• Journal of the Korean Crystal Growth and Crystal Technology
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• 제12권5호
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• pp.229-233
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• 2002

Nano-sized ZnO particles were successfully synthesized at low temperatures by a polymerized complex method via an organochemical route. The polymeric precursors could be prepared using Zn nitrate hexahydrate and a mixed solution of citric acid and ethylene glycol as a chelating agent and a reaction medium. The polymeric precursors were calcined at temperatures from 300 to $700^{\circ}C$ for 3 h, and evaluated for degree of crystallization process, thermal decomposition, surface morphology and crystallite size. The thermal decomposition and crystallization process were analyzed by TG-DTA, FI-IR and XRD. The morphology and crystallite size of the calcined particles were evaluated by scanning electron microscopy (SEM), transmittance electron microscopy (TEM) and Scherrer's equation. Crystallization of the ZnO particles was detected at $300^{\circ}C$ and entirely completed above $400^{\circ}C$. Particles calcined between 400 and $700^{\circ}C$ showed a uniform size distribution with a round shape. The average particle sizes calcined at $400^{\circ}C$ for 3 hour were 30~40nm showing an ordinary tendency to increase with the temperatures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• 제7권1호
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• pp.47-58
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• 1997

In this study single crystalline corundum ($\alpha$-$Al_2O_3$) powders were prepared from gibbsite using hydrothermal growing processes. Addition of a mineralizer and the characteristics of solid substances were investigated to find their effects on the size distribution and crystalllnity of products. Experimental results showed that as the concentration of potassium hydroxide (KOH), a mineralizer, the particle size of corundum powders became larger at lower reaction temperatures. However, the size of corundum powders became smaller as the concentration of gibbsite increased in the feedstock. The hydrothermal synthetic conditions are also strongly dependent on the properties of hydrothermal solutions. Corundum powders which have the weight mean particle size of 1~10 $\mu\textrm{m}$ with shapes of hexagonal were prepared in this experiment.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제13권1호
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• pp.173-178
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• 1993

The most appropriate mixing ratio of fly ash to bottom ash obtained from compaction characteristics and CBR values is varying from 5:5 to 6:4. But these mixed ashes are frost-susceptible materials according to judging by the paticle-size distribution because of a lot of silty-size paticles. In this study, the frost-susceptibility of compacted coal ash with proper mixing ratio is examined experimentally for use of subgrade materials. And, the efforts have been made to find proper cement addition in making these mixed ashes frost-insusceptible. It was revealed that these mixed ashes are frost-susceptible, and 4% of cement content is required to be made frost-insusceptable. It was found that amount of frost heave of these mixed ashes decreases with the unconfined compressive strength, and increases with log k if the permeability coefficient k is as low as the water into the freezing front of these mixed ashes is restricted.

• Applied Chemistry for Engineering
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• 제26권1호
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• pp.74-79
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• 2015

In this study, to obtain isoindoline compounds with the high thermal resistance and reddish yellow color using an environmental friendly method without the use of any surfactants, isoindoline derivatives with different structures were added at various reaction temperatures for the synthesis and the product was then crystallized by controlling temperatures and times in autoclave. Chemical structures, particle sizes, color differences, and optical properties were evaluated by the means of FT-IR, FE-SEM, UV-Vis spectroscopy, PSA (particle size analyzer) and Zeta potential analyzer. The samples with an enhanced dispersibility, highly thermal resistance, uniform particle sizes were achieved possibly due to the addition of isoindoline derivatives into the crystallization processing mixtures. The color change trend was also observed depending upon synthesis conditions.

• Polymer(Korea)
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• 제26권3호
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• pp.400-409
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• 2002

Polyurethane microcapsules containing functional oil (citronella oil) were successfully prepared by conventional interfacial polymerization of tolulene 2,4-diisocyanate (TDI) and ethylene glycol (EG) and characterized by Fourier transform (FT-IR) spectroscopy, Ultraviolet spectroscopy, particle size analysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Tile effects of polymerization variables, such as surfactant concentration and agitation speed, on the particle size and particle size distribution were investigated. FT-IR spectroscopic data showed that citronella oil was successfully encapsulated in the microcapsule. Thermogravimetric analysis data showed that the microcapsule was thermally stable up to $220^{\circ}C$. The controlled release of the citronella oil present in the microcapsule core in a methanol medium was demonstrated by ultraviolet spectroscopy showing that the amount of released citronella oil was increased with increasing time. It was observed that the amount of released citronella oil was increased with increasing stirring speed and emulsifier concentration in the rnicrocapsule preparation step. Polyurethane microcapsules containing citronella oil showed excellent anti-moth property.

