Takahiro Ishizaki

Corrosion Resistance and Durability of Superhydrophobic Surface Formed on Magnesium Alloy Coated with Nanostructured Cerium Oxide Film and Fluoroalkylsilane Molecules in Corrosive NaCl Aqueous Solution

The corrosion resistant performance and durability of the superhydrophobic surface on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution were investigated using electrochemical and contact angle measurements. The durability of the superhydrophobic surface in corrosive 5 wt% NaCl aqueous solution was elucidated. The corrosion resistant performance of the superhydrophobic surface formed on magnesium alloy was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the superhydrophobic surface considerably improved the corrosion resistant performance of magnesium alloy AZ31. American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the superhydrophobic film to the magnesium alloy surface. The corrosion formation mechanism of the superhydrophobic surface formed on the magnesium alloy was also proposed.

Correlation of Cell Adhesive Behaviors on Superhydrophobic, Superhydrophilic, and Micropatterned Superhydrophobic/Superhydrophilic Surfaces to Their Surface Chemistry

A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 microm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 microm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface.

Facile Formation of Biomimetic Color-Tuned Superhydrophobic Magnesium Alloy with Corrosion Resistance

The design of color-tuned magnesium alloy with anticorrosive properties and damping capacity was created by means of a simple and inexpensive method. The vertically self-aligned nano- and microsheets were formed on magnesium alloy AZ31 by a chemical-free immersion process in ultrapure water at a temperature of 120 °C, resulting in the color expression. The color changed from silver with metallic luster to some specific colors such as orange, green, and orchid, depending on the immersion time. The color-tuned magnesium alloy showed anticorrosive performance and damping capacity. In addition, the colored surface with minute surface textures was modified with n-octadecyltrimethoxysilane (ODS), leading to the formation of color-tuned superhydrophobic surfaces. The corrosion resistance of the color-tuned superhydrophobic magnesium alloy was also investigated using electrochemical potentiodynamic measurements. Moreover, the color-tuned superhydrophobic magnesium alloy showed high hydrophobicity not just for pure water but also for corrosive liquids, such as acidic, basic, and some aqueous salt solutions. In addition, the American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the color-tuned superhydrophobic film to the magnesium alloy surface.

Rapid formation of a superhydrophobic surface on a magnesium alloy coated with a cerium oxide film by a simple immersion process at room temperature and its chemical stability.

We have developed a facile, simple, time-saving method of creating a superhydrophobic surface on a magnesium alloy by a simple immersion process at room temperature. First, a crystalline CeO(2) film was vertically formed on the magnesium alloy by immersion in a cerium nitrate aqueous solution for 20 min. The density of the crystals vertically with respect to the magnesium alloy increased with increasing immersion time. Next, the film were covered with fluoroalkylsilane (FAS: CF(3)(CF(2))(7)CH(2)CH(2)Si(OCH(3))(3)) molecules within 30 min by immersion in a toluene solution containing FAS and tetrakis(trimethylsiloxy)titanium (TTST: (CH(3))(3)SiO)(4)Ti). TTST was used as a catalyst to promote the hydrolysis and/or polymerization of FAS molecules. The FAS-coated CeO(2) film had a static contact angle of more than 150 degrees, that is, a superhydrophobic property. The shortest processing time for the fabrication of the superhydrophobic surface was 40 min. The contact angle hysteresis decreased with an increase in the immersion time in the cerium nitrate aqueous solution. The chemical stability of the superhydrophobic surface on magnesium alloy AZ31 was investigated. The average static water contact angles of the superhydrophobic surfaces after immersion in the solutions at pH 4, 7, and 10 for 24 h were found to be 139.7 +/- 2, 140.0 +/- 2, and 145.7 +/- 2 degrees, respectively. In addition, the chemical stability of the superhydrophobic surface in the solutions at pH ranging from 1 to 14 was also examined. The superhydrophobic surfaces had static contact angles of more than 142 degrees in the solutions at pH ranging from 1 to 14, showing that our superhydrophobic surface had a high chemical stability. Moreover, the corrosion resistance of the superhydrophobic surface on the magnesium alloy was investigated using electrochemical measurements.

