• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.687-696
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• 2006

An efficient numerical method is developed to estimate the elasto-plastic post-buckling strength of space-framed structures. The inelastic ultimate strength of beam-columns and frames is evaluated by the parametric study. Applying the improved plastic hinge analysis that evaluate the gradual stiffness decrease effects due to spread of plasticity, elasto-plastic post-buckling behavior of steel frames is investigated considering the various residual stress distributions. Introducing the plastification parameter that represent pread of plasticity in the element and performing parametric study of equivalent element force and member idealization, finite-element solutions for the elasto-plastic analysis of space frames are compared with the results by plastic region analysis, shell elements and experimental results.

• Applied Chemistry for Engineering
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• v.21 no.4
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• pp.405-410
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• 2010

The photovoltaic performance of DSSCs fabricated with different electrode thickness and different annealing temperature with the P25 $TiO_2$ and the Dyesol $TiO_2$ was measured. Thickness change of $TiO_2$ electrodes was measured using cross-sectional FE-SEM before and after annealing. Photovoltaic efficiencies of DSSCs were also measured by changing annealing temperature of platinum (Pt) paste on the counter electrode. Photovoltaic performances of DSSCs made with one layer of P25 (${\sim}20.4\;{\mu}m$) and one layer of Dyesol $TiO_2$ (${\sim}9.1\;{\mu}m$) annealed at $500^{\circ}C$ for 30 min. showed highest efficiencies of 3.8% and 5.8%, respectively.

• Journal of the Korean Wood Science and Technology
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• v.33 no.3 s.131
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• pp.30-37
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• 2005

This study aimed at offering basic data to develop a new use of sawdust and rice husk. Research investigated the variation of density, weight loss and dimensional decreasing rate by the percentage of resin impregnation and carbonization temperature of ceramics, which were formed by the percentage of resin impregnation of 40~80% and carbonization of $600{\sim}1200^{\circ}C$ with board impregnated with phenolic resin made from sawdust and rice husk. The results of this study were as follows:1) As the percentage of resin impregnation increased, the thickness shrinkage and weight loss were decreased; on the other hand, density and modulus of rupture increased. Meanwhile, the carbonization temperature at $1200^{\circ}C$ showed the highest values, as the density was $0.81g/cm^3$ and the bending strength was $77.9kgf/cm^2$ in the percentage of resin impregnation at 70%. 2) As the carbonization temperature grew higher the linear shrinkage, thickness shrinkage and weight loss increased while the density increased until the carbonization temperature of $1000^{\circ}C$; but then decreased slightly at $1200^{\circ}C$.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.3
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• pp.111-122
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• 2021

Purpose: The purpose of this in vitro study was to investigate the flexural strength and translucency of three layers in 5Y-ZP and to assess the effect of additional firings on these properties. Materials and Methods: Sintered zirconia blocks were sectioned according to three layers : incisal, transition, and body. Disc-shaped specimens were fabricated from each layer. The diameter of specimens was 15.0 mm and each thickness of specimens for biaxial flexural strength test and translucency was 1.2 mm and 1.0 mm. The specimens were classified into subgroups according to the number of firing (0, 1, and 3 times; n = 10/subgroup) and the additional firings were performed under 900℃ using a furnace. Biaxial flexural strength and translucency was measured using universal testing machine and uv-vis spectrophotometer. X-ray diffraction (XRD) analysis was used for measurement of the phase identification. One-way ANOVA, Tukey HSD test were performed (α = 0.05). Results: There was no significant difference in flexural strength between the three layers (P > 0.05), while there was significant difference in translucency between different layers (P < 0.05). The flexural strength of incisal and transition layer was decreased by the single additional firing, and the three additional firings significantly decreased the flexural strength of three layers. The translucency of layer was decreased by additional firings except the body layer. The XRD patterns of all groups were similar. Conclusion: Three layers of 5Y-ZP were different only in translucency. Additional firings affected the flexural strength and translucency differently depending on the layers but crystalline phases were not changed.

• Korean Journal of Dental Materials
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• v.44 no.3
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• pp.197-206
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• 2017

The hardening effect by ice-quenching after oxidation of a Pd-Ag-Sn-Au metal-ceramic alloy during porcelain firing simulation was investigated by means of hardness test, field emission scanning electron microscopic observations, and X-ray diffraction analysis. The hardness decreased by ice-quenching after oxidation, which was induced by the homogenization of the ice-quenched specimen. The decreased hardness by ice-quenching after oxidation was recovered from the wash stage which was the first stage of the remaining firing process for bonding porcelain. After wash stage, the hardness of the ice-quenched specimens decreased during the subsequent porcelain firing process. But the final hardness of the ice-quenched specimens after oxidation was higher than that of the specimens cooled at stage 0 after oxidation. The increase in hardness of the specimens during the first firing process was caused by the lattice strains generated at the interface between the face-centered cubic Pd-Ag-rich matrix and the face-centered tetragonal Pd3(Sn, Ga, In) precipitate. The decrease in hardness of the specimens during the remaining firing process was caused by the microstructural coarsening.

