Search

The properties of the coatings formed on the MA8 magnesium alloy by plasma electrolytic oxidation in electrolytes containing halloysite nanotubes in the concentrations of 0, 10, 20, 30 and 40 g/l were investigated. It has been found that the presence of halloysite nanotubes in the composition of the coatings has a positive impact on protective properties of the coatings and leads to the increase of roughness and heterogeneity. Obtained coatings reduce corrosion current density in comparison with the base PEO layers.

Results of studying the properties of composite fluoropolymer-containing coatings formed by the cold spray (CS) method on the surface of constructional steel are presented. Different ways of protective coating formation are proposed. The composition of coatings was studied using SEM/EDX analysis. The incorporation of super-dispersed polytetrafluoroethylene (SPTFE) into the coating increases the corrosion resistance of the copper-zinc-based cold-sprayed coating. Analysis of the electrochemical properties obtained using EIS (electrochemical impedance spectroscopy) and PDP (potentiodynamic polarization) indicates that samples treated with SPTFE on a base copper-zinc coating showed lower corrosion current density and higher impedance modulus (jc = 8.5 × 10−7 A cm−2, |Z|f=0.1 Hz = 5.3 × 104 Ω∙cm2) than the specimen with cold-sprayed SPTFE (jc = 6.1 × 10−6 A cm−2, |Z|f=0.1 Hz = 8.1 × 103 Ω∙cm2). The best anticorrosion properties were revealed for the sample with a cold-sprayed base Cu-Zn layer annealed at 500 °C for 1 h, followed by SPTFE friction treatment and re-annealed at 350 °C for 1 h. The corrosion current density jc of such a coating is 25 times lower than that for the base Cu-Zn coating. The antifriction properties and hydrophobicity of the formed layers are described. Obtained results indicate that cold-sprayed polymer-containing coatings effectively improve the corrosion and wear resistivity of the treated material.

The method of hybrid coating formation on the surface of a bioresorbable wrought magnesium alloy and magnesium obtained by additive technology was proposed. Plasma electrolytic oxidation (PEO) with subsequent treatment of the material using an organic biocompatible corrosion inhibitor and a bioresorbable polymer material was used to obtain the protective layers. The optimal method of surface treatment was suggested. Using SEM/EDX analysis, XRD, XPS, and confocal Raman microspectroscopy, the composition of the formed surface layers was determined. The corrosion protection performance of the formed coatings was studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques in 0.9 wt.% NaCl and HBSS. Hydrogen evolution and mass loss tests were performed to study the corrosion rate of samples with different types of protective coatings. Sealing the pores of PEO coating with a polymeric material contributes to a significant reduction in the amount of the inhibitor diffusing into a corrosive medium. The best barrier properties were established for the hybrid coating formed with a one-stage application of benzotriazole and polycaprolactone. Such layers reduce the rate of alloy degradation due to active protection.

Because of the unique crystal framework, bronze TiO2 (or TiO2(B)) is considered the prospective choice for high-performance lithium-ion battery anodes. Nevertheless, TiO2(B) requires efficient modification, e.g., suitable doping with other elements, to improve the electronic properties and enhance the stability upon insertion/extraction of guest ions. However, due to the metastability of TiO2(B), doping is challenging. Herein, for the first time, TiO2(B) co-doped with Mn, F, and N were synthesized through a successive method based on a hydrothermal technique. The prepared doped TiO2(B) consists of ultrathin nanotubes (outer diameter of 10 nm, wall thickness of 2–3 nm) and exhibits a highly porous structure (pore volume of up to 1 cm3 g−1) with a large specific surface area near 200 m2 g−1. The incorporation of Mn, F, and N into TiO2(B) expands its crystal lattice and modifies its electronic structure. The band gap of TiO2(B) narrows from 3.14 to 2.18 eV upon Mn- and N-doping and electronic conductivity improves more than 40 times. Doping with fluorine improves the thermal stability of TiO2(B) and prevents its temperature-induced transformation into anatase. It was found that the diffusivity of Li is about two times faster in doped TiO2(B). These properties make Mn, F, and N co-doped TiO2(B) nanotubes promising for application as high-performance anodes in advanced lithium-ion batteries. In particular, it possesses a good reversible capacity (231.5 mAh g−1 after 100 cycles at 70 mA g−1) and prominent rate capability (134 mAh g−1 at 1500 mA g−1) in the half-cell configuration. The (Mn, F, N)-doped TiO2(B) possesses a remarkable low-temperature Li storage performance, keeping 70% of capacity at −20 °C and demonstrating potentialities to be employed in full-cell configuration with LiMn2O4 cathode delivering a reversible capacity of 123 and 79 mAh g−1 at 35 and 1500 mA g−1, respectively, at a voltage of ~2.5 V. This research underlies that regulation of electronic and crystal structure is desired to uncover capabilities of nanoparticulate TiO2(B) for electrochemical energy storage and conversion.

