• 한국표면공학회지
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• 제53권4호
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• pp.144-152
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• 2020

In the manufacturing process of joining of aluminum alloy and polymer, the strength of the metal-polymer joining is greatly influenced by the nanostructure of the oxide film. In this study, we investigated the dependence of joining strength on the thickness, structure, pore formation and surface roughness of the formed film. After the two-step anodization process, the surface oxide layer became thinner and rougher resulting in higher joining strength with the polymer. More specifically, after the two-step anodization, the surface roughness, Ra increased from 2.3 to 3.2 ㎛ with pore of three-dimensional (3D) nanostructure, and the thickness of the oxide film was thinned from 350 to 250 nm. Accordingly, the joining strength of the aluminum alloy with polymer increased from 23 to 30 MPa.

• 한국진공학회지
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• 제7권s1호
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• pp.30-36
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• 1998

The plasma-spray technique is currently the most frequently used method to produce calcium phosphate coatings. Hydroxyapatite(HAp), one form of calcium phosphate, is preferred by its ability to form a direct bond with living bone, resulting in improvements of implant fixation and faster bone healing. Recently, concerns have been raised regarding the viable use and long-term stability of plasma-spray HAp coatings due to its nature of comparatively thick, porous, and poor bonding strength to metal implants. Thin layers (maximum of few microns) of calcium phosphate were formed by an e-beam evaporation with and without ion bombardments. The Ca/P ration of film was controlled by either using the evaporants having the different ration of Ca/P with addition of CaO, or adjusting the ion beam assist current. The Ca/P ration had great effects on the structure formation after heat treatment and the dissolution bahavior. The calcium phosphate films produced by IBAD exhibited high adhesion strength.

• Computers and Concrete
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• 제31권2호
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• pp.139-149
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• 2023

This article investigates the statically analysis regarding the thermal buckling behavior of a nonuniform small-scale nanobeam made of functionally graded material based on classic beam theories along with the nonlocal Eringen elasticity. The material distribution of functionally graded structures is composed of temperature-dependent ceramic and metal phases in axial and thickness directions, called two-dimensional functionally graded (2D-FG). The partial differential (PD) formulations and end conditions are extracted by using to the conservation energy method. The porosity voids are assumed in the nonuniform functionally graded (FG) structure. The thermal loads are in the axial direction of the beam. The extracted nonlocal PD equations are also solved by employing generalized differential quadrature method (GDQM). Last but not least, the information acquired is used to produce miniature sensors, providing a unique perspective on the growth of nanoelectromechanical systems (NEMS).

• 공업화학
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• 제28권6호
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• pp.601-606
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• 2017

금속 표면처리의 대표적인 기술인 양극산화를 통하여 일차원 나노구조 금속 산화물을 형성할 수 있다. 여러 가지 금속 산화물 중에 기능성이 뛰어난 $TiO_2$에 대한 관심의 증대로 $TiO_2$ 나노 튜브를 이용한 연구가 많이 이루어지고 있다. 본 총설논문에서는 지금까지 연구되어 밝혀진 $TiO_2$ 나노 튜브가 형성원리에 대한 해설논문으로 전기화학적 측면에서의 양극 산화 공정에 대한 이해를 통하여 나노 튜브 형성을 위한 전기적 조건, 화학적 조건, 물리적 조건에 대하여 다루었다. 특히 $TiO_2$ 나노 튜브 성장의 핵심 요소인 산화물의 형성과 에칭의 평형관계, 다공성 구조의 형성 원인을 다루었다. 나아가 전해질 조건에 따른 $TiO_2$ 나노 튜브의 형태학적 고찰을 함으로써 향후 양극 산화를 통한 $TiO_2$ 나노 튜브 응용에 관한 연구를 하는 연구자에게 이해하기 쉽게 설명하고자 하였다.

• 공업화학
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• 제32권4호
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• pp.442-448
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• 2021

고분자전해질 연료전지에서 분리판 유로 형상은 유체 공급과 물 및 열 확산, 접촉 저항 등에 영향을 주는 중요한 요소이다. 본 연구에서는 25 cm² 단위 전지를 이용하여 공기극에 구리폼을 적용한 분리판을 이용하여 연료전지 성능 평가를 수행하였다. 압력과 상대습도 조건에 대한 영향을 분극 곡선과 전기화학적 임피던스 분광법을 이용하여 분석하였다. 구리폼의 ohmic 저항이 높아 사형유로형상 보다 연료전지 성능은 낮았지만, 다공성 구조로 인한 균일한 연료 분포로 활성화 손실과 물질전달 손실이 적은 것을 확인하였다. 구리폼의 소수성이 높아 물 배출이 유리한 장점이 있지만, 저가습 조건에서는 사형유로에 비하여 전해질막 수화도가 낮은 것을 확인하였다. 다공성 금속 분리판은 균일한 압력 분포와 효과적인 수분 배출로 연료전지 성능을 개선할 수 있을 것으로 판단되며, 저항을 최소화할 수 있도록 금속폼의 물성에 대한 연구가 수행되어야 할 것이다.

