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Fe- 및 Co-질산염을 이용한 Fe-50 wt% Co 나노분말의 합성 및 특성 평가
류도형,오승탁,Riu, Doh-Hyung,Oh, Sung-Tag 한국재료학회 2010 한국재료학회지 Vol.20 No.10
The optimum route to fabricate nano-sized Fe-50 wt% Co and hydrogen-reduction behavior of calcined Fe-/Conitrate was investigated. The powder mixture of metal oxides was prepared by solution mixing and calcination of Fe-/Co-nitrate. A DTA-TG and microstructural analysis revealed that the nitrates mixture by the calcination at $300^{\circ}C$ for 2 h was changed to Fe-oxide/$Co_3O_4$ composite powders with an average particle size of 100 nm. The reduction behavior of the calcined powders was analyzed by DTA-TG in a hydrogen atmosphere. The composite powders of Fe-oxide and Co3O4 changed to a Fe-Co phase with an average particle size of 40 nm in the temperature range of $260-420^{\circ}C$. In the TG analysis, a two-step reduction process relating to the presence of Fe3O4 and a CoO phase as the intermediate phase was observed. The hydrogen-reduction kinetics of the Fe-oxide/Co3O4 composite powders was evaluated by the amount of peak shift with heating rates in TG. The activation energies for the reduction, estimated by the slope of the Kissinger plot, were 96 kJ/mol in the peak temperature range of $231-297^{\circ}C$ and 83 kJ/mol of $290-390^{\circ}C$, respectively. The reported activation energy of 70.4-94.4 kJ/mol for the reduction of Fe- and Co-oxides is in reasonable agreement with the measured value in this study.
조광연,류도형,허승헌,신동근,김현이,최종화,정해원,Cho, Kwang-Youn,Riu, Doh-Hyung,Huh, Seung-Hun,Shin, Dong-Geun,Kim, Hyoun-Ee,Choi, Jong-Hwa,Cheong, Hae-Won 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.7
Ceramic Fiber separator is the promising material for thermal battery system because it reduces the production cost and offers the potential to a new application compared to a pellet type electrolyte. The molten salt electrolytes for thermal battery were prepared by the impregnation of the commercial glass filters such as GF-A, C and F (Whatman, USA) with two types of molten-lithium salts, LiCl-KCl and LiK-LiBr-LiF. The wetting properties were evaluated by wetting balance test and wetting angle measurement. The wetting behaviors were strongly affected by the composition of the molten salts and the pore structure of the glass separators. The optimum wetting conditions for maximum loading and effective retention of the molten electrolyte were also studied.
신대규,류도형,Shin, Dae-Kyu,Riu, Doh-Hyung 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.2
Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric ($Fe^{3+}$) and ferrous ($Fe^{2+}$) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (${\beta}$-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of ${\beta}$-FeOOH and the attaining a proper driving force for the reaction of ${\beta}$-FeOOH and $Fe^{2+}$ ion to give $Fe_3O_4$ are important process variables for the synthesis of uniform magnetite nanoparticles.
석탄계 피치에 요오드를 소량 첨가하여 제조한 탄소복합재의 치밀화 거동
조광연,류도형,신동근,주혁종,구형회,박인서,Cho, Kwang-Youn,Riu, Doh-Hyung,Shin, Dong-Geun,Joo, Heyok-Jong,Koo, Hyung-Hoi,Park, In-Seo 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6
We investigated the viscosity behavior and the carbon yield of coal tar pitch (CTP) treated with iodine. The viscosity of iodine treated pitch showed that the fluidity of iodine treated CTP did not increase within the iodine addition of 1.4%. DTG analysis showed that cross linking was accelerated at the temperature range from $400\;to\;500{^{\circ}C}$ with iodine treatment, which is due to the accelerated dehydrogenative reaction by iodine. The iodine treatment was mainly effective for β-resin content increase of CTP. The carbon yield of CTP increased from 40 to 60% by the iodine non-treated CTP.
