하이브리드 로켓용 파라핀/알루미늄 연료의 알루미늄 입자크기에 따른 열적·유변학적 특성 연구

한승주,김진곤,문희장,김준형,고승원 한국추진공학회 2018 한국추진공학회지 Vol.22 No.2

본 연구에서는 유입후퇴율 거동에 대한 정성적인 예측을 위하여 나노 및 마이크로 알루미늄 입자가 10 wt.% 첨가된 파라핀/알루미늄 연료에 대해 열적특성 및 유변학적 특성에 관한 분석을 수행하였다. 측정결과, 알루미늄 입자 혼합연료에 대하여 열적특성 대비 유변학적 특성에 입자첨가 여부 및 입자크기의 영향이 존재함을 확인하였다. 또한, 열적특성에 나타난 변화에 비해 유변학적 특성에 나타난 변화가 유입후퇴율에 큰 영향을 미치고 민감함을 확인하였다. In this study, the thermal and rheological characteristics of a 10 wt.% addition of aluminum particles and the effect of the particle size were investigated to qualitatively analyze the paraffin fuel entrainment regression rate. The results revealed that the addition of aluminum particles and their relative particle size affected the rheological characteristics, rather than the thermal characteristics. Moreover, it was found that the variation of thermal properties had a minor effect on the entrainment regression rate, in comparison to the variation in rheological properties.

Development of reference materials for cement paste

Lee, Dong Kyu,Choi, Myoung Sung Techno-Press 2020 Advances in concrete construction Vol.9 No.6

This study aimed to develop reference materials (RMs) that are chemically stable and can simulate the flow characteristics of cement paste. To this end, the candidate components of RMs were selected considering the currently required properties of RMs. Limestone, slag, silica, and kaolin were selected as substitutes for cement, while glycerol and corn syrup were selected as matrix fluids. Moreover, distilled water was used for mixing. To select the combinations of materials that meet all the required properties of RMs, flow characteristics were first analyzed. The results revealed that silica and kaolin exhibited bilateral nonlinearity. When an analysis was conducted over time, slag exhibited chemical reactions, including strength development. Moreover, fungi were observed in all mixtures with corn syrup. On the other hand, the combination of limestone, glycerol, and water exhibited a performance that met all the required properties of RMs. Thus, limestone, glycerol, and water were selected as the components of the RMs. When the influence of each component of the RMs on flow characteristics was analyzed, it was found that limestone affects the yield value, while the ratio of water and glycerol affects the plastic viscosity. Based on this, it was possible to select the mixing ratios for the RMs that can simulate the flow characteristics of cement paste under each mixing ratio. This relationship was established as an equation, which was verified under various mixing ratios. Finally, when the flow characteristics were analyzed under various temperature conditions, cement paste and the RMs exhibited similar tendencies in terms of flow characteristics. This indicated that the combinations of the selected materials could be used as RMs that can simulate the flow characteristics of cement paste with constant quality under various mixing ratio conditions and construction environment conditions.

Rheological properties of polyvinylsiloxane impression materials before mixingand during setting related to handling characteristics

