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Magnesium (Mg) and its alloys biodegrade safely in human body for implant applications. The major bottleneck inhibiting their clinical utilizations is the high corrosion rate. Modification with anticorrosive and bioactive coatings is an ideal strategy to break the bottleneck. In this study, a multifunctional coating constructed by Zr‐based metal–organic framework UiO‐66‐NH2 (UiO) and ammonium trifluorotitanate NH4TiOF3 (NTiF) bilayers (UiO/NTiF) is fabricated onto Mg matrix through facile solvothermal method. The inner NTiF layer can be designed to the adjustable crystal structure with different anticorrosion effects, realizing the controllable corrosion of Mg matrix. The outer UiO layer is capable to further boost the corrosion protection; meanwhile it endows the drug delivery property owing to the intramolecular porosity and functional groups of MOFs. The UiO/NTiF coating appears highly effective in controlling the corrosion and retaining the mechanical integrity of Mg matrix as well as maintaining high bonding integrity. The cytocompatibility assays demonstrate the enhanced cell adhesion, spreading and proliferation on UiO/NTiF coating. The loading/releasing behavior of ibuprofen molecule and density functional theory calculations are performed to investigate the drug delivery of UiO/NTiF coating. This study would shed valuable breakthroughs for design of functional coatings for biodegradable metals and promote extensive applications of MOFs in biomaterials. [ABSTRACT FROM AUTHOR]

A loop system was used to investigate flow-assisted corrosion (FAC) of AZ91D magnesium alloy at an elbow based on array electrode technology by potentiodynamic polarization, computational fluid dynamics, simulation and surface analysis. The experimental results demonstrate the fluid hydrodynamics plays a significant role in the FAC of AZ91D magnesium alloy. The corrosion rate increases from the outer wall to the inner wall of the elbow, with the higher corrosion rate corresponding to the higher flow velocity and larger shear stress at the elbow. The maximum corrosion rate appears at the innermost wall of the elbow, the location with the maximum flow velocity and shear stress. [ABSTRACT FROM AUTHOR]

In this work, the effects of the microstructure and phase constitution of cast magnesium alloy ZK60 (Mg-5.8Zn-0.57Zr, element concentration in wt.%) on the corrosion behavior in aqueous NaCl (0.1 mol dm−3) were investigated by weight-loss measurements, hydrogen evolution tests, and electrochemical techniques. The alloy was found to be composed of α-Mg matrix, with large second-phase particles of MgZn2 deposited along grain boundaries and a Zr-rich region in the central area of the grains. The large second-phase particles and the Zr-rich regions were more stable than the Mg matrix, resulting in a strong micro-galvanic effect. A filiform corrosion was found. It originated from the second-phase particles in the grain boundary regions in the early corrosion period. The filaments gradually occupied most areas of the alloy surface, and the general corrosion rate decreased significantly. Corrosion pits were developed under filaments. The pit growth rate decreased over time; however, it was about eight times larger than the general corrosion rate. A schematic model is presented to illustrate the corrosion mechanism. [ABSTRACT FROM AUTHOR]

Ag NPs are incorporated in the surface layer of salicylic (SA) and tartaric (TA) ions co-doped PPy to form compact and stable Ag NPs-PPy(TA+SA)/Zn bilayer coating on ZK60 magnesium alloy, which completely isolates corrosive media before its breakage. Ag NPs form micro-galvanic cells with polarons PPyn+ and block PPy ion channels to inhibit PPy degradation rate, significantly enhancing the coating's protection time in Hank's solution. [Display omitted] • Ag NPs-(salicylic + tartaric) co-doped PPy/Zn bilayer coating is prepared on ZK60. • Ag species (Ag+/Ag0≈0.1) are distributed in PPy's surface layer (hundreds of nm). • Ag species are crucial in prolonging the coating's protection time to 113 ± 2.6 days. • Ag NPs-PPy(TA + SA) shows good cytocompatibility and antibacterial properties. For the biodegradable implant applications, silver nanoparticles (Ag NPs) are incorporated in polypyrrole (PPy) co-dopped with tartrate (TA) and salicylate (SA) anions to obtain multi-functional Ag NPs-PPy(TA + SA)/Zn bilayer coating on ZK60 magnesium alloy with high protective and antibacterial properties. The effects of Ag NPs on the composition, structure, and antibacterial and protective properties of Ag NPs-PPy(TA + SA)/Zn bilayer coating are studied. Incorporating Ag NPs influences the electrochemical growth conditions of PPy(TA + SA), possibly increasing the defects in PPy chains. Its surface morphology and film thickness are similar to PPy(TA + SA). However, Ag species (Ag+/Ag0 ≈ 0.1) are only distributed in the PPy surface layer (hundreds of nm), containing some adsorbed and agglomerated Ag NPs on its surface. In Hank's solution at 37 °C, Ag NPs-PPy(TA + SA) experiences slow degradation, and the Ag content loses slowly to zero. Its protection time is significantly improved to 113 ± 2.6 days, much more prolonged than PPy(TA + SA) (54 ± 1.5 d), suggesting the crucial role of Ag NPs. After Ag NPs-PPy(TA + SA) is broken due to its local destruction, ZK60 displays typical local corrosion. Ag NPs-PPy(TA + SA) exhibited excellent cytocompatibility and antibacterial properties. The corresponding mechanism involved is thoroughly discussed. [ABSTRACT FROM AUTHOR]

