The research team, led by Mohammad Ebrahim Jafarian of the Islamic University of Shahreza together with M. Bagherzadeh and Meysam Karimi of the Nuclear Science and Technology Research Institute in Tehran, prepared their green inhibitor using nothing more elaborate than dried walnut leaves from a private garden in Isfahan Province and double-distilled water. Five grams of washed, dried leaves were heated in 100 milliliters of water at 80 to 90 degrees Celsius, then strained to produce a clear extract. This deliberately simple, traditional preparation matters: if a corrosion inhibitor requires exotic solvents or complex synthesis, much of its environmental and economic appeal evaporates. Walnut leaves are rich in phenolic compounds, including coumaric acid, quercetin derivatives, gallic and ellagic acids, tannins, and juglone, a chemical arsenal that the authors identify as the likely source of the extract’s protective power.

To test the extract, the researchers immersed polished carbon steel coupons for 72 hours in 3.5 percent NaCl solutions containing increasing concentrations of walnut leaf extract, from 5 to 30 percent by volume. The unprotected steel lost a substantial 1.0156 grams per square centimeter over the three days, while inhibitor-treated samples lost dramatically less. The standout result came at the lowest dose tested: a 5 percent extract concentration delivered the maximum inhibition efficiency of 98.53 percent. Counterintuitively, adding more extract did not improve protection. Efficiency plateaued and even declined at higher concentrations, a nonlinear behavior the authors attribute to molecular aggregation, partial coagulation of tannins in solution, and irregular, heterogeneous adsorption that leaves localized weak points vulnerable to chloride attack.

Electrochemical measurements told a consistent story. In potentiodynamic polarization tests, the corrosion current density fell from 2.544 microamperes per square centimeter for the bare steel to 0.606 microamperes per square centimeter with 5 percent extract, and the corrosion rate dropped from 1.478 millimeters per year to 0.352 millimeters per year. Tafel analysis revealed that the inhibitor acts as a mixed-type inhibitor with predominantly anodic suppression, meaning it slows the oxidation of iron into solution more strongly than it slows the cathodic oxygen reduction reaction. The corrosion potential shifted toward more negative values and the anodic Tafel slope decreased, both signatures of a barrier layer interfering with metal dissolution. Statistical analysis confirmed that these electrochemical effects were significant, with triplicate measurements varying by less than 5 percent.

Electrochemical impedance spectroscopy added a second, independent line of evidence. The charge transfer resistance at the steel-electrolyte interface, a direct measure of how hard it is for corrosion reactions to proceed, jumped from 126 ohms per square centimeter for the blank solution to 926 ohms per square centimeter with 5 percent extract, corresponding to the 86.39 percent efficiency peak. The impedance data, fitted to a modified Randles circuit with a Warburg diffusion element, showed enlarged Nyquist semicircles and reduced double-layer capacitance, exactly what is expected when organic molecules displace water at the metal surface and thicken the electrical double layer. Analysis of surface coverage against concentration produced an excellent fit to the Langmuir adsorption isotherm, with a correlation coefficient of 0.989, indicating that the phytochemicals form an orderly monolayer on a largely homogeneous surface.

The molecular mechanism appears to combine physical and chemical adsorption. Polar functional groups such as hydroxyl and carboxyl moieties in the polyphenols and tannins can form hydrogen bonds with surface iron atoms and donate electron density into the vacant d-orbitals of iron, creating Fe-organic coordination complexes. Infrared spectroscopy of the treated surfaces revealed new carbonyl peaks between 1600 and 1700 wavenumbers characteristic of tannins, enhanced carbon-hydrogen stretching near 2900 wavenumbers from aliphatic compounds, and the coexistence of iron-oxygen and carbonyl signals, which the authors interpret as direct evidence of chemisorption alongside physical shielding. The diminished intensity of chloride-related peaks near 850 wavenumbers showed that the film was genuinely keeping the aggressive ions away from the metal.

Surface imaging sealed the case. Scanning electron micrographs of steel after three days in plain salt solution showed the pitted, blotchy texture of uniform chloride-induced corrosion, and energy-dispersive X-ray analysis detected chlorine, sodium, and oxygen on the surface, the fingerprints of iron chlorides and oxide corrosion products. On the inhibitor-treated sample, those chlorine and sodium signals vanished entirely, replaced by a carbon-rich organic film: the carbon weight percentage rose from 23.99 percent on the corroded surface to 42.80 percent on the protected one, a relative increase of 78.41 percent. The overlapping layers with distinct boundaries visible in the micrographs are the physical embodiment of the adsorbed protective barrier that the electrochemistry had already implied.

