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Y₂O₃ 첨가량에 의한 Al₂O₃ 복합재 세라믹스의 균열 치유와 고온 굽힘강도 특성
남기우(K. W. Nam),김해숙(H. S. Kim),손창석(C. S. Son),김성광(S. K. Kim),안석환(S. H. Ahn) 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.11
The four kinds of Al₂O₃ composite ceramics were prepared using a mixture of 85 wt.% Al₂O₃ (mean size 0.5 ㎛), 15 wt.% SiC powder with Y₂O₃ as an additive powder (0, 1, 3 and 5 wt.%). The crack-healing strengths were studied as functions of crack-healing temperature and amount of Y₂O₃. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of Y₂O₃ showed better crack-healing ability than specimen with 1 or 5 wt.% of Y₂O₃. In case of specimen with 3 wt.% of Y₂O₃, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of Al₂O₃ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of Y₂O₃.
남기우(K. W. Nam),이장원(J. W. Lee),김수영(S. Y. Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
The pipelines are apt to erosion/corrosion because of the high-speed flow of water and steam with high temperatures/high pressures. This study was carried out to provide an experimental analysis on the fracture behavior of T pipes with local wall thinning under internal pressure. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area included an eroded ratio of d/t=0.80∼0.963 and an eroded length of l=25 ㎜, 50 ㎜ and 102 ㎜. Three-dimensional elastic-plastic analyses were also carried out using the finite element method, which is able to accurately simulate failure behaviors. In regards to the relation ship between pressure and eroded ratio, the criterion that can be used safely under operating pressure and design pressure were obtained from this calculation. The results of this calculation were in relatively good agreement with that of the experiment.
〈논문〉SiO₂ 콜로이달 첨가에 의한 Si₃N₄ 복합 세라믹스의 Morphology
남기우(K. W. Nam),박승원(S. W. Park),김종순(J. S. Kim),안석환(S. H. Ahn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Surface morphology of Si₃N₄ composite ceramics has been studied as functions of heat-treatment temperature and additive SiO₂. Additive SiO₂ colloidal and SiO₂ colloidal coating on crack could significantly increase the bending strength. Crack healing temperature decreased 300 K by additive TiO₂. Bending strength of specimen with additive SiO₂ is higher than that of non-additive SiO₂. Moreover, bending strength of specimen with SiO₂ colloidal coating is much higher that of non-coating specimen. In in-situ observation, crack-healed specimen at 1,573 K shows phenomenon like a fog on the surface. By SPM, both crack-healed specimen, non-coating and coating with SiO₂ colloidal, at 1,273 K were healed completely but both of 1,573 K exist crack. This was made by evaporation of SiO₂ at high temperature. Crack-healing materials of Si₃N₄ composite ceramics is crystallized Y₂Si₂O?, Y₂Ti₂O? and SiO₂. A large amount of Si and O, and little C were detected by EPMA. Si and a increase but C decreases according to heat treatment temperature. Specimens with additive SiO₂ were more detected Si and a than that of non-additive SiO₂. Specimen with SiO₂ colloidal coatings were much more detected O.
소결보조재 Al₂O₃ 및 Y₂O₃ 첨가에 따른 Sialon 특성
남기우(K. W. Nam),문석재(S. J. Moon),박승원(S. W. Park),안석환(S.H. Ahn),김종순(J. S. Kim) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Various Sialon ceramics were fabricated by hot-pressing mixtures of Si₃N₄, Y₂O₃ and Al₂O₃ powder. The polished specimen of SiAION Ⅰ~Ⅲ showed increased strength by heat treatment, heat treated non-polished specimen were similar or up in strength to polished specimen. The polished specimen of SiAIONN Ⅳ and Ⅴ showed a very high strength, but couldn't obtain increased strength by heat treatment, all specimens were fractured surfaces and inner flaws. Surfaces fractures were initiated from polished surface flaw and comer flaw. inner fractures were initiated from an internal defect.
남기우(K.W. Nam),문희준(H.J. Moon),박상현(S.H. Park),김은선(E.S. Kim),서현수(H.S. Seo),김종순(J.S. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Zinc coatings are widely used in practice for preventing the corrosion of steel. But the zinc coating can be involved by corrosion phenomena with the consequence that some steel surface is unprotected. The reduction of the corrosion rate of zinc is an important topic. In the past a very popular way to reduce the corrosion rate of zinc was the use of chemical conversion layers based on Cr??. However, there is the important problem that the use of chromium salts is now restricted because of environmental protection legislation. Therefore very important to develop new zinc surface treatments environmentally friendly to improve the corrosion resistance of zinc and the adhesion with the final organic protective layer. In this study, Urethane solution (only Urethane 20 % ; S-700) and organic/inorganic solution with Si (Si polysilicate 10 % + Urethane 6 % + hardner 4 % ; LRO317-1)are used. Based on the salt spray test of 72h, S-700 and LRO317-1 had a superior effect on EGI and HGI, respectively.
