a metal, can also be affected by
corrosion due to the presence of reinforcing steel bars, or
rebar, which can rust and expand, causing cracks and
weakening the structure. Additionally, exposure to chemicals or high levels of moisture can also lead to corrosion of
the concrete itself, leading to degradation and potentially
compromising the safety and durability of the structure
(Fuhaid and Niaz 2022).
Moisture can contribute to the corrosion of cement
mortar and concrete. When water comes into contact with
cement, it can cause a chemical reaction that leads to the
formation of new compounds, including calcium hydroxide.
This reaction is necessary for the cement to harden and gain
strength (Kumar et al. 2009). However, if there is too much
moisture in the concrete or if it is stored in a wet environment, it can lead to excessive hydration, which can cause the
concrete to weaken and deteriorate over time. The presence
of moisture can also promote the growth of bacteria and
fungi, which can further contribute to the corrosion of the
material.
In addition to moisture, other factors that can contribute
to corrosion in cement mortar and concrete include exposure to acidic or alkaline substances, high temperatures, and
the presence of certain chemicals or pollutants. To minimize
the risk of corrosion, it is important to store and maintain
cement mortar and concrete in a dry, controlled environment and to avoid exposing it to potentially damaging substances or conditions (El Gamal et al. 2017). The excess water
in fresh concrete can take some time to evaporate, which can
lead to a prolonged period of high moisture content and an
increased risk of corrosion. Therefore, it is important to
carefully monitor the curing process and ensure that the
concrete is properly dried out before it is exposed to external
conditions. In addition to monitoring moisture levels, it is
also important to use high-quality materials and ensure
proper construction techniques to minimize the risk of
corrosion in cement-based materials.
The corrosion rate in Portland cement mortar can vary
depending on the level of moisture in the material. The
corrosion rate can be roughly estimated to be 1:6:25 for dry,
moist, and wet states, respectively (Kim et al. 2019). This
means that the corrosion rate is highest when the material is
wet, and lowest when it is dry. However, it is important to
note that even in the dry state, there is still a risk of corrosion
if the material is exposed to certain chemicals or pollutants.
1.2 Corrosion inhibitors
Corrosion of metals such as steel, copper, and concrete is
inevitable, but it can be controlled by using corrosion inhibitors. For improved corrosion safety of steel incorporated
in reinforced concrete structures, a corrosion-inhibiting
coating process creates a secure, adherent coating film that
is precisely coated onto metal surface. The electrochemical
interaction of metals with the corrosive atmosphere is the
source of this physical phenomenon. Interactions between
the metallic surface and the corrosive environment produce
sulfides, oxides, and other compounds (Leygraf et al. 2016).
Corrosion inhibitors can be used to control and slow
down the corrosion process in metals such as steel and
copper. These inhibitors work by either forming a protective
layer on the metal surface or by reducing the rate of the
corrosion reaction (Palanisamy 2019). In the case of reinforced concrete structures, corrosion inhibitors can be used
to protect the embedded steel from corrosion. This can be
done through a variety of methods, such as the use of
corrosion-inhibiting coatings, which create a secure,
adherent coating film that is precisely applied to the metal
surface. This coating can protect the steel from exposure to
N. Verma et al.: Flavonoids as anticorrosive materials
3
moisture and other corrosive agents, helping to extend the
lifespan of the structure (Thomas et al. 2022).
While corrosion inhibitors can be effective in slowing
down the corrosion process, they are not a complete solution
and must be used in conjunction with other measures, such as
regular inspection and maintenance, to ensure the long-term
durability and safety of the structure (Goyal et al. 2018). It is
important to note that while corrosion is a common and
prevalent process that can cause materials to deteriorate over
time, not all materials are equally susceptible to corrosion.
Materials selection, proper design, and environmental factors
can all play a role in the extent and rate of corrosion in a given
application. By understanding the causes and effects of corrosion and taking appropriate measures to prevent or mitigate it,
materials can be designed and maintained to ensure long-term
performance and safety (Wang et al. 2020).
1.3 Chemistry of flavonoids
The natural products chemistry is important for understanding the natural products isolation and their pharmaceutical importance (Najmi et al. 2022). Similarly, synthetic
organic chemistry is another dynamic field that concerned
with the design and synthesis of organic compounds or
modifications in natural products (alkaloids, amino acids,
flavonoids, terpenoids, fatty acids, steroids, etc.) using
different conventional methods, microwave method, green
concept of synthesis, and solid phase reactions (Mitra et al.
2021). Among them, flavonoids are one of the most fascinating areas of the plant chemistry, and organic synthesis
has many challenges in the transformation of these molecules to obtain higher level of complexity for enhanced
medicinal values as compared to natural flavonoids and biflavonoids. Isolation and identification of unknown natural
products are among the big tasks (Marsafari et al. 2020).
Therefore, synthetic organic chemistry specifically becomes
center of attraction for many organic chemists due to the
capability to produce valuable products such as natural
products, pharmaceuticals, medicinal/drugs, agricultural,
and materials during the organic modification of flavonoids.
Flavonoids are bioactive compounds that prevent
growth of microorganisms and widely distributed phytochemicals that play a role in cellular functions, plant
development, and reproduction, among other things (Shrinet et al. 2021). Two ortho hydroxyl group on the bearing
(catechol) containing flavone derivatives are especially
impressive among this heterogeneous group of compounds
because of their ability to deactivate reactive oxygen species
(ROS) and activate siderophores, both of which are essential
in plant immune mechanisms (Bailly 2021; Sheikh et al. 2020).
Figure 2: Structural flavonoid groups backbones and of related flavonoid
classes.
2 Classification and structural
features of flavonoids
Flavonoids, which are essential to the production of
plants, fruits, leaves, flowers, root stems, and seeds, were
found in over 6,000 species. Flavonoids possess a wide
range of anticorrosive abilities. It exhibited a variety of
health-promoting chemicals, including antioxidant and
chelating properties (Panche et al. 2016). All flavonoids
had a root C6–C3–C6 phenyl-benzopyran or benzofuran
backbone. Division into further groups is made on the
basis of the central ring oxidation. The most valuable
flavonoids are flavones, flavonols, and flavanones, and
abundant is o-flavonoids include isoflavone (Figure 2).
2.1 Chalcone
The name “chalcone” was derived from the Greek word
“chalkos,” which means copper, because of its color (Elkanzi
et al. 2022). Chalcones have been found to have various
biological activities and have been studied extensively in
medicinal chemistry (Al-Ostoot et al. 2021). Chalcone is a type
of open-chain flavonoid that is composed of two aromatic
rings, which are referred to as ring A and ring B. These rings
are connected by a highly electrophilic α, β-unsaturated
carbonyl group, which consists of a carbon atom doublebonded to an oxygen atom (forming a carbonyl group) and a
carbon atom that is also double-bonded to an adjacent carbon atom (forming an unsaturated bond) (Thapa et al. 2021).
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N. Verma et al.: Flavonoids as anticorrosive materials
Figure 3: General structure of chalcone and some examples of its derivatives.
The α, β-unsaturated carbonyl group is highly reactive due to
the presence of both a carbonyl and an unsaturated bond,
which makes it a common target for chemical reactions
(Figure 3). The linear or nearly planar structure of the chalcone
molecule is due to the delocalization of electrons between the
carbonyl and unsaturated bonds, which results in a conjugated
system. This conjugation system gives chalcone its unique
electronic properties, which make it useful in various applications such as organic synthesis and medicinal chemistry
(Rudrapal et al. 2021). The double bonds in the chalcone unit
and the phenyl rings are conjugated, which means that the
π-electrons in these double bonds are delocalized across the
entire molecule. This delocalization of π-electrons creates a
planar structure and gives chalcones their characteristic yellow color. It also makes them interesting from a chemical
perspective, as they exhibit a range of biological and pharmacological activities such as antioxidant, anti-inflammatory, and
anticancer properties (Ullah et al. 2020).
They are important intermediates in the biosynthesis of
other flavonoids, including flavones, flavonols, and anthocyanins, which are responsible for the pigmentation of many
fruits, vegetables, and flowers. Chalcones are known to act as
self-protective compounds in plants, helping to protect them
from environmental stressors such as UV radiation, pathogens, and herbivores (Saddique et al. 2018). They are also
involved in plant–insect interactions, serving as attractants,
repellents, or feeding stimulants for insects, depending on
the specific chalcone and the insect species involved. In
addition to their role in plant biology, chalcones have been
found to have a variety of medicinal properties, such as
antioxidant, anti-inflammatory, antimicrobial, and anticancer activities. Many herbs and medicinal plants contain
chalcones, which may contribute to their therapeutic value
(Pratyusha 2022).
Chalcones are indeed versatile molecules that have been
extensively used in the synthesis of various biologically
important compounds (Marotta et al. 2022). Due to the presence
of these functional groups, chalcones can undergo a wide range
of chemical reactions, making them useful building blocks for
the synthesis of many different types of compounds. One
important class of compounds that can be synthesized from
chalcones is pyrans, which are six-membered rings that
contain one oxygen atom (Asif and Imran 2019).
