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.     

Microstructure and bioactivity of Ca, P and Sr doped TiO2 coating formed on porous titanium by micro-arc oxidation

In the present study, bioactive coatings enriched with micro-pores and Ca-P-Sr elements were formed on pore walls of porous titanium by micro-arc oxidation (MAO). It is found that pore size plays a significant role on the MAO treatment of porous titanium. For samples with pore size smaller than 90 μm, whatever applied voltage and treatment time were employed, MAO coatings were formed only in the near surface region. As to the sample with average pore size of 150 μm, MAO coatings were formed on both outer and inner pore walls throughout the depth. Compared with the untreated one, the specific surface area dramatically increased about 460 times. Further studies found that pore size, thickness and amounts of O, Ca, P and Sr elements of the coating on the outer pore walls were obviously higher than those on the inner pore walls. Additionally, the coating on the outer pore walls was composed of anatase and rutile TiO₂ and other complex Ca-P-Sr phases, in comparison with anatase TiO₂ formed on the inner pore walls. In spite of the distinct features of coatings on the different locations of pore walls, MAO-treated porous titanium overall showed a good apatite-inducing ability.     

Characterization and properties of the MgF2/ZrO2 composite coatings on magnesium prepared by micro-arc oxidation

Through micro-arc oxidation, the MgF₂/ZrO₂ composite coatings were prepared on magnesium at the different applied voltages (in the range of 400-550 V) in a zirconate electrolytic solution. The morphologies, phase components, microhardness, bond strengths, and corrosion resistances of the composite coatings were investigated. The effect of the applied voltages on the characteristics and properties of the composite coatings and the basic formation mechanism of the coatings were also discussed. The results indicate that the composite coatings are relatively dense and uniform in thickness, and predominantly composed of MgF₂, tetragonal ZrO₂ (t-ZrO₂) and monoclinic ZrO₂ (m-ZrO₂). The composite coatings exhibit a gradient distribution in phase component from the surface to the inner part. It is found that the applied voltage plays an important role in the characteristics and properties of the composite coatings. With the increase of the applied voltage, the thickness and the t-ZrO₂ content of the composite coatings increase, while the m-ZrO₂ content decreases and no significant variation is observed in the MgF₂ content. Moreover, the surface microhardness and bond strength of the coatings increases with the applied voltage increasing. The microhardness values display a gradient distribution in the cross sections of the coatings, and the maximum microhardness value and its corresponding position in the cross sections are related to the applied voltage. In addition, the corrosion resistances of the composite coatings on magnesium surface are obviously superior to the magnesium substrate in the NaCl solutions, and the effect is more remarkable at higher voltage.     

纳米颗粒增强TiO_2涂层的制备及其防污性能

为提高二氧化钛涂层的防污性能,采用KH-550硅烷改性锐钛矿型TiO_2颗粒,并充分分散于二氧化钛凝胶涂层中。通过降解亚甲基蓝溶液、细菌贴附试验、藻类贴附试验,分别评价了涂层的光催化性能、抗菌性能及抗藻类附着性能,并利用激光共聚焦显微镜及扫描电子显微镜对藻类在涂层表面的附着情况进行分析。结果表明,添加TiO_2纳米颗粒涂层的防污性能较未添加TiO_2纳米颗粒涂层有较大程度的提高。添加粒径为5~10 nm TiO_2颗粒的二氧化钛涂层对小球藻、三角褐指藻及小新月菱形藻的附着降低率分别达到了92.1%、71.5%和62.1%,相较于纯二氧化钛涂层对3种藻类的附着降低率分别提高了29.7%、68.4%和43.5%。TiO_2颗粒的加入可以有效地提高涂层的光催化性能,光催化使得涂层具有亲水、抗菌及自清洁的性能进而有利于提高涂层的防污性能。     

Electrophoretic enhanced micro arc oxidation of ZrO2-HAp-TiO2 nanostructured porous layers

Micro arc oxidation (MAO) and electrophoretic deposition (EPD) processes were simultaneously employed to grow ZrO₂-HAp-TiO₂ porous layers on titanium substrates under different conditions. Influence of the electrolyte composition and the growth time on surface morphology, topography, phase structure, and stoichiometry of the layers was investigated. The utilized electrolytes consisted of β-glycerophosphate, calcium acetate, sodium phosphate, and micron sized yttria-stabilized zirconia with different concentrations. AFM and SEM evaluations revealed a rough surface with a porous structure with a pores size of 50-750 nm. The pores size increased with the time and the electrolyte concentration. Based on the XRD and XPS results, the layers consisted of anatase, hydroxyapatite, monoclinic ZrO₂, tetragonal ZrO₂, ZrO, CaTiO₃, and α-TCP phases whose fractions were observed to change depending on the synthesis conditions. The average crystalline size of the HAp phase was determined as ∼54 nm. The nano-sized zirconia particles (d = 20-60 nm) were dispersed not only on surface, but also in depth of the layers. Utilizing thicker electrolytes and prolonging the growth time resulted in decomposition of hydroxyapatite as well as tetragonal ZrO₂ to monoclinic ZrO₂. EDX results also showed that the zirconium wt% in the layers increased with the time. EPD-enhanced MAO (EEMAO) technique was expressed as an efficient route to fabricate ZrO₂-HAp-TiO₂ multiphase systems within short times and only in one step.     

