• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.902-910
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• 2018

In recent times, development of nanofluid insulation for power transformers is a hot research topic. Many researchers reported the enhancement in dielectric characteristics of nano modified mineral oils. Considering the drawbacks of petroleum based mineral oil, it is necessary to understand the dielectric characteristics of nanofluids developed with natural ester based oils. Palm oil has better insulation characteristics comparable to mineral oil. However very few research reports is available in the area of nanofluids based on palm oil. Partial discharge (PD) is one of the major sources of insulation performance degradation of transformer oil. It is essential to understand the partial discharge(PD) characteristics by collecting huge data base of PD performance of nano modified palm oil which will increase its confidence level for power transformer application. Knowing these facts, in the present work, certain laboratory experiments have been performed on PD characteristics of nano $SiO_2$ modified palm oil at different electrode configurations. Influence of concentration of nano filler material on the PD characteristics is also studied. Partial discharge inception voltage, Phase resolved partial discharge (PRPD) pattern, PD signal time-frequency domain characteristics, PD signal equivalent timelength-bandwidth mapping, Weibull distribution statistical parameters of PRPD pattern, skewness, repetition rate and phase angle variations are evaluated at different test conditions. From the results of the experiments conducted, we came to understand that PD performance of palm oil is considerably enhanced with the addition of $nano-SiO_2$ filler at 0.01%wt and 0.05%wt concentration. Significant reduction in PD inception voltage, repetition rate, Weibull shape parameter and PD magnitude are noticed with addition of $SiO_2$ nanofillers in palm oil. These results will be useful for recommending nano modified palm oil for power transformer applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.235.2-235.2
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• 2015

The front transparent conductive oxide (TCO) films must exhibit good transparency, low resistivity and excellent light scattering properties for high efficiency amorphous silicon (a-Si) thin film solar cells. The light trapping phenomenon is limited due to non-uniform and low aspect ratio of the textured glass [1]. We present the low cost electrochemically deposited uniform zinc oxide (ZnO) nanorods with various aspect ratios for a-Si thin film solar cells. Since the major drawback of the electrochemically deposited ZnO nanorods was the high sheet resistance and low transmittance that was overcome by depositing the RF magnetron sputtered AZO films as a seed layer with various thicknesses [2]. The length and diameters of the ZnO nanorods was controlled by varying the deposition conditions. The length of ZnO nanorods were varied from 400 nm to $2{\mu}m$ while diameter was kept higher than 200 nm to obtain different aspect ratios. The uniform ZnO nanorods showed higher haze ratio as compared to the commercially available FTO films. We also observed that the scattering in the longer wavelength region was favored for the high aspect ratio of ZnO nanorods and much higher aspect ratios degraded the light scattering phenomenon. Therefore, we proposed our low cost and uniform ZnO nanorods for the high efficiency of thin film solar cells.

• 한국세라믹학회지
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• 제25권1호
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• pp.42-48
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• 1988

Commercially available PTCR (Postive Temperature Coefficient of Resistivity) ceramics which have low room temperature resistance, high PTC effect and temperature coefficient were prepared by La3+ doped semiconducting barium calcium titanate soild solutions. PTCR characteristics were remarkably improved by addition of AST (1/3 Al2O3$.$3/4SiO2$.$1/4TiO2) and MnCl2. That can be explained by formation of liquid phase during sintering and acceptor level on the intergranular layer. Resistivity anormaly increased with decreasing cooling rate. Optimum manufacturing conditions were cooling rate below 100$.$C/hr, Ca and Mn content of 4 mol% &, 0.09-0.12mol% respectively.

