Special Issue "Metals Functionalization via Plasma Electrolytic Oxidation"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Physics".

Deadline for manuscript submissions: closed (31 December 2019).

Special Issue Editor

Prof. Dr. Wojciech Simka
E-Mail Website
Guest Editor
Department of Inorganic Chemistry, Analytical Chemistry and Electrochemistry, Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego Street 6, 44-100 Gliwice, Poland
Interests: anodic treatments of titanium, titanium alloys and more exotic metals; plasma electrolytic oxidation; electropolishing of valve metals; electrosynthesis of organic compounds; corrosion mitigation and bioactivity enhancement of dental and bone implants

Special Issue Information

Dear Colleagues,

Due to the specific applications of many metallic materials, studies on the use of surface modification techniques are in progress. To obtain functional coatings on different metals like Ti, Ti alloys, Mg, Al, Zr, Nb, Ta, many methods could be applied, such as electrophoretic deposition (EPD), anodic oxidation, plasma electrolytic oxidation (PEO) (which is also known as micro-arc oxidation (MAO)), chemical or physical vapor deposition (CVD, PVD), or ion implantation. Modification of the surface by anodic oxidation is relatively easy and inexpensive. It enables good adhesion to the substrate and allows for homogeneous oxide coatings to be obtained, which can be enriched with interesting compounds/elements during the process. There are two types of anodic oxidation processes. The first type involves oxidation at a voltage that is lower than the breakdown voltage of the oxide layer. Such oxidation leads to the homogenization of the natural oxide layer and alters its structure. The second type involves oxidation at a voltage higher than the breakdown voltage of the oxide layer and is called plasma electrolytic oxidation (PEO), anode spark electrolysis, or plasma electrolytic anode treatment. This technique results in the formation of numerous micropores on the anodized metal surface. The compounds from a solution can penetrate into the oxide layer during the course of the glow discharge effect on the sample substrate, which occurs during plasma electrolytic oxidation. PEO coatings offer improved surface performance, increased hardness, and better corrosion resistance. Self-passivating metals (Al, Mg, Ti, Zr, Ta) and their alloys undergo plasma electrolytic oxidation very easily. By applying such a processing method, these metals can be used in new applications. PEO process can be used to formation new types of biomaterials, catalysts, wear resistant materials, corrosion resistant materials.

Prof. Dr. Wojciech Simka
Guest Editor

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Keywords

  • plasma electrolytic oxidation
  • micro-arc oxidation
  • surface modification
  • biomaterials
  • corrosion resistance
  • catalysis

Published Papers (11 papers)

