Nanotubular Oxide Layers Research Articles

Exploring the Impact of Potential, Ammonium Fluoride Concentration, and Anodization Time on the Structure, Surface Characteristics, and Corrosion Resistance of Nanotubular Titanium Oxide Coatings on Biomedical Alloy Ti-6Al-4V ELI

The current research delves into assessing the impact of applied potential, ammonium fluoride concentration, and anodization duration on the structural, phase compositional, microhardness, and surface roughness attributes of nanotubular titanium oxide coatings on anodized Ti-6Al-4V ELI. A meticulous experimental design was executed to systematically investigate the varied effects of these factors. Scanning electron microscopy (SEM) unveiled the presence of well-defined titania nanotubes on the surfaces of the anodized specimens. X-ray diffraction (XRD) analysis discerned the composition of the nanotubular oxide layer, revealing the presence of both anatase and a mixture of anatase and rutile phases contingent upon the anodization parameters. Notably, surface microhardness, surface roughness, and corrosion resistance manifested noticeable variations in response to alterations in applied voltage, NH4F concentration, and anodization duration within the designated experimental ranges.

Formation of Pores on Pure Ti in Highly Concentrated Sulfuric Acids

TiO2 nanotubes formed by anodization in fluoride-containing electrolytes have been extensively examined due to their wide rage of applications. It is reported that fluoride ions move faster to the interface between anodic oxide layer and underlying Ti substrate, forming a fluoride-rich layer at the interface as the ionic radius of fluoride ion is smaller compared to that of oxygen ion. The fluoride-rich layer is also reported to decrease the adhesion of the anodic oxide layer to the substrate. Therefore, the formation of nanotubular oxide layer in fluoride-free electrolytes is highly desired. In the present work, we examined the formation of nanotubular oxide layers on pure Ti in highly concentrated sulfuric acids. Specimens with the dimension of 5 mm x 80 mm x 0.6 mm were prepared from pure Ti sheet (purity ; 99.5%). Prior to anodization, the specimens were cleaned in acetone, methanol and deionized water, successively. Anodization was carried out in highly concentrated sulfuric acids at elevated temperatures using two-electrode configuration cell with platinum counter electrode. The applied voltage was increased with the sweep rate of 1 V/s to desired voltages and then kept at the voltages for various durations. After the anodization, the surface of the specimens was cleaned with deionized water and dried. The structure of the surface was evaluated using FE-SEM. In a highly concentrated sulfuric acid, the anodic current increased with increasing the applied voltage and after switching constant voltage, decreased with time. The formation of oxide layer was confirmed at the surface, but no porous structure was visible. However, a porous structure was observed on the specimen above the electrolyte surface, indicating that the anodization occurred under the meniscus consisting of highly concentrated sulfuric acids. The optimization of water concentration in sulfuric acid and temperature led to the formation of porous structure on pure Ti. This indicates that porous oxide layers can be formed in fluoride-free electrolytes although further optimization is required to improve the ordering of pores.

Selective photoelectrocatalytic CO2 reduction to ethanol using nanotubular oxides grown on metastable Ti-Cu alloy

The photoelectrochemical conversion of CO2 to C2 products such as ethanol is a topic of much current interest and relevance for decreasing the amount of greenhouse gases in the atmosphere. Here, the photoelectrocatalytic selectivity for the CO2 reduction reaction on Ti-O-Cu nanotubes grown on bimetallic alloys (Ti-xCu; x = 0.5, 5.5 and 10 at. %) was investigated. The product selectivity in the CO2 reduction reaction was found to depend on the effects of composition and distribution of the oxidant species along the nanotubes. This behavior was coordinated by the substrate phases obtained from Ti-Cu alloys subjected to different heat treatments (annealed followed by rapid cooling – quenched (Q) or annealed with controlled cooling (A)). A nanotubular (Nt) oxide layer was grown on these substrates and the influence of metastable (quenched) or equilibrium (annealed) phases was related to the diffusion of the copper species. The two types of electrodes were compared in terms of their relative proclivity toward CO2 photoreduction. Methanol was produced as the dominant reduction product on Nt/Ti-10Cu (A). On the other hand, Nt/Ti-10Cu (Q) produced a respectable yield and selectivity for ethanol, reaching 2.32 mmol/L of ethanol. In a broader vein, this study demonstrates the importance of surface defects in an active heterogeneous photocatalyst and provides insights into the key parameters for the precursor design, selection, and optimal performance of materials for the CO2 reduction reaction leading to C2 compounds.

