Corrosion Protection Mechanism Research Articles

Enhanced high-temperature corrosion resistance of Cr-modified phosphate/aluminum powder composite coatings: Mechanisms and thermodynamic insights

Phosphate composite coatings are regarded as one of the tangible solutions for surface protection in salt spray environments, benefiting from their cost-effectiveness and prominent structure stability upon high-temperature exposure. However, rapid curing of these coatings often leads to crack formation, and the underlying corrosion mechanisms in service conditions remain insufficiently understood, limiting their practical applications. In this study, we developed chromium-incorporated phosphate/aluminum powder composite (Cr-P/Al) coatings and evaluated their corrosion resistance under alternating conditions of salt spray corrosion and oxidation at 450 °C. By integrating experimental results, ab initio calculations, and thermodynamic analysis, we demonstrate that the incorporation of Cr significantly enhances the performance of the P/Al coatings. The structural evolution was first revealed that Cr’s modification reduced tensile stress and prevented cracks in the coating. A mixed layer of amorphous oxides and phosphates forms on the surface of the Al powder, providing robust binding strength. A novel corrosion mechanism was identified that Cl2 and volatile chlorides facilitated the removal of Cl-. This process is more ineffective with Cr-P/Al coating, as amorphous Cr oxide has low reactivity at a high log[p(Cl2)] and low log[p(O2)] compared with amorphous Mg and Fe oxide, thereby enhancing the corrosion resistance of the coating. These coating densification methods and corrosion protection mechanisms provide a critical foundation for the future application of phosphate composite coatings.

Research of two kinds of PANI@semiconductor based photocathodic coating corrosion protection effect and mechanism

PurposeThis study aims to report the development and experimental evaluation of two kinds of PANI@semiconductor based photocathodic anti-corrosion coating, for application on stainless steel substrates.Design/methodology/approachPANI was in situ chemical polymerized on TiO2 and BiVO4 particles, and FT-IR and SEM/EDS were used to understand the characteristics and elemental distribution of the composite particles. Composite coatings, which consisted of epoxy, PANI@TiO2 or PANI@BiVO4 and graphene, were prepared on the 304L stainless steel. Photoelectrochemical response measurement, electrochemical tests and immersion tests were used to assess the anti-corrosion performance of the prepared coatings in 45°C 3.5 wt.% NaCl solution. And the corrosion protection mechanism was further explained by combining with surface observation.FindingsThe photoelectrochemical response tests revealed the good photocathodic effect of the coatings, and the reversible oxidation-reduction properties of PANI (pseudocapacitive effect) leading to the repeated usage of the coatings. Consequently, the anti-corrosion mechanism of the composite coating is attributed to the physical barrier effect of the coating, the anodic protection effect of PANI and the photocathodic and energy store effect.Originality/valueThese kind coatings could prevent corrosion from day to night for stainless steel, which has great engineering application prospects on stainless steel corrosion protection.

Chitosan grafted with gallic acid and cerium dioxide hybrid nanocomposites as environmentally friendly corrosion inhibitors for mild steel: An experimental and computational study

Chitosan grafted with gallic acid (CS-GA), along with CS-GA doped with CeO2 nanoparticles (CS-GA-CeO2) were synthesized as novel environmentally friendly mild steel corrosion inhibitors. The formation of these derivatives was confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), hydrogen nuclear magnetic resonance spectroscopy (1H NMR), and thermal analysis (TGA). Based on potentiodynamic polarization curves (PDP) measurements, the inhibitors acted primarily as hybrid inhibitors, while following the Langmuir adsorption theory model. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy(XPS) and 3D surface profiles, confirmed that CS-GA-CeO2 adsorbed on the mild steel forming a protective layer thus preventing the invasion of corrosive media. The corrosion protection mechanism of chitosan derivatives was investigated by molecular dynamics simulations. Electrochemical measurements were used to investigate the corrosion inhibition by CS-GA and CS-GA-CeO2 on mild steel in a 3.5 % NaCl solution. At room temperature, the highest inhibition efficiency (93.58 %) was achieved at 200 ppm CS-GA-CeO2. Modified chitosan nanocomposites were confirmed as promising corrosion inhibitors.

