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Cr과 Mo 합금첨가에 따른 고크롬 백주철에서의 보라이드층 두께 및 특성 변화에 관한 연구
박해웅 한국기술교육대학교 2003 論文集 Vol.10 No.1
A series of high Cr white cast irons were boronized using a pack-cem entation process and characterized in terms of the process temperature and the contents of Cr, Mo, and C in the cast iron. As the contents of Cr and Mo increased from 12 to 30 wt.%, the thickness of the boridelayer decreased, while the hardness of the matrix increased from 43.5 to 52.3 HRC after a boronizing process. The thickness of the boride layer was increased, when the process temperature (up to 1000℃) or the content of carbon (from 2.0 to 3.3 wt.%) was raised. The hardness of the boride layer was about 1800 HV, much higher than that of the matrix. The boronized cast iron showed higher corrosion resistance than that of the non-boronized, and the corrosion resistance improved with the thickness of theboride layer when tested in 6 wt.% FeCl₃ solutions.
Synthesis of bulk Y-Ba-Cu-O superconductor via melt processing of the oxide precursor
Park, Hai-Woong 한국기술교육대학교 2006 論文集 Vol.13 No.1
In this study, textured YBa_(2)Cu_(3)Oy(Y123) superconductors were synthesized through the oxide precursor containing BaCuO_(2.5), Y_(2)O_(3) and CuO which was formed from metallic Y, metallic Cu and Ba(NO_(3))_(2) at 600℃. The precursor was successfully converted to the superconducting Y123 orthorhombic phase with heat treatment at 1020℃ in air without an additional oxygenation process at low temperature. In the melt processing of pellet samples at 1020℃, the superconducting phase was formed within 30 minutes. The directly formed superconducting phases at high temperature from the pellets showed 92K of the critical temperature. The superconducting properties and the microstructures of various samples are also presented. Department of New Materials Engineering
Hai Woong Park,송인규,Sunyoung Park,Dong Ryul Park,Jung Ho Choi 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.4
Palladium catalysts supported on cesium-exchanged heteropolyacid (Pd/Cs_xH_(3.0-x)PW_(12)O_(40), x = 2.0–3.0)were prepared and applied to the decomposition of lignin model compounds. Phenethyl phenyl ether and benzyl phenyl ether were employed as lignin model compounds for representing b-O-4 and a-O-4bonds in lignin, respectively. Phenol, ethylbenzene, benzene, and toluene were mainly produced by the decomposition of phenethyl phenyl ether. On the other hand, phenol, benzene, and toluene were mainly produced by the decomposition of benzyl phenyl ether. Conversion of lignin model compounds (phenethyl phenyl ether and benzyl phenyl ether) and total yield for main products were closely related to the surface acidity of Pd/Cs_xH_(3.0-x)PW_(12)O_(40). Conversion of lignin model compounds and total yield for main products increased with increasing surface acidity of Cs_xH_(3.0-x)PW_(12)O_(40). Among the catalysts tested, Pd/Cs_(2.5)H_(0.5)PW_(12)O_(40) with the largest surface acidity of Cs_(2.5)H_(0.5)PW_(12)O_(40) showed the highest conversion of lignin model compounds and total yield for main products.
(Hai Woong Park),(Hai Gun Lee) 대한금속재료학회 ( 구 대한금속학회 ) 2001 METALS AND MATERIALS International Vol.7 No.3
YBa2Cu3Oy(Y123) phase was synthesized from the oxide precursor containing BaCuO2.5 in two distinct processes. In the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO3)2) were mixed via attrition milling for 20h. After 20h of milling, the particle size of the powder was in the range of 0.05-0.2um. On subsequent heat treatment of the milled powder at 600℃ for 5h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO2.5, Y2O3 and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900-1020℃ in air without any additional low temperature oxygenation process. A DTA experiment at 20℃/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO2.5 constituent of the precursor decomposed at 838℃, which is higher than that of pure BaCuO2.5 (760℃). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO2.5 of the IP. At a heating rate of>50℃/min, the BaCuO2.5 did not decompose completely during heating to 1020℃ and form orthorhombic YBa2Cu3O7-x.
