• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.59-70
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• 1991

ZnO fine powder was prepared by the batch precipitation process using $ZnCl_2$ and hexamethylenetetramine solution as a mother solution. When the concentrations of $ZnCl_2$solution were $0.1mol/\ell$ and 0.05mol/-, the particles of rod shape were obtained when the conentration of $ZnCl_2$solution was $0.01mol/\ell$, the particle of plate shape was obtained. When the hexamethylenetetramine as a precipitants was used, pH was raised slow during a few minute be-cause of slow hydrolysis rate of hexamethylenetetramine. For rapid raising of pH during initial reac-tion time, $NH_4$OH was added as nucleant. When $NH_4$OH as a nucleant was added, obtained particle was shape of granular and the mean particle size was $0.41\mu\textrm{m}$. After calcination at $500^{\circ}C$ during 1hour, all of remained organic phase was removed but the shape of particles was not changed. But pa-rticles were slightly shrunk in comparision with before calcined particles.

• Journal of environmental and Sanitary engineering
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• v.13 no.3
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• pp.58-65
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• 1998

Monodispersed $SiO_2/ZnO$ composite fine powders were prepared by Sol-Gel processing and their surface electrical and UV absorbance properties were investigated. Pseudomorph ZnO fine powders were microcapsuled by $SiO_2/ZnO$ sol fabricated using TEOS[tetraethylorthosilicate, purity 98% and ethanol as a solvent with $NH_3$ catalyst. The effects of experimental parameters such as molar ratio of starting materials on the final particle size and shape of $SiO_2/ZnO$ composite fine powder were discussed. As a result, we could controlled the size of monodispersed $SiO_2/ZnO$ composite fine powders without agglomeration, as well as the good dispersibility in aquous solution. The prepared powders were observed to have the mean particle sizes of $0.26-0.78{\mu}m$ with standard deviations of $0.020-0.063{\mu}m$.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.4
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• pp.323-329
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• 2004

In situ particle size and volume concentration of suspended sediment was measured at the mouth of Seomjin River Estuary In February 2001, using an optical instrument, 'LISST-100'. Time variation of in situ particle size and concentration shows: (1) during ebb tide, Seomjin River supplies relatively fine-grained particles with less-fluctuated, compared to during flood tide, and well-behaved concentrations following the tidal cycle; and (2) during flood tide, relatively coarse-grained particles with highly variable in size distribution and concentration flow upstream from Kwangyang Bay. This explains a poor correlation $(r^{2}=0.10)$ between sediment concentration and beam attenuation coefficient during flood and a high degree of correlation $(r^{2}=0.80)$ during ebb tide. Relatively fine grained and well defined, monotonous size distribution may promote the correlation between concentration and beam attenuation coefficient due to optical homogeneity of particles during ebb tide. Abundance of large aggregates with time-varying size and shape distributions may be mainly responsible for variations in optical properties of the sediment during flood tide, and thus may confound the relationship between the two variables. The difference in particle sizes and shapes between flood and ebb tides can also be observed on SEM images.

• Journal of the Korean Society of Combustion
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• v.8 no.2
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• pp.41-49
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• 2003

Ultrasonic field of 28kHz with sound pressure level 162dB has been employed to agglomerate the fine soot particle produces in a diffusion flame in a chamber. The agglomeration process has been investigated with digital camcorder and analysed in terms of the decrease of number density with exposure time. From the observation of agglomeration process, the initial agglomeration has been carried out during the short time, and it has been dominated by the orthokinetic collision. Thereafter, a slower agglomeration mechanism, driven by acoustic streaming in the chamber takes over and agglomeraters grew to diameters of several millimeters were levitated at the pressure node of the acoustic wave. And, the circular disk shape of large agglomeraters with the rotational and translational motion is observed.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.37-44
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• 1995

TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

• Journal of the Korean Society of Safety
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• v.16 no.1
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• pp.65-72
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• 2001