Mechanism for corrosion protection of β-TCP reinforced ZK60 via laser rapid solidification

It remains the primary issue to enhance the corrosion resistance of Mg alloys for their clinical applications. In this study, β-tricalcium phosphate (β-TCP) was composited with Mg-6Zn-1Zr (ZK60) using laser rapid solidification to improve the degradation behavior. Results revealed rapid solidification effectively restrained the aggregation of β-TCP, which thus homogenously distributed along grain boundaries of α-Mg. Significantly, the uniformly distributed β-TCP in the matrix promoted the formation of apatite layer on the surface, which contributed to the formation of a compact corrosion product layer, hence retarding the further degradation. Furthermore, ZK60/8β-TCP (wt. %) composite showed improved mechanical strength, as well as improved cytocompatibility. It was suggested that laser rapidly solidified ZK60/8β-TCP composite might be a potential materials for tissue engineering.

Effect of precipitated Mg-containing corrosion products on the anodic behavior of steel in aqueous corrosion for Zn-Al-Mg coated steel

The role of precipitated Mg-containing corrosion product in the anodic behavior of the steel in aqueous corrosion was ascertained to analyze the corrosion protection mechanism at steel substrate of the Zn-Al-Mg coated steel. For the Zn-Al-Mg coating, the corrosion products that formed during the immersion test passivated the steel in the deaerated solution at pH 8.2. EDS analysis revealed that Mg-species remained on the steel after polarization. However, the concentration of Mg decreased after polarization. The results indicated that the alkalization and barrier effect by the Mg-containing corrosion products passivated the steel substrate, preventing red rust generation at the cut-edge.

Chromium-Free Coating for Al Alloy Corrosion Protection Based on a Novel Ti/Mg Oxyfluoride

Chromium-free corrosion protection of aluminum alloys comparable to that of chromates (Cr(VI)) is demonstrated using a TiF6 2− fluoro-anion-based coating recipe containing boric acid and a Mg salt. Boric acid drove TiF6 2− hydrolysis enabling up to micrometer-scale thick coatings. The Mg salt led to deposition of a novel crystalline phase Ti/Mg oxyfluoride coating with an approximate composition of Ti5MgO7F8. Corrosion protection performance was characterized by polarization resistance measurements during immersion in 5% aqueous NaCl solution and neutral salt fog exposure following ASTM B.117. The performance is discussed in terms of the presence of fluoride in the coating enabling active behavior during its gradual depletion (in corrosion environments) toward a final composition approaching TiO2. This active corrosion protection mechanism may be more generally applicable for transition metal-based coatings that do not have high oxidation state oxo-anions, but do have stable fluoro-anions.

Development of inorganic anticorrosive coatings for steel bars: Corrosion resistance testing and design

A densely structured three-dimensional geopolymer network could effectively impede the migration and diffusion of chloride ion. This study developed one kind of efficient and cost-effective and multi-component geopolymer coating (MGC) for inhibiting and delaying the corrosion of steel. The influence of alkali content, metakaolin replacement ratio, polyvinyl alcohol content, and titanium dioxide content on the fluidity, setting time, and rheological properties of MGC was investigated. Accelerated corrosion tests were carried out to determine the optimal formulation of MGC. The corrosion resistance of MGC prepared by different coating method was compared to commercial organic metal coatings, for which the salt spray test, adhesion test, and electrochemical impedance spectroscopy test were conducted. The results showed that the dip-coated specimen of MGC exhibited 63.8% decrease in mass loss, 59.5% decrease in adhesive strength loss, and 38.1% increase in impedance modulus compared to commercial organic metal coatings. Furthermore, the corrosion protection mechanism of MGC was elucidated by analyzing its microstructural characteristics including the functional groups formed on the surface of coated steel bars. In terms of cost, MGC reduced the total cost by about 15 times compared to commercial organic metal coatings.