Park, Hai-Woong,La, Kyung-Won,Song, In-Kyu,Chung, Jin-Suk The Polymer Society of Korea 2007 Macromolecular Research Vol.15 No.3
A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for a metal-locene/Ziegler-Natta hybrid catalyst. The prepared $rac-Et(Ind)_2ZrCl_2/TiCl_4$/MAO(methylaluminoxane)/SMB catalyst was applied to the copolymerization of ethylene with l-hexene using a variable triethylaluminum (TEA)/transition-metal (Ti) ratio and fixed MAO/transition-metal (Zr) ratio. The effect of the Al(TEA)/Ti ratio on the physical properties and chemical composition distributions (CCDs) of the ethylene-hexene copolymers produced by the hybrid catalyst was investigated. In the ethylene-hexene copolymers, two melting temperatures attributed to the metal-locene and Ziegler-Natta catalysts were clearly observed. The number of CCD peaks was increased from six to seven and the temperature region in which the peaks for the short chain branches of the ethylene-hexene copolymer were distributed became lower as the Al(TEA)/Ti ratio was increased from 300 to 400. Furthermore, the temperature regions corresponding to the lamellas in the copolymer became lower and those corresponding to the small lamellas in the copolymer became higher as the Al(TEA)/Ti ratio was increased from 300 to 400. In the copolymer produced with Al(TEA)/Ti = 500, however, only four CCD peaks were observed and the short chain branches were poorly distributed.
Park, Young-Jo,Ko, Jae-Woong,Lee, Jae-Wook,Kim, Hai-Doo The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.4
Nitriding and post-sintering behavior of powder mixture compacts were investigated. As mixture compacts are different from simple Si compacts, the fabrication of a sintered body with a mixture composition has engineering implications. In this research, in specimens without a pore former, the extent of nitridation increased with $Si_3N_4$ content, while the highest extent of nitridation was measured in $Si_3N_4$-free composition when a pore former was added. Large pores made from the thermal decomposition of the pore former collapsed, and they were filled with a reaction product, reaction-bonded silicon nitride (RBSN) in the $Si_3N_4$-free specimen. On the other hand, pores from the decomposed pore former were retained in the $Si_3N_4$-added specimen. Introduction of small $Si_3N_4$ particles ($d_{50}=0.3{\mu}m$) into a powder compact consisting of large silicon particles ($d_{50}=7{\mu}m$) promoted close packing in the green body compact, and resulted in a stable strut structure after decomposition of the pore former. The local packing density of the strut structure depends on silicon to $Si_3N_4$ size ratio and affected both nitriding reaction kinetics and microstructure in the post-sintered body.
Fabrication of β-SiAlONs by a Reaction-Bonding Process Followed by Post-Sintering
Park, Young-Jo,Noh, Eun-Ah,Ko, Jae-Woong,Kim, Hai-Doo The Korean Ceramic Society 2009 한국세라믹학회지 Vol.46 No.5
A cost-effective route to synthesize $\beta$-SiAlONs from Si mixtures by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87, in $Si_{6-z}Al_zO_zN_{8-z}$ without excess liquid phase were selected to elucidate the mechanism of SiAlON formation and densification. For RBSN (reaction-bonded silicon nitride) specimens prior to post-sintering, nitridation rates of more than 90% were achieved by multistep heating to $1400^{\circ}C$ in flowing 5%$H_2$/95%$N_2$; residual Si was not detected by XRD analysis. An increase in density was acquired with increasing z values in post-sintered specimens, and this tendency was explained by the presence of higher amounts of transient liquid phase at larger z values. Measured z values from the synthesized $\beta$-SiAlONs were similar to the values calculated for the starting compositions. Slight deviations in z values between measurements and calculations were rationalized by a reasonable application of the characteristics of the nitriding and post-sintering processes.
선형 공진기 구조 광섬유 레이저에서 Sagnac loop를 이용한 수동형 모우드록킹
박희갑,이경화,오왕열,이해용,김병윤 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.17 No.-
광섬유 레이저의 수동형 모우드록킹을 위한 새로운 공진기 구조를 제안하고 이를 실험하였다. 광섬유 레이저 공진기의 한쪽 끝에는 이색성 평면경을 부착하였으며, 다른쪽 끝은 긴길이의 광섬유 Sagnac loop로 이루어진 비선형 loop mirror로 구성하였다. Er 첨가 광섬유 레이저와 Nd 첨가 광섬유 레이저의 각각의 경우에 대한 모우드록킹의 실험결과를 기술하였다. A new cavity configuration for passive mode locking of fiber laser is proposed and demonstrated. It consists of a dichroic mirror at on end of the cavity, and a nonlinear loop mirror, which is a Sagnac loop, at the other end. The experimental observations are described for both Er-doped fiber laser and Nd-doped fiber laser.