Jurnal Akademika Kimia, 14.
: 123-131.
May 2025 ISSN .
2477-5185 | ISSN .
2302-6030 http://jurnal.
id/index.
php/jak/ OPEN ACCESS Atmospheric Corrosion Inhibition of Steel Using Tea Leaf Extract in the Coastal Environment of Air Tawar.
Padang Niko Kurniawan1.
Sabrizal Saputra1, *Dinalia2.
Yerimadesi1, & Sauli Safitri2 1Chemistry Department Ae State University of Padang.
West Sumatera Ae Indonesia 25133 2Master of Chemistry/Pascasarjana Ae Tadulako University.
Central Sulawesi Ae Indonesia 94119 Received 05 May 2025.
Revised 23 May 2025.
Accepted 30 May 2025 doi: 10.
22487/j24775185.
Abstract This study evaluates the effectiveness of tea leaf extract as a corrosion inhibitor for steel under real coastal atmospheric exposure.
The novelty of this work lies in its direct assessment of a plant-derived inhibitor in an open-air marine environment, a setting that has not been adequately addressed in previous studies, which have largely focused on controlled aqueous systems.
In addition, this study employs mature tea leaves, an abundant agricultural byproduct with naturally high tannin content, processed through a simple, solvent-free extraction method, thereby offering a sustainable route for green inhibitor development.
The extract was obtained from mature tea leaves through aqueous boiling, and its tannin content was quantified using UVAeVis spectrophotometry.
ASSAB 760
steel specimens were coated by immersion in tea extract at varying concentrations and soaking durations, followed by natural exposure in a coastal environment for 1 to 30 days.
Corrosion behavior was evaluated using the weight loss method.
The results showed that mature tea leaves contained the highest tannin concentration .
95 pp.
, supporting their selection for inhibitor application.
The optimum extract concentration was identified as 11000 ppm with a 5-hour immersion time.
Under these conditions, treated steel exhibited a substantially lower corrosion rate .
78 y 10a g/cmA/da.
compared to untreated steel .
66 y 10AA g/cmA/da.
, corresponding to a maximum inhibition efficiency of 84.
The inhibition mechanism is attributed to the formation of a stable Feaetannin chelate complex that adsorbs onto the steel surface, forming a protective film that restricts the ingress of aggressive chloriderich moisture in the coastal atmosphere.
Overall, the findings demonstrate the practical viability of mature tea leaf extract as an effective and environmentally benign atmospheric corrosion inhibitor, providing field-relevant insight into sustainable protection strategies for marine-exposed steel infrastructure.
Keywords: Coastal atmospheric corrosion, green tea leafAebased inhibitor, steel surface protection, tannin substances capable of slowing the reaction rate Introduction between a metal and its environment (Al-Baghdadi Steel is one of the most widely used metallic et al.
, 2.
Such inhibitors may consist of either materials in building construction, the automotive inorganic or organic compounds (Ma et al.
, 2.
industry, and various technical applications (Braun In practice, metal protection can also be achieved by et al.
, 2.
Composed primarily of iron, its forming a barrier layer on its surface, such as chemical behavior is strongly influenced by the through coating or painting (Ziganshina et al.
inherent tendency of iron to oxidize when exposed 2.
Traditional paints containing compounds to humid or corrosive environments.
This oxidation like lead oxide or chromates act as inhibitors by process leads to the formation of rust .
ron oxide.
, preventing direct interaction between the metal and which progressively reduces the structural integrity surrounding corrosive agents (Soltanov et al.
, 2.
of the material.
Such characteristics render steel However, these compounds are known for their highly susceptible to corrosion, particularly in high toxicity and potential to cause environmental atmospheric conditions rich in water vapor, pollution (Sodiya & Dawodu, 2.
Consequently, chloride ions, and oxygen, as commonly found in the search for environmentally benign, non-toxic, coastal regions.
Corrosion not only diminishes the and cost-effective alternatives has become a major economic value of steel but may also compromise focus in green chemistry approaches over the past structural safety if not effectively mitigated few decades (REuuE et al.
, 2.
(Hatamov, 2.
In recent years, plant-derived organic Multiple strategies have been developed to compounds such as tannins, alkaloids, organic acids, mitigate the rate of metal corrosion, one of which is amino acids, and natural pigments have been the application of corrosion inhibitors, which are a *Correspondence:
Danalia e-mail: danalia@untad.
A 2025 the Author.
retain the copyright of this article.
