Polymer-derived β-SiAlON:Eu2+ phosphors

A series of β-SiAlON:Eu²⁺ phosphors were synthesized from single-source precursors, perhydropolysilazane chemically modified with Al(OCH(CH₃)₂)₃, AlCl₃, and EuCl₂. The single-source precursors were converted to β-SiAlON:Eu²⁺ phosphors by pyrolysis under flowing N₂ or NH₃ at 1000°C, followed by heat treatment at 1800°C under an N₂ gas pressure at 980 kPa. By varying the molar ratio of the chemical modifiers, β-SiAlON:Eu²⁺ with the compositions close to the theoretical ones expressed as Si_6−zAl_zO_z−2yN_8−z+2y:yEu²⁺ were synthesized, where the z values and Eu²⁺ contents were controlled in the ranges of .44–.78 and .35–1.48 mol%, respectively. The polymer-derived β-SiAlON:Eu²⁺ phosphors exhibited green emission under excitation at 460 nm attributed to the 4f⁷–4f⁶(7f³)5d¹ transition of dopant Eu²⁺. High-angle annular dark-field-scanning transmission microscopy analysis confirmed that the doped-Eu²⁺ existed interstitially within the channels along the c axis of host β-SiAlON. Compared with the conventional powder metallurgy route, the polymer-derived ceramic route in this study offers some advantages in the grain growth of host β-SiAlON and photoluminescence properties in terms of green emission intensity under excitation at 460 nm, and the highest intensity was achieved for the polymer-derived β-SiAlON:Eu²⁺ with z = .64 and .37 mol% Eu²⁺.     

sequential estimation of the hgarginal density function for a strongly mixing process

Suppose that {X_n} is a strongly mixing process with unknow marginal density f(x) and that we estimate f(x) by a kernel estimator [fcirc]_n(x|h_n)and want to achive the MISE no larger than some preassigned postive number w. However,the appropriate sample size n^*depends on a functional of the unknow density function. Therefore some sequential procedure is required and we adopt a fully sequential procedure. In this paper we investigate the asymptotic properties of the procedure and show that the producure is asymptotically efficient in a certain sense as w→0. The results are almost the same in the i.i.d. setting. our result extend a class of models to which the methodology can be applied. For example economic variable,experiments on a single subject in which obervation are not indepent, and so on.     

INFLUENCES OF INTERFACIAL CONVECTION AND PHYSICAL PROPERTIES OF DESICCANT SOLUTIONS ON THE MASS TRANSFER PERFORMANCE OF ABSORPTION SYSTEMS

In order to investigate the mass transfer phenomenon of the absorption of water vapor in desiccant solutions, a system of absorption cell was designed. The gradient in surface tension can result from the contact process between the desiccant solution and water vapor. This induced interfacial disturbance will affect the mass transfer performance. The experimental results demonstrate that the theoretical mass transfer coefficients predicted by boundary layer theory are less than those of the experimental values. In addition, the mass transfer performance of the absorption system can be enhanced by adding ethanol to the absorbent solutions. In order to describe the level of mass transfer performance affected by the interfacial convection resulting from the addition of ethanol, the enhancement factor was defined in this study. The enhancement factor is from 1.26 to 1.56 for adding ethanol to DEG (diethylene glycol) solution, and from 1.36 to 1.61 for adding ethanol to TEG (triethylene glycol) solution.     

Characterization of anisotropic gas permeability and thermomechanical properties of highly textured porous alumina

Porous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure-controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.     

In situ binary sol–gel reaction of various trifunctional alkoxysilane in the silane‐grafted polyolefin matrix and its effect upon the mechanical properties

The vinyltrimethoxysilane‐grafted ethylene‐propylene copolymer/trifunctional methoxysilane (EPR‐g‐VTMS/RTMS) composites were prepared via in situ silica sol–gel reactions. Five trifunctional methoxysilane compounds (n‐hexyltrimethoxysilane, n‐decyltrimethoxysilane, n‐tetradecyltrimethoxysilane, n‐octadecyltrimethoxysilane, and phenyltrimethoxysilane) have been selected for this study. The water‐cross‐linked EPR‐g‐VTMS/RTMS composites were characterized by attenuated total reflectance‐Fourier transform infrared spectroscopy, gel content, solid‐state ²⁹Si CP/MAS NMR, wide‐angle x‐ray scattering, tensile strength, and field emission scanning electron microscopy measurements. The type of RTMS additive has a substantial influence on the nature of siloxane band networks and eventually the mechanical tensile properties. This finding suggests that the interaction and/or entanglement between the EPR‐g‐VTMS matrix and the substituent of the RTMS additives are crucial for the modifying mechanical properties. Moreover, for the water‐cross‐linked EPR‐g‐VTMS/CnTMS (n = 6, 10, 14, and 18) composites, the joint evidence provided by attenuated total reflectance‐Fourier transform infrared spectroscopy, ²⁹Si CP/MAS NMR, and wide‐angle x‐ray scattering results suggested the formation of ladder‐type poly(n‐alkyl silsesquioxane)s and the presence of the highly ordered structure with a thickness equal to the length of two n‐alkyl groups in all‐trans conformation. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Electrochemical properties of N-doped hydrogenated amorphous carbon films fabricated by plasma-enhanced chemical vapor deposition methods

