Plasma Electrolytic Oxidation Process Research Articles

Improvement of biomedical properties of PEO-treated titanium with flurbiprofen and exosome conjugation

Exosome (EXO)-based drug delivery systems have attained a desirable position among scientific researchers and in biomedical applications. In this study, an exosomal coating comprising the anti-inflammatory drug flurbiprofen (FLB) was applied on a commercially pure titanium (cp-Ti) substrate that had undergone surface treatment using plasma electrolytic oxidation (PEO) process. The samples were characterized through field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and water contact angle (WCA) measurement. The results indicated that FLB was loaded onto the EXO and the formation of FLB.EXO was confirmed by FTIR, XRD, AFM and FESEM. Furthermore, FLB.EXO system was treated on PEO-treated substrates and FLB.EXO@PEO system demonstrated a considerable degree of roughness (Ra= 51.16 nm) and exceptional WCA (37.2 ± 0.7 ̊) in comparison to the other samples. The cellular inquiries were assessed through examination of the morphology of bone marrow mesenchymal stem cells (BMMSc) and the MTT assay. The cytotoxicity assessment showed that the FLB.EXO@PEO improved BMMSCs attachment without toxicity. The antibacterial efficacy was determined by means of bacterial adhesion testing against both gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) bacterial strains. FLB.EXO@PEO sample also revealed an excellent antibacterial rate of ∼ 86 % against S. aureus and ∼ 55 % against E. coli. Additionally, in vitro drug release evaluations indicated that sustained drug release was occurred and FLB released from FLB.EXO@PEO during 191 h that was lower than release time in FLB.EXO (120 h). Moreover, the prolonged release was confirmed by constant release rate in both of systems of FLB.EXO and FLB.EXO@PEO after 191 h and 167 h, respectively. The release kinetic of FLB.EXO and FLB.EXO@PEO followed the zero order and first-order model, respectively. Overall, the results indicate that the designed sustained release system have a high potential for development of advanced biomedical implants.

Experimental Design of the Adhesion between a PEI/Glass Fiber Composite and the AA1100 Aluminum Alloy with Oxide Coating Produced via Plasma Electrolytic Oxidation (PEO)

In this study, the AA1100 aluminum alloy underwent the plasma electrolytic oxidation (PEO) process to enhance its adhesion to a thermoplastic composite of polyetherimide (PEI) reinforced with glass fiber, following ASTM D1002:10 standards. A 23 factorial design was employed, varying three parameters in the oxidation process: immersion time, applied electric potential, and electrolyte concentration (Na2B4O7). The joining of aluminum and thermoplastic composite samples was achieved through oxy-fuel welding (OFW), using oxygen and acetylene gases. For the characterization of the joined samples, a universal tensile testing machine was utilized with a displacement speed of 1.5 mm/min. The analysis of the oxide coating involved scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). Through variance analysis, it was determined that the statistical model encompasses approximately 80% of the variability in the adhesion process between materials. An improvement of up to 104% in adhesion between the materials was observed with the process, indicating an effective bond due to the presence of the thermoplastic matrix in the treated aluminum sample. This improvement is attributed to the morphology of the oxide coating, resembling corals, with micro-pores and recesses that facilitated mechanical anchoring.

Improved bioactivity and corrosion resistance of NbO containing plasma electrolytic oxidation coating on ZM21 Mg alloy

ABSTRACT The present study reports the effect of niobium oxide (NbO) phase on the microstructure, corrosion, and bioactivity of coating on ZM21 Mg alloy by plasma electrolytic oxidation (PEO) process. NbO containing coatings are obtained by adding Potassium Niobate (KNbO3) along with the base electrolyte system, while the base electrolyte system consisted of sodium phosphate (Na3PO4⋅12 H2O) and potassium hydroxide (KOH). X-Ray Diffraction (XRD) was used for phase analysis, and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) was employed to extract the microstructural features. Tafel curves were generated to study the corrosion behaviour, and bioactivity test was conducted in the simulated body fluid (SBF) for 14 days to study the bioactivity. XRD results revealed that the PEO coatings consisted of MgO phase, whereas the sample coated in the electrolyte containing KNbO3 showed NbO phase in addition to MgO phase. NbO containing coating showed higher corrosion resistance and excellent bioactivity.

