• 한국세라믹학회지
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• 제34권5호
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• pp.512-518
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• 1997

The high temperature oxidation behaviors of titanium nitride films prepared by PACVD technique were studied in the temperature range of from 50$0^{\circ}C$ to 80$0^{\circ}C$ under air atmosphere. Ti0.88Al0.12N film, which showed the excellent microhardness from the previous work, was investigated on its oxidation resistance compared with pure TiN film. Ti-Al-N film showed superior oxidation resistance up to $700^{\circ}C$, whereas TiN film was fast oxidized into rutile TiO2 crystallites from at 50$0^{\circ}C$. It was found that an amorphous layer having AlxTiyOz formula was formed on the surface region due to outward diffusion of Al ions at the initial stage of oxidation. The amorphous oxide layer played a role as a barrier against oxygen diffusion, protected the remained nitride layer from further oxidation, and thus, resulted in the high oxidation resistive characteristics of Ti-Al-N film.

• 한국세라믹학회지
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• 제43권10호
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• pp.613-618
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• 2006

Graphite is suitable materials as a moderator, reflector, and supporter of a nuclear reactor because of high tolerance to the high temperature and neutron irradiations. Because graphite is so weak to the oxidation, its oxidation study is essentially demanded for the operation and design of the nuclear reactor. This work focuses on the effect of the surface oxidation of graphite according to the surface treatment. With thermogravimeter (TG), oxidation characteristics of the isotropic graphite are measured at the three temperature areas, and oxidation ratio and amounts are estimated as changing the surface roughness. Furthermore, the polished graphite surface produced fom the surface treatment is investigated with the Raman spectroscopic study. Oxidation behaviors of the surface are also evaluated as elimination the polished layer by washing with strong sonication.

• 대한금속재료학회지
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• 제48권10호
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• pp.907-913
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• 2010

Hot-rolled steel plates of SPHC and SS400 were oxidized at 600, 750 and $900^{\circ}C$ for 2 hr in air. With an increase in the oxidation temperature, their oxidation rates increased, and this was accompanied by the formation of pores and cracks in the thickened oxide scales, which were non-adherent. SPHC steels manufactured by either an arc furnace or a blast furnace displayed similar oxidation rates, indicating that their oxidation rates were insensitive to the manufacturing process. Medium-carbon SS400 steel displayed somewhat faster oxidation rates than low-carbon SS400 steel, indicating that the carbon content did not significantly influence the oxidation rates.

• 한국재료학회지
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• 제33권2호
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• pp.77-86
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• 2023

High-temperature oxidation of a Ni-based superalloy was analyzed with samples taken from gas turbine blades, where the samples were heat-treated and thermally exposed. The effect of Cr/Ti/Al elements in the alloy on high temperature oxidation was investigated using an optical microscope, SEM/EDS, and TEM. A high-Cr/high-Ti oxide layer was formed on the blade surface under the heat-treated state considered to be the initial stage of high-temperature oxidation. In addition, a PFZ (γ' precipitate free zone) accompanied by Cr carbide of Cr₂₃C₆ and high Cr-Co phase as a kind of TCP precipitation was formed under the surface layer. Pits of several ㎛ depth containing high-Al content oxide was observed at the boundary between the oxide layer and PFZ. However, high temperature oxidation formed on the thermally exposed blade surface consisted of the following steps: ① Ti-oxide formation in the center of the oxide layer, ② Cr-oxide formation surrounding the inner oxide layer, and ③ Al-oxide formation in the pits directly under the Cr oxide layer. It is estimated that the Cr content of Ni-based superalloys improves the oxidation resistance of the alloy by forming dense oxide layer, but produced the σ or µ phase of TCP precipitation with the high-Cr component resulting in material brittleness.

• 자원환경지질
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• 제34권1호
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• pp.147-156
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• 2001

티탄자철석(titanomagnetite)은 해양지각을 이루는 현무암에 존재하는 중요한 자성광물로서 일반적으로 저온산화에 의해 양이온이 결핍된(cation-deficient) 티탄맥히마이트(titanomaghemite)로 변한다. 실험실에서 철성분 제거방식(removal of iron mechanism)을 통해 자연에서 일어나는 티탄자철석의 수성 저온산화(low-temperature aqueous oxidation)를 재현하였으며, 산화정도에 따라 티탄맥히마이트의 자기적 특성이 민감하게 변화하는 것을 관찰하였다. 본 실험 결과 산화정도에 따라 티탄자철석의 큐리온도(Tc)는 166$^{\circ}C$에서 40$0^{\circ}C$로 증가하였고, 상온에서의 포화자화 강도(Ms)는 126.30 kA/m(25.26 emu/g)에서 16.55 kA/m(3.31 emu/g)로 감소하였으며, 항자기력(Hc)은 6.13 kA/m(77 Oe)에서 38.83 kA/m (488 Oe)로 잔류항자기력(Hcr)은 23.24 kA/m(292 Oe)에서 47.03 kA/m(591 Oe)로 증가함을 관찰하였다. 또한 대자율($\chi$)은 $2023{\times}10^{-6}SI$에서 $84{\times}10^{-6}SI$로 감소함을 나타내었다. 이와 같은 결과를 근거로 현재에서 30 Ma까지의 해양지각의 자화 강도의 변화는 티탄자철석의 저온산화에 의한 결과로 해석하였으며 30~120 Ma에 이르는 해양지각의 자화 강도의 변화는 해양지각에 포함된 티탄자철석의 산화와 산화에 순반되는 광물전에 의한 결과로 추정하였으며 보다 구체적인 원인은 해양지각에서 채취한 시료에 대한 체계적인 연구를 통해서 밝혀질 것으로 기대된다.

