Structure of calcium titanate/titania bioceramic composite coatings on titanium alloy and apatite deposition on their surfaces in a simulated body fluid

In this study, TiO₂-based coatings containing Ca and P ions were prepared on titanium alloy surfaces by microarc oxidation (MAO). After soaking in aqueous NaOH solution and subsequent heat treatment at 700 and 800 °C, calcium titanate/titania bioceramic composite (CTBC) coatings were obtained. The results show that the outer layers (0–1.5 μm) of the CTBC coatings are mainly composed of Ca, Ti, O and Na constituents with a uniform distributions with increasing the depth near the surfaces. The surface phase compositions of the CTBC coating formed at 700 °C are anatase, rutile and CaTi₂₁O₃₈ phases, as well as a few CaTiO₃, while those of the CTBC coating formed at 800 °C are anatase, rutile and CaTiO₃. When incubated in a simulated body fluid (SBF), apatite was deposited on the CTBC coatings probably via formation of hydroxyl functionalized surface complexes on the CTBC coating surfaces by ionic exchanges between (Ca²⁺, Na⁺) ions of the CTBC coatings and H₃O⁺ ions in the SBF. The CTBC coating formed at 800 °C seems to facilitate the deposition of Ca and P probably due to the good crystallographic match between perovskite CaTiO₃ and HA on specific crystal planes.     

Influence of pore structure on ion diffusion property in porous TiO2 coating and photovoltaic performance of dye-sensitized solar cells

The ion diffusion in porous TiO₂ coating determines the limiting current density and the photovoltaic performance of a dye-sensitized solar cell. Nano-TiO₂ coatings with unimodal nano-size distribution and bimodal size distribution were deposited by vacuum cold spray to examine the effects of the pore structure on the ion diffusion property and cell performance. Results show that the I₃⁻ ion diffusion coefficient increased with the increase in the mean pore size. The bimodal size distribution of nanometer-sized and submicrometer-sized pores in the coating was found to have a synergistic enhancement effect on the ion diffusion. Better ion diffusion performance contributed to a higher open circuit voltage. The optimal coating thickness (~ 30 μm) was nearly doubled in the cells with bimodal pore size distribution, compared with the previously reported optimal coating thickness (~ 15 μm) in the cell with unimodal pore size distribution. The reason is attributed to the high ion diffusion coefficient which allows a high limiting current density.     

Effect of heat treatment on the structure and in vitro bioactivity of microarc-oxidized (MAO) titania coatings containing Ca and P ions

Microarc oxidized (MAO) coating containing TiO₂ and amorphous calcium phosphate was formed on Ti6Al4V in an electrolyte containing EDTA-Ca and phosphate. Subsequent heat treatment has significant effects on the structure and in vitro bioactivity of the MAO coating. After heat treatment (400-800 °C), the crystallinity of TiO₂ increases, and micropore numbers of the MAO coating decline. Moreover, Ca₃(PO₄)₂ is formed on the surfaces of the MAO coatings after heat treatment at 700 and 800 °C. The SEM and ICP-OES results indicate that the abilities of apatite-forming and Ca and P releasing of the MAO coating decrease after heat treatment. The apatite-forming ability of the MAO coating is associated with the crystallinities of titanium oxide and calcium phosphate. The MAO coating containing TiO₂ with a low crystallinity and amorphous calcium phosphate facilitates the apatite formation in vitro. In addition, the induced biomimetic apatite by the MAO coating without heat treatment exhibits carbonated structure, controllable crystallinity and pore networks on the nanometer scale.     

Investigations on composition and morphology of electrochemical conversion layer/titanium dioxide deposit on stainless steel

In this study, the formation and characterization of conversion coatings modified by a sol-gel TiO₂ deposit were investigated as a way to develop a new photocatalyst for water and air depollution. The conversion coating, characterised by strong interfacial adhesion, high roughness and high surface area facilitates the sol-gel deposition of titania and enhances its adhesion to the substrate. The conversion treatment is carried out in an acid solution. Observation by Scanning Electron Microscopy (SEM) reveals a rough surface with pores and cavities. According to SIMS measurements, the thickness of the initial conversion layer is evaluated at about 1.5 μm. On this pre-functionalised support, the titanium dioxide was deposited by the sol-gel method. The roughness measurements coupled with SIMS analysis allowed a precise evaluation of the surface state of the final layers. The coating consists of two layers: a TiO₂ outer layer and an inner layer containing iron chromium oxides. Characterization by X-ray diffraction (XRD) showed the existence of the TiO₂ anatase structure as the main compound.     

