Study on bioactivity and bonding strength between Ti alloy substrate and TiO2 film by micro-arc oxidation

In this study, the Ti alloy substrate was simultaneously coated with TiO₂ film and hydroxyapatite using micro-arc oxidation, a relatively new surface modification technique where thick, hard, and anticorrosive oxide coatings can be easily and cost-effectively fabricated. Pulsed DC power and various voltages were applied to the Ti alloy substrate. Citric acid, ethylene diamine, and ammonium phosphate were also dissolved as electrolytes followed by the dispersion of hydroxyapatite nanoparticles into those prepared electrolytes. The effects of the composition and applied voltage on the bonding strength, bioactivity, cell attachment and cytotoxicity were investigated. It was observed that the simultaneously coated TiO₂ and hydroxyapatite samples showed improved bioactivity, cell attachment and viability, while maintaining the bonding strength between the coated film and substrate.     

One-step synthesis of petal-like apatite/titania composite coating on a titanium by micro-arc oxidation

Petal-like apatite/titania (TiO₂) coating was prepared on commercially pure titanium (Ti) by micro-arc oxidation in electrolyte containing calcium and phosphate for the first time. The surface morphology, crystalline structure, chemical composition and binding state of the apatite/TiO₂ composite coating were characterized. The coating consists of a double-layer (apatite layer and TiO₂ layer) structure. The average thickness of the inner TiO₂ layer and the outer apatite layer is about 6 μm and 16 μm respectively. The outer apatite layer is porous and exhibits petal-like pattern. The apatite layer consists of hydroxyapatite (HA) and carbonate-apatite and the inner TiO₂ layer consists of anatase and rutile.     

Ultraviolet-enhanced bioactivity of ZrO2 films prepared by micro-arc oxidation

Macroporous and nano-crystallized monoclinic zirconia (m-ZrO₂) film was prepared by micro-arc oxidation (MAO). The effect of ultraviolet (UV) irradiation on the microstructure, water contact angle and bioactivity of the film were investigated. The MAO-formed ZrO₂ film exhibits high hardness and elastic modulus. UV irradiation of the ZrO₂ film does not alter surface morphology, grain size and phase component, however, can significantly improve hydrophilicity and bioactivity of the film. The enhanced hydrophilicity and bioactivity are thought to result from the abundant basic Zr-OH groups on the UV-irradiated film, which have relative long-term stability.     

Preparation of hydroxyapatite-containing titania coating on titanium substrate by micro-arc oxidation

Hydroxyapatite-containing titania coatings on titanium substrates were formed by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH₃COO)₂Ca·H₂O) and sodium phosphate monobasic dihydrate (NaH₂PO₄·2H₂O) using a pulse power supply. Scanning electron microscopy (SEM) with Energy dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD) were employed to characterize the microstructure, elemental composition and phase components of the coatings. The coatings were rough and porous, without apparent interface to the titanium substrates. All the oxidized coatings contained Ca and P as well as Ti and O, and the porous coatings were made up of anatase, rutile and hydroxyapatite. Such MAO films are expected to have significant applications as artificial bone joints and dental implants.     

Alumina coating formed on medical NiTi alloy by micro-arc oxidation

Al₂O₃ coatings were prepared on NiTi alloy by micro-arc oxidation in an aluminate solution. Thin-film X-ray diffraction (TF-XRD) indicated that the coating consisted of only Al₂O₃ crystal phase. Energy dispersive X-ray spectrometer (EDS) showed that there was about 2.53 at.% Ni in the surface layer, which was greatly lower than that of NiTi substrate. Scanning electron microscopy (SEM) showed that the coating exhibited a typical porous surface and excellent adhesive interface between the coating and the substrate. Direct pull-off test showed that the coating had a mean coating-substrate bonding strength of 28 ± 2 MPa. The results of electrochemical impedance spectroscopy (EIS) study and potentiodynamic polarization test indicated that the corrosion resistance of the coated sample was increased by two orders of magnitude compared with uncoated sample.     

