pH-Triggered Release of NaNO2 Corrosion Inhibitors from Novel Colophony Microcapsules in Simulated Concrete Pore Solution

Unraveling the anti-corrosion mechanisms of a novel hydrazone derivative on steel in contaminated concrete pore solutions: An integrated study

INTRODUCTION

Corrosion-induced deterioration of infrastructure is a growing global concern. The development and application of corrosion inhibitors are one of the most effective approaches to protect steel rebar from corrosion. Hence, this study focuses on a novel hydrazone derivative, (E)-N'-(4-(dimethylamino)benzylidene)-2-(5-methoxy-2-methyl-1H-indol-3-yl)aceto-hydrazide (HIND), and its potential application to mitigate corrosion in steel rebar exposed to chloride-contaminated concrete pore solutions (ClSCPS).

OBJECTIVES

The research aims to evaluate the anti-corrosion capabilities of HIND on steel rebar within a simulated corrosive environment, focusing on the mechanisms of its inhibitory effect.

METHODS

The corrosion of steel rebar exposed to the ClSCPS was studied through weight loss and electrochemical methods. The surface morphology of steel rebar surface was characterized by FE-SEM-EDS, AFM; oxidation states of the steel rebar and crystal structures were examined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) methods. Further, experimental findings were complemented by theoretical studies using self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations. The performance of HIND was monitored at an optimal concentration over a period of 30 days.

RESULTS

The results indicated a significant reduction in steel rebar corrosion upon introducing HIND. The inhibitor molecules adhered to the steel surface, preventing further deterioration and achieving an inhibition efficiency of 88.4% at 0.5 mmol/L concentration. The surface morphology analysis confirmed the positive effect of HIND on the rebar surface, showing a decrease in the surface roughness of the steel rebar from 183.5 in uninhibited to 50 nm in inhibited solutions. Furthermore, SCC-DFTB simulations revealed the presence of coordination between iron atoms and HIND active sites.

CONCLUSION

The findings demonstrate the potential of HIND as an effective anti-corrosion agent in chloride-contaminated environments. Its primary adsorption mechanism involves charge transfer from the inhibitor molecules to iron atoms. Therefore, applying HIND could be an effective strategy to address corrosion-related challenges in reinforced infrastructure.

Electrochemical and DFT Study of NaNO2/NaNO3 Corrosion Inhibitor Blends for Rebar in Simulated Concrete Pore Solution

The use of nitrite- and nitrate-based inhibitors provides corrosion protection by the development of passive oxide film on the metal surface in reinforced concrete applications. However, the impact of the nitrite and nitrate ratio in the mixture has not been widely studied. In this study, the corrosion protection provided by NaNO2:NaNO3 inhibitor blends with ratios of 0.5:1, 1:1, and 1:0.5 were studied to maximize corrosion inhibition efficiency. The nitrite species imparted higher corrosion protection, as shown by cyclic potentiodynamic polarization, with an icorr of 1.16 × 10–7 A/cm2 for the 1:0.5 mixture, lower than for both the 1:1 and 0.5:1 mixtures. Electrochemical impedance spectroscopy was also performed, with the 1:0.5 mixture consistently displaying high resistance values, showing an Rct of 1.31 × 105 Ω cm2. The effect of temperature was also assessed; the Ea’s of the corrosion reaction were calculated to be 12.1, 9.2, and 4.9 kJ/mol for the 0.5:1, 1:1, and 1:0.5 (NO2−:NO3−) mixtures, respectively. Density functional theory was applied to analyze the molecular properties and to determine the relationship between the quantum properties and corrosion inhibition. The ΔE of NO2− was found to be −5.74 eV, lower than that of NO3− (−5.45 eV), corroborating the experimental results. Lastly, commercially available inhibitor mixtures were investigated and nitrite/nitrate concentrations determined to evaluate their corrosion protection performance; amongst the two inhibitor blends tested, Sika was found to outperform Yara due to its greater NO2− concentration.