But the study also delivered a sobering caveat. When the researchers repeated the polarization and impedance experiments at elevated temperatures using the optimal 5 percent concentration, the protection collapsed. At 25 degrees Celsius the extract still delivered 76.2 percent efficiency from polarization data, but by 35 degrees Celsius and above the corrosion rate of the inhibited system exceeded that of the unprotected blank. At 70 degrees Celsius the inhibition efficiency plunged to a negative 255.1 percent, meaning the extract had become a corrosion accelerant, and the charge transfer resistance cratered from 926 ohms per square centimeter to a mere 0.893 ohms per square centimeter. The authors attribute this dramatic reversal to three converging factors: adsorption is exothermic, so heat drives inhibitor molecules off the surface; the phenolic compounds thermally degrade and oxidize, potentially forming soluble iron complexes or porous layers that actively speed up charge transfer; and higher temperatures inherently accelerate both reaction kinetics and chloride diffusion through any compromised film.

That temperature sensitivity points to physisorption as the dominant adsorption mode and defines the practical limits of the technology. Walnut leaf extract, on this evidence, is a strong candidate for near-ambient applications such as cooling water systems, marine and coastal infrastructure protection, and other chloride-rich environments that do not run hot, rather than for high-temperature industrial streams. Compared with other plant-based inhibitors reported in the literature, including rosemary extracts reaching 97 percent efficiency and Ficus tikoua leaf extract at roughly 96 percent in acidic media, walnut leaf extract’s 86.39 percent electrochemical efficiency is competitive, and its preparation as a simple aqueous extract from an abundant agricultural byproduct gives it a distinct edge in cost and sustainability.

The broader significance of the work lies in its demonstration that corrosion protection does not have to come from a petrochemical plant. By systematically combining weight loss, polarization, impedance, adsorption isotherm analysis, and two independent surface characterization techniques, the study builds an unusually complete mechanistic picture of a green inhibitor in a realistic marine simulant, while honestly documenting the concentration and temperature windows where it works and where it fails. The authors note that future work will isolate and identify the specific active compounds within the extract using chromatographic techniques, a step that could allow even more efficient formulations. For now, the humble walnut leaf, usually discarded as garden waste, has earned a place in the growing catalog of nature-derived materials that could help industry fight rust without poisoning the planet in the process.

Subject of Research: Use of walnut leaf extract as a green corrosion inhibitor for carbon steel in sodium chloride solution

Article Title: Walnut leaf extract as a green corrosion inhibitor for carbon steel in NaCl solution across temperatures from ambient to 70 °C

Article References: Jafarian, M. E., Bagherzadeh, M., & Karimi, M. (2026). Walnut leaf extract as a green corrosion inhibitor for carbon steel in NaCl solution across temperatures from ambient to 70 °C. Discover Electrochemistry, 3(1), Article 43. https://doi.org/10.1007/s44373-026-00128-z

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00128-z

Keywords: corrosion inhibition, walnut leaf extract, carbon steel, green inhibitor, electrochemical impedance spectroscopy, potentiodynamic polarization, Langmuir adsorption, phytochemicals, marine corrosion, sodium chloride solution, surface analysis, temperature dependence

The study, published in Discover Electrochemistry by Eric M. Garcia, Hosane A. Taroco, and Julio O. F. Melo of the Federal University of São João del-Rei, demonstrates that the raw aqueous extract of Eugenia dysenterica, the cagaita tree, acts as a highly efficient green corrosion inhibitor for AISI 1020 carbon steel in 10 weight percent hydrochloric acid. What makes the result remarkable is not just the number but the method. Many plant-based inhibitors described in the literature require organic solvents, elaborate purification, or chemical modification before they can protect a metal surface. The Brazilian team skipped all of that, using nothing more than ripe fruit pulp, deionized water, a knife mill, and standard laboratory equipment to produce an inhibitor that performed on par with far more processed alternatives.