Optimization of titanium dioxide film prepared by electrophoretic deposition for dye-sensitized solar cell application

Nanocrystalline TiO₂ films were deposited on a conducting glass substrate by the electrophoretic deposition technique. It was found that the thickness of TiO₂ film increased proportionally with an increase in deposition time and deposition voltage. However, as the deposition duration or deposition voltage increased, the film surface was more discontinuous, and microcracks became more evident. The characteristic of the dye-sensitized solar cell using TiO₂ film as a working electrode was analyzed. The results of the energy conversion efficiency and the photocurrent density exhibited a relationship dependent on the TiO₂ thickness. Curve fitting of energy conversion efficiency vs. TiO₂ thickness revealed the optimum solar cell efficiency ~ 2.8% at the film thickness of ~ 14 μm.     

钛合金表面电泳沉积法制备YSZ/HAp纳米复合涂层

采用电泳沉积法在钛合金基体上制备了YSZ/HAp纳米复合涂层,用场发射扫描电镜、X射线衍射和能量散射谱对复合涂层HAp外层的表面形貌和晶相、复合涂层的断面形貌及元素组成分布进行分析研究,通过粘结-拉伸实验测定了涂层与基体的结合强度.结果表明YSZ/HAp纳米复合涂层与钛合金基体的结合强度明显高于HAp单一涂层与钛合金基体的结合强度,说明YSZ/HAp的复合缓和了HAp涂层与钛合金基体之间的热膨胀系数失配现象,改善了涂层与基体之间的结合.     

Preparation of flat and dense conjugated polymer films from dilute solutions by means of electrophoretic deposition

Some experimental results on the electrophoretic deposition of conjugated polymer are reported. The scanning electron micrographs clearly indicate that the the morphology of filmsof a fluorene-based polymer PDOF-MEHPV by the electrophoretic deposition strongly depends on the toluene/acetonitrile ratio of the parent suspensions. It is also shown that the suspension prepared from a 0.1 g/l toluene solution of the polymer, can give flat and dense polymer films with a thickness in the order of 100 nm by using the electrophoretic deposition. The electrical current originating from the movement of colloial particles has been measured for the suspensions containing polymer more than 0.2 g/l. However, the current due to impurities in the solvent makes it difficult to detect the electrical current corresponding to the particle movement in the suspensions containing smaller amount of the polymer. Polymer light-emitting devices having PDOF-MEHPV films with various thickness prepared by electrophoretic deposition have also been demonstrated.     

Formation of a heterojunction by electrophoretic deposition of CdTe/CdSe nanoparticles from an exhaustible source

Fast and well controlled electrophoretic deposition of CdTe and CdSe nanoparticle (CdTe-np and CdSe-np) layers and nanoparticle layer systems from an exhaustible source has been demonstrated. Using a small volume of pyridine based nanoparticle suspensions with varying concentrations, these were completely drained of nanoparticles during deposition. Our proposed approach is well suited to a practical realization of engineering materials with different band gaps for various promising applications such as fabrication of nanodevices. The formation of a charge selective contact across the CdTe-np/CdSe-np heterojunction was investigated by surface photovoltage methods and evidence of the separation of charge carriers at a CdTe-/CdSe-np heterojunction in‐between was demonstrated.     

TA4微弧氧化陶瓷膜层的结构与性能研究

利用微弧氧化法在纯钛TA4表面制备以Ti O2为主体富含钙磷的多孔陶瓷膜层。采用扫描电镜、X射线能谱仪、X射线衍射仪、拉曼光谱仪、接触角测量仪及电化学工作站观测与分析陶瓷膜层的微观形貌、元素成分及相组成,探讨微弧氧化对其润湿性及耐蚀性能的影响。结果表明,TA4微弧氧化陶瓷膜层表面粗糙多孔,为锐钛矿相与金红石相Ti O2的混晶结构,金红石相的质量分数约为74.39%。TA4经微弧氧化改性后,表面粗糙度增加了1个数量级,接触角明显下降,表面能提高了87.05%,极性力分量增加了166.07%,体现出更好的润湿性能;自腐蚀电位正移0.53 V,腐蚀电流密度与腐蚀速率均减少了3个数量级,表现出更优的耐腐蚀性能。     

