Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Analysis and Testing Methods
2.2.1. Composition, Structure, and Performance Analysis
2.2.2. Neutral Chloride Salt Corrosion System
2.2.3. Simulated Concrete Pore Solution Corrosion System
2.2.4. Electrochemical Testing
2.2.5. Mott–Schottky Test
3. Results
3.1. Structure and Composition Analysis of Lotus Leaf Extract
3.2. Anti-Corrosion Properties of LLE on Rebars in Neutral Chloride Salt Solutions
3.3. Anti-Corrosion Properties of LLE on Rebars in a Simulated Concrete Pore Solution
3.4. Anti-Corrosion Mechanism of LLE on Rebars in Neutral Chloride or Alkaline Chloride Solutions
4. Conclusions
- (1)
- Lotus leaf extract (LLE) is rich in polar functional groups (e.g., O-H, N-H, C=O) and heterocyclic structures, which form a protective film on the steel surface through physical adsorption and chemical chelation. Fourier-transform infrared spectroscopy (FTIR) and liquid chromatography–mass spectrometry (LC-MS) analyses revealed that LLE contains abundant alkaloids and flavonoids, which can coordinate with the 3D orbitals of iron atoms via lone pair electrons, forming a dense adsorption layer that hinders the penetration of corrosive agents (e.g., Cl−). Scanning electron microscopy (SEM) tests demonstrated that LLE forms an adsorption film on the steel surface, with higher concentrations resulting in more uniform and compact layers.
- (2)
- Electrochemical impedance spectroscopy (EIS) measurements in a 3.5% NaCl solution confirmed that the adsorption film significantly increases charge transfer resistance (Rct). The corrosion inhibition performance of LLE exhibits concentration dependence, with 0.2 wt% being the optimal concentration. Although higher concentrations (e.g., 0.5 wt%) form more uniform films, the further reduction in solution pH (pH ≈ 5.04) weakens the corrosion inhibition effect, indicating that the efficiency in neutral environments is jointly regulated by pH and the quality of the adsorption film.
- (3)
- In an alkaline environment (saturated Ca(OH)2 + 3.5% NaCl), LLE inhibits corrosion by promoting passive film formation and suppressing Cl− attack. In the unprepassivated rebar system, 0.4 wt% LLE exhibited the best performance, achieving an Rct of 3.9 × 104 Ω·cm2 and reducing icorr to 0.99 × 10−3 μA/cm2. Mott–Schottky (M-S) tests showed that LLE reduces the carrier density of the passive film, enhancing its n-type semiconductor properties and delaying film breakdown. In the pre-passivated system, 0.5 wt% LLE achieved the highest Rct (4.34 × 104 Ω·cm2), demonstrating its long-term protective effect on the passive film. X-ray photoelectron spectroscopy (XPS) confirmed that 0.5 wt% LLE treatment led to the formation of an Fe2O3/FeO passive film and an organic layer containing C-O bonds, significantly improving corrosion resistance.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Chemical Composition | Fe | C | Si | Mn | S | P | Carbon Equivalent |
