Assembly of particles is one of the build-up methods for fabrication of organized structures in the range from micro- to nanometer scales. We have been developing a new technique to assemble microscale particles for the fabrication of two-dimensionally controlled micro structures. The procedure is as follows : an electrified pattern is formed on a dielectric substrate by scanning charging beams. Tne substrate is then dipped into a suspension in which the particles are dispersed. The particles are arrayed on the electrified pattern. In this paper, we investigated the electrostaric force which attracts the particles in the suspension. Spherical silica particles of 5 μm diameter were used as model particles, and the particles were charged in negative polarity in the suspension. The particles were deposited on both the negatively and positively charged patterns. This result suggests that gradient force plays an important role in attracting particles. The electrostatic forces for a particle in the suspension were calculated using numerical analysis. The result showed that the gradient force is larger than the Coulomb force near the electrified pattern.
This paper summarizes the aerosolization of hazardous air pollutants using three different types of nonthermal plasma reactors such as packed-bed, pulsed corona and capillary tube plasma reactors. The aerosol generation was initiated by the radical and ionic reactions between background gases and pollutants under plasma environment. Most of the aerosols produced under plasma were of a particle size much less than 100 nm (majority were 10 nm or less) through the cluster formation. Also, the core particles generated from the electrode materials by spattering may coagulate with clusters to form aerosols. The particle generation for CFC-113 increased with applied voltage (plasma power), but it was not affected by humidification. Aerosol generation of 1,000 ppm CFC-113 in air using the packed-bed reactor was approximately 10 particles/cm3 at 8 kV for the particle size greater than 10 nm. The particle generation for 600 ppm toluene using the pulsed corona achieved over 35 particles/cm3 for the particle size of 0.3 ∼ 0.5 μm and expected to be significantly higher than CFC-113 for the particle size greater than 10 nm.
An ion mobility/mass spectrometer that incorporates a drift tube and a quadrupole mass analyzer has been developed for the purpose of identifying ion species in the experiments of ion-induced nucleation and also in the ambient tropospheric air. Total ion mobility spectra, mass spectra, and mass-resolved mobility spectra were measured for positive ions aged for 20-30 ms in the laboratory air. The results showed that NH4+ (H2O)n were dominant ions and were responsible for the most intense ion peak (1.66×10-4m2V-1s-1) in total ion mobility spectra. Protonated dimethylamine (46 amu) and protonated pyridine (80 amu) were also found in the mass spectra along with several unidentified ions (135, 149, 152, 279 amu). Mass-resolved mobility spectra of ions other than NH4+ (H2O)n appeared to reflect changes in the ion composition within the drift tube, indicating that information on ion-molecule reactions in the drift tube can be obtained from analysis of mass-resolved mobility spectra.
Recent concerns about environmental protection encourage the use of compact indoor air cleaners, therefore, various types of electrostatic precipitators (ESPs) have been developed. Although a wide range of airborne particles such as dust can be collected effectively with an ordinary ESP using a positive DC corona, it is difficult to remove gaseous compounds such as tobacco smoke which consists of submicron particles and gaseous matters with an offensive odor. In the present study, we investigated the collection of submicron particles using a commercial ESP and the decomposition of acetaldehyde (CH3CHO) using the nonthermal plasma reactors since the offensive odor of tobacco smoke is caused mainly by acetaldehyde molecules. For an ESP, we evaluated the particle-size dependent collection efficiency using monodispersed aerosol because little investigation has been conducted in this area. For acetaldehyde decomposition, more than 90% of decomposition efficiency was obtained with the use of nonthermal plasma under dry condition. However, the decomposition deteriorated under humidified condition. Higher collection efficiency was achieved with a particle size of 0.6 μm than that of 0.3 μm although the overall collection efficiency exceeded 99%. The combination of ESP and nonthermal plasma technologies leads to the breakthrough of conventional indoor electric air cleaner technology.
Since there are strong physical and chemical interactions between gaseous and particulate components in cigarette smoke, it is necessary to clarify their interaction in order to develop an effective removal technique. The present work studied the gas-to-particle conversions in sidestream cigarette smoke by tracing the behavior of key components such as acetaldehyde, isoprene and ethanol. The amount of key components transferred from gas phase to particulate phase was determined from the decrease in gas phase concentration, while the masses of key components trapped in particles were determined by volatilizing these components from the particles into dry clean air for purging. The mass balance between the transferred mass from gas phase to particulate phase and the mass recovered from particles showed that only twenty to thirty percents of these key components were recovered from the particles, suggesting that the transfer mechanisms from gas phase to particulate phase are mostly irreversible. Further, we investigated the formation of particles from cigarette smoke gases, which were obtained by filtering cigarette smoke immediately after burning. Measurements with an optical particle counter showed that high concentration of particles larger than 0.3 μm are newly formed and the nucleation is not suppressed by several times of dilution with clean air. The time scale of nucleation is found to be in the order of ten minutes and the nucleation rate is not affected by the humidity of air. Although the nucleation of gaseous components is intense in the absence of particulate matter, the nucleation has little effect on the overall dynamic behavior of cigarette smoke in the presence of particles.