CuO-Al<sub>2</sub>O<sub>3</sub>/camphene 슬러리의 동결건조 공정에 의한 Al<sub>2</sub>O<sub>3</sub> 입자분산 Cu 다공체 제조
강현지,류도형,오승탁,Kang, Hyunji,Riu, Doh-Hyung,Oh, Sung-Tag 한국분말야금학회 2018 한국분말재료학회지 (KPMI) Vol.25 No.1
Porous Cu with a dispersion of nanoscale $Al_2O_3$ particles is fabricated by freeze-drying $CuO-Al_2O_3$/camphene slurry and sintering. Camphene slurries with $CuO-Al_2O_3$ contents of 5 and 10 vol% are unidirectionally frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by camphene sublimation during air drying. The green bodies are sintered for 1 h at $700^{\circ}C$ and $800^{\circ}C$ in $H_2$ atmosphere. The sintered samples show large pores of $100{\mu}m$ in average size aligned parallel to the camphene growth direction. The internal walls of the large pores feature relatively small pores of ${\sim}10{\mu}m$ in size. The size of the large pores decreases with increasing $CuO-Al_2O_3$ content by the changing degree of powder rearrangement in the slurry. The size of the small pores decreases with increasing sintering temperature. Microstructural analysis reveals that 100-nm $Al_2O_3$ particles are homogeneously dispersed in the Cu matrix. These results suggest that a porous composite body with aligned large pores could be fabricated by a freeze-drying and $H_2$ reducing process.
TiO<sub>2</sub> 나노분말과 수산화알칼리와의 반응으로부터 티탄산 나노튜브의 형성과 나노구조의 전개
진은주,류도형,허승헌,김창열,황해진,Jin, Eun-Ju,Riu, Doh-Hyung,Huh, Seung-Hun,Kim, Chang-Yeoul,Hwang, Hae-Jin 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.2
[ $TiO_2$ ] nanotubes for photocatalytic application have been synthesized by hydrothermal method. $TiO_2$ nanotubes are formed by washing process after reaction in alkalic solution. Nanotubes with different morphology have been fabricated by changing NaOH concentration, temperature and time. $TiO_2$ nanoparticles were treated inside NaOH aqueous solution in a Teflon vessel at $110^{\circ}C$ for 20 h, after which they were washed with HCl aqueous solution and deionized water. Nanotube with the most perfect morphology was formed from 0.1 N HCl washing treatment. $TiO_2$ nanotube was also obtained when the precursor was washed with other washing solutions such as $NH_4OH$, NaCl, $K_2SO_4$, and $Na_2SO_3$. Therefore, it was suggested that $Na^+$ ion combined inside the precursor compound slowly comes out from the structure, leaving nanosheet morphology of $TiO_2$ compounds, which in turn become the nanotube in the presence of hydroxyl ion. To stabilize the sheet morphology, the different type of washing treatment solution might be considered such as amine class compounds.
전처리를 이용한 탄소 나노 섬유의 균일한 SnO<sub>2</sub> 코팅막 형성
김동하,류도형,최병준,Kim, Dong Ha,Riu, Doh-Hyung,Choi, Byung Joon 한국분말야금학회 2018 한국분말재료학회지 (KPMI) Vol.25 No.1
Carbon nanofibers (CNF) are widely used as active agents for electrodes in Li-ion secondary battery cells, supercapacitors, and fuel cells. Nanoscale coatings on CNF electrodes can increase the output and lifespan of battery devices. Atomic layer deposition (ALD) can control the coating thickness at the nanoscale regardless of the shape, suitable for coating CNFs. However, because the CNF surface comprises stable C-C bonds, initiating homogeneous nuclear formation is difficult because of the lack of initial nucleation sites. This study introduces uniform nucleation site formation on CNF surfaces to promote a uniform $SnO_2$ layer. We pretreat the CNF surface by introducing $H_2O$ or $Al_2O_3$ (trimethylaluminum + $H_2O$) before the $SnO_2$ ALD process to form active sites on the CNF surface. Transmission electron microscopy and energy-dispersive spectroscopy both identify the $SnO_2$ layer morphology on the CNF. The $Al_2O_3$-pretreated sample shows a uniform $SnO_2$ layer, while island-type $SnO_x$ layers grow sparsely on the $H_2O$-pretreated or untreated CNF.