Large amplitude voltage oscillations during plasma electrolytic oxidation (PEO) of niobium and their correlation with the porous morphology

Plasma electrolytic oxidation (PEO) is a technique that has been widely studied to obtain thick anodic oxide coatings based on aluminum, titanium, niobium, and other valve metals. In the case of niobium oxides, they are attractive because of their properties as semiconductors, biocompatibility, and high corrosion resistance. The electrochemical behavior during this process can vary according to the PEO parameters and influence characteristics such as coating thickness, adherence, morphology, and crystalline structure of the oxide film. In this study, unusual voltage oscillation transients are observed during the anodization of niobium under a galvanostatic PEO regime. The niobium substrates were anodized in three different electrolytic solutions (H3PO4, KOH, and C2H2O4), and the influence of temperature on the oscillation aspects in each one was investigated. In addition, three different current densities were tested to check the effect of this parameter on voltage oscillations. Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and X-ray Diffraction (XRD) are used to characterize the samples. The results indicate a relationship between the exposed surface area and the pore morphology during the film growth in the oscillatory regime. A simultaneous process of oxide dissolution/pore filling and the micro-discharges observed during the PEO process is proposed.

Hierarchically porous surface of HA-sandblasted Ti implant screw using the plasma electrolytic oxidation: Physical characterization and biological responses.

The surface topological features of bioimplants are among the key indicators for bone tissue replacement because they directly affect cell morphology, adhesion, proliferation, and differentiation. In this study, we investigated the physical, electrochemical, and biological responses of sandblasted titanium (SB-Ti) surfaces with pore geometries fabricated using a plasma electrolytic oxidation (PEO) process. The PEO treatment was conducted at an applied voltage of 280V in a solution bath consisting of 0.15mol L-1 calcium acetate monohydrate and 0.02mol L-1 calcium glycerophosphate for 3 min. The surface chemistry, wettability, mechanical properties and corrosion behavior of PEO-treated sandblasted Ti implants using hydroxyapatite particles (PEO-SB-Ti) were improved with the distribution of calcium phosphorous porous oxide layers, and showed a homogeneous and hierarchically porous surface with clusters of nanopores in a bath containing calcium acetate monohydrate and calcium glycerophosphate. To demonstrate the efficacy of PEO-SB-Ti, we investigated whether the implant affects biological responses. The proposed PEO-SB-Ti were evaluated with the aim of obtaining a multifunctional bone replacement model that could efficiently induce osteogenic differentiation as well as antibacterial activities. These physical and biological responses suggest that the PEO-SB-Ti may have a great potential for use an artificial bone replacement compared to that of the controls.

Mechanism of plasma electrolytic oxidation in Mg3ZnCa implants: a study of double-layer formation and properties through nanoindentation

Plasma electrolytic oxidation (PEO), applied to light metals such as titanium, aluminum, and magnesium, creates a two-layer coating and has become increasingly important in metal coatings. However, due to the high voltage and temperature of the process, no online instrument could monitor the underlying mechanism. This paper presents a new image proving that the surface of PEO-coated Mg3ZnCa boiled during the process and argues that three hypotheses are involved in the PEO mechanism based on boiling caused by tolerating high voltage during the PEO process, which could explain the current‒voltage diagram of the process. Finally, nanoindentation was used to measure the elastic module and hardness of the PEO layers. The nanoindentation test results revealed the similarity of the elastic module of the outer porous layer and the primary alloy, with values of 40.25 GPa and 41.47 GPa, respectively, confirming that the outer porous layer corresponds to the cold plasma-gas phase formed during the PEO process.

