• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.244-251
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• 2005

The relationship between particle size of hydro-thermally synthesized barium titanate powders (BT01, BT02, BT03, BT04, BT05) and the powder properties was investigated by means of particle size, specific surface area, zeta potential, XPS, XRD and SEM. Particle size determined by laser light scattering is closely related with specific surface area and the tetragonality (c/a) obtained from XRD. The specific surface area of the samples inversely decreased with increasing particle size except BT03 powder. BT03 sample showed higher surface area than BT04 sample of equivalent particle size, which was attributed mostly to the agglomeration of particles in terms of SEM image and XRD analysis. Zeta potential increased with increasing particle size with the exception of BT02 and BT03 which showed larger minus value of zeta potential in comparison with other BT powders. Beta potential results of BT02 and BT03 are considered to be related with the dissolution of $Ba^{2+}$ ion in these powers which was examined by XPS.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.416-421
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• 2000

We have developed a simple model for describing the non-spherical particle growth phenomena using modified 1-dimensional sectional method. In this model, we solve simultaneously particle volume and surface area conservation sectional equations which consider particles' irregularities. From the correlation between two conserved properties of sections, we can predict the evolution of the aggregates' morphology. We compared this model with a simple monodisperse-assumed model and more rigorous two dimensional sectional model. For the comparison, we simulated silica and titania particle formation and growth in a constant temperature reactor environment. This new model shows a good agreement with the detailed two dimensional sectional model in total number concentration, primary particle size. The present model can also successfully predict particle size distribution and morphology without costing very heavy computation load and memory needed for the analysis of two dimensional aerosol dynamics.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.574-579
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• 2003

The present study addresses an analytical investigation to understand the characteristics of gas flow in the High-Velocity Oxy-Fuel(HVOF) thermal spray gun. One-dimensional analysis is extended to involve the effects of the wall friction and powder particle diameter. From the present analysis it is well known that the flow characteristics inside and outside the thermal spray gun is varied depending on the combustion chamber pressure. The thermal spray gun flow is characterized by six different patterns. The powder particle size and wall friction significantly influence the powder particle velocity. The particle velocity decreases with an increase in the powder particle size. This implies that the combustion chamber pressure should be increased to achieve a higher velocity of the powder particle.

• 연구논문집
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• s.33
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• pp.123-135
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• 2003

Using the residence time calculated by computer simulation for temperature and gas velocity distribution in CVC reactor, the kinetics on the formation of $TiO_2$ nano powder was analyzed for coagulation process, After abrupt increase of particle size at initial growth stage (< 0.2 $\mus$ ), the particle grew in proportion of cubic root to time. The numerically calculated particle sizes well agreed with the experimental results. However, the coarse rutile $TiO_2$ powders having the particle size of over 40 nm were formed on the surface of quratz rod in the reactor. it is thought that the fine anatase particles condensed on quratz rod were sintered in a heated CVC reactor to grow and transform to coarse rutile phase, and the critical size for phase transformation anstase-to-rutile was around 25 nm tn this study.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.322-325
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• 2009

An enhanced continuum model for the size dependent strengthening of particle reinforced composites is presented. The model accounts explicitly for the enhanced strength in a discretely defined "punched zone" around the particle in a metal matrix composite as a result of geometrically necessary dislocations developed through a CTE mismatch. The size of the punched zone presents an intrinsic length scale, and this results in the size dependence of the overall behavior of the composite. Results show that predicted 0.2% offset yield stresses are increasing with smaller inclusions and larger volume fractions and this length-scale effect on the enhanced strength can be observed by explicitly including GND region around the particle.

• Korean Institute of Interior Design Journal
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• no.26
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• pp.57-63
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• 2001

The aim of this study is to measure sensitivity reaction of human being with a physical properties of color and average size of particle for building materials and predict the influence of color and average size of particle in evaluation of building materials. As a results, 1) In results of qualitative evaluation construction, all 16 adjectives were extracted by higher evaluation items and ,total 14 adjectives were extracted as evaluation adjectives except adjectives of a contrary concept in each other. 2) According to the result of factor analysis, all 4 group of $\ulcirner$potency$\lrcirner$, $\ulcirner$activity$\lrcirner$, $\ulcirner$evaluation$\lrcirner$, $\ulcirner$warmness$\lrcirner$ were extracted. In this time, $\ulcirner$potency$\lrcirner$ as the first factor indicates the most hign original value. Consequently, $\ulcirner$potency$\lrcirner$ factor have an hign influence in evaluation of building materials. 3) As a influence analysis of evaluation variable by evaluation item $\ulcirner$potency$\lrcirner$ factor have an high influence by influence of average size of a particle, $\ulcirner$activity$\lrcirner$ factor have influence hignly by influence of brightness, $\ulcirner$evaluation$\lrcirner$ factor have an hign influence by influence of average site of a particle and the hue, $\ulcirner$warmness$\lrcirner$ factor have an hign influence mainly by influence of the hue