The chemistry behind the protection lies in the fruit’s rich phenolic composition. Cagaita fruits are known to contain gallic, caffeic, vanillic, p-coumaric, syringic, ferulic, and salicylic acids, along with flavonoids such as epicatechin, quercetin, and rutin. Previous work by the same group had established that the aqueous extract is dominated by quercetin and epicatechin. These molecules carry exactly the structural features that corrosion scientists look for in an inhibitor: multiple hydroxyl groups, aromatic rings, and conjugated pi-electron systems that can donate electron density to vacant iron orbitals and form stable adsorbed films. In acidic media, protonation of these molecules shrinks their frontier orbital energy gap, with protonated epicatechin dropping from 4.61 to 0.66 electron volts, a change associated with enhanced electronic reactivity and stronger interaction with the metal surface.

To characterize the extract, the researchers combined several analytical techniques. Fourier-transform infrared spectroscopy of the pulp revealed broad hydroxyl stretching near 3325 inverse centimeters, carbonyl bands at 1726, aromatic carbon-carbon stretching at 1624, and glycosidic features around 817, all consistent with phenolic and polysaccharide constituents. Thermogravimetric analysis showed that fresh cagaita pulp is dominated by moisture, losing most of its mass below 140 degrees Celsius, with only a weak exothermic oxidation event near 450 to 520 degrees. Electrospray ionization mass spectrometry in negative mode detected the characteristic quercetin ion at mass-to-charge ratio 301, while tandem mass spectrometry of the ion at 289 produced fragments exclusively matching epicatechin. Ultraviolet-visible spectroscopy showed a strong absorption maximum near 275 nanometers, the signature of aromatic phenolic chromophores acting in concert.

The electrochemical evidence was compelling. Working with AISI 1020 carbon steel electrodes of one square centimeter exposed area, polished and stabilized for over two thousand seconds at open circuit, the team recorded potentiodynamic polarization curves at one millivolt per second in a standard three-electrode cell at 25 degrees Celsius. Adding just 0.3 grams per liter of the extract slashed the corrosion current density from 8.51 times ten to the minus four to 0.68 times ten to the minus four amperes per square centimeter, an inhibition efficiency of approximately 92 percent. Crucially, the corrosion potential shifted by less than 20 millivolts, and both the anodic Tafel slope, which fell from 123 to 99 millivolts per decade, and the cathodic slope, which dropped from 193 to 124, changed simultaneously. This pattern identifies the extract as a mixed-type inhibitor, suppressing both the anodic dissolution of iron and the cathodic evolution of hydrogen through adsorption-controlled surface blocking rather than selectively targeting one reaction.

Adsorption modeling added a deeper mechanistic layer. Surface coverage, calculated from the reduction in corrosion current, rose steadily with extract concentration and plateaued as the steel surface became saturated. Among the Langmuir, Freundlich, and Temkin isotherm models tested, the Freundlich equation fit best, with a regression coefficient of 0.9973 and the lowest chi-square value, pointing to non-ideal adsorption on a heterogeneous surface, exactly what one would expect from a multicomponent extract interacting with a corroding, chemically varied steel substrate. The Langmuir fit, though slightly weaker, yielded a high apparent affinity constant of 21.99 liters per gram and an estimated standard free energy of adsorption of about minus 31.6 kilojoules per mole at 298 kelvin, indicating spontaneous adsorption with contributions from both physical and chemical interactions.

Temperature experiments reinforced the picture. Arrhenius plots of the corrosion rate at 5, 25, and 45 degrees Celsius showed linear, thermally activated behavior in both media, but the inhibited solution corroded more slowly at every temperature. The apparent activation energy decreased slightly from 53.8 to 48.6 kilojoules per mole in the presence of the extract, suggesting that the adsorbed organic layer modifies the corrosion pathway itself rather than acting as a simple physical barrier. Inhibition efficiency declined modestly at higher temperatures, consistent with partial desorption of the protective film, yet the protection remained significant even as thermal agitation increased.

Surface analysis provided the visual proof. After 24 hours of immersion in the uninhibited acid, scanning electron microscopy revealed a severely degraded steel surface, rough, porous, and scarred by heterogeneous attack. The sample protected by the extract looked markedly more intact, with a compact morphology and far fewer corrosion defects. Energy-dispersive X-ray spectroscopy showed reduced oxygen signals on the protected surface, indicating less formation of iron oxides and oxyhydroxides, while X-ray diffraction confirmed that crystalline corrosion products such as hematite, magnetite, and iron oxyhydroxides were strongly suppressed, leaving metallic iron as the dominant phase. Together, these observations matched the electrochemical data point for point.

