Materials Science Forum Vols. 449-452

Abstract: We examined quenching of growth of ZnO nanoparticles with the injection of various organic surfactants. Aliphatic isocyanides as well as organothiols were found to adsorb on ZnO nanoparticle surfaces. For a carboxylate-terminated thiol, a retardation of growth appeared to be effective presumably due to the adsorption of the carboxylate COO- group on the ZnO surface. Photoluminescence spectra and transmission electron microscopy images were obtained for thiolcapped ZnO nanoparticles. The thiol-capped ZnO nanoparticles was found to fluoresce at the wavelength shorter by ~6 nm than those in the absence of any organic surfactants.

Abstract: This work has attempted to find a new low temperature reduction process for fabrication of Cu nanopowder from fine CuO powder. For this purpose, we used electrochemical reduction method which is conducted in an electrolyte of NaCl aqueous solution at room temperature. It was found that ball-milled CuO powder (particle size ~100 nm and grain size ~40 nm) was completely reduced under the conditions of 20 V power, 0.5 mol NaCl solution and 2 h reaction time, producing Cu nanopowder (particle size ~80 nm and crystallite size ~25 nm). Simultaneously, we observed that sintering of nanopowders occurred during the reduction process, leading to agglomeration of nanopowder. Based upon the experimental results, the correlation between electrochemical reduction process and its related powder characteristics was discussed in terms of material transport.

Abstract: Sintering process of powder injection molded (PIMed) Fe-50wt%Ni nanoalloyed powder was investigated in association with microstructure development and residual impurity effect. Compared to conventional powder metallurgical (PM) processed Fe-Ni nanoalloy powder, the PIM compact showed a homogeneous and uniform densification behavior. This is owing to more homogeneous particle distribution in the PIM resulting from preparation of feedstock which was fabricated by mixing of nano powder with thermoplastic binder. Residual impurities originating from the binder material did not have any apparent influences on sintering behavior. Conclusively, Fe-50wt%Ni nanoalloy powder is effectively applicable to the PIM parts.

Abstract: We studied ZnO nanoparticle formation in a polyimide (PI) film. Polyamic acid (PAA) was spin-coated onto Zn thin films and PAA/metal films were cured at various temperatures. Transmission electron microscopy was used to characterize oxide nanoparticles in the polyimide film. Nanosize ZnO particles were formed in the polyimide film regardless of the curing temperature. The size and the density of ZnO particles depended on the curing temperature. Th

Abstract: Surface nanocrystallization in various steels by shot peening (both air blast and ultrasonic) and particle impact processing was investigated. Nanocrystalline layers with several µm thick were successfully fabricated by these methods. In all the case, the nanocrystalline layers have extremely high hardness and separated from adjacent deformed structure regions with sharp boundaries. By annealing, the nanocrystalline layers showed substantially slow grain growth without recrystallization. Those characteristics are similar to those observed in the samples experienced ball milling and ball drop deformation.

Abstract: Ultrasonic inspection of the cast stainless steel with coarse grain size has not been possible to demonstrate unambiguously that current inspection techniques are adequate, which means it is very difficult for ultrasonic inspector to discriminate the reflected signals at the real flaw from scattered signals. In this paper, wavelet denoising is performed in the stationary wavelet domain by means of scale-varying threshold level to reduce the speckle and to enhance flaw-visibility. Experiments have been carried out on A-scan ultrasonic signals obtained from CCSS material which is a part of narrow gap welds connecting the steam generator to main reactor coolant piping in the nuclear power plant.

Abstract: A series of polybenzoxazine-silica hybrids was papered by blending benzoxazine monomer with various ratios of tetraethoxysilane (TEOS) as a precursor for silica. The blends after hydrolysis and condensation of TEOS were thermally treated gradually up to 240oC to afford the hybrids. The IR spectra and DSC showed the completion of the ring opening of benzoxazine monomer and formation of silica by the end of the 240oC cure. The inclusion of silica into polybenzoxazine matrix has a noticeable effect on the thermal and mechanical properties.

Abstract: Spherical nano-sized SiO2 particles have been synthesized from sodium silicate by emulsion method. The influence of emulsifier content and mixing time on the morphology and particle size distribution of the resulting materials was investigated. The characteristics of the obtained SiO2 particles were examined by means of XRD, SEM, TEM, and PSA. The monodispersed shperical SiO2 with the average particle size 20 nm was obtained at a emulsifer content of 3vol% and mixing time of 60 min using ultrasonic disruptor. After calcining at 1200oC for 2 hrs, the amorphous SiO2 transformed wholly to the crystalline cristobalite. As increase in emulsifier content from 1 to 3 vol% did not nearly influence on the morphology of SiO2 particle but slightly changed the particle size distribution. The average particle size of SiO2 decreased significantly from 100 nm to 20 nm with increasing the mixing time.

Abstract: Novel fabrication routes of oxide/semiconducting hybrid nanotubes or coaxial nanocables with 30~200 nanometers of radius and ~10 micrometers of length using atomic layer deposition (ALD) and soluble nano-templates was reported. In order to fabricate the hybrid nanotubes using nanotemplates, which were treated with surface modification using SAMs in order to achieve selective deposition only onto inner wall of the template. Deposition of metal oxide layers (TiO2, ZrO2) conformally and uniformly onto the wall of templates using ALD. To fabricate metal oxide/CdS nanocables or coaxial nanotubes, CdS was deposited onto metal oxide nanotubes by chemical bath deposition. Coaxial nanocables was also 30-200 nm in diameter and 1-10
in lengths.

Abstract: Ultra-fine Fe2O3 nano-particles are synthesized using H2/O2 co-axial diffusion flame with the state-of-the-art electro-spraying (e-spray) technique at atmospheric condition. Fe(CO)5 is used as a precursor and the liquid phase Fe(CO)5 is injected directly into the center of the flame using the electro-spraying method. The synthesized particle morphology sampled from the inside of flame is analyzed by TEM. The synthesized particles showed different crystal structures for different particle collection method and the collection positions.