• 한국세라믹학회지
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• 제53권5호
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• pp.541-547
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• 2016

In developing high temperature molds with advantages of the sand and precision (investment) castings, mechanical properties of the mold were improved through homogeneous coating of starting powders with an inorganic binder and improvement of fabrication process. Beads with mullite composition were employed for properties of the mold under high temperature, which was compared with artificial sands. Precursors of silica and sodium oxide were used as starting materials for an inorganic binder to achieve homogeneous coating on the starting powders. Strength was enhanced by the glass phase converted from the inorganic binder through heat treatment process. Also, two kinds of process, wet and dry processes, were incorporated to prepare mold specimens. Consequently, fabrication process of the mold with superior strength and high temperature applicability, compared with the previous molds for sand casting, could be suggested through control of the starting material and enhancement of the vitrification efficiency.

• 한국물환경학회지
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• 제28권2호
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• pp.219-223
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• 2012

The fixed solid catalysts such as glass bead, steel mesh, and $TiO_2$ coated ceramic bead were used to investigate effect of radical production at different frequencies. The radical production rate at 300 kHz was faster than that at 35 kHz without solid, but the tendency was changed with the presence of glass bead. The presence of glass beads create non-continuous points between the solid and liquid phases leading to increased formation of cavitation bubbles. However, the radical production decreased when steel mesh was used at 35 kHz although the surface area of contact with liquid was same when glass bead was used. Hence the solid catalyst did not always enhance the radical production. The radical production using $TiO_2$ coated ceramic bead was dramatically increased at 35 kHz due to the breakage of $TiO_2$ coated ceramic bead. Therefore the radical productions at 300 kHz using fixed solid catalysts generally increased while at 35 kHz the results fluctuated according to the experimental conditions.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.48-54
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• 2002

Since photocatalysts are activated by lights of UV wavelengths, plasma is alternatively used as a light source for a photocatalytic reactor. Light intensity generated by plasma is proportional to the surface area of catalytic material, and this, in many practical applications, is prescribed by the geometry of a plasma generator. Thus, it is crucial to increase the surface area far sufficient light intensity for photocatalytic reaction. For example, in a pack-bed type reactor, multitudes of beads are used as a substrate in order to increase the surface area. Honeycomb monolith type substrate, which has very good surface area to volume ratio, has been difficult to apply plasma as a light source due to the fact that light penetration depth through the honeycomb monolith was too short to cover sufficient area, thus resulting in poor intensity for photocatalytic reaction. In this study, nonthermal plasma generation through a photocatalytic reactor of honeycomb monolith substrate is investigated to lengthen this short penetration depth. The ceramic honeycomb monolith substrate used in this study has the same length as a three way catalyst used fur automotive applications, and it is shown that sufficient light intensity for photocatalytic reaction can also be obtained with honeycomb monolith type reactor.

• 대한한의학방제학회지
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• 제28권3호
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• pp.281-287
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• 2020

Objectives : In case of herbs decoction, the ceramic or earthware pots was recommended, but not the metals, particularly iron or aluminum, which could cause unknown chemical reactions. In Korean Medical classics, it has been known that some herbs including Caulis Lonicerae Japonicae (CL) were not recommended to boil with iron pot. This study investigates the physical changes of extracts of CL with or without iron. Methods : CL was decocted with reflux cooling extraction system to prevent evaporation and volatilization. Content of polyphenol was detected by Folin-Denis method and the levels of loganin and chlorogenic acid were evaluated by UPLC. Results : The color of extract with glass beads (GB) is yellowish brown, and the iron beads (IB) is blackish brown. Polyphenol and chlorogenic acid levels were reduced in IB extracts. Conclusions : The color of extract was change to blackish brown, and polyphenol and chlorogenic acid levels were reduced in CL extract with iron. Therefore, iron pots is not suitable for CL extraction.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.257-262
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• 2019

