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Plasma electrolytic oxidation (PEO) is normally carried out under conditions with electrolyte cooling. However, the effect of the temperature of the electrolytes on the PEO behavior and properties of the resulting coatings is seldom investigated. In this study, PEO of pure Al was carried out in a dilute aluminate electrolyte with the electrolyte temperature being controlled under low (~10–30 °C), medium (~40–50 °C) and high (~70–80 °C) temperature ranges, respectively. The morphology, microstructure, composition and phase component of the coatings fabricated under the different temperature ranges were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion resistances of the coatings were evaluated by electrochemical methods. The hardness of the coatings and substrate following the PEO treatment in the different electrolyte temperature ranges were also tested. It was found that a higher electrolyte temperature resulted in a higher growth rate and rougher coatings. Moreover, the α-Al2O3 content was reduced as the electrolyte temperature increased. The highest corrosion resistance was registered for the coating obtained under the lowest temperature range, whereas the corrosion resistance of the coating obtained under the highest temperature range was the worst. The higher growth rate under high electrolyte temperatures was associated with the increased kinetics of the PEO reactions. However, the temperature of the electrolyte should be controlled under a suitable range to ensure reasonable coating properties. [ABSTRACT FROM AUTHOR]

In the present study, the distribution of Ag in the coating formed on Mg-Ag alloy by plasma electrolytic oxidation (PEO) and its ionic release kinetics when exposed to a 0.9 wt.% NaCl solution at 37 °C have been investigated. Both metallic Ag and Ag oxide particles with ∼5 to ∼40 nm in diameters were observed in the PEO coating. Further, an Ag-enriched layer of ∼20 nm in thickness at the substrate/coating interface was also observed. The PEO coating on the Mg-Ag alloy not only increases its corrosion resistance with the corrosion current density decreasing by up to 3 orders of magnitude from 8.04 × 10−3 to 4.03 × 10−6 A/cm2, but also controls the release of Ag+ to the level that is sufficient for anti-infective efficacy without causing cytotoxicity to mammal cells. [ABSTRACT FROM AUTHOR]

In the present work, plasma electrolytic oxidation (PEO) is creatively introduced as a novel method to fabricate multi-layered nanospheres. Titanium (Ti) was oxidized in a phosphate-based electrolyte containing ZnO nanoparticles (NPs), which results in the formation of nanospheres on the ceramic coating. The as-fabricated nanosphere is amorphous with a three-layered architecture. The inner layer of the nanosphere contains Zn, Ca and P whereas Cu and P were detected in the medium layer with the outer layer enriched in Cu, O and Ti, which is promising in the field of bio-medical implanted devices. Herein, a novel one-pot synthesis strategy is proposed to fabricate multi-layered nanospheres, which could enlighten the preparation of hierarchical structures in various fields. [Display omitted] [ABSTRACT FROM AUTHOR]

Currently, biodegradable Mg-based implants used in clinical practice barely degrade after more than ten months of use. To achieve controlled degradation, we prepare a novel surface system on a Mg Mn Ag alloy composed of a ceramic layer produced by plasma electrolytic oxidation (PEO) and a polypyrrole (PPy)-loaded polycaprolactone (PCL) composite coating. The surface system exhibits superior corrosion resistance to prevent premature failure of the Mg alloy. After near-infrared (NIR) irradiation, the photothermal conversion effect of PPy promotes the transformation of PCL from a rubbery state to a viscous state, thereby facilitating the infiltration of external electrolytes for a dramatically increased degradation rate. As a result, the reduction of i corr and | Z | 0.01Hz by 4 orders of magnitude after NIR irradiation could be achieved. Hence, this work provides a new strategy for remotely regulating the degradation rate of Mg-based implants. [Display omitted] • A novel surface layer composed of a PEO ceramic layer and a PCL-PPy composite coating was fabricated on Mg Ag Mn alloy. • PEO/PCL-PPy layer exhibits desired corrosion resistance. • NIR irradiation dramatically decreases the corrosion resistance of the surface layer. [ABSTRACT FROM AUTHOR]

The application of Mg Ag alloy for the fabrication of orthopedic implant requires its enhanced corrosion resistance, desired biocompatibility and bactericidal capability without cytotoxicity. Herein, to achieve those purposes, a novel plasma electrolytic oxidation (PEO) treatment was proposed. The PEO coating with a bimodal pore size distribution could form on Mg Ag alloy surface to enhance its corrosion resistance. Further, the incorporation of magnesium phosphate in the PEO coating may also benefit its biocompatibility. Finally, Ag within the alloy could be gradually oxidized to form incorporated Ag+ and nano-sized Ag 2 O particles in the coating, which potentially optimize the ionic release kinetics of Ag for a desired antibacterial capability without cytotoxicity. Hence, the present work offers a novel PEO method to improve the corrosion resistance and biological response of Mg Ag alloy, which enlightens the application of antibacterial Mg alloy in the field of biomedical devices. • An untraditional voltage response during the PEO process is reported. • Nano-sized magnesium phosphate is incorporated into the PEO coating. • Ag oxide nanoparticle is present in the PEO coating. • PEO coating with bimodal pore size distribution is produced. [ABSTRACT FROM AUTHOR]

