• 열처리공학회지
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• 제12권2호
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• pp.117-128
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• 1999

This study was carried out to investigate the surface characteristics of SCM440 steel nitrided with various nitrogen contents for 7 hours at $520^{\circ}C$ by using micro-pulse plasma nitriding apparatus of hot wall type. The effects of oxidation treatment was also investigated on plasma nitrided in 30% nitrogen and post oxidized SCM440 steel at $500^{\circ}C$ in $H_2O$ atmosphere. The ${\gamma}^{\prime}-Fe_4N$ and ${\varepsilon}-Fe_{2-3}N$ phases were detected in compound layer of the nitrided steel. As the content of nitrogen in plasma gas increased with 30, 50, 70% on the micro-pulse plasma nitriding for SCM440 steel, the thickness of compound, diffusion layer and the surface hardness were increased. From the wear test results, the best wear resistance was appeared in the condition of ductile ${\gamma}^{\prime}-Fe_4N$ phase formed specimen at 30% nitrogen, whereas that of the treated with 50% and 70% nitrogen decreased owing to the exfoliation of brittle ${\varepsilon}-Fe_{2-3}N$ phase in the compound layer. On the nitrided and subsequently oxidized SCM440 steel, the surface layer consisted of $Fe_3O_4$, ${\gamma}^{\prime}-Fe_4N$, and ${\varepsilon}-Fe_{2-3}N$ phases. In these treatments, the dissolution of nitrides affect hardness and hardening depth in compound and diffusion layers. For the nitrided in 30% nitrogen and post oxidized specimen at $500^{\circ}C$ for 1 hour, the wear resistance was lower than that of the only nitrided one in 30% nitrogen but higher than those of the nitrided ones in 50 and 70% nitrogen.

• 한국전기전자재료학회논문지
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• 제15권4호
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• pp.373-379
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• 2002

We investigated the evolution of magnetoresistance and magnetic property of tunneling magnetoresistive(TMR) device with microstructure and plasma oxidation time. TMR devices have potential applications for non volatile MRAM and high density HDD reading head. We prepared the tunnel magnetoresistance(TMR) devices of Ta($50{\AA}$)/NiFe($50{\AA}$)/IrMn($150{\AA}$)/CoFe($50{\AA}$)/Al($13{\AA}$)-O/CoFe($40{\AA}$)/FiFe($400{\AA}$)/Ta(($50{\AA}$) structure which have $100{\times}100\mu\textrm{m}^2$ junction area on $2.5{\times}2.5\textrm{cm}^2$ Si/$SiO_2$(($1000{\AA}$) substrates by an inductively coupled plasma(ICP) magnetron sputter. We fabricated the insulating layer using an ICP plasma oxidation method by with various oxidation time from 30 sec to 360 sec, and measured resistances and magnetoresistance(MR) ratios of TMR devices. We found that the oxidized sample for oxidation time of 80 sec showed the highest MR radio of 30.31 %, while the calculated value regarding inhomogeneous current effect indicated 25.18 %. We used transmission electron microscope(TEM) to investigate microstructural evolution of insulating layer. Comparing the cross-sectional TEM images at oxidation time of 150 sec and 360 sec, we found that the thickness and thickness variation of 360 sec-oxidized insulating layer became 30% and 40% larger than those of 150 sec-oxidized layer, repectively. Therefore, our results imply that increase of thickness variation with oxidation time may be one of the major treasons of the MR decrease.

• 열처리공학회지
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• 제4권4호
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• pp.53-60
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• 1991

This study has been performed to investigate into the internal oxidation characteristics of low carbon steel with respect to the added amount of air in nitrogen-propane atmosphere after gas carburizing for various times at $930^{\circ}C$. The results obtained from the experiment are as follows ; (1) Optical micrographs have shown that the internal oxidation is unlikely to occur in the gas atmosphere without air and that oxidized zone in the outer surface layer is formed in the gas atmosphere with air revealing that the depth of oxidized zone increases with increasing the added amount of air. (2) The formation of internally oxidized zone in the outer surface layer has been found to be inhibited as Ni content increases, i. e, the amount of alloying element increases. (3) The depth of oxidation has been measured to increase with almost parabolically gas carburizing time of up to 6 hours.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.502-506
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• 2001

This paper presents a new method for cutting steel with a diamond tool using electrolysis. The electrolysis is adopted in the diamond cutting to prevent the high chemical activity between a diamond tool and an iron-based workpiece. The basic principle of the method is to oxdize a thin substrate of the workpiece by electrolysis ahead of the diamond tool which cuts the oxidized layer. A desired shape can be obtained by repeating this process. The cutting force is reduced because the diamond tool removes only the weakened material by electroysis. The reduction of the cutting force suppresses the excessive wear of the diamond tool. The oxidization penetrates several micrometers in depth along the previously formed shape. The corrosion rates depend on current density and make suggestions on the optimum cutting conditions.

