Yoshitake Masuda

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.

Room temperature deposition of a TiO2 thin film from aqueous peroxotitanate solution

A transparent, high purity, amorphous titanium dioxide thin film composed of densely packed nanometer-sized grains has been successfully deposited on a glass substrate at room temperature from an aqueous peroxotitanate solution using a simple, inexpensive, reproducible, and environmentally friendly method. The as-deposited thin film was 117 nm thick and composed of closely packed particles of 10–15 nm in diameter, but they aggregated into large grains of 50–100 nm in diameter. The aqueous peroxotitanate solution was obtained by dissolving metatitanic acid (H2TiO3) in a mixture of concentrated H2O2 and NH3·H2O. An anatase TiO2 thin film was obtained by heating the as-deposited thin film at 500 °C for 1 h in air. A chemical composition of TiO1.4(O2)0.5(OH)0.2·1.34H2O is proposed for the as-deposited thin film, based on XPS, FT-IR and TG-DTA data. Band gap energies of 3.20 eV for indirect transition and 3.63 eV for direct transition were obtained for the anatase TiO2 film.

Formation and Photocatalytic Application of ZnO Nanotubes Using Aqueous Solution

Vertically aligned ZnO nanotubes were prepared by etching ZnO rod arrays in aqueous solution, which were previously developed by chemical bath deposition method. The morphological, structural, photoluminescence, as well as photocatalytic properties of the ZnO nanotubes were examined with respect to the pH values of chemical bath solution. The morphology of the products was found to be sensitive to the pH values and chemical bath temperatures. The nanotubes synthesized at a low pH value (5.82) exhibited a strong UV emission and a weak defect-related visible emission. The highest photocatalytic efficiency was also observed at pH = 5.82. The possible mechanism for the difference of photocatalytic efficiency was discussed.

Thermoelectric performance of Bi- and Na-substituted Ca3Co4O9 improved through ceramic texturing

Plate-like particles of Ca3Co4O9 have been prepared in which Bi and Na were partially substituted for Ca to improve the thermoelectric performance. Successfully fabricated dense and highly textured ceramics have been obtained by combining the templated grain growth technique (TGG) with hot-pressing (HP). Ca3Co4O9 single crystals, which have alternating layers of Co–O and Ca–Co–O in the direction of the c-axis, show high electrical conductivity along the layer compared with that across the layer. Hence, a highly oriented TGG + HP specimen showed high electrical conductivity compared with the specimen sintered under uniaxial pressure (UP + PLS). The improved electrical conductivity with high Seebeck coefficient of the highly oriented specimen (TGG + HP) gave a high thermoelectric power factor of 5.9 × 10−4 W m−1 K−2 at 1073 K. The figures-of-merit at 773 K and 1073 K were calculated to be 8.54 × 10−5 K−1 (ZT = 0.066 at 773 K) and 1.69 × 10−4 K−1 (ZT = 0.18 at 1073 K), respectively. These values are quite high among Ca–Co–O polycrystalline systems reported so far.

Selective deposition and micropatterning of titanium dioxide thin film on self-assembled monolayers☆

Ž. We succeeded in fabricating micropatterns of titanium dioxide thin films on SAMs self-assembled monolayers . SAMs of OTS Ž. octadecyltrichloro-silane were formed on Si wafers, and were modified by UV irradiation using a photomask to generate Ž methylsilanol-pattern. They were used as templates to deposit titanium dioxide thin films by the use of TDD titanium . dichloride diethoxide . Amorphous films with approximate compositions TiOClC 1:2.2:0.17:0.37 were selectively deposited on silanol regions. Line width variation of the pattern of an as-deposited film was improved to be well below the electronics Ž. design rule, 5%. Annealing the films at high temperatures 400600C gave rise to an anatase phase, while the resolution of a micropattern remained unchanged. 2001 Elsevier Science B.V. All rights reserved.

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.

Highly mesoporous α-Fe2O3 nanostructures: preparation, characterization and improved photocatalytic performance towards Rhodamine B (RhB)

Single-crystalline porous hematite nanorods and spindle-like nanostructures were successfully synthesized by a low temperature reflux condensation method. Two different iron sources, namely, FeCl3?6H2O and Fe(NO3)3?9H2O, were hydrolyzed in the presence of urea to selectively prepare nanorods and spindle-like nanostructures. Initially, the akagenite phase was obtained by refluxing the precursor for 12?h and then the as-prepared akagenite nanostructures were transformed to porous hematite nanostructures upon calcination at 300??C for 1?h. The shape and the aspect ratio of the 12?h refluxed sample was retained even after calcination and this shows the topotactic transformation of the nanostructure. TEM and HRTEM investigations have shown the porous nature of the prepared sample. Brunauer?Emmett?Teller and Barret?Joyner?Halenda measurements have shown a large surface area and distribution of mesopores in the nanorods sample. The photocatalytic activity of the prepared nanostructures towards RhB has reflected this variation in the pore size distribution and specific surface area, by showing a higher activity for the nanorods sample. Magnetic studies by VSM have shown a weak ferromagnetic behaviour in both the samples due to shape anisotropy.

Controlled growth of single-crystalline, nanostructured dendrites and snowflakes of α-Fe2O3: influence of the surfactant on the morphology and investigation of morphology dependent magnetic properties

Single-crystalline, nanostructured dendrites, single and double-layered snowflakes of hematite (α-Fe2O3) were synthesized by a well controlled, surfactant-assisted hydrothermal reaction of K3[Fe(CN)6]. By varying the preparatory conditions such as precursor concentration and type of surfactant, we could establish precise control on the morphology of the sample. X-Ray diffraction, Raman analysis and X-ray photoelectron spectroscopic studies have confirmed that the as grown morphologies were hematite. Dendrites were obtained due to weak dissociation of the precursor and controlled diffusion of α-Fe2O3 nanoparticles under non-equilibrium conditions which attach and grow along certain preferred crystal facets. In the presence of a surfactant, single and double-layered snowflakes were formed. The type of surfactant and the nature of micelle formation were proposed to be the key factor for the observed snowflakes and the single or double-layered growth. Magnetic studies have shown morphology dependent magnetic properties with variation in the coercivity values for dendrites, single and double-layered snowflakes.

Thermoelectric Performance of Yttrium-substituted (ZnO)5In2O3 Improved through Ceramic Texturing

Thermoelectric oxides with comparatively high figures of merit possess layered structures. Because they exhibit thermoelectric anisotropy, textured crystal-axis-oriented ceramics should be produced in order to realize the best performance. We have succeeded in fabricating textured ceramics of yttrium-substituted (ZnO)5In2O3 by the reactive templated grain growth (RTGG) technique, and achieved the highest figure of merit (ZT~0.33 at 1073 K) among n-type oxide materials reported so far.

Influence of ionic size of rare-earth site on the thermoelectric properties of RCoO3-type perovskite cobalt oxides

Abstract Thermoelectric properties of Ca-doped RCoO3 (R=Pr, Nd, Sm, Gd, Dy, Ho) perovskites were studied in the temperature range of 373–1173 K. Electrical conductivity increased and Seebeck coefficient decreased with increasing the ionic radius of rare-earth elements (Ho3+