Fabrication and Microwave Properties of Three-Dimensional Photonic Crystals With a Diamond Structure Composed of Ceramic Spheres in Resin

Three-dimensional photonic crystals with a diamond structure composed of YSZ (3 mol% Y₂O₃-stabilized ZrO₂) spheres in a resin matrix were fabricated by using stereolithography. The lattice constant was 12 mm and the diameter of the spheres was 5 mm. These photonic crystals made of ceramic spheres showed complete photonic band gaps at around 12 GHz between the eighth and ninth bands. The propagation characteristics of microwaves agreed well with the calculated results using the plane wave expansion method.     

Composite polymer particles with a gradated resin composition by suspension polymerization

We have conducted a study of composite polymer particles with a gradated resin composition by suspension polymerization, in which the resin composition gradually changes from the surface to the center of the particles. The binder resin of the polymer particles consists primarily of styrene, butyl acrylate, and methacrylic acid (MAA). Fourier transform infrared/photoacoustic spectroscopy analysis of the polymer particles by suspension polymerization has proved that MAA, having a higher polarity, concentrates near the surface of the particles, and this results in a formation similar to a core–shell structure. These composite polymer particles are excellent in blocking resistivity because the resin, containing a higher concentration of MAA, has a high glass‐transition temperature. Composite polymer particles with a gradated MAA concentration could be used for toner applications in low‐power hot‐roll fusing electrophotography systems because the melting property of the core resin is controlled and allows fusing at lower temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 682–690, 2005     

Fabrication of Titanium Carbide Ceramics by High-Pressure Self-Combustion Sintering of Titanium Powder and Carbon Fiber

Titanium carbide ceramics have been fabricated from the reactants titanium powder and carbon fiber by the highpressure self-combustion sintering method (HPCS) under two pressure conditions (65 MPa and 3 GPa). Porous TiC with a density of about 50% of theoretical was obtained under a pressure of 65 MPa. A possible model accounting for the formation mechanism of TiC is proposed on the basis of observation of the microstructure of the products formed from the incomplete reaction. On the other hand, dense TiC (>95% of theoretical) was fabricated under 3 GPa. The mean grain size varied, depending on the mixing molar ratio of the reactants. The influence of differences in the carbon (powder and fiber forms) on the structure of TiC compacts is discussed.     

Processing and Mechanical Properties of Dense Si3N4-SiC-Whisker Composites without Sintering Aids

Si₃N₄ with 20 vol% SiC whisker was fabricated without sintering aids by hot isostatic pressing. Density higher than 99.5% was attained after sintering at 2000°C and 170 MPa for 1 h. Careful mixing procedures and the use of an appropriate amount of a dispersant was found to be effective in avoiding whisker segregation and inhomogeneity. Mechanical properties of the composite were investigated by measurements of flexural strength, microhardness, frature toughness, and Young's modulus as a function of temperature. At room temerature, Vickers microhardness and Young's modulus increased from the matrix value about 20% and 5%, respectively. Toughness was about 30% higher, without reduction in flexural strength, up to 1400Deg;C.     

Hot Isostatic Press Sintering and Properties of Silicon Nitride without Additives

Fully densified silicon nitride without additives was fabricated by means of hot isostatic pressing. The sintering process of highly pure powder was investigated with special interest in the evolution of α–β phase transformation, densification, and microstructure development. It was observed that the transformation occurred without a liquid phase below 1730°C, which corresponds to the melting point of SiO₂. Above 1730°C, the densification and β-grain elongation accelerated concurrently because of the appearance of liquid SiO₂. However, full densification was attained at 1950°C together with marked grain growth. Flexural strength, microhardness, fracture toughness, and Young's modulus of sintered bodies were measured as a function of temperature. In the sintered body started from highly pure powder, excellent MOR behavior was found up to 1400°C. Impurity content of a few hundred ppm was found to be sufficient to make densification easy and to degrade high-temperature strength.     

Platinum on Carbon‐Catalyzed Hydrodefluorination of Fluoroarenes using Isopropyl Alcohol‐Water‐Sodium Carbonate Combination

We have developed a platinum on carbon‐isopropyl alcohol‐catalyzed and widely applicable defluorination method for fluoroarenes, and the addition of water and sodium carbonate efficiently accelerated the reaction. The defluorination readily occurred under the reaction conditions in comparison with the dehalogenation of other aromatic halides (fluorine>chlorine>bromine≫iodine).     