Effects of dispersed α-Al2O3 particles into a cold-sprayed aluminium coating on its subsequent oxidation by the PEO process

The present study focused on the use of a duplex surface treatment combining cold-spray deposition and plasma electrolytic oxidation (PEO) to produce an aluminium metal matrix composite coating, including dispersed α-Al2O3 particles, with improved tribological properties. Al/α-Al2O3 composite coatings were first deposited by cold-spray, with various thickness and proportion in α-Al2O3 particles, and, then partially oxidized by PEO under various processing durations and sparking regimes (arcs or soft regime). The feasibility of cold-spraying thick, compact and adherent aluminium coatings containing well-dispersed α-Al2O3 particles (up to 14 vol%) was demonstrated in this work. It was also pointed out that the addition of hard α-Al2O3 particles into the spray composition tends to densify the deposited aluminium coating. This was related to a stronger peening effect which, in turn, decreases the growth kinetic of the subsequent PEO oxide layer. The presence of dispersed α-Al2O3 particles was found to promote the formation of the corundum alumina phase in the PEO oxide layer by triggering the transition to the soft sparking regime earlier. It was also observed that dispersed α-Al2O3 particles remain unaffected throughout the PEO oxide layers formed within the conventional arcs sparking regime while they undergo a morphological transformation within the specific soft sparking regime. This was explained by considering the different type of micro-discharges that initiate during each regime. Finally, sliding wear tests revealed that the incorporation of α-Al2O3 particles into the cold-sprayed coating resulted in a slight decrease in the friction coefficient and the wear rate of the produced PEO layers.

Ceramic metal oxide coatings formation by hybrid plasma electrolytic treatment: Interaction scenarios of ceramic NPs with oxide layers

Understanding the formation of protective ceramic metal oxide (CMO) coatings (layers) on the surface of light alloys remains a pressing task in light of products operating in extreme conditions. Plasma electrolytic oxidation (PEO) of light alloy surfaces has recently been modified by introducing various ceramic nanoparticles (NPs) into the electrolyte to perform hybrid plasma electrolytic treatment (HPET). In this work, the general and distinctive features of the interaction mechanisms of TiC, SiO2 and ZrO2 nanoparticles (NPs) with the CMO coating formed by HPET of Al–Si and Mg-based alloys were summarized and theoretically substantiated. The interaction of charged ceramic NPs accelerated by an electric field with the oxide layer is determined by transformation of the NPs kinetic energy into heating and plastic deformation, into phase transformations, as well as into the creation of new surface defects. One of the controlling factors is the ratio of the particle and the oxide layer hardnesses. In the case of SiO2 in Al–Si alloys, the formed coating is harder than the ceramic NPs while in other cases, the NPs are harder than the CMO coating, which determines the different scenarios for the interaction of NPs with the coating under HPET. In summary 7 different scenarios for the interaction of ceramic NPs added to the electrolyte with the СМO layer during its formation put forward, which depending on the ratio of the hardness of the CMO layer and the added particles, temperature/pressure conditions of the phase transformations in the NP (including its melting), the particles size distribution and the base PEO process parameters.

Characterization of V-containing black plasma electrolytic oxide coatings on aluminium alloy: Impact of base electrolytes

Black oxide coatings on 6061 Al alloy were produced by plasma electrolytic oxidation (PEO) process in silicate- and phosphate-rich base electrolytes with addition of ammonium metavanadate (NH4VO3), respectively. The characteristics of PEO processes and resulting coatings were investigated. The thermal control properties of the coatings were measured. The corrosion protection performances of the coatings in an acidic environment were evaluated. Results show that the base electrolytes have significant influence on the PEO discharge behavior, coating characteristics and properties. There are more intensive discharges in silicate-rich electrolyte with addition of NH4VO3 (denoted as “Si–V″) than that in phosphate-rich electrolyte with addition of NH4VO3 (denoted as “P–V”), leading to higher thickness and more defects for the Si–V coating. Both Si–V and P–V coatings are characterized by black color in appearance due to the formation of V-containing compounds. However, the P–V coating has higher contents of V-containing compounds and therefore lower lightness and higher solar absorptance (αs) than the Si–V coating. In addition, the P–V coating exhibits better corrosion protection performance and color durability compared with the Si–V coating in acidic NaCl solution (pH = 3.1⁓3.3) due to the formation of AlPO4 in the coating. It is demonstrated that phosphate-rich base electrolyte with addition of NH4VO3 is a good candidate for getting stable black therm control coatings on Al alloy for practical applications in harsh environment.