CVD deposition and characterization of coloured Al2O3/ZrO2 multilayers

Coloured Al₂O₃/ZrO₂ multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO₂ process used in the multilayer, with ZrCl₄ as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO₂ phases. However by adding a relatively small amount of AlCl₃ during such a process results in ZrO₂ layers being composed of predominantly tetragonal ZrO₂ phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO₂ phase seem to be less perfect with existence of larger grains of ZrO₂ which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al₂O₃ layers.It is believed that, in the studied Al₂O₃/ZrO₂ multilayers, the observed tetragonal ZrO₂ phase is the result of a size effect, where small enough ZrO₂ crystallites energetically favor the tetragonal phase. However as the ZrO₂ crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO₂ phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO₂ based ceramics.     

多孔ZrO2-8 wt% Y2O3涂层的制备及性能

航空发动机的效率与转动叶片和机匣之间的间隙密切相关。为了控制转子和静子之间的间隙,需要在机匣表面制备可磨耗的封严涂层。在发动机的高温端,ZrO₂-8wt% Y₂O₃涂层是经常采用的封严涂层基体。涂层中的孔隙可以增加涂层的可磨耗性。本文利用聚苯酯(PHB)增加等离子喷涂的ZrO₂-8 wt% Y₂O₃涂层的孔隙率。为了避免聚苯酯在等离子喷涂过程中的烧损,利用溶胶-凝胶法在聚苯酯颗粒表面沉积一层TiO₂层。文中将讨论采用此方法制成的涂层的形态、孔隙率、硬度和可磨耗性。结果表明,在喷涂粉末中混合包覆型的聚苯酯后,涂层的孔隙率将会得到提升,涂层硬度将会下降。磨耗试验的结果表明涂层的磨耗深度随着涂层孔隙率的增加而增加。     

热喷涂法制备的La3+掺杂纳米TiO2粉末的表征

采用等离子热喷涂法以钛酸四丁酯为主要原料制备出稀土离子掺杂的纳米TiO2光催化剂.通过XRD,XPS,TEM,UV-Vis等检测手段对样品进行表征,同时检测了其光催化性能,并分析了掺杂对TiO2的影响机理.结果表明,所制备的La3 掺杂纳米TiO2是锐钛矿相和金红石相混晶结构,粒径分布在10～50nm之间;La3 掺杂能够促进锐钛矿向金红石的转变,同时抑制TiO2晶粒的长大;La3 掺杂使TiO2紫外-可见吸收光谱发生红移;适量La3 掺杂能显著提高TiO2的光催化活性,最佳掺杂浓度为0.5%(与Ti原子摩尔比),甲基橙降解率在90min内可达到82.4%.比纯TiO2高出13.2%.     

Spectroscopic and crystal-field analysis of energy levels of Eu in SnO2 in comparison with ZrO2 and TiO2

We have carried out systematic crystal-field energy level calculations of Eu³⁺ ions doped in SnO₂ based on experimentally acquired luminescence spectra. In addition, with an aim of revealing systematic trends in spectra and crystal-field effects for Eu³⁺ ion in similar hosts, we have analyzed the TiO₂ (anatase):Eu³⁺ spectra as well. The obtained crystal-field parameters yield very good agreement between the calculated and observed energy levels. Emphasis has been put on analysis of the crystal-field-induced J-mixing effects and their roles in getting proper sets of crystal-field parameters and energy levels. A more general theory concerning J-mixing effects has been proposed and the relevant results will be valuable to understanding of the spectral characteristics of Eu³⁺ f-f transition spectra in other hosts. Relations between the maximum crystal-field splitting of some selected J-manifolds with J = 1 and J = 2 and crystal-field invariants have been re-visited and re-derived. The corresponding numbers of crystal-field parameters influencing the splitting of these manifolds have been taken into account in every case. The derived equations have been tested in applications to three systems (SnO₂, TiO₂ (three sites) and ZrO₂). Consistent results have been obtained, which confirms validity of the performed crystal-field analysis and opens a way for possible applications of the suggested calculating technique to other rare-earth ions.     

