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Calcium stearate based super-hydrophobic coating was deposited on plasma electrolytic oxidation (PEO) pre-treated magnesium substrate. The pre-treated magnesium and super-hydrophobic coating covered sample were characterized by scanning electron microscopy, X-ray diffraction and electrochemical corrosion measurements. The cytocompatibility and degradation resistance of magnesium, pre-treated magnesium and super-hydrophobic coating were analysed in terms of cell adhesion and osteoblast differentiation. The results indicate that the calcium stearate top coating shows super-hydrophobicity and that the surface is composed of micro/nanostructure. The super-hydrophobic coating covered sample shows higher barrier properties compared with the PEO pre-treated magnesium and bare magnesium. Human osteoblast proliferation, but not differentiation is enhanced by the PEO coating. Contrary, the super-hydrophobic coating reduces proliferation, but enhances differentiation of osteoblast, observable by the formation of hydroxyapatite. The combination of corrosion protection and cell reaction indicates that this system could be interesting for biomedical applications., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In-situ incorporation of layered double hydroxides (LDH) nanocontainers into plasma electrolytic oxidation (PEO) coatings on AZ91 Mg alloy has been achieved in the present study. Fumarate was selected as Mg corrosion inhibitor for exchange and intercalation into the nanocontainers, which were subsequently incorporated into the coating. It was found that the thickness and compactness of the coatings were increased in the presence of LDH nanocontainers. The corrosion protection performance of the blank PEO, LDH containing PEO and inhibitor loaded coatings was evaluated by means of polarization test and electrochemical impedance spectroscopy (EIS). The degradation process and corrosion resistance of PEO coating were found to be greatly affected by the loaded inhibitor and nanocontainers by means of ion-exchange when corrosion occurs, leading to enhanced and stable corrosion resistance of the substrate. [ABSTRACT FROM AUTHOR]

The influence of sodium dodecyl sulfate (SDS) on morphology and chemical composition of corrosion product layer formed on α-Mg matrix and cathodic Al-Mn intermetallic was systematically investigated by using FIB and TEM analysis for the first time to disclose the underlying inhibition mechanism. A porous corrosion bi-layer composed of crystalline MgO and Mg(OH) 2 was observed on both of α-Mg and Al-Mn intermetallic. It was found that a passive inner layer was deposited on α-Mg after immersion in SDS-containing NaCl solution, which can be ascribed to steady-state growth of magnesium and aluminum oxide under the protection of hydrophobic group of SDS. The inhibition mechanism of the inhibitor was mainly associated with formation of dense oxide layer on α-Mg matrix and preferential adsorption of SDS on the corrosion layer deposited on Al-Mn intermetallic. [ABSTRACT FROM AUTHOR]

The microstructure and composition of corrosion film deposited on pure Mg were systematically investigated, and for the first time DFT was used to reveal the adsorption behavior of carboxylates on the surface of corrosion layer rather than the metallic Mg. Presence of carboxylate inhibitor dramatically modified composition of the corrosion film and bonded directly with Mg atoms in the outermost MgO based corrosion layer by means of carboxyl. The bonded Mg atoms were lifted by 0.8 – 1.1 Å from their original position when abundant inhibitors started to act as complexing agent, leading to deteriorated inhibition effect. [Display omitted] • The corrosion film deposited on pure Mg was systematically investigated. • DFT was used for the first time to reveal the adsorption behavior of inhibitor on corrosion layer. • Carboxylate bonded with Mg atoms in the outermost MgO based corrosion layer. • Adsorption energy of inhibitors was found to be associated with its concentration. [ABSTRACT FROM AUTHOR]

In the present study, to understand the mechanism of Mn on inhibiting Fe-caused Mg corrosion, the corrosion behaviour of commercial pure Mg and Mg-6Mn alloy in 0.6 M NaCl solution is investigated. It is found that in Mg-6Mn alloy, Fe impurity is incorporated into Mn to form Mn (Fe) phase with Fe as solid solute. The initial galvanic corrosion cannot be reduced through converting Fe-rich phase to Mn (Fe) phase, since Mn (Fe) phase also has relatively strong cathodic activity and has much larger volume fraction than Fe-rich phase. However, the cathodic activation behaviour of pure Mg is inhibited. The cathodic activity even decreases for Mg-Mn alloy with increased exposure time, due to the reduced cathodic HER at the Mn (Fe) particles. Mn can be oxidized at the OCP of Mg-6Mn alloy, resulting in relatively dense Mn-rich corrosion film on particle surface, which separates the particle from the electrolyte and, consequently, inhibits HER. [ABSTRACT FROM AUTHOR]

Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy. In this work, the ratio of total acidity to pH (TA/pH) was applied as an indicator, and new principles regarding the design of conversion bath were proposed. The treatment bath should be composed of species that can be categorized into two groups: the first group of species that react with Mg substrate to increase the local pH at the interface; the second group that precipitate and contributes to the growth of coating. The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group. By this way, a thick and crack-free two-layered conversion coating is obtained. Moreover, the nature of the adjustment of TA/pH and the roles of the oxidizing agent and catalyst were discussed. [ABSTRACT FROM AUTHOR]

In order to enhance the corrosion resistance and biocompatibility of Mg based implants, porous MgO-CaP coatings were fabricated on commercial Mg by adding hydroxyapatite (HAp) particles in alkaline phosphate solution for plasma electrolytic oxidation (PEO) treatment. The effects of particle concentration on the coating morphology and composition were investigated under constant current PEO processing. Electrochemical impedance spectroscopy (EIS) and immersion test conducted in simulated body fluid (SBF) environment were applied to evaluate the corrosion performance of the coatings. The results showed that most HAp particles were reactively incorporated into the PEO coatings and the coating microstructure was significantly modified with increasing concentration of HA, which resulted in higher corrosion resistance in return. The consecutive growth of impedance during 72 h immersion resulted from the precipitation and deposition of CaP compound and corrosion product into the pores sealing the defects of PEO coatings. Overall, a higher concentration (20 g/L) of HAp particles addition would bring out a denser and protective PEO-HAp coating. [ABSTRACT FROM AUTHOR]

The influence of electrical parameters on microstructure and composition of coatings by plasma electrolytic oxidation (PEO) with particle addition was investigated. PEO coatings were produced on AM50 magnesium alloy from an alkaline phosphate based electrolyte (1 g/l KOH + 20 g/l Na 3 PO 4 ) with 5 g/l SiO 2 particle (1–5 μm) addition. Besides the most common electrical parameters (voltage and current density), frequency and duty ratio have effect on the uptake of particles during PEO processing. Higher duty ratio and lower frequency allow to incorporate more particles into the PEO coating. The area of the melting pools, as indicated by the size and area of the open pores on the coating surface, can be considered as one important factor to determine the particle uptake during PEO processing. [ABSTRACT FROM AUTHOR]

Amorphous plasma electrolytic oxidation (PEO) coating with sealed discharge channels can be formed in alkaline phosphate electrolyte containing montmorillonite clay particles. The effect of various concentrations of phosphate and hydroxide ions in the clay-containing electrolyte on the microstructure of the coatings was studied in the present work and correlated with the corrosion behavior. The clay particles were reactively incorporated into the coating. Single amorphous phase appears in PEO coatings produced from electrolytes containing higher concentration of phosphate. These amorphous coatings are degrading within a relatively short period in 0.5 wt% NaCl solution. Electrolytes containing higher concentration of KOH tend to produce mixed PEO coatings composed of crystalline and amorphous phases. These layers demonstrate higher corrosion resistance and degradation stability. Thus, the degradation rate of PEO coatings is governed mostly by the stability of their phase composition, which might be controlled by varying electrolyte composition. [ABSTRACT FROM AUTHOR]

Abstract: The influence of incorporating different sizes of Si3N4 particles on the microstructure and corrosion properties of a phosphate-based plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was investigated. The experiments for this study were performed in alkaline electrolytes containing 1 g/L KOH, 10 g/L Na3PO4 with and without three different sized of Si3N4 particles. The corrosion properties of PEO coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.5 wt.% NaCl solution. Microstructure observations by SEM showed that the surface morphology and composition of the PEO coating were affected greatly by particle addition. Si3N4 particles can still be found without decomposition in the final coating due to their high melting point. [Copyright &y& Elsevier]

