• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.84-84
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• 2010

We present an in-situ study of the interaction of a bimetallic Rh50Pd50 bulk crystal with O2, CO, and NO using ambient pressure x-ray photoelectron spectroscopy and compare it to results for 10 nm nanoparticles with the same overall composition. The surface of the bulk crystal has less Rh present under both oxidizing and reducing conditions than the nanoparticles under identical conditions. Segregation and oxidation/reduction proceeds quicker and at lower temperature for nanoparticles than for the bulk crystal. The near surface of the Rh50Pd50 bulk crystal after high temperature vacuum annealing is ca. 9% Rh measured by XPS. Heating in 0.1 Torr O2 to $350^{\circ}C$ increases the Rh surface composition to ca. 40%. The surface can then be reduced by heating in H2 at $150^{\circ}C$, leading to a reduced surface of 30% Rh. Titration of CO from this Rh-rich surface proceeds at a much lower pressure than on the Rh-deficient starting surface.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권1호
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• pp.1-7
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• 2005

Thin films of vanadium oxide(VO/sub x/) were deposited by r.f. magnetron sputtering from V₂O/sub 5/ target with oxygen/(oxygen+argon) partial pressure ratio of 0% and 8% and in situ annealed in vacuum at 400℃ for 1h and 4h. Crystal structure, chemical composition, molecular structure, optical and electrical properties of films were characterized through XRD, XPS, RBS, FTIR, optical absorption and electrical conductivity measurements. The films as-deposited are amorphous, but 0%O₂ films annealed for time longer than 4h and 8% O₂ films annealed for time longer than 1h are polycrystalline. As the oxygen partial pressure is increased the films become more stoichiometric V₂O/sub 5/. When annealed at 400℃, the as-deposited films are reduced to a lower oxide. The optical transmission of the films annealed in vacuum decreases considerably than the as-deposited films and the optical absorption of all the films increases rapidly at wavelength shorter than about 550nm. Electrical conductivity and thermal activation energy are increased with increasing the annealing time and with decreasing the oxygen partial pressure.

• 방사성폐기물학회지
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• 제8권4호
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• pp.303-309
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• 2010

사용후핵연료 건식처리공정(pyrochemical process)에서 LiCl-KCl 공융염의 회수는 방사성폐기물 부피감량과 원료물질 회수를 위해 반드시 필요하다. 본 논문은 진공증류공정을 이용하여 희토류 침전물(희토류 산염화물 또는 산화물)내 잔류하는 LiCl-KCl 공융염 회수에 관한 것이다. 진공증류시험장치에서 희토류 침전물내 공융염은 효과적으로 휘발 및 분리되었다. 분리된 공융염은 감압증류시험장내 세 지점에서 침적되거나 필터에 포집되으며, 침적되거나 포집된 공융염을 회수하는 것은 쉽지 않았다. 이 문제점을 해결하기 위해 감압조건에서 온도구배를 이용하여 공융염 거동을 제어할 수 있는 공융염 진공증류/응축회수 시스템을 개발하였으며, 이 장치를 이용하여 휘발된 공융염을 회수용기에서만 응축시켜 쉽게 회수할 수 있음을 확인하였다.

• Journal of Information Display
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• 제5권4호
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• pp.7-11
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• 2004

Effects of base vacuum level on the electrical and optical characteristics of the plasma display panel (PDP) were investigated. The relationship between efficiency and base vacuum level before filling discharge gas was analyzed. For the base vacuum level of $1{\times}10^{-4}$ torr, firing voltage of a 2-inch diagonal PDP panel was 232 V at the discharge gas pressure of 400 torr and luminous efficiency was 1.5 lm/W at 180V sustaining pulse. On the other hand for $1{\times}10^{-6}$torr, the firing voltage was reduced to 215 V and luminous efficiency was improved considerably to 2.5 lm/W. We successfully demonstrated the smooth operation of tip-less PDP fabricated using vacuum in-line sealing method.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
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• pp.524-526
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• 2007

Polymer dispersed liquid crystal (PDLC) films consist of micro-droplets of liquid crystals dispersed in a polymer matrix. To make wide area PDLC filled devices, it is necessary to develop reliable method of vacuum injection of PDLC solution instead of the capillary injection. However, well-known 2-ethylhexylacrylate (EHA), main element of a prepolymer, exhibits the volatility problems, when the PDLC solution is placed under the low pressure. In this study, we developed the vacuum injection process to fill a wide area cell. Experimental results indicate that the $V_{90}$(turn-on voltage) of the PDLC cell made by a vacuum injection method are lower than that of the PDLC cell made by a capillary injection method.