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1117-1123
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• 2004

The characteristics of soot near the soot inception point for an ethene-air flame was carried out in a WSR (well-stirred reactor). The new sampling tool like the temperature controlled filter system was introduced to minimize the condensation during sampling. The new analysis tools applied include the real time size distribution analysis with the Nano-DMA, particle size by transmission electron microscopy, C/H analysis, g filter analysis, and thermogravimetric analysis using both non-oxidative and oxidative pyrolysis. The WSR can generate young soot particles that can be collected and examined to gain insight into inception. For the current conditions, soot does not form for ${\Phi}$=1.9, inception occurs at or before ${\Phi}$=2.0, and inception combined with soot surface growth and/or coagulation occurs for ${\Phi}$=2.1. The filter samples for ${\Phi}$=1.9 are composed of volatile compounds that evolve at relatively low temperatures when heated in the presence or absence of O$_2$. The samples collected from the WSR at ${\Phi}$=2.0 and ${\Phi}$=2.1 are precursor-like in morphology and size. They have higher C/H ratios and lower organic percentages than precursor particles, but they are clearly not fully carbonized soot. The WSR PAH distribution is similar to that in young soot from inverse flames.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1298-1303
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• 2004

The characteristics of soot near the soot inception point for an ethene-air flame was carried out in a WSR (well-stirred reactor). The new sampling tool like the temperature controlled filter system was introduced to minimize the condensation during sampling. The new analysis tools applied include the real time size distribution analysis with the Nano-DMA, particle size by transmission electron microscopy, C/H analysis, g filter analysis, and thermogravimetric analysis using both non-oxidative and oxidative pyrolysis. The WSR can generate young soot particles that can be collected and examined to gain insight into inception. For the current conditions, soot does not form for ${\Phi}=1.9$, inception occurs at or before ${\Phi}=2.0$, and inception combined with soot surface growth and/or coagulation occurs for ${\Phi=2.1}$. The filter samples for ${\Phi}$=1.9 are composed of volatile compounds that evolve at relatively low temperatures when heated in the presence or absence of $O_2$. The samples collected from the WSR at ${\Phi}=2.0$ and ${\Phi}=2.1$ are precursor-like in morphology and size. They have higher C/H ratios and lower organic percentages than precursor particles, but they are clearly not fully carbonized soot. The WSR PAH distribution is similar to that in young soot from inverse flames.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1270-1276
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• 2005

When gas/particle partitioning of PAHs in the atmosphere approached an equilibrium state, the slope of linear regression between gas/particle partitioning coefficient($logK_p$) and subcooled liquid vapour pressure($logP_L^O$) was -1. But it was alleged that the slope of equilibrium state might not be -1 in real atmospheric environment due to heterogeneous characteristics of particulate matter. In This study, it would be found if gas/particle partitioning of PAHs segregated with particle size in equilibrium state was based on the hypothesis mentioned above. We have calculated the slopes of $logK_p$ v.s. $logP_L^O$ after collecting 10 set samples which consisted of particulate and vaporous phases. The slope was close to -1 in equilibrium states. But despite of equilibrium state, all slopes segregated with particle size were not close to -1 and those were gentler with larger particle size. The difference of slopes in equilibrium states was almost against the assumption of gas/particle partitioning theory. When the gas/particle partitioning was due to adsorption, the desorption enthalpy was different in each particle size. When it was absorption, the activity coefficient was different. The difference of desorption enthalpy and activity coefficient in each particle size indicate the heterogeneous characteristics of the bulk particle. This may be the reason for slope variation with particle size even though in an equilibrium state.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1715-1721
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• 2002

Numerical analysis was conducted to characterize the gas flow field and particle deposition on a horizontal freestanding semiconductor wafer under the laminar flow field at vacuum environment. In order to calculate the properties of gas, the gas was assumed to obey the ideal gas law. The particle transport mechanisms considered were convection, Brownian diffusion and gravitational settling. The averaged particle deposition velocities and their radial distributions fnr the upper surface of the wafer were calculated from the particle concentration equation in an Eulerian frame of reference for system pressures of 1 mbar~1 atm and particle sizes of 2nm~10$^4$ nm(10 ${\mu}{\textrm}{m}$). It was observed that as the system pressure decreases, the boundary layer of gas flow becomes thicker and the deposition velocities are increased over the whole range of particle size. One thing to be noted here is that the deposition velocities are increased in the diffusion dominant particle size range with decreasing system pressure, whereas the thickness of the boundary layer is larger. This contradiction is attributed to the increase of particle mechanical mobility and the consequent increase of Brownian diffusion with decreasing the system pressure. The present numerical results showed good agreement with the results of the approximate model and the available experimental data.