Greatly enhanced corrosion/wear resistances of epoxy coating for Mg alloy through a synergistic effect between functionalized graphene and insulated blocking layer

The poor corrosion and wear resistances of Mg alloys seriously limit their potential applications in various industries.The conventional epoxy coating easily forms many intrinsic defects during the solidification process,which cannot provide sufficient protection.In the current study,we design a double-layer epoxy composite coating on Mg alloy with enhanced anti-corrosion/wear properties,via the spin-assisted assembly technique.The outer layer is functionalized graphene(FG)in waterborne epoxy resin(WEP)and the inner layer is Ce-based conversion(Ce)film.The FG sheets can be homogeneously dispersed within the epoxy matrix to fill the intrinsic defects and improve the barrier capability.The Ce film connects the outer layer with the substrate,showing the transition effect.The corrosion rate of Ce/WEP/FG composite coating is 2131 times lower than that of bare Mg alloy,and the wear rate is decreased by~90%.The improved corrosion resistance is attributed to the labyrinth effect(hindering the penetration of corrosive medium)and the obstruction of galvanic coupling behavior.The synergistic effect derived from the FG sheet and blocking layer exhibits great potential in realizing the improvement of multi-functional integration,which will open up a new avenue for the development of novel composite protection coatings of Mg alloys.

Understanding on corrosion mechanism of oxidized AZW800 alloy in 3.5 wt%NaCl solution

Magnesium alloys are more widely used at higher temperatures.However,it is not well known whether oxide layer,produced at high temperature,could show corrosion protection.Thus,the corrosion behaviors of oxidized AZW800 alloy were investigated by hydrogen evolution and electrochemical measurements to evaluate effect of oxide layer on corrosion resistance.The results showed that corrosion of removed oxide layer AZW800 alloy showed characteristic of localized corrosion,leaving randomly bulky pits.While reserved oxide layer AZW800 alloy exhibited a relatively uniform corrosion.The results indicated that oxide layer could hinder corrosion of oxidized AZW800 alloy in the initial period of immersion.While subsequently,aggravated corrosion would occur owing to defects of oxide layer and less protective products film.Besides,present of oxide layer eliminated micro-galvanic couple on alloy surface.The synergistic effect of elimination of micro-galvanic couple on alloy surface and alkalization effect transforms localized corrosion into relatively uniform corrosion of alloys.

部分浸泡再生混凝土Mg^(2+)-SO_(4)^(2-)-Cl^(-)复合盐侵蚀耐久性损伤特征与机制

为系统研究与揭示西北地区部分掩埋再生混凝土(RAC)结构耐久性损伤特征与机制,以浓度为20%的复合盐溶液为侵蚀介质,开展了14种掺辅助胶凝材料RAC部分浸泡于复合盐溶液的耐久性试验,综合分析RAC动弹性模量、宏观与微观形貌、侵蚀产物物相组成与相对含量的经时变化规律。部分浸泡RAC沿纵向高度分为饱和区、气-液两相界面区、水分传输区及干燥区。侵蚀初期气-液两相界面区损伤程度高于饱和区;侵蚀中后期饱和区的损伤持平或超过气-液两相界面区,水分传输区损伤初现。饱和区侵蚀状态由初期的化学侵蚀转变为中后期的化学-物理双重侵蚀,气-液两相界面区在侵蚀期间均呈现出化学-物理双重侵蚀。化学侵蚀产物为水镁石、硬石膏/石膏、钙矾石、Friedel盐及碱式氯化镁;物理结晶盐包含氯镁石、白钠镁矾、氯化钠、水合硫酸镁、Na_(2)SO_(4)及芒硝,各侵蚀产物与结晶盐的相对含量均随浸泡时间延长而改变。侵蚀后期,Na_(2)SO_(4)和芒硝相互转化使RAC物理力学性能急速退化。粉煤灰-矿渣复掺RAC抗侵蚀性能整体较好,粉煤灰-硅灰复掺最差,后者在浸泡时间180 d时抗压强度损失率高于60%。矿渣-硅灰-偏高岭土三掺RAC耐久性显著高于粉煤灰-矿渣-偏高岭土三掺,后者在侵蚀180 d时已经溃散。四掺辅助胶凝材料RAC性能衰减速度均匀,但抗侵蚀性能仍处于较低水平,相同浸泡时间下,其耐久性指标均与粉煤灰-矿渣复掺RAC差距较大。

