• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.80-89
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• 2002

The flame structure and soot formation in Acetylene-Air nonpremixed jet flame are numerically analyzed. We employed two variable approach to investigate the soot formation and oxidation processes. The present soot reaction mechanism involves nucleation, surface growth, particle coagulation, and oxidation steps. The gas phase chemistry and the soot nucleation, surface growth reactions are coupled by assuming that the nucleation and soot mass growth has the certain relationship with the concentration of pyrene and acetylene. We also employed laminar flamelet model to calculate the thermo-chemical properties and the proper soot source terms from the information of detailed chemical kinetic model. The numerical and physical model used in this study successfully predict the essential features of the combustion processes and soot formation characteristics in the reaction flow field.

• KSBB Journal
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• v.20 no.3
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• pp.164-176
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• 2005

In bioengineering field, current academic trends and informations on crystallization technology for bioproduct separation were summarized. It is essential for utilizing the crystallization technology to understand the fundamental phenomena of crystallization of crystal nucleation, crystal growth, crystal agglomeration and population balance for the design of crystallizers. In general, the crystal nucleation that the crystalline solids occur from the solution is analyzed by Gibb's free energy change in the aspect of thermodynamics and in the present paper the crystal nucleation models based on the above thermodynamics are summarized by their key characteristics. The crystal growth and agglomeration, which have been studied over 50 years and are essential phenomena for separation technology, are reviewed from their basic concept to most leading edge trend of researches. In the material and population balances for the designs of crystallization separation process, the analysis of crystallizers is summarized. Thereon, the present review paper will academically contribute the understanding the crystallization phenomena and the design of the crystallization separation process.

• Journal of Powder Materials
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• v.27 no.5
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• pp.394-400
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• 2020

Molybdenum trioxide (MoO₃) is used in various applications including sensors, photocatalysts, and batteries owing to its excellent ionic conductivity and thermal properties. It can also be used as a precursor in the hydrogen reduction process to obtain molybdenum metals. Control of the parameters governing the MoO₃ synthesis process is extremely important because the size and shape of MoO₃ in the reduction process affect the shape, size, and crystallization of Mo metal. In this study, we fabricated MoO₃ nanoparticles using a solution combustion synthesis (SCS) method that utilizes an organic additive, thereby controlling their morphology. The nucleation behavior and particle morphology were confirmed using ultraviolet-visible spectroscopy (UV-vis) and field emission scanning electron microscopy (FE-SEM). The concentration of the precursor (ammonium heptamolybdate tetrahydrate) was adjusted to be 0.1, 0.2, and 0.4 M. Depending on this concentration, different nucleation rates were obtained, thereby resulting in different particle morphologies.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.73-73
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• 1999

A large area negative metal ion beam source is developed. Kinetic ion beam of the incident metal ions yields a whole nucleation and growth phenomena compared to the conventional thin film deposition processes. At the initial deposition step one can engineer the surface and interface by tuning the energy of the incident metal ion beams. Smoothness and shallow implantation can be tailored according to the desired application process. Surface chemistry and nucleation process is also controlled by the energy of the direct metal ion beams. Each individual metal ion beams with specific energy undergoes super-thermodynamic reactions and nucleation. degree of formation of tetrahedral Sp3 carbon films and beta-carbon nitride directly depends on the energy of the ion beams. Grain size and formation of polycrystalline Si, at temperatures lower than 500deg. C is obtained and controlled by the energy of the incident Si-ion beams. The large area metal ion source combines the advantages of those magnetron sputter and SKIONs prior cesium activated metal ion source. The ion beam source produces uniform amorphous diamond films over 6 diameter. The films are now investigated for applications such as field emission display emitter materials, protective coatings for computer hard disk and head, and other protective optical coatings. The performance of the ion beam source and recent applications will be presented.