• Clean Technology
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• v.15 no.2
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• pp.122-129
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• 2009

The effect of calcination temperature or hydrothermal treatment of commercial Fe-beta zeolites in the range of $450{\sim}900^{\circ}C$ were examined in the direct decomposition of $N_2O$. Fe-beta zeolites used were characterized using XRD, $N_2$ sorption, $^{27}Al$ MAS NMR and XPS. Although the surface area and micropore volume of Fe-beta zeolite after calcination at $900^{\circ}C$ and hydrothermal treatment at $750^{\circ}C$ decreased ca. 30%, a larger decrease in the surface area and micropore volume by hydrothermal treatment was observed than by calcination treatment alone. However, the Al sites in frameworks of zeolite were conserved in stable tetrahedral form resulting from low degree of dealumination which was related to the adjacent Fe ions on the Al sites. This could likely be correlated with the conservation of high surface area and micropore volume of Fe-beta zeolites. The increase in the calcination or hydrothermal treatment temperature caused the increase of decomposition temperature of $N_2O$ and the severe deactivation was observed after hydrothermal treatment than calcination treatment.

• Economic and Environmental Geology
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• v.56 no.6
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• pp.899-909
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• 2023

In this study, the material scientific characteristics of Hobun pigments used as white inorganic pigment for traditional cultural heritage were identified according to the type of shell and calcination and evaluated the stability of the preservation environment. For the purpose of this, we collected 2 different types of Hobun pigments made by oyster and clam shell and its calcined products(at 1,150℃). Hobun pigments before calcined identified calcium carbonate such as calcite, aragonite but calcination derived changing main composition to portlandite and calcite. Results of FE-SEM showed characteristics microstructure for each shell but pigments after calcined observed porous structure. Porous granule highly caused oil adsorption according to increase specific surface area of pigments. In addition, the whiteness improved after calcined pigments compared to non-calcined pigments, and the color improvement rate of Hobun pigment (CS) which made of clam shell was higher. As a result of the accelerated weathering test, the Hobun pigment-colored specimen had a color difference value of less than 2 after the test, which was difficult to recognize with the naked eye. In particular, the color stability has improved as the color difference value of the Hobun pigment is smaller after calcined compared to before non-calcined pigment. However, it was confirmed that the stability of the painting layer was lower in the specimen after calcined pigment. For antifungal activity test, Aspergillus niger, Tyromyces palustris and Trametes versicolor were used as test fungi, and all pigments were found to have preventive and protective effects against fungi. Especially, the antifungal effect of the calcined pigment was excellent, which is due to the stronger basicity of the pigment.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.473-478
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• 2009

The purpose of this study is to evaluate the behaviour of the plastic deformed zone at crack tip on the standard Charpy specimens which were taken from the multi-passed weld block of the pressure vessel steel. Notch was machined on the standard Charpy test specimens and pre-crack which was located around the fusion line was made under the repeat load. Four point bend and acoustic emission tests were carried out simultaneously. The size of plastic region at crack tip was calculated using stress intensity factor. Relationships between characteristics of acoustic emission and plastic zone size at crack tip were discussed through the cumulative AE energy. Regardless of the specimens, AE signals were absent within the elastic region almost and most of AE signals were produced at the plastic deformation region from yield point to the mid-point between yield and maximum load. More AE signals for the weldment were produced compared with the base-metal and PWHT specimen. Relations between plastic deformed zones at crack tip and cumulative AE energy for the weldment and PWHT specimen were different quietly from the base-metal. Besides, number of AE counts for the weldment was the larger than those of the base-metal and PWHT specimen.

• Proceedings of the Materials Research Society of Korea Conference
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• 2000.11a
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• pp.80-80
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• 2000

차세대 대화면 평판 디스플레이에서 가장 주목을 받고 있는 디스플레이 소자는 PDP라고 할 수 있다. PDP 패널 제조 공정 기술에서 난해한 공정 중 하나인 투명 유전체 제조 공정은 현재까지 인쇄법에 의한 연구가 주로 진행되어 왔다. 그러나 인쇄법은 여러 번의 인쇄와 건조, 소성이 반복되어야 함으로써 유전체 제조에 있어서 복잡한 제조 공정이므로 대폭 단순화할 필요가 있다. 이에 대한 해결책으로서 제시된 것이 tape casting을 이용한 건식 공정이다. 본 연구에서는 tape casting용 slurry에 포함되는 유기물인 binder, plasticizer, solvent의 변화에 따른 dry film의 특성 및 소성 조건에 따른 유전체 특성에 관하여 조사하였다. PbO-SiO$_2$-B$_2$O$_3$계 유리 분말과 유기 vehicle을 ball mill을 이용하여 분산, 혼합하여 tape casting용 slurry를 제조하고, 이 slurry를 doctor blade법으로 tape를 제조하고 건조한 후 유리기판에 transfer한 후 소성하였다. Slurry의 조건과 소성 조건에 따른 투광성, 표면 조도 및 단면의 미세구조 등 투명 유전체의 특성을 평가하였다.

• Journal of the Korean Wood Science and Technology
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• v.32 no.1
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• pp.73-79
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• 2004

Research investigated the variation of density, weight loss and dimensional decreasing rate, heat conduction rate by the resin impregnation rate and burning temperature of woodceramics, which were formed by impregnation rate of 40~80% and burning temperature of 600~1500℃ with sawdust board impregnated with phenolic resin made from thinned logs of pinus densiflora, Larix kaemferi and pinus koraiensis. As the resin impregnation rate and the burning temperature increased, the density increased, however, as the burning temperature increased to at 1200℃ or more, the density decreased. The more the resin impregnation rate increased, the more the decreasing rate of weight and size decreased; the more the burning temperature increased, the more the decreasing rate of weight and size increased. When the resin impregnation rate was high, the heat conduction (mm/sec) was superior.