Synthesis of nickel nanoparticles with excellent thermal stability in micropores of zeolite

Nickel (Ni) nanoparticles were synthesized in micropores of zeolite by the adsorption and decomposition of a sublimated Ni organometallic compound, Ni(C₅H₅)₂, to invent metallic catalysts with nanosize, which are smaller than 5 nm and keep the nanosize at high temperature. In the decomposition process, Ni species were partially decomposed by ultraviolet light irradiation and fixed in zeolite pores prior to thermal reduction under H₂ flow. Note that the Ni nanoparticles showed an excellent thermal stability, because they kept the high dispersion with diameters smaller than 5 nm even after heating at 400 °C. On the other hand, the Ni particles supported on zeolite by a conventional method, which is an incipient wetness impregnation process, became larger than 10 nm after heating at the same temperature. The synthesized Ni nanoparticles acted as a metallic catalyst because they showed higher selectivity for H₂ generation than C₂H₄ generation during ethanol steam reforming reaction.     

Characterization of aluminium nitride thin films

Aluminium nitride (AlN) thin films have been synthesized by evaporation of aluminium and simultaneous irradiation with nitrogen ions, ion-vapour deposition method, at the substrate temperature of room temperature or 473K. The kinetic energy of the incident nitrogen ion beam has been kept at 0.5 keV and the deposition rate has been varied from 0.075 to 0.28 nm/s. The structure of the synthesized films has been examined by X-ray diffraction (XRD) and the surface morphology has been characterized by atomic force microscopy (AFM). In the XRD patterns of both films synthesized at room temperature and 473K, the diffraction lines due to the AlN(10.0), (00.2) and (10.1) planes have been discerned. AFM observations reveal that the surface of the films synthesized at 473K becomes rough as compared with the films synthesized at room temperature. This may be attributed to growth of AlN particles on the substrate kept at 473K. Furthermore, in the films synthesized at the 473K substrate, several aggregated protrusions can be observed on the relatively smooth surface at the deposition rate of 0.28 nm/s, while the surface of the films is uniform on nanometre scale at the deposition rate of less than 0.12 nm/s. The present results suggest that the synthesis of the AlN films with uniform surface is feasible by controlling the substrate temperature and the deposition rate.     

Characterization and Adsorption Behavior of ZSM-5 Zeolite Film on Cordierite Honeycombs Prepared by a Novel in situ Crystallization Method

Thin films of ZSM-5 zeolite prepared on three types of cordierite ceramic honeycomb substrates by a novel in situ crystallization method were characterized by XRD, FTIR, XRF, SEM-EDX, NH₃-TPD and propane gas adsorption to examine the effect of the substrate on various properties of the ZSM-5 films. The substrates were both as-prepared and acid treated cordierite honeycombs. The XRD, FTIR and XRF results showed that silica-rich surface layers were formed on the surface of the honeycombs by the acid treatments. The SiO₂/Al₂O₃ ratios of the ZSM-5 zeolite formed on these layers increased with increasing time of acid treatment. Both Al₂O₃ and SiO₂ from the substrates were found to contribute to the formation reaction of the zeolite films corresponding to the composition of the interfacial layer. The porous properties of the honeycomb substrates also varied in relation to the amount of zeolite film, which increased linearly with acid treatment time. The presence of the silica-rich interfacial layer between the substrate and zeolite film increased the amount of ZSM-5 and the physical adsorption but decreased the solid acidity and amount of chemisorption.     

Change of nitrogen functionality of N-enriched condensation products during pyrolysis

Changes in the nitrogen functionality of ¹⁵N-enriched condensation products prepared from glucose and ¹⁵N-glycine were investigated during pyrolysis at 600–1000 °C. The structural changes in the condensation products were studied by means of solid-state ¹³C and ¹⁵N NMR spectroscopies. During pyrolysis, the aliphatic moieties of the condensation products decomposed and evolved as gas and tar. At pyrolysis temperatures above 600 °C, almost all the carbon in the chars were converted to aromatic carbon. After pyrolysis, large amounts of nitrogen remained in the chars as char nitrogen (char-N), and about 30% of the nitrogen was eliminated from the chars as HCN and NH₃. With increasing temperature, the production of HCN and NH₃ increased and the amount of char-N decreased. By combining X-ray photoelectron spectroscopy and NMR results, detailed results for nitrogen fractions in chars were obtained. During pyrolysis, the fraction of unsubstituted pyrrole-N decreased and the fraction of quaternary-N increased. The fraction of pyridine-N remained almost constant at temperatures below 800 °C, but at 900 °C and above, the fraction of pyridine-N decreased. The fraction of substituted pyrrole-N showed minimum at 800 °C. On the basis of these results, structural changes of nitrogen functional groups during pyrolysis are discussed.     

