Plasma Electrolytic Oxidation Of Titanium Research Articles

Nitrilotriacetic Acid Improves Plasma Electrolytic Oxidation of Titanium for Biomedical Applications.

Dental implants have become a routine, affordable, and highly reliable technology to replace tooth loss. In this regard, titanium and its alloys are the metals of choice for the manufacture of dental implants because they are chemically inert and biocompatible. However, for special cohorts of patients, there is still a need for improvements, specifically to increase the ability of implants to integrate into the bone and gum tissues and to prevent bacterial infections that can subsequently lead to peri-implantitis and implant failures. Therefore, titanium implants require sophisticated approaches to improve their postoperative healing and long-term stability. Such treatments range from sandblasting to calcium phosphate coating, fluoride application, ultraviolet irradiation, and anodization to increase the bioactivity of the surface. Plasma electrolytic oxidation (PEO) has gained popularity as a method for modifying metal surfaces and delivering the desired mechanical and chemical properties. The outcome of PEO treatment depends on the electrochemical parameters and composition of the bath electrolyte. In this study, we investigated how complexing agents affect the PEO surfaces and found that nitrilotriacetic acid (NTA) can be used to develop efficient PEO protocols. The PEO surfaces generated with NTA in combination with sources of calcium and phosphorus were shown to increase the corrosion resistance of the titanium substrate. They also support cell proliferation and reduce bacterial colonization and, hence, lead to a reduction in failed implants and repeated surgeries. Moreover, NTA is an ecologically favorable chelating agent. These features are necessary for the biomedical industry to be able to contribute to the sustainability of the public healthcare system. Therefore, NTA is proposed to be used as a component of the PEO bath electrolyte to obtain bioactive surface layers with properties desired for next-generation dental implants.

Plasma Electrolytic Oxidation of Titanium in Ni and Cu Hydroxide Suspensions towards Preparation of Electrocatalysts for Urea Oxidation

The increasing climate crisis requires an improvement in renewable energy technologies. One of them are fuel cells, devices that are capable of generating electricity directly from the chemical reaction that is taking place inside of them. Despite the advantages of these solutions, a lack of the appropriate materials is holding them back from commercialization. This research shows preliminary results from a simple way to prepare black TiO2 coatings, doped with Cu or Ni using the plasma electrolytic oxidation process, which can be used as anodes in urea-fueled fuel cells. They show activity toward urea oxidation, with a maximum current density of 130 μA cm-2 (@1 V vs. Hg|HgO) observed for Cu-enhanced TiO2 and low potential of only 0.742 V (Vs Hg|HgO) required for 50 μA cm-2 for Ni-enhanced TiO2. These results demonstrate how the PEO process can be used for the preparation of TiO2-based doped materials with electrocatalytic properties toward urea electrooxidation.

High photocatalytic activity of TiO2/Al2TiO5 coatings obtained by plasma electrolytic oxidation of titanium

In this work, it was shown that TiO2/Al2TiO5 coatings obtained by plasma electrolytic oxidation of titanium in alkaline electrolyte with added NaAlO2 show significantly better photocatalytic activity (PA) in degradation of methyl orange under simulated sunlight than anatase TiO2 coatings obtained in pure alkaline electrolyte. The TiO2/Al2TiO5 coating with the highest PA was obtained in alkaline electrolyte with the addition of 2.0 g/L NaAlO2, which has approximately 2.4 higher PA than anatase TiO2. Photoluminescence indicates that increased PA of TiO2/Al2TiO5 coatings is associated with increased number of oxygen vacancy and other defects.

Photocatalytic degradation of methyl orange in the presence of transition metals (Mn, Ni, Co) modified TiO2 coatings formed by plasma electrolytic oxidation

The effect of selected transition metals (Mn, Ni, Co) modified TiO2 coatings formed by plasma electrolytic oxidation of titanium on their surface morphology, phase and chemical composition, optical absorption, and photocatalytic degradation of methyl orange (MO) was investigated. Coatings were formed in an alkaline electrolyte with varying concentrations of MnO, NiO, or Co3O4 powders. The morphology, thickness and phase structure of all formed coatings are nearly identical and independent of the content of transition metal ions embedded in TiO2. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that anatase TiO2 coatings were loaded with MnO, NiO, or Co3O4 from electrolytes. When up to 2.0 g/L of MnO, NiO, or Co3O4 is added to the electrolyte, the photocatalytic activity (PA) of the forming coatings is higher than for pure TiO2. The coatings formed in electrolyte with the addition of 0.75 g/L MnO, 1.5 g/L NiO, or 2.0 g/L Co3O4 had the highest PA. Increased PA is associated with a decrease in photogenerated electron/hole recombination rate, according to UV–Vis diffuse reflectance spectroscopy and photoluminescence measurements.

