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Ultrasonic spray pyrolysis method to synthesize porous submicron particles of solid oxide fuel cell (SOFC) electrode materials was developed in which citric acid is added in a precursor solution. This citric acid-addition ultrasonic spray pyrolysis (CA-USP) method was then used to synthesize NiO-Gd0.1Ce0.9O1.95 (GDC) particles for SOFC anodes and La0.8Sr0.2Co3 (LSC) and La0.8Ca0.2MnO3 (LCM) particles for SOFC cathodes. The synthesized particles were submicron-sized, porous, and spherical, and had a sponge-like structure. Energy dispersive X-ray spectrometry images of the synthesized NiO-GDC particles revealed that Ni, Ce, Gd, and O were uniformly distributed within individual particles. NiO-GDC and LCM particles with sponge-like structure were not crushed by a 2-h ball mill grinding test. The formation process of the sponge-like structure was clarified by synthesizing GDC particles at various furnace temperatures between 473 and 1273 K.Copyright 2014 American Association for Aerosol Research

A new ultrasonic spray pyrolysis method, called carbon nanoparticle-addition ultrasonic spray pyrolysis (CNA-USP), is developed to synthesize nanoparticles of electrolyte material for solid oxide fuel cell applications. In CNA-USP, carbon nanoparticles are added in a precursor solution. First, Gd0.1Ce0.9O1.95 (GDC) particles were synthesized from an aqueous solution of Ce(NO3)3 6H2O and Gd(NO3)3 6H2O by using the CNA-USP method. The resulting synthesized GDC particles were agglomerated, porous, primary particles on the order of 10 nm in diameter. EDX images revealed uniform distributions of Ce, Gd, and O in these porous particles. Then, these agglomerated, porous submicron GDC particles were ground into primary nanoparticles by ball milling for 24 h. The average diameter of the ground GDC nanoparticles was about double of their average crystallite size.Copyright 2014 American Association for Aerosol Research

A small mixing-type unipolar charger for nanoparticles (SMUC) was developed to increase the charging efficiency and throughput by using a small charging chamber (0.5 cm 3 ) to reduce particle loss caused by electrostatic dispersion. The two main components of the SMUC are a high-pressure corona ionizer (HPC Ionizer) in which high concentration unipolar ions are generated, and a charging chamber in which the unipolar ions are mixed with nanoparticles without an external electric field. The charging performance of the SMUC was evaluated experimentally by measuring the charging ratio fc and the penetration ratio fp . For positive charging in the particle size range of 5–40 nm, fc + = 0.91–0.95 and fp + = 0.71–0.90, at an ion concentration of Ng + = 5.25 10 9 ions/cm 3 and a charging time t R = 0.025 s. For negative charging, f – c = 0.74–0.93 and fp – = 0.73–0.85, at Ng – = 6.24 × 10 9 ions/cm 3 and tR = 0.025 s. Based on these results, the extrinsic charging efficiency defined as fe = fc ×fp /fd (where fd i...

An aerosol neutralizer called the Mixing-type Bipolar Charger using Corona-Discharge at High Pressure (MBCCHP) was developed. In the MBCCHP, a corona discharge (High-Pressure Corona Ionizer; HPC Ionizer) induced by high frequency voltage (>100 Hz) at high pressure (>0.2 MPa) is used to generate bipolar ions at high concentration (1–3 × 109 ions/cm3) that are then mixed with aerosol particles flowing in a charging chamber where no external electric field is present. The charging performance of the MBCCHP was evaluated by comparing the measured and theoretical number ratios of positively and negatively charged particles to the total number of particles, and by comparing those of negatively charged to positively charged particles for an equilibrium charge distribution. The theoretical and measured results agreed well in the particle size range of 5–80 nm. Particle loss in the MBCCHP for the size range of 5–100 nm was less than 15%, and particle generation from the electrode due to spattering or from the carr...

Particle formation mechanisms in nanoparticle synthesis by ionization chemical vapor deposition (CVD), in which source gases are ionized before being fed into the reactor, were investigated experimentally. First, nonagglomerated nanoparticles were formed from a tetraethylorthosilicate (TEOS)/O 2 mixture ionized with a sonic-jet ionizer at various furnace temperatures, T f, and TEOS concentrations, N TEOS. Then, the electrical mobility of the nanoparticles and ions were measured using a differential mobility analyzer combined with a Faraday cup electrometer, and the particle number concentration by a condensation nucleus counter. Measurements at 293 ≤ T f ≤ 1173 K and 0 ≤ N TEOS ≤ 1.38 × 10 −5 mol/l showed that (a) negative TEOS and TEOS cluster ions were formed at T f = 293 K, (b) gas-phase intermediates forming nanoparticles were formed at T f ≥ 673 K, (c) for T f = 873 K condensation of the intermediates onto ions (i.e., ion-induced nucleation) started at N TEOS ≥ 4.48 × 10 −7 mol/l, and (d) the growth ...

Effects of NO 2 on particle formation in SO 2 /H 2 O/Air mixtures by f -ray irradiation as a source of hydroxyl radicals are investigated to evaluate the contribution of homogeneous and ion-induced nucleation in the nanometer-sized aerosol particle generation. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles and hydrated and solvated ions generated in NO 2 /SO 2 /H 2 O/Air mixtures were measured at NO 2 levels of 0-1.98 ppm, SO 2 levels of 0-3.87 ppm, and H 2 O levels of 6480-9889 ppm. Total particle number concen2 tration first tends to increase with increasing NO 2 concentration up to a certain NO 2 level and then decreases for NO 2 concentrations beyond this point. The charged-particle fraction, indicative of particle formation by ion-induced nucleation, tends to decrease with increasing NO 2 concentration, reaching a minimum value. The peak intensity of the electrical mobility distribution for particles significantly exceeded...

