Chemical treatment of TiO2-based coatings formed by plasma electrolytic oxidation in electrolyte containing nano-HA, calcium salts and phosphates for biomedical applications

TiO₂-based coatings were formed on titanium alloy by plasma electrolytic oxidation (PEO) in an electrolyte containing nano-HA, calcium salts and phosphates. Bioactive surface was formed after chemical treatment (NaOH aqueous solution) of the PEO coating. The surface of the PEO coating was mainly composed of Ti, O, Ca and P showing anatase and rutile; while that of the chemically treated PEO (CT-PEO) coating mainly contains Ti, O, Ca and Na showing anatase, rutile and amorphous phase. And the chemically treated surface exhibits dissolution of P and introduction of Na during the chemical treatment process. The chemical treatment has no effect on the chemical states of Ca and Ti of the PEO coating. In addition, the surface constituents of the CT-PEO coating show a uniform distribution near its surface with increasing depth. When incubated in a simulated body fluid for 7 and 14 days, the PEO coating does not exhibit apatite-forming ability; however, apatite was successfully deposited on the CT-PEO coating after 7 days probably due to the formation of hydroxyl functionalized surface, enhancing the heterogeneous nucleation of apatite. The addition of nano-HA in the electrolyte has effects on the surface character and apatite-forming ability of the PEO coating; however, it has no obvious influence on those of the CT-PEO coatings.     

Formation and structure of sphene/titania composite coatings on titanium formed by a hybrid technique of microarc oxidation and heat-treatment

Sphene/titania composite coatings were fabricated on titanium by a hybrid technique of microarc oxidation (MAO) and heat treatment. The high-applied voltages promote the formation of sphene in the MAO coatings after heat-treatment. Heat treatment could change the surface morphology of the MAO coatings such as roughness, macropores size and density and the thickness of the MAO coatings. Increasing the heat-treatment temperature decreased the atomic concentration ratios of Ti/Si and Ti/Ca of the MAO coatings. The chemical states of Ti⁴⁺, Ca²⁺, Si²⁺ and O²⁻ were observed on all the coatings. Additionally, Ti²⁺ was detected in the MAO and heat-treated MAO coatings at 600 and 700 °C. The heat-treatment has obvious effect on the chemical states of Si, Ti and O elements due to the formation of sphene and oxidation of TiO phase of the MAO coating, but did not affect that of Ca. In the heat-treated MAO coatings at 800 °C (MAO-H8), the titanium surface shows a MAO top layer and oxidized interior layer. A concentration gradient in components in the MAO layer of the MAO-H8 coating was formed.     

Surface modification of pure titanium by hydroxyapatite-containing composite coatings

Micro-arc oxidation (MAO) is commonly applied to modify the surface of titanium (Ti)-based medical implants with a bioactive and porous Ti oxide (TiO₂) coating. The study reports a new method of incorporating hydroxyapatite (HA) within the TiO₂ coating by MAO and alkali heat treatment (AHT) in the solution containing Ca ion and P ion. The morphology, composition and phase composition of the coatings were analyzed with scanning electron microscopy with energy-dispersive X-ray spectrometer and X-ray diffraction. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in the tapping mode. The results showed that TiO₂-based coatings were obtained on pure Ti by MAO with an electrolyte containing Ca ion and P ion; the prepared MAO coatings were mainly composed of Ca, P, O and Ti. AHT transformed Ca and P to HA crystals. In conclusion, the TiO₂/HA composite coatings can be obtained on the surface of pure Ti by MAO and AHT, and the addition of Ca ion and P ion to the AHT solution contributed to the formation of HA.     

Effect of nano-titanium hydride on formation of multi-nanoporous TiO2 film on Ti

The effect of titanium hydride on the formation of nanoporous TiO₂ on Ti during anodization has been investigated by X-ray photoelectron spectroscopy, grazing incident X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Titanium hydride (TiH₂) was formed after cathodization, profoundly impacting the formation of nanoporous TiO₂ on Ti by anodization. Oxide layer and nanocrystal structure were observed after anodization with cathodic pretreatments. A multi-nanoporous TiO₂ layer was formed on the titanium. The titanium hydride is a nanostructure. The nanostructure is directly changed to nanoporous TiO₂ by a dissolution reaction during anodization. The nanoporous layer is difficult to form without cathodization. The nanostructural TiH₂ is important in forming a nanoporous TiO₂ layer. Anodization treatment with cathodic pretreatment not only yields a titanium surface with a multi-nanostructure, but also transforms the titanium surface into a nanostructured titanium oxide surface.     

