• 한국재료학회지
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• 제11권4호
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• pp.329-334
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• 2001

붕산용액에서 양극산화법으로 장벽형 산화피막을 형성시킨 후 미세조직을 관찰하였다. 양극산화시 인가되는 전압에 따른 피막의 성장속도는 1.54nm/v의 직선적인 관계를 나타냈으며 300v의 인가전압에서 생성된 산화피막의 조직은 50$0^{\circ}C$에서 열처리하였을 경우 피막의 상 전이가 일어나지 않았으나 높은 인가전압에서 생성된 산화피막의 경우는 피막의 조직이 비정질에서 ${\gamma}$-alumina로 변태되는 것이 관찰되었다. 또한 피막이 전자빔 조사에 의해서도 ${\gamma}$-alumina로 전이가 일어났다.

• 대한치과기공학회지
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• 제23권2호
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• pp.161-170
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• 2002

The Purpose of this study was to investigate the chemically improvement of metal-ceramics bond strength in the course of recasting Ni-Cr metal composite system with 10wt.%, 20wt.% and 30wt.% aluminum respectively. We have tested the bond strength, micro-structure, chemical composition of each metal composites and metal- ceramic bond interfaces by 3-point bending strength tester, SEM and EDS. We have made the conclusions through this study as follow: 1. The most suitable amount of aluminum to the Ni-Cr metal composite recasting is 20wt. % for improving metal-ceramics bond strength with debonding strength value of 49.54 kgf/mm2. 2. The aluminum must be changed to small spread alumina like phases and second aluminum-metal composites phases in the morphology of Ni-Cr metal composite system by adding during it's casting. These second phases have inclined functional oxide phases mixed with metal elements and they must take roll to improvement of metal-ceramics bond strength. 3. In the case of 30wt.% aluminum appended to Ni-Cr metal composite system, an excess of second inclined functional oxide phases produce cracks and spalling of them apart from it's base material. It must be a important factor of reduction of metal-ceramics bond strength.

• Journal of Welding and Joining
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• 제33권2호
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• pp.14-17
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• 2015

Cleaning effect is well known mechanism of oxide layer removal in DCEP polarity. It is also known that DCEN has higher heat input efficiency than DCEP in GTAW process. Based on these two renowned arc theories, conventional variable polarity arc for aluminum welding was set up to have minimum DCEP and maximum DCEN duty ratio to achieve the highest heat input efficiency and weldability increase. However, recent several variable polarity GTA research papers reported unexpected result of proportional relationship between DCEP duty ratio and heat input. The authors also observed the same result then suggested combination of tunneling effect and random walk of cathode spot to fill up the gap between experiment and conventional arc theory. In this research, suggested combinational work of tunneling effect and rapid cathode spot changing is applied to another unexpected phenomena of variable polarity aluminum arc welding. From previous research, it is reported that wider oxide removal range, narrower bead width and shallower penetration depth are observed in thin oxide layered aluminum compared to the case of thick oxide. This result was reported for the first time and it was hard to explain the reason at that time therefore the inference by the authors was hardly acceptable. However, the suggested combinational theory successfully explains the result of the previous report in logical way.

• 한국분말재료학회지
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• 제22권4호
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• pp.240-246
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• 2015

Anodic aluminum oxide (AAO) has been widely used for the development and fabrication of nano-powder with various morphologies such as particle, wire, rod, and tube. So far, many researchers have reported about shape control and fabrication of AAO films. However, they have reported on the shape control with different diameter and length of anodic aluminum oxide mainly. We present a combined mild-hard (or hard-mild) anodization to prepare shape-controlled AAO films. Two main parameters which are combination mild-hard (or hard-mild) anodization and run-time of voltage control are applied in this work. The voltages of mild and hard anodization are respectively 40 and 80 V. Anodization was conducted on the aluminum sheet in 0.3 mole oxalic acid at $4^{\circ}C$. AAO films with morphologies of varying interpore distance, branch-shaped pore, diameter-modulated pore and long funnel-shaped pore were fabricated. Those shapes will be able to apply to fabricate novel nano-materials with potential application which is especially a support to prevent volume expansion of inserted active materials, such as metal silicon or tin powder, in lithium ion battery. The silicon powder electrode using an AAO as a support shows outstanding cycle performance as 1003 mAh/g up to 200 cycles.