• Porous PEO coated Mg can be sealed by sol-gel and epoxy layer. • Sealing effect is effective if the coating is dipped for longer treatment time. • The coating properties are greatly improved after post-treatment process. In the present work, post-treatment process has been applied to improve the corrosion and wear resistance of plasma electrolytic oxidation (PEO) coated AM50 Mg alloy. The microstructure, chemical composition and corrosion resistance of the PEO/organic composite coatings were studied by means of SEM, FTIR, electrochemical corrosion test and salt spray test. The wear resistance of the coatings was investigated by performing dry sliding wear test. The results showed that sol-gel and epoxy layer were efficient to seal the open pores and therefore greatly enhanced the corrosion performance of PEO coatings, while hybrid coatings sealed by epoxy layer showed better corrosion and wear resistance. It was found that relatively long dipping time applied during post-treatment process is capable of fabricating denser coatings with superior coating properties. The open pores of the PEO coating are penetrated and filled effectively after performing post-treatment process, resulting in high adhesion force for the composite coatings. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) coatings on AZ91 Mg alloy were sealed in calcium nitrate solutions at different pH values (3, 4 and 5). Sodium dodecyl sulfate (SDS) was added to study the effect of SDS on the corrosion resistance of the sealed coatings. The microstructure, chemical composition and corrosion resistance of the coatings were investigated by means of SEM, XPS, XRD and electrochemical corrosion tests. The corrosion performance of the coatings was improved due to precipitation of Ca-containing precipitate. Low pH and SDS addition enhanced hydroxyapatite precipitation and produced hydrophobic coatings with worse paint adhesion but better corrosion resistance. • The corrosion resistance of PEO coatings was enhanced by facile sealing treatment. • Ca containing precipitate was deposited on the coating surface. • The existence of SDS provides hydrophobicity and inhibition effect for the coating. • Increased hydrophobicity has negative influence on the paint adhesion of the coating. [ABSTRACT FROM AUTHOR]

Inhibition mechanism of sodium dodecyl sulphate (SDS) on Mg alloy was disclosed. Cathodic hydrogen evolution and anodic dissolution were kinetically inhibited. Oxidation reaction of the substrate is facilitated in the presence of SDS. Mg surface is covered by a hydrophobic outer corrosion layer and an inner oxide layer. The inhibition mechanism of sodium dodecyl sulfate (SDS) on Mg alloy in 3.5 wt. % NaCl solution was thoroughly investigated by means of SEM, EPMA, XPS, TEM and electrochemical corrosion tests. The active Mg surface is covered by a hydrophobic outer corrosion layer and a passive inner oxide layer in the presence of SDS, which suppress the cathodic hydrogen evolution and anodic dissolution of the substrate. The electrochemical reaction kinetics is inhibited due to adsorption of SDS in the corrosion products, while the oxidation reaction of the substrate is facilitated by the hydrophobic outer corrosion layer. [ABSTRACT FROM AUTHOR]

• A PEO/sol-gel composite coating was prepared on AZ91 Mg alloy. • Mg corrosion inhibitors were incorporated and immobilized into the coating. • The inhibitor-containing coating showed active corrosion protection and self-healing property. A PEO (Plasma Electrolytic Oxidation) /Sol-gel composite coating was prepared on AZ91 magnesium alloy. The porous layer produced by PEO was loaded with corrosion inhibitors (sodium salts of glycolic, 4-aminosalicylic and 2,6-pyridinedicarboxylic acids). Sealed with a thin sol-gel layer, this sandwich-like structure demonstrated durable barrier and active corrosion protection as shown by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The active protection mechanism ensures self-healing ability of the coating system, which was obtained by suppression of the re-deposition of impurity and/or adsorption of the impregnated inhibitors upon the exposed surface. [ABSTRACT FROM AUTHOR]

The influence of micro-sized Cr 2 O 3 particles on the corrosion, mechanical and thermal control performance of plasma electrolytic oxidation coated Mg was studied. More contents of Cr 2 O 3 particles were embedded into phosphate containing PEO coatings compared with coatings produced from silicate based electrolytes, resulting in green coatings with enhanced thermal control and mechanical property. The existence of particles has slightly improved the corrosion resistance and hardness of the coating. It was found that the absorptance of the coating was increased if higher concentration of Cr 2 O 3 particles is incorporated into the layer, which is probably ascribed to low band gap of Cr 2 O 3. [ABSTRACT FROM AUTHOR]

