Solid State Phenomena Vols. 124-126

Abstract: In this study hydroxyapatite (HA) was coated by sol-gel method on Ti6Al4V alloy substrates: on micropolished surface and after titania (titanium oxide) treatment. Former shows the cracks and poor bonding of HA whereas latter shows coating without cracks and higher bonding strength. The higher bonding strength of HA coating in titania treated sample could be attributed to the increased roughness by titanium oxide layer.

Abstract: The TiO2 sol was prepared hydrothermally in an autoclave from aqueous TiOCl2 solutions as starting precursor. Hollow fibers were obtained when sol-gel derived TiO2 sol was treated chemically with NaOH solution and subsequently heated in autoclave under various conditions. A systematic analysis of the influence of different NaOH concentrations on the formation of nanotubes has been carried out using XRD and SEM. The phase structure of the synthesized material was determined by transmission electron microscopy and found that these materials are, infact, hollow fibers widely known as nanotubes. From the TEM images, the outer and inner diameters of the tubes were measured ca. 8 and about 4 nm, respectively, with several hundred nanometers in length.

Abstract: Large areas of one-dimensional ZnO nanostructures (nanorods and nanowires) were prepared by simple solvothermal method. The synthesis involves a template-less and surfactant free aqueous methods. In this study, Zn metal sheet was used as both Zn2+ ion source for the growth of ZnO nano-structures and substrate for oxide film. The mixed solvent of 1-propanol with water was used as solvents for nanorods and ethylene glycol with water was for nanowires. The solvothermal treatment of a zinc metal plate with the solvents at the temperature of 125 oC for 10 hours resulted in the 1-D ZnO nanostructures, which were grown on the Zn metal sheet. The synthesized ZnO was well aligned on whole area of substrate and the nanorods were 150 nm in diameter and 3 μm in lengths, respectively.

Abstract: The paper presents the effect of acid treatment on the structure of single-walled carbon nanotube (SWNT) bundles and on the characteristics of SWNT-based gas sensors. The commercial SWNT powder was treated with a mixture of concentrated H2SO4:HNO3 (3:1 in volume) before used to fabricate sensors for ammonia (NH3) detection at room temperature. The Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) images indicated that the acid treatment not only removed most of catalytic particles from the SWNT bundles, but also caused SWNT bundles to be fragile. The fracture of the SWNT facilitated for gas molecules to adsorb in the SWNT sites, leading to an enhancement in sensitivity of the sensors. Upon exposing to 50 ppm NH3 in 450 sccm of nitrogen flowing rate at room temperature, the resistance of the 2-h-stirred sensors increased to 38% compared to 22% of the 1-h-stirred sensor. The recovery of the SWNT sensor was also accelerated owing to the treatment. These findings opened a new direction to improve the characteristics of SWNT-based gas sensors.

Abstract: Noble metal (Au, Pd, Pt) loaded SnO2 sol solutions have been synthesized under hydrothermal condition. The mixed solution of noble metal chloride (HAuCl4, H2PtCl6, or PdCl2) and SnCl4 was neutralized with NH4HCO3 solution. The precipitate gel obtained was thoroughly washed and finally treated under hydrothermal condition (200 oC for 3 h at pH10.5) to obtain transparent sol solution. From SEM and TEM images of powder or thin film derived from sol, any noble metal particles could not be observed. However, the grain growth was suppressed when calcined at 900 oC for noble metal loaded SnO2. The peaks of Sn3d and O1s levels in XPS were shifted to the lower binding energy side. The electrical resistances of thin films prepared from noble metal loaded SnO2 sol were larger than that of pure SnO2 thin film. These results suggested that the noble metals were certainly loaded on SnO2 surface or included in the film to modify the surface state of SnO2.

Abstract: The texture development and the mechanical properties were investigated in a nanocrystalline Fe-50wt%Ni alloy fabricated by using an electrodeposition method. The as-deposited texture was characterized by a mixture of major <100>//ND and minor <111>//ND fibre components. Grain growth occurred in the specimen during annealing above 410oC, and resulted in the texture change that the <111>//ND fibre component developed strongly with decreasing <100>//ND fibre component. This texture evolution was attributed to the abnormally rapid growth of the <111>//ND grains, which became much coarser than the <100>//ND and other oriented grains in the fully annealed specimen.

Abstract: Cuprous oxide nanoparticles at high concentration (up to 0.3M) were successfully synthesized by modified polyol process. The redispersion stability could be controlled by optimizing various conditions like polymer concentration, temperature, reductant, and catalyst. Reductant and catalyst play a crucial rule in redispersion of cuprous nanoparticles. Under poor conditions, particles grow to larger sizes due to aggregation of nanoparticles. This modified polyol process allows monodispersed cuprous oxide to be obtained on gram scale in a single reaction and make possible a high synthetic yield of more than 80%.

Abstract: The synthesis and characterization of polymer-stabilized silver nanoparticles (Ag NPs) for water-based silver inks are studied. In order to synthesize Ag NPs with spherical shape, the conventional polyol processes require an excess of poly(vinyl pyrrolidone) (PVP) (10 ~ 1000 times than AgNO3) and therefore result in low productivity per reactor volume. In this study, poly(acrylic acid) (PAA) with carboxylic acid group was used instead of PVP. Even at less molar ratio of PAA to AgNO3 (< 2), the spherical Ag NPs with average size of 30 nm were successfully synthesized at 100 gram-scale with high reaction yield of 90%. Furthermore, the Ag NPs were dispersed into alcohol-based solvent and then patterned into metallic lines through inkjet printing technology.

Abstract: Nickel nanoparticles were prepared by reduction of nickel-hydrazine complex with sodium borohydride (NaBH4) in water-in-oil (w/o) microemulsion of PVP/ethanol/toluene/water at 50
C. It was investigated through SEM and TEM photographs that the nickel nanoparticles with a diameter 15~20nm were nearly monodispersed. By the analysis of XRD, the resulting particles were characterized to be pure crystalline nickel with a face-centered cubic structure. The results indicate that the size, shape and distribution of particles depend on the mole ratio of [water]/[PVP] and [NaBH4]/[Ni]. Also, it was found that particle size could be controlled by the kinds of surfactants.

Abstract: A pH sensitive polyacrylonitrile (PAN) fiber, exhibiting soft actuation as a linear actuator, is prepared by electrospinning to investigate the optimum experimental condition of the as-spun fibers and the effect of pH variation on length change of PAN gel fiber. Unbeaded smooth and continuous PAN nanofibers with diameter of ~700 nm are obtained for the 10 wt% PAN fibers at a flow rate of 0.5 mL/h and an electric field of 0.875 kV/cm, suggesting that the value of viscosity is the most significant on the fiber morphology. Diameter and volume changes of PAN filaments are observed as greater than 100% and greater than 720%, respectively for pH activated systems. A typical hysteresis loop is observed for the length change (~38%) of PAN gels with respect to pH variation.