Hydroxyapatite Coating on Ti-6Al-7Nb Alloy by Plasma Electrolytic Oxidation in Salt-Based Electrolyte

Titanium alloys have good biocompatibility and good mechanical properties, making them particularly suitable for dental and orthopedic implants. Improving their osseointegration with human bones is one of the most essential tasks. This can be achieved by developing hydroxyapatite (HA) on the treating surface using the plasma electrolytic oxidation (PEO) method in molten salt. In this study, a coating of titanium oxide-containing HA nanoparticles was formed on Ti-6Al-7Nb alloy by PEO in molten salt. Then, samples were subjected to hydrothermal treatment (HTT) to form HA crystals sized 0.5 to 1 μm. The effect of the current and voltage frequency for the creation of the coating on the morphology, chemical, and phase composition was studied. The anti-corrosion properties of the samples were studied using the potentiodynamic polarization test (PPT) and electrochemical impedance spectroscopy (EIS). An assessment of the morphology of the sample formed at a frequency of 100 Hz shows that the structure of this coating has a uniform submicron porosity, and its surface shows high hydrophilicity and anti-corrosion properties (4.90 × 106 Ohm·cm2). In this work, for the first time, the process of formation of a bioactive coating consisting of titanium oxides and HA was studied by the PEO method in molten salts

Understanding the Unique Thermodynamic Behavior of MgTFSI₂/DME Solutions. Part 1: Phase Diagram, Partial Volumes, and Densities

A unique thermodynamic behavior was observed for solutions of magnesium bis(trifluoromethanesulfonyl) imide in 1,2-dimethoxyethane (DME), highly promising solutions for rechargeable Mg batteries: between 287 and 373 K, the solution exists as two immiscible phases, each with a different salt concentration, volume, and density. These characteristics depend strongly on temperature. To study this dependence, a phase diagram was constructed. In addition, partial phase volumes and densities were measured as a function of temperature. We observed that the temperature–molar fraction phase diagram exhibits closed-loop behavior, which is circumscribed by 287 and 373 K, with 333 K as an inversion locus. Below 287 K, the solution exists as a single homogeneous phase. At 287 K and above, the solution separates into two immiscible phases: a concentrated and dense lower phase and a dilute upper phase. As the temperature increases to 333 K, the lower phase becomes more concentrated and denser, and its partial volume decreases. The reverse trends are observed for the upper phase. From 333 K and above, the trends reverse: the upper phase becomes more concentrated but its partial volume continues to grow at the expense of the lower phase, while the lower phase concentration decreases. At 373 K, the two phases merge into a single homogeneous phase

Electrochemical and Spectroscopic Analysis of Mg²⁺ Intercalation into Thin Film Electrodes of Layered Oxides: V₂O₅ and MoO₃

Electrochemical, surface, and structural studies related to rechargeable Mg batteries were carried out with monolithic thin-film cathodes comprising layered V₂O₅ and MoO₃. The reversible intercalation reactions of these electrodes with Mg ion in nonaqueous Mg salt solutions were explored using a variety of analytical tools. These included slow-scan rate cyclic voltammetry (SSCV), chrono-potentiometry (galvanostatic cycling), Raman and photoelectron spectroscopies, high-resolution microscopy, and XRD. The V₂O₅ electrodes exhibited reversible Mg-ion intercalation at capacities around 150–180 mAh g^–1 with 100% efficiency. A capacity of 220 mAh g^–1 at >95% efficiency was obtained with MoO₃ electrodes. By applying the electrochemical driving force sufficiently slowly it was possible to measure the electrodes at equilibrium conditions and verify by spectroscopy, microscopy, and diffractometry that these electrodes undergo fully reversible structural changes upon Mg-ion insertion/deinsertion cycling

Anomalous Sodium Storage Behavior in Al/F Dual-Doped P2-Type Sodium Manganese Oxide Cathode for Sodium-Ion Batteries

Various types of sodium manganese oxides are promising cathode materials for sodium storage systems. One of the most considerable advantages of this family of materials is their widespread natural abundance. So far, only a few host candidates have been reported and there is a need to develop new materials with improved practical electrochemical performance. Here, P2-type Al/F-doped sodium manganese oxide as well as its unique sodium storage mechanism is demonstrated by a combination of electrochemical characterization, structural analyses from powder X-ray diffraction (XRD) data, and 3D bond valence energy level calculations for the sodium diffusion pathways. The material exhibits a high reversible capacity of 164.3 mAh g−1 (0.3C rate) and capacity retention of 89.1% after 500 cycles (5C rate). The study clearly unravels the beneficial effect of the doping and the unique sodium intercalation mechanism devoid of the low diffusion O3 transformation. © 2020 Wiley-VCH GmbH1