• Title/Summary/Keyword: fluoride reduction

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A Study on the Preparation and Dielectric Characteristic of $\beta$-PVDF Vapor Deposited Thin Films by Applied Electric Field Method (전계인가법을 이용한 $\beta$-PVDF 증착 박막의 제조와 유전특성에 관한 연구)

  • 박수홍;이덕출
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.3
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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.

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Study of the Changes in Composition of Ammonium Diuranate with Progress of Precipitation, and Study of the Properties of Ammonium Diuranate and its Subsequent Products Produced from both Uranyl Nitrate and Uranyl Fluoride Solutions

  • Manna, Subhankar;Kumar, Raj;Satpati, Santosh K.;Roy, Saswati B.;Joshi, Jyeshtharaj B.
    • Nuclear Engineering and Technology
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    • v.49 no.3
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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.

Antimicrobial Effect of Mouthwash against Streptococcus mutans by Visual Staining Method (시각적 염색 방법을 이용한 마우스워시의 구강균에 대한 항균효과 확인)

  • Park, Taehun;Cho, Jeong Hun;Sung, Youngeun;Cho, Jun-Cheol;Shin, Kyeho
    • Journal of the Society of Cosmetic Scientists of Korea
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    • v.40 no.2
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    • pp.187-193
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    • 2014
  • Dental caries are one of the most common oral diseases and Streptococcus mutans (S. mutans) plays an important role in the initiation and progression of dental caries. Oral malodor is primarily the result of microbial metabolism such as Porphyromonas gingivalis (P. gingivalis) that produce volatile sulfur compounds (VSCs), causing oral malodor. Prevotella intermedia (P. intermedia) is known as typical periodontopathic bacteria, and periodontal disease is chronic inflammatory disease that leads to damage of gingival connective tissue and alveolar bone, eventually loss of teeth. In this study, we investigated antimicrobial effect of mouthwash containing cetylpyridinium chloride (CPC), sodium fluoride (NaF), green tea water extract and pine needles water extract against cariogenic and periodontopathic bacteria sucn as S. mutans, P. gingivalis and P. intermedia. As a result, the reduction ratios of S. mutans and P. gingivalis were 4.00 Log and 4.68 Log reduction for 30 s, and P. intermedia were 2.40 Log reduction for 30 s and 2.70 Log reduction for 60 s. Dentocult SM Strip mutans (SM Strip) provides easy detection of visual data showing a significant inhibition on S. mutans. In conclusion, we expected that mouthwash containing CPC, NaF, green tea water extract and pine needles water extract could help preventing the dental disease like dental caries and oral malodor.

Optimum Operation of a PVDF-type Hollow Fiber Membrane Bioreactor for Continuous Sewage Treatment

  • Shin, Choon-Hwan
    • Journal of Environmental Science International
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    • v.19 no.11
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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.

A Mechanism Study on Formation and Reduction of Residual Li of High Nickel Cathode for Lithium-ion Batteries (층상계 하이니켈 양극재의 잔류 리튬 생성 및 저감 메커니즘 연구)

  • MinWook, Pin;Beom Tak, Na;Tae Eun, Hong;Youngjin, Kim
    • Journal of Industrial Technology
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    • v.42 no.1
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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.

Comparison of Sampling Filters for Airborne Hexavalent Chromium in Plating Operation (도금공정 공기중 6가 크롬 시료채취여과지 비교에 관한 연구)

  • 이병규;신용철
    • Journal of Environmental Health Sciences
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    • v.29 no.2
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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).

Enhancing maintenance performance of tunnel drainage using vibration from polyvinylidene fluoride(PVDF) film (압전필름의 진동을 활용한 터널배수재 유지관리 성능 개선)

  • Xin, Zhen-Hua;Moon, Jun-Ho;Song, Young-Karb;Kim, Young-Uk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.1
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    • pp.822-826
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    • 2015
  • This study investigated the possible use of vibration from polyvinylidene fluoride(PVDF) film to enhance the performance of the deteriorated tunnel drainage due to physical/chemical clogging of the fine particles through a series of laboratory experiments. The test program was consisted of two different experiments, fundamental investigation and drainage model test. In the fundamental investigation, flow of clay slurry mixed with 50% water (freshwater and brine) on PVDF film with various frequencies was examined. In the model tests, slurry clogging to the woven fiber attached to drainage pipe and its reduction by vibration was investigated. Results of the experiment show that vibration from PVDF film enhances the drain performance significantly. Based upon the investigation, it gives an essential data that are needed for a potential use of hybrid drainage system with PVDF.

Production of uranium tetrafluoride from the effluent generated in the reconversion via ammonium uranyl carbonate

  • Neto, Joao Batista Silva;de Carvalho, Elita Fontenele Urano;Garcia, Rafael Henrique Lazzari;Saliba-Silva, Adonis Marcelo;Riella, Humberto Gracher;Durazzo, Michelangelo
    • Nuclear Engineering and Technology
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    • v.49 no.8
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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.

Characteristics of Cryolite as an Electrolyte for Reduction of Nd$_2$O$_3$ (네오디뮴 산화물의 전해환원시 전해질로서 빙정석의 특성)

  • 남상욱;백영현
    • Journal of the Korean institute of surface engineering
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    • v.26 no.2
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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.

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Effect of Sulfur Dioxide and Hydrogen Fluoride on Rice Plant Growth in Industrial Estate (공업단지 주변에서의 아황산가스 및 불화수소가 수도 생육에 미치는 영향)

  • Wan Cheol, Park;Kwang-Ho Kim;Ki Joon, Kim
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.36 no.1
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    • pp.17-21
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    • 1991
  • The study was performed to investigate the effects of gaseous emission of sulfur dioxide and hydrogen fluoride on the growth of rice plant under stressed field conditions. This study is specifically dealt with multiple effects of sulfur dioxide and hydrogen fluoride on various plant growth indicators such as leaf damage, weight of grain, panicles per hill, spikelets per panicle and percent fertility. It appears that there is a good correlation between ambient concentrations of sulfur oxides and sulfur contents found in leaves with an average correlation coefficient of 0.868 within a 1% significance level. A better multiple correlation was found between percent leaf damage and sulfur and fluorine contents found in leaf with a significance of 1% level. The correlation coefficient ranges from 0.807 to 0.978 with an average being 0.922. An evaluation of data observed has demonstrated that both panicles per hill and percent fertility are significantly affected by air pollutants. As expected, hydrogen fluorides have more effects than sulfur oxides. It is, however, interesting to note that spikelets per panicle has slightly been affected while no indication of effects on l000-grain weight has been observed. This may lead to a conclusion that a reduction in yield of rice under polluted field conditions may have more been caused by the diminution panicles per hill and percent fertility rather than by the diminution of spikelets per panicle and grain weight.

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