Suppression of sonochemiluminescence reduction at high acoustic amplitudes by the addition of particles

The effect of particle addition to a liquid or liquid surface on the sonochemiluminescence (SCL) was investigated using a luminol aqueous solution under ultrasonic treatment at 154 kHz. The acoustic-amplitude dependence of the SCL intensity was measured, in addition to capturing images of luminescent spatial patterns. At higher acoustic amplitudes, the cavitation efficiency dramatically reduces. This behavior is suppressed in the presence of particles. Particle addition provides nucleation sites for cavitation bubbles, lowering the cavitation threshold, and weakening the liquid surface vibration as the pressure amplitude decreases. It is shown that the reduction in SCL is suppressed under the addition of alumina particles into luminol aqueous solution. As the amount of alumina particles increases, the range of acoustic amplitude for suppressing the reduction in SCL is enlarged toward high amplitude, and the intensity of the SCL increases. Simultaneous addition of alumina particles into the solution and hydrophobic polytetrafluoroethylene (Teflon) particles onto the liquid surface is also effective. Examination of SCL images revealed that alumina particles added to the liquid at high acoustic amplitude caused the entire region of the reaction volume to be homogeneously luminous. If hydrophobic particles cover the solution surface, the surface vibration at high acoustic amplitude is fixed and the sound field becomes stable. This is responsible for suppression of the reduction in SCL and leads to a high rate of sonochemical reaction, even at high acoustic amplitude.     

FEM calculation of an acoustic field in a sonochemical reactor

The spatial distribution of the acoustic amplitude in a sonochemical reactor has been numerically calculated using the finite element method (FEM). In the FEM program, the acoustic field in a sonochemical reactor is coupled with the vibration of the reactor's wall. The present calculations have revealed that the thin (thick) glass or stainless steel wall is nearly a free (rigid) boundary and that the glass wall is freer than the stainless steel wall. The influence of the attenuation coefficient of ultrasound on the acoustic field has also been studied in order to see the effect of bubbles on the acoustic field. As the attenuation coefficient increases, the vibration amplitude of the reactor's wall becomes smaller and the acoustic emission from the vibrating wall becomes weaker. The qualitative feature of the spatial pattern of sonochemiluminescence from an aqueous luminol solution has been reproduced by the calculation when the attenuation coefficient is in the range of 0.5-5m(-1). When the attenuation coefficient is less than about 0.05 m(-1), the standing wave pattern of an acoustic field in the liquid is very complex due to the acoustic emission from the vibrating wall. The present calculations have also revealed that some stripes of pressure antinodes have also been disconnected when the radius of the transducer is much smaller than the side length of the vibrating plate. The dependence of the acoustic field on the liquid height is also discussed.     

2009 ISGS life achievement award

Editorial Note

2009 ISGS life achievement award     

Spontaneous formation of linearly arranged microcraters on sol-gel-derived silica-poly(vinylpyrrolidone) hybrid films induced by Bénard-Marangoni convection

Complex, sophisticated surface patterns on micrometer and nanometer scales are obtained when solvent evaporates from solutions containing nonvolatile solutes dropped on a solid substrate. Such evaporation-driven pattern formation has been utilized as a fabrication process of highly ordered patterns in thin films. Here, we suggested the spontaneous pattern formation induced by Bénard-Marangoni convection triggered by solvent evaporation as a novel patterning process of sol-gel-derived organic-inorganic hybrid films. Microcraters of 1.0-1.5 μm in height and of 100-200 μm in width were spontaneously formed on the surface of silica-poly(vinylpyrrolidone) hybrid films prepared via temperature-controlled dip-coating process, where the surface patterns were linearly arranged parallel to the substrate withdrawal direction. Such highly ordered micropatterns were achieved by Bénard-Marangoni convection activated at high temperatures and the unidirectional flow of the coating solution on the substrate during dip-coating.     

LaCo(1-x)Ni(x)O(3) with Improved Electrical Conductivity

To determine the applicability of LaCo(1-x)Ni(x)O(3) in a conductive material for electrical wiring, the dependence of the electronic transport property on the Ni content is investigated via Hall effect measurements, Rietveld analyses, and band-structure calculations. Ni doping (50 mol %) into the Co sites realizes a high electrical conductivity of 1.9 × 10(3) S/cm, which is an unexpectedly high value for a LaCo(1-x)Ni(x)O(3) system, at room temperature due to the high carrier concentration of 2.2 × 10(22) cm(-3) and the small effective mass of 0.1 m(e). In addition, the high electrical conductivity is maintained from room temperature to 900 °C; that is, the temperature coefficient of the conductivity is smaller than that of standard metals. Thus, the results indicate that LaCo(0.5)Ni(0.5)O(3) is suitable as a conductive material for electrical wiring at high temperatures in air.     

