• 폴리머
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• 제30권1호
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• pp.22-27
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• 2006

상호에스테르 교환반응에 의한 폴리(에틸렌 나프탈레이트)/폴리(부틸렌 테레프탈레이트) (PEN/PBT) 블렌드의 물성 변화에 대하여 살펴보았다. PBT를 PEN에 블렌딩하는 경우 상대적으로 낮은 PBT의 용융점도에 의하여 PEN의 용융점도가 감소됨을 확인할 수 있었으며 PEN과 PBT의 상호에스테르 교환반응에 의하여 추가적인 용융점도 감소가 있음을 알 수 있었다. 윤활제로 calcium stearate(CaST)를 첨가하면 CaST는 윤활제로서의 역할과 함께 PEN과 PBT의 상호에스테르 교환반응을 촉진하는 역할을 하여 용융점도가 현저하게 감소됨을 확인하였다. 상호에스테르 교환반응을 이용한 반응 용융가공은 PEN과 PBT그리고 이들 블렌드의 분자량을 감소시키며 그 결과 기계적 물성 감소를 초래함을 확인할 수 있었다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.154-159
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• 1999

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90$\pm$2$^{\circ}C$, 25 wt% NaOH). All of the specimens, \circled1Si$_3$N$_4$, \circled23Y-TZP and \circled33Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-Hipped, and then polished up to 0.02 ${\mu}{\textrm}{m}$Ra of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress or 3.76 Gra and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_3$N$_4$. 3Y-TZP alloyed with 5 wt% CeO$_2$specimens were not worn after aging and no phase transformation occurred while aging.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.229-234
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• 2003

As electrorheological fluid(ER fluid) has a characteristic that apparent viscosity varies when electric field applied, so rheological characteristic(yield stress & viscosity) changes in proportion to the electric field applied and the response time is very short within a few miliseconds . In case of using ER fluid for journal bearing as lubricant, it is estimated that it's possible to realize very effective journal bearing system that is not complicate and has a very quick response time. It is necessary to examine the influence of rheological characteristic that varies with electric field applied on bearing characteristic to apply ER fluid to journal bearing, however there are few studies for about that. As for the journal bearing, it comes under high shear flow mode that has shear rate range of $10^3\~10^4s^{-1}$ because rotational speed is very high and clearance is small. But most of the studies for about ER fluid issued until now is about the range of $10\~10^2s^{-1}$. So, there are a lot of difficulties to understand the characteristic offish shear flow mode and furthermore it is restricted to make an experiment for about the characteristic of ER fluid because of the limitation of experimental equipment. The equipment was prepared to make an experiment lot high shear flow mode that has the range of $10^3\~10^4s^{-1}$ using ER fluid that is composed of silicon oil with dispersed particle of starch. Using the above system, the fluid characteristic of ER fluid was studied.

• Archives of Pharmacal Research
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• 제23권5호
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• pp.507-512
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• 2000

This study set out to improve the physical and pharmaceutical characteristics of the present formulation using an appropriate experimental design. The work described here concerns the formulation of the dispersible tablet applying direct compression method containing roxithromycin in the form of coated granules. In this study $2^3$ factorial design was used as screening test model and Central Composite Design (CCC) associated with response surface methodology was used as optimization study model to develop and to optimize the proper formulation of roxithromycin dispersible tablet. The three independent variables investigated were functional excipients like binder (X1), disintegrant (X2) and lubricant (X3). The effects of these variables were investigated on the following responses: hardness (Y1), friability (Y2) and disintegration time (Y3) of tablet. Three replicates at the center levels of the each design were used to independently calculate the experimental error and to detect any curvature in the response surface. This enabled the best formulations to be selected objectively. The effect order of each term to all response variable was X3> X2> Xl> X1＊X2> X2＊X2> X2＊X3> X3＊X3> Xl＊X3> Xl＊Xl and model equations on each response variables were generated. Optimized compositions of formula were accordingly computed using those model equations and confirmed by following demonstration study. As a result, this study has demonstrated the efficiency and effectiveness of using a systematic formulation optimization process to develop the tablet formulation of roxithromycin dispersible tablet with limited experiment.

• 대한금속재료학회지
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• 제48권7호
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• pp.630-638
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• 2010

The present investigation has been performed on the mixing behavior and microstructural development during fabrication of Fe micro-nano powder feedstock for a micro-powder injection molding process. The mixing experiment using a screw type blender system was conducted to measure the variations of torque and temperature during mixing of Fe powder-binder feedstock with progressive powder loading for various nano-powder compositions up to 25%. It was found that the torque and the temperature required in the mixing of feedstock increased proportionally with increasing cumulative powder loading. Such an increment was larger in the feedstock containing higher content of nano-powder at the same powder loading condition. However, the maximum value was obtained at the nano-powder composition of not 25% but 10%. It was owing to the 'roller bearing effect' of agglomerate type nano-powder acting as lubricant during mixing, consequently leading to the rearrangement of micro-nano powder in the feedstock. It is concluded that the improvement of packing density by rearrangement of nano-powders into interstices of micro-powders is responsible for the maximum powder loading of about 71 vol.% in the nano-powder composition of 25%.