Preparation of barium titanate nanoparticle sphere arrays and their dielectric properties

Barium titanate (BaTiO3) nanoparticles from 27 to 192 nm were prepared by the 2-step thermal decomposition method from barium titanyl oxalate nanoparticles. These particles were dispersed well into 1-propanol, and dense BaTiO3 nanoparticle sphere arrays without stress-field were prepared by the meniscus method. Temperature dependence of dielectric properties was successfully measured using these dense nanoparticle sphere arrays, and size effect on dielectric properties was discussed.     

Magnetic Susceptibility in Normal States of Quasi-One-Dimensional Superconductors

The longitudinal magnetoresistance of a two-dimensional superconductor, β’-Et₂Me₂P[Pd(dmit)₂]₂ (dmit=C₃S ₅ ²⁻ ) under hydrostatic pressure was measured at low temperatures with the field applied perpendicular to the conducting layers. At 0.58 GPa, the field-dependent isothermal interlayer resistanceR╧ (H) exhibited a peak below the superconducting transition temperature T _C . This peak effect can be explained by a model of resistively-shunted Josephson-Junctions. The peak is strongly suppressed at a higher pressure, 0.71 GPa.     

Comparative study of apatite formation on CaSiO<Subscript>3</Subscript> ceramics in simulated body fluids with different carbonate concentrations

Apatite formation on CaSiO₃ ceramics was investigated using two different simulated body fluids (SBF) proposed by Kokubo (1990) and Tas (2000) and three sample/SBF (S/S) ratios (1.0, 2.5 and 8.3 mg/ml) at 36.5°C for 1–25 days. The CaSiO₃ ceramic was prepared by firing coprecipitated gel with Ca/Si = 0.91 at 1400°C. The bulk density was 2.14 g/cm³ and the relative density about 76%. The two SBF solutions contain different concentrations of HCO₃^– and Cl^– ions, the concentrations of which are closer to human blood plasma in the Tas SBF formulation than in the Kokubo formulation. The pH values in the former solution are also more realistic. The CaSiO₃ ceramics show apatite formation in SBF (Kokubo) after soaking for only 1 day at all S/S ratios whereas different phases were formed at each S/S ratio in SBF (Tas). The crystalline phases formed were mainly apatite at S/S = 1.0 mg/ml, carbonate-type apatite at 2.5 mg/ml and calcite at 8.3 mg/ml. At higher S/S ratios the increase in the Ca concentration became higher while the P concentration became lower in the reacted SBF. These changes in SBF concentrations and increasing pH occurred at higher S/S ratios, producing more favorable conditions in the SBF for the formation of carbonate bearing phases, finally leading to the formation of calcite instead of apatite in the higher HCO₃^– ion concentration SBF (Tas). Apatite is, however, formed in the lower HCO₃^– ion concentration SBF (Kokubo) even though the Ca and P concentrations change in a similar manner to SBF (Tas).     

Mechanical properties of polyoxymethylene whiskers/polyoxymethylene resin composite films

Polyoxymethylene (POM) needle-like crystals, whiskers, are known as trigonal crystals of very high perfection and are thought to have a high Young's modulus. In this study, composite films of the whisker were prepared as one possible method to utilize the whiskers as a new, high performance material. POM resin, i.e. a substance with the same chemical structure as the whisker, was selected as a matrix, having good adhesion with the filler (whisker). The whiskers were mixed with POM resin powder, prior to hot-pressing and made into the composite films, taking advantage of the difference of the melting points. The whisker content of the resulted film reached up to 70%. The Young's modulus of the composite film was increased up to about 14 GPa.     

Polarization reversal of telluric acid ammonium phosphate

Experimental studies are reported concerning polarization reversal in the single crystal of telluric acid ammonium phosphate (TAAP). The switching currents have been measured under various temperatures and external electric fields. The experimental results have been used in order to obtain the effective growth dimension of reversed domain and the characteristic time of the polarization reversal on the basis of the Avrami theory. It becomes clear that the effective growth dimension depends on temperature and applied electric field.