2.2 Flavone
Flavones are the subclass of flavonoids, which are based on
the backbone of 2-phenylchromen-4-one, which consists of a
benzene ring fused to a pyran ring with a ketone group at the
4-position. Flavones are distinguished from other flavonoids
by the absence of a hydroxyl group at the 3-position of the
C-ring (Figure 4). Flavones are widely distributed in the plant
kingdom and can be found in many fruits, vegetables, and
medicinal plants (Roy et al. 2022).
Flavones are the type of flavonoid that is commonly
found in a variety of plants, including cereal grains and
N. Verma et al.: Flavonoids as anticorrosive materials
5
Figure 4: Basic structural unit of flavone and its derivative.
herbs. Flavonoids are a class of plant pigments that have a
wide range of biological activities and are believed to play a
role in protecting plants from environmental stressors such
as UV radiation and pests (Hostetler et al. 2017). Flavones are
specifically characterized by their chemical structure, which
includes two benzene rings connected by a three-carbon
bridge. They are often found in the leaves, flowers, and seeds
of plants and are known for their antioxidant and antiinflammatory properties (Rana et al. 2022).
various fruits and vegetables. Like other flavonoids, flavonones possess antioxidant and anti-inflammatory properties, making them potentially beneficial for health.
Flavonones are structurally characterized by a 3-hydroxyflavone backbone with a ketone group at the C-4 position.
The most well-known flavonone is hesperidin, found in citrus fruits, especially in the peel and membranes of oranges
and lemons. Other flavonones include naringenin, found in
grapefruits and tomatoes, and eriodictyol, found in lemons
and berries.
2.3 Flavonols
2.5 Isoflavones
Flavonols are the class of flavonoids, which belong to a diverse
group of plant compounds known for their antioxidant and
health-promoting properties. Flavonoids are found in various
fruits, vegetables, herbs, and other plant-based foods. Flavonols,
specifically, are a subclass of flavonoids that have a certain
chemical structure characterized by a 3-hydroxyflavone backbone. One of the most well-known flavonols is quercetin, which
is widely studied for its potential health benefits. Flavonols,
including quercetin, are known for their antioxidant and antiinflammatory properties, which can help protect cells from
oxidative stress and reduce inflammation in the body.
2.4 Flavonones
Flavonones are another subclass of flavonoids, which are a
group of polyphenolic compounds commonly found in
Isoflavones are the class of phytoestrogens, which are
naturally occurring plant compounds that have a similar
structure to the hormone estrogen. They are primarily found
in legumes, particularly in soybeans and soy products. Isoflavones have gained considerable attention due to their
potential health effects and their ability to interact with estrogen receptors in the human body.
2.6 Flavan-3-ols
Flavan-3-ols are a class of flavonoids, which are a group of
polyphenolic compounds found in various plant foods. Flavan-3-ols are characterized by their chemical structure
containing a 2-phenyl-3,4-dihydro-2H-chromen-3-ol backbone. The flavan-3-ol subgroup includes several compounds
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N. Verma et al.: Flavonoids as anticorrosive materials
such as catechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, etc. Flavan-3-ols and their derivatives
are known for their antioxidant properties and have been
associated with various health benefits, including cardiovascular health and potential protective effects against
certain diseases.
2.7 Anthocyanins
Anthocyanins are another class of flavonoids, which are
water-soluble pigments responsible for the red, purple, blue,
and magenta colors found in many fruits, vegetables, flowers,
and other plants. These compounds play important roles in
plant biology, acting as antioxidants, UV protectants, and
contributing to pollination by attracting insects and animals.
The chemical structure of anthocyanins consists of a 2-phenylbenzopyrylium (flavylium) cation that can undergo structural modifications, leading to different anthocyanin pigments
with varying colors. The color of anthocyanins can change
depending on the pH of the environment they are in. In acidic
conditions, they appear red, while in more neutral or alkaline
conditions, they exhibit blue or purple hues.
3 Fundamentals of corrosion
inhibition
Corrosion inhibition is the process of protecting metal surfaces from the harmful effects of corrosion by applying a
chemical substance called a corrosion inhibitor. Corrosion
inhibitors work by forming a protective layer on the metal
surface, which prevents the metal from coming into contact
with the corrosive environment. In addition to the type of
inhibitor used, the effectiveness of corrosion inhibition also
depends on several other factors, including the concentration of the inhibitor, the pH of the solution, and the temperature of the environment. It is important to carefully
select the appropriate corrosion inhibitor for a given application and to ensure that it is used in the correct concentration and under the appropriate conditions to achieve
optimal performance. Important selection parameters for
corrosion inhibition are displayed in Figure 5.
Chromium-based inhibitors are effective, but their
use is restricted due to their potential environmental and
health hazards (Vaghefinazari et al. 2022). As an alternative, green corrosion inhibitors that are derived from
plant extract are considered as sustainable and ecofriendly, making them efficient inhibitors of choice (Table 1). The recyclability and reusability of such materials
further enhance their potential as cost-effective corrosion
inhibitors. Additionally, the use of plant extracts as inhibitors is a simple and straightforward process, offering
a significant option for protecting metal from corrosion
and saving large amounts of revenue.
The active components in plant extracts that contribute
to their antioxidant, anti-inflammatory, antiviral, and
antimicrobial properties can vary depending on the plant
species and the extraction method used (Figure 6). In terms
of corrosion inhibition, plant extracts containing active
components with antioxidant and anti-inflammatory
properties may help protect metals from corrosion by
reducing the formation of ROS and inflammation, which
are known to contribute to corrosion. Additionally, plant
extracts with antimicrobial properties may help prevent
microbial-induced corrosion by inhibiting the growth of
microorganisms on metal surfaces (Ituen et al. 2020).
Figure 5: Selection parameters for corrosion
inhibition.
N. Verma et al.: Flavonoids as anticorrosive materials
7
Table : Performance of plant extracts for corrosion inhibition of various materials.
Plant extract
Tested material
Method adopted
Arbutus unedo leaf
Sugarcane purple
rind ethanolic
extract
Artemisia vulgaris
Solanum tuberosum
Houttuynia cordata
MS in HCl medium
C-steel in a  M HCl
Colorimetric method
Polarization method
. g/L . %
 mg/L . %
Abdelaziz et al. ()
Meng et al. ()
MS samples in  M HSO
MS samples in  M HSO
Steel in an aqueous . M
HCl) solution
MS in HCl
Potentiodynamic polarization
Potentiodynamic polarization
EIS
, ppm . %
, ppm . %
, ppm . %
Parajuli et al. ()
Parajuli et al. ()
Vu et al. ()
EIS
, ppm  %
Dehghani et al. (a)
MS in HCl
MS in HCl
EIS
Gravimetric analysis
 ppm  %
.–. g/L . %
Dehghani et al. (b)
Ogunleye et al. ()
Aluminum alloy in aerated
. wt% NaCl solution
AA-T aluminum
alloy in . % NaCl
solutions
Aluminum alloy AAT in a . M HCl
Copper in HSO solution
Electrochemical noise analysis
Chinese gooseberry
fruit shell
Eucalyptus leaf
Luffa cylindrica leaf
extract
Garlic extract
Treculia africana
Newbouldia laevis
Artocarpus heterophyllus Lam.
Citrus reticulata
Papaya leaves
extract
Veratrum root
extract
Rosa laevigata
Artocarpus
heterophyllus
Bagassa guianensis
Ailanthus altissima
Ferula hermonis
Mangifera indica
Inhibitor %IE
concentration
References
Hajsafari et al. ()
EIS
 mL L− , Ω cm to
, Ω cm
. g/L –
Gravimetric analysis
. g/L . %
Udensi et al. ()
Udensi et al. ()
EIS
 ppm . %
He et al. ()
Copper in HSO solution
Copper in HSO solution
EIS
EIS
 ppm  %,
. mol/L . %
Xiang and He ()
Tan et al. ()
Copper in a HSO
EIS
 ppm  %
Feng et al. ()
EIS
Potentiodynamic polarization
methods
Zinc in a chloride medium Electrochemical and XPS
( % NaCl)
studies
Zn in a . M HCl solution Electrochemical measurements
Zn in a HCl
Electrochemical measurements
Zinc ions on MS
Electrochemical measurements
 ppm . %
 ppm  %
Zhang et al. ()
Kusumaningrum et al.
