High transmittance and superhydrophilicity of porous TiO2/SiO2 bi-layer films without UV irradiation

In order to obtain the TiO₂ films with high transmittance and superhydrophilicity without UV irradiation, porous TiO₂/SiO₂ bi-layer films were prepared by spin coated SiO₂ sol and TiO₂ sol including polyethylene glycol 2000 (PEG 2000) onto glass and subsequent calcination at 550 °C. Meanwhile, factors that affect the TiO₂/SiO₂ bi-layer films transmittance and superhydrophilicity were investigated in details by observing their surface morphologies and measuring their water contact angles (WCAs), spreading time and transmittances. The results indicated that the as-prepared TiO₂/SiO₂ bi-layer film showed superhydrophilicity without UV irradiation when 0.5 wt.% PEG 2000 was added in TiO₂ sol. At the same time, its maximum transmittance was as high as 92.3%. The spreading time was only about 0.16 s. More importantly, the resultant film had an excellent stability of the superhydrophilic property.     

类金刚石薄膜表面润湿调控研究综述

表面具有特殊润湿性特别是超疏水性的类金刚石薄膜,可满足在极端服役环境下(比如雨雪、潮湿环境中或者人体组织内)智能界面材料表面改性的需求.概述了类金刚石薄膜的生产工艺和性能优势及制备方法,介绍了具有特殊润湿性,特别是超疏水性的类金刚石薄膜的应用背景,同时提出了类金刚石薄膜表面润湿调控在理论和技术上的限制.在此基础上,阐述了类金刚石薄膜表面本征润湿性及与微观结构(包括杂化状态和短程或中程有序相团簇结构)间的关系.同时,基于经典的Wenzel和Cassie润湿理论,从表面化学组成和粗糙结构两个方面,重点论述了类金刚石薄膜表面润湿调控的方法及研究现状.通过等离子体表面处理、元素掺杂或者化学修饰改变DLC薄膜表面化学组成,实现DLC薄膜表面本征润湿改性.通过基体表面织构化或者薄膜表面形貌控制,构建DLC薄膜表面粗糙结构,控制界面润湿状态.二者共同作用可实现DLC薄膜表面润湿性在超亲水和超疏水之间变化.最后,总结并指出当前类金刚石薄膜表面润湿调控存在的一些关键科学问题,同时展望了未来的发展趋势.     

Preparation and oxygen-sensing properties of TiO2 porous thin films on alumina substrate

The titanium dioxide sols were synthesized with tetrabutyl titanate as precursor, diethanolamine（DEA） as complexing agent , polyethylene glycol （PEG） as organic template. The porous films were prepared by sol-gel method, The structures and morphology of the titanium dioxide porous films were characterized by FE-SEM. The formation mechanism of TiO2 porous films and the relation between the porous structure and oxygen-sensing properties of TiO2 films were studied. Ordered structure was formed by assembling between TiO2 colloid particles and the template molecules. PEG molecules acted on TiO2 colloid particles by hydrogen bond and bridge oxygen. The porous structure was formed after the organic template was decomposed when calcining the films. The diameter, amount and distribution of the pores in the films are related with the content of PEG. The pore diameter increases with increasing of content of PEG and the pore density reaches the maximum at certain content. Oxygen-sensitivity and response speed of porous TiO2 films are improved compared with films without pores. Both the sensitivity and response speed increase with the increasing of pore diameter and pore density. Oxygen-sensitivity reaches 3 order of magnitude at 800 ℃. Its response time from H2/N2 to O2/N2 atmosphere and vice versa is about 0.11 s and 0.12 s respectively. Although the sensitivity and response speed increase, the resistance-temperature properties of porous films are not notably improved with the increasing of the content of PEG.     

