Synthesis of Metal Boride Nanoparticles Using Triple Thermal Plasma Jet System.

Titanium, nickel, and tungsten boride nanoparticles were synthesized in the triple thermal plasma jet system. The coalesced high-enthalpy thermal plasma jet not only generates extensive high temperature regions but also allows the starting materials to penetrate into the center of high temperature regions effectively. The synthesis process of metal boride was investigated according to the nucleation temperature of three metals and boron. In the case of titanium and nickel borides synthesis, metals nucleation temperatures are lower than boron. The crystallinity of synthesized titanium boride nanoparticles was higher than nickel boride nanoparticles, since not only the nucleation temperature of titanium is higher than nickel but also the Gibbs free energy of all titanium boride was lower than whole nickel boride. However, the nucleation temperature of tungsten is higher than boron where nanoparticle synthesis process differed from former synthesis processes. It had influence on the crystal growth time in the high temperature regions where tungsten boride crystal structure was strongly prepared than nickel boride nanoparticles.

Synthesis of Tungsten Carbide Nanomaterials in Triple DC Thermal Plasma Jet System.

The tungsten carbide nanomaterials were synthesized in the triple DC thermal plasma jet system using refractory tungsten, and carbon sources such as multi wall carbon nanotube (MWCNT), amorphous carbon and methane. The starting materials were evaporated in the high temperature region of triple plasma jet, then condensed particles were prepared in nanoscale under 100 nm. The effect of carbon sources was investigated on a view of crystal phase structure and morphology. W2C crystal nanoparticles were mainly synthesized and WC and WC1-x phase nanoparticles were observed additionally with all carbon sources. From MWCNT starting material, tungsten carbide attached MWCNT composite were produced with spherical tungsten carbide nanoparticles. In case of amorphous carbon, spherical and rod-shaped tungsten carbide was synthesized. Only spherical tungsten carbide nanoparticles were synthesized by methane. In addition, it was revealed that the main crystal structure was changed from W2C to WC1-x by increasing W/CH4 composition ratio.

Self-healable soft shield for γ-ray radiation based on polyacrylamide hydrogel composites.

With the growing risk of radiation exposure, there are growing interests in radiation shielding. Because most radiation shields are made from heavy metals, a need to develop a soft shield is raised to protect human body. However, because the shield can easily undergo a mechanical damage by an impact, it would be better to have self-repairing system in the shield. Here, we have fabricated an intrinsic self-healable soft shield for gamma ray by making acrylamide based hydrogel composite. The composite contains lead dioxide nanoparticles for gamma ray shielding and Laponite clays for self-repairing. Although the hydrogel contained a large amount of lead dioxide nanoparticles (3.23 M), the fabricated composites stretched beyond 1400% while showing a high attenuation coefficient of 0.1343 cm-1 against gamma ray from a cobalt-60 source. Then a systematic study was performed to analyze self-healing properties and the 96.55% of maximum self-healing efficiency was obtained. We also analyzed a storage modulus of hydrogel and molecular weight of polyacrylamide to study an effect of gamma ray on the self-healing. The self-healing efficiency was decreased by a gamma ray because the radiation induces scissioning or covalent crosslinking in the chains.

Sewable soft shields for the γ-ray radiation.

Soft shields are required to protect the human body during a radioactive accident. However, the modulus of most soft shields, such as HDPE and epoxy, is high, thereby making it difficult to process them in wearable forms like gloves and clothes. We synthesized a soft shield based on a hydrogel that is very compliant, stretchable, and biocompatible. The shields were fabricated by integrating γ-ray-shield particles into hydrogels with an interpenetrating network. The soft shields containing 3.33 M of PbO2 exhibited a high attenuation coefficient (0.284 cm-1) and were stretched to 400% without a rupture. Furthermore, the fabricated soft shield can be sewn without a fabric support due to its high energy-dispersion ability. A wearable arm shield for the γ-ray radiation was demonstrated using a direct sewing of the soft-shield materials.

Thermal Plasma Synthesis of Crystalline Gallium Nitride Nanopowder from Gallium Nitrate Hydrate and Melamine.

Gallium nitride (GaN) nanopowder used as a blue fluorescent material was synthesized by using a direct current (DC) non-transferred arc plasma. Gallium nitrate hydrate (Ga(NO3)3∙xH2O) was used as a raw material and NH3 gas was used as a nitridation source. Additionally, melamine (C3H6N6) powder was injected into the plasma flame to prevent the oxidation of gallium to gallium oxide (Ga2O3). Argon thermal plasma was applied to synthesize GaN nanopowder. The synthesized GaN nanopowder by thermal plasma has low crystallinity and purity. It was improved to relatively high crystallinity and purity by annealing. The crystallinity is enhanced by the thermal treatment and the purity was increased by the elimination of residual C3H6N6. The combined process of thermal plasma and annealing was appropriate for synthesizing crystalline GaN nanopowder. The annealing process after the plasma synthesis of GaN nanopowder eliminated residual contamination and enhanced the crystallinity of GaN nanopowder. As a result, crystalline GaN nanopowder which has an average particle size of 30 nm was synthesized by the combination of thermal plasma treatment and annealing.

Simultaneous treatment of NO and SO2 with aqueous NaClO2 solution in a wet scrubber combined with a plasma electrostatic precipitator.

NO and SO2 gases that are generally produced in thermal power plants and incinerators were simultaneously removed by using a wet scrubber combined with a plasma electrostatic precipitator. The wet scrubber was used for the absorption and oxidation of NO and SO2, and non-thermal plasma was employed for the electrostatic precipitation of aerosol particles. NO and SO2 gases were absorbed and oxidized by aerosol particles of NaClO2 solution in the wet scrubber. NO and SO2 reacted with the generated NaClO2 aerosol particles, NO2 gas, and aqueous ions such as NO2(-), NO3(-), HSO3(-), and SO4(2-). The aerosol particles were negatively charged and collected on the surface of grounded anode in the plasma electrostatic precipitator. The NO and SO2 removal efficiencies of the proposed system were 94.4% and 100% for gas concentrations of 500 mg/m(3) and a total gas flow rate of 60 Nm(3)/h, when the molar flow rate of NaClO2 and the gas-liquid contact time were /min and 1.25 s, respectively. The total amount and number of aerosol particles in the exhaust gas were reduced to 7.553 µg/m(3) and 210/cm(3) at the maximum plasma input power of 68.8 W, which are similar to the values for clean air.

Synthesis of Cubic Boron Nitride Nanoparticles from Boron Oxide, Melamine and NH3 by Non-Transferred Ar-N2 Thermal Plasma.

Cubic boron nitride (c-BN) which is has extremely high hardness and thermal conductivity comparable to the diamond was synthesized in nanoparticle form by using non-transferred thermal plasma. The input power of arc plasma was fixed at 13.5 kW and the operating pressure was also fixed at atmospheric pressure. Boron oxide (B2O3) and melamine (C3H6N6) were used as raw materials for the sources of boron and nitrogen. Ammonia gas (NH3) was additionally injected to plasma jet as reactive gas providing additional nitrogen. Decomposed B2O3 and C3H6N6 enhance reactivity for synthesizing c-BN with exothermic reactions between carbon, hydrogen and oxygen. Products were collected from the inner wall of reactor. In X-ray diffraction and scanning electron microscope measurements, the collected powder was confirmed as c-BN nanoparticles which have crystalline size smaller than 150 nm.