Cytocompatibility, antibacterial, and corrosion properties of chitosan/polymethacrylates and chitosan/poly(4-vinylpyridine) smart coatings, electrophoretically deposited on nanosilver-decorated titania nanotubes.

The development of novel implants subjected to surface modification to achieve high osteointegration properties at simultaneous antimicrobial activity is a highly current problem. This study involved different surface treatments of titanium surface, mainly by electrochemical oxidation to produce a nanotubular oxide layer (TNTs), a subsequent electrochemical reduction of silver nitrate and decoration of a nanotubular surface with silver nanoparticles (AgNPs), and finally electrophoretic deposition (EPD) of a composite of chitosan (CS) and either polymethacrylate-based copolymer Eudragit E 100 (EE100) or poly(4-vinylpyridine) (P4VP) coating. The effects of each stage of this multi-step modification were examined in terms of morphology, roughness, wettability, corrosion resistance, coating-substrate adhesion, antibacterial properties, and osteoblast cell adhesion and proliferation. The results showed that the titanium surface formed nanotubes (inner diameter of 97 ± 12 nm, length of 342 ± 36 nm) subsequently covered with silver nanoparticles (with a diameter of 88 ± 8 nm). Further, the silver-decorated nanotubes were tightly coated with biopolymer films. Most of the applied modifications increased both the roughness and the surface contact angle of the samples. The deposition of biopolymer coatings resulted in reduced burst release of silver. The coated samples revealed potent antimicrobial activity against both Gram-positive and Gram-negative bacteria. Total elimination (99.9%) of E. coli was recorded for a sample with CS/P4VP coating. Cytotoxicity results using hFOB 1.19, a human osteoblast cell line, showed that after 3 days the tested modifications did not affect the cellular growth according to the titanium control. The proposed innovative multilayer antibacterial coatings can be successful for titanium implants as effective postoperative anti-inflammation protection.

Corrosion Stability of the Anodized Ultrafine-Grained Titanium in the Human Body Solution

Nanostructured surface modification was performed on the ultrafine-grained commercially pure titanium (UFG cpTi) using electrochemical anodization. The characterization of the morphology of the nanostructured surface obtained during different times of electrochemical anodization was done using scanning electron microscopy (SEM). The corrosion resistance of the materials was examined using the potentiodynamic method and electrochemical impedance spectroscopy (EIS), during which the electrochemical characteristics of oxide layers and the evaluation of the corrosion resistance of the mentioned materials were determined. These materials were exposed to a solution simulating conditions in the human body (artificial saliva solution) with a pH of 5.5 at a temperature of 37 ºC. The obtained results indicate the extensive influence of time, as a parameter of electrochemical anodization on the surface morphology. The electrochemical anodization of 60 minutes can lead to the creation of the nanotubular oxide layer on the UFG cpTi surface, while the electrochemical anodization of 30 and 90 minutes did not lead to the creation of the nanotubular oxide layer, but it is up to the surface modification of UFG cpTi. Electrochemical tests showed a slight increase in the corrosion resistance in a solution of artificial saliva after electrochemical anodization. Also, the electrochemical impedance spectra for anodized and non-anodized UFG cpTi show the characteristics of corrosion resistance, but the anodized UFG cpTi has better resistance to the oxide layer. It can be concluded that anodized UFG cpTi has better corrosion stability, but both non-anodized and anodized UFG cpTi show exceptional corrosion stability in simulated conditions of the human body, which makes them equally suitable for use in medicine.

