Significance of Acoustic and Hydrodynamic Cavitations in Enhancing Ozone Mass Transfer

Assessment of both acoustic and hydrodynamic cavitations for intensifying ozone mass transfer was conducted simultaneously. Four process schemes were arranged to evaluate the effect of application of each kind of cavitation as well as both of them, on the ozone mass transfer process. All processes were conducted at pH of 3 to avoid ozone natural self-decomposition initiated by hydroxide ions (OH^?). The chemical and mechanical effects of cavitation were distinguished by using radical scavengers to suppress radical formation. The result showed that hydrodynamic and acoustic cavitations enhanced ozone mass transfer synergistically. The enhancement obtained from the acoustic cavitation was higher than that obtained from the hydrodynamic cavitation, and the chemical effects of cavitation were much significant than that of mechanical effects. The enhancement obtained due to chemical effects of cavitation was about twice the enhancement obtained due to mechanical effects when only one type of cavitation was combined with ozonation. Combination of both type of cavitation and ozonation gave the enhancement obtained due to chemical effect of 3.68 times that obtained due to mechanical effects.     

A Pulse Combustion-Spray Pyrolysis Process for the Preparation of Nano- and Submicrometer-Sized Oxide Particles

The preparation of nano- and submicrometer particles using an integrated pulse combustion–spray pyrolysis process was investigated for the first time. Zinc oxide nanoparticles with average sizes ranging from 20 to 40 nm were synthesized using a salt precursor with a lower decomposition temperature than the pulse combustion (PC) temperature. Particles of a doped-type oxide, gadolinium oxide-doped with europium, were also produced from a precursor, whose decomposition temperature was higher than the PC temperature, and were observed to be ellipsoidal–toroidal in shape and submicrometer in size. The high-intensity fluctuating pressures generated by PC and the precursor decomposition temperature are proposed as the reasons for the formation of either nanoparticles or aspherical particles. In addition, hot gas fluctuating flow in PC enhanced energy transfer, resulting in more crystalline particles, as compared with particles produced by conventional spray pyrolysis.     

An empirical study of domain knowledge and its benefits tosubstructure discovery

Discovering repetitive, interesting, and functional substructures in a structural database improves the ability to interpret and compress the data. However, scientists working with a database in their area of expertise often search for predetermined types of structures or for structures exhibiting characteristics specific to the domain. The paper presents a method for guiding the discovery process with domain specific knowledge. The SUBDUE discovery system is used to evaluate the benefits of using domain knowledge to guide the discovery process. Domain knowledge is incorporated into SUBDUE following a single general methodology to guide the discovery process. Results show that domain specific knowledge improves the search for substructures that are useful to the domain and leads to greater compression of the data. To illustrate these benefits, examples and experiments from the computer programming, computer aided design circuit, and artificially generated domains are presented     

Fabrication of high-performance fluorine doped-tin oxide film using flame-assisted spray deposition

A high-performance fluorine-doped tin oxide (FTO) film was fabricated by flame-assisted spray deposition method. By varying the NH₄F doping concentration, the optimal concentration was established as 8 at.%. X-ray diffractograms confirmed that the as-grown FTO film was tetragonal SnO₂. In addition, the FTO film was comprised of nano-sized grains ranging from 40 to 50 nm. The heat-treated FTO film exhibited a sheet resistance of 21.8 Ω/? with an average transmittance of 81.9% in the visible region (λ = 400-800 nm). The figures of merit shows that the prepared FTO film can be used for highly efficient dye-sensitized solar cells electrodes.     

Decolorization of beads-milled TiO2 nanoparticles suspension in an organic solvent

In this paper, a new method is proposed for the decolorization of a yellow-hued suspension of rutile TiO₂ nanoparticles in an organic solvent (diethylene glycol dimethylether). The presence of color has always been undesirable in a suspension of nanoparticles filler used for industrial needs, particularly for optical applications.A colorless suspension was achieved by irradiating well-dispersed TiO₂ nanoparticles in an organic solvent with UV-light (λ = 254 nm) for 5 h. TiO₂ nanoparticles of 1 and 5 wt.% were dispersed using a beads mill method. Trimethoxytrifluor(propyl) silane was used as a dispersant to achieve stability. The effect of the UV-light irradiation on the TiO₂ nanosuspension was investigated by means of a Fourier transform nuclear magnetic resonance analyzer (FT-NMR). The dispersant was partially desorbed due to the interaction of UV light and the TiO₂/dispersant complex. Thus, an enhanced transparency and the absence of color were obtained for well-dispersed TiO₂ nanoparticles in an organic solvent.     

