Yasuo Kousaka

Orientation-Specific Dynamic Shape Factors for Doublets and Triplets of Spheres in the Transition Regime

ABSTRACT The dynamic shape factor for singly charged doublets and triangular triplets of uniform spheres (polystyrene latex particles) in the Knudsen number range 0.2–1.3 has been measured using a differential mobility analyzer (DMA). The shape factor turned out to be dependent on the intensity of the electric field created in the DMA. Thus, for doublets it was found that at low field strengths the point charge on the particles causes them to be inclined 45° with respect to the electric field, whereas at higher field intensity they become parallel to the field due to induced polarization. The adjusted diameter of the sphere having the same slip-correction factor as the nonspherical particle has also been discussed. The adjusted diameter was found to be almost the same as the volume equivalent diameter in the case of 45°-oriented particles.

Homogeneous Nucleation by Continuous Mixing of High Temperature Vapor with Room Temperature Gas

The formation of aerosol particles by homogeneous nucleation in a supersaturated vapor has been studied experimentally and theoretically. In the laboratory, a particle-free gas at room temperature is continuously mixed with a high-temperature gas containing dibutylphthalate vapor in a new device for the study of aerosol nucleation called a particle size magnifier. A highly supersaturated vapor is rapidly formed in the mixing zone of the particle size magnifier, and the resulting number concentrations of aerosol particles are measured under various temperatures, mixing ratios, and mixing methods. Measured number concentrations are compared with those predicted by the classical and Lothe-Pound nucleation theories. The measured concentrations lie between the predictions of the two theories, and the trends with temperature and saturation ratio are consistent with either nucleation theory, provided vapor depletion is considered.

Experimental control of ultrafine TiO2 particle generation from thermal decomposition of titanium tetraisopropoxide vapor

The generation of ultrafine TiO, particles by the thermal decomposition of titanium tetraisopropoxide (TTIP) vapor was carried out experimentally using a well-controlled cylindrical furnace. The effects of the initial vapor concentration of the TTIP vapor, the reaction temperature, the temperature profile of the furnace and properties of seed particles on the particle size distribution of produced aerosol particles were examined to control the generation of particles. The observed trends agreed semiquantitatively with the simulation results obtained by solving the discrete-sectional aerosol dynamic equation accounting for Brownian coagulation and generation of monomer by chemical reaction.

Facilitated aerosol sizing using the differential mobility analyzer

The electrostatic size analysis of polydisperse aerosols using a differential mobility analyzer (DMA) has been studied from the following two standpoints: (1) the faster measurement of electrical mobility distribution, arid (2) the correction of particle loss by Brownian diffusion in the data inversion, fn electrical mobility measurements, the number of mobility channels in a scan of the full mobility range is decreased and the full electrical mobility distribution is estimated by interpolation with a spline fitting. The correction of the Brownian diffusive losses of particles in the DMA including a neutralizer are combined with the data inversion method in order to evaluate the size distribution of aerosols unaffected by the particle loss. The reliability of the corrected data inversion method is confirmed by the experiment, and the particle size distribution of an aerosol is determined within several minutes by means of a faster scanning technique. This work was performed at the Department of Chemical E...

Direct Preparation of Uniformly-Distributed YBa2Cu3O7-x Powders by Spray-Pyrolysis

Fine powders of the compound YBa2Cu3O7-x have been prepared directly by the spray-pyrolysis of aqueous solutions of corresponding metal nitrates. The powders obtained in a temperature range of 900 to 1000°C were spherical and their diameters were uniformly distributed below 1 µm. The crystallinity of these powders was increased with increasing decomposition temperature; an orthorhombic single phase was indeed obtained at 1000°C. The sintered bodies from these powders showed the offset of superconducting transition at 84 K.

