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용강 및 슬래그에 의한 지르코니아/흑연계 침지노즐의 침식기구
선우식,김환,이종국,Sunwoo, Sik,Kim, Hwan,Lee, Jong-Kook 한국결정성장학회 2000 韓國結晶成長學會誌 Vol.10 No.3
침지노즐(SEN)의 재료로 사용되는 지르코니아/흑연 재질에서 용강 및 슬래그에 의한 침식의 형태를 살펴본 결과, 침식의 첫번째 기구는 부분안정화 지르코니아 내 안정화제인 CaO가 용강 및 슬래그에 의해 용해되면서 입방정 안정화 지르코니아가 단사정상으로 상전이하여 일어났는데, 상전이 시 부피팽창에 의한 균열이 발생하고 파괴가 진행되었고, 이로 인하여 미세 $ZrO_2$입자의 용해 및 탈락이 촉진되었다. 침식의 두 번째 기구는 슬래그가 큰 c-$ZrO_2$입자의 입계를 따라 침투하여 작은 입자들로 분리시키고, 작은 입자들이 용강과 슬래그에 탈락되어 진행되었다. 마지막 기구로는 입방정 지르코니아와 흑연이 반응하여 다공질의 미세한 ZrC 상을 형성하고, 이들이 slag에 용해되면서 침식이 진행되었다. Corrosion mechanisms by molten steel and slag were investigated in the zirconia/graphite composite as a material of submerged entry nozzle (SEN) using for producing high quality steel. Most of corrosions were started by the dissolution of zirconia particles into molten steel and oxidation of graphite, but subsequently three modes of corrosion were observed. Firstly, the penetration of slag into zirconia matrix was induced to the diffusion of stabilizing agent outward cubic zirconia grains, and the destabilization of cubic to fine monoclinic zirconia particles, which is enhanced to the decomposition and dissolution of them into slag. Secondly, molten slag penetrates into large cubic zirconia particles along grain boundary and decomposed them to fine cubic grains, which is also enhanced to the dissolution of zirconia grains into slag. Lastly, reaction between carbon and cubic zirconia was formed porous ZrC and enhanced the dissolution of it into slag.
선우식,변근주,한상훈 연세대학교 산업기술연구소 1982 논문집 Vol.14 No.2
A mathematical model is formulated for the minimum cost design of a reinforced concrete potal frame acting under a uniformly distributed vertical design load. Constraint requirements are imposed to insure structural strength and stability. Additional constraints insure the proper failure mode and restrict maximum and minimum steel percentages in the beam and column. The design variables are selected to be the width and depth of the beam and column, the tensile and compressive steel areas in the beam at the midspan and joint, and the longitudinal steel in the column. An elastic analysis is performed and resulting design is based on the ultimate strength theory of concrete design. The resulting mathematical model is a nonlinear constrained Optimization problem. The SUMT method is suggested as a satisfactory algorithm for obtaining an optimal solution and an example is represented which illustrates the complexity of the problem. It is found that the SUMT method is more efficient than Gradient Projection Method.
국산 지르콘사로부터 부분 안정화 지르코니아의 제조 및 그 응용에 관한 연구 I. 국산 지르콘사로부터 고순도 지르코니아 분말의 제조
김환,선우식,신건철,황규홍,Kim. H.,Sunwoo, S.,Shin, K.C.,Hwang, K.H. 한국세라믹학회 1987 한국세라믹학회지 Vol.24 No.2
ZrO2 powders having high purity were prepared from domestic zircon sand using the caustic fusion method and the soda ash sintering process. In the caustic fusion method, ZrO2 recovery was reached to 96% when 100/140 mesh zircon was reacted with NaOH at the NaOH/Zircon mole ratio 6 and at 650$^{\circ}C$ for 2 hours. And in the soda ash sintering process, ZrO2 was recovered to 88.5% when -325 mesh zircon was reacted with Na2CO3 at the Na2CO3/Zircon mole ratio 1.1 and 1050$^{\circ}C$ for 2 hours. In both cases, Zr component was extracted to ZrOCl2, subsequently crystallized to ZrOCl2$.$8H2O to increase the purity, and converted to ZrO2 by precipitation. And to increase the sinter ability of powder, Cl- ion was removed and strong agglomeration was avoided by methanol distribution of Zr(OH)4 precipitates.
국산 지르콘사를 이용한 부분 안정화 지르코니아의 제조 및 그 응용에 관한 연구 : II. 부분 안정화 지르코니아 소결체의 제조 및 그 특성
김환,선우식,강종봉,심규송,신건철,황규홍,Kim, H.,Sunwoo, S.,Kang, J.B.,Shim, K.S.,Shin, K.C.,Hwang, K.H. 한국세라믹학회 1988 한국세라믹학회지 Vol.25 No.2
The microstructural changes in partially stabilized MgO-ZrO2 alloys during heat treatment and mechanical properties of ZrO2(Y2O3)/Al2O3 systems have been studied. 9mol% MgO-ZrO2 powders were sintered at 1800$^{\circ}C$ for 4 hours and these specimens were aged at 1420$^{\circ}C$ and 1100$^{\circ}C$ secondly. These specimens have high thermal shock resistance and high toughness. The bend strength of Y-PSZ/Al2O3 composites conventially sintered were increased by HIP from 650MPa to 980MPa.