金属表面疏水性研究进展

表面疏水性是近年来科学研究的热点。在生活中观察到荷叶表面上的水滴呈现圆球状,并能在荷叶上滚动而带走灰尘。研究发现荷叶表面具有优越的疏水性和自清洁特性,主要是由其表面微观的粗糙结构和低表面能物质共同引起的。概述了荷叶表面疏水性产生的原因,指出由于荷叶表面存在大量的微米级乳突,在这些微米级乳突上还有一些纳米级结构,这种纳米级结构正是引起荷叶表面超疏水的根本原因。归纳了疏水性表面的重要理论,其中,Young方程针对平整、光滑表面,将液滴在光滑表面上的张力和接触角联系起来;Wenzel模型是在Young方程的基础上引入了粗糙度因子,Wenzel模型中液滴形成的是一种非复合式的润湿状态,液滴和固体表面完全接触;Cassie方程是Wenzel模型的延伸,液滴和固体之间不再是单纯的非复合式接触,而是混有一定空气的复合式接触。在此基础上,综述了近年来表面疏水性的制备方法,包括化学法、特种加工法和微切削法等,最后展望了疏水性表面目前存在的问题。     

超浸润油水分离膜及其研究进展

受到自然界中动植物表面超疏水/超亲水特性的启发,仿生超浸润膜材料作为一种新兴的油水分离材料引起了科研人员的广泛关注。首先通过对影响膜材料表面润湿性的基础模型进行分析,包括Young方程、Wenzel模型和Cassie模型,总结了制备超浸润膜材料需要调控的2个关键因素——表面张力和纳微多级结构。其次,对比分析了不同类型超浸润膜的油水分离过程,概述了超浸润油水分离膜的技术优势,包括油水选择性好、分离效率高、操作简单、能耗低等。揭示了常见超浸润膜对稳定油水乳液的分离机理,即基于膜孔径小于乳液尺寸的筛分效应;通过膜材料对油水截然相反的浸润性实现界面破乳和选择性分离。在此基础上,重点综述了近年来常见超浸润油水分离膜的研究进展,其中包括超疏水/超亲油膜、超亲水/水下超疏油膜、Janus膜、智能响应膜,并对不同类型的超浸润膜材料在分离过程中存在的技术优势和问题进行了分析。最后,提出了该领域研究存在的问题和面临的挑战,并对未来超浸润膜材料的发展方向和应用前景进行了展望。     

Calcination Conditions on the Properties of Porous TiO2 Film

Porous TiO₂ films were deposited on SiO₂ precoated glass-slides by sol-gel method using PEG1000 as template. The strongest XRD diffraction peak at 2θ = 25.3° is attributed to [101] plane of anatase TiO₂ in the film. The increases of calcination temperature and time lead to stronger diffraction peak intensity. High transmittance and blue shift of light absorption edge are the properties of the film prepared at high calcination temperature. The average pore size of the films increases with the increasing calcination temperature as the result of TiO₂ crystalline particles growing up and aggregation, accompanied with higher specific surface area. Photocatalytic activity of porous TiO₂ films increases with the increasing calcination temperature. The light absorption edge of the films slightly moves to longer wavelength region along with the increasing calcination time. The mesoporous film calcinated at 500 °C for 2 h has the highest transmittance, the maximum surface area, and the maximum total pore volume. Consequently, the optimum degradation activity is achieved on the porous TiO₂ film calcinated at 500 °C for 2 h.     

Effects of pH and polyethylene glycol on surface morphology of TiO2 thin film

In this investigation, a sol gel procedure for preparation of TiO₂ thin films was developed using polyethylene glycol (PEG). Effect of pH on the structure of the films was also investigated. The morphology and surface structure of the films were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that the films from the base sols had a porous structure and the surface was considerably rough. However, the films made by the acid sols were very dense and had a relatively smoother surface. It was also found that by using PEG, the surface area of the film became larger as a result of the increase in the film porosity. BET analysis confirmed the increase in the surface area which enhanced the photocatalytic activity of TiO₂ thin film in degradation of Malachite Oxalate Green.     

Photoresponse and donor concentration of plasma-sprayed TiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript>-ZnO electrodes

