Promoting Effect of Cerium Oxide on the Catalytic Performance of Yttrium Oxide for Oxidative Coupling of Methane.

The promoting effect of CeO on the catalytic performance of YO, which is moderately active catalyst, for the oxidative coupling of methane (OCM) reaction was investigated. The addition of CeO into YO by coprecipitation method caused a significant increase in not only CH conversion but also C (CH/CH) selectivity in the OCM reaction. C yield at 750 °C was increased from 5.

Ultrasonic cavitation induced water in vegetable oil emulsion droplets--a simple and easy technique to synthesize manganese zinc ferrite nanocrystals with improved magnetization.

In the present investigation, synthesis of manganese zinc ferrite (Mn(0.5)Zn(0.5)Fe(2)O(4)) nanoparticles with narrow size distribution have been prepared using ultrasound assisted emulsion (consisting of rapeseed oil as an oil phase and aqueous solution of Mn(2+), Zn(2+) and Fe(2+) acetates) and evaporation processes.

Effect of static pressure on acoustic energy radiated by cavitation bubbles in viscous liquids under ultrasound.

The effect of static pressure on acoustic emissions including shock-wave emissions from cavitation bubbles in viscous liquids under ultrasound has been studied by numerical simulations in order to investigate the effect of static pressure on dispersion of nano-particles in liquids by ultrasound. The results of the numerical simulations for bubbles of 5 μm in equilibrium radius at 20 kHz have indicated that the optimal static pressure which maximizes the energy of acoustic waves radiated by a bubble per acoustic cycle increases as the acoustic pressure amplitude increases or the viscosity of the solution decreases. It qualitatively agrees with the experimental results by Sauter et al.

Influence of liquid-surface vibration on sonochemiluminescence intensity.

The influence of surface vibrations on the intensity of sonochemiluminescence (SCL) produced by pulsed ultrasound with a frequency of 151 kHz is investigated through optical measurement of the vibration amplitude. Pulsed ultrasound inhibits the generation of large degassing bubbles that scatter sound waves, thereby restricting the effective spatial region for sonochemical reactions. The vibration amplitude of the liquid surface becomes gradually significant with pulsed ultrasound as the power applied to the transducer increases.

Development and optimization of acoustic bubble structures at high frequencies.

At high ultrasound frequencies, active bubble structures are difficult to capture due to the decrease in timescale per acoustic cycle and size of bubbles with increasing frequencies. However the current study demonstrates an association between the spatial distribution of visible bubbles and that of the active bubble structure established in the path of the propagating acoustic wave. By monitoring the occurrence of these visible bubbles, the development of active bubbles can be inferred for high frequencies.

Spatial distribution of acoustic cavitation bubbles at different ultrasound frequencies.

Images of sonoluminescence, sonophotoluminescence and sonochemiluminescence are recorded in order to semi-quantitatively compare the spatial distribution of the cavitation activity at three different ultrasound frequencies (170 kHz, 440 kHz and 700 kHz) and at various acoustic amplitudes. At all ultrasound frequencies investigated, the sonochemically active cavitation zones are much larger than the cavitation zones where sonoluminescence is observed. Also, the sonochemically active bubbles are observed at relatively lower acoustic amplitudes than that required for sonoluminescence bubbles to appear.

Variations in the spatial distribution of sonoluminescing bubbles in the presence of an ionic surfactant and electrolyte.

It has been established that the addition of sodium dodecylsulfate (SDS) to water to a concentration of 1 mM increased the integrated sonoluminescence (SL) intensity to a maximum. Moreover, further increase in the SDS concentration to 10 mM decreased the SL intensity to a level comparable to that obtained for water. Photographic images of water and 10 mM SDS have revealed a localized distribution of SL bubbles near the liquid surface.

Dependence of sonochemical parameters on the platinization of rutile titania - an observation of a pronounced increase in photocatalytic efficiencies.