An excellent anti-corrosion and initial corrosion-warning composite coating (MAO/Na 2 MoO 4 /8-HQ/PP/WPU) was constructed on AZ31B magnesium alloy using micro-arc oxidation (MAO) technology, vacuum adsorption and spin-coating methods. The microstructure and chemical composition of the coating samples were characterized using XRD, FTIR, SEM, XPS, and Raman technologies. Scratches experiment confirms that MAO/Na 2 MoO 4 /8-HQ/PP/WPU coating could detect early corrosion at a damaged coating area. Electrochemical and optical morphology results show that it still maintains an unexceptionable corrosion protection performance with a high |Z| 0.01Hz value (1.017 × 107 Ω·cm2) after immersion in a 3.5 wt% NaCl solution for 60 days, one order of magnitude larger than that of blank WPU coating. Combined with ion selective test and XPS depth analysis, its corrosion protection mechanism of the coating is clearly explained. This study can provide new insights for the design and protective mechanisms of functional coatings. [Display omitted] • The MAO/Na 2 MoO 4 /8-HQ/PP/WPU composite coating exhibits excellent long-term corrosion resistance. • The color change of PP indicator loaded in the composite coating serves as an initial warning for localized corrosion. • Corrosion protection mechanism is firstly elucidated from the perspective of ion selectivity, corrosion inhibitor and physical isolation behaviors of the composite coating. [ABSTRACT FROM AUTHOR]

To enhance the corrosion protection of the polypyrrole/zinc (PPy/Zn) bilayer coating on biodegradable ZK60 magnesium alloy in Hank's solution at 37 °C, sodium salicylate (NaSA) in different concentrations (C NaSA , 0.5–4.0 mM) is selected as a co-doping reagent of tartrate anions (TA−), and an electropolymerization method that combines potentiostatic and galvanostatic synthesis is developed to prepare PPy(TA + SA)/Zn bilayer coatings. The co-doping of SA− suppresses the growth of PPy and notably increases its synthesis potential (E poly) with increasing C NaSA. The co-doped PPy(TA + SA) films have a surface morphology and thickness similar to the PPy(TA) film. However, their chemical composition, structure, and adhesion strength change notably due to their varying growth conditions. In the long-term immersion test of PPy(TA + SA)/Zn/ZK60 samples, the PPy(TA + SA)/Zn coatings exhibit high stability, and the coating prepared with C NaSA = 1.0 mM has the most prolonged protection time (54 ± 1.5 d). As C NaSA increases, the co-doped PPy(TA + SA) film becomes heavily over-oxidized to produce more defects on PPy chains due to the high E poly , ultimately decreasing the protection time to 40 ± 1.0 d. The corresponding mechanism involved is thoroughly discussed. Salicylic (SA) and tartaric (TA) ions co-doped PPy films are electropolymerized, undergoing potentiostatic and galvanostatic synthesis, to prepare compact and stable PPy(TA + SA)/Zn bilayer coating on ZK60 magnesium alloy. The PPy(TA + SA) film completely isolates the corrosion media from the Zn/ZK60 substrate and degrades very slowly, notably enhancing its protection time in Hank's solution. [Display omitted] • Co-doping salicylic (SA) with tartaric (TA) ions notably increases PPy's stability. • Combine potentio- and galvanostatic synthesis to grow co-doped PPy(TA + SA) • The PPy(TA + SA)/Zn bilayer coating on ZK60 notably enhances corrosion resistance. • The PPy(TA + SA) film prolongs its protection time to 54 ± 1.5 days in Hank's solution. • PPy(TA + SA) shows low antibacterial properties for doping minimal SA ions. [ABSTRACT FROM AUTHOR]

Magnesium alloy has a wide application prospect in the carrier aircraft due to its high strength to weight ratio, high specific strength and stiffness. However, the weak corrosion resistance and radar stealth performance limits its further development. In this work, micro-arc oxidation (MAO) technology was used to improve the corrosion resistance of AZ91D magnesium alloy through the generation of ceramic oxide film; then the porous MAO layer as a bond layer was anchored with silicone resin (SI) coating doped with nano cobalt ferrite (CFO) for further improvement of anti-corrosion performance and radar absorption performance. The composite coatings (MAO, SI, MAO + SI, SI + CFO, MAO + SI + CFO) on AZ91D magnesium alloy were prepared, and their long-term corrosion protection performance and wave-assimilation performance were evaluated by electrochemical impedance spectroscopy (EIS) and microwave vector network analyzer (VNA). The EIS results show that after 63 days immersion in 3.5 % NaCl solution, impedance module value of the MAO + SI + CFO coating at 0.01 Hz still keeps 108 Ω cm2, suggesting its excellent anti-corrosion performance. From the VNA consequences, the minimum reflection loss of MAO + SI + CFO coating is −23.10 dB, and the effective absorption bandwidth is 4.07 GHz, illustrating its good electromagnetic absorption performance. This work provides a new idea for the multi-functionalization of aviation lightweight magnesium alloys. • Advanced Bonding Layer: Combine porous MAO, SI, and nano cobalt ferrite for enhanced durability. • Synergistic Anti-Corrosion: MAO + SI + CFO coating excels after 63 days in 3.5 wt% NaCl solution, showcasing lasting performance. • Dual Defense Capability: Impressive 109 Ω cm2 impedance and −23.10 dB reflection loss demonstrate excellent protection. [ABSTRACT FROM AUTHOR]

