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전기방사된 주석산화물 나노섬유의 공정 변수에 따른 직경 및 형상 제어 연구
장대환,이재은,좌용호,이영인,Jang, Dae-Hwan,Lee, Jae-Eun,Choa, Yong-Ho,Lee, Young-In 한국재료학회 2014 한국재료학회지 Vol.24 No.12
Diameter-controlled tin oxide nanofibers have been successfully prepared using electrospinning and a subsequent calcination process; their diameters, morphologies, and crystal structures have been characterized. The diameters of the as-spun nanofibers can be decreased by lowering the concentration of a polymer and a tin precursor in the electrospinning solution because of the decrease in the solution viscosity. The crystal structure of the nanofibers calcined at various temperatures from $200^{\circ}C$ to $800^{\circ}C$ has been proved to be the tetragonal rutile of tin oxide; crystallinity is improved by increasing the temperature. However, nanofibers with lower concentrations of tin precursor do not maintain their fibrous structures after calcination at high temperatures. In this study, the effect of the relationship between the precursor concentration and the calcination temperature on the diameter and the morphology of the tin oxide nanofiber has been systematically investigated and discussed.
알칼리 침전제에 의해 제조된 아연 중간생성물 및 산화아연 결정화
장대환,김보람,김대원,Jang, Dae-Hwan,Kim, Bo-Ram,Kim, Dae-Weon 한국결정성장학회 2021 韓國結晶成長學會誌 Vol.31 No.6
ZnO는 출발물질인 황산아연과 알칼리 침전제인 NaOH와 Na<sub>2</sub>CO<sub>3</sub>에 의해 생성된 아연 중간생성물의 변이 거동과 결정화 조건에 따라 제조하였다. ZnO 결정화를 위해 아연 중간생성물인 Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O, Zn<sub>5</sub>(OH)<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O를 각각 400℃, 800℃에서 1시간 하소하였고, 하소 온도는 열중량 분석을 기반으로 하였다. 아연 중간생성물인 Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O은 400℃에서 Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O, ZnO 결정상이 혼재됨을 확인하였고, 800℃에서 완전히 열분해되어 순수한 ZnO만 형성되었다. Na<sub>2</sub>CO<sub>3</sub>와 반응하여 생성된 아연 중간생성물인 Zn<sub>5</sub>(OH)<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O는 400℃ 이상에서 완전한 ZnO의 결정상을 확인하였다. Na<sub>2</sub>CO<sub>3</sub>와 반응을 통해 상대적으로 낮은 하소 온도에서 나노 입자의 ZnO를 합성할 수 있었다. ZnO was synthesized according to the transformation behavior and crystallization conditions of Zn-intermediate obtained by zinc sulfate as a precursor and NaOH, Na<sub>2</sub>CO<sub>3</sub> as a alkali agents. For ZnO crystallization, Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O and Zn<sub>5</sub>(OH)<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O as a Zn-intermediate were calcined at 400℃ and 800℃ for 1 h, respectively, based on decomposition temperature from TGA. Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O was confirmed to have mixed Zn<sub>4</sub>(OH)<sub>6</sub>SO<sub>4</sub>·H<sub>2</sub>O and ZnO at 400℃, and was completely thermally decomposed at 800℃ to form ZnO phase. The prepared Zn<sub>5</sub>(OH)<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O as a Zn-intermediate by the reaction with Na<sub>2</sub>CO<sub>3</sub> was transformed to a complete ZnO crystallization over 400℃. Nano-sized ZnO can be synthesized at a relatively lower calcination temperature through the reaction with Na<sub>2</sub>CO<sub>3</sub>.