The photoelectrochemical characteristics of plasma-sprayed porous TiO₂, TiO₂-5%ZnO, and TiO₂-10%ZnO electrodes in 0.1 N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology, and composition of the electrodes were analyzed using an electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscopy, and x-ray diffraction. The results indicate that the sprayed electrodes have a porous microstructure, which is affected by the plasma spray parameters and composition of the powders. The TiO₂-ZnO electrodes consist of anatase TiO₂, rutile TiO₂, and Zn₂Ti₃O₈ phase. The photoresponse characteristics of the plasma-sprayed electrodes are comparable to those of single-crystal TiO₂, but the breakdown voltage is close to 0.5 V (versus that of a saturated calomel electrode). The short-circuit photocurrent density (J _SC) increases with a decrease of donor concentration, which was calculated according to the Gartner-Butler model. For the lowest donor concentration of a TiO₂-5%ZnO electrode sprayed under an arc current of 600 A, the short-circuit J _SC is approximately 0.4 mA/cm² higher than that of the TiO₂ electrodes under 30 mW/cm² xenon light irradiation. The J _SC increases linearly with light intensity. The original version of this paper was published as part of the DVS Proceedings: “Thermal Spray Solutions: Advances in Technology and Application,” International Thermal Spray Conference, Osaka, Japan, 10–12 May 2004, CD-Rom, DVS-Verlag GmbH, Düsseldorf, Germany.     

Surface properties of sol-gel processed TiO2-SiO2 amorphous composite films

TiO₂-SiO₂ amorphous composite films were synthesized via a sol-gel chemical method. Their properties, including wetting behavior, transmittance and hardness, were investigated depending on the content of SiO₂ in the films. The pure TiO₂ film revealed the typical surface properties that have normally been observed in sol-gel processed TiO₂ films. The addition of SiO₂ facilitated the hydrophilic state of the composite films, probably due to an increase of the surface hydroxyl groups. Under ultraviolet exposure, the water contact angle decreased more slowly and its recovery was retarded by increasing the content of SiO₂. Meanwhile, the addition of SiO₂ improved the transmittance in the ultraviolet-visible light region, resulting in a deterioration of the hardness.     

Effect of Na2SO4 and Water Vapor on the Corrosion of Ti3SiC2

The corrosion behavior of polycrystalline Ti₃SiC₂ was studied in the presence of Na₂SO₄ deposit and water vapor at 900°C and 1000°C. The mass gain per unit area of the samples superficially coated with Na₂SO₄ exposed to water vapor was slightly lower than that of the samples corroded without water vapor. The microstructure and composition of the scales were investigated by SEM/EDS and XRD. Pores were observed in the corroded sample surfaces. The main corrosion phases on the sample surface were identified by XRD as TiO₂, Na₂Si₂O₅ and Na₂TiO₃. After Ti₃SiC₂ corroded in the presence of the Na₂SO₄ deposit and water vapor, the scale had a three-layer microstructure, which was different from the duplex corrosion scale formed on Ti₃SiC₂ beneath the Na₂SO₄ film without water vapor. Because water vapor penetrated the corrosion layer and then reacted with SiO₂ to form volatile Si(OH)₄, an intermediate porous and TiO₂-enriched layer formed in the corrosion layer.     

Wettability of pure Ti by molten pure Mg droplets

The wetting behavior of molten pure Mg droplets on pure Ti substrate, a crucial phenomenon in the design of Mg matrix composites reinforced with Ti particles, was investigated by the sessile drop method. The contact angle was measured in high-purity argon (99.999%) at 1073 K. In particular, the effects of two important parameters on the contact angle were evaluated: Mg evaporation during the wetting test; and surface oxide film of the substrate. The calculation method to estimate the modified contact angle involved taking the morphological changes of the droplet outline due to the evaporation into consideration. By changing the thickness of the surface oxide films on the Ti substrate, it was possible to examine the wettability and the chemical reactions at the interface between the solidified Mg drop and the substrate were investigated by scanning electron microscopy–energy dispersive X-ray spectrometry analysis. At the initial wetting stage, a large contact angle with 95–110° was obtained, which depended on the reduction of TiO₂ surface films by Mg droplets. When the molten Mg contacts an area of pure Ti after reduction, the contact angle suddenly decreased. The equilibrium value at the stable state strongly depended on the surface roughness of the Ti plate.     