Characteristics of Corrosion Product Layer Formed on Weathering Steel Exposed to the Tropical Climate of Vietnam

The weathering steel (Corten B) was exposed to out-door atmosphere of Hanoi (urban site) and Donghoi (marine site). The results showed the protective ability of corrosion product layer formed on weathering steel in the initial stage. The SEM-EDX analysis detected the presence of chromium and copper in the inner layers of corrosion product formed on weathering steel. These elements improved corrosion resistance of corrosion product layers. In addition, the dense α-FeOOH phase were appeared early in corrosion product which is detected by X-ray diffraction and Micro Raman investigations. The results of polarization and EIS measurements also demonstrated the protectiveness of the corrosion product of weathering steel.

不同Cl^(-)浓度下SRB对抗微生物腐蚀管材性能的影响

针对油田复杂环境下管材发生腐蚀失效问题,采用SEM、EDS及XRD对试样在不同Cl^(-)浓度下(0 g/L、20 g/L、40 g/L、80 g/L和120 g/L)腐蚀后的表面形貌、腐蚀产物的成分及物相组成进行分析,通过电化学测试,研究了不同Cl^(-)浓度下SRB对抗微生物腐蚀管材性能的影响。结果发现,Cl^(-)浓度为20 g/L时最适宜SRB生长,但此时SRB对抗微生物腐蚀管材的腐蚀性最小,此后随着Cl^(-)浓度升高,生物膜减少,腐蚀速率增大;当Cl^(-)浓度分别为0 g/L、20 g/L时,在腐蚀产物中检测出FeS和Fe_(3)(PO_(4))_(2),且腐蚀均受阴极反应控制。因此,在不同Cl^(-)浓度下,SRB对抗微生物腐蚀管材性能的影响与试样表面形成的生物膜有关,随着Cl^(-)浓度的增加,SRB对抗微生物腐蚀管材腐蚀作用减小。

车轮钢ER8在中性NaCl溶液中的电化学腐蚀行为

为研究ER8车轮钢在沿海中性氯盐环境下的腐蚀行为,通过电化学测试、腐蚀失重试验,结合扫描电镜(SEM)、X射线衍射(XRD)技术对ER8车轮钢在3种不同浓度中性NaCl溶液中的电化学腐蚀行为进行分析。极化曲线结果表明浸泡初期5.0%NaCl浓度下自腐蚀电流密度(Jcorr)最大,576 h后Jcorr在2.0%、3.5%NaCl浓度下均持续增大,腐蚀速率在2160 h时均大于0.12 mm/a。SEM结果显示腐蚀产物形貌主要为片状与团簇状结构,初期腐蚀产物形貌具有较多孔隙,难以阻碍Cl-与基体发生反应,2160 h时腐蚀产物结构更为均匀致密。XRD结果表明腐蚀产物主要由γ-FeOOH、α-FeOOH与Fe3O4组成。

高温高压下P110H套管钢的Cl^(-)腐蚀行为研究

套管的服役环境日益复杂,关于热采井套管在高温高压Cl^(-)溶液中的腐蚀行为需要进一步探索。为此,使用高温高压真空反应釜进行腐蚀模拟实验,并通过腐蚀失重法、扫描电镜、X射线衍射等分析技术,对P110H钢在高温高压Cl^(-)溶液中的腐蚀行为进行了研究。结果表明:高温高压Cl^(-)环境下,P110钢的腐蚀主要为均匀腐蚀,5 MPa时,腐蚀速率随着温度升高先降低后增高,在10 MPa时,腐蚀速率在250℃达到最高;在相同温度时,随着压力的增大,P110H钢在Cl^(-)溶液中的腐蚀越严重。