조광연,류도형,신동근,임경훈,진은주,김현이,하상현,최종화,Cho, Kwang-Youn,Riu, Doh-Hyung,Shin, Dong-Geun,Lim, Kyoung-Hoon,Jin, Eun-Ju,Kim, Hyoun-Ee,Ha, Sang-Hyeon,Choi, Jong-Hwa 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6
Lithium salt have been used mainly as electrolyte of thermal battery for electricity storage. Recently, The 3phase lithium salt(LiCl-LiF-LiBr) is tried to use as electrolyte of thermal battery for high electric power. It is reported that LiCl-LiF-LiBr salt have high ion mobility due to its high lithium ion concentration. Solid lithium salt is melt to liquid state at above $500{^{\circ}C}$. The lithium ion is easily reacted with support materials. Because the melted lithium ion has small ion size and high ion mobility. For the increasing mechanical strength of electrolyte pellet, the research was started to apply ceramic filter to support of electrolyte. In this study, authors used SiOC web and glass fiber filter as ceramic mat for support of electrolyte and impregnated LiCl-LiF-LiBr salt into ceramic mat at above $500{^{\circ}C}$. The fabricated electrolyte using ceramic mat was washed with distilled water for removing lithium salt on ceramic mat. The washed ceramic mat was observed for lithium ion reaction behavior with XRD, SEM-EDS and so on.
분자량이 조절된 폴리카보실란으로부터 제조한 SiC Fiber의 특성분석
신동근,류도형,김영희,김형래,박홍식,김현이,Shin, Dong-Geun,Riu, Doh-Hyung,Kim, Younghee,Kim, Hyung-Rae,Park, Hong-Sik,Kim, Hyoun-Ee 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.8
Polycarbosilane was synthesized by the Kumada rearrangement of polydimethylsilane in the presence of zeolite (ZSM-5) as a catalyst at $350^{\circ}C$. The prepared polycarbosilane had very low molecular weight ($M_w=500$), so that it was not suitable to fabricate SiC fiber by melt spinning. Further polymerization of PCS was conducted around $400^{\circ}C$ to obtain spinnable polycarbosilane. After polymerization, the polycarbosilanes were isolated by distillation according to the molecular weight distributions. The PCS with a controlled molecular weight distribution was spun into continuous polycarbosilane green fibers. The PCS green fiber was successfully transformed into silicon oxycarbide fiber. The room temperature strength of the SiC fiber was around 1.5 - 1.8 GPa. The oxidation behavior and the tensile strength after oxidation were also evaluated.
SiOC 매트(Mat)를 이용한 열전지용 전해질 격리판 제조 및 특성
임경훈,조광연,류도형,신동근,진은주,김현이,정해원,이홍림,Lim, Kyoung-Hoon,Cho, Kwang-Youn,Riu, Doh-Hyung,Shin, Dong-Geun,Jin, Eun-Ju,Kim, Hyoun-Ee,Cheong, Hae-Won,Lee, Hong-Lim 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6
Ceramic fiber separator is the promising material for thermal battery system because it reduces the production cost and offers the potential to a new application compared to a pellet type electrolyte. The electrolyte separator for thermal battery should be easily handled and loaded a large amount of the molten lithium salt. Ceramic fibers were used as an electrolyte separator and the lithium based molten salts were infiltrated into the ceramic filters. Leakage of molten salt (several lithium salts) leads to short-circuit during the thermal battery operation. In this study, a uniform and fine SiOC mat with fibers ranging from 1 to 3 ${\mu}m$ was obtained by electrospinning of polycarbosilane and pyrolysis. The optimum spinning conditions for obtaining fine diameters of SiOC fiber were controlled by the solution composition and concentration, applied voltage and spinning rate, release rate by porosity. The pore structures of the ceramic filter and the melting properties of the lithium salts affected to the electrolyte loading and leakage. The importance of the fiber size and porosity and their control was discussed and the mechanical properties were also discussed.