Microstructure and apatite-forming ability of the MAO-treated porous titanium

Porous titanium was treated by micro-arc oxidation (MAO) in the aqueous electrolytes containing 0.1 and 0.2 M NaOH. The microstructure (including morphology, phase component, element composition and chemical species) and in vitro apatite-forming ability of the oxidized films formed on the inner-pore walls of porous titanium were investigated. It is found that continuous thin films with pore sizes of 20-60 nm are formed in both electrolytes. The films consist of an amorphous TiO₂ outmost layer, a coexisted intermediate layer of amorphous TiO₂ and rutile, and a Ti₂O₃ bottom layer, and tightly bond to the titanium substrate without any cracks. In vitro bioactivity assessment shows that both MAO films possess high apatite-forming abilities. It is also found that, compared with the film formed in the 0.1 M NaOH-containing electrolyte, the film formed in the 0.2 M NaOH-containing electrolyte has a higher roughness and more nanopores which help shorten apatite induction time. It is expected the MAO-formed bioactive porous titanium will not only be beneficial to bone ingrowth into the porous structure, but also be beneficial to achieve a tough chemical bonding at the bone/implant interface.     

钛合金表面GO/HA/MAO复合膜层的制备及其性能

为了改善钛合金种植体在体液中的腐蚀及摩擦腐蚀行为,延长其在人体环境中的服役时间,在微弧氧化 (MAO)膜层上采用溶胶凝胶(Sol-gel)法于羟基磷灰石(HA)和氧化石墨烯(GO)的混合溶胶中浸渍提拉成膜,从而在 Ti6Al4V 合金表面成功地制备了 GO/ HA/ MAO 复合膜层。 结果表明,MAO 膜层表面的微孔及微球被 GO/ HA 薄膜有效的覆盖且较为致密;膜层的物相组成主要为金红石相及锐钛矿相的 TiO₂、HA、SiO₂ 和GO;根据电化学腐蚀和摩擦腐蚀结果分析知,GO/ HA/ MAO 复合膜层在模拟体液(SBF)中的耐蚀性及耐摩擦腐蚀性相比于 MAO 膜层和 Ti6Al4V 基体均得到了显著提高。     

Preparation of Sn4+-Doped Titanium Dioxide Photocatalytic Films on 304 Stainless Steel by Duplex Treatment

Sn⁴⁺-doped titanium dioxide photocatalytic films were synthesized on 304 stainless steel (SS) by a duplex treatment. The SS substrates were alloyed with titanium (Ti) through cathodic-arc ion plating followed by a microarc oxidation (MAO) treatment in different electrolytes. Field-emission scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy were used to characterize the films surface morphology, crystalline phase, and composition, respectively. Photocatalytic activity was measured using an UV-Vis spectrophotometer. It was found that the films with a porous structure are mainly composed of TiO₂, which exists in an anatase and rutile state. Furthermore, small quantities of SnO₂ have been found in the Sn⁴⁺-doped titanium dioxide films. The fraction of anatase varies with the MAO time and electrolytes, whereas the pore size remains the similar with the same MAO current intensity and density and the surface roughness increases slightly with increasing MAO time. It was also found that the photocatalytic activity of the Sn⁴⁺-doped porous film improved, and the film synthesized with a shorter MAO time in a lower Na₂SnO₃-containing electrolyte is superior to the films with longer MAO times and higher Na₂SnO₃ concentrations.     

Osteoblast growth behavior on micro-arc oxidized β-titanium alloy

β-titanium (β-Ti) alloys are known for their excellent physical properties and biocompatibility, and are therefore considered as next-generation metals for orthopedics and dental implants. To improve the osseous integration between β-Ti alloys and bone, this study develops a titanium dioxide (TiO₂) coating on the surface of β-Ti alloys by using micro-arc oxidation (MAO) technique. The anatase (A) rich and rutile (R) rich TiO₂ layer, were formed on β-Ti, respectively. In vitro tests were carried out using pre-osteoblast cell (MC3T3-E1) to determine biocompatibility and bone formation performance. Biocompatibility includes cell adhesion, cell proliferation, and alkaline phosphatase (ALP) activity, while the bone formation performance contains osteopontin (OPN), osteocalcin (OCN) and calcium content. Cell morphology was also observed. In addition, raw β-Ti, A rich TiO₂ and R rich TiO₂ were implanted into the distal femora of Japanese white rabbits for 4, 8, and 12 weeks to evaluate its in vivo performance.Experimental results show that TiO₂ coating can be grown on and well-adhered to β-Ti. The anatase phase formed under a low applied voltage (350 V), while the rutile phase formed under a high applied voltage (450 V), indicating that crystal structure is strongly influenced by applied voltage. A porous morphology was obtained in the TiO₂ coating regardless of the crystal structure and exhibited superior bone formation performance than β-Ti. In vivo analysis and in vitro test show similar trends. It is also noticeable that the R rich TiO₂ coating achieved better biocompatibility, osteogenesis performance. Therefore, a MAO-treated R rich TiO₂ coating can serve as a novel surface modification technique for β-Ti alloy implants.     