()
Lebrini et al. ()
Copper in a . M HSO
Copper in HNO
Rosmarinus officinalis Zinc oxide on low carbon
steel in  M HCl and HSO
solutions
Pyracantha coccinea Zn-coated substrates
Potentiodynamic polarization,
open circuit potential
measurement
Electrochemical measurements
There have been recent reports of novel plant extracts
that have significant corrosion inhibition properties in still,
aluminum, and copper alloys (Wei et al. 2020). Some of the
plant extracts that have shown promising results as corrosion inhibitors include those derived from neem leaves,
pomegranate peel, grapefruit peel, and aloe vera (Umoren
et al. 2019). These extracts have been found to contain
compounds such as alkaloids, flavonoids, tannins, and phenols that are responsible for their inhibitory properties. The
use of plant extracts as corrosion inhibitors could be a
 ppm  %
 ppm . %
 ppm . %
 ppm  %
. M . % in HCl and
. % in HSO
solution
. g/L –
Fouda et al. ()
Fouda et al. ()
Ramezanzadeh et al.
()
Loto ()
Sameh et al. ()
sustainable and effective solution to the problem of corrosion in various industries.
In recent research, various plant extracts, containing
flavonoids, have emerged as promising corrosion inhibitors
due to their eco-friendly nature and effective anticorrosive
properties (Zakeri et al. 2022). Examples of plant extracts
rich in flavonoids include citrus fruits (e.g., oranges, lemons),
onions, tea leaves, and various herbs like parsley and
chamomile. One significant advantage of using plant extracts as corrosion inhibitors is their long-term durability.
8
N. Verma et al.: Flavonoids as anticorrosive materials
Figure 6: Important properties of flavonoids.
Flavonoids form a protective layer on metal surfaces, which
acts as a barrier against corrosive agents, thereby prolonging the lifespan of the metal. Moreover, the molecular
mechanisms underlying the anticorrosion behavior of flavonoids involve their ability to chelate metal ions and form
complexes with metal surfaces, enhancing their corrosion
inhibition performance.
Regarding compatibility with existing coating systems,
plant extract-based inhibitors, including flavonoids, have
shown promising results. They can be incorporated into
various coating formulations without compromising their
effectiveness. Additionally, their eco-friendly nature makes
them suitable for use in environmentally conscious coating
systems. However, it is essential to conduct further research to
optimize the formulation and application of plant extractbased inhibitors for specific metal substrates and environmental conditions. Regarding compatibility with existing
coating systems, plant extract-based inhibitors can be incorporated into various coating formulations without significant
compatibility issues. They can serve as additives or active
components in primers, paints, or coatings designed for
corrosion protection. However, it is essential to consider
compatibility testing to ensure that the plant extract-based
inhibitors do not adversely affect the performance or properties of the coating system. Furthermore, the formulation and
application of plant extract-based inhibitors within coating
systems may require optimization to achieve the desired level
of corrosion protection and compatibility. This optimization
process involves considering factors such as the concentration
of inhibitors, the type of coating matrix, and the method of
application. Overall, plant extract-based inhibitors, including
flavonoids, offer promising long-term durability and compatibility with existing coating systems for corrosion protection
applications in the construction industry. However, thorough
research and testing are necessary to tailor these inhibitors to
specific requirements and ensure their optimal performance in
real-world scenarios.
Lin et al. explored the corrosion inhibition properties of
Pomelo peel extract on mild steel immersed in a solution
containing 1.0 mol/L of H3PO4 (Lin et al. 2021). The findings
indicated effective mitigation of corrosion, particularly with
higher concentrations of Pomelo peel extract, and this
inhibitory effect (92.8 %) persisted over an extended period
of 224 h, suggesting good long-term durability of the inhibitor. It was observed that the functional groups, such as
carbonyl, heterocyclic, and hydroxyl groups found in Pomelo
peel extract, played a key role in covering the steel surface,
thus preventing metal corrosion by forming a protective
layer which likely provides long-lasting defense against
corrosive agents. A more detailed examination of the
adsorption process unveiled that physical adsorption primarily governed the mechanism. Incorporating Pomelo peel
extract into coating formulations could enhance their
corrosion resistance properties, as observed in the study,
where Pomelo peel extract effectively prevented metal
corrosion by forming a protective layer.
N. Verma et al.: Flavonoids as anticorrosive materials
Additionally, different levels of Psidium guajava leaf
extract were introduced into a 1 mol/L solution of phosphoric acid to assess its effectiveness as a GCI for mild steel
samples (Victoria et al. 2015). The study demonstrated
promising inhibition efficiency (IE) of up to 89 % when
800 ppm of P. guajava leaf extract was present in the phosphoric acid solution. This suggests that the inhibitor is
effective in mitigating corrosion in the short term. However,
the minor decline in effectiveness observed as the concentration of GCI reached 1,200 ppm raises questions about its
long-term durability. This decline was attributed to the
detachment of GCI molecules, which could indicate potential
limitations in maintaining the protective barrier over
extended periods. Incorporating P. guajava leaf extract into
coating formulations could enhance their corrosion resistance properties, similar to other natural extracts like
Pomelo peel extract mentioned earlier.
Gunasekaran and Chauhan utilized Zenthoxylum alatum plant extract to inhibit corrosion in mild steel across
different concentrations of phosphoric acid solution. The
most notable performance was observed in the case of 88 %
H3PO4 compared to solutions with acid concentrations of
20 % and 50 % (Gunasekaran and Chauhan 2004). Through
surface analysis and electrochemical experiments, it was
proposed that during the initial stage of metal dissolution, a
reaction occurred between the dissolved iron ions and the
GCI, leading to the creation of an organo-metallic complex
layer. Subsequently, phosphate ions reacted with this layer,
resulting in the formation of a layer primarily consisting of
iron phosphate, catalyzed by the presence of the organometallic complex. Consequently, the progressive dissolution
of iron was impeded owing to the development of the
aforementioned layers.
NaCl solutions simulate the corrosive effects of saltwater or de-icing salts used in road maintenance. These solutions are relevant for buildings located in coastal areas or
regions where de-icing salts are used, as they can lead to
accelerated corrosion of metal components. An assessment
was conducted on peach pomace hydroalcoholic extract as a
GCI for a mild steel surface in a 0.5 mol/L NaCl solution
(Vorobyova and Skiba 2021). Flavonoid and phenolic compounds were identified in the extract, and the most effective
inhibitory characteristic (∼88 %) was witnessed following a
48-h immersion with 800 ppm of GCI present. The study
demonstrated an inhibitory characteristic of approximately
88 % after a 48-h immersion with 800 ppm of peach pomace
extract present. This indicates that the inhibitor is effective
in mitigating corrosion in the short term. The confirmation
of a protective film formation on the steel substrate suggests
that peach pomace extract may provide long-term corrosion
protection by forming a barrier against corrosive agents.
9
The effectiveness of Nigella sativa L. oil extract as a
corrosion inhibitor was investigated to safeguard iron in an
acidic solution comprising Na2SO4, NaHCO3, and NaCl (Chellouli
et al. 2016). As per the findings, N. sativa L. oil extract exhibited
favorable performance as a mixed-type inhibitor, indicating its
potential to provide corrosion protection over a prolonged
period. The observed decrease in corrosion rate with higher
concentrations of the inhibitor suggests that it may offer sustained corrosion inhibition over time. By incorporating N.
sativa L. oil extract into coating formulations resistance properties could potentially be enhanced, similar to other natural
extracts.
Additionally, surface analyses confirmed the outstanding
protective properties of the GCI for iron substrates, achieving
an IE of 99 % at a concentration of 2,500 ppm. Furthermore, in
research conducted by Barbouchi et al., essential oil extracts
derived from different components of Pistacia terebinthus L.
were investigated as a corrosion inhibitor for iron substrates
in a 3 % NaCl solution (Barbouchi et al. 2020). The experimental results demonstrated that the essential oils extracted
from the fruit displayed superior anticorrosion characteristics compared to extracts from twigs and leaves.
Palanisamy et al. investigated the use of Ricinus communis extract as a GCI for a steel substrate in a 3.5 % NaCl
solution (Palanisamy et al. 2018). The current density values
exhibited a decrease, and this decline correlated directly
with the rise in GCI concentration. Furthermore, an
augmentation in charge transfer measurements was unveiled in EIS outcomes, corroborating the interface-type
mode of operation for the R. communis extract. The peak
effectiveness was noted at a concentration of 100 ppm.
In research conducted by Lopes-Sesenes et al., multiple
electrochemical methods were employed to examine the
impact of Buddleia perfoliata leaves extract on the corrosion
prevention of a carbon steel substrate in a 0.5 mol/L H2SO4
solution (Lopes-Sesenes et al. 2013). The investigators conducted investigations at different rotational speeds (up to
2,000 r/min) to assess the influence of rotation speed on the
adsorption of GCI molecules on the steel surface. Variations in
rotation speed were shown to affect the substrate’s corrosion.
The findings indicated that corrosion rate increased up to 500 r/
min; however, it began to decrease at higher rotational speeds.
