• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.265-272
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• 2020

PURPOSE. The aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS. Four groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness. RESULTS. XRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P<.05. CONCLUSION. Hydrothermal aging caused reduction in mechanical properties such as surface hardness, biaxial flexural strength, and fracture toughness of Y-TZP zirconia. However, cubic-containing zirconia (more than 30% by volume of cubic crystal) was assumed to have high resistance to hydrothermal degradation. Clinical significance: Cubic-containing zirconia could withstand the intraoral aging condition. It could be suggested to use as a material for fabrication of esthetic dental restoration.

• 한국세라믹학회지
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• 제36권12호
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• pp.1390-1395
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• 1999

Zr(Y,Ce)O2 TZP ceramics were prepared by sintering compacts of 3 mol% Y2O3-TZP(3Y-TZP) powders with different amount of 12 mol% CeO2-TZP(12Ce-TZP) in air at 140$0^{\circ}C$ for 2 h. The phase changes microstructure and mechanical properties of Zr(Y. Ce)O2 TZP after hydrothermal aging(20$0^{\circ}C$ 5h) were investigated. Although an addition of 12Ce-TZP accelerated the grain growth of Zr(Y, Ce)O2 TZP it restrained the transformation of tetragonal to the monoclinic phase during aging. The degradation in mechanical properties of sintered bodies was governed by the formed monoclinic phase and chemical composition. Induced Vickers indentation crack was propagated intergranually. From SEM observation of the fracture surfaces the pull-out of individual grain was confirmed.

• 동력기계공학회지
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• 제17권5호
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• pp.13-22
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• 2013

This paper reports the investigation of the physical and chemical characteristics of the prepared 3Pt-2MgO-$3ZrO_2$-$2CeO_2/Al_2O_3$ DOC, based on its hydrothermal aging. As a result of impregnating and reducing the $H_2PtCl_6$ $6H_2O$ precursor on a ${\gamma}-Al_2O_3$ basis, it was well dispersed into small particles with the range 2-3nm. This was because the $Al_2O_3$ acted as a barrier to prevent movement of the catalyst particles. For a hydrothermally aged catalyst for 9h at $700^{\circ}C$, its performance when purifying harmful gases decreased compared to a fresh catalyst, but its specific surface area was at the same level. This was because the performance of the catalyst was reduced by the sintering of the precious metal Pt, rather than by washcoat sintering and pore clogging. For an excessively hydrothermally aged catalyst for 9h at $850^{\circ}C$, Pt grew into an approximately 50nm class, formed a cluster compared to a fresh catalyst. The $CeO_2$ promoters also formed clusters among components of the same type, reducing their specific surface area to $114m^2/g$, which was 14% less than a fresh catalyst.

• 한국세라믹학회지
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• 제39권2호
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• pp.190-193
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• 2002

3Y-TZP에 희토류 산화물($CeO_2,\;Tb_2O_3$)을 0.5% 이하로 첨가시킨 지르코니아 단결정을 skull melting법으로 제조하여 오토클레이브 하에서 열수 상 안정성을 조사하였다. 극점도 측정결과, skull melting 법으로 제조한 $CeO_2$와 $Tb_2O_3$가 첨가된 시편들은 단결정이었으며 150∼250$^{\circ}C$에서 5시간 수증기 분위기 하에서 열처리한 후에도 정방정 상이 유지되는 우수한 열수 상 안정성이 관찰되었다.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.

• 대한본초학회지
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• 제35권3호
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• pp.25-32
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• 2020

Objectives : At present, aging-related degenerative muscle diseases are considered a serious problem. However, the effects on muscles regarding the efficacy of blueberry have not been studied. In this study, we tried to find out the correlation between blueberry and muscle. Methods : 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay was performed to confirm the antioxidant efficacy of blueberry hydrothermal extract. To determine the effect of blueberry hydrothermal extracts (BHE) on myoblast activity, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay was performed. To confirm the effect of blueberry hydrothermal extracts on the differentiation of myoblast into myotubes, protein expression levels of myosin heavy chain 3 (Myh3) and paired box 3/7 (pax3/7) were confirmed by immunoblot analysis. In addition, immunofluorescence microscopy was performed to confirm the effect on myotube formation of blueberry hydrothermal extracts. Results : Antioxidative efficacy and low toxicity were confirmed through ABTS assay and MTS assay of blueberry extract for myoblasts. As a result of immunoblot analysis and immunofluorescence analysis, the decrease in myogenic marker Pax3/7 was not confirmed, but myotubes The specific expression inhibitory activity of the forming protein Myh3 was confirmed. Through this, it was confirmed that the blueberry extract has a negative activity against myoblast differentiation. Conclusion : This experiment confirmed that blueberry hydrothermal extract has excellent antioxidant efficacy and negative results in inhibiting the differentiation and proliferation of myoblast. This requires deep study of certain ingredients and requires reassessment of the dietary intake of blueberries.