The effect of Laves phases and nano-precipitates on the electrochemical corrosion resistance of Mg-Al-Ca alloys under alkaline conditions

The electrochemical corrosion mechanisms of Mg alloys were extensively studied in previous investigations of different chemical com-positions,modified surface states and various electrolyte conditions.However,recent research focused on the active state of Mg dissolution,leading to unresolved effects of secondary phases adjacent to a stableα-solid solution passive layer.The present study investigates the fundamental electrochemical corrosion mechanisms of three different Laves phases with varying phase morphologies and phase fractions in the passive state of Mg-Al-Ca alloys.The microstructure was characterized by(transmission-)electron microscopy and synchrotron-based transmission X-ray microscopy.The electrochemical corrosion resistance was determined with a standard three-electrode setup and advanced in-situ flow cell measurements.A new electrochemical activity sequence(C15>C36>α-Mg>C14)was obtained,as a result of a stable passive layer formation on theα-solid solution.Furthermore,nm-scale Mg-rich precipitates were identified within the Laves phases,which tend to inhibit the corrosion kinetics.

Utilizing a defective MgO layer for engineering multifunctional Co-MOF hybrid materials with tailored leaf-like and polyhedral structures for optimal electrochemical and photocatalytic activities

The hybridization of metal-organic framework(MOF)with inorganic layers would lead to the discovery of novel hybrid materials that can provide a compelling strategy for enhancing its photocatalytic and electrochemical response.In the present study,a highly efficient multifunctional hybrid material was developed by exploiting the defective layer formed on AZ31 Mg alloy through plasma electrolytic oxidation(PEO)as a nucleation and growth site for Co-MOF.The concentrations of the organic linker 2-Methylimidazole(2,MIm)and cobalt nitrate as a source of Co^(2+) ions were varied to control the growth of the obtained Co-MOF.Lower concentrations of the 2,MIm ligand favored the formation of leaf-like MOF structures through an anisotropic,two-dimensional growth,while higher concentrations led to rapid,isotropic nucleation and the creation of polyhedral Co-MOF structures.The sample characterized by polyhedral Co-MOF structures exhibited superior electrochemical stability,with the lowest corrosion current density(3.11×10^(-9) A/cm^(2))and the highest top layer resistance(2.34×10^(6)Ωcm^(2)),and demonstrated outstanding photocatalytic efficiency,achieving a remarkable 99.98%degradation of methylene blue,an organic pollutant,in model wastewater.To assess the active adsorption sites of the Co-MOF,density functional theory(DFT)was utilized.This study explores the changes in morphologies of the coatings of Co-MOF with the change of solution concentration to form coatings with enhanced properties on the metallic substrate,which could establish the groundwork for the development of next-generation multifunctional frameworks with diverse applications.

Enhancing the anti-corrosion performance and biocompatibility of AZ91D Mg alloy by applying roughness pretreatment and coating with in-situ Mg(OH)_(2)/Mg-Al LDH

Corrosion-resistant and biocompatible films were fabricated on AZ91D Mg alloy substrates by varying their roughness levels using met-allographic preparation and subsequent hydrothermal procedures.The coated films comprised a mixed structure of Mg(OH)_(2)and Mg-Al layered double hydroxides(LDH)and exhibited excellent compactness.Coating film thickness increased with decreasing surface roughness.Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy.Metallographic pretreat-ment influenced the chemical activity of the Mg alloy surface and helped modulate the dissolution rate of the Mg_(17)Al_(12)phase during the hydrothermal procedure.With decreasing roughness of the Mg substrate,the Al^(3+)concentration gradually increased,accelerating the in-situ formation of the Mg(OH)_(2)/LDH composite coating and improving its crystallinity.A thick and dense Mg(OH)_(2)/LDH coating was synthesized on the Mg substrate with the least roughness,substantially improving the corrosion resistance of the AZ91D alloy.The lowest corrosion current density((5.73±2.75)×10^(−8)A·cm^(−2))was achieved,which was approximately three orders of magnitude less than that of bare AZ91D.Moreover,the coating demonstrated biocompatibility with no evident cytotoxicity,cellular damage,and hemolytic phenomena.This study provides an effective method for preparing coatings on Mg alloy surfaces with excellent corrosion resistance and biocompatibility.

