• 폴리머
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• 제29권2호
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• pp.198-203
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• 2005

용융 압출 발포에 의하여 폴리락틱산(PLLA) 지지체를 제조하고 발포 조건이 지지체의 구조와 기계적 특성에 미치는 영향을 살펴보고 이를 염 추출법에 의하여 제조된 지지체와 비교하였다. 발포제를 함유한 PLLA 용융체가 압출기 및 다이에서 체류하는 시간이 발포제의 무게를 최대로 감소시키는 시간과 일치하여야 최적의 PLLA 지지체의 구조를 얻을 수 있음을 확인하였다. PLLA지지체의 구조를 유지하기 위해서는 발포제의 함량을 $10\;wt\%$ 이하로 조절해야 하며 PLLA 지지체의 다공도는 PLLA의 압출기에서의 체류시간에 가장 큰 영향을 받음을 알 수 있었다. 용융 압출 발포에 의하여 얻어진 지지체는 일반적으로 염 추출법에 의하여 제조된 지지체보다 다소 낮은 다공도를 갖지만 발포 조건의 조절에 의하여 적절한 다공 크기와 다공의 연결성을 가지며 동시에 우수한 기계적 특성을 가져 경조직 재생(hard tissue regeneration)용으로 사용이 가능할 것으로 사료된다.

• 한국결정성장학회지
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• 제13권2호
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• pp.83-87
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• 2003

부유대역용융성장법을 이용한 $(Nd/Y)_{1.8}Ba_{}2.4Cu_{3.4}O_{7-x}$[이하 (Nd/Y)1.8]계 고온초전도체를 대기 중에서 용융성장실험을 하였다. 용융성장에 사용된 (Nd/Y)1.8 시편은 rubber 몰드를 이용해 냉간정수압성형(CIP) 과정을 거쳐 길이방향 원통 형상으로 제조되었다. 용융성장 된 (Nd/Y)1.8 초전도체는 SEM, TEM 그리고 SQUID magnetometer를 이용해 미세구조 및 초전도특성을을 평가하였다. 특히 용융성장 된 (Nd/Y)1.8 초전도체의 SEM에 의한 미세구조 관측 결과 초전도상인 (Nd/Y)123 matrix 내에 비초전도상인 (Nd/Y)211 inclusions이 균질하게 분포되어 있는 것이 관측되었다. 또한 용융성장 된 (Nd/Y)1.8 초전도체는 90K에서 임계온도가 시작되어 77K 이상의 온도에서 포화되는 특성을 보였다.

• 한국주조공학회지
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• 제33권2호
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• pp.69-74
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• 2013

Silicon (Si) wafer was grown by using direct growth from Si melt and contaminations of wafer during the process were investigated. In our process, BN was coated inside of all graphite parts including crucible in system to prevent carbon contamination. In addition, coated BN layer enhance the wettability, which ensures the favorable shape of grown wafer by proper flow of Si melt in casting mold. As a result, polycrystalline silicon wafer with dimension of $156{\times}156$ mm and thickness of $300{\pm}20$ um was successively obtained. There were, however, severe contaminations such as BN and SiC on surface of the as-grown wafer. While BN powders were easily removed by brushing surface, SiC could not be eliminated. As a result of BN analysis, C source for SiC was from binder contained in BN slurry. Therefore, to eliminate those C sources, additional flushing process was carried out before Si was melted. By adding 3-times flushing processes, SiC was not detected on the surface of as-grown Si wafer. Polycrystalline Si wafer directly grown from Si melt in this study can be applied for the cost-effective Si solar cells.

• 폴리머
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• 제27권6호
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• pp.521-527
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• 2003

신디오택틱 폴리프로필렌 (sPP)과 아이소택틱 폴리프로필렌 (iPP)은 용융과정에서 결정의 재배열이 나타나며 이와 같은 재결정 현상을 해석하기 위하여 결정화도와 결정구조의 변화, 동역학적 물성을 고찰하였고 DSC, FT-IR, SAXS, DMA를 이용하였다. 본 연구에서 실험된 조건에서는 sPP의 재결정화 현상을 확인할 수 없었으며, iPP는 용융으로부터 냉각되는 속도가 빠르게 될 수록 재가열시 재결정화 현상이 두드러졌다. iPP의 재결정화가 진행되는 동안 tan $\delta$가 0.119에서 0.101로 감소하여 탄성율이 증가한 결과를 보이나 결정화도는 거의 일정하게 유지되었다. 더욱이 재결정 현상이 진행되는 동안 SAXS 산란피크의 반가폭이 약 30% 감소하여 라멜라의 질서가 증가하는 거동을 보였다.

• 한국전기전자재료학회논문지
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• 제19권6호
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• pp.579-585
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• 2006

We fabricated BSCCO-2212 (2212) rod by the melt casting process (MCP) and evaluated the effect of the melt flowing on the critical current ($I_c$) by using vertical and tilt casting. It was observed that the $2212-SrSO_4$ rod processed by the tilt casting method with homogeneous pre-heating temperature of the mold had a higher $I_c$ than that processed by the vertical casting method. We also evaluated the influence of the strontium sulfates ($SrSO_4$) addition on the texture, microstructure, critical current and temperature, and mechanical hardness of the $2212-SrSO_4$ rods. It was observed that the addition of $SrSO_4$ improved the critical current ($I_c$) and mechanical hardness of the 2212. The $I_c$ of the 2212 increased as the $SrSO_4$ content increased and reached a peak value (260 A at 77 K) at an $SrSO_4$ content of 6 wt.%. In addition, the addition of $SrSO_4$ had a beneficial effect on the mechanical hardness of the 2212. We studied the possible cause of the variation in the $I_c$ with the melt flowing and the $SrSO_4$ content based on the XRD, EPMA analysis and the microstructural observation.

