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Leaching공정으로제조한표면다기공Ti-HA생체재료의표면조직및기계적성질의평가
우기도 ( Kee Do Woo ),강덕수 ( Duck Soo Kang ),문민석 ( Min Seok Moon ),김상혁 ( Sang Hyuk Kim ),( Zhi Guang Liu ),( Abdel Nasser Omran ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.4
Ti-6Al-4V ELI alloy, which is commonly used as a biomaterial, is associated with a high elastic modulus and poor biocompatibility. This alloy presents a variety of problems on several areas. Therefore, the development of good non-toxic biocompatible biomaterials with a low elastic modulus is necessary. Particularly, hydroxyapatite (HA) is an attractive material for human tissue implantation. This material is widely used as artificial bone due to its good biocompatibility and similar composition to human bone. Many scientists have studied the fabrication of HA as a biomaterial. However, applications of bulk HA compact are hindered by the low strength of HA when it is sintered. Therefore, HA has been coated on Ti or Ti alloy to facilitate good bonding between tissue and the HA surface. However, there are many problems when doing this, such as the low bonding strength between HA and Ti due to the different thermal expansion coefficients and mechanical properties. In this study, a Ti-HA composite with a porous surface was successfully fabricated by pulse current activated sintering (PCAS) and a subsequent leaching process. (Received January 12, 2010)
AI-Li 계 합금에서 δ', T_1, S' 석출상의 조대화
禹基道,李旻相 전북대학교 공업기술연구소 1988 工學硏究 Vol.19 No.-
The coarsening behavior of δ', T₁and S' phases in Al-Li based alloys was investigated by TEM. The specimens investigated are Al-2.3wt %Li, Al-3.1wt %Li, Al-2.1wt%Li-1.0wt % Cu and Al-2.3wt % Li-1.3wt %Cu-0.6wt %Mg-0.12wt % Zr alloys. The δ', T₁, S' and β' phases precipitated by aging treatment in the investigated alloys. The results of coarsening of δ', T₁ and S' phases in those precipitates were as follows : 1. With aging time, δ' phase coarsened to followed R^∝ t^t/3 and coarsening kinetics was found to be obeyed to the MLSW theory. Calculated interfacial energies.of δ' and matrix phase were 0.00719J/㎥ in Al-2.3wt%Li and 0.0081J/㎥ in Al-3.1wt% Li alloys. 2. The coarsening kinetics of δ' precipitates was not affected by T₁precipitates forming by the addition of Cu. 3. Plots of the half length and half thickness of T_1 phases versus the square root of aging time showed a linear dependence. Diffusivity of Cu in matrix was obtained to be 1.987 X 10^-15cm/sec. Coarsening of T_1 phases was controlled by the diffusion of cu atoms. 4. The coarsening of S' phases was found to be obeyed to the LSW theory. Plots of {2dV/dV}^3 versus aging time showed a linear dependence up to 48 hours. Diffusivity of Mg in mafrix was obtained to be 1.639 X 10^-17cm/sec.
Al-Zn-Mg-Cu 합금의 강도와 조직에 미치는 RRA처리의 영향
우기도,김대중 전북대학교 공업기술연구소 1989 工學硏究 Vol.20 No.-
The effect of the retrogression and reaging treatments(RRA) on the microstructure and strength of Al-Zn-Mg-Cu alloy was studied by the TEM, hardness and tesion test. The processes occuring in the matrix during the retrogression treatment are principally the dissolution of small n' precipitates, transformation from the large n' precipitates to n, coarsening of the n phase. The main process occuring in the matrix during the reaging treatment is either growth of partially dissoloved n' precipitates or precipitation of n' precipitates. These lead to a microsructure containing lots of fine n' precipitates and some large n precipitates, resulting ina large size of precipitate. The RRAtreatments also result in the increase of the size of grain boundary precipitate spacing between the precipitates, and PFZ width. As a result of the RRA treatment, the strength is comparable to the maximum strength of the T_6 tempered condition. The high strength of RRA condition is believed to arise from the fack that it constains relatively high density of precipitate distribution.