• Korean Membrane Journal
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• v.6 no.1
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• pp.61-69
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• 2004

Small angle light scattering (SALS) and field emission scanning electron microscope (FE-SEM) have been used to investigate the effects of alcohol on phase separation of chlorinated poly(vinyl chloride) (CPVC)/tetrahydrofuran (THF)/alcohol (9/61/30 wt%) solution during water vapor induced phase separation. A typical scattering pattern of nucleation & growth (NG) was observed for all casting solutions of CPVC/THF/alcohol. In the case of the phase separation of CPVC dope solution containing 30 wt% ethanol or n-propanol, the demixing with NG was observed to be heterogeneous. Meanwhile, the phase separation of CPVC dope solution with 30 wt% n-butanol was found to be predominantly homogeneous NG. Although the different phase separation behavior of NG was observed with types of alcohol additives, the resultant surface morphology had no remarkable differences. That is, even though the NG process by water vapor is either homogeneous or heterogeneous, this difference does not play a main role on the final surface morphology. However, it was estimated from the result of hydraulic flux that the phase separation by homogeneous NG provided the membrane geometry with lower resistance in comparison with that by heterogeneous one.

• Journal of the Korean Magnetics Society
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• v.26 no.6
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• pp.196-200
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• 2016

In this study the mechanisms of magnetization reversal and magnetic interaction effects on activation volumes for Sr-ferrite with different particle sizes are investigated. The activation volumes of C2 sample are larger than those of C3 sample in the range of low magnetic fields. But the fields above the coercivity of sample C2, the activation volumes of both samples are decreased linearly with increasing the applied magnetic field. These phenomena can be explained by the strengths of two critical fields representing the reverse domain nucleation field and the domain wall pinning field as well as the strength of dipolar interaction.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.05a
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• pp.134-135
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• 2000

• Journal of Magnetics
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• v.20 no.1
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• pp.31-39
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• 2015

Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by a three-dimensional (3D) model for exchange-coupled Sm-Co/${\alpha}-Fe$/Sm-Co trilayers with in-plane collinear easy axes. These results are carefully compared with the popular one-dimensional (1D) micromagnetic models and recent experimental data. It is found that the results obtained from the two methods match very well, especially for the remanence and coercivity, justifying the calculations. Both nucleation and coercive fields decrease monotonically as the soft layer thickness $L^s$ increases while the largest maximum energy product (roughly 50 MGOe) occurs when the thicknesses of hard and soft layers are 5 nm and 15 nm, respectively. Moreover, the calculated angular distributions in the thickness direction for the magnetic moments are similar. Nevertheless, the calculated nucleation and pinning fields as well as the energy products by 3D OOMMF are systematically smaller than those given by the 1D model, due mainly to the stray fields at the corners of the films. These demagnetization fields help the magnetic moments at the corners to deviate from the previous saturation state and facilitate the nucleation. Such an effect enhances as $L^s$ increases. When the thicknesses of hard and soft layers are 10 nm and 20 nm, respectively, the pinning field difference is as large as 30%, while the nucleation fields have opposite signs.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.26-26
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• 2000

High quality epitaxial Y2O3 thin films were prepared on Si(111) and (001) substaretes by using ion beam assisted deposition. As a substrate, clean and chemically oxidized Si wafers were used and the effects of surface state on the film crystallinity were investigated. The crystalline quality of the films were estimated by x-ray scattering, rutherford backscattering spectroscopy/channeling, and high-resolution transmission electron microscopy (HRTEM). The interaction between Y and Si atoms interfere the nucleation of Y2O3 at the initial growth stage, it could be suppressed by the interface SiO2 layer. Therefore, SiO2 layer of the 4-6 layers, which have been known for hindering the crystal growth, could rather enhance the nucleation of the Y2O3 , and the high quality epitaxial film could be grown successfully. Electrical properties of Y2O3 films on Si(001) were measured by C-V and I-V, which revealed that the oxide trap charge density of the film was 1.8$\times$10-8C/$\textrm{cm}^2$ and the breakdown field strength was about 10MV/cm.

• Journal of Magnetics
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• v.13 no.4
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• pp.167-169
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• 2008

The switching field of a 300 nm wide nanowire has been controlled by attaching a wide wire to it. The width of the wide wires varies from 700 nm to 2000 nm. While the connection of the two wires does not affect the switching field of the wide wires, it strongly affects the 300 nm-wire, resulting in a decrease of the switching field of the isolated wire from 175 Oe to 54 Oe when the 2000 nm-wire is connected to it. This result clearly shows that the switching field of the nanowire can be engineered by attaching a nucleation pad that has a different magnetic anisotropy.