Hyang-Ok Lee,이인복 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

The purpose of this study is to determine and compare the handling and rheological properties of poly\-vinylsiloxane impression pastes before mixing and during setting, and to investigate the effect of its con\-stituents on the properties of the materials. Five polyvinylsiloxane impression materials (Examixfine, Extrude, Honigum, Imprint II, and Express) were used. A flow test and a drip test were performed to deter\-mine the handling characteristics. The rheological properties of each impression material prior to mixing (shear stress, viscosity) and during setting (storage modulus G', loss modulus G'', loss tangent tand) were measured with a stress-controlled rheometer at 25oC and 32oC, respectively. Inorganic filler content of each impression material was measured and observed with a SEM. The molecular weight distribution of polymer matrix was determined with a gel permeation chromatography (GPC). Express and Honigum display lower flow compared to the other materials, due to their high yield-stress values. Examixfine exhibits the greatest flow. All materials display pseudoplastic behavior, excluding the Examixfine catalyst. The viscosities at low shear rate are greatest for Express and Honigum; however, under high shear conditions, the viscosities of Extrude and Honigum are the lowest. Following mixing, each material show an increase in G', finally reach\-ing a plateau, and the tand rapidly decreases with time. Imprint II shows the highest final G' as well as the most rapid decrease in tand. Express and Imprint II present the highest filler content and rough filler surface, while Honigum shows the lowest filler content and small filler particles. Most products are composed of polymers over 30kDa and oligomers less than 1kDa. Each impression material possesses different rheo\-logical properties, which significantly affect the handling characteristics. The yield stress of the impression material minimizes unnecessary flow prior to and after seating. Viscoelastic change during setting of each impression material determines the setting time and the stiffness after setting. These rheological properties of impression materials are affected by the filler content and molecular weight distribution of polymer matrix.

Rheological properties of polyvinylsiloxane impression materials before mixing and during setting related to handling characteristics

Lee, Hyang-Ok,Lee, In-Bog 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

The purpose of this study is to determine and compare the handling and rheological properties of polyvinylsiloxane impression pastes before mixing and during setting, and to investigate the effect of its constituents on the properties of the materials. Five polyvinylsiloxane impression materials (Examixfine, Extrude, Honigum, Imprint II, and Express) were used. A flow test and a drip test were performed to determine the handling characteristics. The rheological properties of each impression material prior to mixing (shear stress, viscosity) and during setting (storage modulus G', loss modulus G", loss tangent $tan{\delta}$) were measured with a stress-controlled rheometer at $25^{\circ}C$ and $32^{\circ}C$, respectively. Inorganic filler content of each impression material was measured and observed with a SEM. The molecular weight distribution of polymer matrix was determined with a gel permeation chromatography (GPC). Express and Honigum display lower flow compared to the other materials, due to their high yield-stress values. Examixfine exhibits the greatest flow. All materials display pseudoplastic behavior, excluding the Examixfine catalyst. The viscosities at low shear rate are greatest for Express and Honigum; however, under high shear conditions, the viscosities of Extrude and Honigum are the lowest. Following mixing, each material show an increase in G', finally reaching a plateau, and the $tan{\delta}$ rapidly decreases with time. Imprint II shows the highest final G' as well as the most rapid decrease in $tan{\delta}$. Express and Imprint II present the highest filler content and rough filler surface, while Honigum shows the lowest filler content and small filler particles. Most products are composed of polymers over 30 kDa and oligomers less than 1 kDa. Each impression material possesses different rheological properties, which significantly affect the handling characteristics. The yield stress of the impression material minimizes unnecessary flow prior to and after seating. Viscoelastic change during setting of each impression material determines the setting time and the stiffness after setting. These rheological properties of impression materials are affected by the filler content and molecular weight distribution of polymer matrix.

함수계와 비수계 ER유체의 온도-점도 특성

이진우,장성철,염만오,김도태,박재범 한국공작기계학회 2002 한국공작기계학회 춘계학술대회논문집 Vol.2002 No.-

This paper describes the properties of Temperature-Viscosity characteristics of hydrous and anhydrous ER fluids containing starch and titanium particle in silicone oil. ER effects arise from electrostatic forces between the starch particles and titanium particles dispersed in the electrically insulating silicone oil induced when electric field is applied. ER fluids under electric field have been found to provide resonable estimates of ER fluid viscosity variation characteristics. Yield shear stress of the ER fluids were measured on the couette cell type rheometer as a function of electric fields. The outer cup is connected to positive electrode(+) and bob becomes ground(-). The electric field is applied by high voltage DC power supply. In this experiment shear rates were increased from 0 to 200_(s^(-1)) in 2 minutes.

