• Clean Technology
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• v.15 no.4
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• pp.233-238
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• 2009

Supercritical fluid processes have gained great attention as a new and environmentally-benign method of preparing the microparticles of energetic materials like explosives and propellants. In this work, RDX (cyclotrimethylenetrinitramine) was selected as a target explosive. The microparticle formation of RDX using supercritical anti-solvent (SAS) recrystallization process was performed and the effect of operating variables on the size and morphology of prepared particles was observed. N,N-Dimethylformamide was used as organic solvent for dissolving the RDX. The size of the RDX particles decreased remarkably up to less than $10\;{\mu}m$ by SAS recrystallization. In the range of operating conditions of the SAS process studied in this work, the finest RDX particles were obtained at 313.15K, 150 bar, and 15wt% RDX concentration in feed solution.

• Journal of KIISE:Information Networking
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• v.37 no.3
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• pp.167-174
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• 2010

Recently the distributed topology control algorithm for constructing the Recrystallization Topology in the unstructured peer-to-peer network was proposed. In this paper, we prove that such a hierarchical topology is a scale-free power-law network. We present a model of a construction process of the distributed protocol, and analyze it based on a mean-field approximation and the continuum theory, so that we show that the constructed Recrystallization Topology is a scale-free network. In the proposed model, all nodes are born with some initial attractiveness and the system incorporates the rewiring of some links at every time step. Some old links are removed with the anti-preferential probability, and some new links are added with preferential probability. In other words, according to the distributed algorithm, each node makes connections to the more-preferential nodes having higher hit-ratio than other nodes, while it disconnects the anti-preferential nodes having lesser hit-ratio. This gives a realistic description of the local processes forming the recrystallization topology in unstructured peer-to-peer network. We calculate analytically the degree distribution. The analytic result indicates that the constructed network is a scale-free network, of which the scaling exponent is 3.

• Proceedings of the Materials Research Society of Korea Conference
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• 2006.05a
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• pp.40.1-40.1
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• 2006

• Polymer(Korea)
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• v.31 no.5
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• pp.447-453
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• 2007

In this study, we fabricated recrystallized PLGA (rPLGA) particles using the vacuum drying method. In order to investigate an applicability of the rPLGA particles for controlled release system of 5-fluorouracil (5-FU) loaded PLGA wafer, we prepared three different wafers using; 1) untreated PLGA (uPLGA), 2) rPLGA, and 3) uPLGA and rPLGA (4 : 1, 1 : 1 or 1 : 4). The rPLGA particles were characterized using NMR, IR and GPC to compare with uPLGA particles. The surface and cross section morphology of the prepared wafers were observed by the scanning electron microscope. The release profile of the 5-FU loaded wafer was measured by HPLC. The 5-FU/rPLGA wafer released the incorporated 5-FU in a sustained manner with low initial burst compared to 5-FU/uPLGA. These results showed that the ratio of pure PLGA/recrystallized PLGA can affect the release behaviors.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.46.2-46.2
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• 2009

휴대전화, 랩톱 컴퓨터 등 각종 모바일기기 및 디스플레이 기기의 경박단소화 및 고기능화에 따라 연성회로기판(FPCB)의 사용량이 증가하고있다. 연성회로기판의 핵심소재인 동박적층필름(FCCL)은 폴리이미드필름과 접착층, Cu 층으로 구성되는데, 이 중접착층으로 사용되는 Ni-20Cr합금은 에칭공정 후 Cr의 잔류에 의해 불량률 증가가 문제되고 있어, Ni-Cr합금 스퍼터링 타깃의 Cr 함량 저감 또는 Cr-free Ni합금 개발 등이 요구되고 있다. 본 연구에서는 차세대 FCCL 본드층에 적합한 Ni기 합금을 개발하기 위한 기초연구로써 Cr 함량 및 가공열처리조건에 따른 미세조직과 집합조직 변화를 조사하였다. 4N급의 고순도Ni과 Cr을 진공 플라즈마 용해장치로 용해하여Ni-xCr (x=5, 10, 15, 20wt.%)합금 잉곳을 만들고, 이를 두께감소율 90%로 냉간압연한 후, $600^{\circ}C$ 및 $800^{\circ}C$에서 10~120분 동안 어닐링하여 시편을 준비하였다. 광학현미경으로 미세조직을 관찰하고, Micro-Vickers 경도시험을 통해 어닐링 조건에 따른 경도변화를 조사하였다. 또한 SEM-EBSD를 이용하여 집합조직 및 입계특성을 분석하였다. $600^{\circ}C$ 어닐링 시 Cr함량이 증가할수록 재결정 완료시간이 증가하여 Ni-20Cr합금의 경우 2시간이상 어닐링에도 재결정이 일어나지 않았다. $800^{\circ}C$ 어닐링 시 10분 어닐링 조건에서 4종류 합금 모두 재결정이 완료되었으며, 동일한 어닐링 조건에서 Cr함량이 증가할수록 결정립이 작아지는 것으로 나타났다. $800^{\circ}C$ 2시간 어닐링 조건에서 Ni-5Cr 합금의 주요 집합조직은 {223}<113>과 {122}<112>로 나타났으며, 이중 {223}<113>은Cr 함량이 증가함에 따라 점차 {122}<112>에 가까운 방향으로 변화되어 Ni-20Cr 합금의 경우 {123}<112>만이 형성되었다. 이러한 집합조직의 변화는 적층결함에너지 감소에 의한 ${\Sigma}3$ 입계의 분율 증가와 밀접한 관련이 있는 것으로 사료된다.