The broader significance of the work extends beyond one fruit and one acid. The researchers harvested wild cagaita fruits on the university campus in Sete Lagoas, Minas Gerais, in compliance with Brazilian native vegetation laws, deposited a voucher specimen in a public herbarium, and processed the pulp with no chemical treatments or high-energy inputs. The extract dispersed readily in the aggressive acid without precipitation, and its inhibition efficiency compares favorably with plant-derived inhibitors reported for carbon steel in hydrochloric media, from henna and fruit peel extracts to essential oils of oregano and juniper. For industrial pickling, acid cleaning, and acid-treatment operations, where carbon steel degradation is a persistent and costly problem, a renewable, biodegradable, essentially free-byproduct inhibitor is an attractive proposition.

Challenges remain before cagaita extract reaches industrial tanks. The authors note that electrochemical impedance spectroscopy, which would quantify charge-transfer resistance and film properties, was not available for this study, and that long-term immersion tests and scale-up trials are needed. The thermodynamic parameters derived from a multicomponent extract are necessarily apparent values rather than exact molecular energies. Still, the central message stands: a simple water infusion of a Cerrado fruit, prepared with a grinder and deionized water, protected steel against one of the harshest corrosive environments in industry with 92 percent efficiency. It is a vivid demonstration that solutions to billion-dollar problems can sometimes be growing, quite literally, in the savanna outside the laboratory window.

Subject of Research: Green corrosion inhibition of carbon steel in hydrochloric acid using aqueous cagaita fruit extract

Article Title: Green corrosion inhibition of carbon steel in 10 wt% HCl solution using cagaita (Eugenia dysenterica) extract

Article References: Garcia, E. M., Taroco, H. A., & Melo, J. O. (2026). Green corrosion inhibition of carbon steel in 10 wt% HCl solution using cagaita (Eugenia dysenterica) extract. Discover Electrochemistry, 3(1), Article 57. https://doi.org/10.1007/s44373-026-00144-z

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00144-z

Keywords: corrosion inhibition, green inhibitor, carbon steel, cagaita, Eugenia dysenterica, hydrochloric acid, phenolic compounds, epicatechin, quercetin, electrochemistry, adsorption isotherm, Brazilian Cerrado

Carbon steel is the workhorse of the petrochemical world. It is inexpensive, strong, and durable, which is why it carries oil and gas through pipelines, lines storage tanks, and forms the backbone of boilers, reactors, and heat exchangers. But wherever steel meets acid, trouble follows. In sulfuric acid, iron atoms at the metal surface lose electrons and dissolve as ferrous ions, while hydrogen ions consume those electrons at cathodic sites to evolve hydrogen gas. The result is gradual thinning, pitting, and eventual failure of equipment, with enormous economic and environmental costs. The standard defense has been organic inhibitor molecules rich in nitrogen, oxygen, or sulfur heteroatoms, which adsorb onto the metal and block the reactive sites. Concerns about the toxicity and environmental persistence of many synthetic inhibitors, however, have pushed corrosion scientists toward greener chemistry.

Chrysanthemum indicum seemed like a promising candidate. Phytochemical analyses of its flowers have revealed volatile compounds such as eucalyptol, alpha-pinene, and germacrene D, along with abundant flavonoids and glycosides including quercitrin, myricetin, and luteolin-7-glucoside. These molecules carry electron-rich oxygen and nitrogen atoms and aromatic pi-systems, exactly the structural features that allow inhibitors to anchor themselves to iron surfaces through donor-acceptor interactions. The Egyptian team collected flowers from the Daqahlia Governorate in June 2023, dried and powdered them, and extracted 200 grams of material in 800 milliliters of methanol for 48 hours before concentrating the crude extract under vacuum.

