• 소성∙가공
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• 제17권4호
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• 한국재료학회지
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• 제14권12호
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• pp.876-884
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• 2004

This study was to investigate whether the bioactivity of the anodized and hydrothermally treated Ti-6Al-7Nb alloy were affected by the time of hydrothermal treatment. Anodizing was performed at current density 30 $mA/cm^2$ up to 300 V in electrolyte solutions containing $DL-{\alpha}-glycerophosphate$ disodium salt hydrate $(DL-{\alpha}-GP)$ and calcium acetate (CA). Hydrothermal treatment was done at $300^{\circ}C$ for 30 min, 1 hr, 2 hrs, and 4 hrs to produce a thin film layer of hydroxyapatite (HA). The bioactivity was evaluated from HA formation on the surfaces in a Hanks' solution with pH 7.4 at $36.5^{\circ}C$ for 10, 20, and 30 days. Anodic oxide films were porous with pore size of $1\sim4{\mu}m\;and\;3\sim4{\mu}m$ thickness. The anodic oxide films composed with strong anatase peak with presence of rutile peak, and showed the increase in intensity of anatase peak after hydrothermal treatment. It was shown that the intensity of anatase peak increased with increasing the time of hydrothermal treatment but was no difference in rutile peak. The corrosion voltage was the highest in the group of hydrothermal treatment for 2 hrs (Ecorr: -338.6 mV). The bioactivity in Hank's solution was accelerated with increasing the time of hydrothermal treatment.

• 한국표면공학회지
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• 제53권2호
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• pp.72-79
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• 2020

Two Fe-Cr steels of T22 steel and STS430 steel were corroded at 650 and 750℃ for 100hr in sewage sludge-(0.3% SO₂-6% O₂-10% H₂O-balance CO₂) mixed gas environment. T22 steel corroded faster than STS430, indicating that the Cr content significantly influence the corrosion rates. T22 formed thick and non-protective Fe₂O₃ as the major oxide and Fe₃O₄ as the minor one. With an increase in corrosion temperature, their corrosion rates increased, being accompanied with formation of pores and cracks in the thickened oxide scales that were non-adherent. STS430 steel formed Fe₂O₃, Fe₃O₄ as the outer scale and (Fe, Cr)-O as the inner layer by which its corrosion rate is greatly reduced. Both the T22 and STS430 steel samples formed multi-layered scales by outward diffusion of Fe ions and inward diffusion of oxygen and sulfur ions at high-temperature more than 650℃.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2207-2212
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• 2012

Dimethylaluminum isopropoxide (DMAI, $(CH_3)_2AlO^iPr$) as a single precursor, which contains one aluminum and one oxygen atom, has been adopted to deposit non-stoichiometric aluminum oxide ($AlO_x$) films by low pressure metal organic chemical vapor deposition without an additional oxygen source. The atomic concentration of Al and O in the deposited $AlO_x$ film was measured to be Al:O = ~1:1.1 and any serious interfacial oxide layer between the film and Si substrate was not observed. Gaseous by-products monitored by quadruple mass spectrometry show that ${\beta}$-hydrogen elimination mechanism is mainly contributed to the $AlO_x$ CVD process of DMAI precursor. The current-voltage characteristics of the $AlO_x$ film in Au/$AlO_x$/Ir metalinsulator-metal (MIM) capacitor structure show high ON/OFF ratio larger than ${\sim}10^6$ with SET and RESET voltages of 2.7 and 0.8 V, respectively. Impedance spectra indicate that the switching and memory phenomena are based on the bulk-based origins, presumably the formation and rupture of filaments.

• Journal of Electrochemical Science and Technology
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• 제13권2호
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• pp.213-226
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• 2022

In the present study, the corrosion behavior of aluminum Al-7075 tempered (T-6 condition) alloy was evaluated by immersion testing and electrochemical testing in 1.75% and 3.5% NaCl environment at acidic, neutral and basic pH. The data obtained by both immersion tests and electrochemical corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy tests) present that the corrosion rate of the alloy specimens is minimum for the pH=7 condition of the solution due to the formation of dense and well adherent thin protective oxide layer. Whereas the solutions with acidic and alkaline pH cause shift in the corrosion behavior of aluminum alloy to more active domains aggravated by the constant flux of acidic and alkaline ions (Cl^- and OH^-) in the media which anodically dissolve the Al matrix in comparison to precipitated intermetallic phases (cathodic in nature) formed due to T6 treatment. Consequently, the pitting behavior of the alloy, as observed by cyclic polarization tests, shifts to more active regions when pH of the solutions changes from neutral to alkaline environment due to localized dissolution of the matrix in alkaline environment that ingress by diffusion through the pores in the oxide film. Microscopic analysis also strengthens the results obtained by immersion corrosion testing and electrochemical corrosion testing as the study examines the corrosion behavior of this alloy under a systematic evaluation in marine environment.

