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4시 20분부터 제1과학관 31214 e+강의실에서 다과를 준비하오니 많은 참석 부탁드립니다
제목: 액체금속 및 물의 과냉각 현상과 국소구조와의 관계 : 정전기 공중부양 기술 및 dynamic diamond anvil cell
연사: 이 근 우 박사님 (한국표준과학연구원)
일시: 2011년 6월 8(수) 오후4:30
장소: e+첨단강의실 (31214호실)
초록: In this talk, new technologies will be introduced that allow studying extreme physical properties at high temperature and high pressure. The first is electrostatic levitation (ESL) which provides containerless and contactless environment. Using the ESL, we can study physical properties of solids and liquids up to about 4000 oC and achieve deep supercooling, since it removes heterogeneous nucleation site by lifting liquid drop. The high temperature and deep supercooling can not be obtained with normal methods. The second is dynamic diamond anvil cell (dDAC) that is able to modulate a given static pressure with high compression rate, ~ 103 GPa/s. This device has been developed to study intermediate strain rate between static (<10-2 /s) and dynamic pressure (> 104 /s), since dDAC can control freely de/compression rate. This capability has been highly desired in high pressure physics community, because there have been discrepancies between static and dynamic pressure study which should be resolved.
Under containerless environment achieved by ESL, I have studied thermodynamics and structure of liquid metals and alloys with quasicrystals, polytetrahedral crystals, and simple crystals. In particular, the relation of the local order of supercooled/supercompressed liquids and nucleation barrier has been focused since it is important to understand (nano) crystallization, glass transition, material synthesis, and so on. In the present, it will be shown that Frank’s hypothesis, i.e., icosahedral short range order as the local order of liquid metals that has been unsolved for over 50 years, is unambiguously vindicated (PRL 2003, PRB 2005, 2008). In addition, liquid metals can have different local orders depending on electronic properties (PRL 2004, JCP 2007).
On the other hand, supercompressed liquid water transforms metastable ice VII phase in stable ice VI phase with fast compression, but not with slow compression, confirmed by time-resolved microRaman scattering and optical image. Our results show that the supercompressed liquid water has bcc-like order, which supports the local order of high density liquid water suggested by simulation studies (PRB 2006). Additionally, it will be demonstrated that fast compression rate can affect crystal morphology during crystal growth, and molecular dynamics (PNAS 2007). In conclusion, the similarity of local order between liquids and crystals determines the path of phase transformation.
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