Controlling the rate of degradation of Mg using magnesium fluoride and magnesium fluoride-magnesium phosphate duplex coatings

The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significant improvement in corrosion resistance for Mg. Magnesium phosphate coating improves the corrosion resistance of Mg, good bioactivity, promotes cell viability and cyto-compatibility and exhibits antibacterial activity. However, rapid dissolution in Mg in acidic magnesium phosphate containing solutions leads to the development of an inhomogeneous coating. The present study attempts to prevent the excessive dissolution of Mg by forming a fluoride conversion coating as a pre-treatment in the first stage followed by deposition of magnesium phosphate coating in the second stage to develop magnesium fluoride-magnesium phosphate duplex coatings. The morphological features, structural characteristics, nature of functional groups, corrosion behavior in Hanks’ balanced salt solution and bioactivity in simulated body fluid are assessed to ascertain the suitability of the magnesium fluoride-magnesium phosphate duplex coating in controlling the rate of degradation of Mg and improving its bioactivity using uncoated Mg and fluoride conversion coated Mg as reference. The findings of the study reveal that the magnesium fluoride-magnesium phosphate duplex coating could offer an excellent corrosion resistance and improve the bioactivity of Mg.

Stabilized cobalt-free lithium-rich cathode materials with an artificial lithium fluoride coating

Iron-substituted cobalt-free lithium-rich manganese-based materials,with advantages of high specific capacity,high safety,and low cost,have been considered as the potential cathodes for lithium ion batteries.However,challenges,such as poor cycle stability and fast voltage fade during cycling under high potential,hinder these materials from commercialization.Here,we developed a method to directly coat LiF on the particle surface of Li_(1.2)Ni_(0.15)Fe_(0.1)Mn_(0.55O2).A uniform and flat film was successfully formed with a thickness about 3 nm,which can effect-ively protect the cathode material from irreversible phase transition during the deintercalation of Li^(+).After surface coating with 0.5wt%LiF,the cycling stability of Li_(1.2)Ni_(0.15)Fe_(0.1)Mn_(0.55O2) cycled at high potential was significantly improved and the voltage fade was largely suppressed.

SYNTHESIS OF DIARYL ETHERS THROUGH PHASE TRANSFER CATALYSIS WITH POTASSIUN FLUORIDE COATED ALUMINA AS A STRONG BASE

Seven diaryl ethers were synthesized with potassium fluoride coated alumina as a strong base and the addition of catalytic amount of PTC. The yield of diaryl ethers with addition of PTC was much higher than that without PTC.A discussion of the catalysis mechanism was given in this paper.

Fluoride Conversion Coating on Biodegradable AZ31B Magnesium Alloy

A fluoride conversion coating was successfully prepared on AZ31B magnesium alloy by chemical reaction in hydrofluoric acid. Morphologies, composition, bonding strength, corrosion properties, in vitro cytotoxicity and antibacterial properties of the coating were investigated, respectively. The scanning electron microscopy observations revealed a dense coating with some irregular pores. The thin-film X-ray diffraction analysis indicated that the coating was mainly composed of MgO and MgF2. The electrochemical impedance spectroscopy results showed that the fluoride conversion coating significantly improved the corrosion resistance of AZ31B. The hydroxyapatite formed on the surface of the fluoride coated AZ31 B after being immersed in the simulated blood plasma indicated the good bioactivity of the material. The in vitro cytotoxicity test showed that the fluoride coated AZ31B alloy was not toxic to BMMSCs （human bone marrow-derived mesenchymal stem cells）. It was also found that the fluoride coated AZ31 B alloy had antibacterial capability.

Characterization and corrosion property of nano-rod-like HA on fluoride coating supported on Mg-Zn-Ca alloy×

The poor corrosion resistance of biodegradable magnesium alloys is the dominant factor that limits theirclinical application. In this study, to deal with this challenge, fluoride coating was prepared on MgeZneCa alloy as the inner coating and then hydroxyapatite (HA) coating as the outer coating was depositedon fluoride coating by pulse reverse current electrodeposition (PRC-HA/MgF2). As a comparative study,the microstructure and corrosion properties of the composite coating with the outer coating fabricatedby traditional constant current electrodeposition (TED-HA/MgF2) were also investigated. Scanningelectron microscopy (SEM) images of the coatings show that the morphology of PRC-HA/MgF2 coating isdense and uniform, and presents nano-rod-like structure. Compared with that of TED-HA/MgF2, thecorrosion current density of Mg alloy coated with PRC-HA/MgF2 coatings decreases from 5.72× 10^-5 A/cm2 to 4.32× 10^-7 A/cm^2, and the corrosion resistance increases by almost two orders of magnitude. Inimmersion tests, samples coated with PRC-HA/MgF2 coating always show the lowest hydrogen evolutionamount, and could induce deposition of the hexagonal structure-apatite on the surface rapidly. Theresults show that the corrosion resistance and the bioactivity of the coatings have been improved byadopting double-pulse current mode in the process of preparing HA on fluoride coating, and the PRC-HA/MgF2 coating is worth of further investigation.