코어-쉘 구조를 갖는 BaTiO<sub>3</sub>@Fe 나노섬유의 합성 및 전자파 흡수 특성
이영인,장대환,성기훈,이규만,좌용호,Lee, Young-In,Jang, Dae-Hwan,Sung, Ki-Hoon,Lee, Kyuman,Choa, Yong-Ho 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.1
$BaTiO_3$-coated Fe nanofibers are synthesized via a three-step process. ${\alpha}-Fe_2O_3$ nanofibers with an average diameter of approximately 200 nm are first prepared using an electrospinning process followed by a calcination step. The $BaTiO_3$ coating layer on the nanofiber is formed by a sol-gel process, and a thermal reduction process is then applied to the core-shell nanofiber to selectively reduce the ${\alpha}-Fe_2O_3$ to Fe. The thickness of the $BaTiO_3$ shell is controlled by varying the reaction time. To evaluate the electromagnetic (EM) wave-absorbing abilities of the $BaTiO_3@Fe$ nanofiber, epoxy-based composites containing the nanofibers are fabricated. The composites show excellent EM wave absorption properties where the power loss increases to the high frequency region without any degradation. Our results demonstrate that the $BaTiO_3@Fe$ nanofibers obtained in this work are attractive candidates for electromagnetic wave absorption applications.
급속소결에 의해 제조된 Al<sub>2</sub>O<sub>3</sub>/Fe-Ni 나노복합재료의 미세조직 및 기계적 특성
이영인,이근재,장대환,양재교,좌용호,Lee, Young-In,Lee, Kun-Jae,Jang, Dae-Hwan,Yang, Jae-Kyo,Cho, Yong-Ho 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.3
A new High Frequency Induction Heating (HFIH) process has been developed to fabricate dense $Al_2O_3$ reinforced with Fe-Ni magnetic metal dispersion particles. The process is based on the reduction of metal oxide particles immediately prior to sintering. The synthesized $Al_2O_3$/Fe-Ni nanocomposite powders were formed directly from the selective reduction of metal oxide powders, such as NiO and $Fe_2O_3$. Dense $Al_2O_3$/Fe-Ni nanocomposite was fabricated using the HFIH method with an extremely high heating rate of $2000^{\circ}C/min$. Phase identification and microstructure of nanocomposite powders and sintered specimens were determined by X-ray diffraction and SEM and TEM, respectively. Vickers hardness experiment were performed to investigate the mechanical properties of the $Al_2O_3$/Fe-Ni nanocomposite.
초음파 분무 열분해법에 의한 산화물 환원 공정의 구형 Bi₂Te₃ 분말 합성
송철한(Chul-Han Song),장대환(Dae-Hwan Jang),진연호(Yun-Ho Jin),공만식(Man-Sik Kong) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.2
Bismuth telluride (Bi₂Te₃) and its alloys are well-known thermoelectric materials for ambient temperature applications. In this study, the dissolved Bi-Te precursor solution was used to synthesis metallic Bi₂Te₃ powder via ultrasonic spray pyrolysis and reduction process. The droplets of the Bi-Te precursor solution were decomposed to Bi-Te oxide powders by ultrasonic spray pyrolysis. The spherical Bi₂Te₃ powders were synthesized by reduction reaction in atmosphere of hydrogen gas at the temperature above 375℃ for 6h. The reduced Bi₂Te₃ powders have a mean particle size of 1.5 μm. The crystal structure of the powder was evaluated by X-Ray diffraction(XRD), and the microstructure with size and shape powders was observed by fieldemission scanning electron microscope(FE-SEM) and transmission electron microscope(TEM).
위궤양 질환에서 99mTC - Sucralfate 스캔의 진단적 가치
최덕주(Duck Joo Choi),장대환(Dae Hwan Jang),이은주(Eun Joo Lee),이범우(Bum Woo Lee),김학산(Hak San Kim),김종순(Chong Soon Kim),박경배(Kyung Pae Park),박원(Won Park) 대한내과학회 1988 대한내과학회지 Vol.35 No.3
N/A Sucralfate is an effective medication for the treatment of gastroduodenal uleers, and techeetium-99m labeled sucralfate has been found to adhere to ulcers. In this study, we examined the diagnostic usefulness of radionuclide imaging for detecting gastric ulcers by means of sucralfate labeled with technetium-99m in vitro or in vivo. Gastroscopic findings were compared in all 44 pateints, including 16 gastic ulcer patients. Of the 44 humans studied, 8 gave true-positive, 8 gave false-negative, 28 gave true-negative and 0 gave false-positive results. Of 9 cases of endoscopically active stage gastric ulcer, all but one showed positive findings. The sensitivity of the scan was 50% and the specificity was 100% for the detection of gastric ulcers, Thus, the TUMI (Tagged Ulcer-avid Material Imaging) scan may have been useful for detecting only the active stage of gastric ulcer in this study.