The control of microstructure is critical for the porous fuel particles used for infiltrating actinide nuclides. This study concerns the effect of heating processes on properties and microstructure of the fuel particles. The uniform gel precursor beads were synthesized by a microfluidic sol-gel process and then the porous $CeO_2$ microspheres, as a surrogate for the ceramic nuclear fuel particles, were obtained by heating treatment of the gel precursors. The fabricated $CeO_2$ microspheres have a narrow size distribution and good sphericity due to the feature of microfluidics. The effects of heating processes parameters, such as heating mode and peak temperatures on the properties of microspheres were studied in detail. An optimized heating mode and the peak temperature of $650^{\circ}C$ were selected to produce porous $CeO_2$ microspheres. The optimized heating mode can avoid the appearance of broken or crack microspheres in the heating process, and as-prepared porous microspheres were of suitable pore size distribution and pore volume for loading minor actinide (MA) solution by an infiltration method that is used for fabrication of MA-bearing nuclear fuel beads. After the infiltration process, $1000^{\circ}C$ was selected as the final temperature to improve the compressive strength of microspheres.

• 멤브레인
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• 제23권4호
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• pp.267-277
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• 2013

고도정수처리를 위한 관형 세라믹 정밀여과와 이산화티타늄($TiO_2$) 광촉매 첨가 PES (polyethersulfone) 구의 혼성공정에서 역세척 주기(FT)와 역세척 시간(BT)의 영향을 막오염에 의한 저항($R_f$) 및 투과선속(J), 총여과부피($V_T$) 측면에서 기존의 질소 역세척 결과와 비교하였다. FT가 짧아질수록 $R_f$는 감소하고 J와 $V_T$는 증가하였다. 탁도의 처리효율은 물과 질소역세척 모두 NBF (no back-flushing)에서 최대이고, FT가 짧아질수록 처리효율이 다소 증가하였다. 유기물질 처리효율은 물역세척 시 FT 4분에서 최대이었으나, 질소 역세척 시 FT가 짧아질수록 증가하였다. BT가 길어질수록 $R_f$와 가역적 막오염 저항($R_{rf}$)은 감소하고, J와 $V_T$는 증가하였다. 탁도 처리효율은 물 역세척 시 98% 이상으로 거의 일정하였으나, 질소 역세척 시 NBF를 제외하고 BT가 길어질수록 증가하였다. 유기물질 처리효율은 물 역세척시 BT 6초에서 최대이고, 질소 역세척 시 NBF를 제외하고 BT가 길어질수록 증가하였다. BT 30초와 FT 2분에서 최대 $V_T$값을 나타내어서, 본 실험 범위에서 최적 조건은 FT 2분마다 BT 30초이다.

• 한국세라믹학회지
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• 제39권3호
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• pp.245-251
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• 2002

깁사이트의 급속 열분해 산물인 비정질 알루미나로부터 γ-alumina bead를 제조하고, 이를 21.87%의 질산($HNO_3$)과 28.57%의 초산($CH_3COOH$)을 혼합한 용액에 침적시킨 다음 200$^{\circ}$C 온도로 3시간 수열처리하여 결정의 변화, 기공특성, $N_2$ 흡/탈착 등온선, 기계적강도 및 내열특성 등을 조사하였다. 0.1∼0.3${\mu}$m 크기의 침상 및 판상 의사베이마이트 결정은 같은 결정구조를 갖는 1∼2${\mu}$m 길이의 침상형 베이마이트 결정으로 변했고, 이를 통해 ${\gamma}$-alumina와 베이마이트 사이에는 수열반응에 기인한 가역적 상 변화가 발생한다는 사실을 알 수 있었다. 수열처리 전 ${\gamma}$-alumina bead에 비해 $N_2$ 흡착 용량이 450㎖/g에서 670㎖/g으로 증가하였고, 100∼1000${\AA}$ 범위의 기공부피는 0.15㎖/g에서 0.77㎖/g으로 증가하였으며, 기계적 강도가 1.4MPa에서 2.2MPa로 증가하였다. 또한 40vol%의 수증기를 포함한 1000$^{\circ}$C의 고온에서도 100∼1000${\AA}$ 범위의 기공을 유지하며 ${\theta}$-alumina 결정구조를 유지하는 높은 내열저항을 나타내었다.