Biodegradable materials, especially Magnesium (Mg) and its alloys, are preferred for bone implants due to their compatibility with host tissue and biomechanical support. However, their rapid corrosion and vulnerability to structural failure, compounded by infections from antibiotic-resistant bacteria, pose significant challenges. Addressing these issues, we developed silicate-based composite coatings with varying CuO concentrations (1, 5, and 7 wt%) on Mg using plasma electrolytic oxidation (PEO). This study evaluated the coatings' surface characteristics, degradation behavior, and optimum composition. Our analyses, including XPS and EDX, confirmed the presence and influence of CuO on the coatings. We observed enhanced hydroxyapatite crystallization in CuO-doped coatings, which is critical for implant biocompatibility. These coatings also showed improved corrosion resistance and controlled ion release, likely due to silicate composition and CuO's sealing effects. Antimicrobial assays revealed that CuO concentration influenced bacterial and fungal adhesion, varying with microorganism type. Our findings demonstrate that incorporating inert copper particles into PEO coatings alters their chemical and elemental properties, enhancing bioactivity, corrosion resistance, and antimicrobial efficacy. These multifaceted improvements position our CuO-doped silicate coatings as a pioneering solution in bone implant technology, potentially setting new standards for safety, efficacy, and longevity in orthopedic and dental implants. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Silicate-based coating enriched in AgNPs were successfully prepared for first time. • The obtained coatings showed high-developed morphology. • Silver addition has positive effect on the anticorrosive properties of coating on Mg. • The presence of AgNPs in the coatings did not change their biocompatibility. Magnesium is a biodegradable material and thus could be a choice for bone fixation devices and implants with a specific purpose. This study aims to enhance the anti-corrosive, biocompatible, and antibacterial properties on magnesium-based materials through ceramic coatings formation. To achieve this the silicate-based electrolyte was used to create of Plasma Electrolytic Oxidation (PEO) coatings. During investigation the bioactive surfaces were presented by highly developed morphology with pore size from 0.008 ± 0.01 to 0.098 ± 0.14 μm2. The thickness of the coatings reached 7 μm, which provides better corrosive behaviour. The silver nanoparticles (AgNPs) added during plasma electrolytic oxidation (PEO) into a silicate electrolytic bath allowed for achieving enhanced bioactive properties of coating. It increased hydrophilicity from 118° to 62° and showed no cytotoxic effects, which made the coatings promising for further biomedical investigations. Moreover, incorporation of AgNPs into the PEO coating led to release of silver during immersion test, which enhanced antibacterial properties of the surfaces. [ABSTRACT FROM AUTHOR]

• Antibacterial PEO coatings are fabricated on pure Mg by incorporation of Ag particles. • Ag particles have been partly oxidized and incorporated into the layer. • Antibacterial rate reaches 99% for coating with high amount of Ag particles. Antibacterial plasma electrolytic oxidation (PEO) coatings have been fabricated by in-situ incorporation of Ag particles on pure Mg. It was found that the Ag particles have been partly oxidized and incorporated into the layer during coating formation process. Ag containing PEO coatings can strongly inhibit the growth of S. aureus and the antibacterial efficiency of the coatings is mainly associated with the Ag concentration in the layer. The antibacterial rate of the coating reaches 99% and is maintained to be stable when sufficient Ag particles (above 1 wt%) are incorporated into the layer. [ABSTRACT FROM AUTHOR]

Corrosion testing of bioabsorbable metallic materials is important at material selection stage and for understanding their degradation mechanisms. A large variety of different corrosive media has been reported for evaluating degradation performance. This review takes magnesium as an example and focuses on discussing the advantages, shortcomings and applicability of commonly used corrosive media. The discrepancies between the published results disclosing Mg corrosion behavior often originate from non-comparable test media. This indicates the urgent need for verified corrosion test protocols. The media selection criteria are outlined. Additionally, the discussion extends to the other bioabsorbable metallic materials, such as zinc and iron. [ABSTRACT FROM AUTHOR]

