Sung Park

Preparation of La0.84Sr0.16CrO3 powders by pH-controlled glycine-nitrate process

The variations in the crystallinity and particle size of La0.84Sr0.16CrO3 powders synthesized using precursor solutions with various pHs in the glycine-nitrate process were investigated. Increasing the pH of the precursor solution promotes the formation of a complex between the Sr nitrate and the COOH group of the glycine. Powders with a higher crystallinity and finer particle size were obtained with increasing the pH of the precursor solution. It is thought that higher crystallinity and finer particle size of the powders synthesized using precursor solutions with high pH are due to homogeneous combustion resulting from the increased degree of complex formation of the Sr nitrate with the carboxylic acid group of the glycine.

Removal of Cu++ Ions from Aqueous Cu-EDTA Solution Using ZnO Nanopowder

Nanometer size zinc oxide (ZnO) powder was prepared by a novel “solution-combustion method (SCM)”, and it was used as a semiconductor photocatalyst to evaluate its photoreduction properties. Aqueous solution of heavy metal ions (Cu-EDTA) was used for the photocatalysis reaction under UV illumination. The result was then compared with other semiconductor photocatalyst powders such as titanium dioxide (TiO2) powder (P25; Degussa) and TiO2 powder prepared by a homogeneous precipitation process at low temperature (HPPLT). The zinc oxide nanopowder showed the highest removal rate of the Cu++ ions from the solution among the photocatalyst powders compared. The superior photoreduction ability of the ZnO nanopowder appears to be due to its excellent UV absorption capacity.

Sealing Behavior of Visco-Elastic Composite Seals for SOFC Applications

Porous composites containing ceramic fiber have been developed for the fabrication of SOFC seals. They were fabricated using glass powder and alumino-silicate chopped fibers. Effect of mixing ratios of ceramic fiber and glass on the leak rates and strength of the composite seals was investigated. In addition, seal performance of commercial glasses was compared with that of SiO2-BaO-B2O3 glass synthesized in this work. The leak rate of the composite seals containing 55 vol% glass was seven times higher than the one containing 75 vol% glass. The flexural strength of the composite seals was reduced to one fourth of the initial value as the porosity increased from 1 to 29%. The incorporation of alumino-silicate chopped fibers into a sealing glass degraded room temperature strength and increased leak rates due to increase in porosity with increasing fiber content. The viscosity of glass at the seal test temperature is presumed to affect the leak rate of the glass seal.

Synthesis of Solution-Combusted ZnO Nanopowder and Its Application to Gold Recovery

Photocatlytic ZnO nanopowders were synthesized by a novel method referred to as “solution-combustion method (SCM)”. They were synthesized using various oxidants and fuels. Single-phase ZnO powders were obtained. The ZnO powder synthesized using Zn(OH)2 and glycine as an oxidant and a fuel at fuel/oxidant ratio of 0.8, showed best powder characteristics such as average grain size of 30 nm and the specific surface area of 120 m2/g. The photocatalytic gold recovery efficiency by this SCM ZnO nanopowders was about 6 fold higher compared to the case by the state of the art commercial TiO2 nanopowders. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating one. This technology is therefore very viable and cost-effective to obtain high purity gold from plating wastewater.

Emissive Carbon Coating for Energy Saving

Emissive carbon coating was prepared using a carbon black powder and a phenolic resin binder suspension. Interior of an alumina tube with an emissivity of 0.75 was coated with the emissive coating and its energy saving performance was investigated using a vacuumed alumina tube up to 1000°C. The vacuumed cavity temperature of the carbon-coated alumina tube embedded in an electrically heated furnace was always higher than that of the uncoated one for the same surface temperature of the tube. The cavity temperature difference between the carbon-coated and uncoated tube increased with the surface temperature of the alumina tube. At the surface temperature of 1000 °C, the cavity temperature difference reached about 20°C. Heating the carbon-coated alumina to raise the cavity temperature from an ambient temperature to 1000°C at a constant heating rate of 5°C/min yielded an energy consumption of 559 Wh, while the uncoated one resulted in energy consumption of 595 Wh. As the holding time to maintain the cavity temperature of 1000°C was extended to 120 min, the energy-saving increased from 6% to 11%.

