• 한국전기전자재료학회논문지
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• 제11권3호
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• pp.221-228
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• 1998

In this study, the $\beta$-Polyvinylidene fluoride(PVDF) thin films were fabricated by physical vapor deposition method. Also, the properties of dielectric relaxation were studied to understand carrier's behavior of PVDF thin films, to be regarded as the excellent piezo and pyroelectricity. In the process of vapor deposition, the $\beta$-PVDF thin films have been fabricated under the condition of the substrate temperature at 3$0^{\circ}C$, the applied electric field at 142.8kV/cm and the pressure at 2.0${\times}10^{-5}$torr. The dielectric properties of PVDF have been studied in the frequency range 10Hz to 1MHz at temperature from 30 to $100^{\circ}C$. The relative dielectric constant of $\alpha$ and $\beta$-PVDF were 6.8 and 9.8, respectively, under a frequency of 1kHz. Such a phenomenon was caused by the decrease in intermolecular forces originated by the phase-transition from the TGTG' molecular conformation to the TT planar zig-zag conformation. And the relative dielectric constant is increased as a measuring temperature increases, because of the reduction of relaxation time caused by the decrease of intermolecular force.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.541-548
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• 2017

Uranium metal used for fabrication of fuel for research reactors in India is generally produced by magnesio-thermic reduction of $UF_4$. Performance of magnesio-thermic reaction and recovery and quality of uranium largely depends on properties of $UF_4$. As ammonium diuranate (ADU) is first product in powder form in the process flow-sheet, properties of $UF_4$ depend on properties of ADU. ADU is generally produced from uranyl nitrate solution (UNS) for natural uranium metal production and from uranyl fluoride solution (UFS) for low enriched uranium metal production. In present paper, ADU has been produced via both the routes. Variation of uranium recovery and crystal structure and composition of ADU with progress in precipitation reaction has been studied with special attention on first appearance of the precipitate Further, ADU produced by two routes have been calcined to $UO_3$, then reduced to $UO_2$ and hydroflorinated to $UF_4$. Effect of two different process routes of ADU precipitation on the characteristics of ADU, $UO_3$, $UO_2$ and $UF_4$ were studied here.

• 대한화장품학회지
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• 제40권2호
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• pp.187-193
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• 2014

충치는 사람의 구강질환 중 가장 흔한 질환으로 Streptococcus mutans (S. mutans)균이 초기 충치를 형성하는데 매우 중요한 역할을 담당한다. Porphyromonas gingivalis (P. gingivalis)는 대표적인 구취 유발균으로 구취 형성에 중요한 휘발성 황화합물을 생성하는데 관여한다. 치주질환은 치은결체조직과 치조골의 파괴를 유발하여 치아의 상실을 초래할 수 있는 만성 염증성 질환으로 Prevotella intermedia (P. intermedia)가 원인균이다. 이번 연구에서는 cetylpyridinium chloride (CPC), sodium fluoride (NaF), 녹차 추출액, 솔잎 추출액을 유효성분으로 하는 마우스워시 제품을 사용하여 S. mutans 균을 포함, 구강질환 균으로 널리 알려진 P. gingivalis, P. intermedia 대해 항균 효과를 확인하고자 하였다. 그 결과 시험군의 경우 S. mutans, P. gingivalis 에 대해 30 s 내에 4.00 Log, 4.68 Log의 사멸력을 확인하였고, P. intermedia의 경우 30 s 2.40 Log, 60 s 2.70 Log 사멸력을 확인하였다. 또한 Dentocult SM Strip mutans (SM Strip) 염색방법을 적용하여 S. mutans 균의 감소여부를 시각적 자료로 쉽게 확인할 수 있었다. 이와 같은 결과를 통해 CPC, NaF, 녹차 추출액, 솔잎 추출액을 포함한 마우스워시 제품은 구강균 사멸을 통해 충치 및 구취와 같은 구강질환 예방에 효과가 있을 것으로 기대한다.

