Microwave Dielectric Properties of Low-Fired ZnNb2O6 Ceramics with BiVO4 Addition

The BiVO₄ additive was found effective for low-temperature firing of ZnNb₂O₆ polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO₄-doped ZnNb₂O₆ samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q · f = 55000 GHz, ɛ_r= 26, and τ_f=−57 ppm/°C. With increasing BiVO₄ addition up to 20 mol% relative to ZnNb₂O₆, while the quality factor Q · f was gradually decreased, the relative dielectric constant, ɛ_r, was linearly increased and the temperature coefficient of resonant frequency, τ_f, was slightly increased. The variations in Q · f and ɛ_r are surely attributable to the residual BiVO₄ in the ZnNb₂O₆ matrix. An unexpected slight increase in τ_f is probably due to the formation of the Bi(V,Nb)O₄-type solid solution.     

Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells

A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm². K₂PtCl₄ and H₂PtCl₆·6(H₂O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs.     

Poly(cytidylic acid) and poly(adenylic acid) analogues: synthesis and catalytic activity for hydrolysis of dinucleotides and nucleic acids

Poly(cytidylic acid) and poly(adenylic acid) analogues, resembling closely the structures of the natural polymers, were synthesized by the alternating cyclocopolymerization of a nucleoside derivative and acrylic anhydride, and subsequent hydrolysis. The polymers catalyzed the cleavage of dinuleotides and nucleic acids (DNA and RNA). Poly(cytidylic acid) and poly(adenylic acid) analogues accelerated the hydrolysis of GpG and TpT, respectively, faster than other dinucleotides due to the base pairing.     

Simple,Mild, and Practical Esterification,Thioesterification, and Amide Formation Utilizing p‐Toluenesulfonyl Chloride and N‐Methylimidazole

We have developed an efficient method for the esterification or thioesterification of equimolar amounts of carboxylic acids and alcohols or thiols using a novel reagent, p‐toluenesulfonyl chloride (TsCl) together with N‐methylimidazole. The present method is simple, mild, and reactive, uses readily available and economical reagents. The choice of amine is critical for the present method. The amine, N‐methylimidazole, has two roles: (i) as an HCl scavenger for the initial smooth generation of mixed anhydrides between carboxylic acids and TsCl and (ii) successive formation of highly reactive ammonium intermediates from mixed anhydrides. This method could be applied to various types of carboxylic acids, alcohols, and thiols: a) several functionalities were tolerated; b) two N‐Cbz amino acids were smoothly esterified without racemization; and c) the labile 1β‐methylcarbapenem key intermediate and a pyrethroid insecticide, prallethrin, were successfully prepared. The related amide formation between carboxylic acids and primary or secondary amines was also performed. The proposed reaction mechanism involves a novel method for producing the reactive acylammonium intermediates. The production of these intermediates was rationally supported by a careful ¹H NMR monitoring study.     

Ceramic sheet hybrid kenaf reinforced polypropylene biocomposites

Hybrid biocomposites are one of the emerging fields in polymer composites. The purpose of this study is the development and characterization of ceramic sheet (CS) hybrid polypropylene (PP) biocomposites for broadening of the field of potential applications of biocomposites. Hybrid PP biocomposites were manufactured with 20 wt % loadings of kenaf and the addition of a CS (single or double sided) by melting and compression molding. The effects of the CS on the mechanical and thermal properties of the hybrid PP biocomposites were analyzed in terms of tensile, flexural, and impact properties, and inflammability, smoke optical density, and toxicity of the combustion gas. Also, the surface morphology of fractured hybrid PP biocomposites was observed by SEM and AFM. In spite of the brittle properties of the ceramic, the mechanical properties of the hybrid PP biocomposites were improved and, also, the inflammability of the hybrid PP biocomposites with the CS was highly improved. As a result, full impregnation of CSs into the kenaf reinforced biocomposite can contribute to the improvement of both the mechanical properties and the inflammability of biocomposites, resulting in a broadening of the field of potential applications of biocomposites such as aerospace. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1917–1922, 2013     

Construction of Micro-Patterned Polymer Structures by Piezoelectric Inkjet Printing

It is not simple to accurately deposit minute quantities of polymeric materials by inkjet printing systems. High viscosity, nozzle clogging, agglomeration, precipitation, and uncontrollable drying patterns are serious problems which are frequently encountered in polymer inkjet printing. In this study, we investigated how inkjet printability of polymers correlates with the polymer ink formulations and inkjet process variables. After a systematic study with different variables, various patterns such as dots, cross stripes, and honeycombs were fabricated on flexible polyimide (PI) films and the pattern morphology and spatial distribution of the resulting polymer deposits after solvent drying were characterized.     