PIIID复合强化处理轴承钢表面TiN膜层的XPS表征

用等离子体浸没离子注入与沉积(PIIID)复合强化新技术在AISI52100轴承钢基体表面成功合成了硬而耐磨的氮化钛薄膜。膜层表面的化学组成和相结构分别用X射线衍射(XRD)和X射线光电子能谱(XPS)表征;膜层表面的原子力显微镜(AFM)形貌显示出TiN膜结晶完整,结构致密均匀。XRD测试结果表明,TiN在(200)晶面衍射峰最强,具有择优取向。Ti(2p)的XPS谱峰泰勒拟合分析揭示出,Ti(2p_1/2)峰和Ti_2p3/2峰均有双峰出现,表明氮化物中的Ti至少存在不同的化学状态;N(1s)的XPS谱峰在396.51, 397.22和399.01 eV附近出现了三个分峰,分别对应于TiNO_y,TiN和N—N键中的氮原子。结合O(1s)的XPS结果,证实膜层中除生成有稳定的TiN相外,还有少量钛的氧化物和未参与反应的单质氮。整个膜层是由TiN,TiO₂,Ti—O—N化合物和少量单质氮组成的复合体系。     

Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium

Events at bone-implant interfaces are influenced by implant surface properties. Our previous work has revealed that osteogenic activity is enhanced by a nanotextured Ti surface, obtained by controlled chemical oxidation using a H₂SO₄/H₂O₂ mixture. To better understand the origin of this biological effect, we have carried out a characterization of the modified surface at the nanoscale. In particular, the morphology, structure, and chemical composition of the Ti surface were examined thoroughly. X-ray photoelectron spectroscopy (XPS), combined with grazing-angle Fourier-transform infrared (FTIR) spectroscopy, revealed that the oxidized Ti surface consists of almost pure TiO₂ with Ti:O ratio ranging between 1:2.02 and 1:2.08. Raman spectroscopy and X-ray diffraction (XRD) indicated that the chemically treated Ti surface is mainly composed of amorphous titania. Scanning electron microscopy (SEM) clearly showed that the treated Ti substrate becomes highly porous and has a surface consisting of nano-sized pits, which have average diameters and fractal dimensions ranging between 20-22 nm and 1.11-1.17, respectively. Atomic force microscopy (AFM) revealed a three-fold increase in surface roughness. The thickness of the oxide layer on the treated Ti surface is estimated to be ∼32-40 nm. Together, these observations provide a detailed characterization of chemically oxidized Ti surfaces at the nanoscale and offer new prospects for understanding and controlling the relationship between the properties of materials and their interactions with cells. Our work brings us closer to the creation of “intelligent” implant surfaces, capable of selectively influencing cell behavior.     

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Friction and wear behaviour of cp Ti and Ti6Al4V following nitric acid passivation

Nitric acid passivation increases the thickness of the TiO₂ passive film formed at the cp Ti and Ti6Al4V surface. The TiO₂ oxide, which has a lubricating nature, reduces the wear rate. A linear ball-on-disc friction test has been carried out at room temperature in ambient air, NaCl 3% and Ringer's solutions, with a sliding velocity of 4 mm s⁻¹ and a normal load of 1 N. Friction coefficient curves obtained from ball-on-disc wear test, as well as following the optical microscopy observation of ball trace, indicated the presence of periodic phenomenon. One period can be divided into four stages. This can be clearly seen for cp Ti (accommodation stage, creation of wear particles, adherence of particles layer on the alumina ball and ejection of this layer). In order to confirm this observation and understand the chemical interfacial phenomena, open circuit potential (OCP) measurements were carried out in the same time of friction tests.     