熱分析에 의한 7075 알루미늄 합금의 二段時效에 關한 硏究
禹基道,尹正模 全北大學校 1984 論文集 Vol.26 No.-
Differential scanning calorimetry (DSC) was used to establish the microstructural effects of various aging treatment on aluminum alloy 7075. DSC was used to characterize the matrix microstructure while hardness tester was used to characterize the mechanical properties. The aging treatments were in three categories: isochronal pre-aging, isothermal pre-aging and isochronal final aging treatments. The results obtained in this study are as follows: 1. The variation in pre-aging treatment did not have much of effect on the final microstructures but that changing the final aging temperature had significant effects on the final microstructures. 2. When the pre-aging treatment was carried out for 6hr, 24hr and 96hr at 90℃ or 120℃ before final aging for 8hr at 150℃, the dissolution of G.P. zones decreased regulary as the time and temperature of pre-aging increased. 3. For two-step treatments where the first aging treatment is 4hr at 95℃, increasing the final aging temperature from 150℃ to 155℃ or 160℃ results in a significant increase in the amount of η' in the microstructure.
자동차 차체재료용 Al-Mg-Si-(Cr,Be) 합금의 기계적 성질에 관한 연구
우기도(Kee Do Woo),이종수(Jong Soo Lee),이민상(Min Sang Lee),김석원(Sug Won Kim) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.2
N/A Al-Mg-Si alloys have good strength, formability, corrosion resistance, and bake hardenability. But there is a weak point to use for the auto body materials. This is because the strength of this alloy was decreased by the precipitation of G.P.I zone formed at room temperature for a long holding time. In practical usage, it is inevitable to hold at room temperature prior to paint baking. The present work is aimed to improve bake hardenability using special heat treatments such as two step aging, and retrogressing and reaging(RRA) in Al-Mg-Si-(Cr, Be) alloys. A differencial scanning calorimeter and tensile test were employed to investigate the precipitation behaviors and the mechanical properties in Al-Mg-Si alloys. The tensile strength of Al-Mg-Si-Be and Al-Mg-Si-Cr-Be alloys were improved by special heat treatments such as two step aging and RRA treatment after pre-aged at 120 and 150˚C for 4 hrs. The combination between strength and ductility of the Cr, Be containing Al-Mg-Si alloy is better than those of no addition of Cr,Be in Al-Mg-Si alloy. (Received February 2,1999)
禹基大 충남대학교 농업과학연구소 1977 農業技術硏究報告 Vol.4 No.2
Sumithion and EPN residues on grapes, EPN and Diazinon on chinese cabbage, Parathion on peaches, Dimethoate on tomatoes, and EPN and Malathion on cucumber were analyzed in terms of 0, 3, 7, 14, 21 and 30 days after last application for the pesticides safty use. From the disappearance rate for various organo-phosphate insecticides on vegetables and fruit crops, following results are obtained. 1. On Chinese cabbage, Diazinon residues were 0.25∼0.38p.p.m three weeks after one application, and EPN were 1.39∼2.69p.p.m seven days after one application and 0.96∼2.34p.p.m two weeks after twice application. 2. EPN residues on grapes were 1.09∼1.80p.p.m seven days after one application and 0.96∼2.34p.p.m two weeks after twice application. 2. EPN residues on grapes were 1.09∼1.80p.p.m seven days after one application and Sumithion were 0.17∼0.53p.p.m fourteen days after one application. 3. On peaches, Parathion residues were 0.40∼0.61p.p.m two weeks after last application. 4. Dimethoate residues on tomatoes were 0.14p.p.m seven days after four times application. 5. On cucumber, EPN residues were 2.11∼2.14p.p.m three days after twice application, and Malathion were 0.46p.p.m 3 day after four times application but 0.062∼0.025p.p.m three days after last application. 6. Rate of degradation of organo-phosphate chemicals is inversely related to half-life of its. 7. Minimum intervals between last treatment and harvest to prevent unsafty residues are as follows. 7 days for EPN with one application and 14 days with twice application on chinese cabbage, 3 days on cucumber and 7 days on grape, 14 days for parathion, 7 days for dimethoate on tomatoes, 0 to 3 days for Malathion on cucumber, 21 days for Sumithion on grape, 21 days on chinese cabbage for Diazinon.