• Restorative Dentistry and Endodontics
• /
• 제29권6호
• /
• pp.520-531
• /
• 2004

The aim of this study was to investigate the effect of monomer and filler compositions on the rheological properties related to the handling characteristics of resin composites. Methods. Resin matrices that Bis-GMA as base monomer was blended with TEGDMA as diluent at various ratio were mixed with the Barium glass (0.7 um and 1.0 um), 0.04 um fumed silica and 0.5 um round silica. All used fillers were silane treated. In order to vary the viscosity of experimental composites, the type and content of incorporated fillers were changed, Using a rheometer, a steady shear test and a dynamic oscillatory shear test were used to evaluate the viscosity ($\eta$) of resin matrix, and the storage shear modulus (G'), the loss shear modulus (G"), the loss tangent ($tan{\delta}$) and the complex viscosity (${\eta}^*$) ofthe composites as a function of frequency ${\omega}{\;}={\;}0.1-100{\;}rad/s$. To investigate the effect of temperature on the viscosity of composites, a temperature sweep test was also undertaken. Results. Resin matrices were Newtonian fluid regardless of diluent concentration and all experimental composites exhibited pseudoplastic behavior with increasing shear rate. The viscosity of composites was exponentially increased with increasing filler volume%. In the same filler volume, the smaller the fillers were used, the higher the viscosities were. The effect of filler size on the viscosity was increased with increasing filler content. Increasing filler content reduced $tan{\delta}$ by increasing the G' further than the G". The viscosity of composites was decreased exponentially with increasing temperature.

• 공업화학
• /
• 제10권5호
• /
• pp.690-695
• /
• 1999

석탄핏치로부터 제조된 메조페이스 핏치의 실험적 연구가 용융상태에서의 유변학적 거동을 알아보고자 수행되었다. 겉보기 점도, 전단변형율, 전단응력, 퀴놀린 불용분(QI), 연화점(SP) 변화 등을 조사하여 다음과 같은 결론을 얻었다. 중합시에 메조페이스의 적당한 함량을 증가시키기 위한 조건으로는 열처리 시간이 5시간, 촉매농도는 3%, 반응온도는 $420^{\circ}C$로 나타났다. 온도상승에 따른 겉보기 점도 변화는 핏치의 열처리 조건에 따라 달라지는데 열처리 온도가 높을수록, 열처리 시간이 길어질수록, 메조페이스 함량이 증가할수록 커지며, 유동도는 작아진다. $270^{\circ}C$ 이후의 용융 메조페이스 핏치의 유변학적 거동은 $375^{\circ}C$ 이하에서는 Newtonian fluid의 성질을 띠며 그 이상에서는 Non Newtonian fluid의 거동을 보이며 Casson 모델에 잘 일치됨을 알 수 있었다.

• Tribology and Lubricants
• /
• 제25권6호
• /
• pp.432-437
• /
• 2009

The effect of oxidation in SAE 5W30 engine oils on friction and wear characteristics was investigated using reciprocating bench tester and shell 4-ball tester. Commercial engine oils were collected and oxidized using the KS M 2021 method modifying the oxidation time. Kinematic viscosity, total acid number(TAN), FT-IR spectrum and total base number(TBN) also measured to examine the chemical change of oils with oxidation. The results showed that TAN was slightly changed and Kinematic viscosity was suddenly increased during the oxidation stage. however, TBN results keep a constant slope after TBN linearly decreased with oxidation time. Spectroscopy results showed that spectrums were orderly increased at $1710cm^{-1}$ during the oxidation time. Friction test results showed that oxidation of oils formed unstable friction layers causing higher fluctuating friction. however, the wear resistance was independent of oxidized time due to the different friction characteristics by oxidation. We found several factors in relation to lubrication properties with oxidation time. This factors were Viscosity, TBN, change of FT-IR spectrum, friction coefficient using reciprocating bench tester and wear scar.