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Research

Open AccessArticle
Ag Nanoparticle-Decorated Oxide Coatings Formed via Plasma Electrolytic Oxidation on ZrNb Alloy
Materials 2019, 12(22), 3742; https://doi.org/10.3390/ma12223742 - 13 Nov 2019
Cited by 1
Abstract
Plasma electrolytic oxidation (PEO) can provide an ideal surface for osteogenic cell attachment and proliferation with further successful osteointegration. However, the same surface is attractive for bacteria due to similar mechanisms of adhesion in prokaryotic and eukaryotic cells. This issue requires the application [...] Read more.
Plasma electrolytic oxidation (PEO) can provide an ideal surface for osteogenic cell attachment and proliferation with further successful osteointegration. However, the same surface is attractive for bacteria due to similar mechanisms of adhesion in prokaryotic and eukaryotic cells. This issue requires the application of additional surface treatments for effective prevention of postoperative infectious complications. In the present work, ZrNb alloy was treated in a Ca-P solution with Ag nanoparticles (AgNPs) for the development of a new oxide layer that hosted osteogenic cells and prevented bacterial adhesion. For the PEO, 0.5 M Ca(H2PO2)2 solution with 264 mg L−1 of round-shaped AgNPs was used. Scanning electron microscopy with energy-dispersive x-ray and x-ray photoelectron spectroscopy were used for morphology and chemical analysis of the obtained samples; the SBF immersion test, bacteria adhesion test, and osteoblast cell culture were used for biological investigation. PEO in a Ca-P bath with AgNPs provides the formation of a mesoporous oxide layer that supports osteoblast cell adhesion and proliferation. Additionally, the obtained surface with incorporated Ag prevents bacterial adhesion in the first 6 h after immersion in a pathogen suspension, which can be an effective approach to prevent infectious complications after implantation. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Anodization of a Medical-Grade Ti-6Al-7Nb Alloy in a Ca(H2PO2)2-Hydroxyapatite Suspension
Materials 2019, 12(18), 3002; https://doi.org/10.3390/ma12183002 - 16 Sep 2019
Abstract
The electrochemical parameters used for surface treatments should be individually determined for each titanium alloy. In this paper, the parameters for the anodization of a medical-grade Ti-6Al-7Nb alloy in hydroxyapatite suspensions were determined. It was found that formation of a favorable porous oxide [...] Read more.
The electrochemical parameters used for surface treatments should be individually determined for each titanium alloy. In this paper, the parameters for the anodization of a medical-grade Ti-6Al-7Nb alloy in hydroxyapatite suspensions were determined. It was found that formation of a favorable porous oxide layer occurred for the plasma electrolytic oxidation process in a Ca(H2PO2)2 solution with 150 g/dm3 hydroxyapatite particles at 350 V and 450 V. The differences in the morphology, chemical and phase composition caused variability in the average surface roughness (up 4.25 μm) and contact angle (strongly hydrophilic) values. Incorporation of the hydroxyapatite ceramic particles into formed TiO2 layer also influenced the layer thickness and adhesion of the layers to the substrate. The oxide layers formed on the Ti-6Al-7Nb alloy were between 5.19 and 31.4 μm in thickness with an average range of approximately 8–15 μm. The formation of a ceramic layer under controlled electrochemical parameters allows the design of a bioactive surface of implants for bone tissue. The hydroxyapatite particles may promote the osseointegration process. Thus, in this study, the formation of ceramic composites on medical-grade Ti surfaces is presented and discussed. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Wear Resistant Coatings with a High Friction Coefficient Produced by Plasma Electrolytic Oxidation of Al Alloys in Electrolytes with Basalt Mineral Powder Additions
Materials 2019, 12(17), 2738; https://doi.org/10.3390/ma12172738 - 27 Aug 2019
Abstract
To achieve a better performance of engineering components, modern design approaches consider the replacement of steel with lightweight metals, such as aluminum alloys. However, bare aluminum cannot satisfy requirements for surface properties in situations where continuous friction is needed. Among the various surface [...] Read more.