TiO2/Bi2O3 coatings formed by plasma electrolytic oxidation of titanium for photocatalytic applications

TiO2/Bi2O3 coatings formed by plasma electrolytic oxidation of titanium for photocatalytic applications

Addition of Organic Acids during PEO of Titanium in Alkaline Solution

This research study describes recent advances in understanding the effects of the addition of organic acids, such as acetic, lactic, citric and phytic acids, on the process of plasma electrolytic oxidation (PEO) on Ti using an alkaline bath. As the plasma developed over the workpiece is central to determine the particular morphological and structural features of the growing oxide, the focus is then on the inter-relationships between the electrolyte and the resultant plasma regime established. In situ optical emission spectroscopy (OES) allowed us to verify a marked plasma suppression when adding low-molecular-weight anions such as acetates, resulting in short-lived and well-distributed discharges. Conversely, when more bulky anions, such as lactates, citrates and phytates, were considered, a less efficient shielding of the electrode caused the build-up of long-lasting and destructive sparks responsible for the formation of thicker coatings, even >30 µm, at the expense of a higher roughness and loss of compactness. Corrosion resistance was tested electrochemically, according to electrochemical impedance spectroscopy (EIS), and weight losses evidenced the coatings produced in the solution containing acetates to be more suitable for service in H2SO4.

One-pot plasma electrolytic oxidation synthesis of TiO2/Sb2O3 coatings for photocatalysis

Anatase TiO2 coatings modified by Sb2O3 particles were formed by plasma electrolytic oxidation of titanium in 10 g/L Na3PO4⋅10H2O with addition of Sb2O3 particles. The photodegradation of methyl orange under simulated sunlight was used to probe the photocatalytic potential of TiO2/Sb2O3 coatings. The photocatalytic activity (PA) of obtained coatings is higher than pure TiO2 for adding up to 2.0 g/L of Sb2O3 particles to electrolyte. The highest PA was observed for coatings formed in electrolyte with the addition of 0.75 g/L Sb2O3. Increased PA is related to a decrease of photogenerated electron/hole recombination rate as a result of TiO2 and Sb2O3 coupling.

Plasma electrolytic synthesis and characterization of oxide coatings with MWO4 (M = Co, Ni, Cu) as photo-Fenton heterogeneous catalysts

Titanium-supported oxide coatings with MWO4 (M = Cu, Ni, or Co) were formed by the single-stage plasma electrolytic oxidation of titanium in alkaline tungstate-phosphate electrolytes with M(II)–EDTA complex ions. All formed coatings exhibited photocatalytic activity in the reaction of degradation of methyl orange (10 mg/L MO, pH = 6.8) in the presence of 10 mmol/L hydrogen peroxide under UV and Vis irradiation. The Ti/TiO2-CoWO4 composite was most effective catalyst: the degree of MO azo dye degradation reached 85 and 55% after 180 min irradiation under UV and Vis light, respectively. The bandgap values determined by the Tauc's method for the direct allowed transition were 2.2, 2.45 and 2.5 eV for Co-, Cu- and Ni-containing samples, correspondingly. The leaching of cobalt, copper and nickel from catalysts during the degradation process was less than 0.88, 0.52 and 1.47 mg/L per cycle, but this fact did not lead to a decrease in MO degradation with the number of cycles. The degradation reaction under UV and Vis irradiation has a first order rate coefficient of (8.9–11.0) × 10−3 and (2.0–8.3) × 10−3 min−1, respectively.

