Effects of deformation processes on morphology,microstructure and corrosion resistance of LDHs films on magnesium alloy AZ31

Highly oriented Mg-Al layered double hydroxide(LDHs)films were deposited on magnesium alloy AZ31 with different deformation processes by an easy in-situ growth method.The characteristics of the films were investigated by optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM),and electrochemical,immersion and hydrogen evolution tests.The corrosion protection performance ranked the LDHs films as the increasing series:CS-LDHs(as-cast sample with LDHs)<AE-LDHs(asymmetric extrusion sample with LDHs)<SE-LDHs(symmetric extrusion sample with LDHs)<RS-LDHs(rolled sample with LDHs).A thicker and more compact LDH conversion coating was formed on the RS sample,and had the best corrosion protection performance.

Self-repairing functionality and corrosion resistance of in-situ Mg-Al LDH film on Al-alloyed AZ31 surface

A novel Mg-Al LDH film was in-situ prepared hydrothermally in an alkaline aqueous solution on an Al-alloyed AZ31 substrate.The structural,chemical and functional characteristics of the film were explored by means of scanning electron microscope(SEM),X-ray diffraction(XRD),energy dispersive spectrometer(EDS),polarization curve,AC impedance and salt immersion tests,respectively.The anti-corrosion results indicated that the Mg-Al LDH film on the Al-alloyed AZ31 surface could effectively protect the AZ31 from corrosion attack even after 90 days of immersion in 3.5 wt.%NaCl solution.The protection performance is surprisingly better than most of the reported coatings on Mg alloys.More interestingly,when the Mg-Al LDH film was scratched,the exposed Al-alloyed surface might gradually release metal ions and re-generate dense LDH nano-sheets in the corrosive environment to inhibit the further corrosion there,exhibiting a self-repairing behavior.The combination of the benign long-term protection and desirable self-repairing performance in this new process of surface-alloying and LDH-formation may significantly extend the practical application of magnesium alloys.

Active corrosion protection of super-hydrophobic corrosion inhibitor intercalated Mg-Al layered double hydroxide coating on AZ31 magnesium alloy

Magnesium alloys,the advanced lightweight structural materials,have been successfully applied in the manufacturing field.Unfortunately,their poor corrosion resistance restrains the potential wide applications.In this work,anti-corrosion coatings were fabricated via the insitu growth of the corrosion inhibitors intercalated magnesium-aluminum layered double hydroxide(Mg-Al LDH)on AZ31 magnesium alloy and then post-sealing it by a super-hydrophobic coating.SEM,XRD,EDS,FTIR,XPS and contact angle test were conducted to analyze physical/chemical features of these coatings.Potentiodynamic polarization curves and electrochemical impedance spectroscopy were recorded to assess the anti-corrosion performance of prepared coatings.Surprisingly,Mg-Al LDH with molybdate intercalation and lauric acid modification achieves the excellent corrosion inhibition performance(99.99%)due to the multicomponent synergistic effect such as the physical protection of Mg-Al LDH,the corrosion inhibition of molybdate and super-hydrophobic properties of lauric acid.This work presents a scientific perspective and novel design philosophy to fabricate the efficient anti-corrosion coating to protect magnesium alloys and then expand their potential applications in other field.

Morphology,structure and corrosion resistance of Mg-Al LDH films fabricated in different Al^(3+)concentration solutions

In situ-grown Mg-Al layered double hydroxide(LDH)films were obtained on an anodized AZ31 substrate,with the immersion of sample in different concentrations of Al^(3+)solution.The structure,composition and morphology of LDH films were investigated by X-ray diffraction(XRD),Fourier transform infrared(FTIR)and scanning electronic microscopy(SEM),and the corrosion behavior of LDH films was further studied by electrochemical impedance spectroscopy(EIS).The influence of Al^(3+)concentration on the growth behavior of LDH was also discussed.The results indicated that the nest-like structure of MgAl-LDH film was composed of interconnected MgAl-LDH nanosheets.Besides,the LDH obtained in0.032 mol·L^(-1)Al^(3+)solution,possessing dense laminated structure,could effectively seal the porous surface of anodic oxide film.EIS results revealed that the samples coated with LDH films showed a higher electrochemical impedance,and thus,the corrosion resistance of samples coated with LDH films was signally improved compared with the anodized alloy.