To achieve a better performance of engineering components, modern design approaches consider the replacement of steel with lightweight metals, such as aluminum alloys. However, bare aluminum cannot satisfy requirements for surface properties in situations where continuous friction is needed. Among the various surface modification techniques, plasma electrolytic oxidation (PEO) is considered as promising for structural applications, owing to its hard and well-adhered ceramic coatings. In this work, the surfaces of two Al alloys (2024 and 6061) have been modified by PEO coating (~180 µm) reinforced with basalt minerals, in order to increase the coefficient of friction and wear resistance. A slurry electrolyte, including a silicate-alkaline solution with addition of basalt mineral powder (<5 µm) has been used. The coating composition, surface morphology, and microstructure were studied using X-ray diffraction, scanning electron, and optical microscopy. Linear reciprocating wear tests were employed for the evaluation of the friction and wear behavior. It was found that the coatings reinforced with basalt mineral showed that the wear and friction coefficients reached values 10−6–10−7 (mm3 N−1 m−1) and 0.7–0.85, correspondingly (sliding distance of 100 m). In comparison with the characteristics of resin-based materials (10−5–10−4 (mm3 N−1 m−1) and 0.3–0.5, respectively), the employment of thin inorganic frictional composites may bring considerable improvement in the thermal stability, durability, and compactness, as well as a reduction in the weight of the final product. These coatings are considered an alternative to the reinforced resin composite materials on steel used in frictional components, for example, clutch disks and braking pads. It is expected that the smaller thickness of the active frictional material (180 μm) reduces the volume of the wear products, extending the service intervals associated with filter and lubricant maintenance. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Effects of a Carbon Nanotube Additive on the Corrosion-Resistance and Heat-Dissipation Properties of Plasma Electrolytic Oxidation on AZ31 Magnesium Alloy
Materials 2018, 11(12), 2438; https://doi.org/10.3390/ma11122438 - 02 Dec 2018
Cited by 1
Abstract
Plasma electrolytic oxidation (PEO) coating was obtained on AZ31 Mg alloy using a direct current in a sodium silicate-based electrolyte with and without a carbon nanotube (CNT) additive. The surface morphology and phase composition of the PEO coatings were investigated through field emission [...] Read more.
Plasma electrolytic oxidation (PEO) coating was obtained on AZ31 Mg alloy using a direct current in a sodium silicate-based electrolyte with and without a carbon nanotube (CNT) additive. The surface morphology and phase composition of the PEO coatings were investigated through field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion-resistance properties of the PEO coatings were evaluated using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution. Furthermore, the heat-dissipation property was evaluated by a heat-flux measurement setup using a modified steady-state method and Fourier transform infrared spectroscopy (FT-IR). The results demonstrate that, by increasing the concentration of CNT additive in the electrolyte, the micropores and cracks of the PEO coatings are greatly decreased. In addition, the anticorrosion performance of the PEO coatings that incorporated CNT for the protection of the Mg substrate was improved. Finally, the coating’s heat-dissipation property was improved by the incorporation of CNT with high thermal conductivity and high thermal emissivity. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Novel Porous Phosphorus–Calcium–Magnesium Coatings on Titanium with Copper or Zinc Obtained by DC Plasma Electrolytic Oxidation: Fabrication and Characterization
Materials 2018, 11(9), 1680; https://doi.org/10.3390/ma11091680 - 11 Sep 2018
Cited by 12
Abstract
In this paper, the characteristics of new porous coatings fabricated at three voltages in electrolytes based on H3PO4 with calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and copper(II) nitrate trihydrate are presented. The SEM, energy dispersive spectroscopy (EDS), glow discharge optical [...] Read more.
In this paper, the characteristics of new porous coatings fabricated at three voltages in electrolytes based on H3PO4 with calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and copper(II) nitrate trihydrate are presented. The SEM, energy dispersive spectroscopy (EDS), glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy (XPS), and XRD techniques for coating identification were used. It was found that the higher the plasma electrolytic oxidation (PEO) (micro arc oxidation (MAO)) voltage, the thicker the porous coating with higher amounts of built-in elements coming from the electrolyte and more amorphous phase with signals from crystalline Ca(H2PO4)2∙H2O and/or Ti(HPO4)2∙H2O. Additionally, the external parts of the obtained porous coatings formed on titanium consisted mainly of Ti4+, Ca2+, Mg2+ and PO43−, HPO42−, H2PO4, P2O74− as well as Zn2+ or copper Cu+/Cu2+. The surface should be characterized by high biocompatibility, due to the presence of structures based on calcium and phosphates, and have bactericidal properties, due to the presence of zinc and copper ions. Furthermore, the addition of magnesium ions should accelerate the healing of postoperative wounds, which could lead to faster patient recovery. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Plasma Electrolytic Oxidation of Magnesium Alloy AZ31B in Electrolyte Containing Al2O3 Sol as Additives
Materials 2018, 11(9), 1618; https://doi.org/10.3390/ma11091618 - 05 Sep 2018
