• Korean Chemical Engineering Research
• /
• 제45권6호
• /
• pp.663-668
• /
• 2007

$Ni/CeO_2-ZrO_2$ 촉매를 이용하여 수소 제조를 위한 메탄의 자열개질반응 특성을 조사하였다. 메탄의 자열개질반응에서 촉매의 활성과 안정성을 향상시키기 위해 알루미나가 코팅된 금속 모노리스를 사용하였으며, 금속모노리스 촉매체는 높은 반응온도에서 분말형태의 촉매에 비해 높은 메탄 전환율을 나타내었다. 자열개질반응에 있어서 $H_2O/CH_4/O_2$의 비는 전환율에 영향을 미치는 중요한 변수임을 알 수 있었다. $H_2O/CH_4$ 비가 증가함에 따라 수소 수율은 증가되고, 또한 $O_2/CH_4$ 비가 증가함에 따라 메탄 전환율은 증가하지만 수소 수율은 감소하였다. $Ni/CeO_2-ZrO_2$ 촉매에 0.5 wt%의 귀금속 촉매인 Ru 첨가로 인해 낮은 반응온도에서 촉매 활성이 향상되었다.

• 한국재료학회지
• /
• 제26권3호
• /
• pp.136-142
• /
• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• 한국건축시공학회지
• /
• 제13권4호
• /
• pp.351-359
• /
• 2013

고로슬래그는 콘크리트의 적용시 효율적인 가치향상과 관련하는 많은 장점도 있으나, 고로슬래그의 사용량 증대에 따른 부작용도 나타나고 있다. 따라서 고로슬래그 미분말의 활용성 증대를 위해 High Volume Slag를 자극제 종류별, 치환율별, 조강제 혼입율별, NaOH, $Na_2SiO_3$ 혼합사용시, 폐알칼리자극제 혼입율별 특성을 알아보기 위해 실험하였다. 실험결과, 압축강도의 경우 수산화나트륨을 제외한 모든 알칼리자극제에서 치환율이 증가함에 따라 강도가 증진되었다. 알칼리자극제 중 규산나트륨이 동탄성계수와 흡수율 등에서 높게 나타났으며, 조강제의 경우 혼입율 1.5%와 고로슬래그 치환율 75%가 높은 강도증진을 나타내었다. 폐알칼리 자극제의 경우 모든 실험에서 각기 다른 결과를 나타내었다.

• 한국세라믹학회지
• /
• 제49권6호
• /
• pp.485-492
• /
• 2012

Dense and single phase $BiFeO_3$ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of ${\approx}3{\mu}m$ by conventional sintering process. A relative density of ${\approx}96%$ with average grain size $7.3{\mu}m$ was obtained when the powder compacts were sintered at $850^{\circ}C$ even for a shorter duration of 10 min. In contrast, densification barely occurred at $800^{\circ}C$ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at $850^{\circ}C$ for 12 h showed enhanced electrical properties with leakage current density of $4{\times}10^{-7}A/cm^2$ at 1 kV/cm, remnant polarization $2P_r$ of $8{\mu}C/cm^2$ at 20 kV/cm, and minimal dissipation factor (tan ${\delta}$) of ~0.025 at $10^6$ Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.

• 한국건설순환자원학회논문집
• /
• 제8권2호
• /
• pp.161-166
• /
• 2020

현재의 석면의 문제는 사용단계에서의 공기 중 석면의 비산 없이 안정적으로 사용하는 문제, 해체단계에서 석면 비산을 최소화하여 해체하는 문제, 해체된 폐석면 건축자재를 안정적으로 최종 처리 하느냐의 문제이다. 석면 폐기물의 처리는 매립 또는 부분적 응용처리 등과 같이 구분할 수 있다. 석면 건축자재를 무해화 하면, 이를 일반 폐기물로 분류하거나 또는 재활용 가능 폐기물로 분류가 가능할 것이다. 따라서 본 연구는 무해화 처리한 폐석면 분체의 물리, 화학적 특성 분석 이를 활용한 2차 제품 적용성을 평가하였다. 본 연구를 통하여 중 저온 화학적 처리를 통핸 석면 무해화 시 촉매반응을 위한 적정한 온도와 압력을 가하는 것이 가장 중요한 요소인 것으로 나타났다.

• Journal of Electrical Engineering and Technology
• /
• 제13권3호
• /
• pp.1166-1172
• /
• 2018

Degradation due to delamination occurs frequently in the high temperature superconductors (HTS) coil of rotating machines made with 2nd generation (2G) HTS wire, and the authors have observed other similar cases. Since an HTS field coil for a rotating machine is required to have stable current control and maintain a steady state, co-winding techniques for insulation material and epoxy resin for shape retention and heat transfer improvement are applied during coil fabrication. However, the most important limiting factor of this technique is delamination, which is known to be caused by the difference in thermal expansion between the epoxy resin and 2G HTS wire. Therefore, in this study, the experimental results of mixing the ratio of epoxy resin and alumina ($Al_2O3$) filler were applied to the fabrication of small and large test coils to solve the problem of degradation. For the verification of this scheme, eight prototypes of single pancake coils with different shapes were fabricated. They showed good results. The energization and operation maintenance tests of the stacked coils were carried out under liquid neon conditions similar to the operation temperature of an MW-class rotating machine. In conclusion, it was confirmed that the alumina powder mixed with epoxy resin in an appropriate ratio is an effective solution of de-lamination problem of 2G HTS coil.