Corrosion Resistant Performances of Alkanoic and Phosphonic Acids Derived Self-Assembled Monolayers on Magnesium Alloy AZ31 by Vapor-Phase Method

Alkanoic and phosphonic acid derived self-assembled monolayers (SAMs) were formed on magnesium alloy by the vapor phase method. AFM and XPS studies showed that SAMs were formed on Mg alloy. The chemical and anticorrosive properties of the SAMs prepared on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. Water contact angle measurements revealed that, although SA and ISA have the same headgroup to anchor to the magnesium alloy surface, the packing density on the magnesium alloy surface could be considerably different. The contact angle hysteresis of SAMs with a carboxylate headgroup is much larger than that of SAMs with a phosphonic acid group. The XPS O 1s peaks indicated more likely a mix of mono-, bi-, or tridentate binding of phosphonic acid SAM to the oxide or hydroxide surface of the Mg alloy. The electrochemical measurements showed that the phosphonic acid derived SAM had better corrosion resistance compared to alkanoic acid derived SAM. The chemical stability of SAMs modified magnesium alloy was investigated using water contact angle and XPS measurements. The water contact angle and XPS measurements revealed that the molecular density of OP and PFEP on magnesium alloy would be higher than those of SA and ISA on magnesium alloy.

Simple one-step synthesis of fluorine-doped carbon nanoparticles as potential alternative metal-free electrocatalysts for oxygen reduction reaction

Fluorine-doped carbon nanoparticles (FCNPs) were synthesized via a simple one-step solution plasma process for the first time. This synthesis strategy can be achieved at relatively low temperature and atmospheric pressure without the involvement of a metal catalyst. A mixture of toluene (C6H5CH3) and trifluorotoluene (C6H5CF3) was used as a precursor for the synthesis. The fluorine doping content can be varied from 0.95 to 4.52 at%, depending on the precursor mixing ratio. The structural analyses reveal that FCNPs mainly exhibit a disordered amorphous structure. The incorporation of fluorine atoms results in the creation of more defect sites and disordered structure in the carbon particles. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of FCNPs in an alkaline solution shows a significant improvement with increasing fluorine doping content, as reflected in an increased limiting current density and a positively shifted onset potential. In association with X-ray photoelectron spectroscopy (XPS) analysis, an improved ORR activity is possibly attributed to the intercalation of ionic C–F and semi-ionic C–F bonds in the carbon structure. In addition, FCNPs possess excellent long-term operation durability and strong tolerance to methanol oxidation compared to those of a commercial Pt-based catalyst. Our results from this study not only confirm the applicability of the solution plasma process to the synthesis of FCNPs with a controllable fluorine doping level but also provide detailed information of FCNPs as potential alternative ORR catalysts for the electrocatalysis research.

In situ solution plasma synthesis of nitrogen-doped carbon nanoparticles as metal-free electrocatalysts for the oxygen reduction reaction

We report the in situ synthesis of nitrogen-doped carbon nanoparticles (NCNPs) by a solution plasma process without the addition of metal catalysts. Organic liquid mixtures of benzene and pyrazine were used as the precursors for the synthesis. The nitrogen-doping content can be easily controlled by changing the amount of pyrazine in the precursor. The NCNPs synthesized from the solution plasma process exhibit a turbostratic structure with highly uniform nanoscale particles. The nitrogen atoms can be homogeneously incorporated into the entire carbon structure due to the in situ doping during the growth and formation of the carbon particles. The electrochemical activity toward the oxygen reduction reaction (ORR) of the NCNPs in an alkaline medium reveals the improvement in terms of both the onset potential and current density as the nitrogen-doping content increases. The enhanced ORR activity of the NCNPS is mainly attributed to the presence of pyridinic-N and graphitic-N bonding configurations. They also possess long-term durability and excellent tolerance to methanol crossover effects. The results obtained in this study have demonstrated that the solution plasma process has great potential for the synthesis of metal-free nitrogen-doped carbon electrocatalysts for the ORR. We expect that this approach can be extended to the synthesis of other heteroatom-doped carbonaceous materials for a broad range of research applications in energy conversion and storage.

Structural, optical and electrical properties of ZnTe thin films electrochemically deposited from a citric acid aqueous solution

ZnTe thin films were electrodeposited onto Au-coated Cu substrates from an electrolytic solution containing ZnSO4, TeO2, citric acid and sodium citrate, and the dependence of structure, composition and surface morphology on the solutions Zn concentration were investigated. Results of examinations for resistivity and optical absorption demonstrated, respectively, that as the Zn concentration in the electrolyte was reduced over the range of 5?50?mmol?dm?3, the resistivity of the films obtained continuously decreased and their band gap increased. Quantative analysis of energy dispersive x-ray analysis and inductively coupled plasma results indicated that the composition ratio (Zn?:?Te) was approximately stoichiometric under all conditions in this study. X-ray diffraction results revealed that all the ZnTe thin films obtained showed a preferred (111) orientation with cubic structure. ZnTe thin films we transferred onto nonconductive epoxy resin also showed the same structure.

Nitrogen-Doped Carbon Nanoparticle–Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction

Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle-carbon nanofiber (NCNP-CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP-CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP-CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP-CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP-CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal-air batteries.

Fabrication and characterization of ultra-water-repellent alumina-silica composite films

Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150°, whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica–alumina system.