• 대한금속재료학회지
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• 제46권7호
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• pp.427-436
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• 2008

The effect of dewpoints on annealing behavior and coating characteristics such as wettability and galvannealing kinetics was studied by annealing 0.3wt%Si - 0.1~0.4wt% Mn added interstitial-free high strength steels(IF-HSS). The 0.3wt%Si-0.1wt%Mn steel exhibited good wettability with molten zinc and galvannealing kinetics after annealing when the dewpoint of $H_2-N_2$ mixed gas was above $-20^{\circ}C$. It is shown that the wettability and galvannealing kinetics are directly related to the coverage of the external(surface) oxide formed by selective oxidation during annealing. At $N_2-15%H_2$ annealing atmosphere, the increase of dewpoint results in a gradual transition from external to internal selective oxidation. The decrease of external oxidation of alloying elements with a concurrent increase of their subsurface enrichment in the substrate, showing a larger surface area that was free of oxide particles, contributed to the improved wettability and galvannealing kinetics. On the other hand, the corresponding wettability and galvannealing kinetics were deteriorated with the dewpoints below $-20^{\circ}C$. The continuous oxide layer of network and/or film type was formed on the steel surface, leading to the poor wettability and galvannealing kinetics. It causes a high contact angle between annealed surface and molten zinc and plays an interrupting role in interdiffusion of Zn and Fe during galvannealing process.

• 한국환경과학회지
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• 제21권3호
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• pp.383-390
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• 2012

For the cost-effective biological nitrogen removal (BNR) process whose characteristics of influent have low COD/N ratios, the automatic control system for the addition of external carbon based on oxidation-reduction potential (ORP) data in an anoxic reactor has been developed. In this study, it was carried out with a pilot-scale Bardenpho process which was consisted of anoxic 1, aerobic 1, aerobic 2, anoxic 2, aerobic 3 tank and clarifier. Firstly, the correlation coefficient ($R^2$) of the dosage of external carbon source and ORP value was about 0.97. Consequently, the automatic control system using ORP showed that the dosage of external carbon source was decreased by about 20% compared with a stable dosage of 75 mg/L based on the COD/N ratio of the anoxic influent.

• 동력기계공학회지
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• 제11권2호
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• pp.44-50
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• 2007

The oxidation behavior of commercial pure titanium is investigated in the temperature range of $727^{\circ}C{\sim}950^{\circ}C$ in mixed gases. The weight change is measured by TGA during oxidation in mixed gases. The oxidation behavior indicated by weight gain or the growth of oxide layer is based on the linear rate law at high temperatures. The structure of the oxide scale formed during oxidation is analysed by optical microscopy, electron probe microanalyzer, scanning electron microscope and x-ray diffraction. Oxide scales have a $TiO_2$ structure, and are constituted with multi-layered or two layered porous external one and a dense internal one. Ti-O solid solution region is formed at the interface of metal and scale layer. The formation of oxide scale is influenced by the oxidation temperature, time, crystal structure and the condition of atmosphere.

• 한국암석학회:학술대회논문집
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• 한국암석학회 1999년도 춘계학술대회
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• pp.25-29
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• 1999

Manganese (Mn) oxides in soils and sediments differ in structure and composition. The influence of that diversity on the chromium (Cr) oxidation is the subject of this report. Oxidation of Cr(III) to Cr(VI) by coarse clay size Mn oxides (synthetic pyrolusite and natural lithiophorite, todorokite, and bimessite) was studied. Chromium oxidation by Mn oxides was initially fast and followed by a slow reaction. More Cr was oxidized by the Mn oxides at lower pH and higher initial Cr(III) concentration in solution. Birnessite had the highest chromium oxidation capacity per unit external surface area (COCUESA) and lithiophorite had the lowest COCUESA. The kinetics of Cr oxidation and COCUESA of Mn oixdes were apparently controlled by reactivity of surface Mn, mineralogy, and solution properties (pH and Cr(III) concentration).

• Bulletin of the Korean Chemical Society
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• 제11권1호
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• pp.71-72
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• 1990

• 한국표면공학회지
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• 제20권2호
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• pp.60-73
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• 1987

For the purpose of improving the cyclic oxidation resistance of Ni-base superalloy, Inconel 600, aluminide coating methods are studied. The formation rate of aluminide coating layers is measured as a function of time and pack composition to find out the optimum coating condition. The evaluation of cyclic oxidation is established by the change in weight, the microphotography and EPMA of cross sectional area during $200^{\circ}C\;{\leftrightarrow}\;950^{\circ}C\;and\;200^{\circ}C\;{\leftrightarrow}\;1100^{\circ}C$, respectively. The thickness of coating layer and weight gains are parabolic behavior in propotion to time and Al contents. In pack of low aluminum contents, 2 wt%, however, weight gain is decreased when activator, $NH_4Cl$ is higher than 2 wt%. The cyclic oxidation resistance of the coating carried out at 1100$^{\circ}C$ are superior to those of the coating diffusion-treated after pack cementation at 800$^{\circ}C$. Aluminide oxide, which is formed in external scale, is barrier to the cyclic oxidation.