HPMC, MC, sodium alginate 등의 검류가 식빵의 품질 특성에 미치는 영향

김미영(Mi-Young Kim),이정훈(Jeong-Hoon Lee),이시경(Si-Kyung Lee) 한국식품과학회 2009 한국식품과학회지 Vol.41 No.3

HPMC, MC, SA 등의 검류를 밀가루 중량대비 0.5% 첨가하였을 때 식빵의 품질 특성에 미치는 영향으로 빵의 수분함량, 수분활성도, 냉각손실, 부피, 레올로지, 관능검사 등을 조사하였다. 빵의 수분함량과 수분활성도는 검류 중 HPMC를 첨가한 경우 가장 높았고, 냉각 손실률은 HPMC를 첨가한 경우 가장 적어 대조구와 2.4% 차이가 있었다. 부피는 SA를 첨가한 경우 2,560±24 mL로 가장 컸으며, 레올로지 특성에서 경도와 max G는 HPMC를 첨가한 경우 가장 낮아 부드러웠고, 탄력성은 SA를 첨가한 경우 가장 컸다. 관능검사에서 HPMC를 첨가한 경우 점수가 높아 가장 선호하는 것으로 나타났다. 결과적으로 SA를 첨가하였을 때 식빵의 부피와 탄력성이 HPMC를 첨가하였을 때보다 높았으나, 수분함량, 수분활성도, 및 관능검사 등의 결과는 HPMC 첨가 구에서 높았으며, 냉각손실률은 낮은 것으로 나타나 HPMC를 첨가하는 것이 식빵의 품질 개선에 더 효과적인 것으로 생각된다. This study was carried out to evaluate the quality characteristics of white pan breads containing 0.5% of gums, including HPMC, MC and SA. Moisture content, water activity, cooling loss, bread volume, rheological, and sensory evaluations were performed to examine the bread quality characteristics. Moisture content and water activity were highest in the bread with added HPMC. HPMC showed the smallest cooling loss among the breads compared to the other added gums. The bread with added SA had the thelargest volume at 2,560±24 mL. In terms of rheological properties, the hardness of the bread containing HPMC was lowest and the springness of the bread with added SA was the highest. In sensory evaluations, the bread containing HPMC was evaluated as the most preferred product by acquiring the highest scores in internal and external evaluations. Consequently, the bread containing 0.5% SA showed better volume and springiness values. However, the bread containing 0.5% HPMC showed greater moisture content, greater water activity, lower cooling loss, and better sensory evaluation scores. Based on the overall results, HPMC was considered to be the most effective hydrocolloid to increase bread quality.

β-Glucan 첨가가 식빵의 물리적 및 품질 특성에 미치는 영향

이정훈(Jeong Hoon Lee) 한국조리학회 2012 한국조리학회지 Vol.18 No.3

This study was carried out to evaluate the effect of β-glucan on rheological properties of flour dough and quality characteristics of white pan bread. Flour dough and white pan bread fortified with β-glucans at levels of 0%, 3%, 6% and 9% w/w. Farinograph and amylograph were analysed for the rheological properties. Loaf volume and specific loaf volume, moisture content, texture and sensory evaluation were also analysed for the quality characteristics. In the farinograph test, water absorption and dough development time of doughs increased with increasing β-glucan content. Especially, water absorption of dough fortified with 9% of β -glucan showed 13% higher than the control. However, the addition of β-glucan to the dough decreased stability. There were no significant differences on gelatinization temperature and maximum viscosity temperature regardless of β-glucan contents, but maximum viscosity increased with increasing β-glucan contents. Loaf volume and specific loaf volume of white pan bread decreased slightly with increasing β -glucan contents. Moisture content showed higher value in tests than that of the control, and the one added with 6% revealed highest moisture content. In terms of texture analysis, the one added with 6% of β-glucan revealed softer than the others. There were no differences between the groups added with 3% and with 6% on sensory evaluation, but the one added with 9% obtained lowest scores. As a result of this study, 6% of β-glucan is considered the resonable level to prepare healthy white pan bread. β-glucan can also be used when making cake and cookies.