Doublely-doped Mg-Al-Ce-V_(2)O_(7)^(4-)LDH composite film on magnesium alloy AZ31 for anticorrosion

A doublely-doped layered double hydroxide(LDH)film was produced on an anodized magnesium alloy AZ31.The Ce-doped Mg-Al LDH film was prepared by in-situ hydrothermal treatment method,and the intercalation of vanadate was realized by ion-exchange reaction.The structure,morphology and composition of as-prepared LDH film were investigated by X-ray diffractometer,field-emission scanning electronic microscope and energy dispersive spectrometry.Results indicated that a uniform and compact LDH film was formed and the intercalation of Ce^(3+)and vanadate would change the crystal structure of LDHs.The results of the potentiodynamic polarization,electrochemical impedance spectra,hydrogen evolution and corrosion weight loss tests showed the Ce^(3+)and vanadate anions significantly improve the impedance of LDH film,and the active double-doped LDH film could effectively protect the magnesium substrate from corrosion.

Enhanced electrochemical and photocatalytic performance achieved through dual incorporation of SnO_(2)and WO_(3)nanoparticles into LDH layer fabricated on PEO-coated AZ31 Mg alloy

This study explores the potential of LDH flakes decorated with metallic oxide nanoparticles to function as both anti-corrosion barriers against chloride anions and heterogeneous photocatalysts for tetracycline degradation under visible light.The process involves modifying the primarily MgO-based inorganic porous film by growing a MgFe LDH film,followed by the individual and dual incorporation of SnO_(2)and WO_(3)nanoparticles.The dual incorporation of these nanoparticles into the LDH matrix leads to synergistic interactions,effectively sealing pre-existing defects within LDH flakes and facilitating the in-situ formation of catalytic sites through oxidation and the induction of surface oxygen vacancy defects,which synergistically contribute to the enhancement of both electrochemical and photocatalytic activities.The enhanced electrochemical stability is reflected in a significant reduction in corrosion current density by 4 orders of magnitude compared to unmodified porous film.Additionally,the decorated film demonstrates sustained photocatalytic functionality,achieving significant degradation(95.5%)of tetracycline within two hours.This study presents a novel approach,highlighting the dual effectiveness of LDHs decorated by dual metal oxides as an anti-corrosive agent and photocatalyst,with promising implications for environmental remediation and wastewater purification.

基于可牺牲中间层制备大规模、可控双金属氢氧化物膜的协同策略

层状双金属氢氧化物(LDHs)作为一种类水滑石薄膜,以其优异的特性在许多领域中具有广泛的应用.然而,现有的LDH膜制备路线具有大规模生长受限和不可控等问题.本文中,我们受一种草本植物“落地生根”(Bryophyllum Pinnatum)具有肆意生长特性的启发,首次引入可牺牲的共溅射锌-铝中间层作为“植物种子”,通过“局部溶解”和“溶液渗透”的结构转化机制在任意形状、大小及材质的基底材料上实现大规模、厚度可控的LDH膜制备.通过调控中间膜的成分、结构和表面形貌,设计具有不同特性的LDH转化膜.实验结果表明,所制备的LDH膜具有较大的厚度和多级微观结构的特性,在严苛的磨损条件下仍能实现良好的机械稳定性.另外,我们设计了一系列基于锌-铝单金属中间层的电偶模拟实验对LDH膜的化学转化机理进行了深入探究,解决了传统复杂水热过程中实时监测困难的问题.本工作不仅开发了一种制备具有多尺度特性的LDH转化膜的新策略,同时揭示了复杂的LDH原位转化机理,为拓宽LDH材料在先进智能材料上的实际应用提供了新的发展思路.