Chemical speciation of chlorine in particulate matter by wavelength-dispersive PIXE technique

Chemical speciation of chlorine (Cl) in atmospheric particulate matter (APM) was performed by using a wavelength-dispersive PIXE spectrograph based on high-resolution measurement of Cl-Kβ emission. Samples of atmospheric particles were size-fractioned and collected by a cascade impactor at an urban area in Tokyo. The target position with respect to the spectrograph was precisely adjusted by a 2D laser displacement sensor to achieve high detection efficiency. The samples were irradiated with 2 MeV protons from a tandem electrostatic accelerator. The beam current was 300-500 nA. During the irradiation, the target was cooled by liquid nitrogen to avoid the evaporation of volatile Cl compounds. The measured spectra for the NaCl standard samples clearly showed the Cl-Kβ series composed of the Kβ₁ and the satellite Kβ_x, Kβ₅ lines. From the measured X-ray yields, it was found that the chemical speciation of samples with Cl concentrations as low as ≈1% is possible by this method. The Cl-Kβ series were also successfully observed in the case of APM samples with particle sizes of 11.0-2.1 μm. The spectra shapes of the NaCl standard samples and an APM sample were slightly different from each other, because of some possible mixing of non-sea salt component in the APM sample.     

Shielding effect of double microelectrode tips in a scanning electrochemical microscope

Electrochemical interaction of coaxial double microelectrodes, in which a ring microelectrode was surrounded by another ring microelectrode, was investigated. Mass-transfer reactions that occurred on both inner and outer microelectrodes interfered with each other and showed a “shielding” effect depending on potentials and geometries of microelectrodes. Application of the inner microelectrode of the double microelectrodes for a probing tip of a scanning electrochemical microscope (SECM) revealed that the shielding effect by the outer microelectrode affected the electrochemistry on the inner microelectrode in the vicinity of the substrate surface. The effect was intensified above the insulator but attenuated above the conductor as the microelectrodes approached in feedback mode of the SECM. Approach to a critical interelectrode distance also intensified the shielding effect in the substrate generation/tip collection mode. An SECM line-scan using a platinum/epoxy resin-model substrate was carried out to investigate the shielding effect on current sensitivity and lateral resolution of an SECM image.     

Fabrication of porous SiC ceramics having pores shaped with Si grain templates

SiC porous ceramics were prepared by heating mixtures of Si powder and carbon black at 900 °C for 24 h in Na vapor. The grains of the Si powder were not only the source of Si for SiC but also served as templates for the pores in the SiC porous ceramics. Angular-shaped pores with sizes of 2-10, 10-150 and 50-150 μm were formed by angular Si grains with sizes of ≤10, ≤50 and ≤150 μm, respectively. The porosity of the SiC porous ceramics was around 55-59%. Spherical pores were also formed when spherical Si grains were used. A bending strength of 14 MPa was measured for the SiC porous ceramics prepared with the Si grains (≤50 μm).     

Temperature dependence and fracture criterion of mixed mode I/II fracture toughness of phenolic resin for friction material

In this study, the temperature dependence of the mixed‐mode fracture toughness of the phenolic resin for friction materials is investigated. For pure mode I, the fracture toughness decreases as the temperature increases, and it increases again after showing its minimum value. For pure mode II, the fracture toughness shows a similar trend but has its minimum value at a higher temperature. The temperature dependence of the mixed‐mode fracture toughness varies depending on the mode mixity, which is attributed to the different sensitivity to the relaxation phenomenon. At room temperature, as the fracture toughness for pure mode I and II are almost the same, the fracture locus shows a circular arc. At elevated temperatures, the locus becomes smaller and noncircular. At high temperature, the fracture locus shows an elliptical arc, where the fracture toughness for pure mode II is smaller than that for mode I. An empirical fracture criterion based on the time‐temperature dependence of the resin is proposed, and the proposed method successfully predicts the fracture toughness under various conditions of the temperature, time, and mode mixity. The crack initiation angles, on the other hand, are almost consistent regardless of the temperature, which agree with the maximum hoop stress theory. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Inserting polyoxomolybdate cluster into poly(?-caprolactone) to create a class of new heteropolymer: Synthesis and supramolecular structures