A nanoscale investigation on the influence of anodization parameters during plasma electrolytic oxidation of titanium by high-resolution electron energy loss spectroscopy

High-resolution electron energy loss spectroscopy (EELS) in a transmission electron microscope is performed on titanium oxide coatings obtained by plasma electrolytic oxidation (PEO) with application of different electrical parameters. Core loss spectra were used to evaluate the structural evolution occurring at the two main regions characterizing a PEO coating, i.e. barrier and porous layers. Local crystalline information, extracted from EELS, was correlated to macroscopic technological parameters such as duty cycle and frequency, based on advanced data analysis. Using the spectral differences, structural maps are, for the first time, provided for titanium oxide grown anodically. Cathodic current was found to favour the growth of a mainly crystalline barrier layer, responsible for abundant O2 evolution during the treatment. A detailed mechanism regarding the stimulation of type-B discharges, when using cathodic polarization at high frequency, is given comparing outcomes from optical emission spectroscopy and structural information. As the result of the intense plasma interaction with the growing layer, the structure evolved towards the formation of 18 nm of titanium oxide characterized by a strong Ti+3 fingerprint, followed by 85 nm of Ti3O5 formed according to high temperatures and the de-oxidative condition encountered.

Fabrication of a Protective Hybrid Coating Composed of TiO2, MoO2, and SiO2 by Plasma Electrolytic Oxidation of Titanium

This work examined the influence of dual incorporation of MoO2 and SiO2 on the corrosion behavior of pure titanium treated via plasma electrolytic oxidation (PEO). To achieve this purpose, pure titanium substrate was treated via PEO in an alkaline-molybdate electrolyte without and with SiO2 nanoparticles. The microstructural observation revealed that the addition of SiO2 nanoparticles into the electrolyte during PEO helped to seal the structural defects in the PEO coating so that a rougher, thicker, and denser coating rich in SiO2 was successfully obtained. From the electrochemical measurements in a 3.5 wt.% NaCl solution, the TiO2-MoO2-SiO2 hybrid coating exhibited a higher corrosion resistance than the TiO2-MoO2 coating which was attributed to the sealing effect by stable SiO2 nanoparticles.

Nanodesigned coatings obtained by plasma electrolytic oxidation of titanium implant and their cytotoxicity.

The titanium implant was treated with plasma electrolytic oxidation and subsequent ionic exchange and thermal treatment in order to obtain bioactive layer consisting of titanium oxide, calcium and sodium titanates and hydroxyapatite, as confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed that the given method, besides corresponding phase composition, enables suitable nanotopology for cell attachment and proliferation. Cytotoxicity investigations by MTT, LDH and propidium iodide assays and light microscopy showed that these coatings were not toxic to L929 cells.

Porous Coatings Containing Copper and Phosphorus Obtained by Plasma Electrolytic Oxidation of Titanium

To fabricate porous copper coatings on titanium, we used the process of plasma electrolytic oxidation (PEO) with voltage control. For all experiments, the three-phase step-up transformer with six-diode Graetz bridge was used. The voltage and the amount of salt used in the electrolyte were determined so as to obtain porous coatings. Within the framework of this study, the PEO process was carried out at a voltage of 450 VRMS in four electrolytes containing the salt as copper(II) nitrate(V) trihydrate. Moreover, we showed that the content of salt in the electrolyte needed to obtain a porous PEO coating was in the range 300–600 g/dm3. After exceeding this amount of salts in the electrolyte, some inclusions on the sample surface were observed. It is worth noting that this limitation of the amount of salts in the electrolyte was not connected with the maximum solubility of copper(II) nitrate(V) trihydrate in the concentrated (85%) orthophosphoric acid. To characterize the obtained coatings, numerous techniques were used. In this work, we used scanning electron microscopy (SEM) coupled with electron-dispersive X-ray spectroscopy (EDS), conducted surface analysis using confocal laser scanning microscopy (CLSM), and studied the surface layer chemical composition of the obtained coatings by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), glow discharge of optical emission spectroscopy (GDOES), and biological tests. It was found that the higher the concentration of Cu(NO3)2∙3H2O in the electrolyte, the higher the roughness of the coatings, which may be described by 3D roughness parameters, such as Sa (1.17–1.90 μm) and Sp (7.62–13.91 μm). The thicknesses of PEO coatings obtained in the electrolyte with 300–600 g/dm3 Cu(NO3) 2∙3H2O were in the range 7.8 to 10 μm. The Cu/P ratio of the whole volume of coating measured by EDS was in the range 0.05–0.12, while the range for the top layer (measured using XPS) was 0.17–0.24. The atomic concentration of copper (0.54–0.72 at%) resulted in antibacterial and fungicidal properties in the fabricated coatings, which can be dedicated to biocompatible applications.