Spontaneous stratification in composite films consisting of conjugated polymers and neat C60 prepared by electrophoretic deposition

The morphology of composite films consisting of conjugated polymers and C₆₀ prepared by electrophoretic deposition (EPD) has been studied. While C₆₀ exists as nanocrystals uniformly embedded in the composite films based on poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene], a spontaneous stratification of the composite films into polymer-C₆₀-mixture and C₆₀-microcrystal layers is observed in the films based on a polyfluorene derivative, poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}]. The results suggest that EPD can be a useful tool for controlling the morphology of bulk heterojunction systems for organic photocells.     

Effect of surfactants on surface morphology of ceramic coatings fabricated on magnesium alloys by micro-arc oxidation

Ceramic coatings fabricated by micro-arc oxidation generally possess a foam-like structure with high bulk porosity which restricts them from even wider technical application. Based on interfacial tension modifying theory, different surfactants are added into the electrolyte to inhibit the generation of pores within ceramic coatings. The results indicate that surfactants influence strongly the morphology of ceramic coatings and play an essential role to fabricate a ceramic coating with low porosity. Once surfactants are added into the solution, all the coatings exhibit almost identical morphology and reveal a considerable decrease of pores' number.     

Influence of cathodic current on composition, structure and properties of Al2O3 coatings on aluminum alloy prepared by micro-arc oxidation process

Alumina coatings on aluminum alloy were prepared by micro-arc oxidation (MAO) process using DC and AC power supplies, respectively. In comparison with the coating deposited by DCMAO, the influence of the cathodic current on the composition, structure and properties of the ACMAO coating was investigated. It is found that the coating deposited by DCMAO is composed of α-Al₂O₃, whereas the coating deposited by ACMAO has a mixture composition of α-Al₂O₃ and γ-Al₂O₃. The results of properties show that compared with the coatings deposited by DCMAO, the ACMAO coatings possess higher density, hardness and corrosion resistance. It can be attributed to that the DCMAO coating is rougher and existing much more micro-cracks in its inner layer. As a result, the adhesion of the DCMAO coating to the substrate decreases.     

TC11微弧氧化膜制备及其结构性能研究

在Na2SiO3-Na2WO4-NaOH混合电解液中,利用微孤氧化(MAO)技术在TC11合金表面制备了氧化膜.用扫描电镜(SEM),X射线能谱仪(EDS),X射线衍射仪(XRD)对氧化膜微观结构、化学成分、厚度以及相组成进行了分析,采用HVS-1000维氏显微硬度计、MFT-4000划痕试验机、电化学测量系统完成氧化...     

In situ studies of the atomic layer deposition of thin HfO2 dielectrics by ultra high vacuum atomic force microscope

We studied in situ the initial stages of atomic layer deposition (ALD) of HfO₂ by an ultra high vacuum atomic force microscope working in frequency-modulation mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and water as precursors, were performed on the Si(001)/SiO₂ substrate maintained at 230 °C. After each ALD cycle we studied the influence of the HfO₂ growth on the surface height histogram, the root mean square roughness, the surface fractal dimension and the autocorrelation function. This detailed analysis of the surface topography allowed us to confirm the completion of the first HfO₂ layer after four ALD cycles.     

电泳沉积法制备ZnO/SnO_2复合薄膜及其光催化性能研究

在导电玻璃FTO基底上,利用电泳沉积技术成功制备了ZnO/SnO2复合薄膜,并对样品进行了SEM和XRD表征,并以降解罗丹明B为模型反应,考察不同条件下制备的复合薄膜的光催化活性。结果表明电泳沉积时间为20min时,可得到表面致密均匀的ZnO薄膜,膜厚为0.5μm,且随着电泳沉积时间的延长,薄膜的光催化速率不断增加,沉积时间为20min时,光催化速率达到最大（0.016min-1）,如此优异的光催化性能可能是由于异质结构光催化剂ZnO/SnO2减小光生电子-空穴的复合几率,提高了复合催化剂的光催化效率。此外,还研究了热处理温度对ZnO/SnO2复合薄膜光催化效率的影响,结果发现在300℃热处理的光催化薄膜对罗丹明B的降解率最好,活性最高。     