• 한국분말재료학회지
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• 제29권6호
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• 한국정보전자통신기술학회논문지
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• 제17권3호
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• pp.146-154
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• 2024

본 논문에서는 액정디스플레이 산업에서 러빙공정의 대안으로 브러시 모(brush hair)를 이용한 편리한 액정분자 정렬 방식을 제시합니다. 졸겔 공정을 이용해서 타이타늄 스트론튬 이트륨 지르코늄 산화물(TiSrYZrO) 용액을 제조하였고, 원스텝(one-step) 브러시 코팅 공정을 통해 TiSrYZrO 배향막 제조와 액정분자 배향을 통합하였다. 경화온도가 높아짐에 따라 액정 셀의 액정분자 정렬 상태가 향상되었고, 코팅 표면의 brush hair 움직임에 의한 전단 응력에 기인하는 물리적 표면 이방성 구조 형성으로 인해 균일한 액정분자 정렬을 유도하였다. 균일하고 균질한 액정분자 정렬은 편광 광학 현미경과 선경사 각 측정을 통해 확인하였다. X-선 광전자 분광법으로 열산화를 통해 금속산화물로 잘 형성된 TiSrYZrO 박막을 확인하였고, 우수한 광학 투명성이 있음을 검증하였다. 이러한 결과로부터 러빙공정의 대안으로 brush hair를 이용한 편리한 액정분자 정렬 방식이 실행 가능한 차세대 기술이 될 것이라고 기대된다.

• 전자공학회논문지A
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• 제32A권11호
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• pp.35-43
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• 1995

To obtain high quality of $Ta_{2}O_{5}$ film, two dielectric layers of $Si_{3}N_{4}$ and $Ta_{2}O_{5}$ were subsequently formed on Si wafer. Silicon nitride films were thermally grown in 10 Torr ammonia ambient by R.F induced heating system. The thickness of thermally grown $Si_{3}N_{4}$ film was able to be controlled in the range of tens $\AA$ due to the self-limited growth property. $Ta_{2}O_{5}$ film of 200$\AA$ thickness was then deposited on the as-grown $Si_{3}N_{4}$ film about 25$\AA$ thickness by sputtering method and annealed at $900^{\circ}C$in $O_{2}$ ambient for 1hr. Stoichiometry film was prepared by the annealing in oxygen ambient. Despite the high temperature anneal process, silicon oxide layer was not grown at the interface of the layered films because of the oxidation barrier effect of Si$_{3}$N$_{4}$ film. The fabricated $Ta_{2}O_{5}$/$Si_{3}N_{4}$ film showed low leakage current less than several nA and high dielectric breakdown strength.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1155-1162
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• 2003

Nanocrystalline semiconductor film electrodes have been prepared by sintering three different sizes of TiO₂ nanoparticle sols on conducting indium-tin-oxide (ITO) glass substrate. The electrochemical and photoelectrochemical properties of the prepared electrodes were comparatively investigated. The particle sizes, surface morphologies and crystallinities of the films were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Cyclic voltammetry and capacitance measurements in the dark implies the formation of depletion layer in the semiconductor films which was usually neglected in the previous studies and shows that flat band potential ($E_{fb}$

• Journal of Welding and Joining
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• 제23권1호
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• pp.69-76
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• 2005

Recently, application of arc welding to galvanized carbon steel sheet is on the increasing Ould in the fields of automobile and construction industries. In arc welding process, zinc is evaporated in weld pool, even under the appropriate welding condition and produce blowhole and/or pit. Zinc gas cause instability of arc and increase spatter and fume. This research is purposed to minimize the heat-input and the formation of porosities in the welded joint of the galvanized carbon steel sheet using variable polarity AC wave pulse MIG welding system. An appropriate welding condition which showed low spatter and good bead appearance was acquired by applying the AC pulse MIG welding machine to DC duplicated MIG welding with the solid wire. When oxygen gas was added to shield gas of MIG welding for galvanized steel sheet, arc length was increased and arc stability was improved. In the AC duplicated welding, the loss of galvanized layer was decreased as the amount of heat-input was decreased when the EN ratio was increased under the condition that average welding current was evenly set.