The researchers then tested the extract at concentrations from 200 to 400 parts per million in 0.5 molar sulfuric acid, using a battery of complementary techniques. Weight-loss measurements on polished steel coupons, performed according to the ASTM G31-72 standard, showed that mass loss fell steadily as extract concentration rose. At the optimum dose of 400 ppm and 25 degrees Celsius, the inhibition efficiency reached approximately 91.53 percent, the highest value recorded in the study. When the temperature was raised to 45 degrees Celsius at the same dose, efficiency dropped to 78.28 percent, a decline that carries important mechanistic information.

That temperature dependence, combined with Arrhenius analysis, told the team that the extract binds to steel largely through physical adsorption. The apparent activation energy of the corrosion process increased with inhibitor concentration, a signature of weak electrostatic interactions between adsorbed molecules and the charged metal surface that weaken as heat disrupts them. Thermodynamic parameters reinforced the picture: the adsorption was exothermic, with negative enthalpy values, while positive entropy changes reflected the displacement of adsorbed water molecules as inhibitor species attached to the surface. The adsorption data fit the Langmuir isotherm almost perfectly, with slopes near one and high correlation coefficients, indicating that the phytochemicals form a monolayer on the steel. Free energies of adsorption fell between the classic thresholds for physisorption and chemisorption, suggesting that both mechanisms contribute, with electrostatic attraction dominating and chemical coordination adding strength.

Electrochemical measurements told a consistent story. Potentiodynamic polarization curves showed that the extract suppresses both the anodic dissolution of iron and the cathodic hydrogen evolution reaction, with corrosion current density falling sharply as concentration increased. Because the corrosion potential shifted by only about 4 millivolts, far below the 85-millivolt threshold, the extract qualifies as a mixed-type inhibitor. The Tafel slopes barely changed with dose, meaning the adsorbed film simply reduces the active surface area rather than altering the fundamental corrosion mechanism. Electrochemical impedance spectroscopy added quantitative depth: charge-transfer resistance jumped from roughly 4.5 ohm-square centimeters in bare acid to about 31.1 ohm-square centimeters at 400 ppm, while double-layer capacitance plunged from about 425 to 108 microfarads per square centimeter, evidence that bulky organic molecules were displacing hydronium ions and thickening the interfacial layer.

Surface imaging provided the most visually striking confirmation. Scanning electron micrographs of steel immersed in uninhibited acid for 24 hours revealed severe roughness and widespread pitting, the classic scars of acidic attack. The surface treated with 400 ppm of the extract, by contrast, appeared smooth and largely free of pits. Energy-dispersive X-ray analysis detected nitrogen and sulfur signals on the protected surface, chemical fingerprints of adsorbed organic constituents, alongside a stronger iron signal indicating suppressed dissolution. Atomic force microscopy quantified the transformation: average roughness fell from 647 nanometers on corroded steel to just 84 nanometers on protected samples, a nearly eightfold smoothing that directly reflects the uniformity of the protective film.

Fourier-transform infrared spectroscopy then identified which functional groups do the anchoring. The free extract shows a broad band at 3237 per centimeter from O-H and N-H stretching; after adsorption this band shifts to 3214 per centimeter, indicating that hydroxyl and amine groups participate in binding through hydrogen bonding and coordination with iron. A carbonyl band at 1635 per centimeter shifted to 1653 per centimeter, consistent with oxygen lone pairs donating electron density into the empty d-orbitals of iron atoms, while C-O and C-N bands near 1032 per centimeter also changed position and intensity. Together, these shifts sketch a mixed-mode mechanism in which electron-rich donor atoms coordinate directly with iron while weaker van der Waals and hydrogen-bonding forces add coverage.

The practical significance is considerable. API 5L X70 steel is a high-strength grade used in long-distance oil and gas transmission pipelines, and acidizing operations, pickling, and industrial cleaning all expose such steels to corrosive acids. An inhibitor derived from an abundant, biodegradable flower, effective at just 400 parts per million, could reduce both the environmental footprint and the health risks associated with conventional formulations. The authors note that this is the first reported use of Chrysanthemum indicum extract for protecting this particular steel grade in sulfuric acid, and they acknowledge that direct comparisons with other plant-based inhibitors remain a task for future work.

The convergence of evidence is what makes the study compelling. Weight loss, polarization, impedance, microscopy, elemental analysis, and spectroscopy all point to the same conclusion: molecules in the chrysanthemum extract spontaneously assemble into an adherent organic film that starves the corrosion reactions of active sites. As industries worldwide face mounting pressure to replace hazardous chemicals with sustainable alternatives, the humble chrysanthemum, already valued for centuries in medicine and ornament, may find a new career guarding the steel arteries of the global energy economy.