---|---|---|---|---|---|---|---|
HRB400 | Balance | 0.25 | 0.80 | 1.60 | 0.045 | 0.045 | 0.54 |
LLE Concentrations | Rs /(Ω·cm2) | Yf × 10−3 /(Ω−1·sn·cm−2) | n1 | Rf /(Ω·cm2) | Ydl × 10−3 /(Ω−1·sn·cm−2) | n2 | Rct /(Ω·cm2) |
---|---|---|---|---|---|---|---|
0 wt% | 7.49 | 2.33 | 0.78 | 11.24 | 0.40 | 0.94 | 1379 |
0.1 wt% | 9.33 | 1.88 | 0.81 | 3.86 | 2.15 | 0.80 | 2757 |
0.2 wt% | 9.26 | 0.07 | 0.59 | 4.76 | 0.46 | 0.89 | 4603 |
0.3 wt% | 8.35 | 0.05 | 0.59 | 17.75 | 0.60 | 0.85 | 3720 |
0.4 wt% | 7.96 | 0.55 | 0.91 | 1626 | 1.37 | 0.84 | 681.9 |
0.5 wt% | 7.38 | 0.60 | 0.90 | 1600 | 2.91 | 0.98 | 481.1 |
LLE Concentrations | Rp/(Ω·cm2) | ηEIS/(%) | RSD |
---|---|---|---|
0 wt% | 1390.24 | -- | -- |
0.1 wt% | 2760.86 | 49.64 | 2.0 |
0.2 wt% | 4607.76 | 69.83 | 2.3 |
0.3 wt% | 3737.75 | 62.81 | 2.2 |
0.4 wt% | 2307.90 | 39.76 | 1.9 |
0.5 wt% | 2081.10 | 33.20 | 1.9 |
LLE concentrations | Ecorr /(V) | icorr × 10−3 /(μA/cm2) | IE/(%) | RSD |
---|---|---|---|---|
0 wt% | −0.70 | 5.76 | -- | -- |
0.1 wt% | −0.70 | 2.88 | 50.00 | 2.2 |
0.2 wt% | −0.80 | 2.00 | 65.28 | 2.1 |
0.3 wt% | −0.81 | 3.52 | 38.89 | 2.3 |
0.4 wt% | −0.82 | 1.55 | 73.09 | 2.4 |
0.5 wt% | −0.83 | 2.36 | 59.03 | 2.2 |
LLE Concentrations | Rs /(Ω·cm2) | Yf × 10−3 /(Ω−1·sn·cm−2) | n1 | Rf /(Ω·cm2) | Ydl × 10−3 /(Ω−1·sn·cm−2) | n2 | Rct /(Ω·cm2) |
---|---|---|---|---|---|---|---|
0 wt% | 7.80 | 0.14 | 0.86 | 132 | 2.81 | 0.53 | 3805 |
0.1 wt% | 8.42 | 0.10 | 0.84 | 630 | 0.98 | 0.58 | 3560 |
0.2 wt% | 7.89 | 0.07 | 0.86 | 845 | 0.82 | 0.64 | 4886 |
0.3 wt% | 8.70 | 0.08 | 0.86 | 1925 | 0.59 | 0.55 | 15,360 |
0.4 wt% | 8.80 | 0.23 | 0.84 | 8035 | 0.28 | 0.65 | 39,000 |
0.5 wt% | 7.23 | 0.07 | 0.88 | 4888 | 0.23 | 0.49 | 33,640 |
LLE Concentrations | Rp/(Ω·cm2) | ηEIS/(%) | RSD |
---|---|---|---|
0 wt% | 3937 | -- | -- |
0.1 wt% | 4190 | 6.04 | 2.2 |
0.2 wt% | 5731 | 31.31 | 2.5 |
0.3 wt% | 17,285 | 77.22 | 2.4 |
0.4 wt% | 47,035 | 91.63 | 2.6 |
0.5 wt% | 38,528 | 89.78 | 2.7 |
LLE Concentrations | Ecorr /(V) | icorr × 10−3 /(μA/cm2) | IE/(%) | RSD |
---|---|---|---|---|
0 wt% | −0.75 | 32.49 | -- | -- |
0.1 wt% | −0.69 | 10.02 | 69.16 | 2.5 |
0.2 wt% | −0.66 | 3.67 | 88.71 | 2.4 |
0.3 wt% | −0.67 | 3.89 | 88.02 | 2.6 |
0.4 wt% | −0.56 | 0.99 | 96.96 | 2.7 |
