• Title/Summary/Keyword: 점도변화

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Study on crystallization of $PbTiO_3$ thin films by the Sol-Gel method (Sol-Gel법을 이용한 $PbTiO_3$ 박막의 결정화에 관한 연구)

  • Kyu Seog Hwang;Byung Wan Yoo;Byung Hoon Kim
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.4 no.2
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    • pp.199-209
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    • 1994
  • $PbTiO_3$ thin films were prepared on soda-lime-silica slide glasses, Si-wafer and sapphire substrate by the dip-coating of precursor solution. As starting materials, titanium tetra iso-propoxide and lead acetate trihydrate were used. Then acetylacetone was added to prepare stable sol. The effect of the parameters such as viscosity and composition of sol were investigated. The optical transmittance at visible range, refractive index, IR spectra were measured in varying compositions, thickness and heat treatment temperature. The crystallization of $PbTiO_3$ films were measured by using XRD and SEM. Diffusion of compositions from slide glass to thin film were investigated by using EDX, too. These sols not precipitated for 20 days. Transmittance of $PbTiO_3$ films at visible range were decreased with the increase of thickness and heat treatment temperatures, and were exhibited flat spectra. Pyrochlore type appeared in the films on slide glass and perovskite type appeared in the films on Si-wafer or sapphire at $600^{\circ}C$. Perovskite crystals transformed to $PbTi_3O_7$ phase at $800^{\circ}C$.

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The Characterizations of Tape Casting for Low Temperature Sintered Microwave Ceramics Composite (저온소성 마이크로파 유전체 세라믹스 복합체의 Tape Casting특성)

  • Lee, Woo-Suk;Kim, Chang-Hwan;Ha, Mun-Su;Jeong, Soon-Jong;Song, Jae-Sung;Ryu, Bong-Ki
    • Journal of the Korean Ceramic Society
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    • v.42 no.2 s.273
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    • pp.132-139
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    • 2005
  • Sintering behavior of $BaO-Nd_{2}O_3-TiO_2$ with a Pb-based glassceramics frit were investigated in order to understand an effect of glassceramics as a low temperature sintering agent on dielectric ceramics. A green sheet form was fabricated through tape casting method with the glassceramic fut added $BaO-Nd_{2}O_3-TiO_2$. The dispersion properties, rheological properties and final density of dielectric composit slurry as a function of amount and composition of organic additives was examined. The dispersants' addition was effective in controlling dispersion of the ceramics in solution. The addition of excessive dispersant showed adverse effect on dispersion. The prepared slurries, containing ceramic : powders, glass-ceramics and various kinds of organic viechles, exhibited typical shear thinning behavior. The best properties of tape casting appeared powder to solvent ratio 65 : 35 and amount of the binder 6 wt$\%$ and plasticizer 3 wt$\%$. The viscosity of the slurry was 677 cps and green/sintered density in the tape was $3.3 g/cm^3,\;5.56 g/cm^3$ respectively.

Study on Temperature Characteristics of Friction Stir Welding Process by Numerical Analysis (수치해석을 활용한 마찰교반용접 공정의 온도 특성 분석 연구)

  • Kim, Moosun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.12
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    • pp.513-518
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    • 2019
  • Friction Stir Welding is a welding technique for metal materials that utilizes the heat generated by friction between the material to be welded and the welding tool that rotates at high speed. In this study, a numerical analysis method was used to analyze the change in the internal temperature of the welded material during friction stir welding. As the welding target material, AZ31 magnesium alloy was applied and the welding phenomenon was considered a flow characteristic, in which a melting-pool was formed. FLUENT was used as the numerical tool to perform the flow analysis. For flow analysis of the welding process, the welding material was assumed to be a high viscosity Newtonian fluid, and the boundary condition of the welding tool and the material was considered to be the condition that friction and slippage occur simultaneously. Analyses were carried out for various rotational speeds and the translational moving speed of the welding tool as variables. The analysis results showed that the higher the rotational speed of the welding tool and the slower the welding tool movement speed, the higher the maximum temperature in the material increases. Moreover, the difference in the rotational speed of the welding tool has a greater effect on the temperature change.

Analysis of Friction Stir Welding Process of Mg alloy by Computational Fluid Dynamics (유동 해석을 통한 마그네슘 합금의 마찰교반용접 분석 연구)

  • Kim, Moosun;Sun, Seung-Ju;Kim, Jung-Seok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.12
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    • pp.679-684
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    • 2017
  • Friction Stir Welding is a metal welding technique, in which friction heat between a welding tool and a welding material is used to weld parts at temperatures below the melting point of a material. In this study, the temperature and velocity changes in a magnesium alloy (AZ31) during the welding process were analyzed by computational flow dynamics technique while welding the material using a friction stir welding technique. For the analysis, the modeling and analysis were carried out using Fluent as a fluid analysis tool. First, the welding material was assumed to be a temperature-dependent Newtonian fluid with high viscosity, and the rotation region and the stationary region were simulated separately to consider the rotational flow generated by the rotation of the welding tool having a helical groove. The interface between the welding tool and welding material was given the friction and slip boundary conditions and the heat transfer effect to the welding tool was considered. Overall, the velocity and temperature characteristics of the welded material according to time can be understood from the results of transient analysis through the above flow analysis modeling.

