Catalytic reduction of no over perovskite-type catalysts

In the present work, we have investigated the reduction of NO by propane over perovskite-type oxides prepared by malic acid method. The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxides. In addition, the reaction conditions, such as temperature, O₂ concentration, and space velocity have been varied to understand their effects on the catalytic performance. In the LaCoO₃ type catalyst, the partial substitution of Ba and Sr into A site enhanced the catalytic activity in the reduction of NO. For the La_0.6Ba (Sr)_o.4 Co_1−x Fe_xO₃ (x=0-1.0) catalyst, the partial substitution of Fe into B site enhanced the conversion of NO, but excess amount of Fe decreased the conversion of NO. The surface area and catalytic activity of perovskite catalysts prepared by malic acid method showed higher values than those of solid reaction method. The conversion of NO increased with increasing O₂ concentration and contact time. The introduction of water into reactant feed decreased the catalytic activity but the deactivation was shown to be reversible over La_0.6Ba_0.4Co_1−x ,Fe_xO₃ catalyst.     

Characteristics of membrane humidifiers for polymer electrolyte membrane fuel cells

Water management plays an important role in obtaining high performance from a polymer electrolyte membrane fuel cell (PEMFC). To reduce the volume and energy consumption of widely-used bubble humidifiers, membrane humidifiers were fabricated by using an ultrafiltration (UF) membrane and Nafion membranes. The performance of the membrane humidifiers was examined as a function of gas flow rate and operating temperature. A single cell was operated using the UF membrane humidifiers exhibiting almost the same performance with that employing bubble humidifiers.     

The permeation resistance of interface and the directional dependence of permeation in plasma-grafted composite membranes

Composite membranes were prepared by grafting plasma-polymerized films onto the surface of nonporous poly (dimethylsiloxane) films. Gas permeabilities of the composite membranes were measured at 35°C, 1 atm for N₂, 0₂, CO₂ and CH₄. The permeation properties of the composite membrane was analyzed using the series resistance model. There was a great interfacial resistance to CH₄ permeation through the composite membrane. The interfacial resistance was negligible for the other gases. The interfacial resistance seems to be a result of an interfacial layer caused by the interaction between the bulk two layers. For CH₄ gas, the permeation rate through the composite membrane was affected by the direction of flow. The directional dependence was negligible for the other gases.     

Control of the photorefractive effect using a low Tg sol-gel glass

Summary We prepared the photorefractive sol-gel glass based on organic-inorganic hybrid materials containing a charge transporting molecule, second-order nonlinear optical chromophore, photosensitizer, and plasticizer. Carbazole and 2-{ 4-[(2-hydroxyethyl) methylamino]benzylidene}malononitrile were reacted with 3-isocyanatopropyl triethoxysilane and the functionalized silanes were employed to fabricate the efficient photorefractive media including 2,4,7-trinitrofluorenone (TNF) to form a charge transfer complex. The simplest way to vary the composition in the matrix was to mix the desired amount of the functionalized alkoxysilane. The prepared sol-gel glass samples contained a large amount of nonlinear optical (NLO) chromophore compared to that of the charge transporting molecules. They showed a large net gain coefficient and high diffraction efficiency at certain conditions. Received:27 May 2002/Revised version:23 August 2002/Accepted:7 September 2002 Correspondence to Dong Hoon Choi E-mail: dhchoi@khu.ac.kr     

Effect of reactive diluents on properties of unsaturated polyester/montmorillonite nanocomposites

Unsaturated polyester (UP)/montmorillonite (MMT) nanocomposite was prepared by using hydroxypropylacrylate (HPA) as a reactive diluent instead of conventional styrene monomer and the effect of polarity of reactive diluent on properties of nanocomposite was investigated. X‐ray and mechanical test data indicated that mixing for an extended period of time is essential to enhance the physical properties of nanocomposites in the UP/Cloisite 6A system. This was attributed to the high polarity of HPA that may disturb the preintercalation of UP resin into the galleries of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 238–242, 2004     

Highly Efficient Overall Water Splitting Through Optimization of Preparation and Operation Conditions of Layered Perovskite Photocatalysts

The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency) was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110) layered perovskite, La₂Ti₂O₇ was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La₂Ti₂O₇, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an external additive enhanced the activity further showing extremely high quantum yields close to 50%.     

Dynamic mechanical properties of three different combinations taken from styrene-co-itaconate, styrene-co-methacrylate, and styrene-co-sulfonate ionomers

Dynamic mechanical properties of three different styrene-based ionomer blends containing ca. 5 mol% of ionic repeat units were investigated; the three ionic units were itaconate (ITANa), methacrylate (MANa), and styrenesulfonate (SNa). For SNa-MANa ionomers, it was observed that this ionomer system showed only two loss tangent peaks, implying that this ionomer system resembles a typical miscible system. When the ion content increased, however, the ionomer blend showed two cluster loss tangent peaks, indicating the presence of phase-separated cluster regions. This suggests that, with increasing ion content, the role of ionic units becomes more important than that of host non-ionic units to determine ionomer properties. In the case of ITANa-MANa and ITANa-SNa ionomers, however, it was suggested that the multiplets of the MANa and SNa ionomers might be disrupted upon the addition of the ITANa ionomers. In addition, the SEM images showed that the fracture surfaces of ionomers changed upon blending.     

On-line identification of interacting two-tank system

In order to demonstrate the effectiveness of the process identification algorithm, on-line parameter estimator is evaluated experimentally by using two-tank system with interaction. On-line parameter estimator used in this paper is based on a recursive parameter estimation algorithm. MIMO linear, bilinear and quadratic models based on ARMA model are used to identify two-tank system. A quadratic model for two-tank system with interaction is developed to confirm the propriety of MIMO quadratic model used in identification of two-tank system. The results of on-line identification experiments on the two-tank system show that the estimated parameters of each model converge and the output tracking errors are bounded by disturbance bound. But, the quadratic model showed the best convergence.     

Monodisperse polymer/metal composite particles by electroless chemical deposition: Effect of surface functionality of polymer particles

Micron‐sized polymer particles were coated with layers of nickel compounds by plating electrolessly in the presence of aqueous solutions of nickel chloride, sodium hypophosphite, sodium citrate, and ammonium chloride at elevated temperature. The uniform functional polymer particle could be obtained by seeded polymerization. To investigate the effect of surface functionality on the conditions for nickel deposition, the polymer particle was functionalized with the thiol group. From morphological observation, it was found that the mode of nickel deposition was greatly dependent on the surface functionality of the polymer particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 420–424, 2003     

Preparation of nano-sized silicon carbide powder using thermal plasma

Nano-sized silicon carbide (SiC) powder was prepared by thermal plasma process using silicon tetrachloride (SiCl₄) and methane (CH₄). The synthesized powder was characterized by X-ray diffraction pattern, scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy and particle size analyzer. The powder was dominated by β-SiC including some of α-SiC and free carbon species. The quality of the powder was varied with process conditions such as the molar ratio of H/Si and C/Si, and collecting positions. It was known that the conversion to SiC was mainly affected by the addition of hydrogen gas because it promoted the decomposition and reduction of SiCL. CH₄ was easily decomposed to carbon species for the formation of SiC as well as removal of impure oxygen, but excessive carbon suppressed the formation of crystalline SiC and resulted in the solid carbon contamination. The optimum ratio of H/Si was approx. 26 and that of C/Si was 1.1. For collecting positions, the powder collected at the vessel and filter was preferable to that at the reaction tube. The average size of the powder synthesized was estimated to be below 100 nm and uniform in distribution.