• 한국진공학회지
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• 제19권1호
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• pp.66-71
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• 2010

PDP를 비롯한 형광체를 이용하는 디스플레이 분야에서 현재 마이크로미터($\mu}$-meter) 이상의 크기를 갖는 기존의 벌크(bulk) 형광체를 능가하는 성능과 새로운 물성을 나타내는 나노형광체(nanophosphor) 개발 및 응용에 대한 연구가 절대적으로 필요한 시점이다. 따라서 본 실험에서는 나노 사이즈의 평균 입자 크기를 갖는 구형의 $Zn_2SiO_4:Mn$ 형광체 입자를 초음파 분무열 분해(ultrasonic spray pyrolysis) 방법을 이용하여 합성하였다. 구형의 형광체 입자의 크기는 분무 장치의 droplet separator를 도입하여 조절하였다. 2 mol%의 망간을 도핑하여 합성한 $Zn_2SiO_4:Mn$ 입자는 시간이 지남에 따라 감소되고, 최근에 고상에서 합성하여 상용화된 물질에 비교할 수 있을 만한 빛 방출의 세기를 가졌다. 형광체 입자의 크기는 무기질 염의 농도가 0에서 5 M로 증가함에 따라 $1\;{\mu}m$에서 $0.2\;{\mu}m$로 감소하였다. 0.5 M 이상의 농도의 전구체 용액에서 얻어진 형광체 입자의 빛 방출은 상용화되어 있는 물질과의 비교를 통해 알아보았다.

• 광물과 암석
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• 제33권4호
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• pp.361-376
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• 2020

전통 회화 및 단청용 채색 안료 중 녹색을 표현하기 위해 사용된 동록안료의 재료과학적 특성 및 안정성을 알아보기 위하여 염화동(Atacamite), 초산동(Verdigris) 2종의 안료를 이용하여 평가를 진행하였다. 구성광물 분석 결과, K-AA는 아타카마이트(Atacamite)가 주요 구성광물로 천연 광물성 재료로 확인되고 K-VA는 호가나이트(Hoganite)로 확인되었다. 동록안료의 안정성을 저해하는 요인을 찾고자 UV 노출, CO2/NO2 가스부식 및 염수분사 시험 등의 분석을 실시하였다. 색상 안정성을 가장 크게 저해하는 요인은 두 안료 모두 염수분사 시험으로 시료 표면에 염생성물이 생성되어 변질되는 등 손상이 가중되었다. 또한 대기오염물질인 NO2의 영향도 두 안료 모두 육안으로 인지될 정도로 색이 변하여 주요 손상 요인으로 작용되는 것으로 판단된다. 특히 K-VA의 경우 K-AA와는 달리 UV 노출 평가 후 녹색에서 흑색으로 변하면서 본래의 색상을 완전히 잃어리는 것으로 K-VA의 주성분인 Hoganite가 UV 노출 후 Tenorite로 물질이 변했기 때문으로 판단된다. 두 안료의 대기환경 영향 평가 결과, K-AA에 비해 K-VA이 대기환경 영향에 상대적으로 취약한 모습을 보였다.

• Journal of Pharmaceutical Investigation
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• 제38권4호
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• pp.249-254
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• 2008

Solid dispersions of poorly water-soluble drug, atorvastatin, were prepared with Eudragit L100 to improve the solubility by spray dryer. To investigate the correlation between physicochemical properties and dissolution rate of solid dispersions, the samples were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and fourier transform infrared spectroscopy (FT-IR). SEM and DSC were found that atorvastatin is amorphous in the Eudragit L100 solid dispersion. FT-IR was used to analyze the salt formation by interaction between atorvastatin and Eudragit L100. The dissolution rate of solid dispersed atorvastatin was markedly increased compared to drug powder in stimulated intestinal juice (pH 6.8). Thus, the solid dispersed atorvastatin using the spray drying method with Eudragit L100 may be effective for the bioavailability.