• 한국자동차공학회논문집
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• 제14권1호
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• pp.8-16
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• 2006

The research was conducted to characterize of Rh-Pd-Pt TWC with a double-layer washcoat for gasoline vehicle. The physical characteristics on surface of catalyst were inspected by BET, SEM and TEM. The characteristics of catalytic reaction were examined by the TPD/TPR and CO-pulse chemisorption. The catalyst $6Hx(0.35\times11\times3)$ showed superior conversion performance after hydrothermal aging process, which was due to small difference of the surface area between. the fresh and the aged catalyst. The CO-chemisorption and surface area were superior in the 600 cpsi catalyst than other catalysts, this catalyst also shown the higher conversion efficiency of the exhaust emissions. From the TPR test, the conversion performance of the aged catalyst was decreased by the agglomeration and sintering of the PM and metal oxides. From the TPD result, it was found that the NO chemisorption was happed on the bottom-layer washcoat with Pd, and the NO chemisorption was re-happened on the upper-layer washcoat with Pt and Rh in the desorption process.

• 한국지열·수열에너지학회논문집
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• 제20권1호
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• pp.8-15
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• 2024

This study aims to investigate the possibility of expanding the support program for green remodeling of fire stations and analyze the standard design guidelines. Green remodeling is essential for reducing greenhouse gas emissions and promoting green buildings, but currently, it is only conducted for buildings with limited purposes. In this study, we conduct green remodeling for fire stations with severe aging to demonstrate energy performance improvement and investigate the potential for expanding the support program to other types of aging buildings. The research methodology includes analysis of previous studies, preliminary investigation and alternative setting, energy analysis, calculation of construction costs, evaluation of the possibility of introducing support programs, and examine of the fire station standard design guidelines. The research results confirm that green remodeling can reduce energy consumption in fire stations and present the possibility of including fire stations as targets in the support program for green remodeling of public buildings.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.147-152
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• 2007

This study investigates the aging characteristics of NOx storage and reduction(NSR) catalyst on the emission conditions of lean burn natural gas vehicles. We designed various NSR catalysts using by the double-layer washcoat technology to increase of a surface area and a thermal durability performance of the catalysts. The experiments were conducted with 3 kinds of the NSR catalysts, which were manufactured using by a honeycomb cordierite substrate. It was found that Ba is weak in the thermal aging because it has lower melting temperature than that of precious metals (PMs). The suitable loading amount of Ba in this study should be about 42 g/L from the results of the NOx adsorption and the NOx reduction efficiency. The major reason in deactivation of the NSR catalyst is the decrease of the adsorption site owing to the agglomeration and sintering of Ba rather than PM aging by hydrothermal aging. It was confirmed by results of BET, SEM and TEM.

• 한국세라믹학회지
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• 제50권6호
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• pp.384-389
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• 2013

Activated alumina was fabricated with aluminum hydroxide in this study. High-purity alumina gel and boehmite were prepared from aluminum hydroxide by a hydrothermal process and fired to activate alumina having a surface area of 380 ~ 480 $m^2/g$ with less loss of ignition. The aging and drying condition during the fabrication process affected the loss of ignition, the sedimentation time of the alumina suspension, as well as the surface area of the activated alumina. For pellet-type activated alumina, the pre-fired alumina gel and boehmite were press-formed and fired at $400^{\circ}C$ and $550^{\circ}C$ for 6 h, respectively. The fired pellets showed a low density of 2.0 ~ 2.2 $g/cm^3$ with 20% firing shrinkage and sufficient handling strength. In this study, a new fabrication process for high-quality activated alumina with aluminum hydroxide is introduced. The effects of the processing parameters on the activated alumina properties are also examined.