• Journal of Hydrogen and New Energy
• /
• v.19 no.2
• /
• pp.132-138
• /
• 2008

금속산화물의 열화학싸이클에 의한 수소생산 소재중 안정성이 우수하고 물분해 수소생산능이 비교적 우수한 $NiFe_2O_4$를 합성하여 열화학수소생산공정 적용시 최적화의 조건에 대하여 검토하였다. 합성한 $NiFe_2O_4$는 격자상수가 $8.34\;{\AA}$이었고, 뫼스바우어에 의해 구조는 Ni이 페라이트 구조인 $AB_2O$의 B위치에 주로 위치하는, A 및 B의 상대적 흡수강도가 57.9:42.1인 역스피넬구조를 보이고 있다. 이러한 구조의 $NiFe_2O_4$의 열적환원은 $610^{\circ}C$부터 시작하여 $1200^{\circ}C$에 이르는 동안 약 1.1 wt%의 무게감소가 관찰된다. 물에 의한 산화과정에서 수소가 발생하게 되는데, $1200^{\circ}C$이하의 환원온도에서 가능한 수소생산량은 약 $0.45\;cm^3/g{\codt}cycle$ 이었다. 산화 환원의 반복과정에서 $NiFe_2O_4$의 XRD에 의한 구조변화는 관찰되지 않아 매우 안정한 구조를 갖는다는 것을 보여주었다. 수소생산을 위한 무게당 싸이클당 수소생산양은 산화 환원과정의 온도범위가 가장 중요하였고 물의 접촉시간은 중요한 요소가 되지 않았다. 열적 환원과정에서 많은 양의 수소생산성능을 보이기 위해서는 $1200^{\circ}C$이상의 고온을 필요로 하는 것을 보여주었다.

• Journal of the Korean Magnetics Society
• /
• v.15 no.1
• /
• pp.42-47
• /
• 2005

Nanocrystalline Nd-Fe-B powder was synthesized by a new thermochemical process that combined with past reduction-diffusion process and spray-dry process. In this process, Ca reduction process is vary important due to formation of hard magnetic$Nd_{2}Fe_{14}B$ phase from various oxides by Ca powder. Therefore, the final products are essentially affected a shape, size, and composition etc. of the Ca reduced powders. Ca reduction was performed to way that raw powders just mixed with Ca powder in proper ratio unlike to compress into compact. The powders after mixture-type Ca reduction mainly composited with $Nd_{2}Fe_{14}B$ phase even relativily low reaction temperature ($800^{\circ}C$) and all particle size of powder were distributed less than 1 ${\mu}m$ except for powder after Ca oxides as magnetic properties of powders after cake-type Ca reduction, with the consequence that high magnetic properties has been expected. The magnetic properties of powders prepared by mixture-type Ca ruduction, with the conseqence that high magnatic properties has been expected. The magnetic properties of powders prepared by mixture-type Ca reduction process showed $_iH_c$ = 5.9 kOe, $B_r$ = 5.5 kG, (BH)max = $Nd_{2}Fe_{14}B{\to}Nd_{2}Fe_{17}B$ decomposition by violent exothermic reaction during washing.

• Korean Chemical Engineering Research
• /
• v.52 no.6
• /
• pp.768-774
• /
• 2014

SI process is a thermochemical process producing hydrogen by decomposing water while recycling sulfur and iodine. Various technologies have been developed to improve the efficiency on Section III of SI process, where iodine is separated and recycled. EED(electro-electrodialysis) could increase the efficiency of Section III without additional chemical compounds but a substantial amount of $I_2$ from a process stream is loaded on EED. In order to reduce the load, a crystallization technology prior to EED is considered as an $I_2$ removal process. In this work, $I_2$ particle sinking behavior was modeled to secure basic data for designing an $I_2$ crystallizer applied to $I_2$-saturated $HI_x$ solutions. The composition of $HI_x$ solution was determined by thermodynamic UVa model and correlation equations and pure properties were used to evaluate the solution properties. A multiphysics computational tool was utilized to calculate particle sinking velocity changes with respect to $I_2$ particle radius and temperature. The terminal velocity of an $I_2$ particle was estimated around 0.5 m/s under considered radius (1.0 to 2.5 mm) and temperature (10 to $50^{\circ}C$) ranges and it was analyzed that the velocity is more dependent on the solution density than the solution viscosity.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.37-41
• /
• 2003