多弧离子镀工艺对TiN/Ti与Cr/Cu界面及微结构的影响

用多弧离子镀技术在铜基上电镀Cr/Ni层进行不同工艺条件下多弧离子沉积TiN/Ti实验.借助X射线衍射(XRD)和扫描电子显微镜(SEM)研究了TiN/Ti与Cr/Cu接触界面形成、微结构及其组分与形貌.XRD分析显示,薄膜表面组分包含TiN,Ti₂N多晶相外,还包含一些Cr-Ti的金属间化合物等.显然,TiN,Ti₂N在表面上已形成.SEM观察指出,在90℃制备的表面膜具有不平整的类枝状结晶结构.随着温度升高至170℃,得到精细TiN/Ti覆盖层表面,XRD峰 关键词： 多弧离子镀 氮化钛 界面形成 微结构     

Characteristic and biocompatibility of the TiO2-based coatings containing amorphous calcium phosphate before and after heat treatment

TiO₂-based coating containing amorphous calcium phosphate (CaP) was prepared on titanium alloy by microarc oxidation (MAO). The increase in the EDTA-2Na concentration was unfavorable for the crystallization of TiO₂. After heat treatment, the amorphous CaP was crystallized. The thickness of the MAO coatings did not change when heat-treated at 400, 600 and 700 °C; while it increased slightly after heat treatment at 800 °C due to the crystallization of amorphous CaP and growth of TiO₂. No apparent discontinuity between the coatings and substrates was observed at various heat-treatment temperatures, indicating the MAO coatings with good interfacial bonding to the substrate. The heat treatment did not alter the chemical composition of the MAO coating and the chemical states of Ti, Ca and P elements. However, it increased the roughness (Ra) of the MAO coating and improved the wetting ability of the MAO coating. In this work, preliminary investigation of the MG63 cell proliferation on the surface of the MAO and heat-treated MAO coatings was conducted. The MAO coating surface with about Ra = 220 nm may be suitable for the MG63 cell adhesion and proliferation. The increased roughness of the heat-treated MAO coatings may result in a decrease in the ability for cell adhesion and proliferation.     

Implementation of Na diffusion layer at Cu2ZnSnSe4/Mo interface for flexible thin film solar cell fabricated on Ti foil by solid state selenization

A Cu₂ZnSnSe₄ (CZTSe) photovoltaic absorber thin films were prepared using a 2-step selenization process on a Ti substrate including a Na precursor layer and a Na-free Ti substrate, and the effect of Na on the solar cell performance was compared. A CZTSe flexible solar cell fabricated on a Ti foil substrate exhibited an efficiency of 3.06%, which was less than half that of a solar cell fabricated on a soda lime glass substrate. This was attributed to the absence of Na and severe Zn crowding near the back contact. By depositing a 100‐nm-thick sodalime glass thin film on a Ti substrate to supply Na, the efficiency increased up to 5.59%. In the Na-doped CZTSe absorber layer grown on the Ti substrate, the back crowding of Zn was eliminated and the upper part of the absorption layer was converted to a Zn-rich environment, which prevented the formation of Cu_Zn antisite defects.     

Structure and apatite induction of a microarc-oxidized coating on a biomedical titanium alloy

An oxide coating with nanostructure was prepared by micro-arc oxidation (MAO) on a biomedical Ti-24Nb-4Zr-7.9Sn alloy. Chemical composition of the coating mainly includes O, Ti, Nb, Ca, P, Na, Zr and Sn, where the ratio of Ca/P is about 1.6. Ti, Nb, Zr and Sn participate in the oxidation to form TO₂, Nb₂O₅, ZrO₂ and SnO₂ nanocrystals, while Ca, P and Na are present in the form of amorphous phases. After alkali treatment, the surface of the MAO coating becomes rough, and Na concentration increases remarkably while P disappears basically. The alkali treated coating shows better apatite forming ability than the untreated one, as evidenced by apatite formation after SBF immersion for 7 days. The improvement of apatite forming ability of the modified coating is attributed to the formation of a sodium titanate layer and numbers of submicron-scale network flakes. The enhancement of the surface wettability of the alkali treated coating also plays an important role in promoting the apatite forming ability.     

