Preferential oxidation of carbon monoxide in hydrogen-rich gas over platinum-cobalt-alumina aerogel catalysts

The performance of the platinum-cobalt catalysts in a carbon monoxide preferential oxidation (PROX) reactor was investigated for polymer electrolyte fuel cell systems. First, the PROX reaction was analyzed based on two major reactions involved in it, i.e., oxidation of carbon monoxide and the H₂-O₂ reaction. Both reactions were affected by the other reaction depending on the reaction temperature regions, but the extent of the influence is not so large. The platinum-cobalt catalysts were found to exhibit high performance in PROX of carbon monoxide in rich hydrogen as a result of catalytic synergy effect between platinum and cobalt. In order to improve such synergy effect, the catalysts were prepared by sol-gel method and subsequent supercritical drying. The platinum-cobalt catalysts prepared by the single step sol-gel procedure exhibited higher activity for PROX than the catalysts prepared by the conventional impregnation. Supercritical drying preserved the active species of platinum-cobalt phase, therefore, the platinum-cobalt composite aerogel catalyst exhibited excellent ability for the carbon monoxide removal.     

Changes in Ba Phases in BaO/Al2O3 upon Thermal Aging and H2O Treatment

The effects of thermal aging and H₂O treatment on the physicochemical properties of BaO/Al₂O₃ (the NO_x storage component in the lean NO_x trap systems) were investigated by means of X-ray diffraction (XRD), BET, TEM/EDX and NO₂ TPD. Thermal aging at 1000 °C for 10 h converted dispersed BaO/BaCO₃ on Al₂O₃ into low surface area crystalline BaAl₂O₄. TEM/EDX and XRD analysis showed that H₂O treatment at room temperature facilitated a dissolution/reprecipitation process, resulting in the formation of a highly crystalline BaCO₃ phase segregated from the Al₂O₃ support. Crystalline BaCO₃ was formed from conversion of both BaAl₂O₄ and a dispersed BaO/BaCO₃ phase, initially present on the Al₂O₃ support material after calcinations at 1000 and 500 °C, respectively. Such a phase change proceeded rapidly for dispersed BaO/BaCO₃/Al₂O₃ samples calcined at relatively low temperatures with large BaCO₃ crystallites observed in XRD within 10 min after contacting the sample with water. Significantly, we also find that the change in barium phase occurs even at room temperature in an ambient atmosphere by contact of the sample with moisture in the air, although the rate is relatively slow. These phenomena imply that special care to prevent the water contact must be taken during catalyst synthesis/storage, and during realistic operation of Pt/BaO/Al₂O₃ NO_x trap catalysts since both processes involve potential exposure of the material to CO₂ and liquid and/or vapor H₂O. Based on the results, a model that describes the behavior of Ba-containing species upon thermal aging and H₂O treatment is proposed.     

Preparation of novel syndiotactic poly(vinyl alcohol) microspheres through the low‐temperature suspension copolymerization of vinyl pivalate and vinyl acetate and heterogeneous saponification

Syndiotactic poly(vinyl alcohol) (PVA)/poly(vinyl pivalate/vinyl acetate) [P(VPi/VAc)] microspheres, with a skin–core structure, were prepared through the heterogeneous saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). For the preparation of P(VPi/VAc) microspheres with various particle sizes and a uniform particle size distribution (which are promising precursors of syndiotactic PVA embolic materials to be introduced through catheters for the management of gastrointestinal bleeders, arteriovenous malformations, hemangiomas, and traumatic rupture of blood vessels), VPi and VAc were suspension‐copolymerized at 30°C with a room‐temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile). The effects of the polymerization conditions were investigated in terms of the size and size distribution of the suspension particles. P(VPi/VAc) microspheres, with various syndiotactic dyad (s‐dyad) contents, were produced through the control of the monomer feed ratio. In addition, monodisperse P(VPi/VAc) particles of various particle diameters were obtained by the separation and sieving of the polymerization product. Monodisperse P(VPi/VAc) microspheres of various particle sizes were partially saponified in the heterogeneous system, and the effects of the particle size and particle size distribution on the saponification rate were investigated in terms of the tacticity and the saponification time and temperature. Novel skin–core PVA/P(VPi/VAc) microspheres of various s‐dyad contents and degrees of saponification were successfully produced through the control of the various polymerization and saponification parameters. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1539–1548, 2005     