4 Corrosion behavior of building
materials
In the context of building materials, corrosion can have
significant implications for the structural integrity and
durability of the construction. Different building materials
10
N. Verma et al.: Flavonoids as anticorrosive materials
exhibit varying degrees of susceptibility to corrosion. When
metals are used in structural engineering applications, they
often come into contact with different mineral building
materials, such as cement and gypsum. These materials
contain compounds that can react with the metals and cause
corrosion over time (Cwalina 2014). For example, when steel
is in contact with cement or concrete, the alkaline environment can cause the formation of a protective layer on the
steel surface, known as a passive film (Ming et al. 2021).
However, this film can be disrupted by the presence of
chloride ions, which can penetrate the concrete and reach
the steel surface. Once the passive film is disrupted, the steel
can become vulnerable to corrosion.
Similarly, when copper or zinc is in contact with cement
or concrete, it can also be subject to corrosion. This is
because these metals can react with the cement and form
compounds that can lead to corrosion. In the case of
aluminum, it can also be susceptible to corrosion when in
contact with cement or concrete, particularly if it is exposed
to chloride ions (Balonis et al. 2019). Aluminum can form a
passive oxide layer on its surface, but this layer can be disrupted by chloride ions, leading to pitting corrosion
(Natishan and O’grady 2014). Lead is less susceptible to
corrosion than other metals, but it can still react with cement
and form lead carbonate, which can be harmful to the
environment (Kong et al. 2022). The interactions between
metals and mineral building materials can have a significant
impact on corrosion in structural engineering applications.
It is important to consider the potential for corrosion when
selecting materials and designing structures to ensure their
longevity and durability (Ismail and El-Shamy 2009).
4.1 Iron/steel
In the presence of oxygen and water, iron undergoes a
series of reactions that lead to the formation of rust, which
is primarily composed of iron (III) hydroxide. The process
starts with the conversion of iron metal into iron (II) hydroxide (Fe(OH)2), which is then oxidized by oxygen to
form FeOOH. This process is known as the rusting of iron
or corrosion (Tahawy et al. 2021). The formation of rust on
iron or steel surfaces is a major concern as it weakens the
material and can lead to structural failures. The pH of the
aqueous medium plays a critical role in the corrosion
process. In a nearly neutral to weakly basic medium, the
corrosion rate of iron is relatively high. This is because the
formation of a protective oxide layer is hindered in such
an environment. Reaction of formation of corrosion
products of iron in neutral or basic medium and in acidic
medium is presented in Figure 7.
Figure 7: Reaction of formation of corrosion products of iron in neutral
or basic medium and in acidic medium.
However, in an acidic environment, the corrosion rate is
even higher as the acid reacts with the oxide layer, leaving
the metal surface exposed to further corrosion. On the other
hand, in a strongly basic environment, the corrosion rate is
reduced as the alkaline medium promotes the formation of a
protective oxide layer on the metal surface (Tamura 2008).
Therefore, it is important to consider the pH of the environment when designing materials for use in corrosive environments. Materials such as stainless steel are often used
in such applications as they have a high resistance to
corrosion due to the formation of a stable and protective
oxide layer on their surface.
In Portland cement-based concrete, steel is protected
against corrosion by the highly alkaline pore water in the
concrete. When Portland cement hydrates, it produces calcium hydroxide (Ca(OH)2), which is highly alkaline and
contributes to the high pH of the concrete pore water. The
high pH of the concrete pore water creates a passivating
layer of hydrated iron oxide (Fe2O3.nH2O) on the surface of
the steel (Plusquellec et al. 2017). This passivating layer acts
as a barrier to prevent the diffusion of oxygen, moisture, and
other corrosive agents to the steel surface, thereby protecting it from corrosion.
The thickness of the passivating layer depends on several
factors, including the pH of the concrete pore water, the
composition of the concrete, and the exposure conditions. In
general, the passivating layer can range from 2 to 20 μm in
thickness (Angst et al. 2017). However, it is important to note
that the presence of aggressive ions, such as chloride or sulfate
ions, can break down the passivating layer and cause pitting
corrosion on the steel surface. Therefore, it is important to limit
the amount of these ions in the concrete mix and to provide
adequate concrete cover to the steel reinforcement to prevent
exposure to aggressive agents.
The corrosion-protective effect of concrete on
embedded steel can be compromised if the pH of the concrete pore water falls below a certain threshold, which is
typically around pH 9.0. At lower pH levels, the passive layer
of hydrated iron oxide on the steel surface breaks down, and
N. Verma et al.: Flavonoids as anticorrosive materials
corrosion can occur (Huet et al. 2005). Carbon dioxide from
the air reacts with the calcium hydroxide in the concrete to
form calcium carbonate, which is a neutral compound. This
reaction reduces the amount of alkaline ingredients in the
concrete and decreases the pH of the pore water, which can
lead to the breakdown of the passive layer on the steel surface and subsequent corrosion.
Another important factor that affects the corrosion of
embedded steel in concrete is the availability of oxygen. The
passive layer on the steel surface can only form and be maintained if there is enough oxygen available to facilitate the formation of the hydrated iron oxide. If oxygen is limited or
prevented from reaching the steel surface, the passive layer can
break down and corrosion can occur (Alhozaimy et al. 2016). The
corrosion protection of steel in concrete is dependent on several
factors, including the pH of the pore water, the presence of
aggressive ions, the amount of free water in the cement stone,
and the availability of oxygen. Proper design, material selection,
and construction practices can help minimize the risk of
corrosion in reinforced concrete structures (Cwalina 2014).
HCl is commonly found in industrial settings and can be
present in building materials due to pollution or chemical
processes. The performance of inhibitors in HCl solutions
provides valuable insights into their effectiveness in environments where acidic substances may come into contact
with building materials. Abdelaziz et al. investigated the use
of leaves extract from the Arbutus unedo leaf plant as a green
corrosion inhibitor for mild steel (MS) in HCl medium
(Abdelaziz et al. 2021). The aqueous extract derived from the
leaves of A. unedo leaf plant was found to be abundant in
polyphenols, specifically flavonoid compounds, which were
quantitatively determined using the aluminum chloride
colorimetric method. The aqueous extract derived from the
leaves of A. unedo leaf plant was found to be abundant in
polyphenols, specifically flavonoid compounds, which were
quantitatively determined using the aluminum chloride
colorimetric method. Among the various extracts tested, the
n-butanol extract exhibited the highest concentration of total phenols and total flavonoid contents, measuring 219.46
gallic acid equivalent (GAE) mg/g extract and 174.66 mg
quercetin equivalents (QE)/g of dry extract, respectively. The
initial corrosion current density (Icorr) and corrosion potential (Ecorr) measured without the presence of leaves
extract from A. unedo leaf extract are 348.98 μA/cm2
and −500.79 mV/SCE, respectively. Furthermore, the introduction of different concentrations of A. unedo leaves extract
results in a reduction in both cathodic and anodic current
densities. The findings indicated that as the concentration of
leaves extract increases, the corrosion current density decreases (reaching 41.55 μA/cm2 at a concentration of 0.5 g/L).
Clearly, even at low concentrations, the addition of the plant
11
extract leads to a significant decrease in current density
values, thereby enhancing the IE up to a maximum of
88.09 % (0.5 g/L). The effectiveness of A. unedo L. leaves
extract as a corrosion inhibitor is influenced by its organic
constituents, particularly the phenol and flavonoid contents.
The total flavonoid content of the extract varies from
9.10 ± 7.70 to 174.66 ± 35.11 mg QE/g of dry extract, with the
n-butanol extract exhibiting the highest concentration.
Meng et al. investigated the corrosion inhibitory properties of sugarcane purple rind ethanolic extract (SPRE) for
carbon steel in a 1 M HCl solution (Meng et al. 2021). The
results revealed that the IE of C-steel in the HCl solution
increased with higher concentrations of SPRE. However,
elevated temperatures moderately decreased the anticorrosive efficacy of SPRE. The maximum IE of 96.2 % was
achieved at 298 K using 800 mg/L of SPRE. The polarization
curves indicated that SPRE suppressed both the anodic and
cathodic reactions, classifying it as a mixed-type corrosion
inhibitor with a predominant anodic effect. The corrosion
current density (icorr-P) decreased as the concentration of
SPRE increased, while the charge transfer resistance (Rct)
increased, indicating enhanced inhibitory properties due to
SPRE adsorption. At higher temperatures, partial desorption
of SPRE occurred, resulting in a slight increase in icorr-P and
a decrease in Rct. However, even at 328 K, SPRE maintained
its morphology and wettability.
Two different alkaloids were extracted from plants
Artemisia vulgaris and Solanum tuberosum. These alkaloids
were then tested as corrosion inhibitors for MS samples in
1 M H2SO4 (Parajuli et al. 2022). The corrosion inhibition
potential of the extracted alkaloids was evaluated using
weight loss and potentiodynamic polarization measurement
methods. The results showed that the corrosion IE of A.
vulgaris alkaloid was 92.58 %, while that of S. tuberosum
alkaloid was 90.79 %, based on the weight loss measurement
after immersing the samples for 6 h in a 1,000 ppm inhibitor
solution. Furthermore, the potentiodynamic polarization
measurement revealed that the corrosion IE of A. vulgaris
alkaloid was 88.06 %, and for S. tuberosum alkaloid, it was
83.22 % for a sample immersed for 1 h in a 1,000 ppm inhibitor solution. These findings suggest that the alkaloids
extracted from A. vulgaris and S. tuberosum plants have
promising efficiency as corrosion inhibitors for MS in H2SO4.