Revisiting aluminum current collector in lithium-ion batteries:Corrosion and countermeasures

With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.

Effective multifunctional coatings with polyvinylpyrrolidone-enhanced ZIF-67 and zinc iron layered double hydroxide on microarc oxidation treated AZ31 magnesium alloy

Modulating metal-organic framework’s(MOF)crystallinity and size using a polymer,in conjunction with a high surface area of layered double hydroxide,yields an effective strategy for concurrently enhancing the electrochemical and photocatalytic performance.In this study,we present the development of an optimized nanocomposite,denoted as 0.5PVP/ZIF-67,developed on AZ31 magnesium alloy,serving as an efficient and durable multifunctional coating.This novel strategy aims to enhance the overall performance of the porous coating through the integration of microarc oxidation(MAO),ZnFe LDH backbone,and ZIF-67 formation facilitated by the addition of polyvinylpyrrolidone(PVP),resulting in a three-dimensional,highly efficient,and multifunctional material.The incorporation of 0.5 g of PVP proved to be effective in the size modulation of ZIF-67,which formed a corrosion-resistant top layer,improving the total polarization resistance(R_(p)=8.20×10^(8)).The dual functionality exhibited by this hybrid architecture positions it as a promising candidate for mitigating environmental pollution,degrading 97.93%of Rhodamine B dye in 45 min.Moreover,the sample displayed exceptional degradation efficiency(96.17%)after 5 cycles.This study illuminates the potential of nanocomposites as electrochemically stable and photocatalytically active materials,laying the foundation for the advancements of next-generation multifunctional frameworks.

Stress corrosion cracking behavior of buried oil and gas pipeline steel under the coexistence of magnetic field and sulfate-reducing bacteria

Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil environment. The SCC behavior of X80 pipeline steel under the magnetic field and sulfate-reducing bacteria(SRB) environment was investigated by immersion tests, electrochemical tests, and slow strain rate tensile(SSRT) tests. The results showed that the corrosion and SCC sensitivity of X80 steel decreased with increasing the magnetic field strength in the sterile environment. The SCC sensitivity was higher in the biotic environment inoculated with SRB, but it also decreased with increasing magnetic field strength, which was due to the magnetic field reduces microbial activity and promotes the formation of dense film layer. This work provided theoretical guidance on the prevention of SCC in pipeline steel under magnetic field and SRB coexistence.

Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

316L不锈钢在不同浓度Cl^(-)和CO_(2)条件下的腐蚀行为

为了探明在辽河油田采出水环境中Cl^(-)和CO_(2)对316L不锈钢腐蚀行为的影响,通过浸泡实验、交流阻抗(EIS)和极化曲线技术分别研究了不同Cl^(-)浓度和CO_(2)分压对316L不锈钢的影响,其中Cl^(-)浓度梯度为0,0.0300,0.0515,0.0700 mol/L,CO_(2)分压为0.2,0.4,0.6 MPa,并结合X射线衍射技术(XRD)对腐蚀产物进行了分析。结果表明:Cl^(-)浓度的增大使容抗弧直径减小,弥散指数降低,腐蚀情况加剧;容抗弧的直径随着CO_(2)分压的增大先变小后变大,弥散指数先降低后升高,腐蚀情况先加剧后减缓。这是由于Cl^(-)会破坏316L表面的钝化膜,而CO_(2)会与基体反应生成FeCO_(3),随着CO_(2)分压升高,FeCO_(3)保护膜愈加致密。