Using a standing wave sonochemical reactor (SWSR), the influences of parameters of ultrasonic power input, sonication time, sonication temperature and the amount of propanol (which generates the reducing radicals) were systemically investigated to ascertain and optimize the best conditions for the sonochemical reduction of Pt from its precursor hexachloroplatinic acid and then its deposition on rutile TiO(2) (platinization of rutile titania) catalysts. Catalytic activity of the prepared platinized catalysts was tested in the reaction of methyl orange degradation. The results of photocatalytic activity study in the degradation of methyl orange further demonstrate that sonochemically as-prepared Pt/TiO(2) catalysts show a pronounced increase ( approximately 2 times) in photodegradation, even with a deposition of small amounts of platinum (1.

The detection and control of stable and transient acoustic cavitation bubbles.

Acoustic cavitation plays a significant role in many applications that include therapeutic medicine, sonochemsitry and materials processing. The type of cavitation bubbles generated, namely transient or stable (repetitive transient), is important for optimizing the efficiency of these applications. We report on a multibubble sonoluminescence (MBSL)-based experimental technique for the detection and the control of type of cavitation at low and high ultrasound frequencies.

Bubble population phenomena in sonochemical reactor: II. Estimation of bubble size distribution and its number density by simple coalescence model calculation.

A simple bubble population model, with emphasis on the bubble-bubble coalescence, is proposed. In this model, the bubble size distribution is simulated through the iteration of fundamental bubble population process: generation, dissolution, and coalescence. With this simple modelling, the bubble size distribution experimentally observed by the pulsed laser diffraction method and the void rate obtained by the capillary system at 443kHz were successfully simulated.

Bubble population phenomena in sonochemical reactor: I estimation of bubble size distribution and its number density with pulsed sonication - laser diffraction method.

To characterize the bubble populations (size and its number distribution) in a sonochemical reactor, a simple but powerful technique based on the Fraunhofer laser diffraction (LD) has been proposed. In this method, the acoustic wave disturbance to the laser probe in the sonochemical reaction field was eliminated by the temporal separation using pulsed sonication (pulsed LD). With this relatively simple strategy, the temporal development of the bubble size distribution could be evaluated by pulsed LD.

Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles.

Numerical simulations of cavitation noise have been performed under the experimental conditions reported by Ashokkumar et al. (2007) [26]. The results of numerical simulations have indicated that the temporal fluctuation in the number of bubbles results in the broad-band noise.

Influence of the bubble-bubble interaction on destruction of encapsulated microbubbles under ultrasound.

Influence of the bubble-bubble interaction on the pulsation of encapsulated microbubbles has been studied by numerical simulations under the condition of the experiment reported by Chang et al. [IEEE Trans. Ultrason Ferroelectr.

Influence of surface active solute on ultrasonic waveform distortion in liquid containing air bubbles.

The influence of sodium dodecyl sulfate (SDS) on waveform distortion of 141 kHz ultrasonic standing waves in liquids containing air bubbles was investigated for various transducer powers. Fast Fourier transform (FFT) operations were performed on the pressure waveform to obtain the harmonic components. In addition, the intensity of sonoluminescence (SL) was measured as a function of the power.

Fabrication of nanosized Pt on rutile TiO2 using a standing wave sonochemical reactor (SWSR)--observation of an enhanced catalytic oxidation of CO.

Fine particles of rutile TiO2 supporting nanosized particles of Pt were prepared by a simultaneous in situ sonochemical reduction and deposition method using a standing wave sonochemical reactor (SWSR). The mean diameter of sonochemically obtained Pt particles are of 2 nm. Following this sonochemical technique, rutile TiO2 was also deposited with different weight percentages of Pt.

Optical cavitation probe using light scattering from bubble clouds.

To understand the behaviour of systems containing clouds of bubbles (multibubble system) in real sonochemical reactors, a new diagnosis method, i.e., optical cavitation probe (OCP), has been proposed.

Spatial distribution enhancement of sonoluminescence activity by altering sonication and solution conditions.