Highly ordered nanotubular niobium oxide obtained by self-organizing anodization: A study of capacitive behavior

Transition metal oxide nanotubes such as niobium have attracted wide scientific attention due to their unique properties such as high ionic mobility and large specific surface area. This study investigates the capacitive behavior of nanotubular niobium oxide obtained under extremely mild anodization conditions, aiming its application in supercapacitors. The nanotubular niobium oxide was obtained by potentiostatic anodization at 90 V at room temperature, in a glycerol electrolyte containing 0.4 M NH 4 F and 0.9% H 2 O. Field Emission Gun Scanning Electron Microscopy analysis (FEG-SEM) was employed to perform morphological characterization. The capacitive behavior of the obtained material was investigated by cyclic voltammetry and galvanostatic charge/discharge in a three-electrode system. The neutral aqueous electrolyte used was 1 M Na 2 SO 4 , in a potential window from −0.2 to −1.2 V vs. Ag/AgCl and 1 M H 2 SO 4 as an acid aqueous electrolyte in a potential window from −0.25 to −0.75 V vs Ag/AgCl. The FEG-SEM images revealed the presence of a self-organized highly ordered nanotubular niobium oxide layer on niobium substrate. Appreciable capacitance values of 20 mF cm −2 and 103 mF cm −2 were achieved in Na 2 SO 4 and H 2 SO 4 electrolytes, respectively. This great capacitive response can be associated with a large surface area achieved through the nanostructured oxide layer as well as the morphology of vertically aligned nanotubes that promote a directional ions transport, which, consequently, improves the capacitive performance. Besides, the results showed a superior performance, in terms of capacitance modulus and stability, for nanotubular niobium oxide in H 2 SO 4 electrolytes. The results obtained in this study highlight the great potential of the self-organized highly ordered nanotubular niobium oxide for application as a supercapacitor electrode.

Influence of microstructural features on the growth of nanotubular oxide layers on β-phase Ti-24Nb-4Zr-8Sn and α + β-phase Ti-13Nb-13Zr alloys

Anodization of titanium alloys allows us to obtain nanotube oxide structures consisting of a mixture of oxides of alloying additives which might extend their scope of application and improve their surface properties. However, the complex microstructure of two-phase α + β Ti alloys presents a much greater influence on the homogeneity of nanotubular layers as compared to a single α-phase pure titanium. In this work, we analyzed how changes at the microstructural level (the amount, size or shape of the precipitates of individual phases) affect the growth of nanotubes on two biomedical alloys Ti-24Nb-4Zr-8Sn and Ti-13Nb-13Zr after different heat treatment. We found that morphology of nanotubular oxide layer imitate the microstructure of the substrate quite accurately what has been clearly seen especially for Ti-13Nb-13Zr alloy with a different size and morphology of α/α’ phase precipitates. The height of nanotubes was highly dependent on the β phase content, i.e. the higher the amount of the β phase, the higher the oxide nanotubes what is presumably due to the preferential growth of Nb 2 O 5 and ZrO 2 oxides. Moreover, the results showed that it is possible to fabricate crystalline nanotubes on the annealed Ti-13Nb-13Zr substrates immediately after the anodization process without a typical post-heat treatment. We suppose that this results from the presence of crystalline transition layer after initial heat treatment as well as internal stresses in the two-phase microstructure that induced the crystalline transformation. • NTs layers were fabricated on α + β-phase Ti alloys with various microstructure. • Morphology of layers imitated the size and shape of α/α’ phase precipitates. • The height of NTs grew with the higher amount of β phase. • Crystalline NTs were obtained on Ti-13Nb-13Zr without typical post-heat treatment.

Incorporation of Ions into Nanostructured Anodic Oxides-Mechanism and Functionalities.

Anodic oxidation of metals leads to the formation of ordered nanoporous or nanotubular oxide layers that contribute to numerous existing and emerging applications. However, there are still numerous fundamental aspects of anodizing that have to be well understood and require deeper understanding. Anodization of metals is accompanied by the inevitable phenomenon of anion incorporation, which is discussed in detail in this review. Additionally, the influence of anion incorporation into anodic alumina and its impact on various properties is elaborated. The literature reports on the impact of the incorporated electrolyte anions on photoluminescence, galvanoluminescence and refractive index of anodic alumina are analyzed. Additionally, the influence of the type and amount of the incorporated anions on the chemical properties of anodic alumina, based on the literature data, was also shown to be important. The role of fluoride anions in d-electronic metal anodizing is shown to be important in the formation of nanostructured morphology. Additionally, the impact of incorporated anionic species, such as ruthenites, and their influence on anodic oxides formation, such as titania, reveals how the phenomenon of anion incorporation can be beneficial.

