• 열처리공학회지
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• 제16권2호
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• pp.71-77
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• 2003

We investigate the phase formation in the compound layer of cast irons during the gaseous nitrocarburising of four different cast irons, that contain different types of graphites in the shape and size. We examine the change in the surface roughness with the nitrocarburising time. The observation of cross-sectional microstructure and X-ray diffraction analysis indicate that the compound layer consists of single ${\varepsilon}-Fe_{2-3}(N,C)$ phase and that its thickness increases in a parabolic manner with the treatment time. The surface roughness parameters, Rz and Ra increase with increasing treatment time. In other words, the roughness parameters increase as the thickness of compound layer increases. The parameters also depend on the shape and size of graphite in the individual cast irons.

• Bulletin of the Korean Chemical Society
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• 제20권3호
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• pp.281-284
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• 1999

Two La1.82Ca1.18Cu2O6+δ (2126) compounds exhibited different properties depending upon how they were synthesized. The compound prepared under high oxygen pressure showed superconductivity. But the compound prepared under low oxygen pressure did not exhibit superconductivity, and showed a metal-insulator transition. Our study on these compounds shows that a small amount of additional oxygen intercalated into the superconducting phase plays an important role for superconductivity. The Fermi surface of non-superconducting 2126 compound possesses nesting phenomena, which is the reason for the M-1 transition. On the other hand, the superconducting 2126 compound does not show Fermi surface nesting. This is because the additional oxygen removes some electrons from Cu d-orbitals, thereby bradking the Fermi surface nesting.

• 오토저널
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• 제4권2호
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• pp.35-46
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• 1982

This paper deals with residual stress characteristics of ion-nitrided metal which is primarilly concerned with the effects of added carbon content in gas atmosphere. A small optimal amount of carbon content in gas atmosphere increase compound layer thickness, as well as to increase diffusion layer thickness and hardness. The residual stress and deflection of the specimens was measured in various elevated temperature at the surface of ion-nitrided metal and the internal stress distribution was calculated. It is found that compressive residual stress at the compound layer is largest at the compound layer, and decreases as the depth from the surface increases.

• 열처리공학회지
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• 제14권2호
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• pp.103-109
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• 2001

Plasma nitrocarburising and post oxidation were performed on SM45C steel using a plasma nitriding unit. Nitrocarburising was carried out with various methane gas compositions with 4 torr gas pressure at $570^{\circ}C$ for 3 hours and post oxidation was carried out with 100% oxygen gas atmosphere with 4 torr at different temperatures for various times. It was found that the compound layer produced by plasma nitrocarburising consisted of predominantly ${\varepsilon}-Fe_{2-3}(N,C)$ and a small proportion of ${\gamma}-Fe_4(N,C)$. With increasing methane content in the gas mixture, ${\varepsilon}$ phase compound layer was favoured. In addition, when the methane content was further increased, cementite was observed in the compound layer. The very thin oxide layer on top of the compound layer was obtained by post oxidation. The formation of Oxide phase was initially started from the magnetite($Fe_3O_4$) and with increasing oxidation time, the oxide phase was increased. With increasing oxidation temperature, oxide phase was increased. However the oxide layer was split from the compound layer at high temperature. Corrosion resistance was slightly influenced by oxidation times and temperatures.

• 한국결정성장학회지
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• 제9권5호
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• pp.459-462
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• 1999

Recent advances in NLO Borate Crystals for UV Generation are reviewed with the particular emphasis on the technique to improve the life time of UV optics. The laser-damage resistance of CLBO and fused silica surfaces was successfully improved after removing polishing compound by ion beam etching. The polishing compound embedded in the CLBO and fused silica surfaces were to a depth of less than 100nm. We were able to remove polishing compound without degrading the surface condition when the applied ion beam voltage was less than 200 V. The laser-induced surface damage threshold of CLBO was improved up to 15J/$\textrm{cm}^2$(wavelength: 355 nm, pulse width: 0.85 ns)as compared with that of the as-polished surface (11 J/$\textrm{cm}^2$). The laser-induced surface damage of fused silica also increased from 7.5J/$\textrm{cm}^2$ to 15J/$\textrm{cm}^2$. For the irradiation of a 266 nm high-intensity and high-repetition laser light, the surface lifetime of CLBO and fused silica could be more doubled compared with that of the as-polished surface.

• Tribology and Lubricants
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• 제13권2호
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• pp.96-104
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• 1997

This paper was focused on the wear characteristics of ion-nitrided metal and with ion-nitride processing, which is basically concerned with the effects of carbon content in workpiece and added carbon content gas atmosphere on the best wear performance. Increased carbon content in workpiece increases compound layer thickness, but decreases diffusion layer thickness. On the other hand, a small optimal amount of carbon content in gas atmosphere increase compound layer thickness as well as diffusion layer thickness and hardness. Wear tests show that the compound layer of ion-nitrided metal reduces wear rate when the applied wear load is small. However, as the load becomes large, the existence of compound layer tends to increase wear rate. Compressive residual stress at the compound layer is the largest at the compound layer, and decreases as the depth from the surface increases. It is found in the analysis that under small applied load, the critical depth where voids and cracks may be created and propagated is located at the compound layer, so that the adhesive wear is created and the existence of compound layer reduces the amount of wear. When the load becomes large, the critical depth is located below the compound layer and delamination, which may explained by surface deformation, crack nucleation and propagation, is created and the existence of compound layer increases wear rate. For the compound layer, at added carbon contents of 0 percent and 0.5 at. percent, the $\varepsilon$ monophase is predominant. But at 0.7 at. percent added carbon, the $\varepsilon$ monophase formation tends to be severely inhibited and r' and $Fe_3C$ polyphase formation becomes dominant. This increased hard $\varepsilon$ phase layer was observed to be more beneficial in reducing friction and wear.

