• Journal of Korean Society for Atmospheric Environment
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• v.23 no.4
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• pp.457-465
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• 2007

This study was performed to estimate the gas-particle partitioning of organochlorine pesticides (OCPs) in atmosphere, the samples were collected by PUF high volume air sampler for two years from June, 2000 to June, 2002. The gas phase fraction of ${\alpha/\gamma}-HCH$, heptachlor epoxide, ${\alpha/\gamma}-chlordane$ and trans-nonachlor was over 90%. But the gas phase fraction of ${\beta}-HCH$, p,p'-DDE, endosulfan sulfate, p,p'-DDD and p,p'-DDT was range of 20% through 80%, which means the gas phase fraction of OCPs components described above is sensitive to temperature. The correlation between the gas phase fraction and molecular weight of each OCPs component was not found in this research. The slope of regression line between gas-particle partitioning coefficient(${\log}K_p$) and subcooled liquid vapor(${\log}{P^o}_L$), gal-particle partitioning coefficient(${\log}K_p$) and octanol-air partitioning coefficient(${\log}K_{oa}$) which show -0.54 and 0.43 was not steep. So the equilibrium state between gas and particle was not reached and in this state the particulate fraction was low.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.2
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• pp.242-249
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• 2007

Deposition fluxes of polycyclic aromatic hydrocarbons (PAHs) were measured at the Chonbuk National University located in Jeonju between June and November 2002. Fluxes of gaseous and particulate PAHs were separately obtained using a water surface sampler (WSS) and a dry deposition plate (DDP). Most of PAHs were deposited in the gaseous form since the low molecular weight PAHs dominates in the atmosphere. The deposition velocity of particulate PAHs was higher than that of gaseous PAHs when the molecular weight was low, but substantially decreased as the fine particle fraction increased with molecular weight. The deposition velocity was generally higher at high wind speeds. However, increase in the deposition velocity in unstable atmospheric conditions was also observed for gaseous PAHs of intermediate molecular weight.

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.338-344
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• 2014

The purpose of this study was to evaluate the dispersion degree of particles using a nanoindentation test for titanium oxide nanoparticles/epoxy resin nanocomposites. Thus, the effects of the particle size and weight fraction, dispersion agent, and position of the sample on the modulus and degree of particle dispersion in the nanocomposites were investigated. As a result, the dispersion degree of large particles was found to be better than that of smaller particles in composites. It could be found that the aggregation or agglomeration of small particles with large surface energy occurred more easily in nanocomposites because of the large specific surface area. The moduli of the upper side of the film-shaped sample obtained from a nanoindentation test were low scattering, while the values for the bottom side were high scattering. Thus, the dispersion situation of the nanoparticles on the upper side of film-shaped samples could be considered to be better than that for the bottom side. This could be concluded due to the non-uniform nanoparticle dispersion in the same sample. The modulus obtained from nanoindentation test increased slightly with the content of nanoparticles and increased with the indented depth for the same sample. The latter is presumably due to the increase in the accumulated particles facing the indenter with the indented depth. The nanoindentation test was found to be a useful method to evaluate the dispersion status of nanoparticles in nanocomposites.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.69-77
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• 2013

The purpose of this study is to improve the properties of epoxy resin using the big-sized titanium oxide nanoparticles. The effects of particle weight fraction and shape of sample on the thermal and mechanical properties in titanium oxide reinforced epoxy resin has been investigated. In addition, the effect of particle dispersion situation on the mechanical properties of nanocomposites has been studied. As a result, the Tg was almost same regardless of the content of nanoparticles. Storage modulus increased up to the content of 3wt% particles and then decreased. Tensile strength and modulus of film-shaped sample with 1wt% was higher than the one of pure epoxy, while other composites were not. The tensile strength of dogbone-shaped sample with 1wt% was only higher than the one of pure epoxy, while other composites were lower than the one of pure epoxy. Tensile modulus of dogbone-shaped samples increased with the content of particles.