• 한국축산식품학회지
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• 제38권5호
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• pp.866-877
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• 2018

Cheese emulsion is an intermediate product for the production of cheese powder and needs to be stable, homogeneous and pumpable characteristics to convey to the spray drier. This study was conducted to evaluate the effects of fat reduction and emulsifying salt (ES) amount in cheese emulsion systems on the physicochemical characteristics. Reduced-fat (RF) and full-fat (FF) white-brined cheese emulsions were produced with different dry matters (DM; 15%-25% excluding ES) and ES concentrations (0%-3% based on cheese weight). Stable cheese emulsion was obtained at lower DM in RF cheese emulsion than that of FF cheese emulsion. Reduction in the amount of ES resulted in instability of both emulsions. Apparent viscosity with pseudoplastic flow behavior significantly increased with the decrease of fat content in stable cheese emulsions. Microstructure of emulsions appeared to be related to the fat content, stability and degree of emulsification. Reduction of fat content caused to get less lightness and more greenness in color, whereas yellowness was significantly decreased by increase in the amount of ES. In conclusion, fat reduction resulted in higher viscosities of cheese emulsion due to inducing the increment of protein, and the addition amount of ES considered as very important factor to produce stable cheese emulsion without protein precipitation or cream separation. Therefore, for preparation of RF cheese emulsion using a variety of white-brined cheese, lower amounts of DM would be suggested in this study to obtain homogenous droplets in the atomizing process of spray drying.

• 한국해양공학회지
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• 제25권1호
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• pp.32-38
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• 2011

Galvanized steel has gone through a chemical process to keep it from corroding. The steel gets coated in layers of zinc because rust will not attack this protective metal. For countless outdoor, marine, or industrial applications, galvanized steel is an essential fabrication component. The reduction of the corrosion rate of zinc is an important topic. In the past, a very popular way to reduce the corrosion rate of zinc was to use chemical conversion layers based on $Cr^{+6}$. However, a significant problem that has arisen is that the use of chromium salts is now restricted because of environmental protection legislation. Therefore, it is very important to develop new zinc surface treatments that are environmentally friendly to improve the corrosion resistance of zinc and adhesion with a final organic protective layer. In this study, a Urethane solution (only Urethane 20 wt.%; S-700) and an organic/inorganic solution with Si (Si polysilicate 10 wt.% + Urethane 10 wt.%; LRO-317) are used. Based on the salt spray test of 72 h, S-700 and LRO-317 had a superior effect for the corrosion resistance on EGI and HDGI, respectively.

• 한국해양공학회지
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• 제24권5호
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• pp.67-74
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• 2010

Chromate conversion coating is a coating technique used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, tin, and their alloys to slow corrosion. The process uses various toxic chromium compounds, which may include hexavalent chromium. The industry is developing less toxic alternatives in order to comply with substance restriction legislation, such as RoHS. One alternative is to develop a Cr-free coating solution. In this study, eco-friendly, Cr-free solutions (urethane solution S-700, organic/inorganic solution with Si LRO-317) were used. Test specimens were dried in a drying oven at $190^{\circ}C$ for 3, 5, 7, and 9 minutes. Corrosion resistance was evaluated using a salt spray test for 72 hours. The results show that the optimum corrosion resistance was achieved at $190^{\circ}C$ for five minutes for EGI and three or five minutes for HDGI, respectively. The adhesive properties of the two types of coating solutions were superior regardless of drying time.

• 열처리공학회지
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• 제19권4호
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• pp.200-207
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• 2006

In addition to the basic properties of the base and top coating agents, corrosion resistance of non-chrome magni 565 coating and characteristics of coating film when coated to steel substrate were studied. The system had a good wettability at room temperature. Moreover, both the contact angle and surface tension were affected little by the viscosity of coating agent and surface roughness of the steel substrate. And the samples coated with optimal conditions showed a great corrosion resistance in salt spray test with 1500 hours or longer of initial appearance time of rust. The coating film was composed of overlapping layer of zinc and aluminium flakes, and the thickness of base coat increased with an increase of base coat viscosity. Based on the C-F peaks of 1,1-Difluoroethaen homo-polymer, it was thought that the base coat was an inorganic polymer bond layer. Meanwhile, the top coat showed C-F peaks of polytetrafluoroethylene with C-H peaks of phenol in FT-IR analysis. From the lower weight loss of base coat in TG analysis, it was thought that cross linking density of base coat was larger than that of top coat. It was thought that the small exothermic reactions observed in DSC curves were due to the thermosetting resins contained in the coating agents. Compared to the non-coated specimen, the coated sample showed more higher polarization resistance and corrosion potential with lower corrosion current density.

