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첨가제와 잔류응력이 탄소 기지상 무전해 니켈도금에 미치는 영향
천소영,임영목,이재호,Cheon, So-Young,Rhym, Young-Mok,Lee, Jae-Ho 한국마이크로전자및패키징학회 2011 마이크로전자 및 패키징학회지 Vol.18 No.4
탄소 기지상에 니켈도금을 하여 다공성 MCFC의 전극으로 사용하기 위하여 탄소 기지위에 산성용액과 염기성용액을 이용하여 무전해 니켈도금을 하였다. 알칼리 용액에서의 도금속도가 산성용액에서의 도금속도보다 빨랐으며 두가지 용액에서 pH가 증가함에 따라 도금속도가 증가하였다. 산성용액에서의 잔류응력은 압축응력을 보였으며 알칼리용액에서는 높은 인장응력을 보였으며 높은 잔류응력으로 인하여 pH 11 이상에서는 표면균열이 발생하였다. Thiourea를 첨가하였을 경우 0.5 ppm까지의 저농도에서 도금속도가 증가하다가 이후 감소하였으며 1.5 ppm 이상에서 두가지 용액에서 모두 도금이 더 이상 진행되지 않았다. Succine 산을 첨가한 경우 5 g/L까지 속도가 증가하다가 감소하여 일정한 값을 유지하였다. Electroless nickel platings on carbon substrate were investigated for porous MCFC electrode applications. Acidic bath and alkaline bath were used in electroless nickel plating on carbon substrates. The rate of electroless plating in alkaline bath was faster than that in acidic bath. As pH was increased, the deposition rate was increased in both baths and the content of phosphorus in nickel deposit was decreased. The residual stresses of nickel deposit from acidic bath showed the compressive stress and on the other hand those from alkaline bath showed the high tensile stress. High tensile internal stress in nickel deposit caused the cracks over pH 11. Thiourea was added to both acidic and alkaline bath. The deposition rate of nickel was increased upto 0.5 ppm of thiourea and decreased. The maximum concentration of thiourea for the electroless nickel plating on carbon substrate was 1.5 ppm in both acidic and alkaline bath. Succinic acid was added to acidic bath. Addition of succinic acid up to 5 g/L increased the deposition rate of nickel and beyond which the deposition rate was decreased and maintained.
가압력 변화에 따른 표면조도처리 강판의 저항 점 용접성 비교
박상순,박영도,김기홍,최영민,임영목,강남현,Park, Sang-Soon,Park, Yeong-Do,Kim, Ki-Hong,Choi, Yung-Min,Rhym, Young-Mok,Kang, Nam-Hyun 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.2
With the development of surface roughness textured steel for automotive body-in-white assemble, one of key issues is to understand the role of the surface roughness in textured steel sheets. To investigate effect of surface roughness on weldability in prepared steels, electrode force was varied. Steel sheets (T-H) with high surface roughness ($Ra\;=\;1.94\;{\mu}m$) reduced electrode life. It was attributed to the higher contact resistance at the electrode-sheet interface in the presence of the high surface roughness. The increased electrode diameter decreased current density, therefore reducing weld electrode life due to small weld button size. When an increased electrode force was used, a significant increase in the electrode life was observed in welding of high surface roughness steel sheet. This study suggested that contact resistance at the electrode-sheet interface was the dominant factor, as compared to the sheet-sheet interface for determining electrode life in welding of surface roughness textured steel.
표면조도 특성에 따른 저항 점 용접성 평가 및 너깃 형성 고찰
김기홍,최영민,김영석,임영목,유지훈,강남현,박영도,Kim, Ki-Hong,Choi, Yung-Min,Kim, Young-Seok,Rhym, Young-Mok,Yu, Ji-Hun,Kang, Nam-Hyun,Park, Yeong-Do 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.5
With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel ($R_{a}=1.70\;{\mu}m$) was higher than that for T-L steel ($R_{a}=1.33\;{\mu}m$), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.