Subject of Research: Plant-derived green corrosion inhibitors protecting carbon steel in acidic media

Article Title: Chrysanthemum indicum extract as a sustainable inhibitor for acid-induced corrosion of API 5L X70 steel

Article References: Chrysanthemum indicum extract as a sustainable inhibitor for acid-induced corrosion of API 5L X70 steel. (n.d.). https://doi.org/10.1007/s44373-026-00170-x

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00170-x

Keywords: Chrysanthemum indicum, corrosion inhibition, green inhibitor, API 5L X70 steel, sulfuric acid, Langmuir isotherm, electrochemical impedance spectroscopy, potentiodynamic polarization, adsorption mechanism, plant extract, carbon steel, sustainable chemistry

The economic stakes are enormous. Corrosion costs the world an estimated 2.5 trillion US dollars every year, roughly 3.4 percent of global gross domestic product, with the oil and gas sector among the hardest hit. Steel pipelines transporting crude oil and natural gas routinely carry produced water dominated by sodium chloride brine, and the chloride ions in that brine attack the protective magnetite layer on steel surfaces, triggering localized pitting that can escalate into leaks, structural failures and safety incidents. Conventional wisdom holds that better corrosion management could save between 15 and 35 percent of these costs, equivalent to hundreds of billions of dollars annually, and the search for inhibitors that are both effective and environmentally benign has become one of the most active frontiers in materials chemistry.

Duplex stainless steel 2205 was the test subject for good reason. With its balanced microstructure of ferrite and austenite phases, DSS 2205 combines exceptional mechanical strength with strong resistance to chloride stress corrosion cracking, making it a mainstay of petrochemical plants, offshore platforms and underwater engineering. Yet even this robust alloy is not immune: chloride ions adsorb onto and infiltrate the passive film, initiating pitting corrosion that has caused significant economic losses. Earlier studies have shown that solution annealing temperature, hydrogen exposure and alternating dry-wet marine conditions all influence how badly 2205 pits, but comparatively little work had explored sustainable, biomass-derived inhibitors specifically for this alloy in brine media, and the molecular details of how such inhibitors bond to the steel’s protective oxide film remained poorly understood.

The Indian team turned to munj grass, a fast-growing plant long used in Ayurvedic medicine for its diuretic, cooling and anti-inflammatory properties, and recognized as the One District One Product of Amethi in Uttar Pradesh, where its stems are woven into baskets, mats and decorative handicrafts. Crucially, munj is rich in phytochemicals including phenolics, saponins, flavonoids and tannins, molecules packed with heteroatoms and aromatic rings that can adsorb onto metal surfaces and block chloride-induced attack. The researchers harvested leaves from the RGIPT campus, dried and ground them, and refluxed 10 grams of powder in 0.2 molar sodium hydroxide solution for two hours at 105 degrees Celsius. After filtration and drying, the process yielded 2.3 grams of extract, a 23 percent extraction yield, which was then dosed into 3.5 percent sodium chloride solution, a standard simulation of seawater salinity, at concentrations ranging from 1 to 5 percent by volume.

Electrochemical testing told a compelling story. Using electrochemical impedance spectroscopy and linear polarization resistance on a three-electrode cell with a platinum counter electrode and Ag/AgCl reference, the team measured polarization resistance rising from just 131 ohm square centimeters in the blank brine to a maximum of 1670 ohm square centimeters at 5 percent extract, corresponding to an efficiency of about 92 percent by the impedance route. Nyquist plots showed a single capacitive semicircle whose diameter, a direct proxy for charge transfer resistance, grew steadily with inhibitor concentration, indicating that the extract does not change the underlying corrosion mechanism but simply erects an increasingly effective barrier. The double-layer capacitance fell from 2.95 to 0.87 microfarads per square centimeter, consistent with inhibitor molecules displacing water at the interface and thickening the protective dielectric layer.