Vu et al. presented a study on the corrosion inhibition
properties of Houttuynia cordata leaf extract for steel in an
aqueous 0.1 M HCl solution (Vu et al. 2020). The research
findings reveal that the H. cordata leaf extract acts as a
mixed-type inhibitor for steel, effectively inhibiting the
corrosion process. It exhibits a high level of inhibition performance, with up to 98.3 % corrosion inhibition achieved by
adding 1,500 ppm of the inhibitor. Dehghani and coworkers
12
N. Verma et al.: Flavonoids as anticorrosive materials
explored the potential of Chinese gooseberry fruit shell
extract as a green and cost-effective corrosion inhibitor for
MS in acidic solutions, especially in HCl environments
(Dehghani et al. 2019a). The extract contains soluble biologically active compounds that effectively inhibit MS corrosion. Electrochemical tests showed up to 92 % IE with
1,000 ppm extract after 2.5 h of metal immersion. Weight loss
experiments also revealed 94 % efficiency after 5 h at 25 °C.
The extract primarily exhibits cathodic inhibition with
minimal impact on the hydrogen evolution reaction.
The study by Dehghani and coworkers investigated the
corrosion inhibition impact of Eucalyptus leaf extract (ELE)
on mild steel (MS) in HCl solution through experimental and
computational analyses (Dehghani et al. 2019b). Electrochemical impedance spectroscopy (EIS) revealed that higher
ELE concentrations led to a significant increase in charge
transfer resistance, resulting in an IE of approximately 88 %
with 800 ppm ELE after 5 h of exposure. Polarization tests
showed mixed inhibition effects of ELE with a slight cathodic
prevalence, reducing the corrosion current density (icorr)
from 0.93 μA/cm2 for the uninhibited sample to 0.25 μA/cm2
for the inhibited sample (800 ppm ELE).
Ogunleye and coworkers investigated the green corrosion inhibition properties of Luffa cylindrica leaf extract
(LCLE) on MS in a HCl environment (Ogunleye et al. 2020).
Various techniques were employed, including gravimetric,
depth of attack, and surface analysis. The study examined
the effect of inhibitor concentrations (0.50–1.00 g/L), temperatures (30–60 °C), and immersion time (4–12 h) on the IE
of the LCLE on MS immersed in a 0.5 M HCl solution. The
optimum IE of 87.89 % was achieved.
4.2 Aluminum
The good corrosion resistance of aluminum is due to the
formation of a passive oxide or hydroxide layer on its surface. This layer acts as a barrier that protects the underlying
metal from further corrosion (Jagtap et al. 2022). The passive
layer on aluminum is formed naturally in the presence of
oxygen and water, and it is stable in a pH range between 4
and 9. In this pH range, the passive layer is largely insoluble
and prevents further corrosion of the metal. As a result,
aluminum materials are resistant to corrosion in nearly
neutral to weakly acidic aqueous media, as well as in humid
air and atmospheric corrosion conditions.
The passive layer on aluminum is also self-renewing,
meaning that if it is damaged or scratched, it will quickly
reform in the presence of oxygen and water. This property of
self-renewal further enhances the corrosion resistance of
aluminum (Chen et al. 2020). The good corrosion resistance of
aluminum makes it a popular material in constructional engineering, particularly in applications where it is exposed to
outdoor or corrosive environments. Additionally, aluminum is
lightweight, strong, and easily fabricated, making it an attractive material for a wide range of structural and decorative
applications.
In strongly acidic solutions, the protective layer on
aluminum can be dissolved, leaving the underlying metal
vulnerable to general corrosion. Similarly, in strongly alkaline solutions, the protective layer can be converted into a
more soluble form, which also leaves the underlying metal
vulnerable to corrosion (Green 2020). The disintegration of
the protective layer on aluminum in more strongly alkaline
media can begin at a pH as low as 9.0, which is why the
application of aluminum and its alloys is not recommended
in strongly alkaline environments. In such environments,
aluminum is susceptible to general corrosion, which can
lead to a loss of strength and durability in structural applications. Therefore, when selecting materials for use in environments with extreme pH levels, it is important to
consider the amphoteric nature of aluminum and its susceptibility to corrosion in strongly acidic or alkaline solutions. Other materials with better resistance to such
environments, such as stainless steel or plastics, may be
more suitable for these applications.
Aluminum materials are highly reactive, as you would
expect from their position in the electrochemical series. Even in
the absence of oxygen, aluminum can react with acids or bases
to produce hydrogen gas and soluble aluminum salts, such as
aluminates (Zhang et al. 2009). For example, in strongly acidic
solutions, aluminum reacts with hydrogen ions (H+) to form
aluminum ions (Al3+) and hydrogen gas (H2):
2Al(s) + 6H+ (aq) → 2Al3+ (aq) + 3H2 (g)
In strongly alkaline solutions, aluminum reacts with
hydroxide ions (OH−) to form soluble aluminum hydroxide
species and hydrogen gas:
2Al(s) + 6OH− (aq) + 3H2 O(l) → 2[Al(OH)4 ]− (aq) + 3H2 (g)
These reactions can contribute to the corrosion of
aluminum in acidic or alkaline environments and can also
result in the evolution of hydrogen gas, which can be hazardous in certain applications. Therefore, it is important to
consider the reactivity of aluminum when selecting materials for use in corrosive environments, and to take appropriate precautions to prevent or mitigate corrosion and
hydrogen gas evolution (Ibrahimi et al. 2021).
In the presence of free alkali hydroxides in the pore solution of Portland cement building materials, aluminum and its
alloys can undergo general corrosion, which can result in the
N. Verma et al.: Flavonoids as anticorrosive materials
formation of soluble aluminum hydroxide species and the loss
of material. This can occur through a process called alkaline
attack, which is a type of chemical corrosion that is driven by
the highly alkaline environment of the concrete (Hansson et al.
2012). Alkaline attack can occur when aluminum is in direct
contact with fresh concrete or with concrete that has not yet
fully cured. During the early stages of curing, the pore solution
of the concrete is highly alkaline due to the presence of free
alkali hydroxides, such as sodium hydroxide and potassium
hydroxide. These hydroxides can react with the surface of the
aluminum to form soluble aluminum hydroxide species, which
can then be washed away by the alkaline pore solution (Wei
et al. 2022).
To prevent alkaline attack of aluminum in Portland
cement building materials, it is important to use appropriate
coatings or barrier materials to protect the aluminum surface
from contact with the alkaline environment. Additionally,
aluminum alloys that are specifically designed for use in corrosive environments, such as those with high levels of chromium or other corrosion-resistant elements, may be used to
mitigate the effects of alkaline attack (Quiambao et al. 2019).
Anodization is an electrochemical process that forms an
oxide layer on the surface of aluminum, which provides
protection against corrosion and enhances the material’s
appearance. However, this anodization layer produced
anodically, also known as Eloxal, can still be vulnerable to
attack by moist alkaline-reacting building materials. This
can occur when the anodized aluminum comes into contact
with such materials, causing the protective layer to break
down and exposing the underlying metal to corrosion (Lee
and Park 2014). To prevent corrosion damage caused by
contact with moist alkaline building materials, it is essential
to apply additional protection to the aluminum.
Metals like aluminum and its alloys can be susceptible to
corrosion when they come into contact with alkaline materials, and the risk of corrosion increases as the pH value of
the material increases. One way to limit the corrosion of
aluminum is to choose an adequate binding agent that can
help protect the metal surface from the corrosive effects of
the alkaline material (Nazeer and Madkour 2018). In the case
of concrete, not all types of concrete are equally aggressive
toward aluminum. Some types of concrete, such as autoclaved aerated concrete (gas concrete), have a relatively low
alkalinity and are not considered aggressive toward
aluminum. Therefore, the risk of corrosion in aluminum
materials can be minimized by choosing the appropriate
type of concrete for the construction project (Herting and
Odnevall 2021).
The study investigates the influence of garlic extract as a
green inhibitor on the uniform and localized corrosion of
aluminum alloy in aerated 3.5 wt% NaCl solution (Hajsafari
13
et al. 2021). The electrochemical noise analysis revealed that
the garlic extract initially increases the pit initiation rate by
forming an antioxidant layer on the aluminum surface.
However, with time, the chemical adsorption of the extract
strengthens, leading to a significant reduction in the propagation of corrosion damage by up to one-tenth. The EIS
results indicated that a garlic extract concentration of
8 mL L−1 induced the most effective inhibition, enhancing
the corrosion resistance from 2,917 Ω cm2 to 14,557 Ω cm2.