Properties of chitosan/CuNPs coatings electrophoretically deposited on TiO2 nanotubular oxide layer of Ti13Zr13Nb alloy

Coatings based on chitosan/CuNPs (chit/CuNPs) were obtained by a one-step electrophoretic deposition (EPD) on nanotubular oxide layer of Ti13Zr13Nb alloy. The deposition was carried out for 1 min applying voltages of 10 and 20 V with and without the addition of dispersing agent (Polysorbate 20) to the suspension. The coatings obtained for the lower voltage were more uniform than for the higher voltage. By adding a dispersing agent, the agglomeration of copper nanoparticles was reduced, resulting in better adhesion of the coating to the metallic substrate, good corrosion resistance and improved wettability.

Effects of Surface Pretreatment of Titanium Substrates on Properties of Electrophoretically Deposited Biopolymer Chitosan/Eudragit E 100 Coatings

The preparation of the metal surface before coating application is fundamental in determining the properties of the coatings, particularly the roughness, adhesion, and corrosion resistance. In this work, chitosan/Eudragit E 100 (chit/EE100) were fabricated by electrophoretic deposition (EPD) and both their microstructure and properties were investigated. The present research is aimed at characterizing the effects of the surface pretreatment of titanium substrate, applied deposition voltage, and time on physical, mechanical, and electrochemical properties of coatings. The coating’s microstructure, topography, thickness, wettability, adhesion, and corrosion behavior were examined. The applied process parameters influenced the morphology of the coatings, which affected their properties. Coatings with the best properties, i.e., uniformity, proper thickness and roughness, hydrophilicity, highest adhesion to the substrate, and corrosion resistance, were obtained after deposition of chit/EE100 coating on nanotubular oxide layers produced by previous electrochemical oxidation.

Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants

Surface modification is used to extend the life of implants. To increase the corrosion resistance and improve the biocompatibility of metal implant materials, oxidation of the Ti-13Nb-13Zr titanium alloy was used. The samples used for the research had the shape of a helix with a metric thread, with their geometry imitating a dental implant. The oxide layer was produced by a standard electrochemical method in an environment of 1M H3PO4 + 0.3% HF for 20 min, at a constant voltage of 30 V. The oxidized samples were analyzed with a scanning electron microscope. Nanotubular oxide layers with internal diameters of 30–80 nm were found. An analysis of the surface topography was performed using an optical microscope, and the Sa parameter was determined for the top of the helix and for the bottom, where a significant difference in value was observed. The presence of the modification layer, visible at the bottom of the helix, was confirmed by analyzing the sample cross-sections using computed tomography. Corrosion tests performed in the artificial saliva solution demonstrated higher corrosion current and less noble corrosion potential due to incomplete surface coverage and pitting. Necessary improved oxidation parameters will be applied in future work.

Synthesis of nanotubular oxide on Ti–24Zr–10Nb–2Sn as a drug-releasing system to prevent the growth of Staphylococcus aureus

The aim in the present study was to explore the potential application of titanium nanotubes developed in the Ti–24Zr–10Nb–2Sn alloy, as drug delivery systems to prevent bacterial infections in medical devices. A nanotubular oxide layer was synthesized by electrochemical anodizing on the Ti–24Zr–10Nb–2Sn superelastic alloy and the electrical variables that control the growth at constant potential were determined. Scanning electron microscopy (SEM) showed that the nanostructures show a positive linear growth as a function of the applied potential, the superficial analysis carried out by X-ray photoelectron spectroscopy (XPS) showed different states of valence evidencing the presence of TiO2, Nb2O5, SnO2, and ZrO2. FTIR spectra confirm the presence of the antibiotic gentamicin in the Ti–24Zr–10Nb–2Sn nanotubes. The developed nanostructures were evaluated in a phosphate buffer solution (PBS) as a controlled release system of antibiotics. It was observed by bacteriological tests that the nanostructured morphology in combination with the chemical composition has bacteriostatic properties; while the release of the antibiotic-loaded inside the nanotubes had a bactericidal effect. The results showed that it is possible to grow and control the morphology of the developed nanostructures on Ti–24Zr–10Nb–2Sn, which can be used for orthopedic purposes to transport and control the local release of molecules like antibiotics at the site of interest and thus prevent postoperative infections.