In the present work, we report our work concerning the synthesis of heteropolymers of poly(?-caprolactone)-polyoxomolybdate-poly(?-caprolactone) using ring-opening polymerization (ROP) of ?-caprolactone monomer initiated by two hydroxyl groups attached on the two sides of a polyoxomolybdate cluster which was organically modified using pentaerythritols. Since the hydroxyl groups on polyoxomolybdate macroinitiator are less reactive, ring-opening polymerization were finally carried out by using 4,4′-(dimethylamino) pyridine to activate ?-caprolactone monomer. The polyoxomolybdate-containing heteropolymers were confirmed in detail by ¹H NMR, FT-IR, GPC, TGA and XPS methods. Although the size of polyoxomolybdate cluster is extremely small compared to PCL chains, it was also found that POM played an important role in crystallization process. Self-assembly of such heteropolymers in mixed solvents were investigated and the analysis of formed spherical aggregates with multiple concaves on the surface was supported by TEM results and 3D electron tomography.     

Study on Heat Transfer and Flow Characteristic Under Phase-Change Process of an Acoustically Levitated Droplet

Acoustic levitation is one of the levitation technique which is expected to be used for analytical chemistry and manufacturing new materials. Thus, it is important to gather the knowledge about acoustically levitated droplet. The purpose of this study is to investigate the heat transfer and flow behavior under phase change process of an acoustically levitated droplet. The following results were obtained from experiments. Evaporation process and external flow structure of the levitated droplet is visualized by a high speed camera and it is found that they differ by the type of fluid. Toroidal vortices are observed near the surface of the ethanol solution droplet. Heat transfer coefficient is estimated from the volume change and temperature gradient. It is substantially higher than that estimated by the existing experimental correlation.     

Intermolecular Interaction of [60]Fullerene with Tröger's Base Analogues

Tröger's base (TB, 1) and its analogues were synthesized and were subject to the titration experiments to evaluate their ability of supramolecular complexation with C₆₀. Results demonstrate clearly that the fluorene-based TB analogue (2) and the bioctylfluorene-based TB analogue (3) show 1:1 binding with C₆₀ to form the corresponding complexes while TB 1 does not. Titration experiments exhibited that the association constant (K_ass) of 3/C₆₀ (48.1 ± 7.9 M ^?1) was larger than that of 2/C₆₀ (13.7 ± 1.4 M ^?1)_. The formation of the 1:1 binding complexes 2/C₆₀ and 3/C₆₀ was also confirmed by MALDI-TOF mass spectrometry. Theoretical calculations suggest that 2 and 3 have appropriate cavities to embrace C₆₀. These findings indicate that not only the π/π interaction between the fluorene moieties and the C₆₀ surface but also the CH/π interaction between the octyl groups and the C₆₀ surface serve efficiently in the supramolecular complexation with C₆₀.     

Excess micromotion compensation of trapped ions in a linear Paul trap for trace isotope analysis

Excess micromotion of trapped calcium ions was detected and compensated in our linear Paul trap apparatus for trace isotope analysis. The micromotion was detected by Charge-coupled device (CCD). camera and radio frequency (rf) correlation method. We found that 230 and 2280 V of compensation voltages were needed for x- and y-axis compensation in our apparatus, respectively. The z-axis micromotion was confirmed by the experiment and its cause was investigated by finding a shape of z-axis confinement field. The confinement field was indeed distorted in our apparatus and it gave rise to the trapped ion to shift from potential center. And the micromotion of r-direction was transferred to the z-axis by the distorted confinement field. The z-axis micromotion was suppressed by increasing cap voltage of trap.