• 한국결정성장학회지
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• 제9권1호
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• pp.89-93
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• 1999

나노 구조를 갖는 다공질 규소의 표면과 투명하고 전도성을 갖는 접촉방법을 얻기 위해 다공질 규소 표면에 CdTe 화합물 박막을 전착시키는 방법을 시도하였다. CdTe 화합물 박막은 1 M의 $CdSO_4$와 1mM의 $TeO_4$가 혼합된 전해액 속에서 전착 전위 2-2.3V(vs. Ag/AgCl)로 다공질규소의 표면에 전착시켰다. X선 회절 측정결과 다공질규소 표면에 CdTe 화합물 박막이 생성되었음이 확인되었고, AES 분석결과 표면에서 약 80nm 깊이까지 Cd 및 Te 원소가 균일하게 존재하였다. 그리고 CdTe 화합물 박막이 전착된 다공질규소의 PL 특성은 발광의 세기는 약간 검소하였고 최대파장값은 고에너지 쪽으로 이동하였다. 이 결과로 보아 CdTe 전착 박막이 나노 구조를 갖는 다공질규소와 투명하고 전도성을 갖는 접촉물질로 이용될 수 있음이 밝혀졌다.

• 한국표면공학회지
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• 제29권6호
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• pp.615-620
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• 1996

Chromium-Molybdenum steel was plasma-nitrided at 823 K for 10.8 ks in an atmosphere of 30% $N_2$-70% $H_2$ gas under 665 Pa without and with a subsidiary cathode of $MoS_2$ to compare ion-nitriding and plasma-sulfnitriding using subsidiary cathode. When the steel was ion-nitrided without $MoS_2$, iron nitride layer of 4$\mu\textrm{m}$ and nitrogen diffusion layer of 400mm were formed on the steel. A compound layer of 15$\mu\textrm{m}$ and nitrogen diffusion layer of 400$\mu\textrm{m}$ were formed on the surface of the steel plasma-sulfnitrided with subsidiary cathode of $MoS_2$. The compound layer consisted of FeS containing Mo and iron nitrides. The nitrides of $\varepsilon$-$Fe_2$, $_3N$ and $\gamma$-$Fe_4N$ formed under the FeS. The thicker compound layer was formed by plasma-sulfnitriding than ion-nitriding. In plasma-sulfnitriding, the surface hardness was about 730 Hv. The surface hardness of the steel plasma-sulfnitrided with $MoS_2$ was lower than that of ion-nitrided without $MoS_2$. This may be due to the soft FeS layer formed on the surface of the plasma-sulfnitrided steel.

• 한국표면공학회지
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• 제29권5호
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• pp.443-448
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• 1996

In order to plasma-sulfnitride by combining ion-nitriding of a steel and sputtering of MoS$_2$, chromium-molybdenum steel was plasma-sulfritrided using hollow cathode discharge with parallel electrodes which are a main of the steel and a subsidiary cathode of $MoS_2$. The treatment was carried out at 823K for 10.8ks under 665Pa in a 30% $N_2$-70% $H_2$ gas atmosphere. Plasma-sulfnitriding layers formed of the steel were characterized with EDX, XRD, micrographic structure observation and hardness measurement. A compound layer of 8-15$\mu\textrm{m}$ and nitrogen diffusion layer of about 400$\mu\textrm{m}$ were formed on the surface of plasma-sulfnitrided steel. The compound layer consisted of FeS containing Mo and iron nitrides. The nitrides of $\varepsilon$-$Fe_2_3N$ and $\gamma$'-$Fe_4N$ formed under the FeS. The thickness of compound layer and surface hardness were different with the gaps between main and subsidiary cathodes even in the same sulfnitriding temperature. The surface hardnesses after plasma-sulfnitriding were distributed from 640 to 830Hv. The surface hardness was higher in the plasma-sulfnitriding than the usual sulfnitriding in molten salt. This may be due to Mo in sulfnitriding layer.

• 한국광물학회지
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• 제17권1호
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• pp.75-83
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• 2004

석조문화재 표면에 형성된 흑화 부위는 미적인 면에서뿐만 아니라 문화재 자체에도 손상을 끼치기 때문에 많은 문제가 되고 있다. 이러한 흑화 부위는 종종 많은 량의 철화합물을 함유하고 있어서, 다른 요소들과 함께 철화합물도 암석 표면의 흑화 현상에 영향을 끼치는 것으로 추정되고 있다. 독일 베를린 시에 있는 석조문화재(Museumsinsel) 내의 표면에서 시료를 채취한 후 함유 철의 이온상태와 화학성분을 결정하기 위하여 뫼스바우어 분광분석법을 사용하였다. 사용된 암석의 원상태와 흑화 부위의 분말시료에 대한 광물학적 및 화학적 분석을 선회절법과 X-선형광법으로 각각 시행하였다. 형성된 철 성분의 기원은 흑화 부위의 제거 등 석조문화재의 보존처리에 중요한 단서를 제공하기 때문에, 철을 다량 함유하고 있는 적색 사암에서 형성된 흑화 부위와 매우 소량 함유하고 있는 백색사암의 표면에 형성된 흑화 부위를 비교하였다. 연구 결과 백색사암 흑화 부위에서는 주변 환경물질에서 기인한 철 성분이, 적색사암 흑색부위에서는 원암에서 보여지는 철 성분이 주성분으로 추정되었다. 적색사암에 있어서는 흑화부위를 제거한 이후에라도 흑화의 주원인인 철 성분이 계속해서 모암의 내부로부터 표면으로 이동될 수 있기 때문에, 제거 이외의 보존처리법이 더 연구되어야한다.