Enhancing the crystallinity and surface roughness of sputtered TiO2 thin film by ZnO underlayer

TiO₂ and TiO₂/ZnO double layer films were sputtered on glass substrates. It was found that a thin ZnO underlayer is helpful for tailoring the microstructure and surface morphology of the TiO₂ film. By applying a 70-nm-thick ZnO underlayer, a TiO₂ thin film of 100 nm in thickness with well crystallized anatase phase and rough surface was successfully fabricated without heating the substrate. Relatively high photo-catalytic activity and good hydrophilic properties were observed in such TiO₂/ZnO double layer films.     

Surface modification of titanium by nano-TiO2/HA bioceramic coating

A nano-TiO₂/hydroxyapatite composite bioceramic coating was developed and applied to the surfaces of pure titanium discs by the sol-gel method. A TiO₂ anatase bioceramic coating was utilized in the inner layer, which could adhere tightly to the titanium substrate. A porous hydroxyapatite (HA) bioceramic coating was utilized in the outer layer, which has higher solubility and better short-term bioactivity. Conventional HA coatings and commercially pure titanium were used as controls. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the crystallization, surface morphology, and thickness of the coatings. The bioactivities of the coatings were evaluated by in vitro osteoblast cultures. Results showed that the nano-TiO₂/HA composite bioceramic coating exhibited good crystallization and homogeneous, nano-scale surface morphology. In addition, the nano-TiO₂/HA coating adhered tightly to the substrate, and the in vitro osteoblast cultures exhibited satisfactory bioactivity.     

Titanium oxide nanostructured films by reactive pulsed laser deposition

Nanostructured titanium oxide thin films have been grown by nanosecond UV pulsed laser deposition (PLD) performed in a reactive background atmosphere. We exploited laser ablation of a Ti target at different pressures of pure oxygen and Ar:O₂ mixtures to show that film growth can be tuned at the nanoscale from compact and dense to columnar and to porous, leading to different morphology, density and structure (oxidized fraction and degree of crystallinity). We observed that the position of the substrate relative to the time integrated visible plume front is fundamental in the determination of film structure and morphology. Film growth and film properties can be related to a non-dimensional parameter L which is the ratio between the target-to-substrate distance and the visible plume length. In particular, surface morphology and degree of structural order are strictly related to L irrespective of the oxygen content, while the latter mainly affects the oxidized fraction in the film.     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜     

Preparation and antibacterial effect of silver-hydroxyapatite/titania nanocomposite thin film on titanium

The composite which contains Ag⁺ and nanosized hydroxyapatite with TiO₂ was deposited onto titanium by dipping method. The morphology, chemical components and structures of the thin film were characterized by XRD, scanning electronic microscope (SEM) and energy dispersive X-ray analysis (EDX). Staphylococcus aureus and Escherichia coli were utilized to test the antibacterial effect. XRD results demonstrated that the films have characteristic diffraction peaks of pure HA. EDX results showed that the deposited films consisted of Ca, P, Ti, O and Ag, all of which distribute uniformly. With regard to the antibacterial effect, 98% of S. aureus and more than 99% of E. coli were killed after 24 h incubation and pictures of SEM showed obviously fewer cells on the surface with coating.     

Numerical modeling and experimental investigation of TiC formation on titanium surface pre-coated by graphite under pulsed laser irradiation

A model for carbonization of titanium surface by pulsed Nd:YAG laser was developed. The Ti substrate was covered with a relatively thick graphite layer prior to be processed under the laser beam. The experiments were performed at 15 J pulse energy with various pulse durations and overlapping factor to validate the results obtained from the numerical calculations. The model results such as temperature gradient, surface temperature, and the cooling rate were correlated with the micro-hardness of the alloyed layer. Higher pulse durations and overlapping factors which lead to the heat input increasing will result in significant rising in the micro-hardness values. The hardness values of the processed layer partially containing TiC, increased up to 10 times of the Ti substrate.     

Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.