• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
• /
• pp.139-156
• /
• 1996

The phase field model is becoming the model of choice for the theoretical study of the morphologies of crystals growth from the melt. This model provides an alternative approach to the solution of the classical (sharp interface) model of solidification by introducing a new variable, the phase field, Ø, to identify the phase. The variable Ø takes on constant values in the bulk phases and makes a continuous transition between these values over a thin transition layer that plays the role of the classically sharp interface. This results in Ø being governed by a new partial differential equation(in addition to the PDE's that govern the classical fields, such as temperature and composition) that guarantees (in the asymptotic limit of a suitably thin transition layer) that the appropriate boundary conditions at the crystal-melt interface are satisfied. Thus, one can proceed to solve coupled PDE's without the necessity of explicitly tracking the interface (free boundary) that would be necessary to solve the classical (sharp interface) model. Recent advances in supercomputing and algorithms now enable generation of interesting and valuable results that display most of the fundamental solidification phenomena and processes that are observed experimentally. These include morphological instability, solute trapping, cellular growth, dendritic growth (with anisotropic sidebranching, tip splitting, and coupling to periodic forcing), coarsening, recalescence, eutectic growth, faceting, and texture development. This talk will focus on the fundamental basis of the phase field model in terms of irreversible thermodynamics as well as it computational limitations and prognosis for future improvement. This work is supported by the National Science Foundation under grant DMR 9211276

• 한국초전도ㆍ저온공학회논문지
• /
• 제1권1호
• /
• pp.15-21
• /
• 1999

Textured bulk $YBa_2Cu_3O_x$ superconductors samples were grown directionally using different precursors of $YBa_2Cu_3O_x$ power. and a mixture of $YBa_2Cu_3O_5, BaCuO_2 and CuO$ powder. The microstructures and superconducting properties of the samples were compared. The mixture powder produced better microstructures i.e. dense and crack-free so that a higher critical current density was achieved at the same hot-zone temperature of 115$0^{\circ}C$ than the reacted powder does. When the reacted powder used as a precursor, as the hot-zone temperature increased upto 1215$^{\circ}C$, the texture of the sample improved and the critical current density increased. The amount of melt in the sample is of secondary importance for the growth of superconducting $YBa_2Cu_3O_x$ grains. The microstructures and superconductivity of good quality superconductors grown directionally were more strongly influenced by the kind of precursor rather than the amount og melt in a sample.

• Nuclear Engineering and Technology
• /
• 제3권3호
• /
• pp.129-140
• /
• 1971

3.25% 규소를 함유하는 규소강을 융해·합금하고 압연·열처리하여 연질 자심재료로서 응용범위가 넓은 방향성 규소강판을 제조·실험했다. 이 연구에서는 잉고트 중의 망간 및 유황함량, 탄화물 석출과 유관한 열간압연 직후의 열처리조건, 2차 냉간 압연율 등이 2차 재결정 및 집합조직에 미치는 영향을 다루었다. 그 중에서도 특히 2차 냉간 압연율이 2차 재결정과 관련한 각종 활성화 에너지와 집합조직에 미치는 영향을 중점적으로 구명하였다. 2차 냉간 압연율이 10%인 시편은 응력 병형의 도입으로 인한 결정입계 이동으로 결정립성장 만이 관찰되었으며 핵생성을 동반한 2차 재결정은 일어나지 않았다. 2차 냉간 압연율이 30%인 시편에서는 2차 재결정을 위한 핵생성만 있었으며 2차 재결정이 완전히는 일어나지 않았다. 이 실험 조건하에서 50%의 2차 냉간압연율이 2차 재결정을 일으키기에 최적 냉간 압연율이며 가장 높은 직접도를 얻을 수 있는 압연율이었다.