Synthesis of Smart Nanofiber Coatings with Autonomous Self-Warning and Self-Healing Functions

Organic protective coatings are widely used to protect metal structures from corrosion but they are vulnerable to undetectable damage. Without timely detection and repair, it could lead to severe consequences. How to warn and heal damaged areas simultaneously and automatically has become a challenging problem. Herein, we report an intelligent protective coating with self-warning and self-healing functions. This strategy was achieved by embedding bifunctional nanofibers containing 1,10-phenanthroline (Phen) in organic coatings. The nanofibers with Phen as a core and a poly(vinyl alcohol) (PVA)─chitosan (CS) blend solution as a shell were synthesized by coaxial electrospinning. The PVA/CS@Phen nanofiber-embedded coating displayed self-healing and high contrast indication function of the damaged area on coatings. Prominent red could warn microdamage and macrosurface damage, which occurred rapidly and healed permanently. The intelligent coating exhibited high healing performance under artificial injury with self-warning characteristics, and the cure rate was about 98.4% without external intervention. In the healing process, free amino groups of CS in the shell of nanofibers enhanced the sustained release of Phen. This convenient, economical, and efficient strategy with cooperative functions of self-warning and self-healing delivers an effective solution for prolonging the service life of protective coatings. This multifunctional coating exhibits excellent potential in the field of marine engineering applications.

Design of Nanostructured Protective Coatings with a Sensing Function

Nanostructured multilayered coatings for metals are prepared to simultaneously provide a function of corrosion mitigation and of corrosion sensing for copper substrates. Silica nanocapsules, embedded in one layer of the coating, are used as a host for a corrosion inhibitor and as a sensor, which detect changes of pH value and release inhibitors via an optical signal. Furthermore, another layer in the coating exists in a nanonetwork loaded with another corrosion inhibitor, which is impregnated with a hydrophobic polymer. We demonstrate that a specific arrangement of layers leads to an optimum anticorrosion and sensing performance while the sensing signal can be prolonged for a long time. It is the first time that the fluorophore detecting corrosion is conjugated to the nanosensor and that nanofibers and nanocapsules are used simultaneously to load and release corrosion inhibitors for anticorrosion applications.

Corrosion Inhibition Mechanism of Steel Reinforcements in Mortar Using Soluble Phosphates: A Critical Review

The corrosion inhibition mechanism of soluble phosphates on steel reinforcement embedded in mortar fabricated with ordinary Portland cement (OPC) are reviewed. This review focuses soluble phosphate compounds, sodium monofluorophosphate (Na2PO3F) (MFP), disodium hydrogen phosphate (Na2HPO4) (DHP) and trisodium phosphate (Na3PO4) (TSP), embedded in mortar. Phosphate corrosion inhibitors have been deployed in two different ways, as migrating corrosion inhibitors (MCI), or as admixed corrosion inhibitors (ACI). The chemical stability of phosphate corrosion inhibitors depends on the pH of the solution, H2PO4- ions being stable in the pH range of 3-6, the HPO42- in the pH range of 8-12, while the PO43- ions are stable above pH 12. The formation of iron phosphate compounds is a thermodynamically favored spontaneous reaction. Phosphate ions promote ferrous phosphate precipitation due to the higher solubility of ferric phosphate, thus producing a protective barrier layer that hinders corrosion. Therefore, the MFP as well as the DHP and TSP compounds are considered anodic corrosion inhibitors. Both types of application (MCI and ACI) of phosphate corrosion inhibitors found MFP to present the higher inhibition efficiency in the following order MFP > DHP > TSP.

pH-Triggered Release Performance of Microcapsule-Based Inhibitor and Its Inhibition Effect on the Reinforcement Embedded in Mortar

The smart release of healing agents is a key factor determining the inhibition efficiency of microcapsules-based corrosion inhibitors for reinforced concrete. In this study, the release behavior of benzotriazole (BTA) in microcapsule-based inhibitors was investigated in mortar sample to clarify the influence of different hydration products on the release process. The results indicated that under high pH environment (pH > 12.4), only about 5% reserved BTA was released from the mortar sample. pH drop resulted in the increased release of BTA from mortar sample. Most BTA in the microcapsule-based inhibitors was released from mortar sample in low pH environment, which was closely related to morphology/composition alterations of hydration products caused by pH drop of the environment. The smart release of BTA dramatically delayed corrosion initiation of reinforced mortar and halted corrosion product accumulation on the steel surface. Therefore, the corrosion resistance of the reinforced mortar was improved after corrosion initiation.