(Invited) Anodic Growth of Oxide Nanotube Layers on Titanium Alloys

Self-organized nanoporous and nanotubular oxide layers can be synthesized on a wide range of transition metals by anodization in fluoride-containing electrolytes. In particular, self-organized TiO2 nanotubular layers have attracted intense attention due to their diverse fields of applications. Anodization of titanium alloys also has been reported, in order to utilize self-organized oxide nanostructures to biomedical titanium alloys for improved biocompatibility and bone conductivity and also to introduce the other element than titanium into TiO2 nanotube matrix for enhanced performance in various applications. In this presentation, we show anodization of titanium alloys, focusing on composition and microstructure of the alloys.

The Effect of Crystal Structure on the Growth of Nanotubular Oxide Layers Formed on Ti-Ni Alloys.

Electrochemical anodization of Ti-Ni alloys with different Ni composition was carried out in an ethylene glycol base electrolyte under the various conditions to investigate the effect of crystal structure and chemical composition of the Ti-Ni alloy. X-ray diffraction patterns indicated that Ti-48.0 Ni and Ti-49.0Ni alloys were the martensitic phase at room temperature, while Ti 50.6Ni and 51.0Ni were the austenitic phase. Self-organized nanotubular oxide layers were formed on four Ti-Ni alloys. The thickness of oxide layers increased with increasing anodization time and applied voltages. Energy-dispersive X-ray analysis indicated that the nanotubular oxide layers consist of two kinds of oxides, one of which is Titanium oxide and the other is Nickel oxide. These results indicate that the growth of nanotubular oxide layer formed Ti-Ni alloys are not affected by crystal structure, but by applied voltage and anodization time.

Tensile and Corrosion Properties of Anodized Ultrafine-Grained Ti–13Nb–13Zr Biomedical Alloy Obtained by High-Pressure Torsion

Severe plastic deformation (SPD) is a popular group of techniques applied to achieve the nanostructuring of the metallic biomaterials and improvement of their mechanical characteristics. One of the most commonly used SPD methods is the high-pressure torsion (HPT) technique which enables the obtainment of the microstructure with small grains and high strength. In the present study, the influence of the plastic deformation and surface modification treatment on the tensile and corrosion properties of the Ti–13Nb–13Zr (wt%) alloy is investigated. In that purpose, the coarse-grained (CG) Ti–13Nb–13Zr (TNZ) alloy was subjected to the HPT processing by applying a pressure of 4.1 GPa with a rotational speed of 0.2 rpm and 5 revolutions at room temperature to obtain the ultrafine-grained (UFG) microstructure. The alloy microstructure before and after HPT processing was analysed using the scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The homogeneity of the UFG TNZ alloy was determined by microhardness testing and microscopic observations. The nanotubular oxide layer on the surface of the TNZ alloy, both in CG and UFG condition, was formed by electrochemical anodization in 1 M H3PO4 + NaF electrolyte for 90 min. SEM analysis was used to characterise the morphology of the anodized surfaces, while energy dispersive spectroscopy was applied to determine the chemical composition of the nanostructured layers formed at the alloy surfaces. Mechanical properties of the TNZ alloy, before and after HPT processing and electrochemical anodization, were determined by tensile testing. After tensile testing, the fractographic analysis was conducted to identify the fracture mechanisms. The potentiodynamic polarization technique was used to determine the corrosion resistance of the alloy before and after plastic deformation and surface modification treatment. The obtained results showed that the alloy is reasonably homogeneous after the HPT processing. The XRD analyses reviled the presence of α′ and β phases in the CG TNZ alloy microstructure, while the additional ω phase was detected in the microstructure of the UFG TNZ alloy. The HPT obtained alloy exhibits higher hardness and improved tensile properties than the alloy in the as-received CG condition, while the electrochemical anodization leads to a decrease of its mechanical properties. Both CG and UFG alloys show excellent corrosion stability in Ringer’s solution. Moreover, electrochemical anodization leads to a decrease or an increase of the corrosion resistance of these materials, depending on the morphology of the formed nanotubular surface layers. The results indicate that the anodized CG TNZ alloy is characterized by a lower modulus of elasticity and better corrosion resistance properties than the anodized UFG TNZ alloy.

