• 한국자기학회지
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• 제12권4호
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• pp.127-131
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• 2002

자성터널접합(magnetic tunnel junction: MTJ)소자의 AlO$_{x}$터널장벽 절연층을 플라즈마 산화법으로 2번에 나누어 금속증착.산화를 반복하여 만들어 보았다. 이중산화I그룹은 10A의 $\AA$의 Al 하부 절연막을 증착하고 산화시간을 10 s로 완성한 후 그 위에 13$\AA$의 Al을성막하고 50, 80, 120s간 산화시켜 완성한 절연막의 특성을 알아보았다. 이중산화II그룹은 10$\AA$봐 Al하부 절연막의 산화시간을 30~120 s간 달리하고 그 위에 13 $\AA$의 Al을 성막하고 210 s간 산화시켜 완성한 절연막의 특성을 알아보았다. 이중산화공정으로 제조된 시편은 전 실험범위에서 자기저항비(magnetoresistance： MR)는 27% 이상으로 우수하였고, 이는 13 $\AA$의 Al을 증착하고 한번만 산화시키는 통상의 단일산화에 비해 MR비가 우수하고 공정범위가 넓었다. 수직단면 투과전자현미경(transmission electron microscope： TEM)으로 미세구조를 확인한 결과 이중산화가 단일산화보다도 더 얇고 균일한 두께를 유지함을 알 수 있었다 X선광전자분석(X-ray photoelectron spectroscopy： XPS)으로 확인한 결과 이중산화는 절연막층 하부 CoFe 자성층의 Fe의 산화를 방지하여, 결과적으로 단일산화법에 비해서 하부자성층의 산화를 방지하여 긴 산화시간 공정 범위에서도 우수한 MR비를 가질 수 있었다.

• 한국표면공학회지
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• 제34권5호
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• pp.494-498
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• 2001

Ferromagnets(FM)-Al-$O_{x}$ -Ferromagnets (FM) tunneling junctions were evaluated by changing the fabricating conditions of an Al-X$/_{x}$ layer. The junction composed of a thicker Al-$O_{x}$ shows the low resistance and the stable MR ratio about 16% in a wide range of oxidation time. For the junctions with the thinner Al-$O_{x}$ , they showed a fast increase of the barrier width as an increase of an oxidation time and exhibited a strong bias dependence. As oxidation time increased, the coercivity ($H_{c}$ ) of bottom Co layer increased gradually due to the local oxidation of Co bottom layer at a interface. However, the small formation of Co oxide did not largely influence on the deterioration of MR ratio.

• 한국재료학회지
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• 제14권4호
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• pp.265-269
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• 2004

Plasma nitrocarburising and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin ferritic oxide layer 1-2 $\mu\textrm{m}$ thick on top of a 15～25 $\mu\textrm{m}$ $\varepsilon$-F $e_{2-3}$(N,C) nitrocarburized compound layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily spalled from the compound layer either for both oxidation temperatures above $450^{\circ}C$, or for oxidation time more than 2 hrs at oxidation temperature $400^{\circ}C$. It was confirmed that the relative amount of $Fe_2$$O_3$, compared with $e_3$$O_4$, increased rapidly with the oxidation temperature. The amounts of ${\gamma}$'-$Fe_4$(N,C) and $\theta$-$Fe_3$C, generated from dissociation from $\varepsilon$-$Fe_{2-3}$ /(N,C) phase during $O_2$ plasma sputtering, were also increased with the oxidation temperature.e.