A polypyrrole/zinc (PPy/Zn) bilayer coating is prepared to significantly improve the corrosion resistance of ZK60 magnesium alloy in 37 °C Hank's solution to meet the requirements for biodegradable metals. The zinc coating composed of dense and uniform flake-like zinc crystals displays good abrasion resistance and adhesion strength, acting as a vital intermediate layer for growing the PPy film doping with tartrate anions (TA−). The prepared PPy/TA films (10, 20 and 28 μm) on the Zn coating are compact and have high stability in Hank's solution. The electrochemical and hydrogen evolution tests for PPy/Zn/ZK60 specimens show that the PPy/TA film's stability determines the protective performance of PPy/Zn coating in a long immersion period. The PPy(20 μm)/Zn coating has the longest protection time (40 ± 4 days), and too thick PPy film (28 μm) damages its structure to accelerate breakage, developing local corrosion quickly on ZK60. The corrosion mechanism involved is discussed. PPy/Zn bi-layered coating prepared on ZK60 magnesium alloy significantly improves its corrosion resistance in Hank's solution. The compact PPy film on the Zn coating is stable under chemical and electrochemical attacks, preventing the entrance of corrosion media to prolong its protection time. After PPy is broken, a local corrosion area develops quickly on ZK60. [Display omitted] • PPy/Zn bi-layered coating is prepared on ZK60 for biodegradable applications. • Zn coating acts as a vital intermediate layer for growing high-stability PPy. • PPy doping with tartrate anions (PPy/TA) has high stability in Hank's solution. • PPy/TA film's stability determines the protective performance of PPy/Zn coating. • Too thick PPy/TA film may damage its structure to accelerate its breakage. [ABSTRACT FROM AUTHOR]

Abstract: 5,10,15,20-Tetraphenylporphyrin (TPP) is synthesized and its inhibition effect on AZ91D magnesium alloy in 0.05wt.% NaCl solution is studied. Electrochemical measurement and immersion corrosion test results indicate that the inhibition efficiency of TPP reaches 90%. SEM, FT-IR, ultraviolet–visible absorption spectrum (UV), fluorescent spectrometry and XPS analyses suggest that TPP molecules can chelate with Mg via their N atoms to form a TPP–Mg complex, which can precipitate as a film on AZ91D alloy. The precipitated TPP–Mg reduces the porosity of the original Mg(OH)2 surface film and retards the dissolution of the Mg alloy. [Copyright &y& Elsevier]

Abstract: The inhibition effects of organic sodium aminopropyltriethoxysilicate (APTS–Na) and inorganic zinc nitrate on the corrosion of Mg-10Gd-3Y magnesium alloy (GW103) in ASTM D1384-87 corrosive water are investigated by electrochemical techniques and immersion test. The results show that individual organic or inorganic inhibitor has low inhibition efficiency. However, when these organic and inorganic inhibitors are used together, a synergistic inhibition behavior is observed. The Mg alloy surfaces after immersion test were analyzed using scanning electron microscope (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The surface in the inhibitor containing solution is found to be covered by a film composed of Mg(OH)2 and silicate. It is believed that the formation of this surface film is responsible for the synergistic inhibition effect of the organic and inorganic inhibitors. [Copyright &y& Elsevier]

Abstract: In this study, the corrosion performance of magnesium-based rare-earth containing alloy Mg–10Gd–3Y–0.5Zr (GW103) was evaluated in an ethylene glycol solution with a group of selected aliphatic, aromatic carboxylates and inorganic salts as inhibitors. The dependence of inhibition efficiency on the concentration ratio of sodium phosphate to sodium dodecylbenzenesulfonate (SDBS) and the total inhibitor concentration was measured by means of electrochemical techniques. It was found that the corrosion rate of GW103 decreased by addition of inorganic–organic inhibitors at both ambient and elevated temperatures. The inhibitors were more effective at the ambient temperature than at the elevated temperature. The corrosion of GW103 in the ethylene glycol solution can be effectively inhibited by 1000ppm of the inorganic–organic inhibitor mixture. It is believed that the added phosphate can interact with SDBS, resulting in a more compact surface film on the GW103 surface. Based on these results, as well as Environmental Scanning Electron Microscope (ESEM) observations, a synergistic mechanism was proposed to explain the inhibition behavior of the sodium phosphate+SDBS combination. [Copyright &y& Elsevier]