• Journal of Welding and Joining
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• 제14권4호
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• pp.99-108
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• 1996

The microstructure and bond strength are examined on the SiC/SiC and SiC/mild steel joints brazed by the Ag-Ti based alloys with different Ti contents. In the SiC/SiC brazed joints, the thickness of the reaction layers at the bond interface and the Ti particles in the brazing alloy matrices increase with Ti contents. When Ti is added up to 9 at% in the brazing alloy. $Ti_3SiC_2$ phase in addition to TiC and $Ti_5Si_3$ phase is newly created at the bond interface and TiAg phase is produced from peritectic reaction in the brazing alloy matrix. In the SiC/mild steel joints brazed with different Ti contents, the microstructure at the bond interface and in the brazing alloy matrix near SiC varies similarly to the case of SiC/SiC brazed joints. But, in the brazing alloy matrix near the mild steel, Fe-Ti intermetallic compounds are produced and increased with Ti contents. The bond strengths of the SiC/SiC and SiC/mild steel brazed joints are independent on Ti contents in the brazing alloy. There are no large differences of the bond strength between SiC/SiC and SiC/mild steel brazed joints. In the SiC/mild steel brazed joints, Fe dissolved from the mild steel does not affect on the bond strength of the joints. Thermal contraction of the mild steel has nearly no effects on the bond strength due to the wide brazing gap of specimens used in the four-point bend test. The brazed joints has the average bond strength of about 200 MPa independently on Ti contents, Fe dissolution and joint type. Fracture in four-point bend test initiates at the interface between SiC and TiC reaction layer and propagates through SiC bulk. The adhesive strength between SiC and TiC reaction layer seems to mainly control the bond strength of the brazed joints.

• Elastomers and Composites
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• 제36권3호
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• pp.177-187
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• 2001

폴리프로필렌(PP)/폴리우레탄(PU) 블렌드를 compositional quenching으로 제조하여 모폴로지, 인장물성, 표면에너지 그리고 열안정성 등을 조사하였다. 블렌드 제조시, 말레인산 무수물이 그라프트된 PP(MPP)와 히드록시에틸 말레이미드가 그라프트된 PP(HPP)를 반응성 상용화제로 도입하였으며, 이들의 생성 및 PU 조성과의 반응을 FT-IR로 확인하였다. Compositional quenching으로 제조한 블렌드는 용융블렌드에 비해 높은 혼화성을 보였으며, 블렌드내의 상용화제의 함량이 증가함에 따라 모폴로지, 인장물성. 표면특성, 그리고 열안정성 등의 물성이 현저하게 향상되었다. 상용화제로 MPP를 도입한 블렌드는 HPP를 도입한 블렌드에 비해, 높은 표면 에너지를 가졌다.

• 한국미생물·생명공학회지
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• 제31권4호
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• pp.311-321
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• 2003

세균은 지방을 분해할 수 있는 다양한 리파제를 생산한다. 리파제는 반응조건에 따라서 지방의 합성도 수행할 수 있는데 , 이러한 효소반응과정에서 고도의 기질특이성과 위치특이성 및 입체특이성을 보이기 때문에 제약산업과 정밀화학산업에서 효소촉매로서 널리 사용되고 있다. 지금가지 200종류 이상의 리파제효소가 보고되었으며, 이것들은 효소생산기원과 아미노산 상동성을 기준으로 6개의 family로 분류된다. 지난 10년 간 세균 리파제 6종에 대한 3D구조가 밝혀졌다. 이것들은 모두 중심부분에$\alpha/\beta$폴딩구조와 세린, 히스티딘, 아스팔틴산으로 구성된 활성부위를 공통적으로 갖고 있다. 활성부위를 양친성 $\alpha$나선구조가 뚜껑처럼 덮고 있으며, 물과 오일의 경계면을 만나면, 이 뚜껑이 열리고 효소활성이 크게 증가하는 '계면활성화' 현상을 보인다. P. cepacia 리파제 구조에는 기질과 결합하는 4개의 포켓이 있는데 이중 하나는 옥시음이온 구멍이고, 다른 세 개는 기질의 sn-1, sn-2, sn-3 지방산과 결합하는 부위이다. 이 포켓의 크기와 방향 및 소수성정도에 의해서 효소의 기질특이성과 입체특이성이 결정된다. 현재 이러한 구조연구를 기반으로 사용목적에 따른 맞춤 효소를 생산하기 위한 효소 개량연구가 활발히 진행되고 있다.