열화학 기상합성법을 이용한 탄소나노튜브의 성장에서 촉매 금속 층의 형성 공정은 탄소나노튜브의 직경 및 길이를 제어해주는 가장 중요한 요소이다. 탄소나노튜브의 대량합성을 위해 자성유체를 이용한 촉매 금속 층의 손쉬운 형성공정을 개발하였다. 수용성 폴리비닐알코올과 마그네타이트 나노 입자들이 혼합된 자성유체를 다양한 기판에 스핀 코팅하여 촉매 금속 층을 간편하게 형성할 수 있었다. 자성유체 제조 시 혼합된 수용성 폴리비닐알코올은 자성유체용액의 점성을 증가 시켜 주었으며, 이러한 점성의 증가는 스핀 코팅 시 용액과 기판간의 접착력을 증대시켜 주었다. 또한 건조 과정 이후에도 잔류되어 탄소나노튜브 합성 공정 중에 촉매금속이 응집되는 현상을 방지 차여 균일한 입자 크기를 유지하도록 하였다. 이는 고밀도의 수직 배열된 탄소나노튜브의 성장의 직접적인 원인으로 생각된다. 또한 탄소나노 튜브의 대량 합성을 위해서 Si 기판 치에 알루미나와 금속 기판에서도 탄소나노튜브의 성장을 시도하였다.

• Journal of the Korean Vacuum Society
• /
• v.14 no.1
• /
• pp.29-34
• /
• 2005

The degradation of the SiGe hetero-junction bipolar transistor(HBT) properties in SiGe BiCMOS process was investigated in this paper. The SiGe HBT prepaired by SiGe BiCMOS process, unlike the conventional one, showed the degraded DC characteristics such as the decreased Early voltage, the decreased collector-emitter breakdown voltage, and the highly increased base leakage current. Also, the cutoff frequency(f/sub T/) and the maximum oscillation frequency(f/sub max/) representing the AC characteristics are reduced to below 50%. These deteriorations are originated from the change of the locations of emitter-base and collector-base junctions, which is induced by the variation of the doping profile of boron in the SiGe base due to the high-temperature source-drain annealing. In the result, the junctions pushed out of SiGe region caused the parastic barrier formation and the current gain decrease on the SiGe HBT device.

• Korean Journal of Materials Research
• /
• v.10 no.2
• /
• pp.128-137
• /
• 2000

A study has been made to investigate the effects of hot isostatic pressing(HIPing) on the microstructure and high temperature fatigue lives of the IN738LC, Ni-base superalloy used in turbine blades, with emphasis on the elimination of casting microporosity and fatigue damage through HIP treatments. Microstructure was observed using OM, SEM and the fatigue life was investigated with rotate bending fatigue tester. The results show that the fatigue lives of properly HIP-processed specimens could be extended be extended by a factor of about sixty. In contrast, no comparable life improvement was achieved with heat treatment only. The repetitive HIP treatment was shown to be very effective as a means of rejuvenating the fatigue life of intentionally fatigue-damaged IN738LC by restoration of the initial alloy microstructure and additional removal of fine casting defects which remained in the HIP-processed material.

