Effects of Alloying Element Ca on the Corrosion Behavior and Bioactivity of Anodic Films Formed on AM60 Mg Alloys

Covalent Pinning of Highly Dispersed Ultrathin Metallic-Phase Molybdenum Disulfide Nanosheets on the Inner Surface of Mesoporous Carbon Spheres for Durable and Rapid Sodium Storage

Two-dimensional (2D) transition-metal dichalcogenide materials show potential for use in alkali metal ion batteries owing to their remarkable physical and chemical properties. Nevertheless, the electrochemical energy storage performance is still impaired by the tendency of aggregation, volume, and morphological change during the conversion reaction and poor intrinsic conductivity. Until now, ultrathin molybdenum disulfide nanosheets with a metallic-phase structure on the inner surface of mesoporous hollow carbon spheres (M-MoS₂@HCS) have rarely been investigated as an anode for sodium-ion batteries. In this work, a novel M-MoS₂@HCS anode was designed and synthesized by employing a template-assisted solvothermal reaction. Structural and chemical analyses indicate that the M-MoS₂ nanosheets with a larger interlayer spacing compared to their semiconductor counterpart grow on the inner surface of HCS via covalent interactions. When used as the anode materials for Na⁺ storage, the M-MoS₂@HCS anode presents durable and rapid sodium storage properties. The developed electrode shows a reversible capacity of 291.2 mAh g^-1 at a high current density of 5 A g^-1. After 100 cycles at 0.1 A g^-1, the reversible capacity is 401.3 mAh g^-1 with a capacity retention rate of 79%. After 2500 cycles at 1.0 A g^-1, the electrode still delivers a reversible capacity of 320.1 mAh g^-1 with a capacity retention rate of 75%. The excellent sodium storage capability of the MoS₂@HCS electrode is explained by the special structural design, which reveals great potential to accelerate the practical applications of transition-metal dichalcogenide electrodes for sodium storage.

Improved Corrosion Resistance of Magnesium Alloy AZ31 in Ringer Lactate by Bilayer Anodic Film/Beeswax–Colophony

A bilayer anodic film/beeswax–colophony is proposed for improving the corrosion resistance of magnesium alloy surface. The bilayer was synthesized on the AZ31 alloy by anodization and subsequent dip coating, and the corrosion behavior was investigated by electrochemical measurements and weight loss test in Ringer lactate at 37 °C. The bilayer improved the electrochemical corrosion resistance by four orders of magnitude, as demonstrated by ~104 times lower corrosion current density in the polarization curves and ~104 higher film resistance in the impedance spectra. The tremendous surface area of the porous anodic film led to a strong attachment of the topcoat beeswax–colophony. Most of the coating remained attached to the surface after 14 days soaking in Ringer lactate. A few small blisters developed under the bilayer contributed to the low mass loss of 0.07 mg/cm2/day compared to the bare substrate, with an average loss rate of 0.25 mg/cm2/day. Local detachment of topcoat layer exposed the underlying anodic film that triggered the deposition of Ca and further nucleation of the Ca–P compound on the surface. The existence of a Ca−P compound with a Ca/P ratio of 1.68 indicated the ability of the bilayer to promote the formation of bone mineral apatite.

Preparation and Characterization of Mg-RE Alloy Sheets and Formation of Amorphous/Crystalline Composites by Twin Roll Casting for Biomedical Implant Application

A new type of Mg-based metallic glass has attracted extensive attention due to its excellent corrosion resistance and favorable biocompatibility. In this study, an amorphous/crystalline composite Mg-RE alloy sheet was prepared by a vertical type twin roll caster (VTRC) method, and its microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM); furthermore, the corrosion behaviors of the Mg-RE alloy sheet were investigated in PBS solution using electrochemical techniques and immersion testing in a simulated physiological condition. Furthermore, it was implanted into the femur of rats to explore its prospect as biological transplantation material. Its microscopic characterization experiments show that the crystal structure is crystalline phase containing amorphous phase. Electrochemical experiments and immersion testing both showed that Mg-RE(La,Ce) sheet with VTRC has a better corrosion resistance than master alloy, and a uniform corrosion layer on the surface. In vivo, as an implant material, tests show that Mg-RE alloy sheets have better biocompatibility and induce new bone formation, and they can be expected to be utilized as implant materials in the future.

