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다꾸치법에 의한 무섬유 세라믹 브레이크 마찰재의 제조변수에 대한 고찰
여정구,최성철,Yeo Jeong-Gu,Choi Sung-Churl 한국재료학회 2004 한국재료학회지 Vol.14 No.1
In the present study, ceramic brake pads without fiber phases were manufactured by the low temperature heat treatment below$ 700 ^{\circ}C$. The manufacturing parameters of ceramic brake pads and those levels were investigated by the analysis results of signal-to-noise ratios, ANOVA based upon the Taguchi method. The ceramic brake pads prepared in the Mg experiment had a friction coefficient of 0.30~0.55 very close to the target coefficient (0.35~0.45) of commercial brake pads utilized in the automobiles. The frictional properties of ceramic brake pads could be stabilized with the adjustment of amounts of lubricating additives. The optimum preparation conditions as well as batch formulations for the fabrication of non-fibrous ceramic brake pads were finally determined using Taguchi method in this study.
비수계 테잎성형공정의 유기공정변수의 변화에 따른 티탄산바륨-붕규산염유리계 현탁액의 분산안정성
여정구,최성철,Yeo, Jeong-Gu,Choi, Sung-Churl 한국재료학회 2003 한국재료학회지 Vol.13 No.11
The effect of organic processing parameters on the dispersion stability of the BaTiO$_3$-based dielectric particles and borosilicate glass particulate suspensions was investigated in a system where organic solvents, dispersant, binder and modifier were used as processing additives in a low temperature cofired ceramic fabrication processes. Two- and three-component organic solvents were used to disperse ceramic particles and it was found the better stability in the particulate suspension prepared in a bi-solvent, which was consists of toluene and ethanol in a non-azeotropic composition. The addition amount of organic additives had a great impact on dispersion in the present investigation. The flow curves of the suspensions prepared with binder and modifier were fitted according to the power-law equation, which indicates that the internal structure of the suspension could be disturbed under the applied shear stress. Finally, the LTCC green tapes were successfully tape-cast based upon the optimum formulation of LTCC suspension and its microstructure was compared with that of the hard-agglomerates.
조철희,여정구,안영수,한문희,김용하,현상훈,Cho, Churl-Hee,Yeo, Jeong-Gu,Ahn, Young-Soo,Han, Moon-Hee,Kim, Yong-Ha,Hyun, Sang-Hoon The Membrane Society of Korea 2007 멤브레인 Vol.17 No.3
다양한 재료특성(Si/Al 몰비, 두께, 구조적 불완전성)을 갖는 Na형 faujasite 제올라이트 분리층을 다공성 $\alpha$-알루미나 튜브 표면에 수열조건에서 이차성장 시키고 $CO_2/N_2$ 분리거동을 $CO_2/N_2$ 몰비가 1인 혼합기체에 대하여 $30^{\circ}C$에서 평가하였다. 수열조건 중에서 수열용액 내의 $SiO_2$ 양은 형성된 제올라이트 분리층의 재료특성에 가장 큰 영향을 주는 변수임을 확인하였다. 즉, 수열용액 내의 $SiO_2$ 양이 증가함에 따라서 형성된 제올라이트 분리층의 Si/Al 몰비, 두께, 구조적 불완전성(discontinuity)은 동시에 증가하였다. 본 논문에서는 불완전한 치밀화에 의해 잔존하는 결정립간 공극(void), GIS Na-P1 상에 의해 형성된 균열(crack) 등 구조적 불완전성이 $CO_2/N_2$ 분리에 가장 큰 영향을 주는 재료특성이며, 투과부에서의 $CO_2$ 탈착이 전체 $CO_2$ 투과의 율속단계(rate-determining step)임을 확인하였다. Sodium type faujasite(FAU) zeolite layers with diverse materials characteristics(Si/Al ratio, thickness, and structural discontinuity) were hydrothermally grown on a porous $\alpha-Al_2O_3$ tube, and then the $CO_2/N_2$ separation was evaluated at $30^{\circ}C$ for an equimolar mixture of $CO_2$ and $N_2$. Among hydrothermal conditions, $SiO_2$ content in hydrothermal solution seriously affected materials characteristics: with an increment in the $SiO_2$ content, Si/Al ratio, thickness, and structural discontinuity of grown FAU zeolite layer simultaneously increased. The present study reveals that structural discontinuity(intercrystalline voids due to an incomplete densification and cracks induced by GIS Na-P1 phase) is the most important variable affecting the $CO_2/N_2$ separation. Also, it was suggested that the $CO_2$ desorption in permeate side be the rate-determining(slowest) step in the overall $CO_2$ permeation.