• 한국토양비료학회지
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• 제49권4호
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• pp.293-299
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• 2016

The chemical properties of paddy fields in Gangwon province were monitored every 4 years from 2003 to 2015 in order to provide basic information for soil fertility management of paddy fields. In 2015, the soil chemical properties of paddy fields were 5.9 in pH, $22g\;kg^{-1}$ in organic matter (OM), and $123mg\;kg^{-1}$ in available (Avail.) phosphate $P_2O_5$. Exchangeable (Exch.) potassium (K), calcium (Ca) and magnesium (Mg) were 0.39, 4.8 and $0.9cmolc\;kg^{-1}$, respectively, and Avail. $SiO_2$ was $170mg\;kg^{-1}$. In the long-term analysis, the contents of Avail. $SiO_2$, Exch. K and pH of paddy soils showed increasing tendency. However, Avail. $P_2O_5$, Exch. Ca and Mg tended to decrease, and there were no significant changes in the contents of OM. Soil OM, Avail. $P_2O_5$ and $SiO_2$ were not different among the different topographical sampling sites. However, the mean value of Exch. K and Ca were different among the different topographical sampling sites, and exceeded optimal values in the fluvio-marine plains. Different soil texture resulted in different soil pH, while no difference for OM, Avail. $P_2O_5$ and $SiO_2$. Paddy soil samples within appropriate pH range increased from 65% in 2003 to 77% in 2007, 68% in 2011, and 71% in 2015. In case of Avail. $SiO_2$, soil samples within appropriate range increased from 20% in 2003, to 37% in 2007, 29% in 2011, and 45% in 2015. Meanwhile, Cd and Pb were distributed to less than 5% of soil pollution standards. Cu, As and Zn were distributed to less than 10%, 15% and 20%, respectively. Therefore, paddy soil in Gangwon Province was judged to be safe. As a result, paddy fields with more or less in nutrient level need to be fertilized based on the soil analysis. And the application of silicate fertilizer is strongly recommended to those of paddy fields in need. In addition, soil management including the cultivation of green manure crop or application of rice straw is necessary to increase the organic matter content of paddy soil.

• 한국토양비료학회지
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• 제18권2호
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• pp.194-200
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• 1985

담수(湛水)에 의한 토양화학성분(土壤化學成分) 함량변화(含量變化)와 수도수량(水稻收量)과의 관계(關係)를 밝히고져 토양화학성(土壤化學性)이 상이(相異)한 9개 토양통(土壤統)으로 실내(室內) 및 포장시험(圃場試驗)을 실시(實施)하였다. 포장시험(圃場試驗) 결과(結果) 토양간(土壤間)의 무비구수량(無肥區收量)과 최고수량(最高收量)은 유의성(有意性)있는 상관(相關)이 있었지만 상대수량(相對收量)은 54~76으로서 토양간(土壤間) 차이(差異)가 컸다. 무비구(無肥區) 수량(收量)과 토양화학성분(土壤化學成分) 함량(含量)과의 관계(關係)는 담수무처리(湛水無處理)의 암모니아태 질소(窒素)에서만 상관(相關)이 있었다. 담수항온시험(湛水恒溫試驗) 결과(結果) pH에서 무비구(無肥區) 수량(收量)이 높았던 부용(芙蓉), 사촌(沙村), 지산통(芝山統) 담수(湛水) 5~25일까지의 건토(乾土)에 대한 pH상승폭(上昇幅)이 다른 토양(土壤)보다 컸고 담수(湛水) 70일까지 건토(乾土)의 pH가(價) 수준(水準)을 유지(維持)하였다. 토양별(土壤別) 암모니아태 질소함량(窒素含量)은 건토(乾土)의 유기물함량(有機物含量)과 관련(關聯)이 적었고 무처리담수구(無處理湛水區)와 삼요소담수구(三要素湛水區)의 함량(含量) 차이(差異)가 컸던 토양(土壤)들이 시비효율(施肥效率)이 높은 편(便)이었다. 건토(乾土)의 유효인산(有效燐酸) 및 유기물함량(有機物含量)이 낮고 점토함량(粘土含量)이 높은 전북(全北), 대정(大靜), 췌동통(萃東統)은 담수(湛水)에 의한 인산유효화량(燐酸有效化量)이 적고 포장시험(圃場試驗)에서의 인산시비효율(燐酸施肥效率)이 컸다. 점토함량(粘土含量)이 낮은 사촌(沙村), 용지(龍池), 예천통(醴泉統)은 그 반대(反對)였다. 대체로 담수(湛水)에 의해서 유효규산함량(有效珪酸含量)은 증가(增加)하였지만 건토(乾土)의 유효규산함량(有效珪酸含量)이 극히 높은 전북(全北), 대정(大靜), 췌동통(萃東統)은 담수무처리(湛水無處理)에서 건토(乾土)와 비슷하거나 오히려 감소(減少)하였다.