• 동력기계공학회지
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• 제13권3호
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• pp.33-39
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• 2009

The aim of this study is to analyze the welds characteristics of the 205 stainless steel pipe for application of street pole material. The welds corrosion behavior of STS 205 pipe in 0.1 N sulphuric acid solution and 5% NaCl solution at room temperature was studied using both salt spray test and potentiodynamic polarization experiment. The morphology and components of corrosion products on surface of STS 205 pipe welds were investigated using SEM/EDX. The tensile strength and yield strength values of STS 205 plate were 715 MPa and 369 MPa respectively. The microvickers hardness values of STS 205 pipe welds were slightly increased than that of STS 304 pipe welds. Corrosion current density($I_{corr.}$) and critical current density($I_{crit.}$) values of STS 205 pipe welds in 3.5% NaCl solution were $1.89{\times}10^{-6}$ $A/cm^2$ and $15.8{\times}10 ^{-6}$ $A/cm^2$. The corrosion resistance of SIS 205 pipe welds was similar to its STS 304 pipe welds. The STS 205 and 304 pipe welds passive films were chromium oxide. Especially, the STS 205 pipe welds showed good corrosion resistance in 0.1 N sulphuric acid. This is attributed to the forming of protective chromium oxide on the surface of STS 205 pipe welds.

• 한국구조물진단유지관리공학회 논문집
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• 제17권6호
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• pp.95-103
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• 2013

비파괴 기법중 반전위 측정법은 부식가능성을 정량적으로 판별할 수 있으므로 꾸준하게 사용되고 있다. 본 연구에서는 피복두께를 10, 30, 60mm, 물-시멘트비를 0.35, 0.55, 0.70으로 변화시킨 RC 시편을 대상으로 비말대 지역을 모사한 촉진염해분무실험을 수행하였다. 45일간의 촉진 염해 분무시험을 수행한 뒤, RC 시편에 대하여 반전위값을 측정하였다. w/c 0.55 조건에서 피복두께가 10mm인 RC 시편은 부식이 발생하였으며, w/c 0.7인 경우 피복두께 30mm인 시편에서도 부식이 발생하였다. 실험결과를 이용하여 물-시멘트비와 피복두께를 변수로 하는 반전위 평가식을 제안하였으며, 비말대지역에서 부식을 억제할 수 있는 조건을 도출하였다. 또한 Life 365 프로그램을 이용하여 비부식 조건의 w/c와 피복두께를 분석하였으며, 본 연구의 결과인 반전위 측정값과 비교하였다.

• 한국재료학회지
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• 제27권7호
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• pp.381-385
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• 2017

In order to replace 14K white gold alloys, the properties of 5K white gold alloys (Au20-Ag80) were investigated by changing the contents of In (0.0-10.0 wt%). Energy dispersive X-ray spectroscopy (EDS) was used to determine the precise content of alloys. Properties of the alloys such as hardness, melting point, color difference, and corrosion resistance were determined using Vickers Hardness test, TGA-DTA, UV-VIS-NIR-colorimetry, and salt-spray tests, respectively. Wetting angle analysis was performed to determine the wettability of the alloys on plaster. The results of the EDS analysis confirmed that the Au-Ag-In alloys had been fabricated with the intended composition. The results of the Vickers hardness test revealed that each Au-Ag-In alloy had higher mechanical hardness than that of 14K white gold. TGA-DTA analysis showed that the melting point decreased with an increase in the In content. In particular, the alloy containing 10.0 wt% In showed a lower melting temperature (> $70^{\circ}C$) than the other alloys, which implied that alloys containing 10.0 wt% In can be used as soldering materials for Au-Ag-In alloys. Color difference analysis also revealed that all the Au-Ag-In alloys showed a color difference of less than 6.51 with respect to 14K white gold, which implied a white metallic color. A 72-h salt-spray test confirmed that the Au-AgIn alloys showed better corrosion resistance than 14K white gold alloys. All Au-Ag-In alloys showed wetting angle similar to that of 14K white gold alloys. It was observed that the 10.0 wt% In alloy had a very small wetting angle, further confirming it as a good soldering material for white metals. Our results show that white 5K Au-Ag-In alloys with appropriate properties might be successful substitutes for 14K white gold alloys.