Silica from rice husk [SiO2(rh)] was used as a mineral base for sequential loading of biogenic selenium nanoparticles (SeNPs) and polyhexamethylene guanidine (PHMG) hydrochloride. As result a filler for polymer coatings with a wide spectrum of antifouling activity was obtained. The complex filler was characterized by scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microscopy. The filler was introduced into epoxy (EP), polydimethylsiloxane (PDMS), and epoxy-siloxane (EP-PDMS) polymer matrices at 3 wt% and 5 wt% to evaluate their antifouling performance and effect on the durability characteristics of coatings. Characterization of the coatings was performed including water contact angle, surface free energy, pseudo-barnacle adhesion strength and modulus of elasticity. The in vitro antimicrobial properties of the prepared samples were evaluated using Staphylococcus aureus and Candida albicans. Antifouling properties were evaluated in field tests for 7 months. The incorporation of a complex filler involving SeNPs and PHMG made it possible to increase the coating resistance to fouling by 2–5 times. The best results were observed for the EP-PDMS sample with 5 wt% SiO2(rh)-SeNPs-PHMG characterized by low values of surface free energy (10.3 mN/m) and pseudo-barnacle adhesion strength (0.32 MPa) and acceptable rate of biocidal components release. The results indicate the promising use of the new filler for development of effective antifouling coatings. [ABSTRACT FROM AUTHOR]

In the present paper, the formation of protective coatings on the MA8 magnesium alloy by plasma electrolytic oxidation (PEO) with subsequent treatment of fluoropolymer is considered. The morphology of coatings after accelerated climatic tests was investigated and the elemental composition of coatings was studied after tests in a salt spray chamber (SSC). The analysis of the obtained results demonstrated a higher corrosion resistance of the fluoropolymer-containing layers in comparison with the base PEO coating.

In this work, composite fluoropolymer-containing coatings were obtained on samples of AMg3 aluminium alloy, MA8 magnesium alloy, and VT1-0 commercially pure titanium treated by plasma electrolytic oxidation (PEO). Superdispersed polytetrafluoroethylene (SPTFE) and a solution of tetrafluoroethylene (TFE) telomers in acetone were applied onto preliminarily formed PEO layers by the spray-coating method. The obtained coatings contained a large amount of crystalline polytetrafluoroethylene embedded in the outer porous layer of the PEO coating and did not have visible defects, which indirectly indicates high protective properties.

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing multi-walled carbon nanotubes in concentrations of 2, 4 and 6 g/l have been investigated. It was found that the introduction of multi-walled carbon nanotubes leads to an increase in the adhesive strength, microhardness and Young’s modulus of the obtained layers.

This paper presents the results of an investigation of the changes in the corrosion, wear resistance, and wettability of composite coatings formed on the AMg3 alloy through plasma electrolytic oxidation (PEO) and subsequent spraying with an organofluorine polymer. The evaluation of the electrochemical properties of the composite layers revealed a decrease in the corrosion current density compared with the PEO coating (from 3.8 × 10−8 to 3.1 × 10−11 A/cm2). The analysis of the wear resistance of composite coatings established that the application of this type of coating reduced the wear of the samples by two orders of magnitude when compared with the PEO layer. Using the contact-angle measurement, it was found that with an increase in the number of polymer spray applications, the wettability of coatings decreased, so the contact angle for the composite coating with triple fluoropolymer application increased by 134.3° compared to the base PEO coating.

In this work, the micro-arc oxidation method is used to fabricate surface-modified complex-structured titanium implant coatings to improve biocompatibility. Depending on the utilized electrolyte solution and micro-arc oxidation process parameters, three different types of coatings (one of them—oxide, another two—calcium phosphates) were obtained, differing in their coating thickness, crystallite phase composition and, thus, with a significantly different biocompatibility. An analytical approach based on X-ray computed tomography utilizing software-aided coating recognition is employed in this work to reveal their structural uniformity. Electrochemical studies prove that the coatings exhibit varying levels of corrosion protection. In vitro and in vivo experiments of the three different micro-arc oxidation coatings prove high biocompatibility towards adult stem cells (investigation of cell adhesion, proliferation and osteogenic differentiation), as well as in vivo biocompatibility (including histological analysis). These results demonstrate superior biological properties compared to unmodified titanium surfaces. The ratio of calcium and phosphorus in coatings, as well as their phase composition, have a great influence on the biological response of the coatings.