Nitrogen-doped hydrogenated amorphous carbon thin films (a-C:N:H, N-doped DLC) were synthesized with microwave-assisted plasma-enhanced chemical vapor deposition widely used for DLC coating such as the inner surface of PET bottles. The electrochemical properties of N-doped DLC surfaces that can be useful in the application as an electrochemical sensor were investigated. N-doped DLC was easily fabricated using the vapor of nitrogen contained hydrocarbon as carbon and nitrogen source. A N/C ratio of resulting N-doped DLC films was 0.08 and atomic ratio of sp³/sp²-bonded carbons was 25/75. The electrical resistivity and optical gap were 0.695 Ω cm and 0.38 eV, respectively. N-doped DLC thin film was found to be an ideal polarizable electrode material with physical stability and chemical inertness. The film has a wide working potential range over 3 V, low double-layer capacitance, and high resistance to electrochemically induced corrosion in strong acid media, which were the same level as those for boron-doped diamond (BDD). The charge transfer rates for the inorganic redox species, Fe^2+/3+ and Fe(CN)₆^4−/3− at N-doped DLC were sufficiently high. The redox reaction of Ce^2+/3+ with standard potential higher than H₂O/O₂ were observed due to the wider potential window. At N-doped DLC, the change of the kinetics of Fe(CN)₆^3−/4− by surface oxidation is different from that at BDD. The rate of Fe(CN)₆^3−/4− was not varied before and after oxidative treatment on N-doped DLC includes sp² carbons, which indicates high durability of the electrochemical activity against surface oxidation.     

Rate acceleration of Diels–Alder reactions utilizing a fluorous micellar system in water

A fluorous micellar system in water has been created to produce a large interfacial area between these media that retains substrates, effectively facilitating intermolecular Diels–Alder reactions due to repulsion effects from both media. Because LiFOS functioned not only as a surfactant but also as a supporting electrolyte, an electrochemical approach could be introduced to evaluate the rate acceleration effects. The measurement of the particle size distribution of the fluorous micelles clearly supported these evaluations.     

Electrochemical examination of the ascorbic acid radical anion in non-aqueous electrolytes

A quasi-reversible redox reaction involving ascorbic acid was observed in non-aqueous electrolytes at conductive diamond electrode. The chemical reversibility of these reactions is consistent with ascorbic acid being reduced to the ascorbic acid radical anion in a one-electron process, with subsequent reoxidation to ascorbic acid. This is the first report on the electrochemical production of the ascorbic acid radical anion in non-aqueous electrolytes. Ascorbyl 6-stearate and 4-hydroxy 2(5H)-furanone, which have somewhat similar structures as ascorbic acid, also showed one-electron transfer reduction reaction producing radicals with a single negative charge, suggesting that these compounds follow the same electrochemical behavior as ascorbic acid. The double bond and hydroxyl substituent on the five-membered ring are shown to be necessary for the stabilization of the radical anions. It was confirmed by the calculation of the total energy using molecular orbital methods that resonance structures involving the double-bond and hydroxyl group provide significant stabilization of the radical anions. Electrochemical preparation may be a useful method for the detailed study of radicals, their molecular structure and reactivity.     

Chemical‐Free Approach for Z‐Isomerization of Lycopene in Tomato Powder: Hot Air and Superheated Steam Heating above the Melting Point of Lycopene

Z‐isomers of lycopene exhibit higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. Therefore, it is important to develop an efficient and environmentally friendly procedure for Z‐isomerization. The current methods for Z‐isomerization of (all‐E)‐lycopene use toxic chemicals such as organic solvents and catalysts. This study is aimed to develop a chemical‐free method for Z‐isomerization of (all‐E)‐lycopene in tomato powder by hot air and superheated steam heating. The Z‐isomerization reaction is promoted by heating above the melting point of lycopene. When heated with superheated steam, the thermal decomposition of lycopene is suppressed compared to that when heated with hot air. When tomato powder is heated at 240 °C for 5 min by superheated steam, the total Z‐isomer content and remaining lycopene are 69.0% and 90.7%, respectively, while with hot air heating, the total Z‐isomer content and remaining lycopene are 69.9% and 68.0%, respectively. These results indicate that the thermal Z‐isomerization of lycopene occurs in the molten state and heating in a low oxygen atmosphere suppresses the thermal decomposition of lycopene. Practical Applications: Tomato powder rich in lycopene Z‐isomers is an important ingredient for the food and animal feed industries. Since Z‐isomers of lycopene are more soluble in solvents including ethanol which is a low‐toxicity and environmentally friendly solvent, the efficiency of lycopene extraction with ethanol can be improved by using the Z‐isomer‐rich tomato powder as a raw material. The obtained Z‐isomer‐rich extract has a high added value because the Z‐isomers have higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. In addition, since lycopene Z‐isomers exhibit higher accumulation efficiency and better color improvement in hen egg yolks than those of the all‐E‐isomer, Z‐isomer‐rich tomato powder is an effective animal feed.