무유화 유화중합에 의해 합성된 Core/shell 형태 PMMA/CdS 나노입자의 특성분석
윤효정 ( Hyo Jung Yoon ),임영목 ( Young Mok Rhym ),심상은 ( Sang Eun Shim ) 한국접착및계면학회 2012 접착 및 계면 Vol.13 No.4
in-situ 무유화 유화중합 및 후속 CdS 코팅 공정으로 이루어진 방법을 이용하여 CdS로 코팅된 PMMA 나노입자를 제조하고 그 특성을 분석하였다. 합성된 CdS/PMMA 나노입자의 크기는 201.7 nm 였으며, TGA 및 원소 분석 결과 10.37 wt%의 CdS를 함유하고 있었다. PMMA 입자 표면에 코팅된 CdS 나노결정의 크기는 3.55 nm였으며 주로 (111) 결정면으로 성장되었다. UV-vis 분석 결과 blue-shifting 현상이 관찰되었으며, 이는 CdS/PMMA 하이브리드 입자상태에서의 CdS는 벌크 상태의 CdS가 갖는 2.41 eV의 밴드갭 에너지보다 큰 2.70 eV를 갖기 때문에 발생하는 양자구속효과에 의하여 기인하였다. Herein, CdS-coated PMMA nanoparticles were prepared by in-situ surfactant-free emulsion copolymerization and subsequent CdS coating process. As-prepared CdS/PMMA hybrid particles had 201.7 nm in diameter. The amount of CdS nanocrystals in the hybrid particles was 10.37 wt% determined by TGA and elemental analysis. The size of CdS crystals was 3.55 nm preferentially grown in (111) plane. UV-vis spectrum of PMMA/CdS nanoparticles showed the significant blue-shift in optical illumination. The reason was found because the synthesized CdS nanocrystals on PMMA particles had a different band gap energy of 2.70 eV which was significantly higher than that of known-value of bulk CdS (2.41 eV) due to a quantum confinement effect.
다공성 탄소전극상 무전해 니켈도금의 산성과 알칼리용액 비교 연구
천소영(So-Young Chun),강인석(In-Seok Kang),임영목(Young-Mok Rhym),김두현(Doo-Hyun Kim),이재호(Jae-Ho Lee) 한국표면공학회 2010 한국표면공학회지 Vol.43 No.2
Electroless nickel plating on porous carbon substrate for the application of MCFC electrodes was investigated. Acidic and alkaline bath were used for the electroless nickel plating. The pore sizes of carbon substrates were 16-20 ㎛ and over 20 ㎛. The carbon surface was changed from hydrophobic to hydrophilic after immersing the substrate in an ammonia solution for 40 min at 60℃. The contact angle of water was decreased from 85˚ to less than 20˚ after ammonia pretreatment. The deposition rate in the alkaline bath was higher than that in the acidic bath. The deposition rate was increased with increasing pH in both acidic and alkaline bath. The content of phosphorous in nickel deposit was decreased with increasing pH in both acidic and alkaline bath. The contents of phosphorous is low in alkaline bath. The minimum concentration of PdCl₂ for the electroless nickel plating was 10 ppm in alkaline bath and 5 ppm in acidic bath. The thickness of nickel was not affected by the concentration of PdCl₂.
Al 7003 합금의 인장 및 피로 특성에 미치는 열처리(T5, T6)의 영향
김민종 ( M J Kim ),김관영 ( K Y Kim ),어광준 ( G J Euh ),임영목 ( Y M Rhym ),이기안 ( K A Lee ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.3
A7003 alloy underwent T5 and T6 heat treatments (T5: 90 ℃ for 5 hrs and 150 ℃ for 16 hrs; T6: 470 ℃ for 3 hrs followed by artificial aging at 80 ℃ for 14 hrs, and 120 ℃ for 42 hrs); the tensile and fatigue properties of the treated materials were then examined. High-cycle fatigue tests were conducted at R (stress ratio)=0.1, and f (frequency)=20 Hz. The average grain size of A7003-T5 alloy was 3.8 μm, and that of A7003-T6 alloy was 4.1 μm. Both of the alloys were found to have MgZn2 (?), Fe-based intermetallic phases in their aluminum matrix. A7003-T6 alloy had finer MgZn2 (?) phases distributed more evenly than A7003-T5 alloy. Tensile test results showed that A7003-T6 alloy had higher strength (Y.S. & T.S.) and lower elongation compared to those of A7003-T5 alloy. High cycle fatigue results showed that A7003-T6 alloy had longer fatigue limit (320 MPa) than that (290 MPa) of T5 alloy. A7003-T6 alloy was found to perform better in all other fatigue stress conditions, too. Based on the observation of tensile and fatigue fracture surfaces, the correlations between microstructures made by heat treatments and mechanical/fatigue properties were also investigated along with the fatigue deformation mechanism of A7003 alloy.(Received April 22, 2014)
페라이트계 및 오스테나이트계 스테인리스강과 IF강의 이종 접합부의 저항 점 용접성 평가
이진범 ( Jin Beom Lee ),김동철 ( Dong Cheol Kim ),남대근 ( Dae Geun Nam ),강남현 ( Nam Hyun Kang ),김순국 ( Soon Kook Kim ),유지훈 ( Ji Hun Yu ),임영목 ( Young Mok Rhym ),박영도 ( Yeong Do Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint`s weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.