Synthesis of magnetic tunnel junctions with full in situ atomic layer and chemical vapor deposition processes

Magnetic tunnel junctions, i.e. the combination of two ferromagnetic electrodes separated by an ultrathin tunnel oxide barrier, are core elements in a large variety of spin-based devices. We report on the use of combined chemical vapor and atomic layer deposition processes for the synthesis of magnetic tunnel junctions with no vacuum break. Structural, chemical and morphological characterizations of selected ferromagnetic and oxide layers are reported, together with the evidence of tunnel magnetoresistance effect in patterned Fe/MgO/Co junctions.     

Interfacial control of uni-directional SiCf/SiC composites based on electrophoretic deposition and their mechanical properties

Interfacial control of uni-directional SiC_f/SiC composites were performed by EPD, and their mechanical properties at room temperature were evaluated. The effect of the thickness of carbon interphase on SiC fibers by EPD on mechanical properties of uni-directional SiC_f/SiC composites was also investigated. The average thickness of carbon coating on SiC fibers increased from 42 nm to 164 nm with an increase in the concentration of colloidal graphite suspension for EPD. Dense SiC_f/SiC composites were achieved and their fiber volume fraction was 47–51%. The SiC_f/SiC composites had a bending strength of 210–240 MPa. As the thickness of carbon coating was below 100 nm, the SiC_f/SiC composites (SC01 and SC02) fractured in almost brittle manner. In contrast, the SiC_f/SiC composites (SC03) showed a pseudo-ductile fracture behavior with a large number of fiber pullout as the thickness of carbon coating was above 100 nm. The fracture energy of SC03 was 3–4 times as high as those of SC01 and SC02 and the value was about 1.7 kJ/m². In consideration of the results of mechanical properties, the thickness of carbon coating on SiC fibers should be at least 100 nm to obtain high-performance SiC_f/SiC composites. The fabrication process based on EPD method is expected to be an effective way to control the interfaces of SiC_f/SiC composites and to obtain high-performance SiC_f/SiC composites.     

Fabrication of BaTiO3 films on titanium by microarc oxidation method and improvement of bioactivity by electric poling treatment

A microarc oxidation (MAO) method was used to deposit a ferroelectric BaTiO₃ (BTO) film on titanium implant metal. The bioactivity of the sample was enhanced by negatively polarizing the film surface. BTO-1 and BTO-2 sample groups were fabricated by applying a constant AC current of 1.2 A/cm² (900 s) and 2.0 A/cm² (600 s), respectively. The BTO film surface was negatively polarized using a high temperature poling treatment. The bioactivity of the non-polarized BTO and polarized BTO films was compared using an immersion test in Eagle's Minimum Essential Medium (MEM). For both groups, 0.5-2 μm diameter pores were evenly distributed over the BTO film surface fabricated using the MAO method. The crystallinity and film-to-substrate bond strength of the BTO-2 film were higher than those of the BTO-1 film. The in vitro MEM immersion test demonstrated more calcium phosphate deposition on the negatively polarized BTO film than on the non-polarized BTO film.     

CSD法在亲水性的FTO基板上制备BiFeO3薄膜及其电性能的研究

利用化学溶液沉积法在亲水性的FTO基板上制备BiFeO3薄膜。利用XRD、FE-SEM、XPS、Agi-lent E4980A精密LCR仪及TF-Analyzer2000等分析手段对BiFeO3薄膜进行表征。结果表明,薄膜为纯相的结晶良好的多晶BiFeO3薄膜,由100～300nm的BiFeO3晶粒紧密的堆积而成,表面均匀平整。薄膜厚度为450nm。Fe的氧化态为Fe3+,并没有Fe2+出现。在10kHz时,介电常数和损耗分别为134和0.005。薄膜的剩余极化率为0.58μC/cm2,在0～250kV/cm的测试电场下漏导电流步伐保持在10-6 A/cm2以下。