Desulfurization property of ultrafine zinc oxide (ZnO) particles produced by laser ablation was investigated. Studied were 1) influence of reactor pressure on the size and specific surface area of produced particles, 2) influence of powder properties on sulfidation rate and 3) desulfurizating model of ZnO particles. The particle size produced by the laser ablation was directly proportional to the reactor pressure, i. e., 7.8 nm at 1.33 × 104 Pa, 16 nm at 6.66 × 104 Pa being independent of the laser power. Sulfidation rate increased with decreasing particle size and became constant when the specific surface area was larger than 20 m2/g. The characteristic desulfurization property could be explained by assuming that ZnO particles produced by laser ablation consist of Zn:O, 1:1.
The national approval test for dust respirator certification in Japan requires that air containing quartz particles less than 2 μm in diameter be used as a test aerosol. In view of the international accordance of respirator certification, we developed a new sodium chloride aerosol and oil mist aerosol generator as an alternative. We confirmed that the concentration of generated particles was 33.5 ± 3.4 mg/m3 for the sodium chloride aerosol and 29.8 ± 0.4 mg/m3 for DOP aerosol. Further we measured the size distribution of generated particles using SMPS for 8 hours. Measured count median diameter of generated particles was 0.078 μm for the sodium chloride aerosol and 0.189 μm for DOP aerosol. The geometric standard deviation was 1.773 for the sodium chloride aerosol and 1.581 for DOP aerosol.
Collection performance of impactor with impaction plate covered with various unwoven fabrics was experimentally studied by using oil mist particles. As a result, it was found that (1) application of high-porosity unwoven fabrics on impaction plate drastically raises the collection efficiency and reduces the 50% cut-off size although it degrades the classification performance, (2) 50% cut-off diameter of impactor with unwoven fabrics is insensitive to the nozzle air velocity, Vn, and the nozzle diameter, W, and it is as small as 1 μm for 15 < Vn < 40 m/s at W = 4. 7 mm, (3) If the pressure drop of a fabric is equal to that of an impactor, the collection efficiency of impactor with the fabric is the same as the filtration efficiency of the fabric.
An atmospheric aerosol sampling campaign was carried out at the mountain top location of Mt. Sefuri (1,050 m) from April, 1998 to October, 1999 to study biochemical characteristics of atmospheric aerosols. Atmospheric aerosols were sampled for the coarse and fine particles over a year with a sampling interval of nearly once a week. In this report, we examined chemical compositions in the individual coarse particles (>2 micro meters) by means of microsampling FT-IR (Fourier Transform Infrared) spectroscopy. It is revealed that these particles often show a -CONH- absorption, which may come from a biological aerosol particle. From longterm observation over one cycle of the year, these aerosol particles were found to show peak occurrence during spring to early summer. Based on the above results and microscopic examination, we suggest a possible origin of these aerosol particles as a piece of exuviae of the arthropods transported to the mountain top location from the nearby forest.
Because of the further integration of semiconductor devices, airborne molecular contaminants (AMC's) in cleanroom air have become of serious problem as they strongly affect device properties. We developed two analysis methods of boron ; filter collecting method for particulate boron and solution absorption method for both particulate and gaseous boron. The result of filter collecting method was compared with that of solution absorption method. There were two comparison results. One case in which boron concentration measured by the solution absorption method was higher than that by the filter collecting method, indicating the existence of gaseous boron compounds. The other case in which both methods gave a similar concentration, suggesting that boron existed mainly in particulate state. Gaseous boron compounds are 1) boron trifluoride emitted from borosilicate glass fibers of high efficiency particulate air filters (HEPA) by the attack of hydrogen fluoride, and 2) boron hydroxide emitted by a reaction of crystallized boron oxide in borosilicate glass with water and/or alcohol vapor in cleanroom. In a well-controlled cleanroom, boron concentration was below 0.1 ng/m3, which meets the cleanliness required for 0.25 μm logic manufacturing process.