This article is published under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.
0 International, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Niko Kurniawan et al.
extensively investigated as potential green corrosion inhibitors (Holla et al.
, 2.
Tannins, belonging to the polyphenol group, exhibit notable potential as corrosion inhibitors due to their ability to form stable complexes with metal ions, coupled with their biodegradability and environmental friendliness (Lebrini, 2.
These complexes adsorb onto the metal surface, thereby acting as a barrier that limits the ingress of oxygen and other aggressive ions.
Consequently, the corrosion rate can be effectively reduced (Shilkamy et al.
, 2.
Tannins can be extracted from various parts of plants, including bark, stems, seeds, roots, buds, and leaves (Das et al.
, 2.
Examples of plant sources rich in tannins include gambier leaves (Andini et al.
, 2.
, guava leaves (Faradilla & Rizal, 2.
, plant galls, oak, chestnut, hemlock, mangrove, grapes, pomegranates, cranberries, red wine, tea extract, coffee (Pourmadadi et al.
, 2.
as well as pine and other coniferous species (Molnar et al.
, 2.
This compound can be obtained through a simple extraction process, such as boiling with water as the solvent (Pourmadadi et al.
, 2.
These environments involve complex phenomena such as chloride transport, cyclic wetting and drying, and aerosol deposition, none of which can be fully reproduced under standard laboratory conditions.
To the best of our knowledge, no prior study has evaluated the effectiveness of tea leaf extract as a corrosion inhibitor for steel under natural openair coastal exposure.
This work further introduces the novel use of mature tea leaves, an abundant agricultural byproduct with high tannin content, processed through a simple solvent-free extraction By integrating a sustainable feedstock with direct atmospheric testing, this study advances the field by providing field-relevant insight into green corrosion mitigation strategies for marine-adjacent Methods The present study was designed to evaluate the performance of tea leaf extracts as atmospheric corrosion inhibitors for steel in a coastal The experimental workflow comprised four key stages: preparation of materials, extraction and quantification of tannin, optimization of coating parameters, and field exposure testing under natural atmospheric Each stage was carefully designed to ensure reproducibility and reliability of the results.
Materials The primary material used in this study was steel (ASSAB 760.
AISI 1148, 0.
5% C) supplied by PT Tira Austenite.
Padang.
Indonesia.
The plant material used was tea leaves (Camellia sinensi.
collected from the Kayu Aro tea plantation.
Solok Regency.
West Sumatra.
Indonesia.
Both mature .
and young .
leaves were selected to compare tannin content and inhibitory efficiency.
The leaves were thoroughly cleaned, air-dried, finely cut, and extracted using deionized water as the The following reagents and chemicals were used, all of analytical grade: Potassium ferricyanide (KCEFe(CN)CI, 0.
016 M), iron.
chloride (FeClCE, 02 M), phosphoric acid (HCEPOCE, 6.
03 M), nitric acid (HNOCE, 1%), and acetone .
Merck.
German.
for colorimetric determination of tannin and surface cleaning.
A 1% gelatin solution was freshly prepared before use.
while distilled water .
was used for all dilutions and rinsing Standard tannic acid (Sigma-Aldrich.
USA) was employed to construct calibration curves for quantitative spectrophotometric analysis.
The main equipment and instruments used included: an analytical balance (Ohaus PA214C, 0001 .
for precise mass determination.
a UVAeVisible spectrophotometer (Shimadzu UV1800.
Japa.
for measuring absorbance at 670 nm during tannin analysis.
an oven (Memmert UN.
for controlled drying at 40 AC.
a desiccator with silica gel for sample cooling before weighing.
Additional equipment comprised a mechanical grinder and polishing unit for surface preparation.
Figure 1.
A stable ironAetannin chelate complex formed via coordination bonding between FeAA ions and the hydroxyl Previous studies have extensively examined the effectiveness of tea leaf extracts as corrosion inhibitors, primarily in aqueous environments such as acidic or saline media.
It has been reported that phenolic compounds from White tea effectively reduce the corrosion rate of mild steel under 1M Hydrochloric acid solution (Kaban et al.
, 2.
a similar study, the use of green tea polyphenols was found to mitigate the corrosion of CT3 steel in an artificial marine environment through salt spray and electrochemical methods.
The results indicated that tea extracts in 3.
5% NaCl solution facilitated the formation of a protective layer through the adsorption of tanninAemetal complexes, which served as corrosion barriers (Tien et al.
, 2.