Effect of Repeated Use of Same Herbicide on Weed Growth in Lowland Rice (제초제(除草劑)의 연용(連用)이 논잡초(雜草) 발생(發生)에 미치는 영향(影響))

  • Choi, C.D.;Kim, S.C.;Hwang, D.Y.
    • Korean Journal of Weed Science
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    • v.9 no.1
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    • pp.39-45
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    • 1989
  • An experiment was conducted at the Yeongnam Crop Experiment Station for 4 years from 1985 to understand the effect of repeated use of same herbicide on weed growth. For this, the most common 6 herbicides, butachlor, bifenox, butachlor/pyrazolate, piperophos/dimethametryne, bentazon and propanil were used as single treatment or combination treatment. For non chemical plots, weed occurrence was rapidly increased with time in terms of number and weight. However no rice plot recorded the least increasing ratio. Similar trend was obtained at the herbicide plot even though the increasing ratio varied by herbicide properties. The least increasing ratio (1200 was recorded at the plot of butachlor/pyrazolate (5 days after transplanting, 5 DAT) followed by bentazon+propanil(25 DAT) while the greatest ratio (28%) was obtained from the plot of bifenox (5 DAT). In general, Scirpus hotarui, Eleocharis kuroguwai and Cyperus serotinus was gradually inereased with time by herbicide application, particularly at the butachlor/pyrazolate treatment. The community dominance and simpson index increased at the plot of bentazon and propanil due to increased of particular species while other herbicide plots exhibited reverse trend. Grain yield was curvilinearly decreased with weed weight for both times, 40 DAT and heading time eventhough the correlation coefficient of heading time was higher than 40 DAT.

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Experimental study on the damping characteristics of a cylindrical structure containing oil and bearing balls (윤활유와 베어링 볼을 내장한 원통형 구조물의 감쇠특성에 관한 실험적 연구)

  • 류봉조;송선호
    • Journal of KSNVE
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    • v.6 no.1
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    • pp.107-114
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    • 1996
  • The damping characteristics of a cylindrical structure containing oil and bearing balls is investigated for external bending forces. The experimental data obtained through the use of bearing balls with viscous oil in a column is given and analyzed. The viscous action of the oil and inertia effects of the balls on the inside of column create a drag force. The drag force dampens the vibration of the column. This study aims to search for an optimum combination of oil and balls which would produce maximum damping. Machining oils of various viscosities along with ball bearings of various sizes place inside cantilevered aluminium tubes of various diameters to create a rig on which the damping properties of the oil and balls can be studied. The contileved tubes are studied in both horizontal and vertical positions in order to gauge the effect of gravity on the system. The actions of the ball in the column and damping characteristics are investigated according to the dimensionless terms. The Buckingham theorem is used to reduce the variables and to predict the damping of an oil ball column. Though the damping ratio remains fairly constant in the horizontal position of column, the damping ratio begins to increase as the ratio of the number of balls and column length rise above 0.28 in the vertical position of oil ball column. The ratio of the ball diameter to column diameter influences the damping ratio with an optimum diameter ratio. Slenderness ratio and gravity effects on the damping ratio ane investigated.

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Effects of Heat Treatment on the Quality of the Onion Juices Prepared with Sulfur-applied Onions (양파 착즙 중 열처리 조건이 유황양파즙의 품질 특성에 미치는 영향)

  • Choi, Bogyoung;Surh, Jeonghee
    • Korean Journal of Food Science and Technology
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    • v.46 no.2
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    • pp.189-197
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    • 2014
  • Onion juices were prepared by various heat treatments (at $105-120^{\circ}C$ for 4.5-5.5 h), from the onions cultivated with increasing numbers of sulfur applications (once for Sulfur-1, four times for Sulfur-4). As heat treatment intensity increased, the onion juices darkened (p<0.001), which adversely affected the sensory preference. In addition, increasing the heating temperature significantly increased the organic acid content of onion juices (p<0.001), and therefore, decreased pH (p<0.001). Heat intensity did not affect the thiosulfinate content of onion juices, suggesting that the rate of decomposition of thiosulfinate into low-molecular weight sulfur derivatives is similar over the temperature range of $105-120^{\circ}C$. Total flavonoids were higher in onion juices derived from Sulfur-4 than in Sulfur-1 onions, and increased with heat treatment intensity (p<0.001). These results indicated that heat-facilitated conversion of bound forms of flavonoids to their free forms increases the extractability of flavonoids from onions.

