• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 추계학술대회논문집
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• pp.120-123
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• 2000

This paper reports a newly developed sol-gel process to synthesize dense YBCO thick films with BaTiO$_3$additives using electrophoretic deposition and metal alkoxide sol/particle suspension, which we successfully produce dense $YBCO+BaTiO_3$ ceramics at a rather low temperature, compared with the sintering temperature used in conventional methods. The thick films of HTS were prepared by electrophoretic deposition, using pre-sintered powder with barium titanate addition in the form of $BaTi(OR)_6$ solution in suspension for electrophoresis. The conditions for applied voltage and deposition times for electrophoretic deposition of HTS thick films were studied in detail.

• 한국표면공학회지
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• 제45권1호
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• pp.43-52
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• 2012

Recently, it has been developed for Eco-environment, Super light, Multi-functional nano materials. As needed mobile parts in Smart phone or TV, computer, information communication for high pass signal, multi-function, Magnetic thin film materials have been developed. As last, magnetic powder, sintered and sputtering parts were thick and low purity than electroplating layer, low pass signal and noise were resulted, vibrated TV screen. Because chemical complex temperature was high and ununiform surface layer, it has been very difficult for data pass in High Frequency (GHz) area. Large capacity data pass is used to GHz. Above GHz, signal pass velocity is dependent on Skin Effect of surface layer. If surface layer is thick or ununiform, attachment is poor, low pass signal and cross talk, noise are produced and leaked. It has been reported technical trend of Electrochemically plating and Surface treatment of Metal, Polymer, Ceramic etc. by dispersion/complex for Multi functional nano-magnetic material in this paper.

• 한국세라믹학회지
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• 제40권9호
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• pp.837-841
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• 2003

Duplex microstructure of zirconia and alumina has been achieved via an organic-inorganic solution technique. Zirconium 2,4-pentanedionate, aluminum nitrate and polyethylene glycol were dissolved in ethyl alcohol without any precipitation. The organicinorganic precursor gels were turned to porous powders having volume expansion through explosive, exothermic reaction during drying process. The volume expansion was caused by abrupt decomposition of the organic groups in the gels during the vigorous exothermic reaction. The volume expanded, porous powders were crystallized and densified at 1500$^{\circ}C$ for 1 h. At the optimum amount of the PEG polymer, the metal cations were well dispersed in the solution and a homogeneous polymeric network was formed. The polymer content also affected on the specific surface area of the synthesized powder and the grain size of the sintered composite.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.120-123
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• 2000

This paper reports a newly developed sol-gel process to synthesize dense YBCO thick films with $BaTiO_3$ additives using electrophoretic deposition and metal alkoxide sol/particle suspension, which we successfully produce dense $YBCO+BaTiO_3$ ceramics at a rather low temperature, compared with the sintering temperature used in conventional methods. The thick films of HTS were prepared by electrophoretic deposition, using pre-sintered powder with barium titanate addition in the form of $BaTi(OR)_6$ solution in suspension for electrophoresis. The conditions for applied voltage and deposition times for electrophoretic deposition of HTS thick films were studied in detail.

• Composites Research
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• 제25권5호
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• pp.159-163
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• 2012

냉매의 비등이나 응축같은 열전달 향상을 위하여 금속 표면위에 탄소나노튜브(CNT)를 코팅하는 것을 연구하였다. 분산제와 PVA(polyvinyl alcohol) 용액으로 분산 처리된 다중벽 탄소나노튜브/CuO의 복합 분말 코팅액을 구리기판위에 도포한 후 소결을 하였다. 본 논문에서는 CNT/CuO 소결 코팅시 다양한 분산제를 사용하여 소결 전후의 조직 형상 변화 및 특징을 실험적으로 평가하였다. 분산제로는 THF(Tetrahydrofuran), SDBS(Dodecylbenzenesulfonic acid sodium salt), SDS(Sodium dodecy sulfate)가 사용되었다. 각각의 시편들은 주사전자현미경, 열중량분석, 시차주사열량측정법, 라만분광법을 사용하여 분석하였다.

• Design & Manufacturing
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• 제13권2호
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• pp.17-21
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• 2019

In this study, selective laser sintered 3D printing mold core and metal core were used to investigate the difference of the thickness shrinkage from the gate of the injection molded part at a constant interval. SLS 3D printing mold core was made of nylon-based PA2200 powder and the metal core was manufactured by conventional machining method. As the PA2200 powder material has low strength, thermal conductivity and high specific heat characteristics compared with metal, molding conditions were set with the consideration of molten temperature and injection pressure. Crystalline resin(PP) and amorphous resin(PS) with low melting temperature and viscosity were selected for the injection molding experiment. Cooling time for processing condition was selected by checking the temperature change of the cores with a cavity temperature sensor. The cooling time of the 3D printing core was required a longer time than that of the metal core. The thickness shrinkage of the molded part compared to the core depth was measured from the gate by a constant interval. It was shown that the thickness shrinkage of the 3D printing core was 2.02 ~ 4.34% larger than that of metal core. In additions, in the case of metal core, thickness shrinkage was increased with distance from the gate, on the contrary, in the case of polymer core showed reversed aspect.