• 공업화학
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• 제9권4호
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• pp.463-468
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• 1998

알루미늄의 부식에 있어서 HCI 용액내에 황산을 첨가하는 경우 황산이온의 화학적 흡착에 의한 부식억제 효과가 나타나며, CV (cyclic voltammetry) 실험결과 황산이온은 핏트내부에 보호성 산화피막을 생성함으로서 에치핏트가 핏트내부와 알루미늄 표면에 함께 생성되어 핏트의 밀도가 증가하였다. 알루미늄 교류에칭시에 핏트분포는 황산이온의 농도와 환원전류량에 의하여 크게 영향을 받으며, 환원전류인가시 $0.8mC/cm^2$ 이하의 전하량에서 핏트내부에 생성된 산화피막은 황산이온 농도의 증가에 따라 핏트발생에 대한 저항성이 중가하였으나, $0.8mC/cm^2$ 이상에서는 산화피막내에 국부적인 구조변화가 발생하며 황산이온 농도에 관계없이 산화피막의 파괴가 빠르게 진행되었다.

• 한국정보통신학회논문지
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• 제14권4호
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• pp.923-928
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• 2010

양극산화 알루미늄(anodic aluminum oxide, AAO) 나노템플레이트는 제작이 쉬우며, 저비용, 대면적 제작이 가능하다는 장점으로 인해 이를 나노 전자소자 제작에 응용하려는 많은 연구가 이루어지고 있다. 이러한 나노템플레이트를 이용하면 기공의 직경이나 밀도를 변화킴으로써 나노구조의 물질의 크기나 밀도를 제어할 수 있다. 따라서 본 논문에서는 나노 전자소자 제작에 응용할 수 있는 AAO 나노템플레이트를 2단계 양극산화법에 의해 제조하였다. 이를 위해 기존의 알루미늄 판 대신 실리콘 웨이퍼 상에 DC 마그네트론 스퍼터법으로 $2{\mu}m$ 두께의 알루미늄 박막을 증착하였고, 전해액으로 사용한 옥살산 용액의 온도 및 양극산화 전압에 따른 다공성 알루미나 막의 미세구조를 조사하였다. 전해액 온도가 $8^{\circ}C$에서 $20^{\circ}C$로 높아짐에 따라 다공성 알루미나 막의 성장속도는 86.2 nm/min에서 179.5 nm/min으로 증가하였다. 최적 조건에서 제작된 AAO 나노 템플레이트의 기공 직경 및 깊이는 각각 70 nm와 $1\;{\mu}m$이었다.

• 구강회복응용과학지
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• 제29권1호
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• pp.69-79
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• 2013