There remains a significant knowledge gap concerning the performance of tannin-based inhibitors under real atmospheric exposure, particularly in coastal microclimates that are enriched with moisture and airborne chloride.
Volume, 14.
No.
2, 2025, 123-131
Jurnal Akademika Kimia class-A borosilicate glassware (Pyre.
for volumetric analyses, and a corrosion exposure rack installed approximately 100 m from the shoreline at Air Tawar Beach.
Padang.
The corrosion tests were conducted under natural atmospheric conditions without artificial control of temperature or humidity, thereby closely representing real coastal exposure environments.
ranging from 1 to 8 hours, followed by the same drying and weighing protocol.
Atmospheric Corrosion Testing Field exposure testing was conducted at a coastal site approximately 100 m from the shoreline of Air Tawar Beach.
Padang.
West Sumatra.
Steel specimens coated under optimum conditions, alongside uncoated controls, were suspended in the open air for exposure periods ranging from 1 to 30 days (Jiao et al.
, 2.
Corrosion rates (CR) were determined using the weight loss method according to equation 2 (Boukhedena et al.
, 2.
Preparation of Steel Specimens Steel bars were cut into discs approximately 5 cm in diameter and 0.
5 cm in thickness.
The surfaces were sequentially polished with emery papers of progressively finer grit to remove surface irregularities and achieve a uniform metallic sheen.
The specimens were then degreased using detergent, rinsed with distilled water, and immersed in 1% nitric acid to remove oxide residues.
Subsequently, the discs were washed with analyticalgrade acetone, oven-dried at 40 AC for 5 minutes, cooled in a desiccator for 15 minutes, and weighed to record their initial mass (W.
(Putra et al.
, 2.
yaycI = Mature and young tea leaves .
g eac.
were chopped into small pieces and subjected to aqueous extraction by boiling in 2 L of distilled The filtrate obtained was diluted, and a 10 mL aliquot was transferred into a 100 mL volumetric flask with distilled water (Fraga-Corral et al.
, 2.
From this solution, 3 mL was pipetted into a 25 mL volumetric flask, followed by sequential addition of 1 mL K3Fe(CN)6 .
016 M) and FeClCE .
02 M).
After gentle shaking and a 15-minute rest period, 3 mL of H3PO4 .
03 M) was added, and the solution was allowed to stand for 2 minutes before the addition of 1% gelatin solution.
The mixture was shaken and made up to volume with distilled water.
Absorbance was measured at 670 nm using a UVAe Vis spectrophotometer, and tannin content was calculated from a previously established calibration curve (Hagerman, 2.
The extract with the highest tannin concentration was selected for coating applications.
yuC(%) = yaycIyc Oe yaycIycu yaycIyc where CRu and CRi are the corrosion rates of uncoated and coated specimens, respectively .
/cm2/da.
This integrated approach allowed a direct comparison between treated and untreated steel under identical environmental conditions, ensuring that the reported inhibition efficiencies accurately reflect the performance of the tea leaf extract under real-world atmospheric exposure.
Results and Discussion Tannin content analysis revealed that mature tea leaves contained a significantly higher tannin concentration .
95 pp.
compared to young tea shoots .
19 pp.
This result aligns with previous findings showing that the tannin concentration in dried tea leaves tends to be higher than that in fresh ones (Rusita et al.
, 2.
The higher tannin level in mature tea leaves supports their selection as the primary source for the corrosion inhibitor in subsequent experiments.
The influence of tea leaf extract concentration on the coating performance is shown in Table 1 and illustrated in Figure 2.
The percentage of steel weight gain increased with extract concentration, reaching an optimum at 11000 ppm.
This trend indicates that the formation of the tanninAeiron complex layer is concentrationdependent, where higher tannin availability enhances surface adsorption and chelation with FeAA ions.
At the optimum concentration, the steel surface exhibited a distinct dark purple color, which Optimization of Coating Parameters To determine the optimum inhibitor concentration, steel specimens were immersed in 50 mL of tea extract at concentrations ranging from 1000 to 13000 ppm for 3 hours.
After immersion, specimens were oven-dried .
AC, 5 minute.
, cooled in a desiccator .
, and weighed (W.
The percentage weight gain (WG) was calculated using equation 1 (Solanki et al.
, 2.
ycOycn Oe ycO0 y 100% ycO0 where Wo is the initial mass before exposure .
Wb is the mass after exposure .
A is the exposed surface area .
mA), and t is the exposure time .