• 대한치과보철학회지
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• 제35권3호
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• pp.557-565
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• 1997

Screw-shaped implants of commercially pure (c.p.) titanium, c.p. niobium, c.p. zirconium, and stainless steel(Sus 304) were inserted in the rabbit tibial bone over 12 weeks of follow-up. New developed torque gauge instrument was used to evaluate the implant holding power and a image analysis program coupled to a microscope was used for histomorphometry. The three best consecutive threads of each implant were measured. Quantitative analyses at 12 weeks revealed a partial bone contact to the four kinds investigated metals. There were no obvious adverse tissue reactions to any of the biomaterials. At 12 weeks the average removal torques for titanium, niobium and zirconium were better than that needed for Sus 304 screws, on the other hand high score of bony contact ratio of titanium and niobium were showed in comparison to those of zirconium and Sus 304. There was no significant differences in the amount of interfacial bone of zirconium and Sus 304 whereas there was significant difference in the torque forces of niobium and Sus 304. Three months after implant insertion, the average removal torque was 6.64 Ncm for the titanium, 6.57 Ncm for the niobium, 6.38 Ncm for the zirconium, and 4.25 Ncm for the Sus 304. On average bone contacts there were 51.24% in the titanium, 48.19% in the niobium, 31.79% in the zirconium, 23.54% in the Sus 304. Biocompatibility of the titanium, niobium and zirconium was acceptable level in comparison to the Sus 304.

• 대한금속재료학회지
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• 제47권8호
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• pp.500-507
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• 2009

Pb-free solder has recently been used in electronics in efforts to meet environmental regulations, and a number of Pb-free solder alloy choices beyond the near-eutectic SnAgCu solder are now available. With increased demand for thin and portable electronics, the high cost of alloys containing significant amounts of silver and their poor mechanical shock performance have spurred the development of low Ag SnAgCu solder, which provides improved mechanical performance at a reasonable cost. Although low Ag SnAgCu solder exhibits significantly higher fracture resistance under high-strain rates, little thermal fatigue data exist for this solder. Therefore, it is necessary to investigate thermal fatigue reliability of low Ag SnAgCu solder under variation of thermal stress in order to allow its implementation in electronic products with high reliability requirements. In this study, the reliability of Sn0.3Ag0.7Cu(SAC0307), a low Ag solder alloy, is discussed and compared with that of Sn3Ag0.5Cu(SAC305). Three sample types and six samples size are evaluated. Mechanical properties and microstructure of the solder joint are investigated under thermal shock cycles. It was observed that the mechanical strength of SAC0307 dropped slightly with thermal cycling relative to that of SAC305. This reveals that the failure mode of SAC0307 is different from that SAC305 under this critical condition.

• 한국지하수토양환경학회지:지하수토양환경
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• 제26권6호
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• pp.18-26
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• 2021

Soil aggregation begins with flocculation of clay particles triggered by interfacial reactions of polyvalent cation such as Ca²⁺ and Fe³⁺, and they are also known as important elements to control the mobility of arsenic in soil environment. The objective of this study was to investigate the feasibility of CMDS (coal mine drainage sludge) for soil loss reduction and stabilization of arsenic-contaminated soil in a 37% sloped farmland under rainfall simulation. The amount of soil loss decreased by 43% when CMDS was applied, and this result was not significantly different from the case of limestone application, which yielded 46% decrease of soil loss. However, the relative amount of dispersed clay particles in the sediment CMDS-applied soil was 10% lower than that of limestone-applied soil, suggesting CMDS is more effective than limestone in inducing soil aggregation. The concentrations of bioavailable arsenic in CMDS amended soil decreased by 46%~78%, which was lower than the amount in limestone amended soil. Therefore, CMDS can be used as an effective amendment material to reduce soil loss and stabilize arsenic in sloped farmland areas.

• Nano
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• 제13권12호
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• pp.1850148.1-1850148.9
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• 2018

The interconnected three-dimensional Ni-Co-S nanosheets were successfully deposited on ZnO nanorods by a one-step potentiostatic electrodeposition. The Ni-Co-S nanosheets provide a large electrode/electrolyte interfacial area which has adequate electroactive sites for redox reactions. Electrochemical characterization of the ZnO@Ni-Co-S core-shell nanorods presents high specifc capacitance (1302.5 F/g and 1085 F/g at a current density of 1 A/g and 20 A/g), excellent rate capabilities (83.3% retention at 20 A/g) and great cycling stability (65% retention after 5000 cycles at a current density of 30 A/g). The outstanding electrochemical performance of the as-prepared electrode material also can be ascribed to these reasons that the special structure improved electrical conductivity and allowed the fast diffusion of electrolyte ions.