• 대한기계학회논문집B
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• 제36권9호
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• pp.931-935
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• 2012

본 연구에서는 저온형 연료전지와 고온형 연료전지의 작동 및 구성 요소 측면 단점들을 보완하기 위해 중온 영역에서 작동하는 박막 연료전지를 제작하였다. 박막 연료전지는 이트륨이 도핑된 바륨 지르코네이트(BYZ) 전해질과 백금 수소극/공기극으로 이루어져 있으며, 성능은 $350^{\circ}C$에서 측정하였다. 350nm의 두께를 가지는 백금 수소극은 다공성 기판 위에 스퍼터링 기법을 이용하여 증착하였다. BYZ전해질은 펄스레이저 기법을 이용하여 $1{\mu}m$ 증착하였고, 상부에 스퍼터링 기법을 이용하여 200nm의 두께를 가지는 백금 공기극을 증착하였다. 개회로 전압은 약 0.81V이었고, 최대 출력 성능은 11.9mW/$cm^2$이었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.163-166
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• 1997

Aluminium foam material is a highly porous material having complicated cellular structure defined by randomly distributed air pores in metallic matrix. this structure gives the aluminium a set of properties which cannot be achieved by any of conventional treatments. The properties of aluminium foam material significantly depend on its porosity, so that a desired profile of properties can be tailored by changing the foam density. Melting method is the one of foaming processes, which the production has long been considered difficult to realize becaues of such problems as the low foamability of molten metal, the varying size of. cellular structures, solidification shrinkage and so on. These problems, however, have gradually been solved by researchers and some manufacturers are now producing foamed aluminum by their own methods. Most of all, the parameters of solving problem in electric furnace were stirring temperature, stirring velocity, foaming temper:iture, and so on. But it has not considered about those in induction heating, foaming velocity and foaming temperature in semi-solid state yet. Therefore, this paper presents the effects on these parameter to control cell size, quantity and distribution.

• Corrosion Science and Technology
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• 제21권3호
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• pp.200-208
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• 2022

Aluminum alloy is used by adding various elements according to the needs of the industry. Aluminum alloys such as 5052 and 6061 are known to possess excellent corrosion resistance by adding Mg. Despite their excellent physical properties, corrosion can occur. To solve this problem, an anodization technique generally can improve corrosion resistance by forming an oxide structure with maximized hydrophobic properties through coatings. In this study, the anodizing technique was used to improve the hydrophobicity of aluminum 5052 and 6061 by creating porous nanostructures on top of the surface. An oxide film was formed by applying anodizing voltages of 20, 40, 60, 80, and 100 V to aluminum alloys followed by immersion in 0.1 M phosphoric acid for 30 minutes to expand oxide pores. Contact angle and corrosion characteristics were different according to the structure after anodization. For the 5052 aluminum, the corrosion potential was improved from -363 mV to -154 mV as the contact angle increased from 116° to 136°. For the 6061 aluminum, the corrosion potential improved from -399 mV to -124 mV when the contact angle increased from 116° to 134°.

• 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.

• 한국환경과학회지
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• 제30권1호
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• pp.97-108
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• 2021

In the current study, MIL-101(Cr)-SO3H[HCl] as metal-organic frameworks (MOFs) was fabricated via a hydrothermal method. The physicochemical properties of the synthesized material were characterized using XRD, FT-IR, FE-SEM, TEM, and BET surface area analysis. The XRD diffraction pattern of the prepared MIL-101(Cr)-SO3H[HCl] was similar to previously reported patterns of MIL-101(Cr) type materials, indicating successful synthesis of MIL-101(Cr)-SO3H[HCl]. The FT-IR spectrum revealed the molecular structure and functional groups of the synthesized MIL-101(Cr)-SO3H[HCl]. FE-SEM and TEM images indicated the formation of rectangular parallelopiped structures in the prepared MIL-101(Cr)-SO3H[HCl]. Furthermore, the EDS spectrum showed that the synthesized material consisted of the elements of Cr, O, S, and C. The fabricated MIL-101(Cr)-SO3H[HCl] was then employed as an adsorbent for the removal of Sr2+ and Cs+ from aqueous solutions. The adsorption kinetics and adsorption isotherm models were studied in detail. The maximum adsorption capacities of MIL-101(Cr)-SO3H[HCl] for Sr2+ and Cs+ according to pH (3, 5.3~5.8, 10) were 35.05, 43.35, and 79.72 mg/g and 78.58, 74.58, and 169.74 mg/g, respectively. These results demonstrate the potential of the synthesized MOFs, which can be effectively applied as an adsorbent for the removal of Sr2+ and Cs+ ions from aqueous solutions and other diverse applications.