• Korea-Australia Rheology Journal
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• v.21 no.3
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• pp.185-191
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• 2009

Polystyrene/multi-walled carbon nanotube (PS/MWCNT) composites were prepared by the use of latex technology. The monodisperse PS latex was synthesized by an emulsifier-free emulsion polymerization from styrene/potassium persulfate/water system in the presence of ethanol. The MWCNTs were first treated with acid mixture to eliminate impurities, dispersed in deionized water driven by ultrasonicator, and then mixed with the PS latex. From these mixtures, PS/MWCNT composites were prepared by freeze-drying and subsequent compression molding. In the small-amplitude oscillatory shear experiments, both complex viscosity and storage modulus increased with increasing MWCNT content. A pronounced effect of MWCNT content was observed, resulting in larger storage modulus and stronger yield behavior at low frequencies when compared to unmodified PS. It showed a transition from viscous to elastic behavior with increasing MWCNT content. Over the MWCNT content of 3 wt%, the storage modulus was higher than the loss modulus across all frequencies.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.1
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• pp.1-8
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• 2012

The thermal properties including volumetric heat capacity, thermal conductivity, thermal diffusivity, and diurnal and annual damping depths of 10 representative soil series of Korea were calculated using some measurable soil parameters based on the Taxonomical Classification of Korean Soils. The heat capacity of soils demonstrated a linear function of water content and ranged from 0.2 to $0.8cal\;cm^{-3}^{\circ}C^{-1}$ for dry and saturated medium-textured soil, respectively. A small increase in water content of the dry soils caused a sharp increase in thermal conductivity. Upon further increases in water content, the conductivity increased ever more gradually and reached to a maximum value at saturation. The transition from low to high thermal conductivity occurred at low water content in the soils with coarse texture, and at high water content in the other textures. Thermal conductivity ranged between $0.37{\times}10^{-3}cal\;cm^{-1}s^{-1}^{\circ}C^{-1}$ for dry (medium-textured) soil and $4.01{\times}10^{-3}cal\;cm^{-1}s^{-1}^{\circ}C^{-1}$ for saturated (medium/coarse-textured) soil. The thermal diffusivity initially increased rapidly with small increases in water content of the soils, and then decreased upon further increases in the soil-water content. Even in an extreme soil with the highest diffusivity value ($1.1{\times}10^{-2}cm^2s^{-1}$), the daily temperature variation did not penetrate below 70 cm soil depth and the yearly variation not below 13.4 m as four times of damping depths.

• Journal of Magnetics
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• v.18 no.3
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• pp.365-369
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• 2013

Coal ash is known to contain a noticeable amount of valuable elements, including transition metals and lanthanides. Therefore it is quite actual problem to extract them for metallurgy and other applications. This paper presents the results of high gradient magnetic and mechanical separation, microscopy, element analyses and optical spectroscopy of brown coal ash taken from the combustion camera and chimney-stalk of Angren thermal power station. The separated magnetic fraction was 3.4 wt.%, where the content of Fe in ferrospheres increased to 58 wt.%. The highest contents of Fe and rare earth elements were found in the fine fractions of $50-100{\mu}m$. Optical absorption spectroscopy of water solutions of the magnetic fractions revealed $Fe^{2+}$ and $Fe^{3+}$ ions in the ratio of ~1:1. The separated coal ash could be used for cleaning of technological liquid waste by means of the high gradient magnetic field.

• Polymer(Korea)
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• v.31 no.4
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• pp.349-355
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• 2007

Poly(N-isopropylacrylamide-co-acrylonitrile) [P(NIPAAm-co-AN)] copolymers with AN content of up to 10 mol% and their hydrogels were synthesized using water as a reaction medium, and the effects of AN unit incorporation on the critical gel transition temperature(CGTT) and swelling behaviors of the hydrogels were investigated. The CGTT of the copolymer hydrogel was $30{\sim}32\;^{\circ}C$, decreasing with increasing AN content. Below CGTT, swelling rate and equilibrium swelling ratio of the copolymer hydrogel decreased with increasing AN content. On the other hand, it exhibited faster deswelling and lower equilibrium deswelling ratio with increasing AN content above CGTT.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.356-364
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• 2004

The hydrides in cladding affect the corrosion and tensile properties. In this study corrosion and tensile properties were evaluated with varying the hydrogen concentration. The charged hydrogen contents were ranged from 200 to 1000 ppm. The corrosion rate in water and LiOH solution increases with the hydrogen concentration. The hydride did not affect the corrosion mechanism in the pre-transition region, but in the post-transition region the corrosion rate was accelerated. Cladding E contained higher Niobium content was slowly accelerated compared with other claddings. The yield and ultimate strengths were independent on the hydrogen content. However, the total elongation decreased gradually with increasing the hydrogen content. SEM observation of fracture surface showed that an average of depth of voids decreased with increasing the hydrogen content and small secondary crack are observed.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.39-50
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• 2008