完全浸泡再生混凝土Mg^(2+)-SO_(4)^(2-)-Cl^(-)侵蚀耐久性损伤规律与机理

我国西北地区的土壤与地下水中含有高浓度Mg^(2+)、SO_(4)^(2-)、Cl^(-),这些离子导致长期掩埋于地下的再生混凝土(RAC)结构耐久性严重退化。为了揭示Mg^(2+)-SO_(4)^(2-)-Cl^(-)侵蚀RAC耐久性损伤规律与机理,采用长期浸泡的方式,系统开展复掺辅助胶凝材料RAC耐久性试验,研究复掺辅助胶凝材料方式与取代率对RAC耐久性退化规律的影响。采用X射线衍射、红外光谱及热重等分析手段,表征RAC侵蚀产物物相组成与相对含量,揭示复合盐侵蚀RAC耐久性损伤机理。结果表明,10%粉煤灰(质量分数)+20%(质量分数)矿渣复掺RAC耐久性较高,硅灰或偏高岭土取代率高于10%时RAC的耐久性较差。侵蚀离子与RAC水化产物产生化学反应并形成晶粒极大的侵蚀产物,加速C-S-H分解向M-S-H转变;高浓度离子间相互作用形成物理盐结晶,促进裂缝的萌生扩展。化学/物理双重作用破坏RAC微观结构,加速离子扩散传输,形成化学侵蚀-结构损伤-离子传输过程。RAC界面过渡区及砂浆中遍布裂缝与孔隙,再生混凝土物理力学性能急速退化。

Effects of reflowing temperature and time on alloy layer of tinplate and its electrochemical behavior in 3.5%NaCl solution

Effects of reflowing temperature and time on the alloy layer of tinplate and its electrochemical behavior in 3.5%NaCl solution were investigated by electrochemical measurements and surface characterization.It is found that the amount of alloy layer increases with the increase of reflowing temperature and time.Then the corrosion potential of detinned tinplate shifts positively and the corrosion rate decreases.After being coupled with tin,the detinned tinplate acts as cathode and tin acts as anode initially.However,after being exposed for some time,the potential shifts of both detinned tinplate and tin reverse the polarity of the coupling system.The galvanic current density decreases with the increase of reflowing temperature and time.

In-situ investigation of atmospheric corrosion behavior of bronze under thin electrolyte layers using electrochemical technique

The atmospheric corrosion behavior of bronze under thin electrolyte layer （TEL） with different thicknesses was monitored using cathodic polarization curves, open circuit potential （OCP） and electrochemical impedance spectroscopy （EIS）. Cathodic polarization result indicates that the cathodic limiting current density increases with decreasing the TEL thickness. EIS result shows that the corrosion rate increases with decreasing the TEL thickness at the initial stage because the corrosion is dominated by the cathodic process, whereas after long immersion time, the corrosion degree with the TEL thickness is in the sequence of 150 μm 〉 310 μm〉 10μm ≈ bulk solution 〉 57 μm. The measurements of OCP and EIS present in-situ electrochemical corrosion information and their results are in good agreement with that of physical characterizations.

EIS Study on Pitting Corrosion of AA5083-H321 Aluminum-Magnesium Alloy in Stagnant 3.5% NaCl Solution

In this research, EIS （electrochemical impedance spectroscopy） technique was utilized to study the pitting corrosion behaviour of AA5083-H321 aluminum-magnesium alloy in 3.5% NaCl solution. Impedance spectra were obtained during 240 h of exposure of the sample to the test solution. The surface and cross-section of the samples were studied by scanning electron microscopy （SEM） and EDAX （energy dispersive analysis of X-ray） analysis. The results indicated that as the resistance of the passive layer on intermetallic particles is very small, this parameter on the sample surface layers is controlled by that of pure passive layer. However, the capacitors in the proposed equivalent circuit are replaced with the constant phase elements （CPE）, due to non-uniformity and occurrence of pitting corrosion on the surface. The outward diffusion of Al^＋3 ions through the passive layer and the thickening of this layer cause the impedance decrease in the first 24 h and increase afterwards. The detachment of intermetallic particles from some of pits and the accumulation of the corrosion products inside some others are factors that prevents the continuation of cathodic reactions on the top of the intermetallic particles.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg-Al layered double hydroxide coating

To further enhance the corrosion resistance of the porous micro-arc oxidation(MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg-Al layered double hydroxide(LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.