Ab initio exploration of modified carbon nanotubes as potential corrosion inhibitors

In order to develop novel unexplored potential corrosion inhibitors, covalently modified single-walled carbon nanotubes (SWCNT) via benzoic (–PhCOOH) and aniline (–PhNH2) groups are being investigated as corrosion inhibitors for the first time. Utilizing a comprehensive approach, this study employed density functional theory (DFT), Monte Carlo (MC), and molecular dynamics simulations (MD) to assess the adsorption behavior of modified nanotubes as corrosion inhibitors on the Cu(111) surface within a simulated aqueous HCl corrosion medium. The results provided molecular information on the adsorption capability, geometry adsorption centers, and adsorption energies (Eads) of carbon nanotubes on the surface of Cu(111). The adsorption energy values unveiled robust interactions between SWCNT–PhCOOH and SWCNT–PhNH2 inhibitors and the Cu(111) surface, suggesting a highly effective corrosion protection mechanism. The calculated Eads values exhibited notable ranges, spanning from –260.82 to –308.18 kcal/mol for SWCNT–PhCOOH and –220.92 to –261.01 kcal/mol for SWCNT–PhNH2 with the maximum probability values, representing the most favorable adsorption scenarios, determined to be –292.96 and –229.39 kcal/mol, respectively. A key insight from Monte Carlo simulations underscored the inherent spontaneity of the adsorption process, corroborated by the consistently negative Eads values. These findings collectively underscore the substantial affinity of the inhibitors to the copper surface, contributing to a deeper comprehension of their corrosion inhibition capabilities.

Optimization of anodizing conditions and hole sealing treatments for enhanced anti-corrosion properties of magnesium alloys

To enhance the corrosion resistance of magnesium alloys, an anti-corrosion composite film was prepared by combining anodic oxidation and sol-gel technology. Experimental results indicate that after anodization at 17.5V for 3 min, the composite film obtained through sealing with an MPTMS-modified sol exhibited significant improvements in physical properties. The thickness of the film reached 24.3 μm, its hardness was measured at 164.7 HV, and it demonstrated good surface uniformity. Electrochemical impedance spectroscopy revealed that the impedance modulus at low frequency (|Z| at 0.01 Hz) increased by nearly two orders of magnitude. Furthermore, this study thoroughly explores the corrosion protection mechanism of the composite film, highlighting the role of the sol-gel layer in occupying micro-pores and micro-cracks to form a denser and more uniform protective layer. The dual-layer protection provided by the combination of anodic oxidation and sol-gel layers significantly enhances the overall corrosion resistance of the magnesium alloy.

Nano-structure and hydrophobicity co-determined barrier properties of corrosion protective ZnAl-LDH film in atmospheric environment

Salt spray is prone to convert superhydrophobic surface from Cassie-Baxter state to Wenzel state, which accelerates the metallic corrosion. Herein, corrosion process of superhydrophobic coatings were investigated by in-situ growth of LDH lamellae with different platelet spacing and modification of stearic acid. The corrosion protection mechanism of the superhydrophobic coating divided into two stages: the well-known air film blocking effect and the hydrophobicity-depended barrier performance, which is a new focus. Through investigating the influences of the nano-structure on corrosion protection via experiments and simulation, a new mechanism on corrosion protection failure of superhydrophobic surfaces in atmospheric environment is proposed.

Corrosion behavior and protection mechanism of carbon steel coated with ethylene chlorotrifluoroethylene (ECTFE)

Corrosion behavior and protection mechanism of carbon steel coated with ethylene chlorotrifluoroethylene (ECTFE)

Innovative phosphorus-containing epoxy resins: A new approach to acidic corrosion protection