Corrosion and biological study on biofunctionalized porous coating on titanium produced by plasma electrolytic oxidation

BackgroundUpon implantation of biomaterials in human body, the risk for electrochemical corrosion within the surrounding environment becomes a critical factor affecting implant biocompatibility. This study endeavors to develop a biofunctionalized and corrosion-resistant TiO2/hydroxyapatite coating using a cost-effective one-step plasma electrolytic oxidation (PEO) process. Initially, magnesium and zinc substituted hydroxyapatite (HA) particles were synthesized to enhance bioactivity and antibacterial properties compared to pure HA. The synthesized particles underwent characterization using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Subsequently, these synthesized particles were utilized in the Plasma Electrolytic Oxidation (PEO) coating process. Polarization and electrochemical impedance spectroscopy (EIS) tests, in addition to bioactivity and antibacterial activity assessments, were conducted to examine the corrosion resistance and biological response of the coatings. The results of biological tests on particle-containing PEO coatings on titanium demonstrated a significant improvement in the bioactivity and antibacterial activity of the biofunctionalized coatings caused by ion-substituted HA particles. Furthermore, polarization and EIS results indicated superior corrosion resistance in the biofunctionalized coatings. Electrochemical tests after one week of immersion in simulated body fluid (SBF) revealed the positive influence of apatite formation on the long-term corrosion behavior of coatings with ion-substituted particles.

Photoelectrocatalytic and photocorrosion behavior of MoS2- and rGO-containing TiO2 bilayer photocatalyst immobilized by plasma electrolytic oxidation

TiO2-based bilayer photocatalysts including MoS2 light-absorbing and rGO conductive layers were immobilized on titanium supports using the plasma electrolytic oxidation process. Their properties were studied to find out the photoelectrocatalytic activity and photocorrosion stability. Investigating the immobilization process revealed that the formation of the bilayer structure increased the photocatalyst's surface porosity, thickness, and roughness. The preparation of the MoS2/TiO2 and rGO/TiO2 layers synergistically enhanced the light-harvesting capability of the photocatalyst in the visible region and slowed down the recombination of the photoinduced charge carriers. The bilayer photocatalyst improved the photoelectrodegradation kinetics of methylene blue pollutant by 1.6 times under 100 W xenon irradiation and 5 V applied bias. Evaluating the photocorrosion stability in sulfate medium by potentiodynamic polarization and electrochemical impedance spectroscopic analysis confirmed that the polarization resistance of the bilayer photocatalyst improved by 4.5 and 3.8 times compared to the pure TiO2 photocatalyst under dark and xenon light, respectively. Moreover, the Mott-Schottky experiment denoted that the corrosive ion adsorption was reduced in the bilayer photocatalyst.

Improved corrosion resistance of AZ31B Mg alloy by eco-friendly flash-PEO coatings