Plasma Electrolytic Oxidation of Titanium in H2SO4–H3PO4 Mixtures

Oxide layers on titanium foils were produced by galvanostatically controlled plasma electrolytic oxidation in 12.9 M sulfuric acid with small amounts of phosphoric acid added up to a 3% mole fraction. In pure sulfuric acid, the oxide layer is distinctly modified by plasma discharges. As the time of the process increases, rough surfaces with typical circular pores evolve. The predominant crystal phase of the titanium dioxide material is rutile. With the addition of phosphoric acid, discharge effects become less pronounced, and the predominant crystal phase changes to anatase. Furthermore, the oxide layer thickness and mass gain both increase. Already small amounts of phosphoric acid induce these effects. Our findings suggest that anions of phosphoric acid preferentially adsorb to the anodic area and suppress plasma discharges, and conventional anodization is promoted. The process was systematically investigated at different stages, and voltage and oxide formation efficiency were determined. Oxide surfaces and their cross-sections were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The phase composition was determined by X-ray diffraction and confocal Raman microscopy.

Temperature-controlled growth of micro- and nanocrystals on the surface of NiO+CuO/TiO2/Ti composites

The functional properties of oxide coatings on metals depend on the composition and structure of their surface. In this work, the change with temperature of air annealing of the surface of NiO + CuO/TiO2/Ti composites formed by the combination of plasma electrolytic oxidation of titanium in the phosphate-borate-tungstate electrolyte containing nickel and copper acetates and impregnation in the solution of nickel and copper nitrates was studied. It has been shown that varying the annealing temperature allows one to form the ensembles of micro- and nano-sized crystals of different composition and structure on the surface. CuO crystals are formed on the surface at annealing temperature T = 500 ÷ 700 °C, NiWO4 crystals are present at T = 750 ÷ 850 °C, and Ni2.62Ti0.69O4 whiskers - at T ≥ 900 °C. The data obtained suggest that the remaining electrolyte and impregnating solution accumulated on the surface and in the pores, as well as the transport of titanium from the coating depth to the surface, play an important role in the formation of crystals. It was summarized that air annealing at given temperatures of complex oxide coatings can be effective for controlling their architecture and surface composition at the micro- and nanolevels and, therefore, their functional properties.

Combined Galvanostatic and Potentiostatic Plasma Electrolytic Oxidation of Titanium in Different Concentrations of H2SO4

We report on plasma electrolytic oxidation of titanium, employing a technique with combined potentiostatic and galvanostatic control. The effect of different H 2 SO 4 electrolyte concentrations on the titanium oxide formation was studied sytematically. The titanium oxide consisted of two distinguishable layers. The upper layer is porous, up to few micrometers thick and primarily rutile, while the interlayer is compact, comparatively thin and is associated to anatase formation. The electrolyte concentration changed substantially layer thickness, porosity and phase composition, as deduced from scanning electron microscopy, X-ray diffraction and Raman spectroscopy.

Effect of Tb3+ doping on the photocatalytic activity of TiO2 coatings formed by plasma electrolytic oxidation of titanium

Tb doped TiO2 coatings are formed by plasma electrolytic oxidation (PEO) of titanium in water solution of 10 g/L Na3PO4⋅12H2O with addition of Tb4O7 powder. Surface morphology, chemical, and phase composition of obtained PEO coatings are investigated utilizing scanning electron microscopy equipped with energy dispersive x-ray spectroscopy and X-ray diffraction. Uniformly distributed Ti, O, P, and Tb are identified as the main constituents of the coatings. Diffraction patterns of obtained coatings show well pronounced reflections inherent to anatase phase of TiO2. Performed photoluminescence measurements indicate that incorporated Tb is in trivalent oxidation state. Photoluminescence emission spectra feature two overlapping regions: the first region is related to band of TiO2 host and the second region which features several emission bands is ascribed to f-f transitions of Tb3+ from excited level 5D4 to lower levels 7FJ (J = 3,4,5, and 6). The photocatalytic activity (PA) of Tb3+ doped TiO2 coatings is probed by measuring the photodegradation of methyl orange under simulated sunlight conditions, suggesting that the main factor affecting PA is concentration of Tb3+ ions incorporated into coatings. Tb3+ doped TiO2 coatings formed for short time have better PA than pure TiO2 coatings formed under the same conditions; the highest PA is observed for the coating formed after 1 min of PEO process. Presence of Tb3+ ions into TiO2 coatings in small concentration improves PA through effective suppression of electron/hole recombination.