Effects of various post-treatments on carbon nanotube films for reliable field emission

In this report, the FE characteristics of carbon nanotubes (CNTs) treated using both thermal annealing and mechanical coatings on the as-grown CNTs systematically studied. It was found that in the high temperature annealed samples, CNTs were attacked at its root during annealing due to a small amount of oxygen, and were pulled out of the substrate in places after FE measurements because of the contact resistance. However, for the mechanically coated samples both with spin on glass (SOG) and polymethyl methacrylate (PMMA), CNTs were found to be nearly intact after FE measurements and showed reliable FE characteristics over repeatable voltage scan. The reliability of CNTs during FE could be owing to the strong adhesion of CNTs to the substrate both by SOG and PMMA coatings.     

The influence of filler on the emission properties and rheology of carbon nanotube paste

CNT paste consists of organic solution, inorganic binder and filler. Organic solution contains organic resins and solvent including surfactants which finely disperse CNTs. Filler affects surface morphology, electron emission property, viscosity, and rheological characteristics of CNT paste. We used different fillers such as silver and alumina in CNT paste for special function. The emission properties of CNT paste with silver are similar to those of CNT paste with alumina if filler portion is the same. From the scanning electron microscope (SEM) different morphologies of CNTs was observed depending on the type of filler. CNT paste which showed good emission property had vertically well-aligned CNTs on the surface after surface treatment using adhesive tape. We measured viscosity and rheological properties with rheometer RS600 from HAAKE. Emission property of CNT paste was evaluated in vacuum chamber of 10^{− 6} Torr with pulse generator and duty was 1/500.     

Aqueous electrodeposition of iron group-vanadium binary alloys

Electrodeposition of binary iron group (IG)-vanadium (V) alloys from aqueous citrate solutions was investigated. Addition of NH₃(aq.) and increasing solution pH resulted in increased deposit V content, but non-metallic deposits were obtained at solution pH > 7. Increasing current density resulted in an almost linear decrease in V content and a sharp increase in hydrogen evolution (decreased current efficiency). In general, the amount of V deposited with the IG metal increased as follows: Ni < Fe ? Co. XRD spectra indicated that preferred orientations from 25 °C solutions were not displaced by elevated temperature deposits. Changes in orientation may contribute to the deposit magnetic properties; e.g., Co-V deposits with (1 0 0) planes exhibit harder magnetization than deposits with (0 0 2) planes.     

Highly sensitive and selective dopamine detection by an amperometric biosensor based on tyrosinase/MWNT/GCE

Dopamine (3,4-dihydroxylphenyl ethylamine) is the most significant neurotransmitter in the human nervous system. Abnormal dopamine levels cause fatal neurological disorders, and thus measuring dopamine level in actual samples is important. Although electrochemical methods have been developed for detecting dopamine with high accuracy, certain substances (e.g., ascorbic acid) in actual samples often interfere with electrochemical dopamine detection. We developed tyrosinase-based dopamine biosensor with high sensitivity and selectivity. An electrochemically pretreated tyrosinase/multi-walled carbon nanotube-modified glassy carbon electrode (tyrosinase/MWNT/GCE) was prepared as an amperometric biosensor for selective dopamine detection. For optimizing the biosensor performance, pH, temperature, and scan rate were investigated. The electrochemically pretreated tyrosinase/MWNT/GCE exhibited not only the highest sensitivity (1,323 mAM^?1 cm^?2) compared to previously reported tyrosinase-based dopamine sensors, but also good long-term stability, retaining 90% of initial activity after 30 days. Additionally, ascorbic acid, a major interfering substances, was not oxidized at the potential used to detect dopamine oxidation, and the interfering effect of 4mM ascorbic acid was negligible when monitoring 1mM dopamine. Consequently, the electrochemically pretreated tyrosinase/MWNT/GCE is applicable for highly selective and sensitive dopamine detection in actual samples including interfering substances, thereby extending the practical use to monitor and diagnose neurological disorders.