• Resources Recycling
• /
• v.17 no.3
• /
• pp.35-41
• /
• 2008

The study of coking technology to upgrade oil sand bitumen which is considered as alternative fuel was performed by using thermogravity analyzer and delayed coking reactor(600ml). To analyzed and compared coking characteristics of oil sand bitumen, the reactivities of oil sand bitumen were measured in the TGA. At the temperature conditions of $400{\sim}550^{\circ}C$ and the temperature rising velocity of $50^{\circ}C/min$. the termination time of coking reaction and conversion efficiencies increased with an increase of bed temperature. However the increase rate decreased over $450^{\circ}C$. So the coking reaction with oil sand bitumen might be over $450^{\circ}C$. Also the termination time decreased with increasing the temperature rising velocity. But the content of coke increased with increasing temperature rising velocity. At the experiments in the delayed coker, the temperature condition at maximum oil yield was $475^{\circ}C$ and the fuel properties of oil from coking reaction was almost equal with conventional diesel. It was verified that the coking process might be useful process to upgrade the oil sand bitumem by using API and SIMDAS.

• Journal of the Korean Vacuum Society
• /
• v.18 no.6
• /
• pp.488-493
• /
• 2009

We developed a simple method to control the length of carbon nanotube array by using oxygen plasma etching. In this way, we could obtain a carbon nanotube with a uniform length (20, 30, 50, $70\;{\mu}m$), that was parallel to the substrate. Moreover, our growing method of carbon nanotube array gives a uniform diameter ~3.5nm, which is consistent with our previous results. Using the same etching method, we demonstrated the carbon nanotube radio frequency identification (RFID) antenna. The results could be useful for carbon nanotube applications such as flexible and transparent conductive films.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.2
• /
• pp.102-105
• /
• 2009

The accelerated life time test of the MLCCs with different $BaTiO_3$ particle sizes were conducted at $150^{\circ}C$, 75 V condition and the effect of $BaTiO_3$ particle size on the breakdown voltage and degradation characteristics of MLCCs was investigated. The MLCCs were prepared by using the $BaTiO_3$ particles having the size of $0.525{\mu}m$, $0.555{\mu}m$, $0.580{\mu}m$ and Ni-electrode, respectively. The MLCCs which have the particle size of $0.525{\mu}m$, $0.555{\mu}m$, and $0.580{\mu}m$, respectively were confirmed to meet the standard requirements of X5R(change capacitance within ${\pm}15%$ at $-55{\sim}85^{\circ}C$) by TCC(Temperature Coefficient of Capacitance). The effect of the $BaTiO_3$ particle size on the insulation resistance behavior of MLCCs was confirmed by BDV(Breakdown Voltage) measurements and the cause and degree of degradation of MLCCs were characterized by XPS analysis after the accelerated life test. The MLCCs with $0.525{\mu}m-BaTiO_3$ showed better insulation resistance and BDV characteristics compare to other MLCCs and XPS analysis revealed that the MLCCs degradation is caused by the NiO peak and $BaTiO_3$ peak decrease.

• Korean Journal of Materials Research
• /
• v.6 no.5
• /
• pp.524-531
• /
• 1996

차세대 소자고립구조로서 연구되고 있는 trench isolation 공정 등에는 실리콘 식각이 요구되며 실리콘 식각 공정중에는 반응성 이온에 의해 격자결함이 발생할 수 있다. 이와같이 생성된 결함은 소자의 전기적 성질을 열화시키므로 열처리를 통하여 제거하여야만 한다. 따라서 본 연구에서는 Ar,Ar/H2 플라즈마로 격자결함을 인위적으로 발생시켜 20$0^{\circ}C$-110$0^{\circ}C$ 질소분위기에서 30분간 열처리에 따른 생성된 격자결함의 소거거동을 관찰하였다. 실리콘 표면에 Schottky 다이오드를 제작하여 I-V, C-V 특성을 측정하므로써 잔류하는 전기적인 손상의 정도를 평가하였다. Ar으로 식각한 경우에는 110$0^{\circ}C$ 30분간 열처리한 결과 모든 격자결함이 제거되나 Ar/H2로 식각한 경우에는 격자결함이 완전히 제거되지 않고 (111)적층결함이 남아있었다.