• International Journal of Aeronautical and Space Sciences
• /
• 제15권2호
• /
• pp.199-204
• /
• 2014

An experimental investigation on the rheological behavior of gelled hydrogen peroxide at different ambient temperature (283.15, 293.15 and 303.15 K) was carried out in this study. The gel propellant was rheologically characterized using a rheometer, in the shear rate ranges of 1 to $20s^{-1}$, and 1 to $1000s^{-1}$. Hydrogen peroxide gel was found to be thixotropic in nature. The apparent viscosity value with some yield stress (in-case of shear rate 1 to $20s^{-1}$) drastically fell with the shear rate. In the case of the shear rate range of 1 to $20s^{-1}$, the apparent viscosity and yield stress of gel were significantly reduced at higher ambient temperatures. In the case of the shear rate range of 1 to $1000s^{-1}$, no significant effect of varying the ambient temperature on the gel apparent viscosity was observed. The up and down shear rate curves for hydrogen peroxide gel formed a hysteresis loop that showed no significant change with variation in temperature for both the 1 to $20s^{-1}$ and the 1 to $1000s^{-1}$ shear rate ranges. No significant change in the thixotropic index of gel was observed for different ambient temperatures, for both low and high shear rates. The gel in the 1 to $20s^{-1}$ shear rate range did not lead to a complete breakdown of gel structure, in comparison to that in the 1 to $1000s^{-1}$ shear rate range.

• 한국도로학회논문집
• /
• 제7권4호
• /
• pp.203-210
• /
• 2005

바인더의 노화로 인한 성능변화는 침입도 또는 점도시험을 실시하여 판정하여왔다. 기존의 시험방법으로 아스팔트 바인더의 점탄성 특성과 실제거동을 평가할 수 없기 때문에 새로운 분석방법이 요구되어 왔다. 본 연구에서는 기존시험 방법을 사용하여 침입도지수와 잔류침입도를 판정하였고, 양방향 반복회전 모드와 일방향 반복회전 모드 시험을 실시하여 단기 노화된 아스팔트 바인더의 유변학적 특성을 분석하였다. 시험결과 단기 노화된 아스팔트 바인더는 시험주기(frequency) 즉, 차량속도의 변화에 따라 서로 다른 복합계수와 위상각을 나타냈으며 단기 노화 전후의 크리프 컴플라이언스 및 전단점도 시험결과에도 영향을 미치는 것으로 나타나서 포장 설계시 이러한 특성이 고려되어야 한다.

• Korean Chemical Engineering Research
• /
• 제47권2호
• /
• pp.157-162
• /
• 2009

본 논문은 소량 다품종 생산체계로 생산되는 정밀화학제품인 고품질 염료제조를 위한 고효율 염료결정화 분리기술에 대한 연구로써 염료 염석결정화계에서 염료의 물성과 최적조업조건에 대해 연구하였다. 먼저 염료의 물리적 특성을 알아보기 위해 밀도, 점도 등을 다양한 조건하에 측정하였다. 염료의 밀도는 물과 비슷한 특성을 보였으며, 염료 용액의 농도가 변화할 때, 밀도 변화는 거의 없었으며, 점도는 농도가 증가 할수록 증가했다. 염료 용액의 온도가 높아짐에 따라 밀도는 증가하였으나, 점도는 감소하였다. 또 염료의 용해도 실험 결과 20 wt% 염료 용액에 15 wt% KCl을 첨가하였을 때 염료결정의 생성량이 최대로 나타났다. 또한, 최적의 조업조건을 찾기 위해 다양한 변수(온도, RPM, 염첨가 방법 등)를 제어하여 시간에 따라 실험하였다. 15 wt% KCl과 20 wt% 염료용액으로 실험한 결과 최적의 조업조건은 $25^{\circ}C$, 100 RPM, 염을 한 번에 넣는 방법으로 나타났다. 또 최적 조업조건으로 실험을 수행한 결과 기존의 공정($35^{\circ}C$, 150 RPM)보다 생성량이 증가하였다. 따라서 최적화 공정을 찾음으로써 생성량 증가와 에너지 저감 효과가 기대된다.