• Food Science and Biotechnology
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• 제15권3호
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• pp.399-403
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• 2006

The effect of flour storage conditions on the lipid oxidation of fried products during storage was studied. Wheat flour was stored at $60^{\circ}C$ in the dark and at water activity (Aw) of 0.3, 0.5, or 0.8 for 21 days. The square-shaped dough ($2{\times}2{\times}0.1\;cm$) made with the stored flour and water was fried in soybean oil at $160^{\circ}C$ for 1 min. The fried products were stored at $60^{\circ}C$ for 15 days in the dark. The degree of lipid oxidation of the fried products was evaluated by conjugated dienoic acid (CDA) content and p-anisidine value (PAV). Both CDA content and PAV of the fried products increased with lengthening storage time of the fried products, suggesting that longer storage of the fried products raised the lipid oxidation. Furthermore, the lipid oxidation of the fried products made with flour that had been stored for a longer time tended to be higher than that of those made with unstored or short-term-stored flour. However, Aw at which the flour was stored did not significantly affect the lipid oxidation of either flour or the fried products during storage. The storage time of flour clearly exerted a greater effect than Aw on the lipid oxidation of the fried products during storage at $60^{\circ}C$ in the dark. This suggests that for the storage stability of fried products, the flour storage time is a more important factor than Aw at which the flour is stored.

• 한국염색가공학회지
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• 제23권4호
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• pp.274-283
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• 2011

Effect of pH on ozone oxidation and peroxone AOP(Advanced Oxidation Process) process was analyzed and the optimal efficiency for both processes was obtained at pH 7.5. In case of ozone oxidation process, the efficiencies of color, $COD_{Mn}$ and $BOD_5$ removal were measured to 93%, 70% and 89% at a reaction time of 50 min(ozone dosage of 111.67mg/$\ell$). When reaction time increased to 90 min(ozone dosage of 201mg/$\ell$), the efficiencies of color, $COD_{Mn}$ and $BOD_5$ removal were increased by 3~5 %, indicating that the increment of removal efficiency was insignificant considering longer reaction time. Similarly, the ozone/$H_2O_2$ ratio was optimized to 0.5 for peroxone AOP process. Removal efficiencies of color, $COD_{Mn}$ and $BOD_5$ were measured 95%, 81% and 94% at a reaction time of 50 min(ozone dosage of 111.67mg/$\ell$). When reaction time increased to 90min(ozone dosage of 201mg/$\ell$), the removal efficiency of color, CODMn, and BOD5 increased slightly by 1~5%.

• 한국재료학회지
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• 제12권3호
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• pp.200-204
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• 2002

We fabricated TMR devices which have double oxidized tunnel barrier using plasma oxidation method to form homogeneously oxidized AlO tunnel barrier. We sputtered 10 $\AA$-bottom Al layer and oxidized it by varying oxidation time for 5, 10, 20 sec. Subsequent sputtering of 13 $\AA$ - Al was performed and the matallic layer was oxidized for 120 sec. The electrical resistance changed from 700$\Omega$ to 2700$\Omega$ with increase of oxidation time, while variation of MR ratio was little spreading 27~31% which is larger than that of TMR device of ordinary single tunnel barrier. We calculated effective barrier height and width by measuring I-V curves, from which we found the barrier height was 1.3~1.5 eV, sufficient for tunnel barrier, and the barrier width(<16.2 $\AA$) was smaller than that of directly measured value by the tunneling electron microscopy. Our results may be caused by insufficient oxidation of Al precursor into $Al_2O_3$. However, double oxidized tunnel barriers were superior to conventional single tunnel barrier in uniformity and density. We found that the external magnetic field to switch spin direction of ferromagnetic layer of pinned layer breaking ferro-antiferro exchange coupling was increased as bottom layer oxidation time increased. Our results imply that we were able to improve MR ratio and tune switching field by employing double oxidized tunnel barrier process.