Udensi et al. evaluated the corrosion inhibition performance of a low-cost and eco-friendly extract obtained from
Treculia africana leaves on AA7075-T7351 aluminum alloy in
2.86 % NaCl solutions (Udensi et al. 2021). The results of
various characterization techniques showed comparable IE
of T. africana. Increasing the T. africana concentration and
temperature of the environment led to an increase and
decrease in η, respectively. The suitability of T. africana as an
eco-friendly inhibitor for the corrosion of AA7075-T7351
aluminum alloy in 2.86 % NaCl solution was investigated.
The IE obtained from gravimetric, EIS, and Tafel polarization
(TP) techniques were in agreement, particularly for T. africana concentrations of 0.6 g/L and above. Higher inhibition
efficiencies were observed at lower temperatures in the
environment. Moreover, increasing T. africana concentrations raised the activation barrier for corrosion initiation,
indicating the inhibitory effect of T. africana on the corrosion process. These findings provide strong justification for
the use of T. africana leaves extract as an eco-friendly and
effective corrosion inhibitor for AA7075-T7351 aluminum
alloy in chloride-containing environments.
Another study by Udensi et al. explored the corrosion inhibition properties of Newbouldia laevis leaves extract on
aluminum alloy AA7075-T7351 in a 1.0 M HCl environment
(Udensi et al. 2020). The extract contains biologically active and
water-soluble compounds such as luteolin 7-glucoside and
phenolic polymeric compounds, which act as organic corrosion
inhibitors for aluminum. Gravimetric analysis revealed that
the optimal IE was 86.1 % at room temperature (298 ± 1 K) and
67.5 % at 338 K for the maximum concentration of 0.6 g/L of N.
laevis extract. The results indicated that the N. laevis extract’s
inhibitory effect was influenced by temperature, and the inhibition process was likely achieved through an electrostatic
attraction of the polymeric components of the N. laevis extract
onto AA7075-T7351 coupons or physical adsorption.
4.3 Copper
The excellent corrosion resistance of copper materials is due
to their “noble” character, which means they have a positive
standard electrode potential of +0.34 VH. This makes them
14
N. Verma et al.: Flavonoids as anticorrosive materials
less likely to undergo oxidation and corrosion compared to
other metals with lower electrode potentials (Jing et al. 2008).
Copper materials also have the ability to form protective
layers in many normal media, chemicals, and on contact
with building materials. In water and neutral salt solutions,
copper materials have excellent corrosion resistance in a
wide pH range. In diluted (nonoxidizing) acids and in the
alkaline region, copper is particularly superior to other
noniron metals.
However, copper and its alloys can become inapplicable
if the formation of protective layers is hampered, and the
material is heavily attacked through the formation of complex salts, such as when in contact with ammonia and
ammoni-alkaline solutions. In these cases, the copper material may corrode more rapidly, and additional measures
such as protective coatings or selection of alternative materials may be necessary to prevent corrosion damage
(Gurrappa 2005). Copper and its alloys are resistant to uniform corrosion when embedded in moist concrete or cement
mortar because of the protective layer of slightly soluble
copper (I) oxide that forms on the surface when exposed to
air. This layer is virtually insoluble in alkalis and helps to
protect the metal from corrosion (Bacelis et al. 2020). As a
result, copper and its alloys are often used in construction
for their corrosion resistance and durability, particularly in
environments where they may be exposed to moisture or
other corrosive agents.
When cements with higher alkalinity (pH value of the
cement stone pores solution > 13.3) are used, the protective
layer of copper (I) oxide on the surface of copper and its
alloys may be disrupted, leading to accelerated corrosion.
Brasses, which are copper alloys that contain significant
amounts of zinc, are especially susceptible to corrosion in
these conditions (Megahed et al. 2020). Zinc is more reactive
than copper and can form complex salts with alkalis, leading
to the breakdown of the protective layer on the surface of the
brass. Therefore, in situations where cements with high
alkalinity are used, it may be necessary to consider alternative materials or protective coatings to prevent corrosion
damage to copper and its alloys, especially brasses (Assad
et al. 2023).
Artocarpus heterophyllus Lam. leaves extract was used
as the corrosion inhibitor for copper in H2SO4 solution (He
et al. 2021). Scanning electron microscope (SEM) and atomic
force microscope (AFM) results showed that when A. heterophyllus Lam. leaves extract was added to a H2SO4 environment, the copper surface remained flat. Electrochemical
experiments revealed that at 500 ppm concentration of A.
heterophyllus Lam. leaves extract, the corrosion IE obtained
from EIS data was 97.3 %. Even at a temperature of 313 K, the
corrosion inhibition nature of A. heterophyllus Lam. leaves
extract remained at 97 %. The A. heterophyllus Lam. leaves
extract was found to be adsorbed onto the copper surface in
a Langmuir monolayer adsorption manner. These findings
indicate the potential of A. heterophyllus Lam. leaves extract
as an effective corrosion inhibitor for copper in a H2SO4
environment.
Xiang and He studied the investigation of the anticorrosion properties of Citrus reticulata leaves extract on copper in a sulfuric acid environment using both theoretical and
experimental approaches (Xiang and He 2021). One of the key
findings of their research is that when the C. reticulata leaves
extract concentration is 500 mg/L, its IE can be as high as
97.3 %, indicating that it is effective in inhibiting the corrosion of Cu in the presence of sulfuric acid. Furthermore, the
researchers investigated the effect of soak time on the
corrosion inhibition nature of C. reticulata leaves extract.
They found that even after 24 h of immersion in a sulfuric
acid solution containing 500 mg/L C reticulata leaves extract,
the IE of C. reticulata leaves extract remains relatively high
at over 93 %. This suggests that C. reticulata leaves extract is
capable of forming a stable barrier film on the surface of the
copper electrode, providing sustained protection against
corrosion over an extended period.
Tan et al. investigated the potential of Papaya leaves
extract (PLE) as an eco-friendly corrosion inhibitor for
copper in a sulfuric acid medium (Tan et al. 2021). The study
demonstrated that PLE exhibits excellent anticorrosion
properties over a specific temperature range. Morphological
analysis tests conducted at different temperatures provided
strong evidence of PLE’s ability to inhibit corrosion. Additionally, X-ray photoelectron spectroscopy (XPS) results
showed the formation of an adsorption film on the copper
surface, specifically consisting of Cu–S bonds and Cu–N
bonds. These bonds contribute to the anticorrosion mechanism of PLE. The research also found that PLE performs
remarkably well in a sulfuric acid corrosion solution with a
concentration of 0.5 mol/L. Even with increasing temperatures within a specific temperature range (298–308 K), PLE
continues to demonstrate excellent anticorrosion performance for copper.
Feng and coworkers explored the potential of Veratrum
root extract as an eco-friendly corrosion inhibitor for copper
in a H2SO4 solution (Feng et al. 2021). It was found that at a
concentration of 200 ppm, Veratrum root extract achieved
an impressive IE of 97 %, signifying its high effectiveness as
an inhibitor. Zhang et al. explored the potential of Rosa
laevigata extract as an environmentally friendly corrosion
inhibitor for copper in a 0.5 M sulfuric acid solution (Zhang
et al. 2022). The electrochemical tests demonstrated that R.
laevigata extract functions as a mixed-type inhibitor, with a
corrosion IE reaching 89.8 % at a concentration of 300 mg/L.
N. Verma et al.: Flavonoids as anticorrosive materials
The inhibitive ability of R. laevigata extract remained significant within a certain temperature range. The adsorption of R.
laevigata extract on the copper surface followed the Langmuir
adsorption model, with Kads (adsorption equilibrium constant)
and ΔG0ads (standard free energy of adsorption) values at 298 K
being 36.97 L/g and −26.07 kJ/mol, respectively. This indicates
that the adsorption process is spontaneous and involves both
chemisorption and physisorption. AFM results revealed that
the immersion of the copper sample in R. laevigata extract
solution led to a decrease in the average roughness value from
38.9 nm to 13.2 nm, suggesting a positive effect on the surface
morphology of copper. Additionally, the theoretical calculations provided insight into the inhibitory properties of specific
molecules present in the R. laevigata extract. The Ebinding values
(binding energies) for 6,7-dimethoxycoumarin, catechin,
kaempferol, and loliolide were determined to be 341.5 kJ/
mol, 514.1 kJ/mol, 500.3 kJ/mol, and 316.0 kJ/mol, respectively. These values indicate that these molecules exhibit a
certain degree of inhibition on copper corrosion in sulfuric acid solution.
Kusumaningrum investigated the potential of A. heterophyllus peel extract, a nontoxic fruit waste containing antioxidants, as a corrosion inhibitor for protecting pure
copper in nitric acid (HNO3) environments (Kusumaningrum et al. 2022). The study explored the corrosion inhibition
properties of the peel extract at varying concentrations (0–
800 ppm) through potentiodynamic polarization methods.