Selective recovery of histidine-containing dipeptides based on metal affinity interactions using chemically modified dextran in combination with ultrafiltration

A recovery system using metal affinity interactions in combination with ultrafiltration (UF) membrane separation was developed for nutraceutically important histidine-containing dipeptides (HCDPs) such as carnosine (Car) and anserine (Ans). Cu(II)-immobilized, chemically modified dextran bearing an iminodiacetic acid group (Cu(II)IDA-EGDE-Dex) was prepared as a complexing material for HCDPs. After the water-soluble Cu(II)IDA-EGDE-Dex captures Car in an aqueous solution, the complex is separated from the aqueous solution with the UF membrane. The recovery of Car using Cu(II)IDA-EGDE-Dex reaches equilibrium within one hour, which is much faster than metal affinity adsorption using a polystyrene chelating adsorbent. Cu(II)IDA-EGDE-Dex captures Car via metal affinity interactions in the presence of 100 mM NaCl, under which conditions the chemically modified dextran does not capture Car. Histidine and the HCDPs were selectively recovered by Cu(II)IDA-EGDE-Dex from a mixed solution containing Car, Ans and 17 amino acids, and from a model solution of bonito broth. The immobilized Car was efficiently eluted from Cu(II)IDA-EGDE-Dex using acetic acid as an eluent.     

Enhanced Surface Crystallization of β-Barium Borate on Glass Due to Ultrasonic Treatment

β-Barium borate (BBO) surface crystallized glass composites were prepared for a glass of composition 40BaO·15Tio₂–45B₂O₃ (in mol%). Enhanced nucleation was attained by ultrasonic surface modification with an aqueous suspension of BBO particles, resulting in dense BBO thin films on the glass surfaces. Second harmonic generation signals were observed for samples subjected to ultrasonic treatment.     

Mechanism of hexavalent chromium adsorption by persimmon tannin gel

Mechanism of chromium adsorption by the persimmon tannin (PT) gel was examined. The PT gel can adsorb Cr highly effectively from aqueous solutions containing Cr(VI), while it adsorbed far smaller amounts of Cr from the solution containing Cr(III). The maximum Cr adsorption from the Cr(VI) solution occurred at pH 3. The Cr adsorption from the Cr(VI) solution by the PT gel was rapid, was faster than VO2+ and Fe3+ adsorptions, and was obeyed the Langmuir adsorption isotherm (Qe= 5.27 mmol g(-1) and K= 16.2 mM). The gel adsorbed Cr from the Cr(VI) solution (pH 1 and 3) showed no ESR signal of Cr(III), while the ESR signal of Cr(III) was observed in the residual solution at pH 1. Hexavalent chromium was, therefore, adsorbed on the PT gel through the esterification of chromate with catechol group. In other words, Cr(VI) should combine with catechol as a hard acid, CrO2(2+) cation. Through the treatment of a Cr(VI) solution with the PT gel, chromium should be recovered as a Cr(IV)-tannin complex at pH 3 or a Cr(III) solution at pH 1 or lower pH region.     

Shell thickness and chemical structure of polyurea microcapsules prepared with haxamethylene diisocyanate uretidione and isocyanurate

To investigate the dependence of the shell thickness on both the microcapsule size and the concentration of hexamethylene diisocyanate (HMDI) and to analyze the chemical structure of the polyurea shell, polyurea microcapsules were prepared by using the reaction between HMDI uretidione/isocyanurate and ethylene diamine (EDA) in an oil‐in‐water emulsion. In the experiment, the concentrations of hexamethylane diisocyanate and EDA were changed. The shell thickness was correlated well with the mean size and the concentration of HMDI on the surface area per unit volume of microcapsule. From the solid‐state ¹³C NMR spectroscopy analysis, the uretidione and isocyanurate ring structures were found to be not changed before and after the reaction. From the wide‐angle X‐ray diffraction analysis, it was suggested that the chemical structure of the polyurea shell was amorphous. From the FTIR spectra analysis, it could be concluded that polyurea microcapsules were prepared by the reaction between HMDI uretidione/isocyanate and EDA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007