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Seongeun Lee,Byunggwan Lee,Jinwook Choi,정용수,오한준,지충수 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.3
Poly(vinylidene fluoride) nanotubes were fabricated by using solution wetting methods with nanoscale AAO templates whose pore diameters were about 90 nm and 190 nm when prepared by anodizing in oxalic-/and phosphoric-acid solutions, respectively. Wetting of the AAO template was done under two conditions of heat treatments, annealing at 200℃ and then cooling to 130℃ and annealing for 1 h at 130℃ after having been kept at room temperatures. The synthesis of nanowires and nantubes was particularly affected by the annealing condition. The attenuated total reflectance (ATR) spectroscopy result suggested that the PVDF nanotubes crystallized exclusively in the α form while the nanowires formed in a mixture of α and γ phases. These results indicate that the morphology and the crystallization of the PVDF nanostructures are affected by the annealing time and temperature and by the solution wetting conditions. X-ray diffraction (XRD) patterns with a relatively high intensity at the (020) plane showed that a texture is induced in α-PVDF nanotubes when a wetting solution of 10 wt% PVDF in DMF is used.
CM247LC 초내열합금에서 일방향응고에 따른 응고조직 변화
이정석 ( Jeongseok Lee ),권석환 ( Seokhwan Kown ),윤병관 ( Byunggwan Yoon ),장병문 ( Byungmoon Chang ),정연길 ( Yongil Jung ),이재현 ( Jehyun Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.11
Directional solidification of CM247LC was performed at a constant growth velocity (300 mm/h) using a Bridgman type furnace. Microstructural features, including the number of grains, PDAS, and EBSD IPF map, were investigated with progressive positions from the starter block. As directional solidification proceeded, the number of grains decreased and PDAS increased. These results indicate that the thermal gradient decreases with distance from the starter block. Thermal gradient changes were estimated by dendrite spacing change in the directionally solidified rod. The EBSD IPF map showed that almost all of the grains were close to the < 001 > preferred direction, but with heights of about 300 mm from the starter block, some grains at the center of the specimen exhibited quite different crystallographic directions near the gate instead of the preferred direction. (Received October 5, 2015; Accepted May 24, 2016)
Surface Characteristics and Phase Transformation of Highly Ordered TiO2 Nanotubes
오한준,Seunghyun Lee,Byunggwan Lee,Yongsoo Jeong,Choong-Soo Chi 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.4
Highly ordered TiO_2 nanotubes with 85 μm length were fabricated by the electrochemical method for 17 h at 60 V in an ethylene glycol/0.5 % NH4F/5 % water mixture solution. The nanotube arrangements and surface morphologies of the anodic titania films were clearly dependent on the electrolytes used in the fabrication process. The activation energy for the transformation from an amorphous to anatase structure was evaluated using differential scanning calorimetry (DSC) results and a Kissinger plot. The activation energy for anatase transformation on the anodic titania nanotubular film was estimated to be 208.9 kJ/mol.