• Journal of Information Display
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• 제4권4호
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• pp.19-24
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• 2003

By using vacuum in-line driving and photoluminescence measuring system, we have examined the electrical and optical characteristics of plasma display panel produced by vacuum in-line sealing technology. In addition, the relationship between luminous efficiency and base vacuum level before filling discharge gas was analyzed. In the case of base vacuum level of $1.33{\times}10^{-1}$ Pa, the firing voltage of a 2-inch diagonal PDP panel was ranged from 312 to 343 V depending on the discharge gas pressure of $2.667{\times}10^4$ to $4{\times}10^4$ Pa at room temperature, Whereas in the case of $1.33{\times}10^{-4}$ Pa, the firing voltage was reduced by 40 V and luminescence was improved slightly.

• Korean Chemical Engineering Research
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• 제58권2호
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• pp.307-312
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• 2020

최근 대기압이하 진공 압력 상태에서 운전되는 유동층 반응기는 진공건조 공정이나 플라즈마 화학증착과 같이 감압 유동화가 요구되기에 관심이 증대되어 왔다. 그러나 대기압 이하에서 운전되는 유동층의 수력학적 특성 연구는 많이 연구되지 않았다. 본 연구에서는 대기압 이하에서 운전하는 유동층의 압력강하를 층내 압력을 1.33 에서 101.3kPa 까지 변화시키며 측정하였다. 유동층의 운전 압력이 진공인 상태에서는 최소유동화속도가 압력이 감소함에 따라 증가하며, 이는 기체 밀도와 평균 자유경로 변화와 같은 slip 흐름에 의한 변화이다. 또한 기존의 상압 상태에서 운전되는 유동층의 최소유동화속도 상관식과 비교함으로써 압력 감소에 따른 slip 흐름의 영향 뚜렷하게 나타남을 가리키는 임계 Knudsen 수를 결정하였다. 이로부터 slip 흐름이 주도하기 시작하는 임계 압력을 실험적으로 결정하였다.

• 한국분말재료학회지
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• 제29권2호
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• pp.118-122
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• 2022

The synthesis of porous W by freeze-casting and vacuum drying is investigated. Ball-milled WO₃ powders and tert-butyl alcohol were used as the starting materials. The tert-butyl alcohol slurry is frozen at -25℃ and dried under vacuum at -25 and -10℃. The dried bodies are hydrogen-reduced at 800℃ and sintered at 1000℃. The XRD analysis shows that WO₃ is completely reduced to W without any reaction phases. SEM observations reveal that the struts and pores aligned in the tert-butyl alcohol growth direction, and the change in the powder content and drying temperature affects the pore structure. Furthermore, the struts of the porous body fabricated under vacuum are thinner than those fabricated under atmospheric pressure. This behavior is explained by the growth mechanism of tert-butyl alcohol and rearrangement of the powders during solidification. These results suggest that the pore structure of a porous body can be controlled by the powder content, drying temperature, and pressure.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.185-192
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• 2004

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB (A) and the 2$\^$nd/ BPF is reduced about 20 dB (A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

• 한국산업융합학회 논문집
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• 제21권1호
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• pp.1-8
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• 2018

The purpose of this study is to develop a high-strength, high-toughness, thin-walled aluminum shock absorber housing product by applying a high vacuum die casting method to improve internal gas defect and formability. The analysis program dedicated for the casting was used because it was too costly and time-consuming to adopt the gating system design. The final casting plan was designed based on the flow pattern of the material filled into the mold and the result of air pressure and air pocket after the material was completely filled in the mold. Gaty shape was designed as a split type. The runner was designed to have the same shape as the initial inlet curve of the cavity, and the flow of the molten metal was prevented from turbulent flow. The most favorable results were obtained when the injection speed was $V_2=4.0m/s$. Defects on pores were reduced by applying high vacuum level inside the mold.