• Advances in materials Research
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• v.1 no.1
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• pp.13-29
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• 2012

In order to simultaneously enhance the strength and plasticity in nanostructured / ultrafine-grained alloys, a strategy of introducing multiple length scales into microstructure (or called bimodal composite microstructure) has been developed recently. This paper presents a brief overview of the alloy developement and the mechanical behavior of ultrafine-grained Ti-Fe-based alloys with different length-scale phases, i.e., micrometer-sized primary phases (dendrites or eutectic) embedded in an ultrafine-grained eutectic matrix. These ultrafine-grained titanium bimodal composites could be directly obtained through a simple single-step solidification process. The as-prepared composites exhibit superior mechanical properties, including high strength of 2000-2700 MPa, large plasticity up to 15-20% and high specific strength. Plastic deformation of the ultrafine-grained titanium bimodal composites occurs through a combination of dislocation-based slip in the nano-/ultrafine scale matrix and constraint multiple shear banding around the micrometer-sized primary phase. The microstructural charactersitcs associated to the mechanical behaivor have been detailed discussed.

• Journal of Powder Materials
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• v.15 no.2
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• pp.107-113
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• 2008

Ultrafine TiC-5%Co powders were synthesized by spray drying of aqueous solution of TiO$(OH)_2$ slurry and cobalt nitrate, followed by calcination and carbothermal reaction. The oxide powders with carbon powder was reduced and carburized at $900^{\circ}C{\sim}1250^{\circ}C$ under hydrogen atmosphere. During reduction, CO gas was mainly evolved by reducing reaction of oxides. Ultrafine TiC-5%Co powders were easily formed by carbothermal reaction at $1250^{\circ}C$ due to using ultrafine powders as raw materials. The ultrafine WC-TiC-Co alloy prepared by sintering of mixed powder of ultrafine WC-13%Co powder and ultrafine TiC-5%Co powder has higher sintered density and mechanical properties than WC-TiC-Co alloy prepared by commercial WC, TiC and Co powders.

• Particle and aerosol research
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• v.7 no.1
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• pp.21-30
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• 2011

The spatial distributions of air pollutants, in particular, ultrafine particles near traffic congestion roads at urban areas need to reduce human exposure levels for protecting public health. In this study, the number concentrations of ultrafine particles larger than 5 nm were measured every second during driving on the major roads of Nowon-gu, Seoul for 1.6 h using a mobile emission laboratory on October 5, 2010. The ultrafine particle number concentrations ranged from 7,009 to $265,600particles/cm^3$ with an average of $55,570particles/cm^3$, and these levels were comparable to concentrations of ultrafine particles larger than 3 or 7 nm on the arterial roads at urban areas in Los Angeles, USA and Zurich, Switzerland. It was frequently observed that the ultrafine particle number increased rapidly when vehicle speed was accelerated and it decreased sharply when vehicle speed was decelerated. The high peak events of ultrafine particle concentration larger than $200,000particles/cm^3$ were observed seven times during the measurement period. From the three repeated measurements during the short period of 50 min, it was concluded that the ultrafine particle number concentration on the road was significantly time-dependent. This on-road measurement approach can be utilized to manage vehicle-related air pollution in urban.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.274-277
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• 2009

There have been a number of works on manufacturing ultrafine grained steels with average ferrite grain sizes of smaller than a few micrometers to develop beneficial high strength steels. Among microstructures in low carbon steels, lath martensite is known to be useful to produce an ultrafine grained ferrite matrix and finely globular cementite particle. Thus, severe plastic deformation and subsequent annealing at lower temperature of lath martensite would become an effective way to produce ultrafine grained steels. However, most ultrafine grained steels exhibited a total elongation of a few per cent in tensile tests. Such a defect is one of the primary factors restricting the potential applications of ultrafine grained steels. Therefore, the improvement of the strength-elongation balance is required for the application of ultrafine grained structural steels. In this study, the effect of deformation temperatures on microstructure, such as ferrite grain size and the distribution of cementite particles, and mechanical property of lath martensite steels, was investigated. Specimens were fabricated through cold rolling or warm rolling and subsequent annealing.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.832-838
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• 1995

The densifying behavior of ultrafine amorphous Si3N4 (about 20 nm)-$\beta$-SiC (about 40~80 nm) powders (O2 : 1.3~15wt%, 0$700^{\circ}C$ within 15 sec and then immediately cooled and held at 135$0^{\circ}C$ for 10 min in N2 atmosphere without resorting to additives using a Xe image heating apparatus. Using an ultrafine pure Si3N4 powder with particle size less than 30nm, further more, mixed with an appropriate amount of $\beta$-SiC, was found to be advantageous to obtain uniform and homogeneous microstructure. In addition, ultrafine Si3N4 powders were also proved to be effective as sintering additive on densifying large sized Si3N4 powder compacts.