The main challenges in the corrosion field for steel include its high susceptibility to acidic degradation and the need for sustainable and efficient corrosion inhibitors. The main objective was to synthesize a novel phosphorus-containing trifunctional epoxy resin, named phosphoric ester triglycidyl ether hydroquinone (TGEHEP), through a two-step process. Initially, the intermediate known as phosphoric ester trihydroquinone was synthesized. Subsequently, epichlorohydrin was added in the second step to produce the new TGEHEP epoxy resin. For the structural characterization of this compound, FTIR, 1H and 13C NMR were used. These techniques confirmed the final chemical structure of the synthesized macromolecule. The newly developed TGEHEP epoxy resin was subsequently utilized as a protective agent for carbon steel in 1.0 M HCl. This study incorporated various techniques, including PDP, EIS, EFM, DFT, MC, and MD simulations. Additionally, SEM/EDS was applied to examine the surface. These methods allowed us to analyse the surface structure and chemical composition of the sample, providing further insights into the adsorption process and corrosion protection mechanism. Electrochemical test results revealed that the TGEHEP concentration significantly enhanced protection. Notably, EIS demonstrated an outstanding protection efficiency of 96.70% with 10−3 M TGEHEP epoxy resin. The polarization findings also indicate that the resin acts as a mixed inhibitor. In line with the Langmuir isotherm, epoxy resin was effectively used to protect the metal surface. Furthermore, thermodynamic kinetic parameters were estimated to evaluate the adsorption of the inhibitor. TGEHEP showed a greater adsorption energy (-195.05 kcal/mol) than did its protonated form (-178.65 kcal/mol), indicating that the interaction with the iron surface was stronger in its neutral form. A significant increase in the concentration of TGEHEP was detected, reaching a maximum of 762.4 Ω.cm² at a concentration of 10−3 M. This suggests that TGEHEP forms a barrier that impedes electron transfer, a key factor in corrosion processes. The ΔGads is −44.3 kJ/mol, which is within the typical range for chemisorption. This suggests that the adsorption of TGEHEP onto the metal surface includes more than just physical adsorption; it likely involves electron transfer, which is characteristic of a chemisorptive bond. Comparatively, TGEHEP demonstrates superior performance to previously published corrosion inhibitors, with its efficacy not only attributed to its unique chemical structure but also to its environmentally benign nature.

Recent advances in anticorrosive coatings based on sustainable polymers: Challenges and perspectives

The present paper provides a comprehensive review of sustainable polymer-based anticorrosive polymeric coatings. We have presented the economical and environmental impact of corrosion in terms of Gross National Product (GDP) in a pie chart to highlight the motive behind using sustainable polymer-based anticorrosive coatings as an effective and most convenient method for protecting the underlying metal surface. Also, consumer awareness for eco-friendly considerations, followed by health protection, has driven a significant change in the aforementioned sector. Accordingly, about 16.8 % increase has been found in the use of sustainable resource-based coatings during the last two decades. Besides presenting literature on different sustainable polymers, the review also highlights the corrosion protection mechanism of barrier, sacrificial, and inhibitive coatings. A comparative study of different coating systems, along with their corrosion protection summaries and relevant industrial applications, has been given in a separate table.

Hydroxyl transport mechanisms upon passivation of Cr-Fe-Co-Ni-Mo multi-principal element alloy surfaces investigated by isotopic labelling

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with deuterium labelling (D2O), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the interfacial transport mechanisms of hydroxyls between aqueous electrolyte and outer part of the protective oxide film during passivation of Cr15Fe10Co5Ni60Mo10 multi-principal element alloy surfaces. A ToF-SIMS signal treatment methodology was developed to retrieve the in-depth distribution of deuterated hydroxides in the nanometer-thick surface oxide film. After immersion at free potential or anodic passivation in acidified D2O, the initial bilayer structure is retained. The use of heavy water electrolyte has no effect on the composition alterations induced by passivation. Deuterated species were detected mostly in the outer layer of the surface oxide film. Pure inward hydroxyl diffusion from electrolyte/oxide to oxide/metal interface is excluded from being primarily responsible for oxide film growth induced by anodic passivation. The hydroxyls from the dissolving hydroxide species are retained in the oxide film and participate in forming Cr hydroxide, thus reducing the hydroxyl surface uptake from the electrolyte. This work provides deeper insight into the mechanisms of oxide growth and corrosion protection induced by anodic passivation.