• 멤브레인
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• 제24권1호
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• pp.39-49
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• 2014

고도정수처리를 위한 관형 세라믹 정밀여과와 이산화티타늄($TiO_2$) 광촉매 첨가 PES (polyethersulfone) 구의 혼성공정에서 pH 및 산소 역세척의 영향을 막오염에 의한 저항($R_f$) 및 투과선속(J), 총여과부피($V_T$)의 관점에서 고찰하였다. pH가 높아질수록 $R_f$가 감소하고, J는 증가하는 경향을 보였다. 결과적으로 pH 9에서 최대의 $V_T$를 나타내었다. 탁도의 처리효율은 pH와 무관하게 98.7~99.0%의 비슷한 처리효율을 보였다. 용존유기물질(DOM)의 처리효율은 pH가 높아질수록 감소하였다. 산소와 질소 역세척의 차이를 비교한 결과, $R_{f,180}$ 값이 산소 역세척 시 질소보다 낮게 나타났고, 초기투과선속($J_0$)으로 무차원 화한 최종투과선속($J_{180}/J_0$)은 역세척 주기(FT) 10분과 12분을 제외하고 산소 역세척이 질소 보다 높게 유지되었다. 산소 역세척 시 탁도물질의 처리효율은 질소 보다 다소 높게 나타났지만, 그 차이는 미비하다. 질소 역세척 시 DOM의 처리율은 산소보다 높게 나타났다. 또한, 포화산소 조건에서 탁도물질의 처리율은 산소 또는 질소 역세척 경우와 비슷하게 나타났지만, 포화산소가 광촉매와 반응하여 OH 라디칼을 생성하였기 때문에 DOM의 처리효율은 큰 폭으로 증가하였다.

• 한국세라믹학회지
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• 제42권7호
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• pp.461-468
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• 2005

Transparent TiO$_{2}$ sols were prepared by hydrothermal synthesis to heat Ti precursor solutions, from Ti hydroxides obtained with neutralizing aqueous TiOCl$_{2}$ solutions having various concentrations of NaCI by aqueous NaOH solution, in the autoclave at 120$^{\circ}C$ The photocatalytic abilities of glass beads coated with the sol for gaseous benzene were evaluated. As a result, it was found that due to the increase of brookite phase in TiO$_{2}$ by controlling the concentration of Na ion the optical absorption of TiO$_{2}$ increases toward long wavelength but that in the area of short wavelength becomes relatively low and consequently the photocatalytic performance of TiO$_{2}$ thin film for benzene gas rather decreases, compared to that of composite film of anatase and brookite phases. These results suggest that in order for coated TiO$_{2}$ thin film to have high dissociation performance for benzene gas it is effective to form anatase and brookite phases compositely in TiO$_{2}$.

• 한국미생물·생명공학회지
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• 제24권6호
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• pp.738-742
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• 1996

An efficient packed-bed type biofilm reactor charged with immobilized phototrophs was developed to treat organic wastewater at an extremely high volumetric loading rate. The packed bed reactor (PBR) charged with porous ceramic beads was superior to a fluidized-bed reactor suspended with activated carbon powders in terms of many aspects such as BOD removal efficiency, operational stability, and overall economics. For wastewater with BOD concentration as high as 20, 000mg/l, the BOD removal efficiency was maintained above 90% when the hydraulic retention time (HRT) was longer than 1 day. The allowable volumetric BOD loading rate of this reactor (20gBOD/l day) is more than ten-folds higher than that of an ordinary activated sludge method. The behaviour of the reactor was represented well by a Monod type kinetic equation with a maximum specific BOD loading rate(P) of 22.2gBOD/l day and a half saturation constant(K$_{s}$) of 1, 750 mgBOD/l.