• International Journal of Ocean System Engineering
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• v.3 no.2
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• pp.102-110
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• 2013

The purpose of this study was to improve the properties of epoxy resin using titanium oxide nanoparticles. The effects of particle weight fraction, dispersion agent, and curing agents with different molecular weights on the thermal and mechanical properties of titanium-oxide-reinforced epoxy resin were investigated. In addition, the effect of the particle dispersion condition on the mechanical properties of nanocomposites was studied. As a result, it was found that the glass transition temperature of film-shaped nanocomposites decreased with an in-crease in the nanoparticle content. Because nanoparticles interrupted the cross linkage between the epoxy resin and the amine curing agent, the cross-link density of the epoxy became lower and led to a decrease in $T_g$ in the nanocompo-sites. The tensile strength and modulus in film-shaped nanocomposites also increased with the particles content. But in the case of dog-bone-shaped nanocomposites, the values were not similar to the trend for the film-shaped nanocompo-sites. This was probably a result of the different nanoparticles dispersions in the epoxy resins resulting from the respective-thicknesses of the film and dog-bone-shaped samples.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.249-255
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• 2017

Using a magnetic separation process, pond ash generated in thermoelectric power plants was separated into magnetic materials and nonmagnetic materials in order to make it into a raw material of geopolymers and unburned carbon; screening characteristics according to the particle sizes and magnet strength levels of the pond ash were observed. Based on the results of magnetic separation into fine particle (0.15~0.84 mm) and rough particle (0.84~2.4 mm) pond ash using 3000 G magnets, the weight fraction and ignition loss of nonmagnetic materials were found to be higher than those of magnetic materials, regardless of the particle size. In the case of fine particle pond ash, when the magnet strength was increased from 3000 G to 10000 G, even those materials that were weakly magnetic were separated into magnetic materials, leading to drastic increases in the weight fraction of magnetic materials, such that the ignition loss accounted for 66.9 % (22.8 wt%) of the entire ignition loss of 32.6 wt%, despite of the low ignition loss. Based on the results of measurement of the compressive strength levels of geopolymers made of magnetic-separated rough particle pond ash, the compressive strength of geopolymers made of magnetic materials containing small amounts of unburned carbon was found to be 20 MPa.

• Resources Recycling
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• v.10 no.4
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• pp.48-57
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• 2001

The main consistent materials and main elements of the bottom ash in municipal solid waste incineration ash according to particle size were investigated and the environmental hazards were considered by investigating the content of dioxin and heavy metals in bottom ash and the concentration of heavy metals in its leachate. The main materials of bottom ash are glasses, ceramics, scraps of iron. As the particle size increases, their percentage weight also increases and their percentage weight was over 70% in 4 mesh~25 mm particle size fraction. The main elements of bottom ash are CaO, $SiO_2$, $Fe_2$$O_3$,$ A1_2$$O_3$and the content of CaO decreases and the content of $SiO_2$increases as particle size increases. The heavy metals accumulate in small particle size fraction. The concentration of heavy metals in each leachate by domestic leaching test is almost similar. As the aging period is prolonged, pH of bottom ash lowers gradually and the leached concentration of Cu and Pb diminishes.

• Journal of the Korean Wood Science and Technology
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• v.28 no.4
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• pp.41-50
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• 2000