Characterization of nanotubular oxide layer grown on Ti14wt.%Nb alloy by anodization and its performance in photoelectrocatalytic process

The development and application of well-organized nanostructured materials with high absorption on visible light for application in photoelectrodegradation of polluting organic compounds are challenging problems. This paper presents the formation of nanotubular oxides grown on Ti14wt.%Nb substrate (NT/Ti14wt.%Nb) by an anodizing process, as well as the influence of the temperature in the oxide crystallization and in the photocatalytic activity performance. The oxide layers were characterized by SEM, EDX, Raman, XRD, and photocurrent studies. Electrochemical impedance spectroscopy measurements and polarization curves were also investigated. The diffusion reflectance UV-Vis-NIR spectroscopy assays showed higher absorption in the visible region for Nb-modified TiO2 nanotubes. The characterization of the nanoscale oxide layer grown on Ti14wt.%Nb alloy showed a hybrid (partially Nb-doped) semiconductor behavior with high current density under UV/visible and visible light. Besides that, NT/Ti14wt.%Nb demonstrated greater resistance to corrosion and low recombination of charges compared with TiO2 nanotubes. In general, the results have shown that NT/Ti14wt.%Nb presents a potential for its application in photoelectrocatalytic (PEC) degradation processes. PEC tests of the Reactive Blue 4 (RB4) dye showed total decoloration (k = 0.17 min−1) and 88% degradation under UV/visible light for the oxide layer grown on Ti14wt.%Nb alloy annealed at 450 °C in comparison with those for the oxide layer grown on TiO2 nanotubes.

Effect of Anodized TiO2-Nb2O5-ZrO2 Nanotubes with Different Nanoscale Dimensions on the Biocompatibility of a Ti35Zr28Nb Alloy.

Some important factors in the design of biomaterials are surface characteristics such as surface chemistry and topography, which significantly influence the relationship between the biomaterial and host cells. Therefore, nanotubular oxide layers have received substantial attention for biomedical applications due to their potential benefits in the improvement of the biocompatibility of the substrate. In this study, a nanotubular layer of titania-niobium pentoxide-zirconia (TiO2-Nb2O5-ZrO2) was developed via anodization on a β-type Ti35Zr28Nb alloy surface with enhanced biocompatibility. Scanning electron microscopy (SEM) and surface profilometry analysis of the anodized nanotubes indicated that the inner diameter (Di) and wall thicknesses (Wt) increased with an increase in the water content of electrolyte and the applied voltage during anodization, while the nanotube length (Ln) increased with increasing the anodization time. TiO2-Nb2O5-ZrO2 nanotubes with different Di, Wt, and Ln showed different surface roughnesses (Ra) and surface energies (γ), which affected the biocompatibility of the base alloy. MTS assay results showed that the TiO2-Nb2O5-ZrO2 nanotubes with the largest inner diameter (Di) of 75.9 nm exhibited the highest cell viability of 108.55% due to the high γ of the surface, which led to high adsorption of proteins on the top surface of the nanotubes. The second highest cell viability was observed on the nanotubular surface with Di of 33.3 nm, which is believed to result from its high γ as well as the optimum spacing between nanotubes. Ra did not appear to be clearly linked to cellular response; however, there may exist a threshold value of surface energy of ∼70 mJ/m2, below which the cell response is less sensitive and above which the cell viability increases with increasing γ. This indicates that the TiO2-Nb2O5-ZrO2 nanotubes provided a suitable environment for enhanced attachment and growth of osteoblast-like cells as compared to the bare Ti35Zr28Nb alloy surface.

Electrochemical Evaluation of the Compact and Nanotubular Oxide Layer Destruction under Ex Vivo Ti6Al4V ELI Transpedicular Screw Implantation.

