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원자력 극한환경용 세라믹 열교환기 소재로서 반응소결 SiC 세라믹스 제작성
정충환,박지연,Jung, Choong-Hwan,Park, Ji-Yeon 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.1
Silicon carbide (SiC) is a candidate material for heat exchangers for VHTR (Very High Temperature Gas Cooled Reactor) due to its refractory nature and high thermal conductivity. This research has focused on demonstration of physical properties and mock-up fabrication for the future heat exchange applications. It was found that the SiC-based components can be applied for process heat exchanger (PHE) and intermediate heat exchanger (IHX), which are operated at $400{\sim}1000^{\circ}C$, based on our examination for the following aspects: optimum fabrication technologies (design, machining and bonding) for compact design, thermal conductivity, corrosion resistance in sulfuric acid environment at high temperature, and simulation results on heat transferring and thermal stress distribution of heat exchanger mock-up.
폴리머 용액법에 의한 금속 양이온 전구체의 합금거동 고찰
정경환 ( Kyung Hwan Jung ),정충환 ( Choong Hwan Jung ),장진성 ( Jin Sung Jang ),이상진 ( Sang Jin Lee ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.8
The alloying behavior of Ni-Co-Cr nano-sized powders was studied via a polymer solution approach as a substitute method for mechanical alloying processes. Metal nitrate salts were dissolved in distilled water with a 5 wt% polyvinyl alcohol (PVA) solution, and the homogeneous sols were dried to gels and heated under a reducing atmosphere consisting of an argon-hydrogen (Ar-N2) gas mixture. In this study, the effects of processing parameters, specifically PVA content, composition of the gas mixture, and heating temperature, on alloying behavior were examined. The PVA ensured a homogeneous distribution of metal ions in the solution and it resulted in nano-sized metal particles after heating at 500 ℃. In particular, nano-sized Ni particles were oxidized when they were exposed to air after the heat treatment. However, a Ni-Co alloy was observed at higher heating temperature of 700 ℃, showing significant particle growth. Nano-sized Cr particles were not alloyed and instead oxidized to Cr2O3, showing a relative smaller particle size when they were exposed to air after heating at 700℃ and higher. In general, the metal particle sizes decreased as the H2 concentration increased in the gas mixture. (Received December 08, 2014)
TiCl$_4$ 수용액에서 침전법에 의한 결정상 TiO$_2$ 초미분체 제조
김선재,정충환,박순동,권상철,박성,Kim, Sun-Jae,Jung, Choong-Hwan,Park, Soon-Dong,Kwon, Sang-Chul,Park, Sung 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.4
Crystalline TiO2 ultrafine powders were prepared simply by heating and stirring aqueous TiOCl2 solution with {{{{ {Ti }^{4+ } }} concentration of 0.5 M from room temperature to 10$0^{\circ}C$ under 1 atmoshpere. The crystallinity and the particle shape of TiO2 ultrafine powders obtained by simple precipitation method were analyzed us-ing XRD(X-ray diffractometer). SEM(scanning electron microscopy) and TEM(transmission electron mi-croscopy) TiO2 crystalline precipitate with rutile phases is fully formed at the temperatures of up to $65^{\circ}C$ and then TiO2 crystalline precipitate with anatase phase starts to be formed above temperatures $65^{\circ}C$ showing its full formation at 10$0^{\circ}C$ These behaviors of TiO2 crystalline precipitate directly from an aqueous TiOCl2 solution would be caused due to the existence of {{{{ OMICRON ^2+ }} ions from distilled water which oxydize TiOCl2 to TiO2 not hydrolyzing it to Ti(OH)4 Here thermodynamically stable TiO2 rutile phase generally formed at higher temperature is practically precipitated at lower temperatures in this study This may be due to the precipitation by very slow reaction enough to make TiO2 particles allocated into stable rutile structure.
저압화학기상증착법을 이용한 ZrC 성장에 잔류시간이 미치는 영향
박종훈,정충환,김도진,박지연,Park, Jong-Hoon,Jung, Choong-Hwan,Kim, Do-Jin,Park, Ji-Yeon 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.5
In order to investigate residence time effect on the growth of ZrC film, the ZrC films grew with various system total pressure (P) and total flow rate (Q) by low pressure chemical vapor deposition because residence time is function of system total pressure and total flow rate. Thermodynamic calculations predict that the decomposition of source gases ($ZrCl_4$ and $CH_4$) would be low as increasing the residence time. Thermodynamic calculations results were proved by investigating deposition rate with various residence time. Deposition rate decreased with residence time of source gas increased. Besides, depletion effect accelerated diminution of deposition rate at high residence time. On the other hands, the deposition rated was increased as decreasing the residence time because fast moving of intermediate gas species decrease the depletion effect. The crystal structure was not changed with residence time. However, the largest size of faceted grain showed up to specific residence time and the size of grain was decreased whether residence time increase or not.