Poisoning prevention of TiO2 photocatalyst coatings sputtered on soda-lime glass by intercalation of SiNx diffusion barriers

Amorphous titanium dioxide coatings were deposited at high pressure (about 5 Pa) on cold soda-lime glass by reactive magnetron sputtering. In order to obtain anatase form known for its photocatalytic properties, an annealing at 450 °C was required. The morphology of the photocatalyst coating, examined by scanning and transmission electron microscopy, exhibits a columnar structure with closed intercolumnar porosity. The concentration profile obtained by means of sputtered neutral mass spectrometry revealed the presence of sodium into the TiO₂ coating due to the Na diffusion from the soda-lime glass during the annealing step. This level of contamination reaches 5.5 at.% in the whole film thickness. Since the presence of Na in TiO₂ coatings is harmful to the photocatalytic properties, a silicon nitride (SiN_x) coating, acting as a Na diffusion barrier, was intercalated between the glass substrate and the TiO₂ coating. The concentration profiles showed that the TiO₂ coating deposited on SiN_x/glass substrate is sodium-free. Furthermore, photocatalytic tests revealed that TiO₂/SiN_x/glass system is about threefold more efficient than TiO₂/glass, showing both the poisoning effect of Na and the superior efficiency of SiN_x as a diffusion barrier. To illustrate this, diffusion barriers made of silicon dioxide have also been grown and compared to SiN_x.     

电射流法沉积的ZrO2织构化表面及其摩擦磨损特性∗

精密器械中的微摩擦零件的增摩需求逐渐被重视,电射流沉积法可以低成本制备出增摩表面。 利用溶胶凝胶法制作 ZrO₂ 溶液,通过电射流沉积技术结合掩膜板在 316L 不锈钢表面制备具有仿生图案的二氧化锆(ZrO₂ )织构化表面,测试织构化表面的亲水性和不同加载力下的摩擦磨损性能,并与相同试验条件下的光滑基体、薄膜作对比。 结果表明:利用电射流沉积技术通过掩膜板制备织构化增摩表面的方法简单可行,织构化表面与基体和薄膜相比亲水性更弱,与光滑基体相比在小加载力下其摩擦因数增加约 70%,磨损率下降约 50%,有明显的增摩、耐磨效果。 电射流法借助掩膜板沉积的 ZrO₂ 织构化表面可为微摩擦零件表面的增摩耐磨提供一种新方式。     

Oxidation Behavior of ZrO2 Reinforced MoSi2 Composite Coatings Fabricated by Vacuum Plasma Spraying Technology

In this work, MoSi₂, MoSi₂-20 vol.% ZrO₂, MoSi₂-40 vol.% ZrO₂ (denoted, respectively, as MZ0, MZ2, and MZ4) coatings were fabricated by vacuum plasma spraying technology. The oxidation behavior of the coatings was examined at 500, 1200, and 1500 °C, respectively. Some basic properties of the coatings, including microhardness, porosity, and surface roughness were characterized. The tests at 500 °C showed that the pest oxidation phenomenon of MoSi₂ coatings was restrained by the addition of ZrO₂. The MZ2 coating exhibited excellent oxidation-resistant behavior both at 1200 and 1500 °C. However, the MZ4 coating presented the impaired oxidation-resistant behavior at 1500 °C, though the comparable oxidation property at 1200 °C was still obtained.     

原位合成ZrO2/MgO膜层及自修复裂纹研究

微弧氧化熔融冷却成膜过程出现的裂纹将影响膜层的强韧性和磨损性能。本研究利用ZrO₂自身的强韧性,原位合成具有自修复裂纹作用的ZrO₂/MgO膜层,研究原位合成的ZrO₂对膜层磨损性能的影响。结果表明,微弧氧化原位合成的ZrO₂在高温放电通道发生相变产生体积膨胀使得氧化锆界面萌生微裂纹并阻碍裂纹尖端的裂纹扩展,从而实现了膜层裂纹的自修复。通过控制锆源含量实现了对膜层中ZrO₂含量的调控,膜层中原位ZrO₂含量为32%时,ZrO₂/MgO膜层裂纹呈现细小分散化,裂纹密度较传统膜层下降63.4%,摩擦系数减小53.4%,磨损量降低66.7%。研究认为,原位合成的ZrO₂在膜层制备过程实现裂纹自修复并有效降低摩擦系数和磨损量,改善ZrO₂/MgO膜层表面磨损性能。     