Solvothermal synthesis of micron-sized spherical particles in TiO2–ZrO2 binary system

We prepared TiO₂–ZrO₂ binary oxide particles with various Ti/(Zr+Ti) mole ratios (x) from the solutions containing Ti(OC₃H₇ⁱ)₄, Zr(OC₃H₇ⁿ)₄ and acetylacetone (acac). The spherical particles of 1–5 μm in diameter were obtained via solvothermal treatment at 150 °C. The spheres were anatase at x=1 and amorphous at x=0–0.8. The spheres were thought to be formed through the moderate hydrolysis and nucleation provided by the chelation of the alkoxides by acac. Crystalline TiO₂–ZrO₂ particles were obtained by the heat treatment of the as-precipitated spheres, and the crystalline phase changed with the Ti/(Zr+Ti) mole ratios. Pure ZrO₂ and TiO₂, ZrO₂ doped with Ti⁴⁺, TiO₂ doped with Zr⁴⁺ and ZrTiO₄ phases were produced, and the spherical shape remained after the heat treatment at 500–750 °C.     

Thermoplasticity of sol–gel-derived titanoxanes chemically modified with benzoylacetone

Titanium tetra-n-butoxide was hydrolyzed in the presence of benzoylacetone (BzAc), and the solution obtained was concentrated and served for spin-coating or dropping on substrates, followed by successive drying at 120, 200 and 250 °C. The dried products were transparent and amorphous, and the infrared absorption and Raman spectroscopic studies showed that BzAc forms chelate rings. Thermomechanical analysis showed that the 120 and 200 °C-dried products showed steep, thermoplastic shrinkage at around 30 and 70–85 °C, respectively, whereas the 250 °C-dried product did not show thermoplasticity. Thus as the drying temperature was increased, the thermoplasticity appeared at a higher temperature and finally disappeared. These changes in thermoplasticity with drying temperature were concluded to result from the progress of condensation between titanoxane polymers and/or clusters, which was evidenced in gel permeation chromatographic analysis.     

Photoxidation of di-t-butyl thioketone

The photo-oxygenation of the title compound leads to the corresponding ketone and sulfine. A mechanism for the reaction is elucidated.     

Electrical Properties of Transparent Doped Oxide Films

In the present study n-type and p-type transparent conductive TiO₂ films were prepared by using sol-gel method. The n-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Ru and Ta. The films were uniform and transparent in all the conditions, and their crystalline phases were anatase when HCl or HNO₃ was used as a catalyst. The resistivity decreased with increasing Ta content and increased with increasing Ru content. Most of the films showed resistivity minima at a heat-treatment temperature of 700°C. The lowest resistivity of 10¹ 10² cm was attained. The p-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Co and Nb (Sb). The films were also uniform and transparent when AcAc was used, while samples heat-treated at 800°C became opaque when HCl was added. Rutile single phase appeared when the films were heat-treated at 700°C. Logarithmic resistivity of films co-doped with Co and Nb was directly proportional to the reciprocal absolute temperature. On the other hand, the slopes for films co-doped with Co and Sb were different below and above 200°–220°C. The activation energy at the low-temperature region is as low as 0.17 eV, and the resistivity at room temperature is 10⁴ 10⁵ cm.     

Stress evolution on gel-to-ceramic thin film conversion

In situ cracking observation, uncracking critical thickness evaluation and in situ stress measurement were conducted during heating for alkoxide-derived gel coating films. Higher water-to-alkoxide ratios and lower heating rates were shown to cause cracking at lower temperatures. The in situ stress measurement suggested that higher water-to-alkoxide ratios in solutions and lower heating rates result in larger in-plane tensile stress to be generated in the heating-up stage, which was thought to cause the cracking at lower temperatures. Methyltriethoxysilane, chelating agents and polyvinylpyrrolidone were shown to be effective in increasing uncracking critical thickness and/or thick film formation. The in situ stress measurement suggested that these additives or components are effective in suppressing the stress evolution during heating.