Portland cement concrete is made with coarse aggregate, fine aggregate, portland cement, water and, in some cases, selected chemical admixture such as air-entraining agents, water reducer, superplasticizer, and so on, and mineral admixture such as fly ash, silica fume, slags, etc. Typically, in the concrete, the coarse aggregate and fine aggregate will occupy approximately 80 percent of the total volume of the finished mixture. Therefore, the coarse and fine aggregates affect to the properties of the portland cement concrete. As the deposits of natural sands have slowly been depleted, it has become necessary and economical to produce crushed sand(manufactured fine aggregate). It is reported that crushed sand differs from natural sands in gradation, particle shape and texture, and that the content of micro fines in the crushed sand affect to the quality of the portland cement concrete. Therefore, the purpose of this paper is to investigate the characteristics of fresh and hardened concrete with higher micro fines. This study provides a firm data to apply crushed sand with higher micro fines.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.73-78
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• 2001

Portland cement concrete is made with coarse aggregate, fine aggregate, portland cement, water and, in some cases, selected chemical admixtures such as air-entraining agents, water reducer, superplasticizer, and so on, and mineral admixtures such as fly ash, silica fume, slags, etc. Typically, in the concrete, the coarse aggregate and fine aggregate will occupy approximately 80 percent of the total volume of the final mix. Therefore, the coarse and fine aggregates affect to the properties of the portland cement concrete. As the natural sands are drained, it is necessary and economical to utilize crushed sands(manufactured fine aggregate). It is reported that crushed sands differ from natural sands in gradation, particle shape and texture, and the micro fines in the crushed sands affect to the quality of the portland cement concrete. Therefore, the purpose of this paper is to investigate the characteristics of fresh and hardened concrete with high content of micro fines. This study provides firm data for the use of crushed sands with higher micro fines.

• Journal of Industrial Technology
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• v.16
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• pp.105-112
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• 1996

This paper presents coal mine waste (CMW) for use in concrete manufacture as a replacement of normal aggregates. The CMW in this study was collected from Sabook, Jungson-kun, Kangwon-do. Fine and coarse asggregates from CMW were prepared by crushing it in a jaw crusher and separating debris with #4 sieve. CMW aggregates showed good physical and mechanical properties with having specific gravity over 2.65, absorption less than 1%, and abration ratio below 20%, but particle shape of CMW was long or flat, which caused a poor workability in mixing. Therefore, to make workability better, a 1/4 of CMW coarse aggregate was replaced with normal aggregate which had a good particle shape, and a superplasticizer was added to the mix. Compressive strength and other mechanical properties of CMW concrete was very good. In conclusion, characteristics of CMW concrete was acceptable for use as a concrete structural material.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.739-744
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• 2000

YAG(Y3Al5O12) as host material of YAG:Tb3+ was studied via hydrothermal synthesis of metal hydroxides. We changed the kind of mineralizer, the concentrations and process conditions in hydrothermal synthesis. As a result, we found, acicular YAG powders were obtained by the use of KOH as a mineralizer, the concentration of KOH affected the shape and size of YAG powder. Fine grained YAG were perpared by the use of NH4OH as a mineralizer and the concentration of NH4OH affected crystal phases but did not affect particle size. We could finally get the spherical looking YAG powder at 8 M NH4OH and at 35$0^{\circ}C$ for 12h. The average particle size was about 0.2${\mu}{\textrm}{m}$.

• Geomechanics and Engineering
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• v.36 no.3
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• pp.295-301
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• 2024

Understanding the post-liquefaction shear behavior is crucial for predicting and assessing the damage, such as lateral flow, caused by liquefaction. Most studies have focused on the behavior until liquefaction occurs. In this study, we performed undrained multi-stage tests on clean sand, sand-silt mixtures, and silty soils to investigate post-liquefaction shear strain based on soil compressibility. The results confirmed that it is necessary to consider the soil compressibility and the shape of soil particles to understand the post-liquefaction shear strain characteristics. Based on this, an index reflecting soil compressibility and particle shape was derived, and the results showed a high correlation with post-liquefaction small resistance characteristic regardless of soil type and fine particle content.