Antifouling properties of micro arc oxidation coatings containing Cu2O/ZnO nanoparticles on Ti6Al4V

Micro arc oxidation (MAO), as a new special surface treatment method, has been introduced to the marine antifouling field for titanium alloys because of the anatase and rutile TiO₂ with antibacterial effects obtained during the oxidation process. Despite this, metallic oxide antifouling additives have been added into MAO coatings to improve the antibacterial and antifouling abilities of titanium alloy. In this study, MAO coatings containing nanometer particles were obtained by adding nano Cu₂O and nano ZnO into the electrolyte. Structure, morphology, phase constitution and chemical composition of the MAO coating film were studied by SEM, XRD and EDS. The antibacterial properties of the film were evaluated by exposing the specimens to Escherichia coli and comparing the Ti-MAO and Ti-bared controls. The results showed that the MAO process on Ti6Al4V has an outstanding antibacterial property which can be further enhanced by nano Cu₂O and nano ZnO. The Ti-MAO–Cu₂O group had the best antibacterial ability. These findings indicate that by means of this process adding nanometer metallic oxide into an MAO coating film via an electrolyte is useful for enhancing the antibacterial and antifouling abilities of titanium.     

大变形纯钛微弧氧化膜层的生物摩擦学性能研究

采用微弧氧化法在纯钛及大变形纯钛表面制备多孔氧化膜层,研究微弧氧化膜层在干摩擦、模拟体液和小牛血清不同润滑介质条件下的生物摩擦学性能,探讨钛基材组织细化对其膜层表面摩擦磨损性能的影响。结果表明：与纯钛微弧氧化膜层相比,大变形纯钛微弧氧化膜层耐磨性能更优的原因在于钛基材晶粒的细化使得晶体缺陷增多,为微弧氧化膜层的形核提供了更多的能量,反应生成的TiO2膜层硬度更强,膜层表面更致密均匀光滑,提高了其摩擦磨损性能所致。大变形纯钛微弧氧化膜层在小牛血清润滑时的摩擦系数和磨损程度都优于干摩擦和模拟体液润滑条件下的摩擦系数与磨损情况。这归因于小牛血清于摩擦表面形成的化学反应膜及物理吸附膜,起到了更有效的润滑、冷却与承载作用。     

Characterization and corrosion behavior of ceramic coating on magnesium by micro-arc oxidation

In this study, the commercial pure magnesium was coated in different aqueous solutions of Na₂SiO₃ and Na₃PO₄ by the micro-arc oxidation method (MAO). Coating thickness, phase composition, surface and cross sectional morphology and corrosion resistance of coatings were analyzed by eddy current method, X-ray diffraction (XRD), scanning electron microscope (SEM) and tafel extrapolation method, respectively. The average thickness of the coatings ranged from 52 to 74 μm for sodium silicate solution and from 64 to 88 μm for sodium phosphate solution. The dominant phases on the coatings were detected as spinal Mg₂SiO₄ (Forsterite) and MgO (Periclase) for sodium silicate solution and Mg₃(PO₄)₂ (Farringtonite) and MgO (Periclase) for sodium phosphate solution. SEM images reveal that the coating is composed of two layers as of a porous outer layer and a dense inner layer. The corrosion results show the coating consisting Mg₂SiO₄ is more resistant to corrosion than that containing Mg₃(PO₄)₂.     

