• 한국재료학회지
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• 제11권10호
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• pp.869-878
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• 2001

Alumina $(Al_2O_3)$ green bodies were fabricated by gel-casting using three kinds of alumina with different particle size (mean particle size: 4.6 $\mu\textrm{m}$, 0.32 $\mu\textrm{m}$, 10nm). The effects of particle size on gel-casting process and green microstructure were investigated. The optimum dispersion conditions using ammonium salt (D-3019) as dispersant were 0.2 wt% (4.63 $\mu\textrm{m}$), 0.5 wt% (0.32 $\mu\textrm{m}$), and 5.0 wt% (10 nm), in high solid loading. The optimum solid loading of each starting material for gel-casting was obtained as 59 vol% (4.63 $\mu\textrm{m}$), 57 vol% (0.32 $\mu\textrm{m}$), 15 vol% (10 nm), depending on particle size, indicating that nano-size particle (10 nm) represent lower solid loading as high specific surface area than those of other two starting materials. The drying at ambient conditions (humidity; $\thickapprox$90%) was performed more than 48hrs to enable ejection of the part from the mold and then at $120^{\circ}C$ for 2hrs in an air oven, showing no crack and flaw in the dried green bodies. The pore size and distribution of the gelcast green bodies showed the significant decrease with decreasing particle size. Green microstructure was dependent on the pore size and distribution due to the particle size, and on the deairing step. The green density maximum obtained was 58.9% (4.63 $\mu\textrm{m}$), 60% (0.32 $\mu\textrm{m}$), 47% (10 nm) theoretical density (TD), and the deairing step applied before gel-casting did not affect green density.

• 한국분말재료학회지
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• 제22권2호
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• pp.111-115
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• 2015

This study investigates the microstructure and thermal shock properties of polycrystalline diamond compact (PDC) produced by the high-temperature, high-pressure (HPHT) process. The diamond used for the investigation features a $12{\sim}22{\mu}m$- and $8{\sim}16{\mu}m$-sized main particles, and $1{\sim}2{\mu}m$-sized filler particles. The filler particle ratio is adjusted up to 5~31% to produce a mixed particle, and then the tap density is measured. The measurement finds that as the filler particle ratio increases, the tap density value continuously increases, but at 23% or greater, it reduces by a small margin. The mixed particle described above undergoes an HPHT sintering process. Observation of PDC microstructures reveals that the filler particle ratio with high tap density value increases direct bonding among diamond particles, Co distribution becomes even, and the Co and W fraction also decreases. The produced PDC undergoes thermal shock tests with two temperature conditions of 820 and 830, and the results reveals that PDC with smaller filler particle ratio and low tap density value easily produces cracks, while PDC with high tap density value that contributes in increased direct bonding along with the higher diamond content results in improved thermal shock properties.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.949-952
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• 2006

We have measured the excited Xe atoms density in the $1s_5$ metastable states by laser absorption spectroscopy in accordance with various barrier ribs. In this experiment, the average density of one cell in the panel with stripe barrier rib has been measured to be $1.8{\times}10^{12}cm^{-3}$. The panel with close type barrier rib has been measured to be $5.1{\times}10^{12}cm^{-3}$.

• International Journal of Aeronautical and Space Sciences
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• 제12권3호
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• pp.296-304
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• 2011

In order to design a shear coaxial injector of solid particles with water, basic experiments on a particle laden jet are necessary. The purpose of the present study is to understand the effect of particle loading ratio on the particle spray characteristics (i.e. spreading angle, distribution of particle number density, velocity profiles, and particle developing region length). Hydro-reactive Al2O3 particles with a primary particle diameter of 35~50 ${\mu}m$ are used in this experiment. An automated particle feeder was designed to supply constant particle mass flowrates. Air is used as the carrier gas. To determine the air velocity at the orifice exit, tracers (aluminum oxide, 0.5~2 ${\mu}m$ primary diameter) are also supplied by a tracer feeder. A plain orifice type injector with 3 mm diameter, and 20 mm length was adopted. Particle image velocimetry is used to measure the mean and fluctuating velocity components along the axial and radial directions.

• 대한기계학회논문집B
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• 제24권4호
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• pp.504-511
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• 2000

PIV(Particle Image Velocimetry) is a recently developed technique for visualizing the fluid velocity fields. Because it has several advantages over the LDV(Laser Doppler Velocimetry), it became one of the most popular diagnostic tools in spite of its short history. However, its application to combustion is restricted by some problems such as flame illumination, scattered light refraction, particle density variation due to heat release, the combined effect of abrupt change in particle density and fluid velocity on flame contour, and thermophoresis which is particle lagging due to temperature gradient. These problems are expected to be originated from the non-continuous characteristics of flames and the limitations of particle dynamics. In the present study, these problems were considered for the visualization of the instantaneous coaxial hydrogen diffusion flame. And the instantaneous flame contour was detected using particle density difference. The visualized diffusion flame velocity field shows its turbulent and meandering nature. It was also observed that the flame is located inside the outer shear layer and flame geometry is largely influenced by the vorticity.