• 한국식품위생안전성학회지
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• 제13권3호
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• pp.252-257
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• 1998

죽염은 예로부터 위궤양 등의 소화기 질환에 민간요법으로 사용되어 왔으며 대나무 통속에 천일염을 넣고 소나무 장작불로 9번 구워서 만들어진다. 본 연구에서는 죽염의 특성분석시험과 항위궤양 시험 중 위산분비 억제도 시험을 실시하였다. 특성분석시험으로 ICP(Inductively Coupled Plasma) spectrometer, IC(Ion Chromatograph), XRD(X-ray Diffractrometer), 전자현미경을 이용하여 천일염과 죽염제품 A, B, C의 성분 및 구조분석을 실시하였다. 그 결과, 성분분석시험에서 죽염은 천일염에 비하여 칼륨, 규소, 철 및 인삼염의 농도가 증가하였으며 황산염은 감소되었음을 알 수 있었다. 죽염 중 물불용분에 포함된 화합물은 MgO가 가장 많았고, $SiO_2,\;Mg_2Si_O4\;및\;CaMgSiO_4$등도 확인되었다. 구조분석에서 죽염은 천일염에 비하여 대체로 표면이 매끄럽고 용융되어 있는 것으로 나타났다. 죽염제품 A, B, C 중 A를 사용하여 위산분비에 미치는 영향을 측정하였다. SD계 랫드에 죽염, 천일염, 시약급 NaCl, 증류수를 1일 1회 28일 동안 각 0.2, 1.0, 2.0 g/kg으로 경구 투여하여 마지막 투여 후 24시간 절식시켜 Shay 유문 결찰법을 이용하여 채취한 위액의 총량, pH, 총위산도, 펩신활성도를 측정하였다. 실험결과 각 투여 용량군에서 용매 대조군에 비하여 통계학적으로 유의성 있는 차이를 나타내지 않았으며 죽염을 포함한 여러 가지 염투여는 위산분비에 영향을 주지 않았다. 따라서 28일간 죽염투여에 의한 위궤양 치료효과는 기대하기 어려울 것으로 사료된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.236.1-236.1
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• 2015

The surface morphology of front transparent conductive oxide (TCO) films is very important to achieve high current density in amorphous silicon (a-Si) thin film solar cells since it can scatter the light in a better way. In this study, we present the low cost hydrothermal deposited uniform zinc oxide (ZnO) nano-flower structure with various aspect ratios for a-Si thin film solar cells. The ZnO nano-flower structures with various aspect ratios were grown on the RF magnetron sputtered AZO films. The diameters and length of the ZnO nano-flowers was controlled by varying the annealing time. The length of ZnO nano-flowers were varied from 400 nm to $2{\mu}m$ while diameter was kept higher than 200 nm to obtain different aspect ratios. The ZnO nano-flowers with higher surface area as compared to conventional ZnO nano structure are preferred for the better light scattering. The conductivity and crystallinity of ZnO nano-flowers can be enhanced by annealing in hydrogen atmosphere at 350 oC. The vertical aligned ZnO nano-flowers showed higher haze ratio as compared to the commercially available FTO films. We also observed that the scattering in the longer wavelength region was favored for the high aspect ratio of ZnO nano-flowers. Therefore, we proposed low cost and vertically aligned ZnO nano-flowers for the high performance of thin film solar cells.