The aim of this work was the preparation of an environmentally friendly protective coating on the AZ31B alloy using Flash plasma electrolytic oxidation (F-PEO) process. It was developed with different electrolyte compositions, that determine the morphology and properties of the coatings, this being crucial to understand the anti-corrosion properties. The incorporation of carbonate ions to the electrolyte proved to enhance the electrical response of the F-PEO process, resulting in a more efficient process with an energy reduced consumption of 1.1 kW h m−2μm−1. Surface and cross-sectional morphology analysis of the coatings revealed the presence of isolated pores structure with small pore size (less than 1 µm) that delays the infiltration of aggressive ions towards the substrate. The characterisation by XRD, EDX and Raman spectroscopy showed the presence of amorphous carbonate and phosphate phases in the FPEO-CO layer, that provide a self-restauration effect through a dissolution/reprecipitation mechanism. The lowest value of the corrosion current density was obtained for FPEO-CO coating, 4.60 × 10−7 A·cm−2, together with the highest impedance modulus (f<0.1 Hz), ⁓104 Ω·cm2, two orders of magnitude higher than the AZ31B Mg alloy. Furthermore, the corrosion protection properties of FPEO-CO coating were also analysed through an immersion test in 3.5 wt.% NaCl, confirming the excellent response of the coating for long times up to 336 h (2 weeks). The synergy between a more compact coating and the self-repairing ability of carbonate amorphous species plays a critical role in improving the corrosion resistance properties of the AZ31B Mg alloy, offering an eco-friendly alternative to chromate conversion coatings.

Fabrication and characterization of graphene oxide/zirconium dioxide coatings produced by plasma electrolytic oxidation of Zr–1%Nb alloys

In this investigation, a graphene oxide (GO)/zirconium dioxide (ZrO2) composite coating was fabricated on Zr–1%Nb alloy by plasma electrolytic oxidation (PEO) process to improve the wear behavior and reduce friction performance of the Zr alloy. The GO-containing composite coating was mainly composed of the monoclinic (m-ZrO2) and tetragonal (t-ZrO2) phases and had a higher intensity of surface reactions, density, and thickness than the GO-free coating. Furthermore, the GO-containing coating exhibited lower icorr and more positive Ecorr than the GO-free coating. The optimal amount of GO sheets for improving the composite coating properties was found to be 2 wt%; use of more than 2 wt% of the GO sheets, however reduced the coating properties due to the increase in the conductivity of the electrolyte, the creation of stronger micro-discharges on the surface of the coating, and their aggregation. Additionally, the GO sheets improved the hydrophobicity of the PEO coating.

Photocatalytically active Ag-doped TiO2 coatings developed by plasma electrolytic oxidation in the presence of colloidal Ag nanoparticles

The plasma electrolytic oxidation process of Ti foil in the presence of a colloidal solution of Ag nanoparticles was used for the synthesis of exceptionally photocatalytically active Ag-doped TiO2 coatings. UV–Vis absorption spectroscopy was applied to follow the changes in the surface plasmon resonance band of the Ag nanoparticles as a function of the Ag:PO43− ratio in a phosphate-based electrolyte solution. Transmission electron microscopy revealed the size of the Ag nanoparticles in the range of 3–12 nm. The XRD patterns of the Ag-doped TiO2 coatings confirmed the crystalline anatase TiO2 phase regardless of the dopant concentration and without metallic Ag or crystalline Ag oxide forms. The typical porous morphology of the Ag–TiO2 coatings was observed by scanning electron microscopy. A significantly improved photocatalytic activity of the Ag–TiO2 coatings in the degradation process of the insecticide lindane (gamma isomer of benzene hexachloride) and test molecule methyl orange compared to pure TiO2 was determined using the GC technique. The degradation efficiency of Ag-doped TiO2 coatings is higher for lindane than for methyl orange.

Activating continuous dislocation pinning enhanced toughness of nanocomposite coating through specially oriented semicoherent heterointerface lattice distortion

Ionic crystal ceramics are known to be susceptible to brittle cracks along the intergranular due to the strong ionic bond forces. Accordingly, an outstanding toughened coating consisting of yttria-stabilized tetragonal zirconia (YSTZ) and MgO, with a reinforced heterointerface, has been successfully achieved through the plasma electrolytic oxidation process. The results demonstrate that the enhanced Zr/Y–O bond strength improves the interfacial strength of the ionic crystal, while the lattice distortion activates continuous dislocation pinning at the (101) YSTZ//(111) MgO semicoherent heterointerface effectively hinders crack propagation of the coating. With the YSTZ content approaching 65 %, the toughness (KIC) value surpasses that of PEO coating by 42 %. These findings not only elucidate the scientific foundation for the improved toughness of the YSTZ/MgO nanocoating but also provide valuable insights into design strategies for improving ceramic toughness.