0.5 wt% | −0.61 | 1.04 | 96.80 | 2.6 |
LLE Concentrations | Rs /(Ω·cm2) | Yf × 10−5 /(Ω−1·sn·cm−2) | n1 | Rf /(Ω·cm2) | Ydl × 10−3 /(Ω−1·sn·cm−2) | n2 | Rct × 104 /(Ω·cm2) |
---|---|---|---|---|---|---|---|
0 wt% | 8.04 | 7.99 | 0.89 | 219 | 1.42 | 0.60 | 0.51 |
0.1 wt% | 8.20 | 0.89 | 0.85 | 645 | 1.07 | 0.45 | 0.80 |
0.2 wt% | 7.19 | 5.81 | 0.90 | 3488 | 0.28 | 0.56 | 1.03 |
0.3 wt% | 6.88 | 8.96 | 0.89 | 3073 | 0.41 | 0.62 | 1.11 |
0.4 wt% | 8.23 | 5.90 | 0.89 | 5411 | 0.23 | 0.52 | 2.23 |
0.5 wt% | 8.64 | 6.93 | 0.88 | 9093 | 0.13 | 0.47 | 4.34 |
LLE Concentrations | Rp/(Ω·cm2) | ηEIS/(%) | RSD |
---|---|---|---|
0 wt% | 5324 | -- | -- |
0.1 wt% | 8666 | 38.56 | 2.3 |
0.2 wt% | 13,828 | 61.50 | 2.5 |
0.3 wt% | 14,133 | 62.33 | 2.7 |
0.4 wt% | 27,701 | 80.78 | 2.8 |
0.5 wt% | 52,443 | 89.85 | 3.1 |
LLE Concentrations | Ecorr /(V) | icorr × 10−3 /(μA/cm2) | IE/(%) | RSD |
---|---|---|---|---|
0 wt% | −0.71 | 5.65 | -- | -- |
0.1 wt% | −0.74 | 6.32 | -- | -- |
0.2 wt% | −0.70 | 3.76 | 33.45 | 2.7 |
0.3 wt% | −0.67 | 1.64 | 70.97 | 2.9 |
0.4 wt% | −0.68 | 1.47 | 73.98 | 3.2 |
0.5 wt% | −0.63 | 0.55 | 90.27 | 3.1 |
Plant Extract Source | Corrosive Medium | ηEIS/(%) | IE/(%) | Reference |
---|---|---|---|---|
Urtica dioica leaf | 0.3 M KOH + 0.1 M NaOH in saturated Ca(OH)2 solution containing 1 wt% NaCl | 77.00% | - | [38] |
Phragmites australis leaf | Concrete specimens immersed in 3% NaCl electrolyte | - | 76.98% | [27] |
Damask rose leaf | 0.5 M Ca(OH)2 + 0.5 M KOH + 0.1 M NaOH + 0.5 M NaCl | 81.90% | 81.60% | [16] |
lotus leaf | 3.5% NaCl electrolyte | 69.83% | 73.09% | This paper |
lotus leaf | Non-passivated steel rebar in saturated Ca(OH)2 solution | 91.63% | 96.96% | This paper |
lotus leaf | Pre-passivated steel rebar in saturated Ca(OH)2 solution | 89.85% | 90.27% | This paper |
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Song, D.; Wang, J.; Guan, H.; Zhang, S.; Zhou, Z.; Zhang, S. Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition. Metals 2025, 15, 510. https://doi.org/10.3390/met15050510
Song D, Wang J, Guan H, Zhang S, Zhou Z, Zhang S. Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition. Metals. 2025; 15(5):510. https://doi.org/10.3390/met15050510
Chicago/Turabian StyleSong, Dan, Juhang Wang, Hao Guan, Sijie Zhang, Zhou Zhou, and Shuguang Zhang. 2025. "Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition" Metals 15, no. 5: 510. https://doi.org/10.3390/met15050510
APA StyleSong, D., Wang, J., Guan, H., Zhang, S., Zhou, Z., & Zhang, S. (2025). Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition. Metals, 15(5), 510. https://doi.org/10.3390/met15050510