• Korean Journal of Materials Research
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• v.28 no.10
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• pp.551-563
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• 2018

Visible and IR windows require a combination of high optical transparency and superior thermal and mechanical properties. Materials, fabrication and characterization of transparent ceramics for visible/IR windows are discussed in this review. The transparent polycrystalline $Y_2O_3$, $Y_2O_3-MgO$ nanocomposites and $MgAl_2O_4$ spinel ceramics are fabricated by advanced ceramic processing and the use of special sintering technologies. Ceramic processing conditions for achieveing fully densified transparent ceramics are strongly dependent on the initial powder characteristics. In addition, appropriate use of sintering technologies, including vacuum sintering, hot-pressing and spark plasama sintering methods, results in outstanding thermal and mechanical properties as well as high optical transparency of the final products. Specifically, the elimination of light scattering factors, including residual pores, second phases and grain boundaries, is a key technique for improving the characteristics of the transparent ceramics. This paper discusses the current research issues related to synthesis methods and sintering processes for yttria-based transparent ceramics and $MgAl_2O_4$ spinel.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.274-278
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• 2002

Surface finishing is still indispensable for most rapid prototyping (RP) processes because of the inherent stair-stepped surface and shrinkage of the parts. These problems can be minimized in the $VLM-_ST$ Process, because it uses expandable polystyrene foam sheets, each of which has a thickness of3.9 mm and a linear-interpolated side slope. The use of thick layers, however, limits the process capability of constructing fine details. This study focuses on the design of post-processing tool for fine details of $VLM-_ST$ parts and investigation of thermal characteristics during EPS foam cutting using the post-processing tool. To calculate the heat flux from the tool into the foam sheet, the tool was modeled as a heat source of radiation for finite element analysis. Results of the analysis agreed well with those of the experiment.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.133-140
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• 2010

Carbon fiber has many potential applications in a wide array of fields of solar cell, fuel cell, batteries, and polymer matrix composites due to an exceptional mechanical properties and chemical stability. In this study, the effects of catalysts on the property of carbon nanostructures grown on the carbon fiber were systematically investigated. The surface treatment of carbon fiber and catalysts synthesis for carbon nanostructures growth were carried out by one-pot ELP method and thermal CVD, respectively. The surface morphology and crystal structure of carbon nanostructures were examined using a field emission scanning electron microscope and transmission electron microscope. Depending on the type of catalysts and the molar ratio, various types of carbon nanostructures like carbon nanotube, carbon nanofilament, carbon nanospring and etc. were synthesized on the surface of carbon fibers surface.

• Korean Journal of Food Science and Technology
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• v.24 no.5
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• pp.463-469
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• 1992

Effect of thermal processing upon the structure formation of surimi was investigated by differential scanning calorimeter (DSC), rigidity changes during heating, and scanning electron microscopy (SEM). DSC studies showed the transition temperatures and heat capacity of the proteins during heating. Thermal transition peaks of the proteins were shifted to the lower temperatures or disappeared by the addition of salt and higher heating rate or setting treatment ($4^{\circ}C$ or $40^{\circ}C$). Whereas setting at $4^{\circ}C$ for 24hr produced elastic component and showed a permanent effect in rigidity development during heating, setting at $40^{\circ}C$ for 30 min produced a temporary effect. SEM studies in conjunction with rigidity scanning provided an insight into the structural features of the gel and helped clarify the setting and protein modification effects.

• Journal of Korea Foundry Society
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• v.24 no.5
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• pp.281-289
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• 2004

The present study focused on the estimation of the interfacial heat transfer coefficient as a function of the surface temperature of the aluminum casting at the mold/casting interface to investigate the effects of superheat and coating layer. The casting experiments of aluminum into a cylindrical copper mold were systematically conducted to obtain the thermal history during solidification. The thermal history recorded by four thermocouples embedded both in the mold and the casting was used to solve the inverse heat conduction problem using Beck's method. The effects of superheat and coating on the interfacial heat transfer coefficient in the liquid state, during the solidification, and in the solid state were comparatively discussed. In the liquid state, the interfacial heat transfer coefficient is thought to be affected by the roughness of the mold, the wettability of the casting on the mold surface, and the thermophysical properties of the coating layer. When the solidification begins, the air gap forms between the casting and the mold, and the interfacial heat transfer coefficient becomes a function of the air gap as well as surface roughness and the superheat. In the solid phase, it depends only upon the thermal conductivity and the thickness of the air gap. The coating layer reduces seriously the interfacial heat transfer coefficient in the liquid state and during the solidification.

• Journal of Applied Biological Chemistry
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• v.61 no.3
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• pp.219-226
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• 2018

The purpose of this study was to investigate the effect of thermal treatments, such as a sous-vide and a conventional hot water cooking, on the texture changes of soybean sprout. A novel method to measure texture properties of soybean sprout have been determined because of the irregular geometry of soybean sprout. The shape of cotyledon of bean spout was accurately analyzed using an image processing and a geometry model. To minimize the effect of the contact area on the texture measurement, a blade type of probe was selected for the measurement. True stress was evaluated to reflect the shape changes during deformation, and demonstrated that the measurement accurately distinguished the effect of thermal treatment on the texture. Different heating time (i.e., 0, 10, 20, and 30 min) was applied for both sous-vide and conventional cooking. Thermal processing caused hardening of textures for both cotyledon and hypocotyl of soybean sprout. The conventional cooking method showed higher stress values than those of sous-vide cooking. Sprouts cooked by sous-vide released the moisture after thermal processing while sprout cooked by a conventional water bath method could hold the moisture content during thermal processing. The soybean sprouts treated by conventional cooking method showed a higher score in sensory evaluation.

• Proceedings of the Korean Society for Food Science of Animal Resources Conference
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• 1997.06a
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• pp.94-94
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• 1997

• Proceedings of the Korean Ceranic Society Conference
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• 2004.04b
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• pp.46.3-46.3
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• 2004

• Proceedings of the Korean Society for Food Science of Animal Resources Conference
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• 1997.11a
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• pp.154-154
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• 1997

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1653-1665
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• 2002

One of the most significant problems in the processing of composite materials is residual stresses. The residual stresses may be high enough to cause cracking in the matrix even before external loads are applied and can degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in the polymeric composite cylinder are investigated. This type of structure is used for the launch vehicle fuselage. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite structures during cure. A launch vehicle experiences high thermal loads during flight and re-entry due to aerodynamic heating or propulsion heat, and the thermal loads may cause thermal buckling on the structure. In this study the thermal buckling analysis of composite cylinders are performed. Two boundary conditions such as all clamped and all simply supported are used for the analysis. The effects of laminates stacking sequences, shapes and residual stresses on the critical buckling temperatures of composite cylinders are investigated. The thermal buckling analysis is performed using ABAQUS.