• Journal of Electrochemical Science and Technology
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• 제13권3호
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• pp.407-415
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• 2022

Surface coating of cathodes is an essential process for all-solid-state batteries (ASSBs) based on sulfide electrolytes as it efficiently suppresses interfacial reactions between oxide cathodes and sulfide electrolytes. Based on computational calculations, Li₃PO₄ has been suggested as a promising coating material because of its higher stability with sulfides and its optimal ionic conductivity. However, it has hardly been applied to the coating of ASSBs due to the absence of a suitable coating process, including the selection of source material that is compatible with ASSBs. In this study, polyphosphoric acid (PPA) and (NH₄)₂HPO₄ were used as source materials for preparing a Li₃PO₄ coating for ASSBs, and the properties of the coating layer and coated cathodes were compared. The Li₃PO₄ layer fabricated using the (NH₄)₂HPO₄ source was rough and inhomogeneous, which is not suitable for the protection of the cathodes. Moreover, the water-based coating solution with the (NH₄)₂HPO₄ source can deteriorate the electrochemical performance of high-Ni cathodes that are vulnerable to water. In contrast, when an alcohol-based solvent was used, the PPA source enabled the formation of a thin and homogeneous coating layer on the cathode surface. As a consequence, the ASSBs containing the Li₃PO₄-coated cathode prepared by the PPA source exhibited significantly enhanced discharge and rate capabilities compared to ASSBs containing a pristine cathode or Li₃PO₄-coated cathode prepared by the (NH₄)₂HPO₄ source.

• 한국재료학회지
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• 제3권1호
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• pp.33-42
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• 1993

세라믹스를 공업분야에 응용범위를 확대하기 위한 최선의 수단으로 금속과의 복합화를 들수 있다. 금속과 복합화하는 방법중에서 세라믹스/금속접합은 부품의 제조등에 이용될 수 있는 수단으로 많은 연구가 행하여져서 이미 몇몇 부품에 대해서는 실용화가 되고 있고 현재에도 활발히 연구가 되고 있다. 따라서 본 연구에서는 여러가지 접합법중에서도 비교적 공정이 간편한 활성 브레이징법을 이용해 $Al_2$$O_3$ 와 304 스테인레스강을 접합하였으며 이때 삽입금속으로는 Cu-Ti합금을 사용하였고 접합온도 및 접합시간 범위는 각각 110$0^{\circ}C$-120$0^{\circ}C$, 0.5h-1.5h, 그리고 브레이징로 내의 분위기는 $10^{-3}$-$10^{-4}$ torr로 유지하였다. 접합후 접합부 조직에 대한 접합조건의 영향을 검토하고 반응생성물을 EDX, WDX 및 XRD을 이용해 분석하였으며 반응층형성을 위한 계면화학반응을 고찰하였다. 그 결과 알루미나와 삽입금속의 계면에서 접합을 유도하는 반응층은 T$i_2$$O_3$임을 확인할 수 있었다.

• 마이크로전자및패키징학회지
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• 제6권1호
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• pp.51-58
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• 1999

지르코니아에 접합과 반응성이 정합되며 고온에서 물리화학적으로 안정성을 갖는 접합재를 제조하기 위하여 silicate계 유리의 조성에 따른 적심특성, 결정화 및 반응성등 제반 특성을 고찰하였다. 지르코니아와의 열팽창계수가 정합 될 수 있는 유리계에 대한 조성 실험하였다. Alkaline earth silicate 유리는 적심성이 우수하였으며 적심각이 낮으며 $B_2O_3$의 첨가함로써 유리의 점도를 조절 및 결정화를 억제할 수가 있었다. $900^{\circ}C$ 이하에서 적심공정에 일어났으며 $800^{\circ}C$에서 10시간동안 유지한 후에 결정화와 계면 반응을 조사한 결과 기공이 많이 발생하였으며 $B_2O_3$를 15mo1% 첨가한 경우 흐름성이 증가하였으며 기판과의 반응성이 높아졌다. 기공을 없애기 위해서는 공정변수를 조절하여 유리의 소결을 촉진할 필요가 있으며 유리점도와 반응성에 관한 최적화가 요구된다. 본 연구에서는 유리-세라믹필러 복합체의 고온적심성에 대하여 조사하였다. Filler로서 $ZrO_2$분말을 여러 조건으로 열처리하여 분말종류와 첨가량에 따라 기공, $ZrO_2$ filler의 형상 및 계면반응 등을 고찰하였다.