조철희,여정구,안영수,한문희,문종호,이창하,Cho, Churl-Hee,Yeo, Jeong-Gu,Ahn, Young-Soo,Han, Moon-Hee,Moon, Jong-Ho,Lee, Chang-Ha The Membrane Society of Korea 2007 멤브레인 Vol.17 No.3
분리층 두께가 5${\mu}m$이며 Si/Al 몰비가 1.5인 Na형 faujasite 제올라이트 분리막을 이차성장 공정에 의하여 제조하였고, 투과부에 13X 제올라이트 흡착제 충진 전후의 진공모드에서의 $CO_2/N_2$ 분리거동을 $CO_2/N_2$ 몰비가 1인 혼합기체에 대하여 $30^{\circ}C$에서 평가하였다. 충진된 13X 제올라이트 흡착제는 $CO_2$ 투과도와 $CO_2/N_2$ 선택도를 동시에 증진시켰다. 이 현상은 13X 제올라이트 흡착제 충진이 다공성 $\alpha$-알루미나 지지체의 기공채널을 통한 $CO_2$ 탈출을 증진시킴으로써 faujasite 제올라이트/$\alpha$-알루미나 상계면에서의 $CO_2$ 탈착을 증진시켰기 때문으로 설명되었다. 본 논문으로부터 흡착제와 분리막의 혼성화는 일반적으로 보여지는 선택도와 투과도의 역비례 관계를 획기적으로 개선할 방법임이 확인되었다. Sodium type faujasite(FAU) zeolite membranes with a thickness of 5${\mu}m$ and a Si/Al molar ratio of 1.5 were prepared by the secondary growth process. The $CO_2/N_2$ separation in the vacuum mode was investigated at $30^{\circ}C$ for an equimolar $CO_2-N_2$ mixed gas before and after embedding 13X zeolite beads in the permeate side. The embedded 13X zeolite beads improved both $CO_2$ permeance and $CO_2/N_2$ separation factor, simultaneously. The phenomenon was explained by an increment in the $CO_2$ desorption rate at the FAU zeolite/$\alpha-Al_2O_3$ phase boundary due to an enhanced $CO_2$ escaping through the pore channels of the $\alpha-Al_2O_3$ support layer. In the present paper, it will be emphasized that a hybridization of a membrane with an adsorbent can provide a key to break through the trade-off between permeance and separation factor, generally shown in a membrane separation.
김정훈,이준규,안영수,여정구,이진석,강기환,조철희,Kim, Jeong-Hun,Lee, Jun-Kyu,Ahn, Young-Soo,Yeo, Jeong-Gu,Lee, Jin-Seok,Kang, Gi-Hwan,Cho, Churl-Hee 한국재료학회 2019 한국재료학회지 Vol.29 No.11
In this study, we investigate the relationship between the peeling behavior of the backsheet of a photovoltaic(PV) module and its surface temperature in order facilitate removal of the backsheet from the PV module. At low temperatures, the backsheet does not peel off whereas, at high temperatures, part of the backsheet remains on the surface of the PV module after the peeling process. The backsheet material remaining on the surface of the PV module is confirmed by X-ray diffraction(XRD) analysis to be poly-ethylene(PE). Differential scanning calorimetry(DSC) is also performed to investigate the interfacial characteristics of the layers of the PV module. In particular, DSC provides the melting temperature($T_m$) of laminated ethylene vinyl acetate(EVA) and of the backsheet on the PV module. It is found that the backsheet does not peel off below the $T_m$ of ethylene of EVA, while the PE layer of the backsheet remains on the surface of the PV module above the $T_m$ of the PE. Thus, the backsheet is best removed at a temperature between the $T_m$ of ethylene and that of PE layer.
습식 화학 공정에 의한 태양전지로부터 고순도 실리콘 회수 및 이를 이용한 태양전지 재제조
노민호,이준규,안영수,여정구,이진석,강기환,조철희,Noh, Min-Ho,Lee, Jun-Kyu,Ahn, Young-Soo,Yeo, Jeong-Gu,Lee, Jin-Seok,Kang, Gi-Hwan,Cho, Churl-Hee 한국재료학회 2019 한국재료학회지 Vol.29 No.11
In this study, using a wet chemical process, we evaluate the effectiveness of different solution concentrations in removing layers from a solar cell, which is necessary for recovery of high-purity silicon. A 4-step wet etching process is applied to a 6-inch back surface field(BSF) solar cell. The metal electrode is removed in the first and second steps of the process, and the anti-reflection coating(ARC) is removed in the third step. In the fourth step, high purity silicon is recovered by simultaneously removing the emitter and the BSF layer from the solar cell. It is confirmed by inductively coupled plasma mass spectroscopy(ICP-MS) and secondary ion mass spectroscopy(SIMS) analyses that the effectiveness of layer removal increases with increasing chemical concentrations. The purity of silicon recovered through the process, using the optimal concentration for each process, is analyzed using inductively coupled plasma atomic emission spectroscopy(ICP-AES). In addition, the silicon wafer is recovered through optimum etching conditions for silicon recovery, and the solar cell is remanufactured using this recovered silicon wafer. The efficiency of the remanufactured solar cell is very similar to that of a commercial wafer-based solar cell, and sufficient for use in the PV industry.
물-에틸렌 글리콜 기반 알루미나 나노유체의 관내 대류열전달 특성에 관한 실험적 연구
이기웅(Ki Woong Lee),이욱현(Wook-Hyun Lee),박기호(Ki-Ho Park),여정구(Jeong Gu Yeo),배화영(Hwa Young Bae) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In this paper, the laminar forced convection heat transfer of ethylene glycol/water-based Al₂O₃ nanofluids is experimentally investigated in a circular tube with constant heat flux. For the purpose, a mixture of ethylene glycol and water with a component ratio of 1 to 1 is used as a basefluid. Ethylene glycol/water-based Al₂O₃ nanofluids are manufactured by two-step method. The experimental results are compared with theory which is used for single-phase convective heat transfer for fully developed laminar flow. In general, it is observed that the inclusion of nanoparticles has increased considerably the heat transfer at the tube wall for both the laminar and turbulent regimes. It is shown that the enhancement of the ethylene glycol/water-based Al₂O₃ nanofluids is dramatically increased in comparison with that of the ethylene glycol/water base fluid.