High luminance YAG:Ce nanoparticles fabricated from urea added aqueous precursor by flame process

High luminance Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) nanoparticles were prepared from urea-added nitrate aqueous precursor by flame-assisted spray pyrolysis (FASP). The addition of urea into nitrate precursor plays an important role in YAG:Ce nanoparticle formation and in improving its optical performance. The decomposition and combustion of urea in the flame zone provides additional heat to the particles, which coupled with the evolution of large volumes of gasses, contributes to nanoparticle formation. The as-prepared nanoparticles are hexagonal YAlO₃, that are nearly spherical, rough on the surface and dense—and they can be converted to YAG:Ce after being annealed at 1200 °C for 4 h. The heat-treated particles are single crystalline, smooth in surface and dense with an average size around 50 nm. The optimum cerium-doping concentration of YAG:Ce nanoparticles is 4.0 at.%, which exhibits quantum efficiency of 45.0%. This quantum efficiency is comparable with that of YAG:Ce nanoparticles produced from other processes. The efficient emission of YAG:Ce nanoparticles also originates from a relatively good distribution of Ce ions incorporated into the host material of YAG as evidenced from the elemental mapping analysis.     

Formation of BaTiO3 nanoparticles from an aqueous precursor by flame-assisted spray pyrolysis

By manipulating process parameters, BaTiO₃ nanoparticles with tunable size were successfully prepared by flame-assisted spray pyrolysis (FASP) from an aqueous solution of barium acetate and titanium-tetra-isopropoxite. Particle size was controlled over a wide range (from about 23 to 71 nm) by varying the concentration of precursor and methane flow rate. Flame temperature was a key factor in producing particles with a narrow size distribution. The BaTiO₃ nanoparticles were cubic in crystal structure, dense, spherical and softly agglomerated. The particles contained OH, carboxyl and CO₂ bonding groups that could be completely removed by post-heat treatment. At room temperature, BaTiO₃ pellets had relatively high dielectric constants (2578.8–3611.8) with loss factors ranging from 2.6% to 7.1% at the frequency of 1 kHz. The results of this study indicate that BaTiO₃ nanoparticles can be fabricated using continuous and industrially applicable FASP.     

Hydrogen production from biogas using hot slag

Possibility of hydrogen production from biogas using hot slag has been studied, in which decomposition rate of _CO2${\mathrm{CO}}_2$–_CH4${\mathrm{CH}}_4$ in a packed bed of granulated slag was measured at constant flow-rate and pressure. The molten slag, discharged at high temperature over 1700 K from smelting industries such as steelmaking or municipal waste incineration. It has enough potential for replacing energy required for hydrogen production due to the catalytic steam reforming or carbon decomposition of hydrocarbon. However, heat recovery of hot slag has never been established. Therefore, the objective of this work is to generate hydrogen from methane using heated slag particles as catalyst, in which the effect of temperature on the hydrogen generation was mainly investigated at range from 973 to 1273 K. In the experiments a mixed gas of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was continuously introduced into the packed bed of hot slag at constant flow-rate and atmospheric pressure and then the outlet gas was monitored by gas chromatography. The results indicate that slag acted as not only thermal media but also good catalyst, for promoting decomposition. The product gases were mainly hydrogen and carbon monoxide with/without solid carbon deposition on the surface of slag, depending on the reaction temperature. Increasing temperature led to large hydrogen generation with decreasing un-reacted methane in the outlet gas, at when the largest methane conversion was about 96%. The results suggested a new energy-saving process of hydrogen production, in which the waste heat from molten slag can replace the energy required for hydrogen production, reducing carbon dioxide emission.