• 한국세라믹학회지
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• 제34권5호
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• pp.453-460
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• 1997

Sr-ferrite having magnetoplumbite structure is similar to Ba-ferrite in magnetic characteristics, but better magnetic characteristics for using motor application. To improve remanence magnetic flux density(Br) and coercive force(iHc), it is necessary that sintered ferrites must have high density and grain size less than 1 $\mu$m. By varying n values in SrO.nFe2O3 basic composition, calcination temperature, and BaO addition, Sr-ferrite powder and sintered specimen was prepared. The n values, calcination temperature, and BaO addition affected secondary phase formation, particle size, and particle shape. BaO addition enhanced Fe2O3 secondary phase and hexagonal shape particle. Fe2O3 phase reduced sintered density which greatly decreased Br.

• Bulletin of the Korean Chemical Society
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• 제32권1호
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• pp.83-88
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• 2011

The bone density fractionation method is a potential palaeodietary tool in tracing lifetime dietary changes as well as separating diagenetically altered fractions. This paper presents a workable bone density fractionation method that uses a devised mathematical model and the particle size distribution. Different grinding methods, i.e., a Spex $LN_2$ mill, a Disc mill and a Micronising mill, were used to reduce archaeological bone particles to an appropriate size range, which was then analyzed by a Laser particle sizer. It was found that density profiles are in good agreement with the diagenetic parameters, and with their stable isotope results.

• Journal of the Korean Wood Science and Technology
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• 제16권3호
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• pp.22-37
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• 1988

In tendancy of manufacturing beam with laminating particleboard, it was thought that if the properties, especially mechanical properties, of particleboard be reinforced, the mechanical properties of particleboard-laminated beam would be also improved. So in this study the particleboard was reinforced with composing of wood particle and steel wire. This study was carried out to obtain the basic physical and mechanical properties of board composed of wood particle and steel wire, especially tensile strength and compressive strength which are the important factors of the lamina of beam, in order to estimate whether the board, composed of wood particle and steel wire could be to improve the properties of the particleboard- laminated beam. The results obtained were summarized as follows: 1. The board composed of wood particle and steel wire in accordance with lower board density took better thickness swelling. 2. The board with lower board density was improved in higher value of tensile strength with more steel wires in prescribed cross section area of the board. for example, the board of density 0.5 showing 140% improved value. 3. In compressive strength, the board with lower board density was also improved in hjgher value with more steel wires in prescribed cross section area.

• Journal of the Korean Wood Science and Technology
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• 제33권2호통권130호
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• pp.40-55
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• 2005

This study was carried out to discuss the feasibility of wood and plastic wastes as the raw materials for wood particle-plastic composites. For this purpose, composites were manufactured from coarse and fine wood particles and polypropylene fibers by nonwoven web process. And the effect of wood particle size on the performance of the composites were analyzed according to ASTM D 1037-93. In the physical properties of composites, water absorption decreased with the increase of target density and polypropylene fiber content. And the composites with fine wood particles appeared to have slightly lower water absorption than those with coarse wood particles. Thickness swelling did not vary significantly with the increase of target density but increased with the increase of wood particle content. And the composites with fine wood particles were significantly lower in thickness swelling than those with coarse wood particles. In the mechanical properties of composites, dry and wet MOR showed the increasing tendency with the increase of polypropylene fiber content and target density. Dry and wet MOE showed the increasing tendency with the increase of target density but only wet MOE exhibited the increasing tendency with the increase of polypropylene fiber content. Composites with fine wood particles appeared to be generally higher in wet MOR and MOE than those with coarse wood particles. In conclusion, composites with fine wood particles showed generally higher performance than those with coarse ones. Also, composites were significantly superior to control particleboards in the performance, especially in water absorption and thickness swelling.

• 한국대기환경학회지
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• 제32권2호
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• pp.158-166
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• 2016

To characterize the features of particle apparent density, continuous measurements of particle number size distributions from optical particle sizer (OPS) and 24 hr integrated particle mass concentrations from filter based sampler were conducted at the National institute of environmental research NamBu Supersite (NNBS, $35.22^{\circ}N$, $126.84^{\circ}E$) in Gwangju for 16 days from Nov. 4 in 2014. Source apportionment model was carried out by applying Positive Matrix Factorization (PMF) to particle size distribution data. Three different distributions related to primary and secondary sources were investigated by the diurnal patterns of identified factors. Density estimated by gaussian model has been calculated as $1.69g/cm^3$ with 95% confidence bounds ($1.57{\sim}1.81g/cm^3$).