• Tribology and Lubricants
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• 제34권6호
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• pp.235-240
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• 2018

Superlubricity refers to the lubrication phenomenon that occurs when the friction coefficient is lower than 0.01. In recent years, this phenomenon has received a significant amount of attention because it can greatly contribute to the reduction of economic and environmental losses caused by friction and wear. In the case of acid lubricants, only ceramic materials can be used for superlubricity, and it takes a long running-in period to enter the superlubricity regime. In this work, we investigated the superlubricity effect of vitreous enamel coating on SUS304. We also examined the running-in period of vitreous enamel coating under phosphoric acid lubricant condition with respect to surface treatments. Drying and polishing methods were used to treat the vitreous enamel coating on the specimen. The friction experimental results revealed that superlubricity could be achieved with vitreous enamel coating. It was also found that the drying and polishing methods can significantly reduce the running-in period and improve the wear properties of vitreous enamel coating. In particular, the polishing method shortened the running-in period by approximately 99% and reduced the wear rate by approximately 99%, compared to nontreated vitreous enamel coating.

• 청정기술
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• 제19권3호
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• pp.264-271
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• 2013

본 연구에서는 지르코늄 피복관 제조공정에서 발생되는 스크랩을 원전급(nuclear grade)으로 재활용하기 위해 스크랩 표면에 부착되어 있는 오염물 제거조건을 최적화하였다. 주 오염물은 피복관 제조시 필거링 공정에서 사용하고 있는 수용성 냉각윤활제 잔류물로서 튜브 표면에 압착 및 탄화된 것으로 가정된다. 스크랩 발생 빈도가 높은 ${\phi}9.50mm$, zirlo 합금 튜브를 피 세정 대상물로 선정하여 세정 후 피 세정물 표면에 잔존하고 있는 오염물의 특성분석과 피 세정물의 표면 성분분석으로 세정성을 평가하였다. 세정제별 세정능력을 평가하기 위하여 수산화나트륨(sodium hydroxide) 계열 2종과 수산화칼륨(potassium hydroxide) 계열 3종을 선정하여 비교하였다. 또한 온도 및 초음파 강도에 따른 세정 효과 분석을 위해 상온, $40^{\circ}C$, $60^{\circ}C$에서 각각 세정한 결과, 세정온도 및 초음파 강도가 높을수록 세정효과도 높은 것으로 나타났다. 육안검사 결과 수산화나트륨 계열은 초음파 강도와 무관하게 모두 양호한 것으로 나타났으나 수산화칼륨 계열은 초음파 강도 120 W 이상에서 피 세정물의 표면상태가 양호한 것으로 나타났다. 중량측정법에 의한 세정효과 분석결과 수산화나트륨 계열은 세정효율이 97.6% ($60^{\circ}C$, 120 W)까지 나타났으나 수산화칼륨 계열은 피 세정물의 표면상태 불량으로 중량측정 방법을 적용하는 것이 부적합한 것으로 나타났다. 피 세정물의 표면 오염물 분석 결과 C, O, Ca, Zr 성분이 검출되었으며 그 중 C, O의 성분이 대부분을 차지하였음을 알 수 있었다. 피 세정물의 세정 정도에 따라 C, O 구성 비율의 변화가 큰 것으로 나타났으며 세정이 잘될수록 C의 구성비율이 감소되며 상대적으로 O의 구성 비율이 증가되었다. 본 연구 결과를 바탕으로 산업현장에 적용하기 위하여 세정공정을 알카리세정, 수세, 건조의 3단계로 구분하고 각 단계별로 세정변수를 조정함으로써 세정효과의 극대화를 기대할 수 있다.

• 한국세라믹학회지
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• 제42권2호
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• pp.88-93
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• 2005

아크 이온 플레이팅과 스퍼터로 구성된 하이브리드 시스템을 이용하여 다성분계 Ti-Al-Si-N 코팅막을 WC-Co 기판에 증착하였다. 증착시 Si 함량을 변화시켜 코팅막의 마모특성에 Si 함량이 미치는 영향에 대하여 조사하였다. 마모 특성을 관찰하기 위하여 Ti-Al-Si-N 코팅막이 증착된 WC-Co 원판에 3N의 하중, 0.1 m/s의 속도로 볼 온 디스크(ball-on-disk) 형태의 마모시험기를 이용하여 건식 마모 실험을 하였다. 상대재로는 스틸볼과 지르코니아볼을 사용하였다. 상대재가 스틸볼의 경우 Ti-Al-Si-N 코팅막의 마찰계수가 Ti-Al-N 코팅막의 마찰계수보다 낮게 나타났다 이는 Si가 첨가되어 마모시 상대재와 코팅막 사이에 자기윤활효과(self-lubricant effect)에 의한 것으로 여겨진다. 코팅막과 스틸볼 사이에 응착 마모 거동을 보였으며, Si의 함량이 증가함에 따라 마찰계수는 감소하였다. 한편, 상대재가 지르코니아 볼의 경우 코팅막과 지르코니아 볼 사이에서 연삭마모 거동이 더 지배적이었고, Si 함량이 증가할수록 마찰계수는 증가하였다.