Formation of nanometer-sized particles in NH3/SO2/H2O/Air mixtures by α-ray irradiation was studied experimentally to evaluate the effect of NH3 gas on the gas-to-particle conversion process. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles generated in the ionization chamber were measured at various NH3, SO2, and H2O vapor concentrations and residence times of the gas mixture. Particle generation was enhanced in the presence of NH3, but the enhancement depends greatly on the SO2, NH3, and H2O concentrations; particle number concentrations at NH3 mixing ratios of 0.71–3.6 ppm were 2–4 times higher than those in the absence of NH3, but were constant in this range of NH3 concentration. The charged-particle fraction decreased with the addition of NH3, which indicated that ion-induced nucleation was decreased and homogeneous nucleation was enhanced. To evaluate the number concentrations of gaseous products, kinetic equations...

Alpha-ray radiolysis of SO2/H2O/N2 gas mixtures is carried out to investigate the competitive processes of ion-induced and binary homogeneous nucleation in this system. Charged particles in the system are indicative of ion-induced nucleation and most likely involve water clusters. Charged particle neutralization was prevented by application of a dc electric field, therefore, uncharged particles in the system result from homogeneous nucleation. Hydroxyl (OH) radicals are generated by the a-ray radiolysis. Oxidation of SO2 by OH radicals leads to sulfuric acid (H2SO4) vapor molecules and to subsequent binary homogeneous nucleation of H2SO4/H2O. At increased SO2 concentrations the contribution of binary homogeneous nucleation increases relative to that of ion-induced nucleation. Electrical mobility distributions of bipolar ions and nanometer-sized charged particles were measured with a cluster-differential mobility analyzer combined with a Faraday cup electrometer. In this system, ion-induced nuclea...

A new aerosol neutralizer, which makes use of a corona ionizer to produce bipolar ions, has been designed and evaluated. The corona neutralizer consists of three components: a dual-needle ionizer for the generation of bipolar ions, an opposing-jet mixer for the uniform mixing of ions and particles, and a charging chamber for particle charge neutralization by ions. The bipolar ionizer consists of two unipolar ionizers for producing positive and negative ions, respectively. They are mixed to obtain the appropriate mixture of bipolar ions. Aerosol particals are then mixed with the bipolar ions in the mixer and are electrically discharged by collision with the bipolar ions in the charging chamber. The charge distribution of aerosol particles exiting the new corona neutralizer is found to depend on the ratio of electric current of positive ions and negative ions I − / I − and to attain the Boltzmann charge distribution at I + / I − = 1.0. The neutralizer has been shown to effectively reduce the particle charge...

Experiments of unipolar diffusion charging of ultrafine aerosol particles (10–50 nm) at low pressure (0.2–0.5 atm) were performed. Aerosol charging was achieved using a novel unipolar charger which made use of a low-intensity α-ray radioactive source. The results of the experiments were compared with numerical solutions to the fundamental equations of charging. The Fuchs' limiting-sphere charging theory in the transition regime was used for the calculation of the combination coefficients between ions and particles. Good agreement was found between experimental results and numerical predictions of the charged fraction as a function of particle diameter. This is Particle Technology Laboratory Publication No. 767.

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...

The size analysis of ultrafine aerosol particles using a differential mobility analyzer combined with a CNC is discussed from two standpoints: (1) particle loss caused by Brownian diffusion in the analyzer, and (2) data reduction procedure where Fuchs' charging theory is applied. As a result, it has been found that (1) particle loss becomes significant when particle size is smaller than about 15 nm, and (2) a simple and practical data reduction procedure may be used, where the stationary bipolar charge distribution given by Boltzmann's law is modified by using Fuchs' charge distribution in the smaller size range.

The diffusion charging of polydisperse and monodisperse aerosol particles by bipolar ions was theoretically studied under various conditions. Approximate equations in the simple form were derived to evaluate the changes in the particle charge and the ion number concentration. These approximate equations were applied to analyze the performance of the ionization-type smoke detector. The output response of an ionization-type smoke detector was experimentally tested with monodisperse aerosols, and the experimental response on the particle size and number concentration dependence were found to be explained by the simple approximate equations.

The bipolar diffusion charging of aerosol particles in the transition and continuum regimes was studied theoretically and experimentally under the conditions of high particle / ion concentration ratios. The basic equations for the bipolar diffusion charging of monodisperse and polydisperse aerosols were numerically solved for geometric mean diameters of 0.01–1.0 μm, geometric standard deviations of 1–2, and for various concentrations of bipolar ions. From the calculation results presented in terms of dimensionless parameters, the ion number concentrations and charging times required to attain the equilibrium charge distributions were determined. In the experiment, the changes in the particle charge distribution and ion number concentration in the flow-type chamber were measured for various particle number concentrations, ion generation rates, and residence times. For bipolar ion generation rates > 3.5 × 1011 m−3 s−1, the experimental results were found to agree with the theoretical predictions. For smalle...