Improved Corrosion Protection of Acrylic Waterborne Coating by Doping with Microencapsulated Corrosion Inhibitors

Herein, a waterborne acrylic coating doped with pH sensitive colophony microcapsules containing corrosion inhibitors was studied on carbon steel plates. The changes in the physical properties of the coatings were studied. The microcapsule coating specimens maintained more noble Ecorr values compared to the control in deionized water and simulated concrete pore solutions with −513 and −531 mVSCE, respectively. Additionally, the microcapsule polarization results for both pH 12.6 and 6.2 electrolyte solutions showed lower icorr values of 1.20 × 10−6 and 3.24 × 10−6 A·cm−2, respectively, compared to the control sample (1.15 × 10−5 and 4.21 × 10−5 A·cm−2). Therefore, the microcapsule coating provided more protection from chloride attack on the substrate as well as the deleterious effects of low pH on carbon steel. The electrochemical impedance spectroscopy analysis corroborated the DC polarization results, showing increased corrosion resistance for the microcapsule coated specimens compared to the control. Moreover, the Rpore and Rct are much higher than the control, indicating the protection of the inhibitors. The Ceff,dl also shows lower values for the microcapsule coating than the control, showing a more protective and less doped double layer.

Conifer Cone (Pinus resinosa) as a Green Corrosion Inhibitor for Steel Rebar in Chloride-Contaminated Synthetic Concrete Pore Solutions

The present study has been focused on the environment-friendly corrosion inhibitor. Conifer cone (Pinus resinosa) has been used as a novel corrosion inhibitor to mitigate the corrosion of steel rebars in simulated concrete pore solutions (SCPS) in the presence and absence of chloride ions. The corrosion inhibitor is extracted by simple chemical methods. The functional groups present in the extracted conifer cone (ECC) powder are characterized as well as the surface morphology of ECC has been examined. The corrosion inhibition performance has been evaluated by the electrochemical and weight loss methods. The experimental results indicate that ECC possesses a corrosion inhibition efficiency of 81.2% at a dosage of 1000 mg·L^-1, after 720 h of immersion in chloride-contaminated SCPS. Adsorption isotherm and their standard Gibbs free energy (ΔG_ads⁰) values are calculated by Langmuir, Freundlich, and Temkin isotherm methods, and the results indicate that the ECC is initially adsorbed on the steel rebar surface by physisorption and then it turns to chemisorption. The steel rebar surfaces have been characterized after exposure to the ECC containing SCPS, and the results indicate that the ECC containing cationic adsorbate molecules, which interact with steel rebar, leads to retardation of metal dissolution in corrosive chloride medium.

Electrochemical Corrosion of Galvanized Steel in Binary Sustainable Concrete Made with Sugar Cane Bagasse Ash (SCBA) and Silica Fume (SF) Exposed to Sulfates

This research evaluates the behavior corrosion of galvanized steel (GS) and AISI 1018 carbon steel (CS) embedded in conventional concrete (CC) made with 100% CPC 30R and two binary sustainable concretes (BSC1 and BSC2) made with sugar cane bagasse ash (SCBA) and silica fume (SF), respectively, after 300 days of exposure to 3.5 wt.% MgSO4 solution as aggressive medium. Electrochemical techniques were applied to monitor corrosion potential (Ecorr) according to ASTM C-876-15 and linear polarization resistance (LPR) according to ASTM G59 for determining corrosion current density (icorr). Ecorr and icorr results indicate after more than 300 days of exposure to the sulfate environment (3.5 wt.% MgSO4 solution), that the CS specimens embedded in BSC1 and BSC2 presented greater protection against corrosion in 3.5 wt.% MgSO4 than the specimens embedded in CC. It was also shown that this protection against sulfates is significantly increased when using GS reinforcements. The results indicate a higher resistance to corrosion by exposure to 3.5 wt.% magnesium sulfate two times greater for BSC1 and BSC2 specimens reinforced with GS than the specimens embedding CS. In summary, the combination of binary sustainable concrete with galvanized steel improves durability and lifetime in service, in addition to reducing the environmental impact of the civil engineering structures.

Protection of Carbon Steel Rebars by Epoxy Coating with Smart Environmentally Friendly Microcapsules

The protection of mild steel by modified epoxy coating containing colophony microencapsulated corrosion inhibitors was investigated in this study. The corrosion behavior of these epoxy coatings containing colophony microcapsules was studied by electrochemical analysis using cyclic potentiodynamic polarization and electrochemical impedance spectroscopy. The microcapsule coating showed decreased corrosion current densities of 2.75 × 10−8 and 3.21 × 10−8 A/cm2 along with corrosion potential values of 0.349 and 0.392 VSCE for simulated concrete pore solution and deionized water with 3.5 wt.% NaCl, respectively, indicating improved corrosion protection in both alkaline and neutral pH. Electrochemical impedance spectroscopy analysis also showed charge transfer resistance values over one order of magnitude higher than the control sample, corroborating the electrochemical corrosion potential and current density testing results. Overall, the use of colophony microcapsules showed improved corrosion protection in simulated concrete pore solution and DI water solutions containing chloride ions.