• 마이크로전자및패키징학회지
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• 제8권2호
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• pp.1-7
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• 2001

저열팽창성 금속인 Kovar표면을 유리와 접합하기에 적합한 spinel을 주상으로 하는 균일한 산화막을 형성할 수 있도록 $N_2/H_2$에 $H_2O$가 첨가된 분위기에서의 산화 거동에 대하여 조사하였다. Kovar 산화는 확산에 의해 지배되는 공정이며, 이때 산화 활성화 에너지는 31.61 kacl/mol 이었다. $600^{\circ}C$에서 열처리한 결과 spinel을 주상으로 하는 0.5 $mu extrm{m}$ 이하의 연속적이고 균일한 외부 산화막을 얻을 수 있었다. TEM 분석 결과 격자 상수가 7.9 $\AA$인 spinel 임을 확인할 수 있었다. 그러므로, 가습된 $N_2/H_2$분위기에서 산화한 Kovar는 유리와 접합에 적용 가능할 것으로 판단된다.

• 한국표면공학회지
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• 제28권3호
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• pp.142-151
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• 1995

In this research, a thin layer of Cr was coated on the pure Ni and Inconel 601 by PECVD (Plasma Enhanced Chemical Vapor Deposition) in order to study the effect of Cr on the oxidation behavior at high temperature. Cr coated Inconel 601, which was oxidized at $1100^{\circ}C$ for 24 hours, formed a protective $Cr_2O_3$ oxide layer and the resistance to isothermai oxidation was improved. On the other hand, oxidation resistance of Cr coated Inconel 601 at 100$0^{\circ}C$ was not significantly improved, probably due to the formation or insufficient $Cr_2O_3$ layer. But, when oxidized at $1000^{\circ}C$ and $1100^{\circ}C$ for 100 hours, Cr coated Inconel 601 improved isothermal oxidation resistance by the formation of continuous $Cr_2O_3$ external scale and by the development of $Al_2O_3$ subscales. Cr coated Ni formed inner layer of $Cr_2O_3$ within almost pure NiO, which provided additional cation vacancies, thus increasing the mobility of Ni ions in this region. It is believed that this doping effect resulted in an increase in the observed oxidation rate compared with pure Ni and did not improve the oxidation resistance.

• 대한화장품학회지
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• 제39권2호
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• pp.149-158
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• 2013

피부 미백, 콜라겐 합성 및 노화방지 등에 좋은 효능을 나타내는 대표적인 항산화제인 L-ascorbic acid를 사용하여 다양한 보관 조건(분말 상, 수용액 상, 온도 변화, 자외선 조사 및 외부공기 유입 등)에서 산화특성을 조사하였으며, 열에 의한 산화 및 분해특성을 조사하였다. 또한 이중 공간을 갖는 파우치를 사용하여 L-ascorbic acid를 분말 상태 및 에센스와 혼합한 상태에서 각각 보관 조건에 따른 산화특성을 분석하여 파우치의 유효성을 검증하였다. 열 특성조사를 위해서는 TGA, DSC 및 FT-IR을 사용하여 분석하였고, 산화특성 조사를 위해서는 UV-visible spectrophotometer와 산화환원 적정법을 병행 시행하였다. 실험 결과, L-ascorbic acid는 금속이온, 하이드록시이온 등이 많이 함유된 수용액 상에서 고온, 자외선 조사 및 외부공기가 유입되는 상태가 가장 빠른 산화조건인 것으로 나타났고, 순수한 분말 상으로 보관할 경우에는 가열, 자외선 조사 및 외부공기 유입 시에도 오랜 기간 동안 산화되지 않는 특성이 있었다. 이러한 결과를 바탕으로, L-ascorbic acid와 같은 산화 안정성이 떨어지는 활성 성분을 분리하여 보관할 수 있도록 설계 제작 중인, 진공포장이 가능한 이중 공간 구조의 파우치를 사용할 경우 화장품 보관기간을 획기적으로 증가시킬 수 있음을 확인하였다.

• 한국표면공학회지
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• 제29권1호
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• pp.36-44
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• 1996

Fe-Cr-Al and Fe-Cr-Al-Hf alloys prepared either by arc melting or by single roll casting(melt spinning) were exposed to air isothermally at 900~$1100^{\circ}C$. Whisker-like alumina was observed on the surface of the specimens when oxidized at $900^{\circ}C$, but convoluted alumina above $1000^{\circ}C$. All the Hf-free specimens and Hf-added specimens produced by single roll casting formed only external scale mainly composed of $Al_2O_3$ after oxidation at 900~$1100^{\circ}C$ for 100 hours, but Hf-added specimen produced by arc melting formed Hf-rich internal oxides below the thin external $Al_2O_3$ scale except at $900^{\circ}C$. Most of the rapidly solidified Fe-Cr-Al alloys showed smaller weight gains than conventionally casted ones besides Hf-added one oxidized at $1100^{\circ}C$.