Sealing Properties of Ceramic Fiber Composites for SOFC Application

For the sealing of solid oxide fuel cells (SOFCs), mid-term (~1,000 h) sealing performance was examined using composite seals prepared with mixtures of a glass and alumino-silicate ceramic fiber. Leak rate could be reduced to < ~0.04 sccm/cm when using a composite seal with 60 vol% glass. Viscosity of the glass at the seal operating temperature of 650 was 2.0×108 dPa·s (log η = 8.3) as estimated by beam-bending method, and found to be suitable for sealing operation.

Removal of Heavy Metal Ions from Aqueous Pb-EDTA and Cu-EDTA Solutions Using Nanosized ZnO Powders by Solution-Combustion Method

ZnO nanopowder was prepared by a novel “solution-combustion method (SCM)” and it was used as a semiconductor photocatalyst to evaluate its photoreduction properties. Aqueous Pb-EDTA and Cu-EDTA solutions of heavy metal ions (Pb and Cu) were used for the photocatalysis reaction under UV illumination. The result was then compared with other semiconductor photocatalyst powder such as TiO2 powder (P25; Degussa) and TiO2 powder prepared by homogeneous precipitation process at low temperature (HPPLT). In the removal of Pb++ ions, the ZnO nanopowder showed 2.6 fold higher removal rate than P25 TiO2 powder and 1.8 fold higher than HPPLT TiO2. Also the ZnO nanopowder showed the highest removal rate of the Cu++ ions from the solution among the different photocatalyst powders compared. The superior photoreduction ability of the ZnO nanopowder appears to be due to its excellent UV absorption characteristics. This was confirmed by the photoluminescence (PL) measurement.

Thermal and Electrical Conductivities of Porous Carbon-Coated Ceramic Fiber Composites

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of infiltrated phenolic resin in a nitrogen atmosphere at 800. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ shows linearly increasing tendency and is fitted by the effective conductivity according to the parallel rule of a mixture σeff = ΣΧi ·σi with an effective conductivity of pyrolytic carbon σc= 0.42 S/cm. The thermal conductivity of the coated composites is in the range 0.05-0.08 W/mK and increases with carbon content.

Electrical and Thermal Properties of Carbon-Coated Porous Ceramic Fiber Composites

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of propane in a nitrogen atmosphere at 900°C. The amount of carbon coating was varied through adjusting deposition time to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire method, respectively. Up to 7 wt% pyrolytic carbon, the electrical conductivity σ is linearly increased to 0.02 S/cm and well fitted by the effective conductivity according to the parallel rule of a mixture σ eff = Σ Χ i ·σ i with a conductivity of pyrolytic carbon σ c= 20 S/cm .The thermal conductivity of the uncoated and coated composites is in the range 0.065-0.075 W/mK and little affected by carbon coating presumably owing to the small amount of coated carbon in this work.

Removal of Total Organic Carbon from Aqueous Phenol Solution Using Photocatalytic ZnO Nanopowders Prepared by Solution Combustion Method

ZnO nanopowders were prepared by Solution Combustion Method (SCM). The ZnO nanopowders synthesized using Zn(OH)2 and glycine as an oxidant and a fuel (with fuel/ oxidant ratio, F/O=0.8), showed excellent crystalline and photocatalytic characteristics. To confirm photocatalytic activities of the prepared ZnO powder, total organic carbon (TOC) was tried to remove from aqueous phenol solution. Surprisingly, SCM ZnO nanopowder shows 1.6 fold higher destruction rates of the organic pollutant than P-25 TiO2 nanopowder which is known as a kind of standard photocatalyst.