• Journal of Preventive Medicine and Public Health
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• v.19 no.1 s.19
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• pp.130-136
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• 1986

The particle size of suspended particulates was measured by a Anderson air sampler from Mar. 1982 to Feb. 1984 in a part of Seoul. It was concluded as follows : 1) The arithmetic concentration of suspended particulates was $147.8{\mu}g/m^3$ in Spring, 136.9 in Summer, 131.9 in Autumn and 158.1 in Winter respectively. 2) The cumulative distribution of suspended particulates size in logarithmic diagram showed similar to normal log distribution. 3) The atmospheric particulate matters showed a bimodal size distribution on the base of unit particle concentrations, which divided at approximately $2{\mu}m$ in the diameter. 4) While the fine particulates less than $2.1{\mu}m\;was\;35.4{\sim}45.0%$, the coarse particulates was $55.0{\sim}64.5%$. 5) The higher the concentration of suspended particulates, the more increased the ratio of fine particulates. The higher the concentration of suspended particulates, the lower median size of suspended particulate as well. 6) The respirable dust particulates less than $4.7{\mu}m\;was\;52.2{\sim}62.9%$ in seasonal average through the 2 year samples. With the above result, air pollution concerned with public health could be evaluated and the control measures also are suggested.

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.63-67
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• 2014

The effects of reactant composition on the particle size distribution, synthetic yield, and density of Phenol-formaldehyde bead were examined in the synthesis of resol-type phenolic resin. Decrease of the content of DI water as dispersion media can increase the viscosity of suspension, which may cause the difference of particle size distribution and aggregation. The average particle size of synthesized beads was also decreased with the increasing content of stabilizer which can affect the interfacial area. The amount of crosslinking agent showed no effect on the size distribution and synthetic yield, but it made a decrease in the density of synthesized bead due to the macropore in the bead.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.622-627
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• 2013

Colloidal silica is used in various industrial products such as chemical mechanical polishing slurry for planarization of silicon and sapphire wafer, organic-inorganic hybrid coatings, binder of investment casting, etc. An accurate determination of particle size and dispersion stability of silica sol is demanded because it has a strong influence on surface of wafer, film of coatings or bulks having mechanical, chemical and optical properties. The study herein is discussed on the effect of measurement results of average particle size, sol viscosity and electrophoretic mobility of particle according to the volume fraction of eight types of silica sol with different size and surface properties of silica particles which are presented by the manufacturer. The measured particle size and the mobility of these sol were changed by volume fraction or particle size due to highly active surface of silica particle and change of concentration of counter ion by dilution of silica sol. While in case the measured sizes of small particles less than 60 nm are increased with increasing volume fraction, the measured sizes of larger particles than 60 nm are slightly decreased. The mobility of small particle such as 12 nm are decreased with increase of viscosity. However, the mobility of 100 nm particles under 0.048 volume fraction are increased with increasing volume fraction and then decreased over higher volume fraction.

• Macromolecular Research
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• v.12 no.2
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• pp.213-218
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• 2004

We have performed dispersion polymerization of acrylamide in tert-butyl alcohol/water mixture-using hydroxypropyl cellulose and ammonium persulfate as the stabilizer and the initiator, respectively - to study the effects that the concentration of monomer, initiator, and stabilizer, the tert-butyl alcohol/water ratios as polymerization media, and the reaction temperature have on, among other things, the polymerization kinetics, particle sizes, and molecular weights. The polymerization rate increased upon increasing the concentration of the monomer, initiator, and stabilizer, the water content in the tert-butyl alcohol/water media, and the polymerization temperature. The average particle size of the lattices increased upon increasing the concentration of initiator, the polymerization temperature, and the water content in the tert-butyl alcohol/water media, but it decreased upon increasing the concentration of monomer and stabilizer. The viscosity-average molecular weight increased upon increasing the concentration of monomer and stabilizer and the water content in the tert-butyl alcohol/water media, but it decreased upon increasing both the concentration of initiator and the polymerization temperature.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.539-543
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• 2018

We report the structural, morphological and magnetic properties of the $Ni_{70}Mn_{30}$ alloy prepared by Planetary Ball Mill method. Keeping the milling time constant for 30 h, the effect of different ball milling speeds on the synthesis and magnetic properties of the samples was thoroughly investigated. A remarkable variation in the morphology and average particle size was observed with the increase in milling speed. For the samples ball milled at 200 and 300 rpm, the average particle size and hence magnetization were decreased due to the increased lattice strain, distortion and surface effects which became prominent due to the increase in the thickness of the outer magnetically dead layer. For the samples ball milled at 400, 500 and 600 rpm however, the average particle size and hence magnetization were increased. This increased magnetization was attributed to the reduced surface area to volume ratio that ultimately led to the enhanced ferromagnetic interactions. The maximum saturation magnetization (75 emu/g at 1 T applied field) observed for the sample ball milled at 600 rpm and the low value of coercivity makes this material useful as soft magnetic material.

