Materials Science Forum Vols. 534-536

Abstract: Colloid stability of the suspensions of Ni nanoparticles has been investigated with adding polymeric dispersant in various organic media. We characterized the dispersion stability of Ni nanoparticles by means of visual inspection, transmission profiles measured by Turbiscan, the particle size distribution, and the zeta potential. 0.01 wt% of Ni nanoparticles were found to be optimally dispersed in ethanol among various organic media employed in this study with adding the dispersant (0.6 wt%-2 wt%). As the concentration of the dispersant increased, the particle size decreased in size from 300 nm to 200 nm due to less coalescence. The zeta potential values of the Ni nanoparticles in suspensions with the dispersant were greater than -40mV. Such stable Ni nanoparticle suspensions are attributed to the electrosteric effect of the polymeric dispersant.

Abstract: Branched sulfonated poly(ether sulfone-ketone) copolymer was prepared with bisphenol A, 4,4-difluorobenzophenone, sulfonated chlorophenyl sulfone (40mole% of bisphenol A) and THPE (1,1,1-tris-p-hydroxyphenylethane) as a branching agent. THPE was used 0.4 mol% of bisphenol A to synthesize branched copolymers. Organic-inorganic nano composite membranes were prepared with copolymer and a series of SiO2 nanoparticles (20 nm, 4, 7 and 10 wt%). The composite membranes were cast from dimethylsulfoxide solutions. The films were converted from the salt to acid forms with dilute hydrochloric acid. The membranes were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. Branched copolymer and nano composite membranes exhibited proton conductivities from 1.12x10-3 to 6.04x10-3 S/cm2, water uptake from 52.9 to 62.4%, IEC from 0.81 to 1.21 meq/g and methanol diffusion coefficients from 1.2x10-7 to 1.5x10-7 cm2/S.

Abstract: We demonstrate the methodology of engineering the multi-component ceramic nanopowder with precise morphology by ‘nano-blast’ calcinations decomposition of preliminary engineered nanoreactors. Multiple explosions of just melted C3H6N6O6 embedded into preliminary engineered nanoreactors break apart the agglomerates due to the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during each nano-explosion in surrounding area. This methodology was applied for production of agglomerate-free nanoaggregates of Gd20Ce80O1.95 with an average size of 42 nm and LaSrGaMgO3-x nanopowder with an average aggregate size of 83 nm.

Abstract: Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum monohydroxide, boehmite(AlO(OH)), was predominantly formed by the application of an electrical potential above 30V, while the mixture of the bayerite(Al(OH)3) and boehmite(AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure which is controlled on a nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of an aggregation of the various crystals stacked together. The specific surface area of the boehmite nanofiber was remarkably high, reaching about 300m2/g.

Abstract: Ni59Zr20Ti16Si2Sn3 bulk metallic glass (BMG) powders were produced by a gas atomization process, and ductile Cu powders were coated on the Ni-based BMG powders using a spray drying process in order to increase the ductility. Characteristics of the as-prepared powders with the atomization and spray drying process conditions were investigated. The atomization was conducted at 1450oC under the vacuum of 10-2 torr and the powders were mixed with water-soluble Cu nitrate. The mixture was sprayed at the temperature of 130oC to prepared initial powder. After reduction treatment, sub-micron size Cu powders were successfully coated on the surface of the atomized Ni BMG powders.

Abstract: Synthesis of iron nanopowder by room-temperature electrochemical reduction process of α-Fe2O3 nanopowder was investigated in terms of phase evolution and microstructure. As process variables, reduction time and applied voltage were changed in the range of 1~20 h and 30~40 V, respectively. From XRD analyses, it was found that volume of Fe phase increased with increasing reduction time and applied voltage, respectively. The crystallite size of Fe phase in all powder samples was less than 30 nm, implying that particle growth was inhibited by the reaction at room temperature. Based on the distinct equilibrium shape of crystalline particle, phase composition of nanoparticles was identified by TEM observation.

Abstract: Synthesis of nano TiC powder by carbothermal reduction procedure of TiO2 was investigated. TiO2 was mixed with resin or carbon powder as reduction agent and was reacted at 1500oC for 0 ~ 45 minutes under Ar atmosphere. Conglomeration of the powders mixed with TiO2 and resin were observed in the initial stage of the reduction and the unreacted TiO2 was not found even after 5 minutes elapsed. The fine TiC particles with a size of 80 nm were formed by complete reaction between Ti, a reduction product, and C after 15 minutes. However, the conglomerated particles were not the powders added with carbon powder as carbon source in the initial stage. The unreacted TiO2 particles were kept for 15 minutes. Finally, TiC particles were formed and were partially grown after 20 minutes.

Abstract: The carbothermal reduction synthesis process of titanium diboride (TiB2) particles was studied. In the synthesis of TiB2 using carbothermal reduction from a mixture of TiO2, B2O3 and carbon, solid-solid reactions occur. TiO2 particles rapidly react with carbon to TiC, which then reacts with boron oxide and carbon to TiB2. In the vacuum condition, TiB2 particles were formed within 10 minutes at temperature of 1300oC. It seems that a high exothermic reaction eventually results in the increase of reaction rate. In flowing argon atmosphere, TiB2 particles were formed at temperature of 1550oC after a reaction of 0 minute and it showed a finer particle size than that in the vacuum condition. This is attributed to the faster heat elimination due to the flowing argon. In high atmospheric pressure of argon gas such as 20 atm in reaction or cooling state, the synthesized TiB2 particles shows a mixture of diverse sized particles.

Abstract: Mono-sized silicon particles were effectively fabricated by a novel way named pulsated orifice ejection method (POEM). The particles are with very narrow particles size distribution and very small standard deviation of mean particle size. There are two different types spherical silicon particles were found. One consists of many grains mainly in random boundaries. The other consists of two or three grains with only twin orientation relationships, even single crystal in cross-section was also found within this type spherical silicon particles.

Abstract: The present investigation has attempted to optimize hydrogen reduction process for the mass production of Fe-8wt%Ni nanoalloy powder from Fe2O3-NiO powder. In-situ hygrometry study was performed to monitor the reduction behavior in real time through measurement of water vapor outflowing rate. It was found that the reduction process can be optimized by taking into account the apparent influence of water vapor trap in the reactor on reduction kinetics which strongly depends on gas flow rate, reactor volume and reduction.