纯Ti表面微弧氧化-碱热处理仿生陶瓷膜的制备及耐蚀性

采用微弧氧化-碱热处理在纯Ti表面制备了含有羟基磷灰石(HA)的仿生陶瓷膜。利用SEM,XRD和电化学工作站等手段研究了膜层的形貌、物相及其耐蚀性。结果表明:在乙酸钙-磷酸二氢钙电解液体系中微弧氧化(MAO),纯Ti表面形成一层含Ca和P的TiO2多孔陶瓷膜。经水热处理后,膜层表面的孔洞变小、致密性增加,膜层中还出现了鳞状、层片状以及针棒状的HA。在Hank's模拟体液中,MAO膜和微弧氧化-碱热处理(MAOAH)膜均表现出较好的耐蚀性。MAO膜经模拟体液腐蚀后,形成了缺钙型HA(Ca8.86(PO4)6(H2O2)2)和CaTiO3;而模拟体液中的阴离子与MAOAH膜层的氧化物作用使膜层孔洞直径和深度增加。     

Effect of voltage on microstructure and corrosion resistance of microarc oxidation coatings on CP-Ti

The surface modification of commercially pure titanium (CP-Ti) by microarc oxidation (MAO) under different voltages was investigated using 1%H₃PO₄ solution as an electrolyte. The microstructure, phase composition and elemental distribution of ceramic coatings were investigated using scanning electron microscopy (SEM) and X-ray diffraction. The corrosion behaviour of the coating was also examined by potentiodynamic polarisation testing in a 3·5 wt-%NaCl solution. Micropore oxide films were formed on all the sample groups by MAO. The thickness and micropore size of the MAO coating increased with the increasing voltage. Energy dispersive X-ray spectroscopy results indicate that Ti, O and P became incorporated into the MAO coatings. At a low voltage of 250 V, the MAO coatings were composed of amorphous, P₂O₅, TiP₂O₇ and titania phases (rutile and anatase). Variation of treatment voltages increased the ceramic coatings from an amorphous structure to a phase structure, and the P₂O₅ phase disappeared. The corrosion potential Φ_corr of the MAO sample shifted towards nobler directions, and the corrosion density I_corr fell significantly compared with that of the bare CP-Ti. Corrosion testing showed that the sizes of the micropore of the MAO samples obviously decrease, and the MAO surface becomes smooth.     

Photocatalytic Activity of Nanostructured Anatase Coatings Obtained by Cold Gas Spray

This article describes a photocatalytic nanostructured anatase coating deposited by cold gas spray (CGS) supported on titanium sub-oxide (TiO_2?x ) coatings obtained by atmospheric plasma spray (APS) onto stainless steel cylinders. The photocatalytic coating was homogeneous and preserved the composition and nanostructure of the starting powder. The inner titanium sub-oxide coating favored the deposition of anatase particles in the solid state. Agglomerated nano-TiO₂ particles fragmented when impacting onto the hard surface of the APS TiO_2?x bond coat. The rough surface provided by APS provided an ideal scenario for entrapping the nanostructured particles, which may be adhered onto the bond coat due to chemical bonding; a possible bonding mechanism is described. Photocatalytic experiments showed that CGS nano-TiO₂ coating was active for photodegrading phenol and formic acid under aqueous conditions. The results were similar to the performance obtained by competitor technologies and materials such as dip-coating P25^® photocatalysts. Disparity in the final performance of the photoactive materials may have been caused by differences in grain size and the crystalline composition of titanium dioxide.     

Effects of the electric conditions of AC-type microarc oxidation and hydrothermal treatment solution on the characteristics of hydroxyapatite formed on titanium

This study examined the effects of the conditions for AC-type microarc oxidation (MAO) and the type of hydrothermal treatment solution on the characteristics of hydroxyapatite(HAp)-containing oxide films deposited on commercially pure titanium (CP-Ti). The MAO treatments were carried out in an electrolyte containing 0.2 M calcium acetate monohydrate and 0.02 M β-glycerophosphoric acid disodium salt pentahydrate (β-GP) using AC-type rectangular electric pulses at different voltages and frequencies. HAp formation on the surface of the MAO-treated group was induced by a hydrothermal treatment in either an alkaline solution to form HT-treated groups or a 0.002 M β-GP solution (pH = 11.0) to produce HTP-treated groups. A mixed crystalline structure consisting of anatase TiO₂, rutile TiO₂ and CaTiO₃ was observed on the MAO-treated groups treated with a low frequency and voltage. When the AC frequency was increased, anatase TiO₂ became the dominant crystalline structure and there was an even distribution of pores. HAp particles were formed more densely on the HTP-treated groups than on the HT-treated groups. Among the HTP groups, the groups fabricated at higher frequencies contained more evenly distributed and crystallized HAp crystallites.     

