• Polymer(Korea)
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• v.33 no.5
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• pp.463-468
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• 2009

Syntheses of monodisperse and micron-sized hollow plastic pigment (HPP) were carried out through the core-shell reaction. The effects of the reaction parameters, such as the particle size, molecular weight, the swelling time, agitation rate, and the solid contect were investigated. This micron-sized HPP could be made by using the alkali soluble core with at least bigger than 200 nm size. To obtain a higher opacity ratio, the swelling time and molecular weight of the core should be controlled. The agitation rate affected the particle's morphology. To prevent the shell destruction, the agitation rate must be sufficiently low in case of the syntheses of micron-sized HPP. In this study, micron-sized HPP exhibiting the high hiding power and narrow particle distribution could be obtained.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.125-137
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.625-625
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Electrical & Electronic Materials
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• v.10 no.3
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• pp.239-246
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• 1997

The ZnO is stabilize dielectric constant over a broad temperature range because its addition makes the relaxation time short. In this study, the composite oxide material (B $a_{0.85}$ $Ca_{0.15}$)Ti $O_{3}$ was mixed by ZnO additive material and the dielectric polarization characteristics was studied. The relative density was over 90[%] at all specimen in the structural characteristics. Among of the specimen, the relative density of (B $a_{0.85}$ $Ca_{0.15}$)Ti $O_{3}$ with ZnO (0.4mol) has a 95[%]. The grain size of composite oxide material with an increasing ZnO increased and it was 1.0[.mu.m]-1.22[.mu.m]. In the electrical characteristics, the charge and discharge current was increased by ZnO addition. The dielectric relaxation time was increased by space charge polarization at above 110[.deg. C] and the dielectric relaxation time was fixed by space charge polarization of para-dielectric layer at below 110[.deg. C]. The dielectric relaxation time was maximum when the grain size was small. The dielectric relaxation time is decreased with an additive material ZnO and interface polarization, existing void at the grain and grain boundary. The remnant polarization is increased and the coercive electric field is decreased by ZnO.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.337-343
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• 2020

Oxide dispersed strengthened (ODS) steel is an important candidate for Gen-IV reactors. Oxide embedded in Fe can help to trap irradiation defects and enhances the strength of steel. It was observed in this study that the size of oxide has a profound impact on the depinning mechanism. For smaller sizes, the oxide acts as a void; thus, letting the dislocation bypass without any shear. On the other hand, oxides larger than 2 nm generate new dislocation segments around themselves. The depinning is similar to that of Orowan mechanism and the strengthening effect is likely to be greater for larger oxides. It was found that higher shear deformation rates produce more fine-tuned stress-strain curve. Both molecular dynamics (MD) simulations and BKS (Bacon-Knocks-Scattergood) model display similar characteristics whereby establishing an inverse relation between the depinning stress and the obstacle distance. It was found that (110)_oxide || (111)_Fe (oriented oxide) also had similar characteristics as that of (100)_oxide || (111)_Fe but resulted in an increased depinning stress thereby providing greater resistance to dislocation bypass. Our simulation results concluded that critical depinning stress depends significantly on the size and orientation of the oxide.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.834-839
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• 2000

The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

• Analytical Science and Technology
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• v.17 no.2
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• pp.163-172
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• 2004

The molecular size distribution and fluorescence properties of soil fulvic acids (FA) were characterized by using gel filtration chromatography (GFC) and luminescence spectroscopy. The objectives of this work were to fractionate the FA extracted from a forest soil into different nominal molecular size using GFC system and to characterize the fluorescence properties (excitation, emission and synchronous) of these fractions using luminescence spectrometer. The GFC column was calibrated with polyethylene glycols, acetone and dextrane Blue. The total permeation volume of the GFC system was 404 mL and the void volume 130 mL. The GFC molecular weight of the soil FA was in the range of 190~8,900 Dalton and the molecular weight at the peak on the chromatogram was 930 Dalton. The fluorescence intensity ratio ($I_{498nm}/I_{390nm}$) was found to be increased with an increasing molecular weight. This results may suggest that the fulvic acid fractions with high molecular weight have large amount of the condensed aromatic compound.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.3
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• pp.107-116
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• 1983

This paper is concerned with the permeability through a decomposed granite soil layer which is influnced by change of grain sizes and crushed soils made by varied compaction energy. The change in the content of crushed soils can be described in terms of the ratio of surface area ($S_w{^{\prime}}/S_w $). The experiments were carried out to obtain the relationships of the coefficient of permeability(K) versus the optimum moisture content($w_{opt}$) by the variable head permeability test with the samples that were preapared by compaction test. The results are found as follows; (1) By the change in compaction energy, the crush ratio increased whereas the void ratio decreased with a larger maximum dry density running in parallel with the zero air void curve. (2) The ratio of surface area was $0.33(P)^{0.96}$ in $S_w{^{\prime}}/S_w $ with no relation to the compaction energy. (3) The grain size which produced the largest crush of soil particles ranged from 0.5 to 1 millimetre (4) The relationship of K versus $e^3$/1+e appeared as a straight line on the full-log-scale paper under the optimum moisture state. (5) As the compaction energy was larger, the passing percentage of #200-sieve grains increased linearly. The increment in the surface area ratio was deemed to have been caused by the decreased in the permeability.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.2
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• pp.109-112
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• 2014

A porous ceramic which has fine porosity and small specific gravity is made with Cenosphere and Ball Clay under condition of $1,250^{\circ}C$ in calcination temperature and 30 minutes of calcination time. The average size of porous ceramic was about $2.5{\times}10^{-5}$ m and pores are well developed. The void-fraction of porous ceramic was 67.1% under the input of Cenosphere and Ball clay with the weight ratio of 100 to 5. However, as weight ratio of Ball Clay increased to 20, 40, 100, the void fraction decreased to 58.4, 56.7, 47% respectively. When the weight ratio of Cenosphere and Ball Clay was 100 to 100, the apparent density of porous ceramic was $1.04g/cm^3$. which is twice the density when the weight ratio of Ball Clay was 5. On the other hand, absorption rate decreased by at least 100%. In condition of weight ratio of Cenosphere and Ball Clay was 100 to 100, compressive strength of porous ceramic was 30 (MPa), improve by about 76% or more when the weight ratio of Ball Clay was 5.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.1-8
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• 2018

FRP is a new material that is light, has high strength and high durability, and is emerging as a third construction material inside and outside of countries. However, very few studies have been done on curved FRP construction materials that can be used for tunnels or arched bridges. Because a small composite panel specimen is smaller than a full-size specimen, it can be used in a variety of experiments under different conditions. Therefore, in this study, experiments were performed on a void section, a solid section, a connected solid section, and a sand-coating solid section. The results of the experiment show that the connection of composite curved panels with longitudinal connections provides almost equivalent performance to that of a single panel. However, it is necessary to strengthen the connections, since the connections that are most susceptible to damage will break first.