• Both metallic Ag and Ag oxide exist in the coating. • A nano-sized Ag-rich layer exists at the substrate/coating interface. • PEO affects corrosion morphology and susceptibility of Mg-Ag alloy. • A sustained Ag+ release is achieved after PEO of Mg-Ag alloy. The application of biodegradable Mg alloys as implanted devices has been hindered by their low corrosion resistance and potential risk associated with microbial infection. In the present work, a rolled Mg-Ag alloy was studied, which was subjected to plasma electrolytic oxidation (PEO) to achieve a favoured balance between corrosion resistance and antimicrobial capability. The Ag distribution, corrosion resistance and Ag ionic release behaviour have been examined in details. It is revealed that PEO process leads to both incorporated Ag+ and Ag-rich nanoparticles in forms of metallic Ag and Ag oxide across the coating. In addition, a nano-sized Ag-enriched layer also exists at the substrate/coating interface. The microstructural modification associated with PEO process results in an increased corrosion resistance and a sustained Ag ionic release, indicating that it is a promising surface modification technique for antibacterial Mg-Ag alloy. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, the early-stage growth behaviour of titania on titanium (Ti) substrate during plasma electrolytic oxidation (PEO) process in an aqueous electrolyte rich in Ca and P was investigated. Microstructural characterization reveals the dramatic evolutions of morphology, porosity, phase component and chemical composition of titania during the early stage of PEO process. The PEO coating initially exhibits ultrafine pores with a completely amorphous structure after oxidation for 5 s, which displays a relatively low Ca/P ratio. With the extension of oxidation periods, titania gradually transforms to grooved morphology with an increased Ca/P ratio, which mainly consists of crystalline anatase phase. Finally, with the prolongation of oxidation period to 1 min, titania exhibits porous morphology typical for PEO coating, which comprises of both rutile and anatase crystals. Along with the prolongation of oxidation periods, the surface wettability of titania remains relatively stable whereas the corrosion resistance changes dramatically, which is closely associated with the combined effects of its porosity and thickness. The results of our present work advance the understanding of early-stage growth of titania during the PEO process, which offer theoretical guidance for the controllable synthesis of PEO coating on Ti and its alloys. • The growth behaviour of titania prior to dielectric breakdown was examined. • Titania initially displays ultrafine pores, transforms to grooved morphology and finally stabilizes as porous structure. • The initial titania is amorphous, which transforms to anatase and finally becomes the mixture of rutile and anatase. • The Ca/P ratio gradually increases with the prolongation of oxidation periods and finally reaches ~0.9. • The combined effect of porosity and thickness results in the dramatic modification of corrosion resistance in titania. [ABSTRACT FROM AUTHOR]

The hydroxyapatite (HA)-based/TiO 2 -based composite coating was produced through plasma electrolytic oxidation (PEO) method in the present work. The microstructural evolution of the composite coating was examined as a function of PEO duration. It was observed that Ca P phase initially appears at the cracks of TiO 2 -based layer in form of plates of micrometre scales after PEO duration of 5 min and then transforms to the hybrid of plates and floccules, which finally convert to clusters composed of nano-sized plates by self-assembly. After 15 min oxidation, a two-layered composite coating was revealed, including TiO 2 -based inner layer and HA-based outer layer. It is also noticed that the thickness of HA-based layer continuously increases as the oxidation period extends whereas both the thickness of TiO 2 -based layer beneath the HA-based layer and the coverage rate of Ca P phase on TiO 2 -based layer remain relatively stable at the late stage of PEO process. The microstructural variation inevitably affects the biocompatibilities and corrosion properties of the composition coatings. With the extension of oxidation periods, an increased amount of Ca P phase was produced in the composite coating, which thus results in an improved corrosion resistance due to its insulation property, hydrophobicity and physical barrier effect. Meanwhile, the enhanced biocompatibility of the composite coating could also be achieved with the prolongation of PEO duration, which is associated with the high bioactivity of Ca P phase. • The hydroxyapatite/TiO 2 composite coating has been successfully produced through plasma electrolytic oxidation. • The formation of hydroxyapatite is closely associated with cracks in the TiO 2 -based layer. • The presence of hydroxyapatite retards the growth of underlying TiO 2. • The coverage rate of hydroxyapatite initially increases dramatically and finally remains stable at approximately 80%. • An increased amount of hydroxyapatite results in an improved corrosion resistance and biocompatibility of the coating. [ABSTRACT FROM AUTHOR]

In this work, a Cu-incorporated Al 2 O 3 coating has been successfully produced through the one-step plasma electrolytic oxidation (PEO) method. Unexpectedly, the resultant Cu-incorporated Al 2 O 3 coating displays a multi-layered structure, which exhibits significant variations in morphology, composition and crystallinity. Compared to the compact outer layer of the PEO coating, both medium and inner layers are highly porous even the average pore size of the medium layer is obviously higher than that of the inner layer. The medium layer has a higher Cu content in comparison to both outer and inner layers. And the outer layer mainly consists of crystalline γ-Al 2 O 3 phase whereas both medium and inner layers are in amorphous states. Further, it was found that Cu specie could exist as Cu 2 O and CuO in the Cu-incorporated PEO coating. Finally, it was revealed that the incorporation of Cu into the porous PEO coating significantly improves the antifouling property of Al metallic substrate against SRB, which successfully prevents the formation of SRB biofilm. Hence, PEO method is a promising surface modification technique for the fabrication of antifouling coating. [ABSTRACT FROM AUTHOR]