Mg-Containing Hydroxyapatite Coatings Produced by Plasma Electrolytic Oxidation of Titanium

Plasma Electrolytic Oxidation (PEO) is promising for the processing of biomaterials because it enables the production of surfaces with adjustable composition and structure. In this work, aimed at the improvement of the bioactivity of titanium, PEO has been used to grow calcium phosphide coatings on titanium substrates. The effects of the addition of magnesium acetate to the electrolytes on the composition of the coatings produced during 120 s on Ti disks using bipolar voltage pulses and solutions of calcium and magnesium acetates and sodium glycerophosphate as electrolytes have been studied. Scanning electron microscopy, X-ray energy dispersive spectroscopy, Rutherford backscattering spectroscopy, X-ray diffractometry with Rietveld refinement and profilometry were used to characterize the modified samples. Coatings composed of nearly 50 % of Mg-doped hydroxyapatite have been produced. In certain conditions up to 4% Mg can be incorporated into the coating without any observable significant structural modifications of the hydroxyapatite.

Characterization and photocatalytic activity of SiO2, FeOx coatings formed by plasma electrolytic oxidation of titanium

SiO2, FeOx coatings were fabricated by plasma electrolytic oxidation of titanium in a silicate electrolyte with an addition of K3[Fe(CN)6]. The structure and elemental and phase compositions of the formed coatings and their surface morphology were characterized by scanning electron microscopy (SEM) in combination with energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). According to XPS, iron is present on the surface of SiO2, FeOx coatings in the form of Fe2O3. Band gaps are equal to 2.6 and 1.4 eV for oxide layers containing 0.6 and 3.4 at.% Fe, respectively. Photocatalytic activity of the coatings was determined by phenol photodegradation in aqueous solution containing hydrogen peroxide under UV-irradiation. In the presence of H2O2, all Fe-containing coatings exhibit photocatalytic activity in phenol degradation. The phenol degradation degree increases along with K3[Fe(CN)6] concentration in silicate electrolyte. The removal of phenol on the SiO2, FeOx coating containing 3.4 at.% Fe reaches 80% after 120 min UV-irradiation. SiO2, FeOx composite oxide layers on titanium are considered to be promising as heterogenic Fenton-like photocatalysts, which can find an application in water purification.

Effects of reagent purity on plasma electrolytic oxidation of titanium in an aluminate–phosphate electrolyte

The effect of reagent purity on AC plasma electrolytic oxidation of titanium in aluminate–phosphate-based electrolytes has been studied under constant rms current conditions. The resultant coatings were examined by high-resolution electron microscopy and X-ray diffraction, revealing rutile, Al2TiO5, α-Al2O3 and γ-Al2O3, with an aluminium-enriched outer region and phosphorus-enriched band near the coating base. A lower purity of the electrolyte led to an erratic voltage response and delamination of coating material in scratch tests. A thin chlorine-enriched region near the substrate, attributed to the inward migration of chloride ions during coating growth, is suggested to be the cause of the delamination. Deliberate additions of chloride to the electrolyte resulted in highly porous coatings.

Process modelling and analysis of plasma electrolytic oxidation of titanium for TiO2/WO3 thin film photocatalysts by response surface methodology

Plasma electrolytic oxidation of titanium in 12-tungstosilicic acid solution was investigated as a model reaction. The influence of the process parameters (concentration of 12-tungstosilicic acid solution, current density, and time) on the selected process response (efficiency of the methyl orange photodecolorization on the TiO2/WO3 coatings) was studied. A mathematical model was developed using a second-order response surface model with a central composite design incorporating the above-mentioned process parameters. The statistical analysis of experimental data indicates that a concentration of 12-tungstosilicic acid solution; process time, interaction between concentration and process time, and interaction between concentration and quadratic of process time have a significant effect on the methyl orange photodecolorization. Besides, the results show that obtained data were adequately fitted into the second-order polynomial model, since the calculated model F value (39.28) is higher than the critical F value. The values of coefficient of determination (R2=0.960) and adjusted coefficient of determination (RAdj.2=0.937) are close to 1, indicating a high correlation between the observed and the predicted values. This model can also be useful for setting an optimum value of the process parameters for achieving the maximum efficiency of the methyl orange photodecolorization. Under the optimum conditions established in the region of experimentation (C=1.14·10−3M, j=153mA/cm2, and t=58.9s), a 38.6% (test duration of 8h) efficiency of the methyl orange photodecolorization is obtained.