• 한국분말재료학회지
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• 제18권6호
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• pp.575-582
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• 2011

MAO(Micro-Arc Oxidation) method was used to make $Al_2O_3$ surface on 6063 Al specimen. This study was focused on an influence of voltage, density of electrolyte and a period of treatment on the change of surface microstructure by using SEM(Scanning Electron Microscope), EDS(Energy Dispersive X-ray Spectroscopy). The microstructure shows higher roughness and thicker oxidized layer with increase of voltage and maintaining period of treatment. The density of electrolyte affected a formation of more dense surface and increase of a oxidized layer.

• 융복합기술연구소 논문집
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• 제3권2호
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• pp.39-43
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• 2013

Titanium has been used to satisfy various applications such as bio engineering, aerospace, electronics, automobile. Recently, micro fabrication technologies of metals such as titanium have been required to satisfy many conditions in various fields. To satisfy these demands, micro electrochemical process using laser marking can be an alternative method because it is one of the precision machining and efficient process. Micro electrochemical process using laser marking needs to accomplish form of the oxidized recast layer on metal surface by laser marking. The laser beam marking conditions such as average power, pulse repetition rate and marking speed should be properly selected to form oxidized recast layer. So, the characteristics of titanium surface according to laser marking conditions was investigated through SEM(scanning electron microscope), EDS(energy dispersive spectrometer) and surface roughness analysis.

• 한국표면공학회지
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• 제48권5호
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• pp.185-193
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• 2015

Anodization of die-casted AZ91D magnesium alloy was carried out using silicate based electrolyte solution instead of fluoride based solution to improve biocompatibility of oxidized layers. The anodic layer obtained from silicate based solution has smaller size of pore and smoother surface, resulting in lower corrosion rate in simulate body solution (SBF). Effect of enhanced structural and chemical properties in oxidized layer on biocompatibility was carefully considered.

• 한국식품영양과학회지
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• 제23권3호
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• pp.530-539
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• 1994

최근 지방 섭추의 증가에 따른 혈관계 질병이 증가 추세에 있다. 이러한 동맥경화 및 고지질의 질병은 지질 단백질(lipoprotein)과 관련하여, LDL 및 산화 LDL의 특성을 중심으로 고찰하였다. 인체의 혈장에 함유된 LDL 함량의 증가는, 동맥경화와 직결되는 것을 의미하며, 이러한 LDL은 매우 hydrophobic한 특성을 가진 550Kd의 단일 polypeptide인 Apo B-100라는 단백질이, 지질성분인 triglyceide, phospholipid 및 cholesterol와 결합되어 있다. 최근 이러한 LDL은 산화(oxidation)되는 경우, 정상적인 LDL-receptor pathway를 따르지 않고, macrophang와 결합하므로서, foarn cell을 형성하여 동백경화가 촉진되는 것으로 알려지고 있다.

• 센서학회지
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• 제8권5호
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• pp.421-426
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• 1999

본 논문에서는 반절연성 GaAs(semi-insulating GaAs) 기판위에 $Al_2O_3$ 절연막이 게이트 절연막으로 이용된 공핍형모드 p-채널 GaAs MOSFET (depletion mode p-channel GaAs MOSFET)를 제조하였다. 반절연성 GaAs 기판위에 $1\;{\mu}m$의 GaAs 버퍼층(buffer layer), $4000\;{\AA}$의 p형 GaAs 에피층(epi-layer), $500\;{\AA}$의 AlAs층, 그리고 $50\;{\AA}$의 캡층(cap layer)을 차례로 성장시키고 습식열산화시켰으며, 이를 통하여 AlAs층은 완전히 $Al_2O_3$층으로 산화되었다. 제조된 MOSFET의 I-V, $g_m$, breakdown특성 측정을 통하여 AlAs/GaAs epilayer/S I GaAs 구조의 습식열산화는 공핍형 모드 p-채널 GaAs MOSFET를 구현하기에 적합함을 알 수 있다.