Study of acid-resistant behavior of hydroxylated hexagonal boron nitride/isobutyltriethoxysilane composite coatings on sulfoaluminate concrete surfaces

Concrete, as the most common building material, is susceptible to erosion in acidic environments, leading to issues such as surface cracking and aggregate exposure. This study employs iso-butyltrimethoxysilane (IBTS) as the coating matrix and incorporates h-BN as a filler material to prepare h-BN/IBTS hybrid latex for addressing the problem of acid corrosion in concrete. By characterizing the binding state between h-BN and IBTS, tracking changes in mortar specimen composition during the corrosion process, this study analyzes the acid corrosion protection mechanism provided by h-BN/IBTS hybrid latex on the surface of mortar specimens. The experimental results demonstrate that hydroxylation-modified h-BN can effectively disperse within IBTS, thus alleviating the agglomeration phenomenon caused by silane volatilization. This enhancement improves the film quality of silane and increases coating tightness. The h-BN/IBTS hybrid latex significantly reduces the corrosion rate of cement mortar specimens in a sulfuric acid environment. This reduction is attributed to the introduction of h-BN, which substantially prolongs the erosion pathway for H+ and SO42- in sulfuric acid, reduces the formation of gypsum within the concrete's internal structure, and effectively preserves the microscale pore structure within the concrete.

Improving the corrosion protection of plasma electrolysis-treated light metal by polymeric functionalization

Suppressing the rate of corrosive degradation has been the primary challenge in the widespread use of lightweight metals across a variety of potential applications because their native passive layer is still susceptible to chemical attacks in aqueous or humid environments. This work explores the roles of polyaniline in tandem with a TiO2 layer in improving the corrosion properties of pure Ti. The anodic TiO2 surface is a result of a plasma electrolysis treatment in a non-acidic, phosphate-based electrolyte. The emeraldine base form of the polymer is subsequently applied to modify the surface properties of the plasma-electrolyzed Ti samples to further protect the surface against polar species that might interact with TiO2. The deposition of the thin layer of polyaniline retains the original surface microstructure of the plasma electrolysis layer. Nevertheless, the presence of polyaniline successfully reduces the corrosion current density and passive current density of plasma-electrolyzed Ti by ~50%. The corrosion protection mechanism is explained in the context of equivalent circuit models based on impedance measurements.

Bio-inspired Ti3C2Tx MXene composite coating for enhancing corrosion resistance of aluminum alloy in acidic environments

Aluminum alloy (Al alloy) suffers from severe corrosion in acidic solution. Two-dimensional (2D) MXene-based composite coatings show great prospects for corrosion protection on metals used in special conditions. The composite coatings still face challenges in complex functionalization and orientation control. In harsh conditions, the long-term ability and roles of MXene in corrosion protection are still not clear. Here, a bio-inspired myristic-calcium chloride-Ti3C2Tx MXene (MA + CaCl2 + MXene) composite coating is successfully prepared on aluminum alloy (Al alloy) by electrodeposition process. Electrochemical tests, surface morphology, and chemical composition are analyzed to investigate the corrosion resistance and protection mechanism of the MXene coating in acidic solution (0.5 M H2SO4 + 2 ppm HF). As a result, the incorporation of MXene can significantly reduce corrosion current density (7.498 × 10-8 A/cm2) by ∼ 5 orders of magnitude and impedance modulus at 0.01 Hz (|Z|0.01 Hz) value of the composite coating is 196.8 Ω·cm2, which is over 4 times higher than that of bare Al alloy (40.74 Ω·cm2) after immersion test for 72 h. Furthermore, the in-situ corrosion test confirms the enhanced corrosion resistance of the MA + CaCl2 + MXene composite coating. The MXene can increase coating thickness to 23.6 ± 0.4 μm, reduce porosity to (5.845 ± 1) × 10-5, decrease the diffusion coefficients of H+ to (1.587 ± 0.3) × 10-9 cm2/s, and enhance the adhesion of the coating to the substrate (the delamination time exceeds 5 h), thus providing improved anti-corrosion ability. This strategy opens up new prospects for construction of 2D MXene-based anti-corrosion coatings.