Corrosion Resistance and Apatite-Forming Ability of Composite Coatings formed on Mg-Al-Zn-Ca Alloys

The properties of composite coatings formed by plasma electrolytic oxidation (PEO) were affected by the alloy composition. The corrosion resistance and apatite-forming ability of PEO coatings formed on Mg–6Al–1Zn–xCa alloys with a variation of Ca content were investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements showed an order magnitude improvement of corrosion resistance in the AZ61 alloy as a result of the coating. A higher enhancement in polarization resistance was obtained in the Mg–6Al–1Zn–1Ca and Mg–6Al–1Zn–2Ca alloys due to thicker coatings were formed as a result of the incorporation of calcium oxide/hydroxide. However, the underlying substrates were more prone to localized corrosion with increasing Ca content. The microstructure investigation revealed an enlargement in precipitates (Al₂Ca, Mg₂Ca) sizes with increasing Ca content in the alloys. The growth of larger size precipitates increased the danger to micro galvanic corrosion. Apatite layers were formed on all of the coatings indicating high apatite-forming ability, but the layers formed on the Mg–6Al–1Zn–1Ca and Mg–6Al–1Zn–2Ca alloys contained higher Mg, possibly due to the accumulation of corrosion product, than that on the Mg–6Al–1Zn alloy. The alloying element Ca should be limited to 1 wt.% as the excess tended to degrade the corrosion resistance and apatite-forming ability of the PEO coating.

The current trends of Mg alloys in biomedical applications-A review

Magnesium (Mg) has emerged as an ideal alternative to the permanent implant materials owing to its enhanced properties such as biodegradation, better mechanical strengths than polymeric biodegradable materials and biocompatibility. It has been under investigation as an implant material both in cardiovascular and orthopedic applications. The use of Mg as an implant material reduces the risk of long-term incompatible interaction of implant with tissues and eliminates the second surgical procedure to remove the implant, thus minimizes the complications. The hurdle in the extensive use of Mg implants is its fast degradation rate, which consequently reduces the mechanical strength to support the implant site. Alloy development, surface treatment, and design modification of implants are the routes that can lead to the improved corrosion resistance of Mg implants and extensive research is going on in all three directions. In this review, the recent trends in the alloying and surface treatment of Mg have been discussed in detail. Additionally, the recent progress in the use of computational models to analyze Mg bioimplants has been given special consideration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1970-1996, 2019.

The Corrosion Behavior of AZ91D Magnesium Alloy in Simulated Haze Aqueous Solution

The corrosion process of AZ91D magnesium alloy in simulated haze aqueous solution has been studied by electrochemical measurements, immersion tests and morphology characterization. Results show that AZ91D was corroded heavily in simulated haze aqueous solution due to the loose and breakable product film on the surface providing little corrosion barrier. The effect of different ions was investigated. It was found that both NO3− and NH4+ played an important role in the corrosion process. NO3− helped to form passive film to protect the matrix, yet NH4+ consumed OH⁻, resulting in the absence of Mg(OH)₂ and serious corrosion. Meanwhile, SO42− and Cl⁻ had influence on pitting corrosion. Magnesium aluminum oxide and MgAl₂(SO₄)₄·22H₂O instead of Mg(OH)₂ were the dominate products, which is different from the former study. Corrosion rate changed with time, especially in the first 3 h. A two-stage corrosion mechanism is proposed after considering both the corrosion process and the influence of ions.

Effect of Homogenization on Microstructure Characteristics, Corrosion and Biocompatibility of Mg-Zn-Mn-xCa Alloys

The corrosion behaviors of Mg-2Zn-0.2Mn-xCa (denoted as MZM-xCa alloys) in homogenization state have been investigated by immersion test and electrochemical techniques in a simulated physiological condition. The microstructure features were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA), and the corrosion mechanism was illustrated using atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and confocal laser scanning microscopy (CLSM). The electrochemical and immersion test verify the MZM-0.38% Ca owns the best corrosion performance with the corrosion rate of 6.27 mm/year. Furthermore, the film layer of MZM-0.38% Ca is more compact and denser than that of others. This improvement could be associated with the combined effects of the suitable content of Zn/Ca dissolving into the α-Mg matrix and the modification of Ca-containing compounds by heat-treatment. However, the morphologies were transformed from uniform corrosion to localized pitting corrosion with Ca further addition. It could be explained that the excessive Ca addition can strengthen the nucleation driving force for the second phase formation, and the large volumes fraction of micro-galvanic present interface sites accelerate the nucleation driving force for corrosion propagation. In addition, in vitro biocompatibility tests also show the MZM-0.38% Ca was safe to bone mesenchymal stem cells (BMSCs) and was promising to be utilized as implant materials.

Rare Earth Element Yttrium Modified Mg-Al-Zn Alloy: Microstructure, Degradation Properties and Hardness

The overly-fast degradation rates of magnesium-based alloys in the biological environment have limited their applications as biodegradable bone implants. In this study, rare earth element yttrium (Y) was introduced into AZ61 magnesium alloy (Mg-6Al-1Zn wt %) to control the degradation rate by laser rapid melting. The results showed that the degradation rate of AZ61 magnesium alloy was slowed down by adding Y. This was attributed to the reduction of Mg₁₇Al₁₂ phase and the formation of Al₂Y phase that has a more active potential, which decreased galvanic corrosion resulting from its coupling with the anodic matrix phase. Meanwhile, the hardness increased as Y contents increased due to the uniform distribution of the Al₂Y and Mg₁₇Al₁₂ phases. However, as the Y contents increased further, the formation of excessive Al₂Y phase resulted in the increasing of degradation rate and the decreasing of hardness due to its agglomeration.