• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.276-285
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• 2003

In the undercooled melt of $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy, the solidification behavior including nucleation and growth of crystals at the micrometer level has been observed in-situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy specimens were cooled from the liquid state to glass transition temperature. 575 K, at various cooling late under a helium gas flow. According to the cooling rate, the morphologies of the solidification front are changed among various types, irregular jog like front, columnar dendritic front, cellular grain, star like shape jog and fine grain, etc. The velocities of the solid-liquid interface are measured to be $10^{-5}{\sim}10^{-8}$ m/s which are at least two orders higher than the theoretical crystal growth rates. Combining the morphologies observed in terms of cooling rates and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy. The continuous cooling transformation (CCT) diagram was constructed from solidification onset time at various linear cooling conditions with different rate. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.5 K/s, which is in agreement with the previous calorimetric findings.

• Journal of Magnetics
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• v.18 no.4
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• pp.395-399
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• 2013

The metallic glass ribbons of $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Mo_4$ (x = 0, 0.3, 0.6, 0.9 at.%) and $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Nb_4$ (x = 0, 0.3, 0.6, 0.9 at.%) were obtained by melt spinning with 25-30 ${\mu}m$ thickness. The thermal stability, mechanical properties and magnetic properties of Fe-Co-B-Si based systems were investigated. The values of thermal stability were measured using differential scanning calorimetry (DSC), including glass transition temperature ($T_g$), crystallization temperature ($T_x$) and supercooled liquid region (${\Delta}T_x=T_x-T_g$). These amorphous ribbons were identified as fully amorphous, using X-ray diffraction (XRD). The mechanical properties of Febased samples were measured by nano-indentation. Magnetic properties of the amorphous ribbons were measured by a vibrating sample magnetometer (VSM). The amorphous ribbons of $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Mo_4$ (x = 0, 0.3, 0.6, 0.9 at.%) and $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Nb_4$ (x = 0, 0.3, 0.6, 0.9 at.%) exhibited soft magnetic properties with low coercive force ($H_c$) and high saturation magnetization (Ms).

• Korean Journal of Materials Research
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• v.22 no.7
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• pp.368-373
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• 2012

Glasses were prepared with compositions of $(13-x)BaO-80B2_O_3-7Li_2O{\cdot}xSm_2O_3$, BBLSx(x=0.5, 0.4, 0.3) by melting the starting materials of boron oxide(99.9%), lithium oxide(99.9%), barium carbon oxide(99.9%), and samarium oxide(99.9%) and then quenching the melt at $1350^{\circ}C$. This led to good-quality BBLSx(x=0.4, 0.3) and poor-quality BBLSx(x=0.5) glasses. The physical and structural properties of the BBLSx glasses were studied by means x-ray diffraction, scanning electron microscopy(SEM), differential scanning calorimetry(DSC), and dielectric spectroscopy. From the x-ray diffraction and SEM results, the quality of the BBLSx glasses significantly depends on the $Sm_2O_3$ concentration. The x-ray diffraction pattern showed that the crystallites in the BBLSx glasses after heat treatment at $700^{\circ}C$ may be $LiBaB_9O_{15}$. From the DSC results, the glass transition temperatures($T_g$), crystallization temperatures($T_c$), and the maximum temperatures of the crystallized($T_p$) BBLSx glasses all changed with the $Sm_2O_3$ concentration. According to the dielectric spectroscopy results, the values of the real dielectric constant and Tan ${\delta}$ of the BBLSx glasses depended on the $Sm_2O_3$ concentration. The values of the real dielectric constant and Tan ${\delta}$ were also shown to depend on the measuring temperature, possibly due to the ion migration in the bulk of the BBLSx glasses.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.8
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• pp.134-139
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• 2000

In order to understand the removal mechanism and seek the optimal conditions. KrF excimer laser ablation of Cr films on glass substrates is investigated. The surface morphology of the laser-irradiated spot is examined by SEM. The measured single-shot ablation rate is found to be about two times the result of numerical analysis based on a surface vaporization model and heat conduction theory. Surface morphology examination indicates that the Cr film is removed by the sequence of melting-surface vaporization-,melt expulsion by plasma recoil and that the outmost ripple of the diffraction pattern gives a strong effect on the morphology of molten Cr during the melting and vaporization processes. To seek the optimal process parameters for micro patterning morphological investigation is carried out experimentally on samples having different chromium film thicknesses. Optimal processing conditions are determined to enhance the accuracy and quality of thin film removal for micro patterning.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.5
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• pp.208-214
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• 2019

The glass of $BaO-GeO_2-La_2O_3-ZnO$ system with a transmittance of more than 75 % at mid-wave infrared (MWIR) region in the range of $3{\mu}m$ to $5{\mu}m$ is manufactured and its property is evaluated. After selecting construction that can melt glass through flow button test, $BaO-GeO_2-La_2O_3$ system where 10 mol%, 20 mol% of ZnO were added respectively were melted at $1350^{\circ}C$ for 1 hour and $BaO-GeO_2-La_2O_3$ system of glass was manufactured. Among them, with 20 mol% of ZnO, 16 mol% BaO-56 mol% $GeO_2-8mol%$ $La_2O_3-16mol%$ ZnO system of glass was found to has less than $660^{\circ}C$ of glass transition temperature, more than 1.70 of refractive index, and more than 530 of knoop hardness. Therefore, it is concluded that glass of $BaO-GeO_2-La_2O_3-ZnO$ system of glass with 20 mol% ZnO has good melting conditions at low temperatures and excellent optical properties, thus, can be utilized for special optical materials field.