Potentiodynamic polarization confirmed the picture over immersion periods stretching from one hour to 96 hours. Corrosion current density at the one-hour mark dropped from 0.227 microamperes per square centimeter in uninhibited brine to 0.027 microamperes per square centimeter with 5 percent extract, and the same monotonic decline appeared at every time point tested. The corrosion potential shifted by less than 85 millivolts with inhibitor addition, classifying munj extract as a mixed-type inhibitor that suppresses both anodic metal dissolution and cathodic reactions. Efficiency climbed during the first 24 hours as adsorbing molecules gradually built their film, dipped slightly at 48 hours in what the authors attribute to partial desorption or competitive chloride adsorption, and recovered again by 96 hours as a more stable adsorption equilibrium established itself on the surface, with a headline inhibition efficiency of 87 percent.

Surface and structural analyses corroborated the electrochemical findings. X-ray diffraction verified the duplex ferrite-austenite microstructure and showed that uninhibited exposure weakened diffraction peak intensities through chloride-driven dissolution, while samples protected with 3 and 5 percent extract retained peak sharpness essentially matching the unexposed alloy, with no new crystalline corrosion products detectable. Field-emission scanning electron microscopy revealed severe pitting and rough, corroded morphology on unprotected coupons, whereas inhibited samples stayed comparatively smooth, with the extract visibly coating and shielding the surface. Energy-dispersive spectroscopy of the pit regions showed iron depletion in uninhibited specimens and recovered iron content in inhibited ones, and Fourier-transform infrared spectroscopy of the extract identified O-H, C-H, C-O-C and C=C functional groups characteristic of polyphenols, carboxylic acids and oligosaccharide-linked sapogenins.

Gas chromatography-mass spectrometry pinpointed the chemistry behind the protection. The extract’s major constituents included gamma-sitosterol at nearly 30 percent, the fatty amide 13-docosenamide, also known as erucamide, at 21 percent, phytyl linoleate at about 9 percent, along with methyl stearate, squalene, tetracontane-1,40-diol and hexacontane. Docosenamide, a long-chain amide already valued in the oil and gas industry as a corrosion-inhibiting additive, emerged as the likely workhorse molecule, donating its polar CONH2 head group to anchor onto oxidized steel while its hydrocarbon tail adds hydrophobic shielding.

To probe that anchoring at the atomic scale, the team ran density functional theory calculations using plane-wave pseudopotential methods in Quantum ESPRESSO, adsorbing the CONH2 fragment onto the (110) surfaces of hematite and chromia, the dominant oxides in the passive film. The results were strikingly surface-dependent: chemisorption on Fe2O3 (110) was strongly exothermic, at 7.72 electronvolts for the FCC form and 4.27 electronvolts for the trigonal form, while Cr2O3 (110) adsorbed more weakly at 3.59 electronvolts, and the Fe2O3 (100) surface was energetically unfavorable altogether. Under-coordinated iron atoms on the (110) plane, the authors argue, act as Lewis acid sites that bind the amide’s nitrogen and oxygen, meaning that inhibitor performance is governed not just by molecular structure but by which oxide phases and crystallographic faces the passive film actually exposes.

Beyond the laboratory, the findings carry real sustainability weight. Munj grows on infertile land with little water, its extract is non-bioaccumulating and non-polluting, and the study’s authors frame the work as a direct contribution to United Nations Sustainable Development Goals 9, 12 and 14 on industry, responsible production and life below water. If amide-rich plant extracts can protect even a premium alloy like DSS 2205 at percent-level dosages, the door opens to greener pipeline treatments across the energy sector, and to a rural Indian grass playing an unlikely starring role in the trillion-dollar fight against corrosion.

Subject of Research: A plant-extract green corrosion inhibitor protecting duplex stainless steel 2205 in chloride-contaminated brine solutions.

Article Title: Anti corrosion and anti-pit resistant munj extract inhibitor for DSS 2205 in chloride contaminated solutions

Article References: Chaudhary, S., Mylapilli, S. V. P., Pandey, S., Kumar, V., & Dwivedi, D. (2026). Anti corrosion and anti-pit resistant munj extract inhibitor for DSS 2205 in chloride contaminated solutions. Journal of Materials Science: Metallurgy, 1(1), Article 21. https://doi.org/10.1007/s44492-026-00022-0

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00022-0

Keywords: corrosion, green inhibitor, duplex stainless steel 2205, munj grass, Saccharum munja, chloride pitting, electrochemical impedance spectroscopy, docosenamide, density functional theory, biomass extract, brine solution, sustainable materials