Preparation and characterization of weather resistant silicone/acrylic resin coatings

Preparation and characterization of weather resistant silicone/acrylic resin coatings were conducted. In order to prepare these coatings, a silicone/acrylic resin (KLD) was first prepared by an addition polymerization reaction of monomers, including n-butyl acrylate, methyl methacrylate, n-butyl methacrylate, and 3-methacryloxypropyltrimethoxysilane (MPTS). In the preparation of the silicone/acrylic resin, T_g of the acrylic copolymer was fixed at 40°C and the contents of MPTS were varied to be 10, 20, and 30 wt%. The weather resistant silicone/acrylic resin coatings were then prepared by blending the synthesized silicone/acrylic resin and TiO₂. The viscosity of the synthesized resin decreased with the content of MPTS, whereas the thermal stability at high temperature increased. The prepared coatings exhibited excellent adhesion to various substrates, and various physical properties of the coatings were satisfactory. The weatherability of the coatings was tested three ways: outdoor exposure test, Weather-Ometer (WOM), and QUV accelerated weatherability tester (QUV). The gloss retention, yellowness index difference, color difference, and lightness index difference were improved at high MPTS concentration. The coatings containing 30 wt% MPTS have especially good weather properties. Dept. of Chem. Eng., Yongin 449-728, Korea. Ansan 425-110, Korea.     

Structural insights into a novel molecular‐scale composite of soluble poly(vinyl pyrrolidone) supporting uniformly dispersed nanoscale poly(vinyl pyrrolidone) particles

Structural insights into a novel, molecular‐composite poly(vinyl pyrrolidone) consisting of a soluble, film‐forming poly(vinyl pyrrolidone) (PVP) polymer and in situ formed, minute, crosslinked, nanoscale, insoluble poly [poly(vinyl pyrrolidone)] (PPVP) polymer particles are reported. A technique for determining the PVP molecular weight and PPVP weight fraction by gel permeation chromatography/multi‐angle light scattering (MALS) is described. Particle size studies by quasi‐elastic light scattering and field flow fractionation/MALS demonstrate that the nanoscale, insoluble polymer particles are nominally 370 and 325 nm in diameter, respectively. Rheological experiments on this dispersed system yield a complex macroscopic behavior. Atomic force microscopy images confirm a substantial heterogeneous nature for a film cast from this molecular‐composite material. Finally, this polymeric molecular composite in film form exhibits, among many other interesting properties, a dramatic enhancement in water resistance, as demonstrated by a simple image water resistance test for an ink‐jet printing application. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 734–741, 2003     

Synthesis of (3S, 4aS, 8aS)-N-(t-butyl)Decahydro-3-Isoquinolinecarboxamide by Diastereoselective Hydrogenation over Supported Metal Catalysts

The heterogeneous catalytic hydrogenation of (S)-N-(t-butyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide was carried out over supported metal catalysts. Except for Pt, all the catalysts were very selective toward the formation of (3S, 4aS, 8aS)-N-(t-butyl)decahydro-3-isoquinolinecarboxamide. However, Pd and Ni catalysts deactivated fairly quickly, while Ru and Rh did not deactivate at all for more than 100 h. Among these catalysts, Ru showed the best performance. The high diastereoselectivity was assumed to be the result of the rigidity of the appended chiral group which helps the preferential adsorption of the reactant in one direction.     