• Tribology and Lubricants
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• 제18권6호
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• pp.396-401
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• 2002

ln this paper, the fuction of molybdenum dialkyl dithiophosphate (MoDTP) as an oxidation inhibitor of mineral oils was investigated and compared with 2,6-Di-tert-Butyl-4-Methylphenol (DBMP). Oxidation tests were conducted using an oxygen absorption apparatus. MoDTP showed anti-oxidation property, and length of induction time prolonged by increasing MoDTP concentration. However the induction time of DBMP was longer than those of MoDTP. The anti-oxidation property of MoDTP was found to be inferior to that of DBMP The capability of hydroperoxide decomposition ability with MoDTP was much greater than that with DBMP. However the rate constant of radical scavenging with MoDTP was much better than that with DBMP. It was found that the performance of MoDTP is exellent with respect to hydroperoxide decomposition but it is susceptible to chemical decomposition. From the fact that formation of phenol was observed when MoDTP was added to hexane solution of cumene hydroperoxide (CHPO), it is indicated that the decomposition of hydroperoxide with MoDTP occurs by means of ionic mechanism.

• 한국표면공학회지
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• 제44권1호
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• pp.13-20
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• 2011

This study investigated the high temperature oxidation behavior of Fe-22%Cr-5.8%Al alloy and the oxidation kinetics of the alloy were discussed. Bulk samples were prepared by VAM (vacuum arc melting) and hot forging. High temperature oxidation testes were isothermally conducted up to 100 hours in 79%$N_2$+21%$O_2$ environment at three different temperatures ($900^{\circ}C$, $1000^{\circ}C$, $1100^{\circ}C$). The weight gain was measured after oxidation according to oxidation time (2, 4, 6, 8, 10, 15, 20, 25, 30, 60, 80, 100 hours). The weight gain significantly increased with increasing oxidation temperature. As the temperature increased, the oxidized samples showed sequential formation of $Al_2O_3$, Cr-rich oxide, Fe-rich oxide. The activation energy of high temperature oxidation was obtained as 306.63 KJ/mol. $Al_2O_3$ were developed on the surface in the early stage of oxidation, representing protective role of oxidation. However, Fe-based and Cr-based oxides leaded to breakaway of oxide layer, thus resulted in the significant increase of additional oxidation.

• 환경위생공학
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• 제18권1호
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• pp.23-29
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• 2003

The effect of ozone oxidation on bio-degradability of leachate was studied. Ozone oxidation process was used as pre-treatment process to enhance performance of biological process in treating landfill leachate. Optimum ozone injection rate and contact time in this experiment was $160{\;}mg{\;}O_/{\ell}{\cdot}hr$ and 45 minutes, respectively. Bio-degradability was enhanced 5.08% by ozone oxidation. The ratio of ozone demand/DOC concentration was $0.049~0.091{\;}mg{\;}O_3/mg{\;}DOC$. The increase of bio-degradability depending on ozone injection rate(D) and contact time(T) can be expressed as follows ; The rate of bio-degradation of DOC was increased proportionally with the increase of ozone injection rate and contact time irrespective of landfill site age. The increase of bio-degradability by ozone addition was not satisfactory. It is hard to expect significant increase in bio-degradability by ozone treatment only. Thus, it is evaluated that ozone oxidation can not increase biodegradability significantly in concentrated wastewater composed of complex organic compound such as leachate.

• 한국물환경학회지
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• 제21권1호
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• pp.1-6
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• 2005

The effect of ozone oxidation on biodegradability of leachate was studied. Ozone oxidation process was used as pre-treatment process to enhance performance of biological process in treating landfill leachate. Optimum ozone dosing rate and contact time in this experiment was $160mg\;O_3/L$ hr and 45 minutes, respectively. Biodegradability was enhanced 5.08% by ozone oxidation. The ratio of ozone demand/DOC concentration was $0.049{\sim}0.091mg\;O_3/mg$ DOC. The increase of biodegradability depending on ozone dosing rate(D) and contact time(T) can be expressed as follows ; ${\Delta}E=0.00479{\cdot}D^{0.773}{\cdot}T^{0.800}$ The biodegradation rate of DOC was increased proportionally with the increase of ozone dosing rate and contact time irrespective of landfill site age. The increase of biodegradability by ozone addition was not satisfactory. It is hard to expect significant increase in biodegradability by ozone treatment only. Thus, it is evaluated that ozone oxidation can not increase biodegradability significantly in concentrated wastewater composed of complex organic compound such as leachate.