• 공업화학
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• 제22권5호
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• pp.467-472
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• 2011

본 연구에서는 천연물을 이용한 기능성 섬유를 제조하기 위하여 미처리 및 불소화 일라이트를 첨가하여 일라이트/PP 복합섬유를 용융방사로 제조하고 그 물리적 특성을 고찰하였다. 복합필라멘트 형성 시 층상구조를 가지는 일라이트의 윤활특성으로 순수 PP 필라멘트에 비해 복합필라멘트의 직경이 감소하는 현상이 나타났으며, 불소화의 효과로 인한 계면 친화성 향상 및 분산성 향상으로 불소화 일라이트/PP 복합필라멘트의 직경이 순수 PP 필라멘트의 2/3 정도로 감소하였다. 미처리 및 불소화 일라이트 모두 일라이트/PP 복합필라멘트의 열안정성을 향상시키는 효과가 있는 것으로 확인되었다. 또한, 미처리 일라이트/PP 복합필라멘트는 연신 공정을 거칠 때 절사가 발생하여, 복합섬유로서 활용될 수 없었으나, 불소화 일라이트/PP 복합필라멘트는 연신 후 순수 PP 필라멘트와 비슷한 인장강도를 가지고, 50% 정도 증가한 탄성률을 가지는 것으로 보아 복합섬유로서 사용될 수 있음을 확인할 수 있었다. 일라이트/PP 복합필라멘트를 형성 시, 불소화를 통하여 일라이트/PP간의 계면 친화성이 향상되고 고분자 내 분산성은 향상이 되었으나, 층간 결합력이 강한 비팽윤성 일라이트 고유의 성질로 인하여 일라이트의 박리나 PP의 일라이트 내 층간삽입이 충분히 발생하지 않은 것으로 보아 나노복합체가 아닌 마이크로 복합체를 형성하는 것으로 여겨진다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2001년도 추계학술강연 및 발표대회
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• pp.7-7
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• 2001

The increasing interest in light weight materials coupled to the need for cost -effective processing have combined to create a significant opportunity for aluminum P/M. particularly in the automotive industry in order to reduce fuel emissions and improve fuel economy at affordable prices. Additional potential markets for Al PIM parts include hand tools. Where moving parts against gravity represents a challenge; and office machinery, where reciprocating forces are important. Aluminum PIM adds light weight, high compressibility. low sintering temperatures. easy machinability and good corrosion resistance to all advantages of conventional iron bm;ed P/rv1. Current commercial alloys are pre-mixed of either the AI-Si-Mg or AL-Cu-Mg-Si type and contain 1.5% ethylene bis-stearamide as an internal lubricant. The powder is compacted in closed dies at pressure of 200-500Mpa and sintered in nitrogen at temperatures between $580~630^{\circ}C$ in continuous muffle furnace. For some applications no further processing is required. although most applications require one or more secondary operations such as sizing and finishing. These sccondary operations improve the dimension. properties or appearance of the finished part. Aluminum is often considered difficult to sinter because of the presence of a stable surface oxide film. Removal of the oxide in iron and copper based is usually achieved through the use of reducing atmospheres. such as hydrogen or dissociated ammonia. In aluminum. this occurs in the solid st,lte through the partial reduction of the aluminum by magncsium to form spinel. This exposcs the underlying metal and facilitates sintering. It has recently been shown that < 0.2% Mg is all that is required. It is noteworthy that most aluminum pre-mixes contain at least 0.5% Mg. The sintering of aluminum alloys can be further enhanced by selective microalloying. Just 100ppm pf tin chnnges the liquid phase sintering kinetics of the 2xxx alloys to produce a tensile strength of 375Mpa. an increilse of nearly 20% over the unmodified alloy. The ductility is unnffected. A similar but different effect occurs by the addition of 100 ppm of Pb to 7xxx alloys. The lend changes the wetting characteristics of the sintering liquid which serves to increase the tensile strength to 440 Mpa. a 40% increase over unmodified aIloys. Current research is predominantly aimed at the development of metal matrix composites. which have a high specific modulus. good wear resistance and a tailorable coefficient of thermal expnnsion. By controlling particle clustering and by engineering the ceramic/matrix interface in order to enhance sintering. very attractive properties can be achicved in the ns-sintered state. I\t an ils-sintered density ilpproaching 99%. these new experimental alloys hnve a modulus of 130 Gpa and an ultimate tensile strength of 212 Mpa in the T4 temper. In contest. unreinforcecl aluminum has a modulus of just 70 Gpa.