• 한국재료학회지
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• 제15권4호
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• pp.257-262
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• 2005

Nano-sized ZrVFe alloy powders were prepared by the ablation of powder compact in alcobol using a Nd-YAG pulsed Laser. The $Zr_{57}V_{35.}8Fe_{7.2}$ alloy commercially designated as ST707 has long been known as the ideal solution for various vacuum applications. The target for the ablation was sintered pellets of $Zr_{57}V_{35.}8Fe_{7.2}$ alloy powder. The alloy was prepared by arc melting and Hydride-DeHydride method. The ablated powders were mostly circular having fairly large size distribution smaller than 200 nm in all cases. The X-ray diffraction study revealed that the ablated alloy retained the crystal structure of the target alloy. Nevertheless, Fe and V contents in the ablated powder were lower than those in the target alloy. This was believed to result from the high vapour pressures of Fe and V compared to that of Zr. The size of the powders ablated at high energy fluence tends to decrease due at least partly to the breakdown of previously made ones.

• 한국주조공학회지
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• 제19권6호
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• pp.493-500
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• 1999

Squeeze casting was used for fabricating a light metal base composite having high strength and wearresistance. Reactive sintering was used to prepare the preform of Squeeze casting. To utilize Fe-Al intermetallic compounds and SiC particle as a reinforcement, there needs to prepare Fe-Al mixed powder at 50, 60, 70at.%Al, and add SiC powder to the above mixture at 4, 7, 16, 24wt.%. The prepared mixture with SiC was reactive sintered in a tube furnace at $660^{\circ}C$ to get a porous hybrid preform of intermetallic compound and SiC. The preform prepared above was placed in a metal mold, preheated at $660^{\circ}C$ AC4C matrix was injected into the mold with the temperature of the melt at $610^{\circ}C$ After these processes, 66MPa was applied to the mold for 5 minute to finish the whole procedure. The maximum reaction temperature was increased with the increased Al amount, but decreased with the increased SiC amount. The density of the preform was decreased with SiC amount increase in the compacts due to swelling of the preform. An optical microscope was applied to observe the micro structure and the dispersion of the reinforcements. To analyze phases, We utilized XRD, EDS. Hardness test were chosen to get the information of mechanical properties. There were no significant changes in micro structure between the composite and preform. However, it was shown that uniform dispersion of the reinforcers and complete infiltration of the melt into the preform were achieved through the procedure of the squeeze casting. It was observed that the hardness of the composite is decreased with increased SiC amount, resulting from the volumetric expansion of the preform.

• 한국분말재료학회지
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• 제17권4호
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• pp.312-318
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• 2010

High speed steels (HSS) were used as cutting tools and wear parts, because of high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. Conventional manufacturing process for production of components with HSS was used by casting. The powder metallurgy techniques were currently developed due to second phase segregation of conventional process. The powder injection molding method (PIM) was received attention owing to shape without additional processes. The experimental specimens were manufactured with T42 HSS powders (59 vol%) and polymer (41 vol%). The metal powders were prealloyed water-atomised T42 HSS. The green parts were solvent debinded in normal n-Hexane at $60^{\circ}C$ for 24 hours and thermal debinded at $N_2-H_2$ mixed gas atmosphere for 14 hours. Specimens were sintered in $N_2$, $H_2$ gas atmosphere and vacuum condition between 1200 and $1320^{\circ}C$. In result, polymer degradation temperatures about optimum conditions were found at $250^{\circ}C$ and $480^{\circ}C$. After sintering at $N_2$ gas atmosphere, maximum hardness of 310Hv was observed at $1280^{\circ}C$. Fine and well dispersed carbide were observed at this condition. But relative density was under 90%. When sintering at $H_2$ gas atmosphere, relative density was observed to 94.5% at $1200^{\circ}C$. However, the low hardness was obtained due to decarbonization by hydrogen. In case of sintering at the vacuum of $10^{-5}$ torr at temperature of $1240^{\circ}C$, full density and 550Hv hardness were obtained without precipitation of MC and $M_6C$ in grain boundary.

• 에너지공학
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• 제12권1호
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• pp.17-22
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• 2003

본 연구는 소형 CPL히트파이프의 제작 및 작동 특성에 대한 기초 지식을 얻기 위하여 수행되었다. CPL 히트파이프는 중력장 내에서 먼 거리까지 효과적으로 열을 이송할 수 있는 능력을 가지고 있다. 컴퓨터 칩에서 발생되는 열을 냉각하기 위하여 원판형 증발부로 구성된 소형 CPL을 설계 및 제작하여 그 작동 성능을 실험하였다. 두께 3mm, 직경 50mm의 원판형 청동 분발 소결 (equation omitted)를 사용하여 작동유체를 순환하기 위한 압력 구배를 얻을 수 있었으며 작동유체는 에탄올을 사용하였다. 실험은 응축부의 주위온도를 13$^{\circ}C$로 고정시킨 후 각각 다른 열부하에서의 CPL 작동 상태를 확인해 보았다.