• Polymer(Korea)
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• v.29 no.6
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• pp.575-580
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• 2005

The hydroxy terminated aliphatic hyperbranched polyesters having different generations were synthesized by using melt polycondensation procedure. Then, the terminal groups of hyperbranched polyesters were modified by using acryloyl chloride and characterized by $\^{1}H$-NMR and GPC techniques. As a result of the modification of terminal groups for hyperbranched polyesters, the phase of the polymers were changed from sticky solid to high viscous liquid indicating that the glass transition temperatures of modified hyperbranched polyesters were lower than the original one. The thermal stabilities of hydroxy terminated hyperbranched polyesters were higher than those of terminal group-modified polymers.

• Elastomers and Composites
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• v.52 no.3
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• pp.173-179
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• 2017

Side-chain liquid crystalline polymers having polysiloxane skeletons were synthesized by a thiol-ene reaction, using two kinds of mesogenic groups: a cholesteryl group for induction into a cholesteric liquid crystal phase and a triazomesogenic group for imparting light-sensitivity. All the synthesized polymers were crystalline, except the one with a single cholesteryl group. Crystallinity, glass transition temperature, and melt transition temperature increased with increasing content of the azomesogenic group. The polymer (P-C10A0) with a single cholesteryl group has a cholesteric phase, the one (P-C0A10) with a single azomesogenic group has a smectic phase, and those with both types of mesogenic groups showed both smectic and cholesteric phases. The temperature ranges of the two liquid crystalline phases in the co-polymers were independent of the contents of the two types of mesogenic groups. The rate of photoisomerization of the light-sensitive azobenzene group in the polymer decreased with increasing azobenzene content due to steric hindrance between the azomesogenic groups.

• Analytical Science and Technology
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• v.12 no.5
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• pp.436-440
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• 1999

Antistatic property and crystallization behavior of antistatic poly(ethylene terephthalate) (PET) were studied by feeding antistatic agents into polycondensation reactor. Glass transition and melting temperature of antistatic PET were decreased by poly(ethylene glycol) (PEG) component of antistatic agent. The crystallization rate of antistatic PET was inhibited by decreasing crystallization temperature. Thermal properties and crystallization behavior was affected POAG content of antistatic agent rather than sodium alkylsulfonate of it. The main antistatic component of antistatic agent was POAG. The main role of sodium alkylsulfonate was increasing melt viscosity of antistatic poly(ethylene terephalate) polymer.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.105-112
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• 2010

Weldlines are generated during the injection molding process when two or more melt flows are brought into contact. The weldlines are unavoidable in the cases of presence of holes or inserts, multi-gated delivery systems, significant thickness change, etc. At the welded contact region, a 'V'-shaped notch is formed on the surface of the molded part. This 'V'-notch deteriorates not only surface appearance but also mechanical strength of the molded part. To eliminate or reduce weldlines so as to improve the weldline strength, the mold temperature at the corresponding weld locations should be maintained higher than the glass transition temperature of the resin material. The present study implements high-frequency induction heating in order to rapidly raise mold surface temperature without a significant increase in cycle time. This induction heating enables to local mold heating so as to eliminate or reduce weldlines in an injection-molded plastic part. The effect of induction heating conditions on the weldline strength and surface appearance of an injection-molded part is investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.103-103
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• 2009

본 논문에서는 기존의 GST(GeSbTe=2:2:5)와 비교하여 상변화 재료로서의 Ga 도핑된 $Ge_2Sb_2Te_5$의 가능성을 확인하고자 하였다. 실험에 사용된 Ga 도핑된 $Ge_2Sb_2Te_5$ 박막은 전통적 melt-quenching 방법에 의해 비정질로 제작된 벌크를 Thermal evaporation을 통하여 Si(100) 및 유리 (coming glass, 7059) 기판 위에 200nm의 두께로 증착하여 제작하였다. 각 박막의 상변화 특성은 여러 온도에서 열처리된 박막을 X-ray diffraction (XRD) 측정을 통하여 확인하였다. 각 조성 박막의 비정질-결정질 상변화속도 비교를 위하여 나노-펄스 스캐너 (nano-pulse scanner)를 사용하여 power; 1~17mW, pulse duration; 10~460ns 범위에서 박막의 상변화에 따른 반사도 차이를 측정 분석하였다. Ga의 도핑농도에 따른 전기적 특성 차이를 확인하기 위하여 4-point probe를 이용하여 박막의 면 저항을 측정하였고 또한 hall 측정을 통하여 박막의 흘 계수, 흘 농도 및 이동도를 확인하고 Ga가 상전이에 미치는 영향에 대하여 분석하였다.