High pressure phase behavior for carbon dioxide-1-butanol and carbon dioxide-1-octanol systems

Pressure-composition isotherms are obtained for binary mixtures of carbon dioxide-1-butanol and carbon dioxide-1-octanol systems at 40, 60, 80, 100, and 120 °C and pressures up to 220 bar. The accuracy of the experimental apparatus was tested by comparing the measured phase equilibria data of the carbon dioxide-1-butanol system at 40 °C with those of Ishihara et al. [1996]. The solubility of 1-butanol and 1-octanol for the carbon dioxide-1-butanol and carbon dioxide-1-octanol systems increases as the temperature increases at constant pressure. The carbon dioxide-1-butanol and carbon dioxide-1-octanol systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of carbon dioxideand 1-butanol or 1-octanol. The carbon dioxide-1-butanol system exhibits type-I phase behavior, characterized by a continuous critical line from pure carbon dioxide, to the second component with a maximum in pressure. Also, the carbon dioxide-1-octanol system exhibits type-I curve at 60–120 °C, and shows liquid-liquid-vapor phase behavior at 40 oC. The experimental results for the carbon dioxide-1-butanol and carbon dioxide-1-octanol systems have been modeled by the Peng-Robinson equation of state. A good fit of the data is obtained with the Peng-Robinson equation by using two adjustable interaction parameters for the carbon dioxide-1-butanol system and a poor fit using two adjustable parameters for the carbon dioxide-1-octanol mixture.     

The development of a quality prediction system for aluminum laser welding to measure plasma intensity using photodiodes

Lightweight metals have been used to manufacture the body panels of cars to reduce the weight of car bodies. Typically, aluminum sheets are welded together, with a focus on weld quality assurance. A weld quality prediction system for the laser welding of aluminum was developed in this research to maximize welding production. The behavior of the plasma was also analyzed, dependent on various welding conditions. The light intensity of the plasma was altered with heat input and wire feed rate conditions, and the strength of the weld and sensor signals correlated closely for this heat input condition. Using these characteristics, a new algorithm and program were developed to evaluate the weld quality. The design involves a combinatory algorithm using a neural network model for the prediction of tensile strength from measured signals and a fuzzy multi-feature pattern recognition algorithm for the weld quality classification to improve predictability of the system.

     

Constitutive modeling and understanding of the hot compressive deformation of Mg–9.5Zn–2.0Y magnesium alloy with reduced number of strain-dependent constitutive parameters

The hot compressive flow behavior of the cast Mg–9.5Zn–2.0Y alloy as a function of strain was analyzed, and the degree of dependence of the parameters (A: material constant, n ₂: stress exponent, Q _c: activation energy for plastic flow and α: stress multiplier) of the constitutive equation (\(\dot \varepsilon = A{\left[ {\sinh \left( {\alpha \sigma } \right)} \right]^{{n_2}}}\exp \left( {\frac{{ - {Q_c}}}{{RT}}} \right)\)) upon the strain was examined in a systematic manner. This is to explore the possibility of representing the hot compressive deformation behavior of metallic alloys in a simple way by using a reduced number of strain-dependent constitutive parameters. The analysis results for several different cases can be interpreted as follows: (1) Q _c can be treated as being strain-independent, which is physically sensible; (2) while only the microstructure changes as a function of strain at low flow stresses, as the flow stress increases, the power-law creep deformation and power-law breakdown mechanisms change; (3) the regime where only A is strain dependent expanded to higher strain rates and lower temperatures as the strain increased, suggesting that the number of the strain-dependent parameters decreases as the initial microstructure is refined by dynamic recrystallization, and the microstructure approaches a steady state.     

Microstructural Developments and Tensile Properties of Lean Fe-Mn-Al-C Lightweight Steels

Concepts of Fe-Al-Mn-C-based lightweight steels are fairly simple, but primary metallurgical issues are complicated. In this study, recent studies on lean-composition lightweight steels were reviewed, summarized, and emphasized by their microstructural development and mechanical properties. The lightweight steels containing a low-density element of Al were designed by thermodynamic calculation and were manufactured by conventional industrial processes. Their microstructures consisted of various secondary phases as κ-carbide, martensite, and austenite in the ferrite matrix according to manufacturing and annealing procedures. The solidification microstructure containing segregations of C, Mn, and Al produced a banded structure during the hot rolling. The (ferrite + austenite) duplex microstructure was formed after the annealing, and the austenite was retained at room temperature. It was because the thermal stability of austenite nucleated from fine κ-carbide was quite high due to fine grain size of austenite. Because these lightweight steels have outstanding properties of strength and ductility as well as reduced density, they give a promise for automotive applications requiring excellent properties.