Effect of zinc content on the microstructure, in vitro bioactivity, and corrosion behavior of the microarc oxidized Mg-xZn-0.6Ca (x = 3.0, 4.5, 6.0) alloy.

Bioceramic calcium phosphorus (CaP) coatings were prepared on self-designed Mg-xZn-0.6Ca (x = 3.0, 4.5, 6.0 wt. %) alloy by microarc oxidation (MAO). The corrosion resistance, bioactivity, and biodegradability of the CaP coatings prepared on alloys with different zinc (Zn) contents were systematically studied and discussed by potentiodynamic polarization and in vitro immersion tests in the simulated body fluid solution. The CaP coatings and corrosion products were characterized by scanning electron microscopy, energy dispersive spectrometry, x-ray diffraction, and Fourier transform infrared spectroscopy. Based on the difference of microstructure caused by zinc content, the effect of microstructure on the properties of MAO coatings was analyzed by taking grain boundary and second phase defects as examples. Results showed that the CaP coatings could be prepared on the surface of the self-designed Mg-Zn-0.6Ca alloy by MAO. The CaP coatings have good bioactivity. Meanwhile, the Zn content has a significant effect on the microstructure of the CaP coatings. When the Zn content is 3.0 wt. %, the corrosion resistance and biocompatibility of the CaP coatings are obviously improved with good biological properties.

Mixed-valent MnSiO3/C nanocomposite for high-performance asymmetric supercapacitor.

In this work, carbon-coated manganese silicate (MnSiO3/C) nanocomposite with excellent cycling stability was fabricated via a cost-effective process. The carbon coating followed with a CO2 heat treatment process on the manganese silicate results in mixed-valent hierarchically-porous nanoparticles, which tightly connects with an ultrathin (∼1.5 nm) and ordered carbon coating layer. This composite features rectangular-like cyclic voltammetry curve with two couples of redox peaks, suppressing the irreversible reactions and thus providing a broad and stable working voltage. By fitting the CV curves, the MnSiO3/C demonstrates a capacitive energy-storage behavior. The as-assembled activated carbon//MnSiO3/C asymmetric supercapacitor in 1 M Na2SO4 aqueous electrolyte is found to have excellent cycling stability, with 95.5% retention of initial after 10,000 cycles. This device could deliver 25.8 W h kg-1 energy density at the power density of 1 kW kg-1 with ∼10 mg cm-2 high mass loading, suggesting a bright prospect in practical application.

Effect of calcium on the microstructure and corrosion behavior of microarc oxidized Mg-xCa alloys.

Magnesium alloys are potential biodegradable implants for biomedical applications, and calcium (Ca) is one kind of ideal element being examined for magnesium alloys and biodegradable ceramic coatings owing to its biocompatibility and mechanical suitability. In this study, microarc oxidation (MAO) coatings were prepared on Mg-xCa alloys to study the effect of Ca on the microstructure and corrosion resistance of Mg-xCa alloys and their surface MAO coatings. The electrochemical corrosion behavior was investigated using an electrochemical workstation, and the degradability and bioactivity were evaluated by soaking tests in simulated body fluid (SBF) solutions. The corrosion products were characterized by scanning electron microscopy, x-ray diffractometry, and Fourier transform infrared spectrometry. The effects of Ca on the alloy phase composition, microstructure, MAO coating formation mechanism, and corrosion behavior were investigated. Results showed that the Mg-0.82Ca alloy and MAO-coated Mg-0.82Ca exhibited the highest corrosion resistance. The number and distribution of Mg2Ca phases can be controlled by adjusting the Ca content in the Mg-xCa alloys. The proper amount of Ca in magnesium alloy was about 0.5-0.8 wt. %. The pore size, surface roughness, and corrosion behavior of microarc oxidized Mg-xCa samples can be controlled by the number and distribution of the Mg2Ca phase. The corrosion behaviors of microarc oxidized Mg-Ca in SBF solutions were discussed.

In vitro degradation and electrochemical corrosion evaluations of microarc oxidized pure Mg, Mg-Ca and Mg-Ca-Zn alloys for biomedical applications.

Calcium phosphate (CaP) ceramic coatings were fabricated on pure magnesium (Mg) and self-designed Mg-0.6Ca, Mg-0.55Ca-1.74Zn alloys by microarc oxidation (MAO). The coating formation, growth and biomineralization mechanisms were discussed. The coating degradability and bioactivity were evaluated by immersion tests in trishydroxymethyl-aminomethane hydrochloric acid (Tris-HCl) buffer and simulated body fluid (SBF) solutions, respectively. The coatings and corrosion products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and fourier transform infrared spectrometer (FT-IR). The electrochemical workstation was used to investigate the electrochemical corrosion behaviors of substrates and coatings. Results showed that Mg-0.55Ca-1.74Zn alloy exhibits the highest mechanical strength and electrochemical corrosion resistance among the three alloys. The MAO-coated Mg-0.55Ca-1.74Zn alloy has the potential to be served as a biodegradable implant.

Effect of current density on the microstructure and corrosion resistance of microarc oxidized ZK60 magnesium alloy.

The application of magnesium alloys as biomaterials is limited by their poor corrosion behavior. Microarc oxidation (MAO) treatment was used to prepare ceramic coatings on ZK60 magnesium alloys in order to overcome the poor corrosion resistance. The process was conducted at different current densities (3.5 and 9.0 A/dm(2)), and the effect of current density on the process was studied. The microstructure, elemental distribution, and phase composition of the MAO coatings were characterized by scanning electron microscopy, energy-dispersive x-ray spectrometry, and x-ray diffraction, respectively. The increment of current density contributes to the increase of thickness. A new phase Mg2SiO4 was detected as the current density increased to 9.0 A/dm(2). A homogeneous distribution of micropores could be observed in the coating produced at 3.5 A/dm(2), while the surface morphology of the coating formed at 9.0 A/dm(2) was more rough and apparent microcracks could be observed. The coating obtained at 3.5 A/dm(2) possessed a better anticorrosion behavior.

Dissolution and precipitation behaviors of silicon-containing ceramic coating on Mg-Zn-Ca alloy in simulated body fluid.

We prepared Si-containing and Si-free coatings on Mg-1.74Zn-0.55Ca alloy by micro-arc oxidation. The dissolution and precipitation behaviors of Si-containing coating in simulated body fluid (SBF) were discussed. Corrosion products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectrometer (XPS). Electrochemical workstation, inductively coupled plasma atomic emission spectrometer (ICP-AES), flame atomic absorption spectrophotometer (AAS) and pH meter were employed to detect variations of electrochemical parameter and ions concentration respectively. Results indicate that the fast formation of calcium phosphates is closely related to the SiOx(n-) groups, which induce the heterogeneous nucleation of amorphous hydroxyapatite (HA) by sorption of calcium and phosphate ions.