Enhancing corrosion resistance in Mg[sbnd]Li alloy through plasma electrolytic oxidation coatings — Exploring the impact of ionic liquids (BmimBF4)

The wide application of MgLi alloys is limited by the poor corrosion resistance, which needs to be improved by surface treatment. Plasma electrolytic oxidation (PEO) method is one of the most promising methods for the formation of oxide coatings on MgLi alloys. However, the conventional PEO technique with high energy consumption causes poor coating compactness and hampers efforts to enhance corrosion resistance. In this study, various concentrations of ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, BmimBF4) are introduced into the concentrated alkaline electrolyte to facilitate the formation of a PEO coating on the surface of LA91 magnesium‑lithium (MgLi) alloy. The influence of BmimBF4 on PEO coatings has been investigated. The results indicate that a concentrated electrolyte significantly lowers the working voltage of PEO, thereby enhancing energy efficiency. Uneven adsorption on the substrate surface, resulting from the low concentration of BmimBF4 (≤20 mL/L) in the electrolyte, induces partial discharge, leading to high surface roughness and the formation of large pores. However, when an excessive amount of BmimBF4 (>20 mL/L) is present, it uniformly adsorbed onto the substrate surface during the initial stage of PEO process, forming a corrosion inhibitor layer. This leads to a consistent discharge on the surface of substrate throughout the entire PEO process, resulting in a reduction in both surface roughness and micropore size. Among these coatings, the one prepared in an electrolyte containing 20 mL/L BmimBF4 exhibits the highest contact angle (66.8° ± 3.8°) and the best long-term corrosion resistance (hydrogen evolution rates <0.02 mL·cm−2·h−1). These properties can be attributed to the physical and chemical adsorption of BmimBF4, which contains hydrophobic long alkyl chains, as well as the maximum thickness with extended discharging channels. This study offers a guiding strategy for further reducing energy consumption and enhancing the corrosion resistance of PEO coatings.

Cu ions release and the formation of CuO/Cu2O during PEO based on the work function

The Cu ions release was investigated by the work function by scanning kelvin probe (SKP), and the formation of CuO/Cu2O was also researched by recording plasma discharges during plasma electrolytic oxidation (PEO) of Ti-14Cu alloy with different morphologies Ti2Cu phase. It is found that L-Ti2Cu phases with lower work function enhances the escape of Cu valence electrons from the 4 s energy level more easily compared to the G-Ti2Cu and GL-Ti2Cu phases. Consequently, this leads to earlier Cu ions released from L-Ti2Cu phases as opposed to the G-Ti2Cu and GL-Ti2Cu phases. The earlier Cu+ released from L-Ti2Cu phases increases the formation of Cu2O and further oxidizes into CuO with increasing voltage, which lead to the enhanced the relative content of CuO. This enhancement contributes to improving antibacterial activity and tribocorrosion resistance due to stress response and lubrication effect by high relative content of CuO. This research provides a theoretical reference for the metal ions release of Ti-14Cu alloy in oxidation dissolution process of PEO and the formation of corresponding metal oxides.

Effect of electrolyte composition on the formation of PEO coatings on AA2024 aluminium alloy