• 한국분말재료학회지
• /
• 제9권6호
• /
• pp.381-393
• /
• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

• 한국염색가공학회지
• /
• 제2권4호
• /
• pp.237-244
• /
• 1990

Syntheses and liquid-Crystallinites of thermotropic copoly (ester amide)s were investigated. The three components melt polycondensation of 4,4'-dicarboxy-$\alpha$, $\omega$-diphenoxyalkane as an A component, 4-4'diacetoxybiphenyl as a B, and p-N-acetoxy-aminobenzoic acid as a C gave the thrmotropic copoly(ester amide)s containing a flexible splacer in the polymer backbone. Diacetylated hydroquinone, methyl hydroquinone, chlorohydroquinone, and phenyl hydroquinone were used as anther B components. A polymer(6BPAB) having 10 mol% of C component and hexamethylene space. showed a typical nematic texture between $245^{\circ}C(T_m)\; and\; more\; than\; 360^{\circ]C(T_i)$. The melting points of the members of this series of polymers increased with decreasing methylene spacer. The polymer structure and mesomorphic nature were examined by solid and solution ^{13}C-NMR4 spectroscopy, cross polarizing microscopy with a hot stage, and X-ray diffactometry.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2006년도 High Temperature Superconductivity Vol.XVI
• /
• pp.63-63
• /
• 2006

• 한국염색가공학회지
• /
• 제5권2호
• /
• pp.109-116
• /
• 1993

Synthesis and liquid-crystallinites of thermotropic polyamides and copolyamides were investigated. Thermotropic polyamides and copolyamides containing a flexible spacer in the backbone were obtained by the two or three components melt polycondensations of 4,4'-dicarboxy-${\alpha}$${\omega}$-diphenoxy alkane as an A components, 4,4'-diacetoamido-3,3' dimethoxybiphenyl as a B, 1,4-diacetoamido-benzene (diacetylated p-phenylenediamine) was used as another amide-group-forming minomer. The content of the amide groups in the thermotropic polyamide and Copolyamide widely varied depending on the structure of the amide-group forming diacetoamido monomers. A polymer (9CLDI) showed a typical nematic texture between 218$^{circle}C$ ($T_m$) and 345$^{circle}C$($T_i$) The melting points of the members of this series of polymers increased with decreasing methylene spacer. The polymer structure and mesmorphic nature were examined by solid and solution ${^13}C$-NMR spectroscopy, cross polarizing microscopy with a hot stage.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2005년도 High Temperature Superconductivity Vol.XV
• /
• pp.63-63
• /
• 2005

• 동아시아식생활학회지
• /
• 제23권3호
• /
• pp.357-364
• /
• 2013

The purpose of this study is to investigate the quality characteristics of choco-chip when using the baking soda. Medium flours are more commonly used for choco-chip cookies than cake flours due to the higher pH levels. The L and b values of the flours decreased but the redness colors were increased with the increased percentage of baking sodas. The hardness, brittleness and gumminess of cake flours and increased baking sodas were lower than the medium flours. Micrographs of the choco-chip cookies showed that the baking sodas with the medium flours had better tendency to melt the proteins than cake flours. Sensory characteristics suggested that the additional 2% of baking soda generated good appearance, flavor, color, texture and over all acceptance. According to the results, we gained knowledge on the effects of adding baking soda to the quality of cookies. And, the most recommended percentages of baking sodas base as suggested by bakers are 2%.

• 한국축산식품학회지
• /
• 제29권5호
• /
• pp.545-549
• /
• 2009

The functional properties of cheese, such as texture and melt, are known to be controlled by several important parameters. Recently, the characteristics of Ca in cheeses, especially the form of Ca (insoluble (INSOL) or soluble) and the shift in Ca equilibrium (i.e., from INSOL to soluble Ca), during aging has received a lot of attention. The INSOL form of Ca, which is present as a structural form in casein, plays a critical role in determining the functional properties of cheese during the early period of ripening (~1 mon). It seems that there is always a reduction of INSOL Ca content in cheese during ripening and there are also factors that can affect the shift in Ca equilibrium. These factors may include the composition of cheese milk, cheese manufacturing pH, acid development during aging, adopting curd-washing in various methods, pre-acidification of milk, etc. There have been many studies showing that the rheological and melting properties of cheese during ripening were significantly (p<0.05) affected by the shift in Ca equilibrium. Therefore, for cheese makers, it is now possible to predict/manage the functional properties of cheese by monitoring and controlling Ca equilibrium in cheese during aging.