본 연구의 목적은 각각 다른 표면처리를 한 지르코니아를 레진시멘트로 접착한 후 전단결합강도를 평가, 비교하는 것이다. 디스크 모양의 산화 지르코늄(3-TZP, Kyoritsu, Tokyo, Japan) 시편 120 개를 다음과 같이 표면처리 하였다. (1)110 ${\mu}m$ 산화 알루미나 분사 처리 (2)Silica coating(RocatecTM, 3M ESPE) (3)처리하지 않음 시편을 한 군당 10 개씩 총 6 개군으로 나누어 두 개의 지르코니아 시편을 자가 접착형 레진 시멘트(RelyX U-200, 3M ESPE)로 합착하였다. (1)처리하지 않음/처리하지 않음 (2)처리하지 않음/110 ${\mu}m$ 산화 알루미나 분사처리 (3)처리하지 않음/Silica coating (4)110 ${\mu}m$ 산화 알루미나 분사 처리/110 ${\mu}m$ 산화 알루미나 분사 처리 (5)110 ${\mu}m$ 산화 알루미나 분사 처리/Silica coating (6)Silica coating/Silica coating. 각 군의 전단결합강도를 만능시험기로 측정하였다. 표면처리에 따른 결합강도의 차이를 살펴보기 위해 일원변량분석(One-way ANOVA)을 이용하고 사후 분석으로 Tukey HSD test를 실시하였다. Silica coating을 한 두 개의 시편을 접착한 군이 가장 높은 결합 강도를 보였다(P<0.05). 표면 처리하지 않은 시편을 접착한 군과 두 개의 시편 모두 알루미나 분사 처리한 시편을 접착한 군은 서로 간에 유의한 차이를 보이지 않았으며, 그 외의 군에 비해서는 유의하게 낮았다(P<0.05). 본 연구의 결과에 따르면 Silica coating은 자가중합형 레진시멘트를 이용하여 접착한 두 지르코니아 간의 결합을 증진시키는데 효과적이었다.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3258-3264
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• 2012

Aluminum oxide ($Al_2O_3$) nanofibers were treated thermally under an ammonia ($NH_3$) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of $Al_2O_3$/epoxy nanocomposites. The micro-structural and morphological properties of the $NH_3$-assisted thermally-treated $Al_2O_3$ nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and $N_2$/77 K isothermal adsorptions. From the results, the formation of AlN on $Al_2O_3$ nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified $Al_2O_3$ nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated $Al_2O_3$/epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers.

• Corrosion Science and Technology
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• 제18권6호
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• pp.228-231
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• 2019

Aluminum and its alloys have been widely used in various fields because of low weight, high strength, good conductivity, and low price. It is well known that aluminum alloys that cause natural oxide film can inhibit corrosion in wet, salty environments. However, these oxides are so thin that corrosion occurs in a variety of environments. To prevent this problem, an electrochemical anodizing technique was applied to the aluminum alloy surface to form a thick layer of oxide and a unique oxide shape, such as a hierarchical pore structure simultaneously combining large and small pores. The shape of the structures was implemented using stepwise anodization voltages such as 40 V for mild anodizing and 80 V for hard anodizing, respectively. To maximize water repellency, it is crucial to the role of surface structures shape. And a hydrophobic thin film was coated by 1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane (FDTS) to minimize surface energy of the structure surface. Thus, such nanoengineered superhydrophobic surface exhibited a high water contact angle and excellent corrosion resistance such as low corrosion current density and inhibition efficiency.

• Journal of Pharmaceutical Investigation
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• 제13권1호
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• pp.1-9
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• 1983

The effect of humidity on crystallization and polymorphic transformation of hydrous aluminum oxide under various humidity at $37^{\circ}$ was examined by means of X-ray diffraction, scanning electron micrograph, IR spectra and DTA. The humidity was an important factor influencing crystallization of hydrous aluminum oxide. The growth or crystal was strongly accelerated by humidity. The aging process is assumed that it is composed of two seperate steps, an increase of the diffraction around $36{\sim}42^{\circ}$, and an appearance and its development of the peak at $18{\sim}20^{\circ}$ of $2{\theta}$ value. The former is considered to be nucleation and the latter correspond to the growth period on crystallization. The crystalline form of aging products was various depending on the degree of humidity, directly it leads to the eventual formation of bayerite in more than 72%, $b{\"{o}}hmite$ in 50% and resembled to Nordstandite in 0% relative humidity, respectively but once formed, it was mostly stable in each surroundings and does not transform to the other more stable form in solid state even after aging for five years. The mechanism responsible for aging is further polymerization process of six-membered rings by deprotonation-dehydration reaction in which positively charged polynuclear hydroxy aluminum complexes formed in the presence of moisture are joined at their edges by double hydroxide bridges.