Dispersion of aggregates of fine powder by acceleration in an air stream and its application to the evaluation of adhesion between particles

Abstract Dispersion of aggregate particles by acceleration in an air stream is examined both experimentally and theoretically. In the experiments, several kinds of powders composed of particles of around 1 μm are dispersed by a high speed air stream at the throut of an ejector type disperser. The dispersed particles are observed with an optical or electron microscope. A numerical simulation is made with aggregates of different sized spheres, comparing the dispersion force acting on each aggregate with the adhesion force between spherical particles. The experimental dispersion results obtained for some kinds of powders agree with the simulation results. In the case of a few other kinds of powders, dispersion of the aggregate particles is actually more difficult than suggested by the calculation based on the assumption of spherical primary particles. Comparison between the experimental results using an ejector type disperser and the numerical simulation results is useful for the evaluation of adhesion between particles.

Generation of Aerosol Particles by Boiling of Suspensions

A new method for generation of aerosol particles, which will be called “boiling method,” is proposed. This method consists of (1) suspending particles in a liquid, (2) passing the suspension through a heated capillary tube, and (3) boiling of suspension to generate an aerosol. Aerosol particles thus generated are found to be effectively dispersed into primary (not coagulated) particles in high concentration. Such a dispersion is difficult if not impossible to produce by conventional nebulizers.

Influence of particle inertia on aerosol deposition in a stirred turbulent flow field

Abstract The influence of particle inertia on aerosol deposition is investigated in a turbulent flow field inside a vessel. In the experiment, the depositional loss rate of monodisperse latex particles of 0.1–2 μm in diameter is measured in a stirred tank. The dependence of deposition rates on the particle size and the turbulent intensity indicates that the minimum deposition rate exists in the range of particle size between 0.3 and 0.5 μm. From a comparison with representative theoretical deposition rates, the influence of particle inertia is found to appear in the deposition of particles larger than about 0.2 μm in diameter. The enhancement of the deposition rate due to particle inertia is satisfactorily explained by a model in which the inertial stopping distance of particles proposed by Sehmel ( J. geophys. Res. 75 , 1766, 1970) is taken into account. In addition, the deposition velocity induced by particle inertia is evaluated from the measured deposition rates, and the dimensionless inertial deposition velocity is found to be nearly proportional to the first power of the dimensionless particle relaxation time.

Enhancement of brownian and turbulent diffusive deposition of charged aerosol particles in the presence of an electric field

Abstract The effect of an electric field upon diffusive deposition of aerosol particles is investigated. In the experiments, charged and uncharged monodisperse particles of 0.02–0.2 μm are confined in a metal stirred tank inside which an electric field exists. It is found from measurements of the particle concentration decay inside the tank that the deposition rates of charged particles are enhanced as the electric field strength increases. To evaluate the electrostatic enhancement theoretically, the diffusion and transport of particles in an electric field are described, accounting for Brownian and turbulent diffusion and coulombic force acting on the particles. Deposition rates predicted by numerically solving the convective diffusion equation agree with those measured.

Preparation of ultrafine zirconium dioxide particles by thermal decomposition of zirconium alkoxide vapour

Ultrafine zirconia particles are produced by thermal decomposition of zirconium tetratertiary butoxide (ZrTB) vapour. The introduction of ZrTB vapour into the cylindrical electric furnace, is achieved by three different methods: (evaporator, pressurized nebulizer and ultrasonic nebulizer). The properties of the fine particles obtained by these methods are mainly analysed by X-ray diffraction and transmission electron microscopy. It is found that ultrafine zirconia particles produced at relatively low temperatures from 600 to 700° C are spherical in the diameter range 0.035 to 0.15 μm and of tetragonal phase. Furthermore, two-component fine particles of zirconia-ilver are generated by putting the silver solid inside the furnace containing alkoxide vapour, and are deposited by inertia on to a glass substrate under low pressure to form films having a thickness of 17 to 33 μm. The electrical characteristics of the films are evaluated, and the conductance of the film is found to increase with the content of the silver component.