• 한국환경과학회지
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• 제19권11호
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• pp.1315-1322
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• 2010

A membrane bioreactor (MBR) was designed using polyvinylidene fluoride(PVDF)-type hollow fiber membrane modules with a treatment capacity of 10 ton/day. A pilot plant was installed in a sewage treatment plant and was operated with an intermittent aeration method which avoids any concentration gradient of suspended solids (SS) in the MBR. For continuous operation, the pilot plant was first tested with influent (mixed liquor suspended solid:MLSS of 1000-2000 mg/L) of aeration tanks in the sewage treatment plant. The MBR was pre-treated with washing water, 10% ethanol solution, 5% NaOCl solution and finally washing water, one after another. To demonstrate the effect of the MBR on sewage treatment, compared with conventional activated sludge processes, we investigated the relationships among permeate amount (LMH), change in operation conditions, influent MLSS level and sludge production. It was found that the optimum aeration rate and suction pressure were $0.3\;m^3$/min and 30~31 cmHg, respectively. Under stable conditions in aeration, suction pressure, influent flow rate and drainage, the SS removal efficiency was more than 99.99% even when the MLSS loading rate changes. Compared with conventional activated sludge processes, the MBR was more effective in cost reduction by 27% based on permeate amount and by 51.5% on sludge production.

• 산업기술연구
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• 제42권1호
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• pp.7-12
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• 2022

High nickel layered oxide cathodes are gaining increasing attention for lithium-ion batteries due to their higher energy density and lower cost compared to LiCoO₂. However, they suffer from the formation of residual lithium on the surface in the form of LiOH and Li₂CO₃ on exposure to ambient air. The residual lithium causes notorious issues, such as slurry gelation during electrode preparation and gas evolution during cell cycling. In this review, we investigate the residual lithium issues through its impact on cathode slurry instability based on deformed polyvinylidene fluoride (PVdF) as well as its formation and reduction mechanism in terms of inherently off-stoichiometric synthesis of high nickel cathodes. Additionally, new analysis method with anhydrous methanol was introduced to exclude Li⁺/H⁺ exchange effect during sample preparation with distilled water. We hope that this review would contribute to encouraging the academic efforts to consider practical aspects and mitigation in global high-energy-density lithium-ion battery manufacturers.

• 한국환경보건학회지
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• 제29권2호
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• pp.69-76
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• 2003

Hexavalent chromium may reduce on polyvinyl chloride (PVC) filter during sampling and storage of sample. Recently, new or modified filters for preventing Cr(VI) from the reduction has been introduced. Thus, this study was performed to compare the reduction behaviors of Cr(VI) on several sampling filters and to find the most appropriate filter for airborne Cr(VI) sampling in plating operation. The results were as follows. 1. There were statistically significant differences among PVC, polytetrafluoroethylene (PTFE). glass fiber (GF) and polyvinylidene fluoride (PVDF) filters in recovery rates of spiked Cr(VI) samples by storage time(p<0.05). There was no significant difference between PVC and PTFE filters(p>0.05). The PVC and PTFE filters showed higher recoveries than GF and PVDF filters(p<0.05). 2. The quartz fiber(QF) filter treated with an alkali solution(2% NaOH/3% Na$_2$CO$_3$, 1% NaOH) showed a significantly higher recovery of Cr(VI) by storage time than other filters(GF and QF filter)(p<0.05). There was no difference in recovery of Cr(VI) between alkali-treated and untreated GF it filters(p>0.05). But the QF filters treated with two alkali solution showed a significantly higher recovery than the untreated QF filter(p<0.05). There was no significant difference in recovery of Cr(VI) between QF filters treated with 1% NaOH and 2% NaOH/3% Na$_2$CO$_3$(p>0.05). In conclusion, treatment of QF fillers with alkali solution was most effective in protecting from the reduction of Cr(VI).