The results indicated that the A. heterophyllus peel extract
acts as a mixed inhibitor, primarily of the anodic type. The
highest IE observed was 98 % at a concentration of 800 ppm
and a temperature of 25 °C. The adsorption of inhibitor
molecules on the pure copper surface followed the Frumkin
adsorption isotherm equation, with physical adsorption
being the dominant mechanism.
4.4 Zinc
Zinc has a negative standard electrode potential (−0.76VH)
and is, therefore, thermodynamically susceptible to corrosion (Hoang Huy et al. 2021). However, like aluminum, it also
has the ability to form protective coatings made of solid
corrosion products in many normal environments and
building materials by reacting with its surroundings
(Popoola et al. 2014). These protective coatings, which are
primarily composed of zinc oxide and zinc hydroxychloride,
help to prevent further corrosion of the underlying zinc
material by acting as a physical barrier and inhibiting the
movement of ions and other corrosive agents. As a result,
zinc is often used in construction for its corrosion resistance,
durability, and aesthetic qualities.
15
Zinc is an amphoteric metal, which means it can react
with both acids and bases. As such, it is not resistant in both
acidic environments with a pH below 5 and alkaline environments with a pH above 12. In more alkaline solutions,
zinc hydroxide can form and react with the alkaline compound to create readily soluble and nonprotective zincates,
while also producing hydrogen gas. This reaction can lead to
the breakdown of any protective coatings on the surface of
zinc, increasing the susceptibility of the metal to further
corrosion. Therefore, it is important to consider the pH of the
surrounding environment when using zinc in construction
and to implement appropriate protective measures, such as
coatings or galvanization, to prevent corrosion damage
(Hale et al. 2012).
In alkaline concrete with high pH values of the pore’s
solution (between 12.6 and 13.8), zinc can be susceptible to
corrosion due to its amphoteric reaction. However, it has
been observed that for pH values of the pores solution ≤ 13.3,
the dissolution rate of zinc under the formation of hydrogen
quickly diminishes (Andrade and Alonso 2004). This can be
explained by the passivation of the zinc surface, which occurs when a thin and stable layer of corrosion products
forms on the surface of the metal. This layer acts as a barrier
and prevents further corrosion of the zinc substrate.
Therefore, when using zinc in construction applications
where it will be exposed to alkaline environments, it is
important to consider the pH of the environment and ensure
that appropriate measures, such as passivation or galvanization, are taken to prevent corrosion damage (Pokorný
et al. 2017). The formation of the slightly soluble calcium
hydroxozinkat Ca[Zn(OH)3]2·2H2O in the presence of Ca(OH)2
and Zn(OH)2 is believed to be responsible for the passivation
of zinc in concrete. This corrosion product forms a protective
layer on the surface of the zinc, which slows down the
corrosion process (Pokorný et al. 2019). While zinc is still
susceptible to corrosion in alkaline building materials, it is
less susceptible than aluminum and lead and slightly more
susceptible than copper materials. The critical pH value of
13.3, the passivatability of zinc is more restricted with
increasing alkalinity, and zinc corrosion increases significantly. However, in carbonated concrete, the corrosion rate
of zinc can be slightly higher than in alkaline concrete, but it
is still considerably lower than that of steel. Therefore,
galvanized reinforcing steels are often used if premature
carbonation is expected.
Chromium in cement can form a passive layer on the
surface of the zinc, which can protect it from further corrosion.
The passivation process is accelerated in the presence of
chromium, and the resulting protective layer is more stable
and durable. Chromium can also react with other components
in the cement to form insoluble compounds that further protect
16
N. Verma et al.: Flavonoids as anticorrosive materials
the zinc from corrosion. However, it is important to note that
excessive amounts of chromium can have negative environmental impacts and may lead to health concerns, so the amount
of chromium in cement must be carefully controlled (Ai et al.
2016).
Lebrini et al. focused on evaluating the effect of Bagassa
guianensis extract on the corrosion behavior of zinc in a
chloride medium (3 % NaCl) (Lebrini et al. 2020). The results
of the study demonstrated that the plant extract from B.
guianensis served as a sustainable and environmentally
friendly inhibitor for zinc corrosion in a 3 % NaCl solution.
At a concentration of 100 ppm, the extract exhibited an
impressive IE of approximately 97 %. The presence of the
green inhibitor influenced the electrochemical reactions, as
observed from the polarization curves. In the presence of the
extract in the 3 % NaCl solution, a shift toward more positive
potentials was detected.
In a study conducted by Fouda et al., the corrosion inhibition properties of Ailanthus altissima extract were
investigated for Zn in a 0.5 M HCl solution (Fouda et al. 2018).
The researchers found that the extract from A. altissima
demonstrated effective corrosion inhibition for Zn in the
acidic solution. Chemical and electrochemical measurements provided evidence supporting the inhibitive nature of
the A. altissima extract. The IE increased with higher doses
of the extract and decreased with elevated temperatures.
The maximum IE value recorded was 77.5 % at a concentration of 500 ppm.
Fouda et al. reported the use of Ferula hermonis plant
extract as a corrosion inhibitor for Zn in HCl solution (Fouda
et al. 2021). The results of the study indicated that the F.
hermonis extract exhibited good efficiency in preventing
zinc corrosion and displayed high inhibition efficiencies. The
maximum IE was observed to be approximately 90.6 % at a
concentration of 300 ppm of the extract. This suggests that
the extract has a significant inhibiting effect on zinc corrosion in HCl solution. Furthermore, the study revealed that
the %IE increased with an increase in the concentration of
the F. hermonis extract, indicating a concentrationdependent inhibition effect. However, the IE was found to
decrease with increasing temperature, implying that higher
temperatures might weaken the inhibiting properties of the
extract.
Ramezanzadeh investigated the combined corrosion
inhibition properties of different compounds found in
Mangifera indica leaves extract and zinc ions on MS in
simulated seawater (Ramezanzadeh et al. 2019). The corrosion inhibitory capability of M. indica extract in saline solution was evaluated using electrochemical techniques. The
results from polarization tests revealed that the highest
corrosion inhibition power, reaching 91 %, was achieved
when a combination of 400 mg/L of M. indica extract and
400 mg/L of zinc cations was used. This indicates that the
presence of both M. indica extract and zinc ions together
provides a strong synergistic effect, leading to enhanced
corrosion inhibition of MS in the simulated seawater
environment.
Loto et al. investigated the corrosion inhibition and
surface protection properties of a combined admixture of
Rosmarinus officinalis (a plant extract) and zinc oxide on low
carbon steel in 1 M HCl and H2SO4 solutions (Loto 2018). The
results obtained from the study confirmed that the plant
extract showed higher effectiveness in the presence of HCl
solution compared to H2SO4 solution. In 1 M HCl, the optimal
IE reached 93.26 %, while in H2SO4, it was 87.7 %. The compound exhibited mixed-type inhibition behavior in both
acids, indicating that it can inhibit the corrosion of low
carbon steel through multiple mechanisms. The plant
extract caused a shift in the corrosion potential values of the
low carbon steel, which indicates specific corrosion inhibition behavior without the application of an external potential. In HCl, the corrosion potential shifted cathodically,
while in H2SO4, it shifted anodically.
Sameh investigated the potential of Pyracantha coccinea
phenolic extracts as eco-friendly plating additives in zinc
electroplating processes (Sameh et al. 2021). The study explores the effect of these extracts on the electrodeposition
process, coating morphology, and corrosion resistance of
zinc-plated substrates. The results demonstrated that the
electrodeposition process was significantly influenced by
both the concentration of the additives and the specific type
of extract used. Moreover, the study showed that the presence of the P. coccinea extracts during the plating process
enhanced the corrosion resistance of the zinc-coated substrates compared to coatings formed without the extracts.
Specifically, when 1.2 g/L of EAE (presumably one of the P.
coccinea extracts) was added, it led to a significant decrease
in the corrosion rate and current density. The corrosion rate
was measured at 6.2 × 10−4 mg/cm2 h, while the current
density was reported to be 6.6 × 10−3 mA/cm2. These values
indicate a considerable enhancement in the corrosion protection properties of the zinc coatings due to the presence of
the P. coccinea extracts.