• 동아시아식생활학회지
• /
• 제20권2호
• /
• pp.313-320
• /
• 2010

In this study, kiwi fruit, which has various medical actions and excellent functionality, was used together with gruels for comparison and analysis of to compare and analyze the changes in physico-chemical quality of a kiwi fruit-gruel according to the amount of kiwi concentrate added to the gruel. Analysis on the sensual quality of kiwi fruit-gruel spread was done to indicate to it was executed to find out the merchandising potential of the preparation and to provide basic data for gruel commercialization. Increasing content of kiwi concentrate decreased the solid content and pH of kiwi fruit, and increased sweetness and viscosity. Significant changes in chromaticity to L(lightness) and a(redness), texture qualities of hardness and cohesiveness, gumminess, springiness, color, flavor, sourness, and sweetness were evident with increasing kiwi concentrate. Concerning overall acceptability and sensory evaluation, 20% softness samples were most preferred. The findings may lead to enhanced medical/nutritional activity and functionality of kiwi fruit-supplemented gruel. The more the kiwi concentrate was added to the gruel, solid content and pH of the kiwi fruit-grue decreased. The sweetness and viscosity of kiwi fruit-gruel increased. For chromaticity to L(lightness) and a(redness) of the gruel decreased and showed significant difference between sample groups. For texture, there were significant changes shown for hardness and cohesiveness the amount of kiwi concentrate added was different, increased There was a significant change between samples for gumminess. As for springiness, there was a significant change between samples. There were significant difference between each sample for color, flavor, sourness, sweetness. For softness, overall-acceptability and sensory evalution 20% group was most preferred based on this study, from the physico-chemical and sensual perspective, 20% group is highly recommended for adding kiwi concentrate into gruel. In conclusion, this study is meaningful as it enhanced the functionality and quality of a gruel by combining kiwi fruit with various medical action and excellent functionality, with Kiwi Fruit and presented a basic material for creating a kiwi concentrate combined gruels.

• 한국산학기술학회논문지
• /
• 제15권3호
• /
• pp.1305-1310
• /
• 2014

MR 댐퍼는 자기장의 영향으로 인한 MR 유체의 응집현상으로 자기전단력을 발생한다. MR 유체는 기존유체와 자기입자로 구성되어 있다. 본 연구에서 밀도 1.3, 1.5, $1.7g/cm^3$ 그리고 점도 1,000, 10,000cP를 가지는 MR 유체 6종과 오리피스 형상 6종에 대한 MR 댐퍼의 댐핑력을 조사하였다. MR 유체의 밀도와 점도 변화에 따라서 MR 댐퍼의 댐핑력이 변하였다. 오리피스 형상변화에 대한 댐핑력은 오리피스 갭이 적고 길이가 짧을수록 크게 나타났다. 이들 연구결과로부터 MR 댐퍼의 최적설계를 위해서는 MR 유체의 선정과 오리피스 형상이 중요한 설계변수임을 확인하였다.

• 폴리머
• /
• 제26권1호
• /
• pp.88-97
• /
• 2002

ortho-cresol novolac형 에폭시/페놀 경화제/triphenylphosphine 수지 시스템의 화학 레올로지 특성에 미치는 아민 실록산 개질제의 영향을 검토하였다. DSC측정으로부터 아민 개질제에 의해 경화 속도와 전환량이 증가하였으며 유리전이온도의 증가도 관찰할 수 있었다. 또한, 저장 탄성률과 손실 탄성률의 교차점으로부터 구한 겔화 시간 및 임계 전환량의 감소를 확인할 수 있었다. 이것으로부터 등온 경화반응이 빠르게 진행됨으로써 점도가 상승하는 것을 알 수 있었다. 전환량의 함수로 얻어진 유리전이온도와 측정된 점도로부터 modified WLF 방정식에서의 $C_1$ 및 $C_2$를 온도 함수로써 나타낼 수 있었으며, 유리전이온도와 $C_1$ 및 $C_2$를 modified WLF 방정식에 적용함으로써 등온 경화반응에 따른 점도변화를 정확히 예측할 수 있었다.

• 대한기계학회논문집B
• /
• 제24권9호
• /
• pp.1277-1284
• /
• 2000

To enhance heat transfer characteristics of water, micro-encapsulated octadecane of about $10{\mu}m$ diameter was added to water. Viscosity of the slurry was measured by using a capillary tube viscometer. The measured viscosity decreased as the temperature of the slurry increased, and it increased as the fraction of the capsules in the slurry increased. Thermal characteristics of the octadecane were studied by using a differential scanning calorimeter. The melting temperature and the melting energy of the octadecane were found to be $28.6^{\circ}$ and 34.4kcal/kg, respectively. The convective heat transfer characteristics of the slurry were investigated in a flow loop with a constant heat flux test section. Friction factor of the slurry flow was found to be similar to the expected curve by Petukhov. The Nusselt number of the slurry flow was highest when the octadecane melted. Effective thermal capacity of the 14.2% slurry was found to have 1.67 times of the thermal capacity of water.