SLM-Ti仿生微纳米复合结构超疏水表面的构建

以选区激光熔化技术制备的金属钛为基体,采用阳极氧化法在SLM-Ti表面微米级球形"模板"上一步制备仿生微纳米复合结构。结果表明,未经紫外光照或高温处理的SLM-TiO_2纳米管在经全氟辛基三乙氧硅烷(1H,1H,2H,2H-perfluorooctyltriethoxysilane molecules, POTS)修饰后即获得了超疏水表面,其静态水接触角约163.8°,滚动角1°。对比分析了阳极氧化后商用纯钛CP-TiO_2和SLM-TiO_2的表面形貌特征和POTS修饰后的静态/动态水接触角。测得POTS修饰后的CP-TiO_2和SLM-TiO_2表面静态水接触角分别约为149.0°和163.8°,即二者均显现出静态超疏水特性。但在有自清洁、防水、防污特性要求时,材料表面的动态接触角才是更为重要的参数,在相同条件下获得的CP-TiO_2表面在倾斜至90°后水滴依然粘附在材料表面,而SLM-TiO_2表面水滴在倾斜不足1°时即快速地(155 ms内)从材料表面滚落。     

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.     

玻璃Cr2O3陶瓷涂层表面液态重金属润湿角的测量与表征

金属材料的腐蚀性能与其表面润湿特性有着密切的关系。采用亚音速火焰喷涂技术制备了玻璃-Cr2O3陶瓷涂层,设计了一套运行在高温环境中且密封的专用试验平台,研究经过不同保温时间后,重金属在45钢与喷有玻璃-Cr2O3陶瓷涂层的45钢表面的润湿角及相关现象的变化。结果表明:相同质量的重金属液滴在45钢表面的润湿角为18°,在玻璃-Cr2O3陶瓷涂层表面的润湿角为114°,玻璃-Cr2O3陶瓷涂层抗液态重金属润湿性能较好。固化后重金属颗粒与试样之间的接触面积及剪切强度均有所不同,304不锈钢与颗粒剪切强度为1.42MPa,而涂层与颗粒剪切强度为0.21MPa。     

In vitro bioactivity and osteoblast response on chemically modified biomedical porous NiTi synthesized by capsule-free hot isostatic pressing

Porous biomedical NiTi with an average porosity of 56% and a general pore size of 50-800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP) with NH₄HCO₃ as a space holder. In order to enhance the surface bioactivity, the porous alloy was subjected to H₂O₂ to form a TiO₂ coating followed by a NaOH treatment. Scanning electron microscopy (SEM), thin film X-ray diffraction (TF-XRD), and X-ray photoelectron spectroscopy (XPS) revealed that a porous sodium titanate (Na₂TiO₃) film formed on the surface of the porous NiTi due to the chemical reaction between NaOH and pre-formed TiO₂ at the interface between the NaOH solution and porous NiTi. An apatite layer was formed on the film after immersion in simulated body fluids (SBF) at 37 °C while no apatite could be found on the surface of the untreated porous NiTi. Formation of the apatite layer indicates that the chemically treated porous NiTi possesses excellent bioactivity and this bodes well for applications in bone implants. In our preliminary cell culture tests, osteoblast cells were found to attach and proliferate better on the chemically treated samples compared to the untreated alloys.     

Fabrication of Nano-TiO2 Coating for Dye-Sensitized Solar Cell by Vacuum Cold Spraying at Room Temperature

Deposition of nanocrystalline TiO₂ coating at low temperature is becoming more attractive due to the possibility for continuous roll production of the coating for assembly lines of dye-sensitized solar cell (DSC) at a low cost. In this study, porous nano-TiO₂ coating was deposited by vacuum cold spraying (VCS) at room temperature on a conducting glass substrate using commercial P25 nanocrystalline TiO₂ powder. The microstructure of TiO₂ coating was characterized by field emission scanning electron microscopy (FESEM) and nitrogen adsorption test. A commercial dye (N719) was adsorbed on the surface of TiO₂ particles within the coating to assemble a DSC. The cell performance was evaluated by employing simulated solar light at an intensity of 100 mW/cm². The results showed that TiO₂ coating was deposited by the agglomerates of nano-TiO₂ powders. The Brunauer-Emmett-Teller (BET) test of the as-sprayed TiO₂ coating yielded a porosity of 49% and an average pore size of 17 nm. The assembled solar cell yielded a short-circuit current density of 7.3 mA/cm² and an energy conversion efficiency of 2.4%. The test results indicate that VCS was a promising method to deposit nanocrystalline TiO₂ coatings at low temperature applied to DSCs. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Hierarchical structures of anodised cold gas sprayed titanium coatings