Since the electrolyte composition plays a crucial role in the plasma electrolytic oxidation (PEO) coating formation process, a systematic and in-depth study was proposed to identify an electrolyte composition for fast PEO coating growth on AA2024 alloy. Different concentration ratios of mixed alkaline electrolytes (hydroxide, silicate and phosphate) were investigated. PEO process was conducted at low constant current density of 50 mA/cm2, which is intended for lowering the energy consumption. Results demonstrated that the breakdown voltage of PEO coatings is directly proportional to the logarithm of electrolyte resistivity. The coating growth mechanism showed two main directions. The thickening of the coating mainly depends on the rapid deposition of electrolyte compounds in Si-based electrolyte, and the coating growth occurs mainly towards the electrolyte/coating interface. Contrary, in OH-, and P-based electrolytes, the inward coating growth was dominating mainly by substrate oxidation. A variety of phases as a function of different electrolyte compositions and final voltages were observed. With high final voltages (over 470 V) for coatings produced in mixed electrolytes with low concentrations of hydroxide, silicate or phosphate (2 and 6 g/L), γ-Al2O3 crystalline phase predominates in the PEO layer composition. However, only a low efficiency of coating growth can be reached. In the electrolytes with high silicate concentrations accompanied by an increase of phosphate concentration, the final voltage is around 455 V and the coating composition is dominated by an amorphous phase in combination with crystalline mullite and γ-Al2O3. High silicate-phosphate contents (18–24 g/L) in mixed electrolytes with low final voltages of about 360 V results in a fully amorphous PEO layer and significantly increases coating thickness. A combination of low content of hydroxide, high silicate with increasing content of phosphate in mixed electrolyte increases the coating thickness, and improves the density and uniformity of the overall PEO layers.

Assessing the wear properties of plasma electrolytic oxidation TiO2 coatings incorporated ZrO2 nanoparticles on Cp-Ti in simulated body fluid

TiO2 oxide coatings incorporated ZrO2 nanoparticles were prepared on Cp-Ti using the plasma electrolytic oxidation (PEO) process in electrolyte solutions containing dispersed ZrO2 nanoparticles. The coatings’ microstructure, roughness, and composition were characterized using scanning electron microscopy (SEM), roughness profilometry, and X-ray diffractometry (XRD) analyses, respectively. The coatings’ friction and wear characteristics were examined using a ball-on-disk sliding test in a simulated body fluid (SBF) electrolyte. The as-prepared oxide coatings had a rough and porous surface structure, primarily consisting of rutile and/or anatase TiO2, tetragonal ZrO2, and ZrTiO4. ZrO2 nanoparticles were incorporated into the TiO2 coating layers and were found on the surface or in the pores. The wear and friction behavior of the oxide coatings were influenced by the quantity of ZrO2 nanoparticles (1 g/L, 3 g/L, and 5 g/L) in the electrolyte solution. The wear resistance of coatings improved by decreasing the wear rate by about 8 % (from 2.31 × 10−6 mm3/Nm to 2.11 × 10−6 mm3/Nm) when the ZrO2 nanoparticles concentration in the electrolyte solution rose from 1 g/L to 5 g/L, because of the formation of more of harder ZrO2 and ZrTiO4 phases in the coatings.

Frequency Response Evaluation as Diagnostic and Optimization Tool for Pulsed Unipolar Plasma Electrolytic Oxidation Process and Resultant Coatings on Zirconium.

This study aims to bridge various diagnostic tools for the development of smart plasma electrolytic oxidation (PEO) technologies. PEO treatments of commercially pure Zr were carried out using the pulsed unipolar polarisation (PUP) regime with frequency sweep in an alkaline phosphate-silicate electrolyte. Methods of in situ impedance spectroscopy and electrical transient analysis were used for the process diagnostics under the video imaging of the PEO. Two cutoff frequencies, 170-190 Hz and 620-650 Hz, were identified for the PEO-assisted charge transfer process. An equivalent circuit for the metal-oxide-electrolyte system under PUP PEO conditions was developed; from the capacitance values, two geometrical dielectric barriers were evaluated: a thinner 0.5-1 µm inner layer of the coating and a thicker 4-6 µm outer layer. These estimates were in agreement with the coating cross-sectional morphology. Based on comparing the results obtained using different techniques, the frequencies at which the uniform coatings with the best protective properties were formed were identified. For the selected electrolyte system and polarisation regime, these frequencies ranged from 2 to 5 kHz where the overall circuit reactance was minimal; therefore, the power factor was as close to one as possible. This opens the possibilities for the optimization of the pulsed PEO process and online control of unobservable surface characteristics, e.g., the thickness of the coating layers, thus contributing towards the development of smart PEO technologies.