An intensified charge-couped device (CCD) camera was used to capture raw images of multibubble sonoluminescence, generated by 168 and 448 kHz ultrasound. The effect of various air and surfactant concentrations, and pulse conditions on the acoustic pressure distribution, percentage of standing wave component, the structure of the sonoluminescence activity, and speed of streaming was investigated. It was observed that the enhancement in the sonoluminescence intensity by appropriate degassing, pulsing, and addition of sodium dodecylsulfate were closely related to an expansion in the spatial distribution of sonoluminescence activity.

The range of ambient radius for an active bubble in sonoluminescence and sonochemical reactions.

Numerical simulations of nonequilibrium chemical reactions inside an air bubble in liquid water irradiated by ultrasound have been performed for various ambient bubble radii. The intensity of sonoluminescence (SL) has also been calculated taking into account electron-atom bremsstrahlung, radiative attachment of electrons to neutral molecules, radiative recombination of electrons and ions, chemiluminescence of OH, molecular emission from nitrogen, etc. The lower bound of ambient radius for an active bubble in SL and sonochemical reactions nearly coincides with the Blake threshold for transient cavitation.

Mechanism of enhancement of sonochemical-reaction efficiency by pulsed ultrasound.

The enhancement of sonochemical-reaction efficiency by pulsed ultrasound at 152 kHz has been studied experimentally through absorbance measurements of triiodide ions from sonochemical oxidation of potassium iodide at different liquid volumes to determine sonochemical efficiency defined by reacted molecules per input ultrasonic energy. The mechanism for enhancement of the reaction efficiency by pulsed ultrasound is discussed using captured images of sonochemiluminescence (SCL), and measured time-resolved signals of the SCL pulses and pressure amplitudes. The high sonochemical-reaction efficiency by pulsed ultrasound, compared with that by continuous-wave ultrasound, is attributed both to the residual pressure amplitude during the pulse-off time and to the spatial enlargement of active reaction sites.

Protein release from yeast cells as an evaluation method of physical effects in ultrasonic field.

The release rate of intercellular protein from yeast cells by the ultrasonic action is proposed as a method for evaluating the physical (mechanical) effects of the ultrasonic field. The protein concentration was quantitatively determined using UV absorbance of proteins by spectrophotometry. The detail of the procedures, such as the effects of the origin of yeast cells, pretreatment of the cells, and the wavelengths for spectrophotometric determination of protein content, are examined.

Strongly interacting bubbles under an ultrasonic horn.

Numerical simulations of bubble pulsations have been performed for a system of two bubble clouds in order to study the experimentally observed bubble motion under an ultrasonic horn by high-speed video camera. The comparison between the calculated results and the experimental observation of the bubble pulsation has indicated that the bubble pulsation is strongly influenced by the interaction with surrounding bubbles. The expansion of a bubble during the rarefaction phase of ultrasound is strongly reduced by the bubble-bubble interaction.

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.

Relationship between the bubble temperature and main oxidant created inside an air bubble under ultrasound.

Numerical simulations of nonequilibrium chemical reactions in a pulsating air bubble have been performed for various ultrasonic frequencies (20 kHz, 100 kHz, 300 kHz, and 1 MHz) and pressure amplitudes (up to 10 bars). The results of the numerical simulations have indicated that the main oxidant is OH radical inside a nearly vaporous or vaporous bubble which is defined as a bubble with higher molar fraction of water vapor than 0.5 at the end of the bubble collapse.

Ultrasound induced formation of paraffin emulsion droplets as template for the preparation of porous zirconia.

The paraffin particles were prepared by quenching process after sonicating the solution of paraffin and water at 80 degrees C. The resultant paraffin particles were then used as template for the preparation of macroporous zirconia materials. For this, zirconium normal butoxide (ZNB) modified with triethanolamine (TEA) was first hydrolyzed by water containing the dispersed paraffin particles with the surfactant, Sodium di(2-ethylhexyl) sulfosuccinate.

Bubble motions confined in a microspace observed with stroboscopic technique.

Dynamic motions of gas bubble confined in a microspace, i.e., in a channel of a microreactor, were observed with a video microscope and stroboscopic technique using a light emitting diode operated in a pulsed mode.