Cold gas spray (CGS) titanium coatings have been produced to obtain porous and rough coatings with enhanced mechanical performance. The coatings from optimal spraying conditions reached tensile strength values up to 40?MPa, shear strength up to 39?MPa and a loss mass of 37?mg/100 cycles in abrasive testing, values in accordance with the ASTM standards to be applied for orthopaedic joint prostheses. An innovative hierarchical structure (micro-nano) consisted of a TiO₂ nanotubes top layer obtained by anodisation onto a CGS Ti coating. The present paper focuses on the characterisation of both surfaces, as-sprayed CGS Ti layer and double Ti-TiO₂ layer, in terms of mechanical properties, surface topography and wettability (contact angle). There were not significant changes in micro-roughness, Ra～40?µm and Ra～30?µm, but a significant decrease in contact angle, from ≈26° up to 0°, was observed between these two structures. This behaviour indicates that the combination of the CGS?+?anodising results in promising high roughness superhydrophilic surfaces, ideal for biomedical applications.     

Morphology and photocatalytic activity of highly oriented mixed phase titanium dioxide thin films

Thin TiO₂ films on quartz substrates were prepared by spin coating of undoped and metal-ion-doped Sol-Gel precursors. These films were characterised by Scanning Electron Microscopy, Laser Raman Microspectroscopy, X-ray Diffraction and UV-Vis Transmission. The photocatalytic performances of the films were assessed by the photo-degradation of methylene-blue in aqueous solution under UV irradiation. Films exhibited a high degree of orientation and a thermal stabilization of the anatase phase as a result of substrate effects. In the absence of dopants, the rutile phase formed as parallel bands in the anatase which broadened as the transformation progressed. TiO₂ films doped or co-doped with transition metals exhibited the formation of rutile in segregated clusters at temperatures under ~ 800 °C as a result of increased levels of oxygen vacancies. Photocatalytic activity of the films synthesised in this work was low as likely a result of poor TiO₂ surface contact with dye molecules in the solution. The presence of transition metal dopants appears detrimental to photocatalytic activity while the performance of mixed phase films was not observed to differ significantly from single phase material.     

Microstructure and corrosion behaviour of Al2O3–13 wt-% TiO2 laser alloyed magnesium alloys

Nanostructured Al₂O₃–13?wt-% TiO₂ was prepared on AZ91D magnesium alloy surface by laser surface alloying to improve its corrosion resistance. The microstructure of the laser surface alloyed specimens before and after corrosion tests was characterised by scanning electron microscope and optical microscope (OM). The phase and element composition were investigated by X-ray diffractometer and energy-dispersive spectrometry. An electrochemical workstation was used to evaluate the corrosion behaviour of the specimens. Results showed that the laser surface alloyed layer was primarily composed of Mg and Mg₁₇Al₁₂. Al₂O₃ and TiO₂ existed in the form of agglomerated particles. The corrosion resistance was improved after laser surface alloying.     

化学刻蚀制备亲水性铝及润湿性变化规律

目的通过化学刻蚀的方法制备具有亲水性的纯铝与高纯铝表面,在室温下进行时效,分析润湿性随时效时间的变化规律。方法实验以2 mol/L浓度的盐酸进行刻蚀,将试样分别刻蚀4、8、12、16、20 min,吹干制备好的试样。利用OCA15EC接触角测量仪测定润湿角,将试样放置在室温下进行时效,并记录时效后的润湿角,分析润湿角变化的规律;采用场发射扫描电子显微镜观察试样表面的微观形貌,结合Wenzel理论与Cassie理论分析润湿角变化的原因;对试样进行EDS分析,分析时效后试样所含元素含量的变化情况,阐述润湿性变化的机理。结果不同刻蚀时间制备的样品润湿角存在差异,经过室温时效,润湿角呈现增大的趋势。结论纯铝在刻蚀时间16 min时能够获得超亲水的表面,在室温下时效5天能维持润湿角在20°以下。高纯铝在刻蚀时间为12 min时能够获得超亲水表面,经过5天的室温时效,12 min刻蚀的样品润湿性保持得较为稳定,润湿角维持在12°以下,其他刻蚀时间的样品亲水性及稳定性略差。