The inhibition efficiency () was calculated according to equation 3 (Lin et al.
, 2.
Extraction and Quantification of Tannins ycOya(%) = ycO0 OeycOyca where Wo and Wi are the steel mass before and after coating, respectively .
Similarly, the optimum immersion time was established by exposing steel specimens to the optimum concentration extract for durations Niko Kurniawan et al.
is characteristic of ironAetannin complex formation.
(Yldz & Sahiner, 2.
A similar observation was reported that polyphenolic extracts from green tea promote the formation of protective FeAeOAeC coordination bonds that suppress electrochemical dissolution (Tien et al.
, 2.
At concentrations below 11000 ppm, incomplete coating coverage likely occurred, leading to lower weight gain.
Conversely, exceeding this concentration resulted in a decline in mass gain, suggesting that the surface had reached saturation.
Excess tanninAeiron complexes likely remained suspended in the bulk solution rather than depositing on the steel surface.
Such over-saturation behavior is also reported in plant-based inhibitor systems, where excessive organic molecules hinder compact film formation due to aggregation or solubility limits (Bhardwaj et al.
, 2.
Therefore, 11000 ppm was identified as the optimum concentration that balances adsorption density and film stability.
The effect of immersion time on coating formation at this optimum concentration is presented in Table 2 and Figure 3.
Table 1.
Steel weight gain at different tea leaf extract concentrations Concentration of tea extract .
%WG Average A SD 0099 A 0.
0112 A 0.
0190 A 0.
Table 2.
Steel weight gain at different immersion times .
00 ppm extrac.
Immersion Time (Hour.
0196 A 0.
0197 A 0.
0198 A 0.
0265 A 0.
0250 A 0.
0240 A 0.
0234 A 0.
Figure 2.
Effect of Tea Leaf Extract
Concentration on Steel Weight Gain after 3 hours Immersion
%WG
Average A SD 0145 A 0.
0124 A 0.
0197 A 0.
0285 A 0.
0337 A 0.
0190 A 0.
0167 A 0.
Figure 3.
Effect of Immersion Time in Tea Leaf Extract on Steel Weight Gain Volume, 14.
No.
2, 2025, 123-131
Jurnal Akademika Kimia The steel weight gain increased with immersion duration, peaking at 5 hours, after which it began to decline.
This indicates that sufficient contact time is crucial for uniform adsorption and chelate film formation.
Similar kinetic behavior was observed in the optimum immersion period for the equilibrium between adsorption and desorption processes (Bian et al.
, 2.
Shorter immersion times (<5 .
likely produced incomplete surface coverage, while longer exposure may have led to desorption or hydrolysis of weakly bound complexes, resulting in decreased film mass.
Prolonged immersion can also increase the acidity or organic content of the solution, inducing partial corrosion of the protective layer.
The effect of exposure time on the corrosion rate of steel in an open-air coastal environment is presented in Table 3 and Figure 4.
Table 3.
Corrosion rate of uncoated and tannin-coated steel under open-air coastal exposure Corrosion Corrosion Rate Exposure Time Without Tannin With Tannin .
91 x 10-3 A 1.
66 x 10-4 1.
95 x 10-3 A 4.
32 x 10-4 56 x 10-4 A 7.
00 x 10-5 97 x 10-4 A 5.
68 x 10-6 40 x 10-4 A 1.
56 x 10-4 93 x 10-4 A 1.
50 x 10-4 95 x 10-4 A 1.
23 x 10-4 26 x 10-4 A 1.
19 x 10-4 30 x 10-4 A 9.
82 x 10-6 89 x 10-4 A 2.
22 x 10-6 66 x 10-4 A 2.
97 x 10-5 78 x 10-5 A 5.
64 x 10-5 61 x 10-4 A 2.
49 x 10-5 83 x 10-5 A 2.
64 x 10-5 72 x 10-4 A 4.
11 x 10-5 60 x 10-5 A 2.
54 x 10-5 01 x 10-4 A 1.
12 x 10-5 92 x 10-5 A 7.
13 x 10-6 19 x 10-4 A 2.
00 x 10-5 83 x 10-5 A 1.
32 x 10-5 37 x 10-5 A 3.
99 x 10-6 63 x 10-5 A 2.
61 x 10-7 The highest corrosion rates occurred within the first three days for both coated and uncoated steel, a phenomenon attributed to the high aggressiveness of chloride (ClA) and sulfate (SOCEAA) ions during the early exposure period, which can penetrate and damage the initial protective film (Bernardi et al.