Cited by 1
Abstract
Plasma electrolytic oxidation (PEO) coatings were produced on AZ31B magnesium alloys in alkaline electrolytes with the addition of various concentrations of Al2O3 sols. Effects of Al2O3 sol concentrations on the microstructure, phase composition, corrosion resistance and hardness [...] Read more.
Plasma electrolytic oxidation (PEO) coatings were produced on AZ31B magnesium alloys in alkaline electrolytes with the addition of various concentrations of Al2O3 sols. Effects of Al2O3 sol concentrations on the microstructure, phase composition, corrosion resistance and hardness of PEO coatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness testing and potentiodynamic polarization measurements, respectively. It was revealed that the Al2O3 sol mostly participated in the formation of the ceramic coating and transferred into the MgAl2O4 phase. With the increase of the Al2O3 sol concentration in the range of 0–6 vol%, the coating performance in terms of the microstructure, diffraction peak intensity of the MgAl2O4 phase, corrosion resistance and microhardness was improved. Further increase of Al2O3 sol addition did not generate better results. This indicated that 6 vol% might be the proper Al2O3 sol concentration for the formation of PEO coatings. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Microstructure and Corrosion Resistance of PEO Coatings Formed on KBM10 Mg Alloy Pretreated with Nd(NO3)3
Materials 2018, 11(7), 1062; https://doi.org/10.3390/ma11071062 - 22 Jun 2018
Cited by 5
Abstract
Plasma electrolytic oxidation (PEO) technique is one of the important methods used in the surface modification of magnesium alloys. In this paper, the ceramic coatings on pretreated KBM10 magnesium alloy with Nd(NO3)3 solution were prepared by PEO. The effects of [...] Read more.
Plasma electrolytic oxidation (PEO) technique is one of the important methods used in the surface modification of magnesium alloys. In this paper, the ceramic coatings on pretreated KBM10 magnesium alloy with Nd(NO3)3 solution were prepared by PEO. The effects of Nd(NO3)3 solution concentration on the microstructure and corrosion resistance of PEO coatings on magnesium alloys were investigated by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electrochemical workstation. It was found that the surface of the coatings was porous after PEO, and element Nd could be deposited on the surface of the coatings by pretreatment and existed in the PEO coatings. The coating formed at Nd(NO3)3 solution concentration of 0.06 mol/L exhibited the best corrosion resistance among all the as-prepared coatings. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessFeature PaperArticle
Effect of DC Plasma Electrolytic Oxidation on Surface Characteristics and Corrosion Resistance of Zirconium
Materials 2018, 11(5), 723; https://doi.org/10.3390/ma11050723 - 03 May 2018
Cited by 2
Abstract
Zr is a valve metal, the biocompatibility of which is at least on par with Ti. Recently, numerous attempts of the formation of bioactive coatings on Zr by plasma electrolytic oxidation (PEO) in solutions that were based on calcium acetate and calcium β-glycerophosphate [...] Read more.
Zr is a valve metal, the biocompatibility of which is at least on par with Ti. Recently, numerous attempts of the formation of bioactive coatings on Zr by plasma electrolytic oxidation (PEO) in solutions that were based on calcium acetate and calcium β-glycerophosphate were made. In this study, the direct current (DC) PEO of commercially pure zirconium in the solutions that contained Ca(H2PO2)2, Ca(HCOO)2, and Mg(CH3COO)2 was investigated. The treatment was conducted at 75 mA/cm2 up to 200, 300, or 400 V. Five process stages were discerned. The treatment at higher voltages resulted in the formation of oxide layers that had Ca/P or (Mg+Ca)/P ratios that were close to that of hydroxyapatite (Ca/P = 1.67), determined by SEM/EDX. The corrosion resistance studies were performed using electrochemical impedance spectroscopy (EIS) and DC polarization methods. R(Q[R(QR)]) circuit model was used to fit the EIS data. In general, the coatings that were obtained at 200 V were the most corrosion resistant, however, they lacked the porous structure, which is typical for PEO coatings, and is sought after in the biomedical applications. The treatment at 400 V resulted in the formation of the coatings that were more corrosion resistant than those that were obtained at 300 V. This was determined mainly by the prevailing plasma regime at the given process voltage. The pitting resistance of Zr was also improved by the treatment, regardless of the applied process conditions. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation
Materials 2018, 11(4), 545; https://doi.org/10.3390/ma11040545 - 03 Apr 2018
Cited by 8
Abstract
Tantalum has recently become an actively researched biomaterial for the bone reconstruction applications because of its excellent corrosion resistance and successful clinical records. However, a bare Ta surface is not capable of directly bonding to the bone upon implantation and requires some method [...] Read more.