This study are decided the mix proportion method of latex modified concrete for agricultural concrete structures from the results of workability and strength test with mix proportion factor. For mix proportion factor, this study are selected the water-cement ratio, unit cement amount and latex content. Also, this study were performed the slump, compressive strength test and microstructure analysis using the scanning electron microscope(SEM). The strength and slump of LMC are dependent with unit cement amount, latex content, and water-cement ratio. Especially, the strength of LMC are not controlled by single mix proportion factor but effected by combined mix proportion factor. Microstructure investigation are showed the LMC are reduced the internal pore volume and enhanced the transition zone between cement paste and aggregate interface. This effect get by consist of latex films in the concrete. Also, this study were recommended the mix proportion method for LMC. These mix proportions method are estimated the mix design for satisfied the target performance which are applied the agricultural concrete structure.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.997-1004
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• 2018

The brine leakage is a tough problem in artificial freezing engineering. This paper takes the common soft clay in Wujiang District as the study object, and calcium chloride solutions with six salinity levels were considered. The 'classic' cooling curve method was employed to measure the freezing point of specimens after freeze-thaw. Results indicate that four characteristic stages can be observed including supercooling, abrupt transition, equilibrium and continual freezing, strongly dependent on the variation of unfrozen water content. Two characteristic points were found from the cooling curves, i.e., freezing point and initial crystallization temperature. A critical value for the former exists at which the increment lowers. The higher the saline content approximately linearly, lower the freezing point. In the initial five cycles, the freezing point increases and then stabilizes. Besides, the degree of supercooling was calculated and its correlations with water, salt and freeze-thaw cycles were noted. Finally, an empirical equation was proposed for the relationship of freezing point and three main factors, i.e., water content, saline content and freeze-thaw cycles. Comparison of calculated and measured data proves that it is reliable and may provide guidance for the design and numerical analysis in frozen soil engineering.

• Computers and Concrete
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• v.19 no.1
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• pp.69-78
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• 2017

This study aimed at exploring the effect of presoaking degree of lightweight aggregate (LWA) on the fresh and hardened properties of concrete. Two series (i.e., Series A and Series B) of concrete mixes that were made of LWA with different moisture states were prepared. The presoaking degree of LWA was divided into three types: oven dry state, 1 hour prewetted and 24 hours prewetted. For the Series A, the water content of the lightweight aggregate concrete (LWAC) mixes was adjusted in accordance with the moisture condition of the LWA. Whereas the amount of water added in the Series B mixes was deliberately not adjusted for the moisture condition of the LWA. Slump test, mechanical tests, interfacial transition zone microscopical tests and thermal conductivity test were carried out on the specimens of different concretes and compared with control normal-weight aggregate concretes. The test results showed that the effect of mixing water absorption by LWA with different moisture states was reflected in the fresh concrete as the loss of mixture workability, while in the hardened concrete as the increase of its strength. With the use of oven-dried LWA, the effect of reduction of water-cement ratio was more significant, and thus the microstructure of the ITZ was more compact.

• Macromolecular Research
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• v.15 no.1
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• pp.10-16
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• 2007

In this work, we prepared epoxy/BMI composites by using N,N'-bismaleimide-4,4'-diphenylmethane (BMI), epoxy resin (diglycidyl ether of bisphenol-A (DGEBA)), and 4,4'-diamino diphenyl methane (DDM). The thermal properties and water sorption behaviors of the epoxy and BMI composites were investigated. For the epoxy/BMI composites, the glass transition and decomposition temperatures both increased with increasing BMI addition, which indicates the effect of BMI addition on improved thermal stability. The water sorption behaviors were gravi-metrically measured as a function of humidity, temperature, and composition. The diffusion coefficient and water uptake decreased and the activation energy for water diffusion increased with increasing BMI content, indicating that the water sorption in epoxy resin, which causes reliability problems in electronic devices, can be diminished by BMI addition. The water sorption behaviors in the epoxy/BMI composites were interpreted in terms of their chemical and morphological structures.

• Journal of the Korean Society of Combustion
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• v.7 no.3
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• pp.16-22
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• 2002

Combustion performance of an internally cycloned circulating fluidized bed for paper sludge was discussed through a series of batch type experiments. Operation parameters such as water content, feeding mass of sludge and secondary air injection rate were varied to find out the effect on the combustion performance, which was examined with carbon conversion rate and pollutant emission such as CO and NOx. A conventional solid fuel reaction was observed in the experiments of varying water content and feeding mass of the sludge, which is characterized with kinetic limited reaction zone, diffusion limited reaction zone and transition zone. Secondary air injection with swirl enhances the mixing of the gas phase as well as the solid phase, and improves combustion efficiency accompanied with higher carbon conversion rate and lower pollutant emission rate.