5 Mechanism of corrosion
inhibition
The mechanism of corrosion inhibition by plant extracts is
indeed diverse, reflecting the varied chemical composition
of different extracts. Adsorption is a common mechanism,
17
N. Verma et al.: Flavonoids as anticorrosive materials
where organic compounds like polyphenols, flavonoids, and
tannins form a protective film on the metal surface, hindering
corrosive agents’ access. Some extracts facilitate the formation
of passive films, offering inherent corrosion resistance to
metals like aluminum and stainless steel. Redox reactions
involve plant extract constituents participating in electron
transfer processes with metal ions, altering the metal’s electrochemical behavior and reducing corrosion rates. Chelation
is another mechanism where extract compounds bind metal
ions, preventing them from engaging in corrosive reactions. pH
adjustment by plant extracts can modify the corrosive environment, influencing corrosion rates, particularly in acidic
conditions. Formation of protective layers through precipitation or deposition provides physical barriers against corrosive
agents. Finally, oxygen scavenging by certain extracts limits
oxygen availability for corrosion, particularly in oxygensensitive metal corrosion scenarios. These mechanisms
collectively demonstrate the versatility of plant extracts as
corrosion inhibitors and highlight their potential in corrosion
protection applications across various industries.
For examples, the physicochemical adsorption of A. unedo
L. leaves extract molecules onto the metal surface creates a
protective film layer, effectively reducing the corrosion process caused by water and HCl (H+, Cl−) ions (Abdelaziz et al.
2021). This extract is abundant in polyphenol compounds,
especially flavonoids, renowned for their antioxidant properties. The organic components of the extract interact with
metal surfaces through their free electrons (O, N, etc.) bonding
with vacant d-orbitals of iron atoms, and aromatic ring
π-electrons chemically donate to iron’s active site, as indicated
by DRIFT spectra. Additionally, physical adsorption can occur
through electrostatic interaction. In acidic conditions, MS
carries positive charges (Fe2+, Fe3+), allowing Cl ions to be
adsorbed at corroded metal sites. Cationic constituents of
A. unedo L. leaves extract, formed by protonation in the acidic
environment, can also be adsorbed on the metal surface
through electrostatic interaction with chloride ions. The extract’s efficiency as an organic inhibitor primarily lies in its
ability to replace water molecules and get adsorbed on the
metal surface, following the equation outlined:
Org (sol) + nH2 O(ads) → Org (ads) + nH2 O(sol)
Additionally, the film’s formation provides a comprehensive shield, inhibiting the anodic process and impeding
oxygen diffusion to the MS surface. The degree of protection
against corrosion depends on the film’s thickness and
adherence. A compact layer leads to both cathodic and
anodic inhibition, resulting in a flat film on the MS (Figure 8).
Consequently, the adsorbed inhibitor can interact with Fe2+
and contribute to the creation of (Fe − Org)2+
( ads) .
−
Fe → Fe2+
Fe2+
(ads) + 2e
(ads) + Org (sol) − (Fe − Org)(ads)
2+
Based on the experimental and theoretical analyses, the
corrosion inhibition mechanism of SPRE for C-steel in a
1 M HCl solution is depicted in Figure 9. When C-steel is
immersed in HCl, Cl− ions adsorb on the metal surface,
Figure 8: Mechanism of corrosion inhibition efficiency of Arbutus unedo for steel. Adapted from (Abdelaziz et al. 2021).
18
N. Verma et al.: Flavonoids as anticorrosive materials
Figure 9: Corrosion inhibition mechanism of the
constituents of SPRE for C-steel in 1 M HCl
solution. Adapted from (Meng et al. 2021).
creating a negatively charged layer. Clotrimazole (CTM),
3-acetamidocoumarin (ATC), 3-amino-1,2,4-triazole (ATA),
and copper-chrome-arsenate (CCA), which have moderately
positive charged surfaces, migrate from the solution to the
steel surface through electrostatic attraction. The constituents of SPRE repel preadsorbed water molecules and corrosive species due to their high molecular weight and
affinity. They then adsorb onto the C-steel surface, providing
protection to both cathodic and anodic sites. CTM and ATC
compounds contain a pyran structure that favors a chair
conformation in the ground state. As a result, they exhibit
weak physisorption interactions with the C-steel surface.
However, in other parts of CTM and ATC molecules, the O
heteroatoms and conjugated systems can donate lone pair
electrons to the unoccupied d-orbitals of Fe atoms, while the
electron-deficient regions (e.g., aromatic rings) accept electrons from the metal surface through back-donation. This
leads to chemisorption via charge transfer in the reactive
regions of CTM and ATC. Due to the weak adsorption portion,
SPRE shows desorption behavior at high temperatures. On
the contrary, ATA and CCA, with reactive sites distributed
throughout their backbones, exhibit strong binding energy
and parallel adsorption configuration, effectively covering
most active regions on the C-steel surface.
The corrosion inhibition mechanism of Catharanthus
roseus involves the interaction between polyphenolic fused
rings and polyhydroxy carbonyl groups with the MS surface
through nonbonding electrons (Palaniappan et al. 2020). This
interaction results in the C. roseus extract acting as a Lewis
base, while the MS surface acts as a Lewis acid. Consequently, the inhibitor molecules chemisorb onto the steel
surface. Chemisorption occurs through the involvement of pi
electrons from phytochemicals, whereas physisorption involves the attraction between opposite charges of flavonoids
Figure 10: The corrosion inhibition mechanism
of Catharanthus roseus for MS. Adapted from
(Palaniappan et al. 2020).
N. Verma et al.: Flavonoids as anticorrosive materials
and the MS surface. Additionally, the polyhydroxy groups of
flavonoids interact specifically with the surface irons. The
interaction between the inhibitor molecules and the MS
surface leads to an increase in the HOMO energy and a
decrease in the LOMO energy (Figure 10). This phenomenon
arises from the electrostatic interaction between the inhibitor molecules and the MS surface. Moreover, the values of
the frontier molecular orbital DE energy gap are close,
facilitating the adsorption of inhibitor molecules onto the MS
surface. The phytochemicals of C. roseus act as a mixed type
corrosion inhibitor in a 3.5 % NaCl medium, which allows
them to control both the anodic and cathodic reactions on
the alloy surface.
The state of the art in corrosion inhibition research, as
presented in this review article, underscores the remarkable
potential of plant extracts as sustainable and effective solutions for protecting metals from corrosion. By elucidating
the diverse mechanisms through which plant extracts
inhibit corrosion, ranging from adsorption and formation of
passive films to redox reactions and chelation, the article
highlights the versatility of natural compounds in corrosion
protection. Furthermore, the identification of specific plant
extracts rich in polyphenols, flavonoids, and other bioactive
compounds showcases the promising avenues for further
investigation. This comprehensive understanding of the
corrosion inhibition properties of plant extracts not only
advances the field of corrosion science but also serves as a
source of inspiration for researchers seeking innovative and
eco-friendly solutions. Through interdisciplinary collaboration and a focus on sustainability, researchers can harness
the potential of plant extracts to develop novel corrosion
protection strategies that address environmental concerns
while meeting the demanding requirements of diverse industrial applications.
6 Conclusion and future prospects
In conclusion, the utilization of plant extracts for corrosion
inhibition represents a promising avenue for addressing the
pervasive issue of material degradation. The effectiveness of
these inhibitors’ hinges on a multitude of factors, ranging
from the specific extracts used to environmental conditions
such as pH and temperature. Recent advancements have
illuminated the potential of plant extracts rich in flavonoids
as corrosion inhibitors, offering both eco-friendly and efficacious protection against corrosion. One of the key advantages of plant extract-based inhibitors lies in their ability to
form robust protective layers on metal surfaces, thereby
extending the lifespan of metals. This protective mechanism
involves complex interactions with metal ions, effectively
19
thwarting the corrosive process. Furthermore, the compatibility of these inhibitors with existing coating systems enhances their versatility and applicability across various
industries.
Studies focusing on specific extracts have demonstrated
significant corrosion inhibition in diverse corrosive environments. However, further optimization and research are
imperative to tailor these inhibitors to specific environmental conditions and substrates, ensuring sustained effectiveness over prolonged periods. The multifaceted
mechanisms through which plant extracts inhibit corrosion,
including redox reactions and oxygen scavenging, underscore their versatility and potential in corrosion protection
applications. The exploration of these mechanisms fosters
innovation, prompting researchers to devise novel approaches for combatting corrosion across diverse industrial
settings. In sum, the inclusion of plant extracts in corrosion
inhibition studies offers a sustainable and environmentally
friendly approach to safeguarding metals from corrosion. By
harnessing the diverse chemical composition of natural extracts, researchers can pave the way for the development of
innovative technologies and strategies for corrosion mitigation, thereby addressing both industrial needs and environmental concerns.
Research ethics: Not applicable.
Informed consent: Not applicable.
Author contributions: Nishant Verma: study conception and
design, data collection. Tarun Kumar: formal analysis, data
interpretation, draft revision preparation. Vinod Kumar
Vashistha: study conception and design, analysis and interpretation of results, finalization of manuscript. Suman
Yadav: draft manuscript preparation. Dipak Kumar Das:
draft manuscript preparation, data collection. Rajasekhar
VSR Pullabhotla: draft manuscript preparation, formal
analysis. Gaurav Sharma: data collection, interpretation of
data. All authors reviewed the results and approved the final
version of the manuscript.
Competing interests: No conflict of interest to declare.
Research funding: None received.
Data availability: Not applicable.
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