In this work, the properties of the coatings formed on the Mg-Mn-Ce alloy by plasma electrolytic oxidation (PEO) in electrolytes containing halloysite nanotubes (HNTs) were investigated. The incorporation of halloysite nanotubes into the PEO coatings improved their mechanical characteristics, increased thickness, and corrosion resistance. The studied layers reduced corrosion current density by more than two times in comparison with the base PEO layer without HNTs (from 1.1 × 10−7 A/cm2 to 4.9 × 10−8 A/cm2). The presence of halloysite nanotubes and products of their dihydroxylation that were formed under the PEO conditions had a positive impact on the microhardness of the obtained layers (this parameter increased from 4.5 ± 0.4 GPa to 7.3 ± 0.5 GPa). In comparison with the base PEO layer, coatings containing halloysite nanotubes exhibited sustained release and higher adsorption capacity regarding caffeine.

This paper presents a method for the formation of composite-polymer-containing coatings on MA8 Mg alloy by plasma electrolytic oxidation (PEO), followed by the deposition of a fluoropolymer from an aqueous suspension of superdispersed polytetrafluoroethylene. The Scanning Electron Microscope(SEM), Energy Dispersive Spectroscopy(EDS), and X-ray Diffraction(XRD) analyses established morphological features as well as elemental and phase composition of composite coatings. The fact that the pores are filled with a fluoropolymer has been experimentally confirmed. An assessment of the corrosion properties of formed composite coatings revealed a decrease in the corrosion current density by more than four orders of magnitude in comparison with the base PEO layer. The highest resistance to the damaging effects of a corrosive environment, according to the results of long-term exposure tests, was demonstrated by coatings after three treatments with polytetrafluoroethylene. The obtained polymer-containing coatings have antifriction properties, reducing the wear of the coatings by more than 27-fold in comparison with the base PEO layer. It was revealed that composite coatings have superhydrophobic properties: the value of the contact angle reaches 154°, and the hysteresis of the contact angle is less than 10°.

The plasma electrolytic oxidation is an innovative method for the surface treatment of titanium and its alloys. This review provides an overview of the historical development of the process and summarizes the current state of the art. The chemical as well as the electro- and plasma-chemical basics of the layer forming mechanisms, which comprises the substrate/electrolyte interface before discharge initiation and the different types and stages of plasma electrolytic discharge phenomena are explained within the context of titanium-based materials. How these phenomena can be influenced by the use of suitable electrolytes and controlled by the electrical regime is described. Subsequently, the microstructures and composition of the layers are described in detail, and the properties for specific applications are then discussed. The resistance of a PEO coating to corrosive environments, tribological factors, and alternating mechanical stress is viewed critically, and the extensive functional properties such as physiological compatibility, photocatalytic activity, and decorative properties are revealed. Finally, examples of various practical applications in the medical engineering, aviation, automotive, and environmental technology fields, as well as other branches of industry, are presented.

The gray-colored oxygen-deficient TiO2–δ(B) nanobelts have been synthesized through a combination of the hydrothermal method followed by an ion exchange process and vacuum annealing. Electron paramagnetic resonance reveals an existence of F-centers in the form of electron-trapped oxygen vacancies within the anionic sublattice of the gray bronze TiO2 that induces its colouration. The diffuse reflectance spectroscopy showed that the formation of oxygen vacancies into TiO2(B) significantly increases its absorption intensity in both visible and near infrared ranges. The band gap of TiO2(B) with anionic defects is equal to 3.03 eV (against 3.24 eV for white TiO2(B) treated in air). Room temperature ferromagnetism associated with the defects was detected in gray TiO2–δ(B), thus indicating it belongs it to the class of dilute magnetic oxide semiconductors. It was found that in the low-temperature range (4 K), the magnetic properties of vacuum annealed TiO2(B) do not differ from those for TiO2(B) treated in air. We hope that the findings are defined here make a contribution to further progress in fabrication and manufacturing of defective TiO2-based nanomaterials for catalysis, magnetic applications, batteries, etc.

This paper presents the results of an evaluation of anti-icing properties of samples obtained by plasma electrolytic oxidation (PEO) with a subsequent application of superdispersed polytetrafluoroethylene (SPTFE) and polyvinylidenefluoride (PVDF). A combined treatment of the samples with SPTFE and PVDF is also presented. It is revealed that impregnation of a PEO layer with fluoropolymer materials leads to a significant increase in surface relief uniformity. Combined PVDF–SPFTE layers with a ratio of PVDF to SPTFE of 1:4 reveal the best electrochemical characteristics, hydrophobicity and icephobic properties among all of the studied samples. It is shown that the decrease in corrosion current density Ic for PVDF–SPFTE coatings is higher by more than five orders of magnitude in comparison with uncoated aluminum alloy. The contact angle for PVDF–SPFTE coatings attain 160.5°, which allows us to classify the coating as superhydrophobic with promising anti-icing performance. A treatment of a PEO layer with PVDF–SPFTE leads to a decrease in ice adhesion strength by 22.1 times compared to an untreated PEO coating.