A hybrid PEO-epoxy coating was developed for magnesium. A highly-efficient corrosion inhibitor (3-methysalicylate) was impregnated into the anodized layer, which was sealed by an epoxy layer through dip-coating process. Influence of dip-coating parameters on coating properties was investigated. The corrosion performance was evaluated through general and localized electrochemical techniques. As a result, the epoxy layers registered superior resistance, whereas the anodized layer suppressed corrosion expansion. Longer immersion and triple-dipping favored the production of better sealed epoxy layer. The active protection mechanism was achieved by suppression the re-deposition of detrimental impurity and/or adsorption upon the exposed surface from incorporated inhibitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three different Mg sources were used to form PEO layers on titanium. • Bioactive Ca, P, and Mg was successfully introduced into the Ti surface during PEO. • The Mg-incorporated PEO coatings exhibited a fungi- and bacteriostatic effect. • The fungi- and bacteriostatic effect depends of the chemical form of Mg. This paper reports the surface modification of titanium via a plasma electrolytic oxidation (PEO) process in baths based on 0.1 M Ca(H 2 PO 2) 2 with Mg-containing additives: insoluble MgO or MgHPO 4 or highly-soluble Mg(CH 3 COO) 2. The surface morphology and roughness were investigated using scanning electron microscopy (SEM), which showed that porous oxide layers were formed and the roughness increased. To determine the presence of bioactive Ca and P and bacteriostatic Mg, energy-dispersive X-ray spectroscopy (EDX) analysis was performed, as well as XPS analysis and Raman spectroscopy, which proved their successful incorporation into the oxide layer. All investigated oxide coatings were continuous and the thickest one was observed on Ti-PEO-MgP surface (5.2 µm–7.5 µm). The bacteriostatic and fungistatic properties of the investigated surfaces were determined via Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Candida albicans ATCC 2091 adhesion tests. The concentration of Mg and Ti released from the PEO-modified Ti surfaces after immersion up to 14 days in Ringer's solution was evaluated via ICP-OES technique. All studied Mg-containing PEO coatings exhibited bacteriostatic and fungistatic properties, which suggests the possible application of Mg-doped titanium PEO coatings as long-term implant materials dedicated to bone tissue. [ABSTRACT FROM AUTHOR]

The influence of different constituents in silicate containing alkaline electrolytes on PEO-coated AZ91D magnesium alloy has been systematically studied using response surface methodology (RSM) coupled with electrochemical measurements and microstructure characterization methods. The results indicate that the most dominant factor that determines the coating performance is the interaction between Na 2 SiO 3 and NaOH, where better corrosion resistance could be achieved when their concentrations are tuned in different directions. Infrared spectrum analysis of the electrolytes innovatively indicates that the degree of polymerization of silicate ions (from one to two- and three-dimensional), varied by the concentration of Na 2 SiO 3 and NaOH, influences the kinetic mechanism of coating formation and thermal-driven gel-forming process under sparking. When silicates species exist as a relatively higher polymerized state, which indicates lower mobility of silicates in the electrolyte and better affinity for trapping Al 3 + to form gel-like networks, the resulting coating is inhomogeneous and susceptible to corrosive ions; otherwise, the coating is more homogeneous and exhibits improved corrosion resistance. The work herein aims to provide guidelines for designing PEO electrolyte via correlating the intrinsic nature of the electrolyte with coating properties. [ABSTRACT FROM AUTHOR]

The influence of different concentrations of 2,6-dihydroxybenzoic acid (2,6-DHB) on corrosion performance and discharge properties of AZ31 Mg alloy is studied by means of EIS, potentiodynamic polarization and half-cell discharge test. It was found that low concentration of 2,6-DHB (0.01 M) can enhance the corrosion resistance of Mg alloy, since it acts as complexing agent to decrease the self-corrosion rate and suppress cathodic hydrogen reaction. High amount of additive in NaCl solution accelerates the dissolution rate of the substrate, leading to deteriorated corrosion performance. The discharge properties of the Mg anode have been greatly modified by the presence of 2,6-DHB. 76.86% of utilization efficiency and 1668.17 mAh g−1 of specific capacity have been achieved for AZ31 Mg alloy in 3.5 wt % NaCl solution with addition of 0.01 M organic additive. High amount of complexing agent promotes self-corrosion and dissolution rate of the substrate, which is detrimental to the discharge properties of the anode. • Corrosion and discharge performance of Mg are influenced by complexing agent. • Low amount of 2,6-DHB suppress cathodic hydrogen reaction, while increased concentration accelerates anodic dissolution rate. • High concentration of additive accelerates self-corrosion rate and increases weight loss of the anode. • Utilization efficiency of AZ31 reaches 76.86% after addition of 0.1 M 2,6-DHB. [ABSTRACT FROM AUTHOR]