Tantalum has recently become an actively researched biomaterial for the bone reconstruction applications because of its excellent corrosion resistance and successful clinical records. However, a bare Ta surface is not capable of directly bonding to the bone upon implantation and requires some method of bioactivation. In this study, this was realized by direct current (DC) plasma electrolytic oxidation (PEO). Susceptibility to corrosion is a major factor determining the service-life of an implant. Therefore, herein, the corrosion resistance of the PEO coatings on Ta was investigated in Ringer’s solution. The coatings were formed by galvanostatic anodization up to 200, 300 and 400 V, after which the treatment was conducted potentiostatically until the total process time amounted to 5 min. Three solutions containing Ca(H2PO2)2, Ca(HCOO)2 and Mg(CH3COO)2 were used in the treatment. For the corrosion characterization, electrochemical impedance spectroscopy and potentiodynamic polarization techniques were chosen. The coatings showed the best corrosion resistance at voltages low enough so that the intensive sparking was absent, which resulted in the formation of thin films. The impedance data were fitted to the equivalent electrical circuits with two time constants, namely R(Q[R(QR)]) and R(Q[R(Q[RW])]). The inclusion of W in the circuit helped to fit the low-frequency part of the samples PEO-ed at 400 V, hinting at the important role of diffusion in the corrosion resistance of the PEO coatings described in the research. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
Rough Titanium Oxide Coating Prepared by Micro-Arc Oxidation Causes Down-Regulation of hTERT Expression, Molecular Presentation, and Cytokine Secretion in Tumor Jurkat T Cells
Materials 2018, 11(3), 360; https://doi.org/10.3390/ma11030360 - 28 Feb 2018
Cited by 1
Abstract
The response of the human Jurkat T cell leukemia-derived cell line (Jurkat T cells) after 24 h of in vitro exposure to a titanium substrate (12 × 12 × 1 mm3) with a bilateral rough (Ra = 2.2–3.7 μm) [...] Read more.
The response of the human Jurkat T cell leukemia-derived cell line (Jurkat T cells) after 24 h of in vitro exposure to a titanium substrate (12 × 12 × 1 mm3) with a bilateral rough (Ra = 2.2–3.7 μm) titanium oxide coating (rTOC) applied using the micro-arc method in a 20% orthophosphoric acid solution was studied. A 1.5-fold down-regulation of hTERT mRNA expression and decreases in CD3, CD4, CD8, and CD95 presentation and IL-4 and TNFα secretion were observed. Jurkat T cell inactivation was not correlated with the generation of intracellular reactive oxygen species (ROS) and was not mediated by TiO2 nanoparticles with a diameter of 14 ± 8 nm at doses of 1 mg/L or 10 mg/L. The inhibitory effect of the rTOC (Ra = 2.2–3.7 μm) on the survival of Jurkat T cells (Spearman’s coefficient rs = −0.95; n = 9; p < 0.0001) was demonstrated by an increase in the necrotic cell count among the cell population. In turn, an elevation of the Ra index of the rTOC was accompanied by a linear increase (r = 0.6; p < 0.000001, n = 60) in the magnitude of the negative electrostatic potential of the titanium oxide surface. Thus, the roughness of the rTOC induces an electrostatic potential and decreases the viability of the immortalized Jurkat T cells through mechanisms unrelated to ROS generation. This may be useful for replacement surgery applications of rough TiO2 implants in cancer patients. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle
The Study on the Overall Plasma Electrolytic Oxidation for 6061–7075 Dissimilar Aluminum Alloy Welded Parts Based on the Dielectric Breakdown Theory
Materials 2018, 11(1), 63; https://doi.org/10.3390/ma11010063 - 02 Jan 2018
Cited by 3
Abstract
Electrical connection of dissimilar metals will lead to galvanic corrosion. Therefore, overall surface treatment is necessary for the protection of dissimilar metal welded parts. However, serious unbalanced reactions may occur during overall surface treatment, which makes it difficult to prepare integral coating. In [...] Read more.
Electrical connection of dissimilar metals will lead to galvanic corrosion. Therefore, overall surface treatment is necessary for the protection of dissimilar metal welded parts. However, serious unbalanced reactions may occur during overall surface treatment, which makes it difficult to prepare integral coating. In this paper, an overall ceramic coating was fabricated by plasma electrolytic oxidation to wrap the 6061–7075 welded part integrally. Moreover, the growth mechanism of the coating on different areas of the welded part was studied based on the dielectric breakdown theory. The reaction sequence of each area during the treatment was verified through specially designed dielectric breakdown tests. The results showed that the high impedance overall of ceramic coating can inhibit the galvanic corrosion of the 6061–7075 welded part effectively. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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