Key Engineering Materials Vols. 317-318

Abstract: AlN powders were synthesized by gas-reduction- nitridation of γ-Al2O3 powders using NH3 and C3H8 as reactant gases. AlN was identified from the products that synthesized at 1100-1400 oC for 120 min in the NH3-C3H8 gas flow, and it was confirmed that AlN can be easily fabricated by the gas-reduction-nitridation of γ-Al2O3. The products synthesized at 1100oC for 120min contained unreacted γ-Al2O3. By the 27A1 MAS NMR spectra, Al-N bonding in the product increased with an increase in the nitridation ratio of the tetrahedral AlO4 shoulder which decreased prior to that of the octahedral AlO6 shoulder. It seems that γ-Al2O3 was preferentially nitrided from AlO4 rather than AlO6. AlN nano particles were easily converted directly from γ -Al2O3 at a low temperature because the AlO4 within γ-Al2O3was preferentially nitrided.

Abstract: The influence of reaction temperature on phase evolution of iron oxide hollow nanoparticles during chemical vapor condensation (CVC) process using iron acetylacetonate was investigated. X-ray diffraction (XRD) analyses revealed that three iron oxide phases (α-Fe2O3, γ-Fe2O3, and Fe3O4) and a mixture of β-Fe2O3 and small amount of γ-Fe2O3 were synthesized at 700oC and 900oC, respectively. TEM observation disclosed that the iron oxide particles are almost composed of hollow structured nanoparticles of 10~20 nm in size and 3~5 nm in shell thickness. This result implies that reaction temperature determining various reaction parameters plays an important role for the phase- and structural evolutions of iron oxide hollow nanoparticles. Especially, the present investigation attempted to explain temperature dependence of the phase evolution of β-Fe2O3 hollow nanoparticles in association with the decomposition of iron acetylacetonate.

Abstract: Nano-sized MWO4 and MMoO4 (M = Ca, Ni) powders, which have scheelite and wolframite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heattreated at temperatures from 300 to 600 °C for 3 h. Crystallization of the MWO4 and MMoO4 precursors was detected at 400 °C and completed at a temperature of 500 °C. Most of the MWO4 and MMoO4 powders heat-treated between 300 and 600 °C showed primarily spherical and homogeneous morphology. The average crystallite sizes of MWO4 (M = Ca, Ni) were between 22 and 39 nm, and those for MMoO4 (M = Ca, Ni) were between 19 and 35 nm respectively, showing an ordinary tendency to grow with temperature.

Abstract: TiO2-SiO2 nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) within the micro-emulsion. The average size of synthesized TiO2-SiO2 nanoparticles was about in the size range of 20-100 nm. The effects of synthesis parameters, such as the molar ratio of water to precursor and the molar ratio of water to surfactant, are discussed.

Abstract: Nano-sized metal particles have recently attracted considerable interest owing to their application potential. Such particles can be synthesized using physical and chemical methods. In this study, nano-sized noble metals were synthesized through the reaction of metal oxides by ultrasonic. This means that the chemical reactions which take place under conventional conditions can be accelerated by ultrasonic cavitations. In general, the chemical effects of ultrasonic irradiation fall into three areas: homogeneous sonochemical efffects of liquids, heterogeneous sonochemical effects of liquid-liquid or liquid-solid systems, and sonocatalytic effects. It has been proposed that liquid-liquid systems are used for the fabrication of nano-metal particles in the past. In this study, the fabrication of nano-metal particles and supported composites was investigated for the liquid-solid system from a viewpoint of economy and ecology. By choosing suitable conditions, it is reasonable to expect that these simple ultrasonic processes can be extended to obtain nano-sized metal particles. Thus applications by using these reactions were investigated to prepare the nano-sized metal particle supported materials, and mechanisms were investigated.

Abstract: Au coated γ-Fe2O3 nanoparticles were prepared by the changing of surface charge of Au and γ-Fe2O3 nanoparticles with pH. Well Au coated γ-Fe2O3 nanocomposite particles developed in the range between isoelectric point of Au and that of γ-Fe2O3 nanoparticles. Immobilization of glutathione (GSH), crystalline polypeptide containing mercapto group, was successfully performed on the well Au coated γ-Fe2O3 nanocomposite particles. Properties of nanoparticles and GSH immobilized Au/γ-Fe2O3 were characterized by UV-vis, LPA, XRD, and TEM.

Abstract: Accumulative roll-bonding (ARB) process was applied to an oxygen free copper for improvement of the mechanical properties via ultra grain refinement to nanometer order level. Two copper sheets 1mm thick, 30mm wide and 300mm long are degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and cold-roll-bonded by 50% reduction rolling. The sheet is then cut to the two pieces of same length and the same procedure was repeated to the sheets. The ARB process up to eight cycles (an equivalent thickness strain of 6.4) is successfully performed at ambient temperature. TEM observation reveals that ultrafine grains, hardly containing the dislocation interior, begin to develop at the third cycle, and after the sixth cycle they cover most of regions of samples. The morphology of ultrafine grains formed is different from that of aluminum alloys. Tensile strength of the ARB-processed copper increases with the equivalent strain up to a strain of ~3.2, in which it reached 390 MPa, ~2.1 times higher than the initial value. However, the strength hardly changed at the strain above ~3.2.

Abstract: Via the direct hydrothermal processing using natural rutile as a starting material, long titanate nanofibers (typically 10-500 μm in length and 20-50 nm in diameter) have been successfully synthesized in high yield Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), electron diffraction, and UV-Vis spectroscopy demonstrated that the as-synthesized nanofibers presumably consisted of sodium hydrogen trititanate ((Na,H)2Ti3O7, e.g., Na0.4H1.6Ti3O7) including some hexatitanate-type defects ((Na,H)2Ti6O13). The direct hydrothermal treatment for natural rutile will be a promising low-cost processing for 1-D nanomaterials, which can act not only as the reaction step but also as the purification.

Abstract: In this study, the synthesis of nanotubular titanate was attempted though heat-treatment in an oil bath (non-hydrothermal treatment), heat-treatment with stirring in an oil bath (non-hydrothermal treatment), or hydrothermal treatment for metal Ti in NaOH aqueous solution systems. Obtained products were characterized by various methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results suggested that products obtained by both hydrothermal treatment and heat-treatment in an oil bath with and without stirring could be identified as H2Ti4O9
H2O. From TEM observations, however, various morphologies for products obtained by these treatments were confirmed. Therefore, it was considered that morphologies of these products strongly depended on synthesis conditions.

Abstract: We have investigated a synthesis of metal (Nb, V, Cr, Mn, Co) -doped titania nanotubes using a solution chemical processing in order to control optical and electrical properties. Titania nanotubes doped with a small amount of cations up to 1 wt% exhibited similar morphology and XRD pattern as the pure titania nanotubes, however, color of nanotubes was changed depending on the dopants. It was found that Cr, Mn and Co doped titania nanotubes formed new absorption bands in UV spectra. On the other hand, electrical resistivity of doped titania nanotubes was lower than that of pure titania nanotubes.