Cement-bonded particleboard is being used as outdoor siding material all over the world, because this composite particularly bears a light weight, high resistance against fire, decay, and crack by cyclic freezing and thawing, anti-shock property, and strength enhancement. Construction systems are currently changing into a frame-building style and wooden houses are being constructed with prefabrication type. Therefore, they require a more durability at outdoor-exposed sides. In this study, the cement hydration property for Korean pine particle, Japanese larch particle and face- and middle layer particles (designated as PB particle below) used in Korean particleboard-manufacturing company was investigated, and the rapid manufacturing characteristics of cement-bonded particleboard by supercritical $CO_2$ curing was evaluated. Korean pine flour showed a good hydration property, however, larch flour showed a bad one. PB particle had a better hydration property than larch flour. The addition of $Na_2SiO_3$ indicated a negative effect on hydration, however, $MgCl_2$ had a positive one. Curing by supercritical $CO_2$ fluid gave a conspicuous enhancement in the performances of cement-bonded particleboards compared to conventional curing. $MgCl_2$ 3%-added PB particle had the highest properties, and $MgCl_2$ 1%-added Korean pine particle had the second class with the conditions of cement/wood ratio of 2.7, a small fraction-screened particle and supercritical curing. On the contrary, the composition of non-hammermilled or large fraction-screened particle at cement/wood ratio of 2.2 was poorer. Also, the feasibility for actual use of 3%-added, small PB particle-screened fraction was greatest of all the conventional curing treatments. Relative superiority of supercritical curing vs. conventional curing at dimensional stability was not so apparent as in strength properties. Through the thermogravimetric analysis, it was ascertained that the peak of a component $CaCO_3$ was highest, and the two weak peaks of calcium silicate hydrate and ettringite and $Ca(OH)_2$ were present in supercritical treatment. Accordingly, it was inferred that the increased formation of carbonates in board contributes to strength enhancement.

• Journal of Korean Society for Atmospheric Environment
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• v.11 no.1
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• pp.37-44
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• 1995

Concentration of particulate nitrate classified by formation mechanism and particle diameter in ambient air was determined from Feb. to Oct. 1993. Sampling was carried out using a two-stage Andersen air sampler at the top of a five-story building located at Kon-Kuk University in seoul. Concentration of N $H_{4}$N $O_{3}$ in TSP was measured by pyrolysis of sample filters at 160.deg.C for 1hr. concentration of N $H_{4}$N $O_{3}$ was higher in winter time compared with that in summmer time. Also, concentration of N $H_{4}$N $O_{3}$ was higher in fine particles compared with that in coarse particle. The range of N $H_{4}$N $O_{3}$ concentration was between 2.9 and 9.9.mu.g/ $m^{3}$. Weight fraction of N $H_{4}$N $O_{3}$ in total particulate nitrate was 31.1 .sim. 59.5%, and weight fraction of N $H_{4}$N $O_{3}$ in TSP was 2.1 .sim. 11.2%. Concentration of NaN $O_{3}$, which originated from sea salt, was highest in spring time and lowest in summer time,and the concentration range was between 0.1 and 0.7.mu.g/ $m^{3}$. NaN $O_{3}$/TSP ratio was very low (0.1 .sim. 0.4%) indicating that the portion of NaN $O_{3}$in TSP was negligible. Concentration of particulate nitrate originated from soil was 2.4 .sim. 2.9.mu.g/ $m^{3}$. Weight fraction of that in total particulate nitrate was 14.0 .sim. 37.1%.

• Journal of Korean Society for Atmospheric Environment
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• v.10 no.2
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• pp.130-136
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• 1994

Concentration of volatile particulate nitrate(NH$_4$NO$_3$) in TSP in ambient air was determined from Feb. to Oct 1993. Sampling was carried out using a two-stage Andersen air sampler at the top of a five-story building located at Kon- Kuk University in Seoul Concentration of NH$_4$NO$_3$ in TSP was measured by Pyrolysis of sample filters at 16$0^{\circ}C$ for 1hr. Concentration of NH$_4$NO$_3$ was higher in winter time compared with that in summer time. Also, concentration of NH$_4$NO$_3$ was higher in fine particles compared with that in coarse particle. The range of NH$_4$NO$_3$concentration was between 2.99 and 9.86 $\mu\textrm{g}$/㎥. Weight fraction of NH$_4$NO$_3$ in total particulate nitrate was 31.1~59.5%, and weight fraction of NH$_4$NO$_3$ in YSP was 2.1~11.2%.