, 2.
After this initial stage, corrosion rates decreased and stabilized, likely due to the formation of a passive oxide film that inhibited the diffusion of oxygen and aggressive ions to the metal surface (Gui-Rong et al.
, 2.
Figure 4.
Effect of Atmospheric Exposure Time on the Corrosion Rate of Steel Niko Kurniawan et al.
A temporary increase in the corrosion rate of uncoated steel on day six was observed, possibly due to the mechanical disruption of the passive layer, as evidenced by visible oxide deposits at the bottom of the container.
Quantitative analysis confirmed that tannin-coated steel exhibited a much lower corrosion rate .
78 y 10a g/cmA/da.
compared to uncoated steel .
66 y 10AA g/cmA/da.
, demonstrating the effectiveness of the tannin-based film in mitigating corrosion.
This finding aligns with recent studies showing that polyphenolic inhibitors can reduce corrosion rates by up to 70Ae90% depending on their surface binding strength and environmental conditions (Sheokand et al.
, 2.
The variation in inhibition efficiency throughout the exposure period is shown in Table 4 and Figure 5.
Table 4.
Inhibition efficiency of tannin-coated steel during atmospheric exposure Corrosion Exposure Time .
Inhibition Efficiency (%) Figure 5.
Variation of Inhibition Efficiency Over the Atmospheric Exposure Period The maximum efficiency .
71%) was recorded on day 27, followed by a slight decline on This minor decrease may be attributed to the reduced stability of the protective film or a saturation effect, where the extractAos ability to form additional tanninAemetal complexes had reached its Nevertheless, the decrease was not significant, indicating that the inhibitor maintained strong protective performance toward the end of the testing period.
A comparable study reported an inhibition efficiency of 81.
71% for Commelina benghalensis leaf extract in 1 M HCl solution, demonstrating a similar trend of sustained protection despite varying corrosion environments (Akaaza et al.
, 2.
Both findings highlight the promising potential of plant-derived organic compounds as efficient and sustainable corrosion The overall inhibition mechanism can be rationalized in three main stages: First.
Fe atoms at the steel surface oxidize to FeAA and subsequently to FeAA to achieve a half-filled 3dAA configuration, which is thermodynamically more stable.
Second.
FeAA ions form coordination bonds with the Volume, 14.
No.
2, 2025, 123-131
Jurnal Akademika Kimia hydroxyl and carbonyl groups of tannins, producing stable FeAeOAeC chelate complexes.
Finally, these complexes adsorb onto the steel surface through both physisorption and chemisorption, generating a compact, adherent barrier that prevents the ingress of aggressive ions such as ClA and SOCEAA (Bacca et , 2.
The strong correlation between the observed inhibition efficiency and the stability of the FeAetannin chelate supports this mechanistic interpretation, consistent with findings from other natural inhibitor systems involving flavonoids and lignin derivatives (Sesia et al.
, 2.
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Conclusions This study demonstrates that tannin-rich extracts from mature tea leaves are highly effective as a green corrosion inhibitor for steel in open-air coastal environments.
The extract, containing 95 ppm tannins, exhibited optimal coating performance at a concentration of 11000 ppm with a 5-hour immersion period, resulting in the formation of a dense and adherent ironAetannin complex layer.
Under these conditions, the corrosion rate of coated steel was reduced to 7.
78 y 10a g/cmA/day, significantly lower than that of uncoated steel .
66 y 10AA g/cmA/da.
, with a maximum inhibition efficiency of 84.
71% observed on day 27.
The protective action is attributed to the strong coordination between FeAA ions and tannin hydroxyl groups, producing a stable chelate film that effectively impedes the ingress of aggressive chloride and sulfate ions.
The sustained high efficiency over the 30-day exposure highlights the durability of this natural protective barrier.
Beyond its scientific relevance, these findings underscore the untapped potential of mature tea leaves, an agricultural byproduct often treated as waste, as a cost-effective, biodegradable, and environmentally benign alternative to synthetic corrosion inhibitors.
This work not only expands the scope of atmospheric corrosion mitigation strategies but also aligns with the principles of green chemistry, offering a viable path toward sustainable marine-adjacent Conflict of Interest The authors confirm that there is no conflict of interest regarding the publication of this research.
Acknowledgment The authors sincerely thanks to Chemistry Laboratory.
Mathematics and Natural Sciences Faculty.
State University of Padang.
References