Y<sub>2</sub>O<sub>3</sub> 첨가량에 의한 Al<sub>2</sub>O<sub>3</sub> 복합재 세라믹스의 균열 치유와 고온 굴힘강도 특성
남기우,김해숙,손창석,김성광,안석환,Nam, K.W.,Kim, H.S.,Son, C.S.,Kim, S.K.,Ahn, S.H. 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.11
The low kinds of $Al_2O_3$ composite ceramics were prepared using a mixture of 85 wt.% $Al_2O_3$ (mean size $0.5\;{\mu}m$), 15 wt.% SiC Powder with $Y_2O_3$, as an additive powder (0, 1, 3 and 5 wt.%). The crack-healing strengths were studied as functions of crack-healing temperature and amount of $Y_2O_3$. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of $Y_2O_3$ showed better crack-healing ability than specimen with 1 or 5 wt.% of $Y_2O_3$. In case of specimen with 3 wt.% of $Y_2O_3$, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of $Al_2O_3$ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of $Y_2O_3$.
〈학술논문〉 또는 〈응용논문〉 : 장 균열을 가지는 질화규소의 SiO₂ 나노 콜로이드에 의한 균열 치유 특성
남기우(K.W. Nam),박상현(S.H. Park),은경기(K.K. Eun),최창민(C.M. Choi),김종순(Jong Soon Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
본 연구에서는 장균열을 가지는 Si₃N₄ 세라믹스의 균열 길이와 코팅 방법에 따르는 균열 치유 특성을 규명하였다. 약 100 ∼ 500 ㎛의 균열 길이는 24.5 ∼ 98 N의 하중을 사용하여 비커스 압자를 이용하여 만들었다. 24.5N의 하중으로 만든 단균열의 경우, SiO₂ 나노 콜로이드 코팅된 균열재는 모재보다 약 140 % 증가한 가장 높은 굽힘 강도를 보였지만, 장균열은 모재보다 낮은 굽힘 강도를 나타내었다. 그러나 대부분의 장균열 시험편의 굽힘 강도는 균열재보다 약간 증가하였다. 이러한 결과에 따라서, 복수 압입에 의한 Si₃N₄ 세라믹스의 균열 치유 특성을 코팅방법에 따라 연구하였다. 장균열 시험편의 가장 효과적인 코팅 방법은 정수압코팅방법이었다. This study analyzed the crack-healing characteristics of specimens according to the crack lengths and the coating methods of Si₃N₄ ceramics with long cracks. Crack lengths of about 100 ~ 500 ㎛ was obtained from a Vickers indenter using the load of 24.5 ~ 98 N. In the case of a crack using a load of 24.5 N, the crack-healed specimen with SiO₂ nano colloid coating exhibited the highest bending strength, which increased by about 140% compared to that of a smooth specimen, but the multiple crack-healed specimens with SiO₂ nano colloid coating had a lower bending strength than that of a smooth specimen. However, the bending strength of most multiple crack specimens slightly increased compared to that of the cracked specimens. Based on these results, the crack healing characteristic of Si₃N₄ ceramics with multiple indentation was studied according to the coating methods. The most effective coating method on the long-crack specimens was hydrostatic pressure coating.
SiO₂ 콜로이달에 의한 Si₃N₄ 복합 세라믹스의 상온굽힘강도 및 균열치유 현상
남기우(K. W. Nam),김종순(J. S. Kim),이희방(H. B. Lee) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.7
Strength characteristics of Si3N4 composite ceramics has been studied as functions of heat-treatment temperature and additive SiO₂. SiO₂ colloidal could significantly increase the bending strength. Crack healing temperature decreased 300 K by additive TiO₂. Bending strength of specimen added SiO₂ is higher than that of non-added SiO₂. Moreover, bending strength of specimen with SiO₂ colloidal coating is much higher that of non-coated specimen. In in-situ observation, crack-healed specimen at 1,573 K shows phenomenon like a fog on the surface. By SPM, both crack-healed specimen, non-coating and coating of SiO₂ colloidal, at 1,273 K were healed completely but both of 1,573 K exist crack. This was made by evaporation of SiO₂ at high temperature. Crack-healing materials of Si₃N₄ composite ceramics is crystallized Y₂Si₂O?, Y₂Ti₂O? and SiO₂. A large amount of Si and O, and little C were detected by EPMA. Si and O increase but C decreases according to heat treatment temperature. Specimens with additive SiO₂2 were more detected Si and O than that of non-additive SiO₂. Specimen with SiO₂ colloidal coatings were much more detected O.