Nano-engineered implants are a promising orthopedic implant modification enhancing bioactivity and integration. Despite the lack of destruction of an oxide layer confirmed in ex vivo and in vivo implantation, the testing of a microrupture of an anodic layer initiating immune-inflammatory reaction is still underexplored. The aim of this work was to form the compact and nanotubular oxide layer on the Ti6Al4V ELI transpedicular screws and electrochemical detection of layer microrupture after implantation ex vivo by the Magerl technique using scanning electron microscopy and highly sensitive electrochemical methods. For the first time, the obtained results showed the ability to form the homogenous nanotubular layer on an Ti6Al4V ELI screw, both in α and β-phases, with favorable morphology, i.e., 35 ÷ 50 ± 5 nm diameter, 1500 ± 100 nm height. In contrast to previous studies, microrupture and degradation of both form layers were observed using ultrasensitive electrochemical methods. Mechanical stability and corrosion protection of nanotubular layer were significantly better when compared to compact oxide layer and bare Ti6Al4V ELI.

Nanotubular oxide layers formation on Ti–24Nb–4Zr–8Sn and Ti–13Zr–13Nb alloys in the ethylene glycol-based electrolyte: The role of alloying elements and phase composition

In this work, the self-organized mixed-oxide nanotubes (NTs) have been fabricated on a commercially pure α-phase titanium, single β-phase Ti–24Nb–4Zr-8Sn alloy and α+β-phase Ti–13Zr–13Nb alloy. Anodization process was performed in ethylene glycol-based electrolyte with fluoride ions at constant voltage of 20 V for 2 h. Morphology of obtained NTs was characterized by scanning and transmission electron microscopy and the chemical analysis was performed by Auger electron and X-ray photoelectron spectroscopy methods. Despite of applying the same process parameters in all cases, NTs obtained on three different substrates showed a different morphology: ribbed walls for titanium and smooth walls for Ti–24Nb–4Zr–8Sn and Ti–13Zr–13Nb alloys. The presence of alloying additives as well as phase composition of both Ti alloys strongly affected the uniformity and height of the obtained nanotubular layers. NTs layers formed on the surface of both Ti alloys were significantly higher but also more inhomogeneous in comparison to pure Ti. Moreover, NTs of different heights were observed on Ti–13Zr–13Nb, the higher growing on the β phase and lower on the α phase. Anodization of titanium alloys led to obtaining layers with mixture of stoichiometric oxides – TiO2, Nb2O5, ZrO2, SnO2.

Anodic Oxide Growth on Heat-Treated Titanium

It has been reported that self-organized nanotubular oxide layers are formed on various metals and alloys by anodization in fluoride containing electrolytes. In particular, the nanotubular structure of TiO2 has been extensively studied due to a wide range of application of TiO2. To tune the properties of the layers, the optimization of anodization condition has been carried out. However, in such trials, the chemical aspects of anodization condition have been mainly focused, that is, only few works has reported the metallurgical aspects of the condition. In the present work, we examined the effects of heat-treatment on anodization behavior and resulting morphology of the TiO2 architecture. Specimens were cut from pure titanium sheets (purity; 99.5 %). The specimens were encapsulated into a silica quartz tube where the vacuum level was controlled less than approximately 2x10-5 torr. The specimens in the silica tube were heat-treated under several conditions. After the heat-treatments, the surface of the specimens was ground with SiC abrasive papers and then mirror-finished with diamond pates and colloidal silica suspension. The specimens were anodized at 50 V in a mixture of ethylene glycol, water and ammonium fluoride. After the anodization, the surface and cross-sectional morphology of resulting oxide layers was observed. Under an optimized heat-treatment condition examined, the specimen consisting of large grains in millimeter range was obtained. The anodization of the specimen revealed that its current behavior was similar to that obtained on as-received specimen. In addition, the obtained structure of anodic oxide layer on the heat-treated specimen was also similar to that on as-received specimen, that is, nanotubular structure was obtained. However, the thickness of the nanotubular oxide layer and the ordering of nanotubes were clearly different. Higher thickness of nanotubular oxide layer was obtained and improved ordering of nanotubes was found on the heat-treated specimen. These results indicate that the substrate property could affect not only the growth but also arrangement of nanotubes.