• 한국토양비료학회지
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• 제49권3호
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• pp.275-281
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• 2016

The aim of this study was to examine the selected soil chemical properties of paddy fields in different topographic areas to efficiently manage nutrient valances of the paddy fields in Jeonbuk Province. Three-hundred soil sampling sites in paddy fields were selected from the different topographic areas in Jeonbuk Province. The soil samples were collected every four years from 1999 to 2015. Soil pH and exchangeable K and Mg concentrations declined during the experimental periods. However, almost all the chemical properties were within the proper levels for paddy soil, except exchangeable Mg concentration. Distributed areas of the paddy fields with soil pH below 5.5 continuously increased, but the paddy fields with lower concentrations of soil organic matter and available $P_2O_5$ than the proper levels declined after 2007. In addition, the paddy fields with available $SiO_2$ below the proper concentration decreased from 83.3% of the total paddy fields studied in 1999 to 61.0% of the total fields investigated in 2015. The paddy fields with lower exchangeable K and Mg than the proper levels increased after 2003 whereas the fields with lower exchangeable Ca concentration decreased. Dominant landform of coastal and plain areas was fluvio-marine plains that was distributed in 53.7% and 40.9%, respectively. Local valley and fans was a dominant landform of mountainous and middle-mountainous areas, which was 51.8% and 67.6%, respectively. Dominant soil textures distributed in coastal and plain areas were silty loam and loam. Those in mountainous and middle-mountainous areas were sandy loam and loam, respectively. Soil pH was relatively higher in coastal area and the comparatively higher content of soil organic matter was found in costal area than other areas. The concentrations of available $P_2O_5$, exchangeable Ca, and exchangeable Mg were generally higher in mountainous, coastal, plain areas, respectively, but available $SiO_2$ and exchangeable K concentrations were not significantly different among the different topographic areas.

• 한국세라믹학회지
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• 제41권5호
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• pp.381-387
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• 2004

현재 상용화되어 있는 PDP용 형광체의 물성에 있어서 청색 형광체는 열화, 색도변화, 휘도, 그리고 녹색 형광체는 잔광시간과 색순도, 적색 형광체의 경우에는 색순도에 대한 개선이 필요한 것으로 알려져 있다. 그 중 녹색 형광체로 Willemite 구조의 ZnSiO:Mn 형광체의 경우 발광효율은 우수하나 반면에 잔광시간이 길고 색순도(color purity)가 좋지 않다는 단점을 가지고 있다. 따라서 본 연구에서는 미세조정 조합화학기법을 이용하여 PDP에 적합한 새로운 고효율 형광체를 개발하였다. 화학적으로 정량인 가돌리늄 인산염(gadolinium phosphorous) 대신 인산을 과잉으로 첨가하여 탐색한 다음 과잉인산(excess phosphorous) 첨가 조성을 유지한 채로 가돌리늄(gadolinium)의 일정분율을 이트륨(yttrium)으로 치환하였다. 그 결과 최적 형광체 조성은 (G $d_{0.74}$ $Y_{0.11}$T $b_{0.15}$) $P_{1.15}$ $O_{{\delta}}$이였으며, 현재 상용화된 Z $n_2$ $SiO_4$:Mn 형광체에 비해 상대적으로 높은 발광효율을 나타내었으며, 잔광시간도 줄일 수 있게 되었다.

• Transactions on Electrical and Electronic Materials
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• 제12권1호
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• pp.32-34
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• 2011

A zero-shrinkage sintering process in which the shrinkage of the x-y axis is controlled to be zero is in great demand due to the high integration trend in ceramic modules. Among the zero-shrinkage sintering processes available, the glass infiltration method proposed in the preliminary study with an $Al_2O_3/Glass/Al_2O_3$ structure is one promising method. However, problems exist in regard to the glass infiltration method, including partially incomplete joining between $Al_2O_3$ and glass layers due to the precipitate of Ti-Pb rich phase during the sintering process. Therefore, we wish to solve the de-lamination problems and suggest a mechanism for delamination and the solutions in the zero-shrinkage low temperature co-fired ceramic (LTCC) layers. The de-lamination problems diminished using the Pb-BSi-O glass without $TiO_2$ in Pb-B-Ti-Si-O glass and produced a very dense zero-shrinkage LTCC.