• 한국결정성장학회지
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• 제1권2호
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• pp.23-33
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• 1991

Mn-Zn Ferrite는 단결정을 성장하기 위하여 용융하는 동안 불균질 용융과 ZnO휘발의 고유특성을 갖는 재료이다. 그 결과로, 결정성장축을 따라 양이온의 분포가 불균일 하게 된고 또한 기존의 Bridgman법에서는 도가니내에서 용융대가 장시간 유지됨으로써 백금입자가 결정안으로 침입하게된다. 이들은 훼라이트의 자기적 성질을 저하시키는 성질을 갖고 있다. 그러나 새로운 성장법에서는 이러한 단점들을 극복하고 양질의 단결정을 얻기 위하여 결정성장 인자들의 관계를 고찰하였으며 그 인자들은 다음과 같다 : 도가니내의 melt 높이, melt의 표면장력과 밀도, 계면에서의 melt거동, 도가니와 고액계면의 형상, 원료공급속도, 결정성장속도. 아울러, 성장된 결정의 조성을 분석하였을 때 초기조성과 비교하여 $\textrm{Fe}_2\textrm{O}_3$ 1.5 mol%, MnO, Zn 2.0 mol% 이내로 조성 변동은 각각 억제되었고 성장결정면 (110)에서 화확적인 etching 법을 이용하여 광학현미경을 통해 결정내부등을 관찰하였으며, 자기적 특성등을 측정하였다.

• 대한금속재료학회지
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• 제47권12호
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• pp.828-833
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• 2009

As a fundamental study in the development of a distillation process for ferromanganese alloy melts, the evaporation behavior of an electrolytic manganese melt under reduced pressure was investigated. The melt temperature, vacuum degree, surface area of the melt, and reaction time were considered as experimental variables. The amount of vaporized manganese increases linearly as the reaction time increases, and the evaporation of manganese was promoted by increasing the temperature and surface area of the melt. In the pressure range below the equilibrium vapor pressure of manganese, the amount of vaporized manganese per unit surface area of the melt increased sharply with a decrease of the pressure in the reaction chamber. An empirical equation for the evaporation rate of manganese was derived by regression analysis. The evaporation coefficient of manganese was determined to be approximately $3.84{\times}10^{-3}(g{\cdot}K^{1/2})/(Pa{\cdot}cm^2{\cdot}min)$ under the investigated conditions.

• 한국결정성장학회지
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• 제18권5호
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• pp.191-194
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• 2008

We will focus on the horizontal Bridgman growth system to analyze the transport phenomena numerically, because the simple furnace system and the confined growth environment allow for the precise understanding of the transport phenomena in solidification process. In conventional melt growth process, the dopant concentration tends to vary significantly along the crystal. In this work, we propose the modification of crucible geometry for improving the productivity of silicon single-crystal growth by controlling axial specific resistivity distribution. Numerical analysis has been performed to study the transport phenomena of dopant impurities in conventional and proposed Bridgman silicon growth using the finite element method and implicit Euler time integration. It has been demonstrated using mathematical models and by numerical analysis that proposed method is useful for obtaining crystals with superior uniformity along the growth direction at a lower cost than can be obtained by the conventional melt growth process.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1680-1690
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• 2006

As a promising and novel manufacturing technology, laser aided direct metal deposition (DMD) process produces near-net-shape functional metal parts directly from 3-D CAD models by repeating laser cladding layer by layer. The key of the build-up mechanism is the effective control of powder delivery and laser power to be irradiated into the melt-pool. A feedback control system using two sets of optical height sensors is designed for monitoring the melt-pool and real-time control of deposition dimension. With the feedback height control system, the dimensions of part can be controlled within designed tolerance maintaining real time control of each layer thickness. Clad nugget shapes reveal that the feedback control can affect the nugget size and morphology of microstructure. The pore/void level can be controlled by utilizing pulsed-mode laser and proper design of deposition tool-path. With the present configuration of the control system, it is believed that more innovation of the DMD process is possible to the deposition of layers in 3-D slice.

• 한국안전학회지
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• 제8권2호
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• pp.3-9
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• 1993

For comparison, we used Ca and Mg as reducers to produce TiFe hydrogen stroage alloy from Fe and TiO$_2$by the Reduction-Diffusion process. The results obtained were as follow. \circled1 Ca was found to be effective both for reduction and diffusion processes. Moreover, Ca oxide was easily removed in an NH$_4$Cl solution after the reaction. \circled2 In the case of using Ca as a reducer, the Reduction-Diffusion process is considered to take place in the foiling three steps. First, TiO$_2$is reduced to Ti by Ca over 100$0^{\circ}C$. Second, the atomic Ti drifts in the Ca melt and meets Fe particles. Finally, the atomic Ti diffuses in to the Fe particles. \circled3 In the case of using Mg as a reducer, We found that the reduction reaction of TiO$_2$went well. But the reduced Ti scarcely diffused into Fe particles. This was probably because no Mg melt was formed due to the high vapor pressure of Mg.