Characteristics of Job′s tear gruel by various mixing ratio, particle size and soaking time of Job′s tear and rice flour (쌀가루 및 율무가루의 배합비율, 입자크기 및 수침시간에 따른 율무죽의 특성)

  • 이정은;서문희;이현규;양차범
    • Korean journal of food and cookery science
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    • v.18 no.2
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    • pp.193-199
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    • 2002
  • The Job's tear gruels were prepared by various mixing ratios, particle size and soaking times of Job's tear and rice flours, and the physical and sensory properties of these gruel samples were measured by using a Brabender visco-amylograph and sensory evaluation. Also, the changes in the pH and viscosity of the gruel samples stored for 14 days at 4$\^{C}$ were measured as the parameters of gruel quality. The results showed that the peak viscosity was decreased by increasing the ratio of Job's tear flours. The values of peak viscosity and consistency of rice and Job's tear flours increased as the particle size decreased. As the soaking time of rice and Job's tear flours increased, the initial pasting temperature decreased. In sensory characteristics, the nutty taste was increased as the Job's tear flour levels increased. Overall acceptability of Job's tear gruel was the highest in the one of rice and Job's tear flours at 50:50 ratio. During 14 days of storage, the pH and viscosity of Job's tear gruels were increased till the sixth day, and then decreased slightly.

Modification of Physico-chemical Properties of Wheat Bran by Twin-screw Extrusion Process -1. Effect of Screw Configuration and Process Parameters on System Parameters- (이축 압출성형 공정에 의한 밀기울의 물리화학적 변형 -1. 스크류의 조합과 공정변수 조절에 따른 시스템 변수의 변화-)

  • Kim, Chong-Tai;Hwang, Jae-Kwan;Cho, Sung-Ja;Kim, Chul-Jin;Kim, Hae-Sung
    • Korean Journal of Food Science and Technology
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    • v.27 no.3
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    • pp.404-413
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    • 1995
  • System parameters (extrusion temperature, extrusion pressure, specific mechanical energy, mean residence time) were analysed on three different screw configurations during twin-screw extrusion of wheat bran. Experiments were conducted over a screw speed of $280{\sim}380\;rpm$, feed rate of $22{\sim}38\;kg/hr$ and moisture content of $17{\sim}33%$ using screws assembled with 3, 4, and 5 reverse screw elements (RSE) adjacent to the heating zone of the barrel. Extrusion temperature increased with increasing RSE but it decreased with increasing feed rate and moisture content. Decreasing the filling ratio of the screw resulted in a lower extrusion pressure, and increasing the length of the RSE gave similar results due to the higher temperature and lower viscosity of melted dough. It was also observed that increasing the feed rate and decreasing moisture content resulted in the reduced extrusion pressure. Specific mechanical energy (SME) decreased when the feed rate and moisture content increased, and SME increased when using RSE posses from 3 to 5. Screw configuration posses with 4 RSE yielded the longest RT, and the smaller the die hole, the higher the RT. In contrast, RT decreased when the feed rate increased. With increasing moisture content RT for 3 RSE increased, but that for 4 and 5 RSE decreased.

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Adsorption Properties of U, Th, Ce and Eu by Myogi Bentonite Occurring in Japan (일본 묘기광산 벤토나이트의 물리화학적 성질 및 U, Th, Ce 및 Eu 흡착특성)

  • Song Min-Sub;Koh Sang-Mo;Kim Won-Sa
    • Journal of the Mineralogical Society of Korea
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    • v.18 no.3 s.45
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    • pp.183-194
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    • 2005
  • The mineralogical, physicochemical and thermal properties of the Myogi bentonite occurring in Japan were measured. A adsorption properties of U, Th, Ce and Eu ions on the Myogi bentonite were also investigated in different solution concentrations and pH conditions. The Myogi bentonite showed a strong alkaline character (pH 10.4), very high swelling, viscosity property and CEC, and a slow flocculation behavior due to the strong hydrophilic property. By the thermal analysis, the dehydroxylation of crystal water in bulk and clay fractions of the Myogi bentonite occur at $591^{\circ}C$ and $658^{\circ}C$, respectively, The adsorption experiments of ions such as U, Th, Ce and Eu were conducted for 0.2 g bentonites with 20mL solutions of various concentrations and different pH conditions with pH 3, 5, 7, 9, and 11. As a result, the Myogi bentonite showed excellent adsorption capacities for Ce, Th and Eu ions, whereas U ion showed very low adsorption capacity. Generally, Ce, Th and Eu ions showed the similar adsorption properties for the different concentrated solutions and pH conditions. These adsorption properties seem to be affected by the formation of various forms of chemical species and precipitation as well as ionic exchange reaction and surface adsorptions on smectite. Some associated zeolite minerals perhaps have some effects on the adsorption of U, Th, Ce and Eu on Myogi bentonite.