• 한국전기전자재료학회논문지
• /
• 제15권1호
• /
• pp.67-74
• /
• 2002

A phosphor for Plasma Display Panel, BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$, showing a blue emission band at about 450nm was prepared by a solid-state reaction using BaCO$_3$, $Al_2$O$_3$, MgO, Eu$_2$O$_3$ as starting materials wish flux AlF$_3$. The study of the behaviour of Eu in BAM phosphor was carried out by the photoluminescence spectra and the Rietveld method with X-ray and neutron powder diffraction data to refine the structural parameters such as lattice constants, the valence state of Eu, the preferential site of Mg atom and the site fraction of each atom. The phenomenon of the concentration quenching was abound 2.25~2.3wt% of Eu due to a decrease in the critical distance for energy transfer of inter-atomic Eu. Through the combined Rietveld refinement, R-factor, R$_{wp}$, was 8.11%, and the occupancy of Eu and Mg was 0.0882 and 0.526 at critical concentration. The critical distance of Eu$^{2+}$ in BAM was 18.8$\AA$ at 2.25% Eu of the concentration quenching. Furthermore, c/a ratio was decreased to 3.0wt% and no more change was observed over that concentration. The maximum entropy electron density was found that the modeling of $\beta$-alumina structure in BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$correct coincided showing Ba, Eu, O atoms of z= 1/4 mirror plane.e.ane.e.

• 대한한방부인과학회지
• /
• 제18권1호
• /
• pp.142-155
• /
• 2005

Objective: This study was undertaken to evaluate the dose dependent effects of Epimedii Herba extract solution on the spermatogenic abilities such as concentration, motility and morphological normality of sperm from the testis, and the activities of spermhyaluronidase and antioxidants. Materials and Method: We choose the 2-month-old mice, and administered the extract powder of Epimedii Herba in the different concentration once in a day for 60 days. The control group was administerde to normal water in the isolated testis tissue. Also we observed changes of isolated testis at the before and after administration of Epimedii Herba extracts in the mice. And we compared to the testicular tissue especially seminiferous tubules between control and treated group by histochemical methods. Results: The significant dose dependent differences were observed in the concentration of total sperm, the motility and normality of spermatozoa of the Epimedii Herba extract administered groups compared than that of control group, respectively. In the histological analysis of the testicular lobes were observed in the Epimedii Herbaextract administered groups than control group, respectively. Also, the activity hyluronidase was significantly increased in the Epimedii Herba extract administered groups than that of the control group. In case of antioxidant activity analysis, the activity of peroxidase and catalase were significantly increased in the Epimedii Herba extract administered groups than that of control group, respectively. Conclusion: This study shows that Epimedii Herba can effect the count and motility of sperm, the important ractor in male fertility and also promote the activity of antioxidants, catalase and peroxidase, which is the important factor in spermatogenesis.

• 대한한방소아과학회지
• /
• 제22권1호
• /
• pp.103-111
• /
• 2008

Objectives Seunggal-tang is one of the prescriptions of oriental herbal medicine, which has been applied to several allergic diseases such as atopic dermatitis. This study was planned to compare differences of anti-allergic effects based on different form of Seunggal-tang by manufacturing differently. Methods Two types herb medicine products were used; aqueous extract (SG-T, Seunggal-Tang) and powder (SG-S, Seunggal-San) which were made from the same mixed formula of Seunggal-tang. To investigate in vitro anti-allergic activities, rat basophilic leukemia (RBL-2H3) cells were treated with SG-T and SG-S for 1 hour, and then stimulated with the phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187. We examined the release of beta-hexosaminidase, as a marker of degranulation, and the releases of tumor necrosis factor (TNF)-alpha and interleukin (IL)-4, as proinflammatory cytokines. Results SG-T and SG-S didn't have effects on cell viabilities in concentrations under 2㎎/㎖. In additionto that, SG-T more inhibited releasing ${\beta}$-hexosaminidase, TNF-${\alpha}$ and IL-4 than SG-S. Conclusions These results indicate that SG-T is more effective against mast cell-mediated allergic reactions than SG-S.

• Journal of Periodontal and Implant Science
• /
• 제49권3호
• /
• pp.193-204
• /
• 2019

Purpose: The reaction of cells to a titanium implant depends on the surface characteristics of the implant which are affected by decontamination. The aim of this study was to evaluate the cytocompatibility of titanium disks treated with various decontamination methods, using salivary bacterial contamination with dental pellicle formation as an in vitro model. Methods: Sand-blasted and acid-etched (SA) titanium disks were used. Three control groups (pristine SA disks [SA group]; salivary pellicle-coated SA disks [pellicle group]; and biofilm-coated, untreated SA disks [NT group]) were not subjected to any decontamination treatments. Decontamination of the biofilm-coated disks was performed by 14 methods, including ultrasonic instruments, rotating instruments, an air-powder abrasive system, a laser, and chemical agents. MG63 cells were cultured in the presence of the treated disks. Cell proliferation assays were performed on days 2 and 5 of cell culture, and cell morphology was analyzed by immunofluorescence and scanning electron microscopy (SEM). A vascular endothelial growth factor (VEGF) assay was performed on day 5 of culture. Results: The cell proliferation assay revealed that all decontaminated disks, except for the 2 groups treated using a plastic tip, showed significantly less cell proliferation than the SA group. The immunofluorescence and SEM analyses revealed that most groups showed comparable cell density, with the exception of the NT group, in which the cell density was lower and bacterial residue was observed. Furthermore, the cells grown with tetracycline-treated titanium disks showed significantly lower VEGF production than those in the SA group. Conclusions: None of the decontamination methods resulted in cytocompatibility similar to that of pristine SA titanium. However, many methods caused improvement in the biocompatibility of the titanium disks in comparison with the biofilm-coated, untreated titanium disks. This suggests that decontamination is indispensable for the treatment of peri-implantitis, even if the original biocompatibility cannot be restored.