• Geotechnical Engineering
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• 제13권3호
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• pp.63-76
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• 1997

To investigate the engineering characteristics of crushed rockfill material, the large-scaled triaxial tests have been carried out, The rpckfill is made from the greywacke, and the 3 parallel gradations with different maximum particle size(dmu=38.1mm, 25.4mm and 19.1mm) were designed for the test. The dimension of the specimen is 300mm in diameter and 600mm in height, and the applied confining stress varied from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$. The test results show that the influence of the maximum particle size on the stress -strain r$51.6^{\circ}\; to\; 40.5^{\circ}$ when the confining stress increases from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$ The hyperbolic parameter values estimated from the test result for rockfill are much different from the recommended values by Duncan et. at(1980) for GW and GP material, especially in the $\phi$ ad K-values.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.521-524
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• 2008

The purpose of this study is to identify the character and condition of Cr in the clinker and thereby contribute to the research for reduction in utilizing Cr in the cement manufacturing process. The concentration of chromium by cement particle size and the distribution of chromium by clinker mineral were measured. Next, correlation was considered between chromium and the soluble components in cement. As a result, in the range that cement particles were 20${\mu}$m or less, highest soluble hexavalent chromium was found. When the concentration of chromium was measured through mineral separation, belite and the interstitial phase were higher in chromium than in alite. soluble hexavalent chromium was contained in domestic cement less than 20ppm, and its conversion ratio was somewhat high as 10 to 40% or so.

• Applied Chemistry for Engineering
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• 제24권3호
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• pp.260-265
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• 2013

In this study, nano-emulsions containing 0.01, 0.03, 0.05, and 0.10% ethyl acetate fraction of Hippophae rhamnoides (H. rhamnoides) leaf extracts were prepared. The particle size, particle size distribution and skin permeability of the nano-emulsions were evaluated for five weeks. Nano-emulsion was prepared by the sequential use of homogenizer and microfluidizer. Nano-emulsion containing the ethyl acetate fraction exhibited a monodispersed form. Nano-emulsion containing 0.03% ethyl acetate fraction was the most stable for five weeks. The in vitro skin permeation study of nano-emulsion containing 0.03% ethyl acetate fraction was carried out using Franz diffusion cell. The nano-emulsion showed a better skin permeability than that of O/W emulsion. These results indicate that the nano-emulsion containing the ethyl acetate fraction of H. rhamnoides leaf extract showed a remarkable stability and skin permeability than that of O/W emulsion.

• Journal of the Korean GEO-environmental Society
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• 제8권5호
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• pp.15-21
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• 2007

This study was investigated to evaluate the effect of electric fields application for the reduction of membrane fouling, the inactivation of microorganisms and the enhancement of particle coagulation in microfiltration/coagulation. Cumulative permeate in the case with electric field treatment showed high value compared to the case without electric field. Particularly, the increase of HRT (Hydraulic retention time) showed the increase of cumulative permeate as well as the decrease of total resistance. By electric field treatment, the amount of small particle size less than 100 ${\mu}m$ is increased and the survival fraction is reduced by the increase of electric field intensity. This may be attributed to the cleavage of particle or cytological destruction resulting from the inactivation of microorganism. Coagulant dosage of PAC compared with no electric field application could also be saved about 75% for the 95% of turbidity removal at 10 kV/cm.

• Polymer(Korea)
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• 제26권2호
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• pp.168-173
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• 2002

Poly (vinyl butyral) (PVB) was synthesized by acetalization of poly (vinyl alcohol) (PVA) PVB was prepared in particulate forms in water, and chemical and physical properties of the products were characterized using various techniques. The prepared PVB had size distribution from 100 to 700 $\mu\textrm{m}$ with mean diameter of about 380 $\mu\textrm{m}$. The chemical structure of PVB was characterized using FT/IR and NMR, and the average degree of acetalization was determined to be 77% from the titration measurement. DSC data showed that the crystalline structure of PVA vanished as acetalization reaction proceeded to produce PVB, and the glass transition temperature emerged at about $70^{\circ}C$. TGA data showed that PVB was much more thermally stable than PVA, and showed no degradation up to $300^{\circ}C$. Solubility test showed that PVB was soluble in alcohols but Insoluble in water, being totally different from PVA.