치과용 복합레진의 중합 전 slumping resistance와 점탄성

서희연,이인복 大韓齒科保存學會 2008 Restorative Dentistry & Endodontics Vol.33 No.3

본 연구의 목적은 복합례진의 slumping resistance를 측정할 수 있는 방법을 개발하고, 그 유용성을 평가하기 위해 rheometer를 이용해 측정된 복합레진의 여러 유변학적 성질과 slumping resistance의 상호 관련성을 밝히고자 하였다. 상용되는 hybrid composites (Z100, Z250, DenFil, Tetric Ceram, ClearFil)와 nanofll composite (Z350)를 2 ㎜두께의 디스크 모양의 시편으로 만들었다. 사각형의 단면을 가진 알루미늄 형판으로 레진 디스크를 눌러 표준화된 자국을 남겼다. 이것을 즉시 광중합하거나 (no-slump) 25℃에서 3 분간 방치 한 후에 광중합 하였다 (slumped).흰 경석고로 광중합된 레진을 복제한 후 laser 3-D profilometer로 표면의 단면 영상을 얻었다. Slumping 전 후 홈의 깊이의 비를 구해 slumping resistance index (SRI)라 정의하였다. 각 복합레진의 중합 전 전단 점탄성을 측정하기 위해 회전형 rheometer를 이용하여 동적회전전단실험과 squeeze test를 시행하였다. 더불어 flow test를 시행하였다. 동적회전전단실험 및 압착실험의 결과와 8RI와 상호관련성을 조사하기 위해 상관분석을 하였다. 여섯 가지의 재료의 SRI 값에는 차이가 있었다 (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). SRI는 전단 점성(손실)계수 G" 와 가장 큰 양의 상관관계를 보였으며 Tan δ는 SRI와 상관관계가 없었다. SRI는 수직 가압에 대한 저항 보다 전단흐름에 대한 저항과 관련성이 높았다. 본 연구에서 도입된 imprint method와 SRI는 복합레진이 slumping 되는 경향을 정량화하였으며 복합레진 조작성의 평가방법으로 사용할 수 있었다. The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to relate it to the rheological characteristics. Five commercial hybrid composites (Z100, Z250, DenFil, Tetric Ceram, ClearFil) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2 ㎜ thickness. An aluminum mold with square shaped cutting surface was pressed onto the composite discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 3 minutes at 25℃ (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the non-slumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Flow test was also performed using a flow tester. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and the SRI. SRI varied between the six materials (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). The SRI was strongly correlated with the viscous (loss) shear modulus G ' but not with the loss tangent. Also, slumping resistance was more closely related to the resistance to shear flow than to the normal stress. Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.

Fabrication of solid oxide fuel cells by tape casting with solvent control

권영진,한영배 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

Solid oxide fuel cells (SOFCs) convert chemical energy of H₂ and O₂ to electrical energy. Tape casting fabricates green tapes by casting the slurry mixture of ceramic powder, binder, plasticizer, dispersant and solvent. The fabricated green tapes are heat-treated to form final unit cells so the slurry mixture is the most significant. High solid loading and binder concentration are required but changes rheological behavior and high viscosity as they increase network strength of particles in green tapes, leading to higher electrochemical performance of SOFC. In this study, to fabricate green tapes with high particle network by increasing solid loading and binder concentration, a method to control slurry and tape characteristics by changing solvent ratio in tape cast slurry is proposed. As a result, uniform green tapes with good flexure strength and packing density are fabricated with well-controlled slurry composition and rheological characteristics.

와이오밍 벤토나이트의 유변학적 특성: 염분농도의 역할

정승원 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.10

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S = 0g/L and bilinear, Herschel-Bulkley and power-law for S = 30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.