• 대한화학회지
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• 제55권5호
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• pp.842-845
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• 2011

Wet air oxidation (WAO) of oily sludge was carried out using $Fe^{3+}$ as catalyst, placed in a 0.5 L batch autoclave in the temperature range of $250-330^{\circ}C$. Experiments were conducted to investigate the effects of temperature, the initial COD, reaction time, concentration of catalyst and $O_2$ excess (OE) on the oxidation of the oily sludge. The results showed that in the WAO 88.4% COD was achieved after 9 min reaction at temperature of $330^{\circ}C$, OE of 0.8 and the initial COD of 20000 mg/L. Temperature was found to have a significant impact on the oxidation of oily sludge. Adding a catalyst significantly improved the COD removal. Homogenous catalyst, $Fe^{3+}$, showed effective removal for pollutants. COD removal was 99.7% in the catalytic wet air oxidation (CWAO) over $Fe^{3+}$ catalyst. The results proved that the CWAO was an effective pretreatment method for the oily sludge.

• 한국수소및신에너지학회논문집
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• 제20권4호
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• pp.337-343
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• 2009

Noncatalytic partial oxidation of methane for producing synthesis gas was studied in a lab-scale experimental apparatus. Partial oxidation developed for high-temperature, fuel-rich combustion and it is exothermic process. but Steam reforming and Caron reforming is highly endothermic process to need much energy. Noncatalytic partial oxidation of methane is affected by temperature and equivalent ratio, so we studied effect about composition of synthesis gas at lab scale reactor. We used electronic heater to control the temperature of reactor. The quality of synthesis gas is improved and reduced heat value to require at Noncatalytic partial oxidation because the reacting temperature is lower at oxy condition.

• 한국분말재료학회지
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• 제6권3호
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• pp.209-214
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• 1999

The oxidation behavior of the simulated spent fuel of burn up 33 MWD/kgU was investigated to predict that of the spent fuel in the temperature ranges of 400 to $700^{\circ}C$ and was compared with those of $UO_2$. The forms of uranium oxides after the oxidation were conformed by XRD analyses. The oxidation rate at each the temperature and the activation energy were obtained. After complete oxidation, the simulated spent fuel was converted to $U_3O_8$ and pulverized to powder due to the density difference between the simulated spent fuel and uranium oxides. The activation energies were 85.35 and 30.77kJ/mol in the temperature ranges of 400$\leq$T($^{\circ}C$)$\leq$500 and 500$\leq$T($^{\circ}C$)$\leq$700, respectively.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권3호
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• pp.165-171
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• 2000

Experiments were carried out to measure variations in the oxidation potential and current density using the polarization curves of polycarbonate. The results were then examined to identify the influences affecting the oxidation potential related to various conditions, such as temperature, pH, and oxydase(citrate and lipase). The lines representing the active anodic and cathodic dissolution shifted only slightly in the potential direction relative to temperature, pH, and the effect of the enzyme. The Tafel slope for the anodic and cathodic dissolution was determined such that the reversibility polarization was indicated as being effected by various conditions. The slope of the polarization curves describing the active-to-passive transition region shifted noticeably in their direction. Also, by varying the conditions, the optimum conditions for the most ready transform were identified, including temperature, pH, oxidation rate, and resistance of oxidation potential. The critical oxidation sensitivity(I(sub)r/I(sub)f) of the anodic current density peak and maximum passive current density was also determined, which is used in measuring the critical corrosion sensitivity of a polycarbonate.

• 열처리공학회지
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• 제35권5호
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• pp.246-254
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• 2022

The high-temperature oxidation behavior of Cr-Mo steel AISI 4115 in air at different temperatures (600, 850, 950℃) for 120 min was studied by mass gain analysis, phase analysis (optical microscopy, electron probe micro-analysis, x-ray diffraction) and hardness measurement of each iron oxide-phase. The oxidation scales that formed on oxidation process consisted outer layer (Hematite), middle layer (Magnetite) and the inner layer (Chromite). In the case of 850 and 950℃, the oxidation mass gain per unit area of AISI 4115 steel increased according to the logarithmic rate as atmospheric pressure increased. Especially, It has been observed that with an increase in the atmospheric pressure at 600℃, the oxidation mass gain per unit area changed from a linear to logarithmic relationship.