Effect of microplasma modes and electrolyte composition on micro-arc oxidation coatings on titanium for medical applications

A method of micro-arc oxidation (MAO) has been used for the obtaining of the bioactive calcium-phosphate coatings on the surface of nanostructured titanium. A homogeneous alkaline electrolyte containing phosphate ions and calcium (II) complexes with EDTA was used. An effect of changes of current modes on the coating characteristics has been studied. Obtained coatings have the molar ratio Ca/P up to 1.5 and include the phase of calcium phosphate β-Ca₃(PO₄)₂. The adhesion strength of coatings to the titanium substrate is in the range 10-35 MPa, the thickness is up to 100 μm. The experiments in vivo have been carried out. They have shown 75% probability of new bone tissue growth on coatings with roughness of 2.5-5.5 μm.     

Electrodeposition of sol-enhanced nanostructured Ni-TiO2 composite coatings

A novel electroplating method has been developed to produce nanocrystalline metal-matrix nano-structured composite coatings. A small amount of transparent TiO₂ sol was added into the traditional electroplating Ni solution, leading to the formation of nanocrystalline Ni-TiO₂ composite coatings. These coatings have a smooth surface. The Ni nodules changed from traditional pyramid-like shape to spherical shape. The grain size of Ni was also significantly reduced to the level of 50 nm. It was found that the amorphous anatase TiO₂ nano-particles (∼ 10 nm) were highly dispersed in the coating matrix. The microhardness was significantly increased from 320 HV₁₀₀ of the traditional Ni coating to 430 HV₁₀₀ of the novel composite coating with 3.26 wt.% TiO₂. Correspondingly, the wear resistance of the composite coating was improved by ∼ 50%.     

Effects of plasma treatment on bioactivity of TiO2 coatings

In this work, nano-TiO₂ powders were deposited on titanium alloy substrates by atmospheric plasma spraying, followed by plasma immersion ion implantation (PIII) using hydrogen, oxygen and ammonia gases. The bioactivities of PIII-treated TiO₂ coatings were evaluated by the formation of apatite on their surface after soaked in simulated body fluids (SBF) for a period of time. As-sprayed TiO₂ coating is composed of rutile, anatase and TiO_2−x (most of them is Ti₃O₅). After immersion in SBF for two weeks, the hydrogen PIII-treated TiO₂ coating can induce bone-like apatite formation on its surface but apatite cannot be formed on the surface of as-sprayed and oxygen, ammonia PIII-treated TiO₂ coatings. The results obtained indicated that a hydrogenated surface plays a very important role to induce bioactivity of TiO₂ coatings.     

Characteristics and biological responses of novel coatings containing strontium by micro-arc oxidation

The modification of micro-arc oxidation (MAO) technique is an effective method to improve biocompatibility of titanium. This study aimed to investigate the coatings formed in the electrolytes with different strontium content, which is beneficial for biological performance. The physicochemical characteristics and cell behavior were assessed. The physicochemical characteristics were investigated using scanning electron microscope (SEM) observation, energy dispersive X-ray spectrometer (EDX), thin film X-ray diffraction (TF-XRD) analysis, electron spectroscopy for chemical analysis (ESCA) and surface roughness test. Cell behavior included morphology observation by SEM and number count by methylthiazoletetrazolium assay of hFOB cells. The TF-XRD results indicated that phase of coatings was anatase and rutile. The calcium, phosphorus, and strontium were detected in the coatings by EDX and ESCA. Using the SEM, the surface morphology exhibited uniform porous structure on titanium. Cell culture experiments demonstrate that MAO coating formed in the electrolytes with different strontium content would not alter initial cell morphology and 1-day and 7-day cell numbers. The cell proliferation of coatings containing 1% or 5% strontium content at 14-day culture was higher than coatings without strontium content at 14-day culture, but the higher strontium content (10%) could not be beneficial to cell growth. Consequently, this study indicates that strontium incorporated into MAO coatings did not change the physicochemical characteristics but exhibited an effect on biological responses.     

Effect of the structure of the oxidized titanium surface on the particle size and properties of the deposited copper–molybdate catalyst

The parameters of wetting of oxide coatings on titanium formed by the method of plasma electrolytic oxidation (PEO) in an aqueous silicate electrolyte with subsequent deposition of a layer of TiO₂ nanoparticles and ultrasonic treatment by a polymer–salt gel including copper and molybdenum compounds have been investigated. The effect of the oxidized surface microrelief, TiO₂ nanoparticle layer, and pore shape and size on impregnation solution spreading and the structure of the copper–molybdenum catalytic coating formed at further thermal treatment has been demonstrated. Complex oxide composites with ultradispersed catalyst particle sizes characterized with high activity in oxidation of carbon black particles have been obtained.