• 한국산학기술학회논문지
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• 제16권1호
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• pp.822-826
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• 2015

이 연구에서는 터널 시공 시 터널 배수관으로 유입되는 미세입자의 흐름과 이에 의한 물리/화학적 폐색현상에 따른 터널배수재의 성능저하를 PVDF film의 진동을 이용하여 성능을 향상시키는 방법의 적용 가능성에 대해 실내실험을 통하여 고찰하였다. 연구에서 터널로 유입되는 미세입자 슬러리 유입의 터널 환경을 모사하여 진행하였고 PVDF film을 이용한 기초 실험과 배수재를 모사한 모형실험으로 나누어 수행하였다. 기초 실험에서는 PVDF film에 50% 함수비(민물과 바닷물)의 점토를 흘려 주파수별 점토 슬러리의 흐름특성에 대한 효율성을 고찰하였으며 배수재 모사 실험에서는 배수관에 부직포를 부착시켜 슬러리의 흐름과 막힘 현상 해소에 대한 진동 효과를 고찰하였다. 실험결과는 진동에 의한 배수재의 배수성능, 즉 슬러리의 흐름과 막힘 해소현상이 아주 높게 나타났다. 이상의 실험결과를 종합하여 배수관을 기존 배수재와 융합, 응용, 활용할 수 있는 하이브리드 배수시스템을 개발할 수 있는 기초 자료를 확립하였다.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1711-1716
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• 2017

Uranium tetrafluoride ($UF_4$) is the most used nuclear material for producing metallic uranium by reduction with Ca or Mg. Metallic uranium is a raw material for the manufacture of uranium silicide, $U_3Si_2$, which is the most suitable uranium compound for use as nuclear fuel for research reactors. By contrast, ammonium uranyl carbonate is a traditional uranium compound used for manufacturing uranium dioxide $UO_2$ fuel for nuclear power reactors or $U_3O_8-Al$ dispersion fuel for nuclear research reactors. This work describes a procedure for recovering uranium and ammonium fluoride ($NH_4F$) from a liquid residue generated during the production routine of ammonium uranyl carbonate, ending with $UF_4$ as a final product. The residue, consisting of a solution containing high concentrations of ammonium ($NH_4^+$), fluoride ($F^-$), and carbonate ($CO_3^{2-}$), has significant concentrations of uranium as $UO_2^{2+}$. From this residue, the proposed procedure consists of precipitating ammonium peroxide fluorouranate (APOFU) and $NH_4F$, while recovering the major part of uranium. Further, the remaining solution is concentrated by heating, and ammonium bifluoride ($NH_4HF_2$) is precipitated. As a final step, $NH_4HF_2$ is added to $UO_2$, inducing fluoridation and decomposition, resulting in $UF_4$ with adequate properties for metallic uranium manufacture.

• 한국표면공학회지
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• 제26권2호
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• pp.82-86
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• 1993

An attempt was made to reduce directly Nd2O3 in a cryolited based fluoride bath. Neodymium metal was electrodeposited on the iron cathode to produce the Fe-Nd eutectic alloy in a liquid state at 90$0^{\circ}C$. Graphite was adopted for the anode and pure iron for the cathode. Electrolyte was composed of Na3AlF6 50wt.%. AlF3 34wt.% and Nd2O3 16wt.%. Analysis of typical alloy product showed Al 63.4wt.% Fe 26.9wt.% and Nd 7.0 wt.% The enrichment of neodymium in the alloy couldn't be obtained because aluminum codeposited with ne-odydmium. Experimental results proved that the cryolited based electrolyte was unstable for the electrolysis of rare earth oxides even though their prominent solubilities.

• 한국작물학회지
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• 제36권1호
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• pp.17-21
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• 1991

다량의 대기오염물(SO2, HF)이 배출되고 있는 공업단지 주변에서 재배되고 있는 수도의 생육에 이들 대기오염물이 미치는 영향을 구명하기 위하여 수도의 각종 형질, 수량, 대기중의 오염물 농도, 엽내유황 및 불소함량과 엽피해율을 조사하여 시험한 결과는 다음과 같다. 1. 엽내유황함량과 대기중 아황산가스 농도간에는 높은 정의 상관이 인정되었다. 2. 엽피해율 조사치는 대기오염에 의한 수량감소의 가장 중요한 지표로 이용 할 수 있다. 3. 본 조사지역에서는 아황산가스보다 불화수소의 배출량이 적지만 엽피해의 발생에는 불소의 관련성이 아황산가스보다 높았다. 4 수량형질의 수량에 대한 기여정도는 주당수수가 제일 컸으며, 주당수수는 엽내 불소함량과 깊은 관련성이 인정되었다. 5. 엽내 유황함량은 수량 및 수량형질과 상관성이 인정되지 않았다.