Nanocrystalline layer-structured monoclinic Na2Ti3O7 is currently under consideration for usage in solid state electrolyte applications or electrochemical devices, including sodium-ion batteries, fuel cells, and sensors. Herein, a facile one-pot hydrothermal synthetic procedure is developed to prepare self-assembled moss-like hierarchical porous structure constructed by ultrathin Na2Ti3O7 nanotubes with an outer diameter of 6–9 nm, a wall thickness of 2–3 nm, and a length of several hundred nanometers. The phase and chemical transformations, optoelectronic, conductive, and electrochemical properties of as-prepared hierarchically-organized Na2Ti3O7 nanotubes have been studied. It is established that the obtained substance possesses an electrical conductivity of 3.34 × 10−4 S/cm at room temperature allowing faster motion of charge carriers. Besides, the unique hierarchical Na2Ti3O7 architecture exhibits promising cycling and rate performance as an anode material for sodium-ion batteries. In particular, after 50 charge/discharge cycles at the current loads of 50, 150, 350, and 800 mA/g, the reversible capacities of about 145, 120, 100, and 80 mA∙h/g, respectively, were achieved. Upon prolonged cycling at 350 mA/g, the capacity of approximately 95 mA∙h/g at the 200th cycle was observed with a Coulombic efficiency of almost 100% showing the retention as high as 95.0% initial storage. At last, it is found that residual water in the un-annealed nanotubular Na2Ti3O7 affects its electrochemical properties.

Today, osteoporosis has become a major global health issues. The World Health Organization declares that 320 billion people have osteoporosis now, and more than 1.5 billion osteoporosis traumatic events occur every year. Bones become fragile and fracture risk is high; thus, it is crucial to choose the right biodegradable implants in order to minimize reoperations of patients with systemic osteoporosis. This investigation aimed to carry out a morphological assessment of the state of bone tissue with osteosynthesis of a femoral fracture in rats, using a model of osteoporosis with the installation of magnesium alloy implants coated with hydroxyapatite and sealed with polytetrafluoroethylene. According to this study, the indicators of angiogenesis and bone formation in experimental animals were significantly higher when an implant coated with hydroxyapatite sealed with polytetrafluoroethylene was used, compared to an implant coated only with hydroxyapatite and in rats without an implant. Based on the data obtained, it is possible to consider a magnesium implant coated with hydroxyapatite and sealed with polytetrafluoroethylene as a promising material for fracture therapy in patients with reduced bone density.

Magnesium is very light metal which possesses many useful properties, such as a high strength to weight ratio and good electrical and thermal conductivity. Magnesium and its alloys can be used in implant surgery as biodegradable materials. Taking into account the rapid degradation process of Mg alloys in chloride-containing solutions and the very complex composition of human body media, it is worthwhile to study the mechanism and kinetics of Mg alloy corrosion in solutions which closely resemble those of human body fluids. A comparative analysis of the corrosion activity of MA8 magnesium alloy (intended to be a bioresorbable material) in a medium for the cultivation of mammalian cells (minimum essential medium, MEM) and 0.83% NaCl solution was performed using the scanning vibrating electrode technique; local pH measurements; hydrogen evolution tests; and OCP, PDP, and EIS tests. Corrosion products formed on the alloy surface were characterized using XRD, SEM-EDX analysis and Raman spectroscopy. The hydrogen evolution rate was higher for samples in NaCl solution compared with MEM. The impedance modulus in the frequency range from 105 Hz down to 10−1 Hz for the sample immersed in MEM was higher than that for the sample immersed in NaCl. This indicates higher protective ability of the corrosion film formed in MEM compared to that formed during immersion in NaCl solution. Ca- and P-rich deposits were formed in the corrosion layer. The model of corrosion mechanism of MA8 magnesium alloy in MEM, which includes three stages of the development of corrosion product film, is hereby proposed. The corrosion product layer formation on the surface of the magnesium alloy sample in MEM), which included magnesium-substituted hydroxyapatite, stabilized the local pH below 9.0 and, along with the organic acids, did not allow the pH to increase during the corrosion of the Mg alloy. The obtained results indicate the prospect of using bioresorbable magnesium in implant surgery [1,2].