• Analytical Science and Technology
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• v.5 no.3
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• pp.319-325
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• 1992

Plasma are melting method was used in making Mo-1.17 Ti-0.18 Zr-0.06 C ingot having over 99% of the theoretical density. Oxygen content herewith, decreased from the origin of 830ppm to 40ppm. After cold rolling of Mo alloy by 50%, the recrystallization behaviors were studied in the temperature range from $800^{\circ}C$ to $2100^{\circ}C$ for 1 hr isochronical holding time and also at $1400^{\circ}C$, $1500^{\circ}C$, $1600^{\circ}C$ for varying isothermal holding time 0 to 108000sec. The complete recrystallization temperature of Mo was $1400^{\circ}C$ but that of Mo alloy was $1700^{\circ}C$. 50%-1 hr recrystallization temperature of Mo alloy sheet was about $1500^{\circ}C$ and when compared to Mo there was an increase of over $300^{\circ}C$. The activation energy of recrystallization of Mo alloy sheet was 508kJ/mol.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.422-429
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• 2000

To investigate the effect of annealing temperature and time on the recrystallization behavior and microstructure of Zr-based alloys, the specimens of Zr-0.8Sn-0.4Nb-0.4Fe-0.2Cu, Zr-1Nb, Zircaloy-4, and unalloyed Zr were cold-worked and annealed at 400, 500, 600, 700, 800, $900^{\circ}C$ for 30 to 5000 minutes. The hardness, microstructure and precipitate of the specimens were investigated by using micro-hardness tester, optical microscope and transmission electron microscope, respectively. The recrystallization of Zr-based alloys occurred between $400^{\circ}C$ and $600^{\circ}C$. As the content of alloying elements increased, the hardness and recrystallization temperature of the alloys increased though the grain sizes after recrystallization decreased. It was supposed that the hardness of Zr-based alloy with Fe or Cu increased during recovery by the formation of Fe or Cu precipitates.

• 기계와재료
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• v.23 no.3
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• pp.6-14
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• 2011

기존의 소성가공공정에서의 미세조직 예측 기술은 온도 및 외력에 의한 금속학적 변화를 모사하기 위해 다수의 실험에 기반한 경험적 모델링 작업이 요구되고 이를 구현할 수 있는 기계 및 재료적 지식 기반이 동시에 요구되기 때문에 현재까지는 신뢰성을 갖는모델 및 수치해석기술은 충분히 확보되지 못한 상태이다. 이러한 미세조직 예측기술의 정확도를 향상시키고자 하는 일환으로, 최근에는 매크로 스케일의 FE 해석과의 결합을 통해 소성가공공정과 이후의 열처리 공정에서의 정적 재결정 동적 재결정 상변태 변형유기변태 등 복잡한 미세조직 현상을 그 변화가 일어나는 실제 메조 스케일에서 예측하고자 하는 연구가 시도되고 있다. 본고에서는 그 중에서도 소성가공에서 발생하는 재결정 거동 예측에 주로 적용되고 있는 데조스케일 해석 기법과 매크로-메조 다단위 스케일 해석 기법의 국내외 연구 현황에 대해 알아보고자 한다. 또한, 이를 이용한 소성가공공정에서의 미세조직 예측 사례와 미세조직 예측기술의 전망에 대해 기술하고자 한다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.129-138
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• 1998

The objective of this study is to demonstrate the ability of a computer simulation of microstructural evolution in hot forging of C-Mn steels. The development of microstructure is strongly dependent on process variables and metallurgical factors that affect time history of thermodynamical variables such as temperature, strain. and strain rate during deformation. Then finite element method is applied for the prediction of microstructural evolution, and it should be coupled with heat transfer analysis to consider the change of thermodynamical properties during forming process. In this study, Yada's recrystallization model and rigid-thermoviscoplastic finite element method are employed in order to analyze microstructural evolution during hot forging process. To show the validity and effectiveness of the proposed method, experiments are accomplished and the results of experiments are compared with those of simulations.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.05a
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• pp.153-158
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• 1998

현재 변압기 철심 재료는 주로 방향성 전기 강판이 사용되고 있으며, 우수한 자기유도 특성과 낮은 철손이 중요한 요건이다. 방향성 전기강판은 약 3%Si을 함유하며 2차 재결정에 의해 {100}<001> Gross texture로 배향된다. 극박 3%Si-Fe의 2차 재결정에 미치는 냉간 압연율의 효과에 대한 연구결과 보고는 거의 없다. 본 연구의 목적은 다단 냉간압연에 의해 제조되는 박판 3%Si-Fe strip의 자기유도에 미치는 최종 냉간 압연율의 효과를 밝히는 것이다. (중략)