• Resources Recycling
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• v.27 no.2
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• pp.32-37
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• 2018

This study was conducted as a preliminary study for the recycling of palladium and palladium oxide. In this study, thermodynamic equations for the formation of palladium oxide (PdO) are established. Palladium chloride is dissolved into hydrochloric acid to generate a palladium chloride solution. Nanosized palladium oxide powder with an average particle size below 30 nm were generated from this raw material solution by means of a spray pyrolysis process. The palladium oxide particles were composed of a single solid crystal. The results of XRD analysis showed that only a PdO phase of the generated powder was formed. And, the specific surface area of the generated palladium powder was approximately $32m^2/g$.

• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1307-1314
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• 1994

The aim of this work is to show the way of manufacturing the SiC mechanical seal at the low temperature of 130$0^{\circ}C$ using clay and frit as source of secondary phase. $\alpha$-SiC and $\beta$-SiC powder which showed different distribution of particle were used as starting materials, i.e. average particle size of $\alpha$-SiC was larger than that of $\beta$-SiC. The mechanical and tribological properties of two groups of specimen, i.e. one contained mainly larger $\alpha$-SiC powder and the other mainly fine particle $\beta$-SiC, were measured. The specimen consisted of larger $\alpha$-SiC exhibited lower density flexural strength and wear resistance is comparison with these of sample containning mainly $\beta$-SiC . This difference could be originated from the dependence of capillary force on the particle size. For the larger SiC particle, the liquid phase may not fill the whole pores during sintering, due to low capillary force, whereas the liquid phase can infiltrate into the small ores surrounded small $\beta$-SiC particle. Thus, the course of high flexural strength and high wear resistance of specimen prepared using small particles can be explaced from the easy infiltration of liquid phase.

• Korea-Australia Rheology Journal
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• v.15 no.1
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• pp.35-41
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• 2003

It is expected that particle size distribution of any portion obtained through screening, is of more uniform than that of the original mixture, typically following such as log-normal, Rosin-Rammler distributions and so on. In this study, therefore, a new relation between parameters of the uniform distribution and flow characteristics of the coarse particle suspensions is derived based on the continuous polydisperse model (Ookawara and Ogawa, 2002b), which is derived from the discrete polydisperse model (Ookawara and Ogawa,2002a). The derived model equation predicts a linear increase of viscosity with shear rate, viz., dilutant flow characteristics. Further, the increase of viscosity is expected to be proportional to the square of volume fraction of particles, and to show the linear dependency on density and average diameter of particles. It is also shown that the uniform distribution model includes additional term that expresses the effect of distribution width. For verification of the model, the experimental results of Clarke (1967) are cited as well as in our previous work for the monodisperse model (Ookawara and Ogawa,2000) since most parameters were varied independently in his work. It is suggested that the newly introduced term expands the applicable range compared with the monodisperse model.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.443-446
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• 2006

Carbon-supported Platinum (Pt) is the potential electro-catalyst material for anodic and cathodic reactions in fuel cell. Catalytic activity of the metal strongly depends on the particle shape, size and distribution of the metal in the porous supportive network. Conventional preparation techniques based on wet impregnation and chemical reduction of the metal precursors often do not provide adequate control of particle size and shape. We have proposed a novel route for preparing nano sized Pt colloidal particles in solution by oxidation of ethylene glycol. These Pt nano particles were deposited on large surface area carbon support. The process of nano Pt colloid formation involves the oxidation of solvent ethylene glycol to mainly glycolic acid and the presence of its anion glycolate depends on the solution pH. In the process of colloidal Pt formation glycolate actsas stabilizer for the Pt colloidal particle and prevents the agglomeration of colloidal Pt particles. These mono disperse Pt particles in carbon support are found uniformly distributed in nearly spherical shape and the size distribution was narrow for both supported and unsupported metals. The average diameter of the Pt nano particle was controlled in the range off to 3 nm by optimizing reaction parameters. Transmission electron microscopy, CV and RRDE experiments were used to compliment the results.

• Journal of Powder Materials
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• v.10 no.6
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• pp.395-405
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• 2003

In the conventional metallothermic reduction (MR) process for obtaining tantalum powder in batch-type operation. it is difficult to control morphology and location of deposits. On the other hand, a electronically mediated reaction (EMR) process is capable to overcome these difficulties and has a merit of continuous process, but it has the defect that the reduction yield is poor. MR-EMR combination process is a method that is able to overcome demerits of MR and EMR process. In this study, a MR-EMR combination process has been applied to the production of tantalum powder by sodium reduction of $K_2$TaF$_{7}$. The total charge passed through external circuit and average particle size (FSSS) were increased with increasing reduction temperature. The proportion of fine particle (-325 mesh) was decreased with increasing reduction temperature. The yield was improved from 65% to 74% with increasing reduction temperature. Considering the charge, impurities, morphology, particle size and yield, an reduction temperature of 1,123 K was found to be optimum temperature for MR-EMR combination process.