• Textile Coloration and Finishing
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• v.22 no.4
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• pp.325-331
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• 2010

The alkaline dissolution behavior of sea-island type ultrafine nylon fiber were dependent on the concentration of NaOH and treatment time, and the most appropriate condition for alkaline dissolution was to treat with 20g/l NaOH for 30 min at $80^{\circ}C$. The dyeing properties of sea-island type ultrafine nylon fiber and regular nylon fiber were examined with 3 different types of acid dyes in this study. The dye uptakes of ultrafine nylon fiber were higher than regular nylon fiber because of large surface area per unit mass, which increased as the dye bath pH decreased. The dyeing rates on ultrafine nylon fiber were faster and dye exhaustions were higher than regular nylon fiber, however color strength and rating of wash fastness were lower. It was also found that levelling type acid dye showed fast dyeing rate on both nylon fibers than metal-complex and milling type acid dyes.

• Molecular & Cellular Toxicology
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• v.4 no.1
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• pp.52-60
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• 2008

In order to investigate whether the particles reduced to almost nano grade might affect the chemical and physical properties of organic materials, whole Korean Black-Red Ginseng was pulverized into almost nano size and then ginsenosides, minerals, carbohydrates, lipids and proteins in the ultrafine particles were compared with those in the regular particles as control. The mean size of the ultrafine particles was in the 350 nm range, while that of the regular particles was $127{\mu}m$. More ginsenosides, minerals, carbohydrates, lipids and proteins were detected in the ultrafine particles than in the regular particles. Interestingly, more lipids from the ultrafine particles dissolved in the water than those from the regular particles in the ethanol. Absorption and transport of carbohydrate, lipid or antioxidant activity across the intestinal wall using everted intestine sacks of mice was also enhanced by particle size reduction at the almost nano scale. More cytotoxic effect against hepatoma cell growth by ultrafine particles was also found. These results could be used as the basic data for the understanding and evaluation of the effects of organic nanomaterials on the human health.

• Food Science and Biotechnology
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• v.17 no.4
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• pp.833-838
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• 2008

Size effects of rice product powders on physical properties including suspension stability were investigated in this study. Endosperm, bran, and husk powders of rice with different size particles were prepared using the pin crusher or the ultrafine air mill. The physical properties of the powders were examined using particle size analysis, scanning electron microscopy, and spectrophotometry. The peak of the volume-weighted particle distribution of ultrafine endosperm particles was at $5.4\;{\mu}m$ whereas those of the bran and the husk appeared at 65 and $35\;{\mu}m$, respectively. Ultrafine particles of the endosperm and the husks dispersed better than larger-sized particles. As time elapsed, the dispersibility decreased, but the ultrafine particles were precipitated at the slowest rate. Our results suggest that ultrafine particles, including future nanosized particles, provide improved solubility and dispersibility resulting in better stability in the food colloidal suspension.

• Journal of the Korea Institute of Building Construction
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• v.9 no.2
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• pp.77-83
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• 2009

In this study, a test has been carried out to solve the problem with ground granulated blast-furnace slag, low early strength & lack of supply and to find out a way to use as concrete admixture of the ultrafine blaine air cooling slag which is all disposed as the by product of air cooling slag and its test was conducted to the replacement rate of ultrafine blaine air cooling slag & mixing condition of every concrete admixtures by type for the purpose of obtaining later a basic data for practical use of the cement that used ultrafine blaine air cooling slag by conducting comparative analysis. If ultrafine-blaine air cooling slag is used to the concrete following the results, a high efficiency water reducing agent won't be needed much for flow acquisition due to a high increase in flow, and the stripping time of concrete form will be shortened thanks to the acquisition of early strength, And though, it has the problems with long term strength which is similar or a little lower than the 3 types of ground granulated blast-furnace slag, it's still applicable as the substitute materials for 3 types of ground granulated blast-furnace slag at 10, 15% replacement rate of ultrafine-blaine air cooling slag, at which it shows higher activation index than 3 types of ground granulated blast-furnace slag.

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.474-487
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• 2011

Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route $B_c$, and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.