• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.258-263
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• 2021

ZnO varistor is a semiconductor device which can serve to protect the circuit from surge voltage because its non-linear I-V characteristics by controlling the microstructure of grain and grain boundaries. In order to obtain desired electrical properties, it is important to control microstructure evolution during the sintering process. In this research, we defined a dataset composed of process conditions of sintering and relative permittivity of sintered body, and collected experimental dataset with DOE. Meta-models can predict permittivity were developed by learning the collected experimental dataset on various machine learning algorithms. By utilizing the meta-model, we can derive optimized sintering conditions that could show the maximum permittivity from the numerical-based HMA (Hybrid Metaheuristic Algorithm) optimization algorithm. It is possible to search the optimal process conditions with minimum number of experiments if meta-model-based optimization is applied to ceramic processing.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.5
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• pp.383-389
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• 2000

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made o matsuoka’s composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. Gases used in sintering process were oxygen nitrogen argon and air. Using XRD and SEM the phase and microstructure of samples were analyzed respectively. The conditions of DC degradation tests were conducted at 115$\pm$2$^{\circ}C$ for 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Frequency analysis are performed to understand electrical properties as DC degradation test. From above analysis it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test and degradation phenomenon of ZnO varistor is caused by the change of electrical properties in grain boundary. These results are in accordance with Gupta’s degradation model.

• Journal of the Korean Geotechnical Society
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• v.38 no.5
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• pp.35-46
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• 2022

The in-situ resource utilization (ISRU) for sustainable lunar surface and deep space explorations has recently gained attention. Also, research on the development of construction material preparation technology using lunar regolith is in progress. Microwave sintering technology for construction material preparation does not require a binder and is energy efficient. This study applies microwave sintering technology to KLS-1, a Korean lunar simulant. It is crucial to secure the homogeneity to produce a sintered specimen for construction material. Therefore, understanding the interactions between microwaves, cavities, and raw materials is required. Using a numerical model in terms of efficient assessment of several cases and establishment of equipment operating conditions is a very efficient approach. Therefore, this study also proposes and verifies a coupled electric-thermal numerical model through cross-validation and comparison with experimental results. The numerical model proposed in this study will be used to present an efficient method for producing construction material using microwave sintering technology.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.119-127
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• 2003

In this study we propose an unsteady I-dimensional model of bed combustion with multiple solid phases, which confers a phase on each solid material. This model can be applied to a variety of bed combustion cases of various configurations and ignition methods. It contains fuel combustion, gaseous reaction, heat transfers between each phase, and geometric changes of the solid particles. An iron ore sintering pot is selected for verifying the model validity and simulation results are compared with the limited experimental data set of various coke contents and air supply rates. They predict the experimental results well and show applicabilities to the various system of the fuel bed with various solid materials.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.04a
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• pp.17-17
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• 1997

• Proceedings of the Korean Society of Laser Processing Conference
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• 2000.06a
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• pp.24-30
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• 2000

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.747-754
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• 2004

Thermo-fluid characteristics in coke oven, sintering machine and blast furnace in iron-making facility are key processes related to the quality and productivity of the pig iron. Solid material in the processes usually forms a bed in a gas flow. For simulation of the processes by mathematical model, the solid beds are idealized to be a continuum and a reacting solid flow in the gas flow. Governing equations in the form of partial differential equations for the solid material can be constructed based on this assumption. Iron ore sintering bed is simulated and limited amount of parametric study have been performed. The results have a good agreement with the experimental results or physical phenomena, which shows the validity and applicability of the model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2182-2195
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• 1996

Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

• Korean Journal of Computational Design and Engineering
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• v.13 no.6
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• pp.421-428
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• 2008

This article investigates the fabrication of polycaprolactone (PCL) composites filled with different volume fractions (10-30%) of tricalcium phosphate (TCP) by selective laser sintering (SLS) for tissue engineering scaffolds. Optimal processing parameters for each composition were developed by design of experiments (DOE). Specimens for compressive testing for each composition were fabricated and tested. The results showed that the compressive modulus increases as a function of TCP volume fraction. The experimentally measured compressive moduli were compared with moduli predicted by Halpin's theoretical model and were found to be in excellent agreement. This result proved that experimentally determined processing parameters for each composition were well optimized.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.213-219
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• 2006

A Monte Carlo simulation based on Potts model in a three dimensional lattice was studied to analyze and design microstructures in porous sintered compacts such as porosity, pore size, grain (particle) size and contiguity of grains. The effect of surface energy of particles and the content of additional fine particles to coarse particles on microstructure development were examined to obtain fundamentals for material design in porous materials. It has been found that the larger surface energy enhances sintering (necking) of particles and increases contiguity and surface energy does not change pore size and grain size. The addition of fine particles also enhances sintering of particles and increases contiguity, but it has an effect on increment of pore size and grain size. Such a simulation technique can give us important information or wisdom for design of porous materials, e.g., material system with high surface energy and fine particle audition are available for higher strength and larger porosity in porous sintered compacts with applications in an automobile.