Catalytically active cobalt-copper-oxide layers on aluminum and titanium

Oxide coatings modified with cobalt and copper oxides are obtained on titanium and aluminum by means of combining plasma electrolytic oxidation (PEO) in silicate and zirconate electrolytes and impregnation in nitrate solutions followed by annealing. The effect of PEO coatings that were preliminarily formed on aluminum and titanium in different electrolytes on the composition and surface morphology of cobaltcopper oxide composites and their activity with respect to CO oxidation is studied. The maximum total concentration of cobalt and copper is found to be typical of composite layers based on SiO₂ + Al₂O₃/Al, while the minimum content is observed in the case of layers based on ZrO₂ + TiO₂/Ti, the PEO bases being characterized by the highest and lowest water-absorbing capacity, respectively. The effect of PEO coatings on the catalytic activity of cobalt-copper oxide catalysts decreases in the series SiO₂ + TiO₂/Ti > SiO₂ + Al₂O₃/Al > Ce₂O₃ + ZrO₂ + TiO₂/Ti > ZrO₂ + TiO₂/Ti.     

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

Degradation behaviour of ZrO2-Ni/Al gradient coatings in molten Zn

In order to improve the corrosion resistance of metallic materials in molten zinc, ZrO₂-Ni/Al gradient coatings were sprayed on the surface of the Fe-0.35-0.44 wt.% C steel. The corrosion behaviour and corrosion mechanism of the ZrO₂-Ni/Al gradient coatings in molten zinc were studied. The ZrO₂-Ni/Al gradient coatings on the surface of steels prolonged the lifetime of samples and changed the corrosion behaviour of the samples in molten zinc. The lifetime of the ZrO₂-Ni/Al gradient coatings immersed in molten zinc at 620 °C is 28 days, which is 4 times as long as that of the general ZrO₂ coatings. The ZrO₂-Ni/Al gradient coatings were corroded in molten zinc at 620 °C, which was caused by zinc atom diffusing along the crystal boundary and pores of the ZrO₂-Ni/Al gradient coatings, and reacting with Ni/Al particle in the ZrO₂-Ni/Al gradient coatings. The corrosion mechanism of the coatings in molten zinc at 620 °C was crystal boundary corrosion, pitting corrosion and reaction corrosion.     

钛基表面TiO_2-HA生物陶瓷膜层的血液相容性研究

采用微弧氧化法及微弧氧化-水热法对纯钛进行改性,制备了TiO_2与TiO_2-HA生物陶瓷膜层,通过溶血率实验、动态凝血时间实验和血小板黏附实验等方面评价其血液相容性。结果表明:各试样的溶血率都远小于5%,均符合医用材料的溶血率要求,不会产生溶血作用。与钛基TiO_2生物陶瓷膜层和钛基材相比,钛基TiO_2-HA生物陶瓷膜层的溶血率更低,动态凝血时间曲线变化更为缓慢,黏附的血小板更少,且变形程度更轻,具有更好的抑制血小板的聚集与变形的性能,血液相容性更优。     

Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

Thermodynamic study of CVD–ZrO2 phase diagrams

Chemical vapor deposition (CVD) of zirconium oxide (ZrO₂) from zirconium acetylacetonate Zr(acac)₄ has been thermodynamically investigated using the Gibbs’ free energy minimization method and the FACTSAGE program. Thermodynamic data Cp°, ΔH° and S° for Zr(acac)₄ have been estimated using the Meghreblian–Crawford–Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO₂ can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO₂ and the other one corresponds to a mix of monoclinic phase of ZrO₂ and graphite carbon.     

Electrophoretic deposition of functionalized polystyrene particles for TiO2 multi-scale structured surfaces

Titanium is an interesting material for biomedical implants thanks to its physical and chemical properties. In particular, TiO₂ coatings with a surface characterized by micro-patterning combined with nano-topography are extremely attractive for orthopaedic implants in terms of enhanced osteointegration and consequently improved implant fixation. In the present work, a new method for the preparation of TiO₂ multi-scale structured coatings is presented. This method is based on three steps. Firstly, monodispersed polystyrene (PS) microsized beads are functionalized with TiO₂ submicron particles by a wet process involving a cationic polyelectrolyte. Secondly, the resulting TiO₂-PS composite particles in suspension are used to prepare coatings by electrophoretic deposition (EPD), a simple and flexible electrochemical technique. The EPD is performed cathodically, avoiding uncontrolled oxidation of the substrate. Finally, after removal of the PS spacers during the sintering process, TiO₂ coatings with a combined micro- and nano-topography are achieved from deposits thicker than 100 µm. This achievement presents two relevant aspects: potential applications of the multi-scale structured TiO₂ surfaces (particularly in the biomedical field); the simplicity and flexibility of the process used.