Corrosion protection and failure mechanism of ZrO2 coating on zirconium alloy Zry-4 under varied LiOH concentrations in lithiated water at 360 °C/18.5 MPa

Maintaining a good corrosion resistance in primary coolant loop during normal operations is a prerequisite for ZrO2 as a protective coating on zirconium alloy cladding. Research on corrosion performance of ZrO2 coating in nuclear water chemistry is relatively deficient, and existing reports failed to provide an in-depth explanation for the failure causes of ZrO2 coating. Here, we proposed a detailed corrosion process of ZrO2 coating in lithiated water at 360 °C and 18.5 MPa based on experimental study and molecular dynamics simulation. The protective effect and failure mechanism of ZrO2 coating on Zry-4 under varied LiOH concentrations was further revealed. ZrO2 coating provided a favorable corrosion protection with the occurrence of localized corrosion at low LiOH concentrations. Factors influencing the corrosion resistance include pitting corrosion extension, enhanced Li+ permeation, short-circuit diffusion of O2– and ZrO2 phase transformation. In highly-concentrated LiOH solutions, intergranular corrosion, internal oxidation and perforation result in coating failure. Zr ions were released to the coating surface to form flocculent ZrO2 and ZrO2 clusters due to the strong diffusion and dissolution tendency of α-Zr in the Zry-4 substrate. This work can give some references to understand the service behavior of nuclear coatings under variable water chemistry conditions and promoting in-pile application of ZrO2 coating.

Zinc-rich polyester powder coatings with iron Phosphide: Lower zinc content and higher corrosion resistance

Many conductive fillers such as carbon black, carbon nanotube and graphene, have been developed to reduce zinc content for zinc-rich coatings, but very few of them could reduce zinc content by 10 % while maintaining the original corrosion protection ability. The carbon-based conductive additives have the issue of corrosion promotion after cathodic protection. In this study, low-cost iron based conductive additive, iron phosphide was used to reduce zinc content in environmentally friendly zinc-rich polyester powder coatings. We investigated the anti-corrosive performance of the prepared coatings by open circuit potential, electrochemical impedance spectroscopy measurements and neutral salt spray tests. The corrosion products were analyzed with Raman spectroscopy, X-ray diffraction and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. It was found that iron phosphide, due to its conductive nature, inert chemistry, activation function and barrier effect of the lamellar shape, can establish cathodic protection at a low zinc content of 45 wt% with an active protection period of 20 days. It can replace 10 wt% of zinc in 75 wt% zinc-rich polyester powder coatings while maintaining the original cathodic protection ability, as long as 86 days for a 40 μm film. In addition, iron phosphide can significantly inhibit localized corrosion and decrease corrosion creepage by about 20 % during 2500 h salt spray tests. Moreover, a possible corrosion protection mechanism for iron phosphide in zinc-rich polyester coatings was proposed.

A comparative study of novel synthesized sulfamide compounds: Electrochemical, morphological, XPS, and theoretical investigations on copper corrosion inhibition in 1.0 M HCl

This study investigates the corrosion inhibition performance of N-phenyl sulfamide (NPS) and N-phenyl piperazine sulfamide (NPPS) for copper in a solution of 1.0 M hydrochloric acid (HCl) through a comprehensive combination of experimental and theoretical approaches. Electrochemical methods (polarization measurements and electrochemical impedance spectroscopy (EIS)), characterization techniques (FTIR, ATR, SEM and XPS investigations), and theoretical calculations are employed to analyze the inhibitive properties and provide insights on how the inhibitors and copper surface interact. Results from polarization and EIS analyses reveal that NPS and NPPS, both at a concentration of 400 mg/L, deliver substantial corrosion inhibition, achieving rates of 92.33 % and 98.70 % for polarization, and 93.60 % and 96.51 % for EIS, respectively, which gives NPPS an advantage over the other inhibitor with high inhibitor efficiency. SEM and XPS investigations confirm the adsorption of these inhibitors to the copper surface, resulting in a notably smoother and more uniform appearance with minimal damage, especially for NPPS. Theoretical calculations employing the DFT-B3LYP method provide valuable insights into the molecular properties of NPS and NPPS. These simulations support the outcomes of the tests and give insight into how NPPS inhibitor act as stronger inhibitor compared with NPS inhibitor. Overall, this study enhances our understanding of corrosion protection mechanisms and offers crucial information in order to establish robust copper corrosion inhibitors for acidic conditions. The combination of theoretical and experimental approaches offers a thorough framework for investigating corrosion inhibition and opens the door for the creation of sophisticated and effective inhibitors to protect copper from corrosive attacks.